The present invention relates to a process for preparing (i.e. a process of making) furan- 2,5-dicarboxylic acid (FDCA) (compound of the formula (I)).

(I)

Further aspects of the present invention and the preferred configurations thereof are apparent from the description which follows, the working examples and the appended claims. FDCA is an important starting compound for production of various products, for example surfactants, polymers and resins. In many cases, FDCA is co-polymerized with ethylene glycol to give polyethylene furanoate (PEF), a polyester with properties similar and in certain aspects even superior to polyethylene terephthalate (PET). FDCA is prepared, for example, by oxidation of 5-hydroxymethylfurfural (HMF) (compound of the formula (II)) in the presence of a catalyst. As well as HMF, it is also possible for derivatives of HMF, for example 2,5-diformylfuran (DFF) (compound of the formula (III)), 5-hydroxymethylfuran-2-carboxylic acid (HMFCA) (compound of the formula (IV)) 5-formylfuran-2-carboxylic acid (FFCA) (compound of the formula (V)) and 2,5- bishydroxymethylfuran (BHMF) (compound of the formula (VI)) to serve as reactants, and to be converted by means of oxidation in the presence of a catalyst to FDCA. However, the greatest significance as a reactant is possessed by HMF, which can be obtained in significant amounts from biomass, especially from biomass comprising hexoses.

10

(VI)

The properties and quality of polyethylene furanoate (PEF) heavily depend on monomer quality. Especially traces of mono-functional molecules such as mono carboxylic acids or mono-alcohols which terminate chain growth in the polymerization should therefore be avoided in the monomer. Regarding the production of FDCA by means of HMF-oxidation, these requirements impose an exceptional challenge in the manufacture of FDCA as the oxidation usually proceeds stepwise. Mono-carboxylic acids such as (IV) and especially 5-formylfurane-2-carboxylic acid (FFCA, (V)) are inevitably formed as intermediates. Therefore, if full conversion of these intermediates cannot be achieved, problems with FDCA quality will arise. Typically, the FFCA-content in pure-FDCA should be lower than 200 ppm, in most cases lower than 50 ppm. 5-Formylfurane-2-carboxylic acid (FFCA, (V)) is particularly problematic. Moreover colored impurities in the monomeric FDCA should be reduced to minimal amounts in order to be able to obtain a colorless resin.

The oxidation of HMF or HMF derivatives is typically conducted in the presence of a suitable catalyst; suitable catalysts in this respect are, for example, heterogeneous catalysts comprising gold and/or metals of the platinum group, such as iridium, rhodium, ruthenium, palladium and/or platinum. These heterogeneous catalysts typically comprise a support material, for example carbon containing support materials, for example in particular activated carbon.

US2013/0345451 and US2013/0345452 disclose a process for the production of purified FDCA comprising oxidation of HMF (or a HMF-derivate) to crude-FDCA followed by hydrogenation of the crude-FDCA composition to yield purified FDCA after crystallization.

In the disclosed processes the oxidation is conducted using an oxygen-containing gas as the oxidant, using either a heterogeneous or homogeneous catalyst comprising at least one component selected from Co, Mn and bromine. The solvent is an oxidation solvent composition, preferably an aliphatic carboxylic acid, e.g. acetic acid. The oxidation step yields a slurry of crude-FDCA in the oxidation solvent composition. The crude-FDCA is crystallized, separated from the solvent (containing the catalyst), optionally washed and dried and re-dissolved in a hydrogenation solvent which is preferably water. Hydrogenation is then conducted over conventional hydrogenation catalysts (group VIII metal on solid support), especially Pd- and Pt-catalysts on a carbon support. Crystallization of the thus obtained purified FDCA is then achieved by lowering the temperature. Although the disclosed process provides a purified FDCA composition, the process has specific disadvantages as it requires a multitude of time- and energy- consuming unit operations which also require high investments. The complexity of the disclosed process to a high extent is caused by the fact that the solvent has to be changed between oxidation and hydrogenation. In more detail, several unit operations require multiple sequential steps in multiple apparatuses, e.g. multiple crystallizers or phase-separators. Due to the corrosive nature of the oxidation solvent all these apparatuses need to be made of specialty materials (hastelloy or the like) and are I BASF SE I 0000077070 | 0000077070WO01 | therefore costly. When considering the whole value chain starting from fructose the solvent switch (from oxidation to hydrogenation solvent) appears even more inefficient. Sugars such as fructose are highly hydrophilic and usually handled as aqueous solution. The same holds true for HMF which is usually obtained as aqueous solution from the dehydration of fructose. When conducting the oxidation in acetic acid, the solvent needs also to be switched prior to oxidation which causes an effort comparable to the second solvent change. In summary, the disclosed process has the disadvantage that one has to work in the oxidation step at low water concentrations using a specific oxidation solvent, and in order to purify the FDCA produced one has to change the solvent to water or another hydrogenation solvent before conducting the hydrogenation and crystallization.

US 2008/0103318 discloses a method of oxidizing hydroxymethyl furfural (HMF), comprising: providing a starting material comprising HMF in a solvent comprising water into a reactor; providing at least one of air and 0 ₂ into the reactor; and contacting the starting material with a catalyst comprising Pt, on a support material, the contacting being conducted at a reactor temperature of from about 50' C. to about 200' C. The document does not disclose how to isolate furan-2,5-dicarboxylic acid (FDCA) from the crude mixture obtained in the oxidation step. FDCA has a comparatively low solubility in aqueous solutions (especially in water), especially in aqueous solutions having a pH less than 7. Water or aqueous solutions are suitable solvents for preparation of FDCA from HMF and HMF derivatives. However, the use thereof frequently leads to disadvantages in the industrial scale preparation of FDCA, since FDCA can be present in dissolved form only in a very low concentration in an aqueous product solution, in order thus to avoid precipitation of FDCA out of the aqueous phase. Therefore, in practice, the volume of the product solution selected is frequently very large, in order to avoid precipitation of the product and/or a possible reduction in the catalyst activity, or even a deactivation of the catalyst. The solubility of FDCA in basic aqueous solutions is much higher than in neutral or acidic aqueous solutions, because the FDCA is neutralized and forms a water soluble salt. However, the catalytic conversion of HMF to FDCA in aqueous solutions regularly leads, unless counter-measures are taken, to a lowering of the pH in a corresponding reaction solution, since FDCA is a diprotic organic dicarboxylic acid which dissociates in aqueous solution. Thus, if the pH of the reaction solution is to remain within a tightly defined range of basic pH values, in order to assure improved solubility of the FDCA in the reaction solution, monitoring of the pH and, for example, recurrent addition of a base are required in order to produce a soluble FDCA-salt. However, this disadvantageously causes additional costs and increased apparatus complexity in industrial scale production. This is because obtaining free FDCA requires reprotonation of the deprotonated FDCA present in the form of its dissolved salt under basic conditions by addition of stoichiometric amounts of mineral acids (e.g. HCI, H ₂ S0 ₄ , etc.). Depending on the pH, up to 2 positively charged cations are assigned to every FDCA anion (FDCA is an organic acid having a total of two carboxyl groups). By addition of mineral acids, these cations are exchanged for protons with formation of free FDCA. The international patent application published as WO 2008/054804 A2 relates to a process for oxidizing HMF. It is disclosed that a reaction mixture having a mild basic pH can be provided by addition of sodium carbonate, the salts of FDCA having a distinctly elevated solubility in said reaction mixture compared to reaction mixtures having a neutral or acidic pH (cf. paragraph [0049]). The international patent application published as WO 2008/054804 A2 additionally discloses that twice as high a solubility of FDCA in an acetic acid/water mixture (volume ratio 40:60) is achieved, compared to the solubility in pure water (cf. paragraph [0058]).

The maintenance of a pH greater than pH 7 is also advantageous with a view to the catalysts typically used. A pH less than 7 in a corresponding reaction solution leads very frequently to a reduced catalytic activity, extending as far as complete deactivation of such catalysts, as stated for similar catalyzed oxidation reactions in "On the deactivation of supported platinum catalysts for selective oxidation of alcohols", Journal of Catalysis, Volume 31 1 (2014) pages 295-305, as well as in "Selective Oxidation of Glycerol over Platinum-Based Catalysts Supported on Carbon Nanotubes" Industrial & Engineering Chemistry Research, Volume: 52, Issue: 49, Pages: 17390-17398.

The solubility of FDCA in aqueous solutions can also be increased by addition of solubilizers. The European patent application published as EP 0 356 703 A2 relates to a process for oxidizing 5-hydroxymethylfurfural (HMF) and discloses that the precipitation of reaction products during the oxidation of 5-hydroxymethylfurfural can be avoided, especially at relatively high concentrations, when a solubilizer which is inert with respect to the reaction participants under the selected reaction conditions is added to the reaction mixture. EP 0 356 703 A2 additionally discloses that suitable solubilizers are, for example, glycol ethers lacking free OH groups, especially dimethyl glycol ether, diethyl glycol ether and methyl ethyl glycol ether. However, the use of such solubilizers leads disadvantageously to higher operational costs, and the solubilizers used may need to be removed again, or ultimately lead to by-product formation due to their oxidation, which leads to additional apparatus complexity. The effect of the use of suitable reaction mixtures having a slightly basic pH or the addition of solubilizers is frequently that the concentration of FDCA in the product mixture can be increased somewhat in comparative terms (compared to pH-neutral aqueous reaction mixtures without addition of solubilizers) without precipitation of FDCA. However, the increase thus attained in the concentration of FDCA in such reaction mixtures is still considered to be small compared to other chemical reactions which are conducted on the industrial scale and which allow supply of the reactants in high concentrations and withdrawal of the products in concentrated form.

It is thus considered to be disadvantageous in quite general terms that, in the conversion of HMF or HMF derivatives to FDCA in aqueous solutions (without solubilizer), only relatively low concentrations of FDCA (and hence also only correspondingly small amounts of HMF or HMF derivatives) can be tolerated in a product mixture. It is similarly disadvantageous having to continuously monitor the pH of a corresponding reaction mixture and, if necessary, to keep it within a desired pH range by addition of a base. It is likewise disadvantageous to have to use solubilizers and, if necessary, to remove them again.

The volume of an aqueous reaction mixture can be reduced if the precipitation of FDCA in the reaction mixture is permitted. In this case, it is also possible to conduct the reaction with a comparatively high concentration of HMF or HMF derivatives (i.e. a high concentration of organic reactant compounds) to be present in the reaction mixture. However, it is highly disadvantageous that, in the preparation and precipitation of FDCA in the presence of a heterogeneous catalyst, the effect of the precipitation of FDCA is that both heterogeneous catalyst and FDCA are in solid form and can no longer be separated from one another in a simple manner. Very frequently, precipitation of FDCA leads, incidentally, additionally to deactivation of the heterogeneous catalyst. This is confirmed in the international patent application published as WO 2013/191944 A1. It is disclosed therein that, because of the very low solubility of FDCA in water, the oxidation of HMF has to be conducted in very dilute solutions, in order to avoid precipitation of the FDCA on the catalyst surface, since the process otherwise can no longer be conducted economically (cf. page 3). The precipitation of FDCA on the internal and/or external catalyst surface of a heterogeneous catalyst can lead to contamination and possible deactivation of the heterogeneous catalyst. This involves coverage or coating of the catalytically active constituents of the heterogeneous catalyst by the precipitated FDCA, such that the catalytic constituents no longer come into contact with the reactants. The effect of such a contamination of the catalyst is that the catalyst does not display the same initial activity, if at all, and has to be replaced by new catalyst material which increases the costs. Especially in the case of utilization of costly catalysts, for example platinum catalysts, such a course of action is frequently uneconomic.

There is therefore a need to provide a process for preparing FDCA from HMF and HMF derivatives, which does not have the disadvantages of the processes known to date to the same degree, if at all, and which can be operated in an economically viable manner. More particularly, there is a need to provide a process which allows use, regeneration if needed and recycling of heterogeneous catalysts, especially with a low level of operational complexity with regard to the process to be performed.

WO 2015/041013 discloses a method of producing furan-2,5-dicarboxylic acid by subjecting 5-hydroxymethylfurfural to an oxidation reaction in the presence of oxygen, water, and an activated carbon-supported metal catalyst containing a precious metal, characterized in that steps (1 ) and (2) are performed under conditions of pH 7 or less and 0.1 MPa to less than 1 .0 MPa, and the oxygen supply quantity until step (2) is completed is 120 mol% to 140 mol% relative to the stock of 5-hydroxymethylfurfural. Step (1 ): A step for performing an oxidation reaction at a temperature of 50°C to 1 10°C until the 5- hydroxymethylfurfural content of a reaction solution is in a range of 0 mg/kg to 1 ,000 mg/kg. Step (2): A step for performing an oxidation reaction at a temperature of 140°C to 250°C after step (1 ). It is disclosed that the furan-2,5-dicarboxylic acid as produced can be refined, e.g. by combining an HMF oxide obtained by filtering after the oxidation reaction is completed with a liquid containing water, cooling to form a slurry, and hydrogentating in the presence of a hydrogenation catalyst. Thus, also according to WO 2015/041013 a solvent change is conducted.

It was thus an object of the present invention to provide a process for preparing (process of making) FDCA, which overcomes one or more of the above-described disadvantages. A process was preferably to be specified which allows both comparatively high reactant concentrations and comparatively high product concentrations in a reaction mixture with a comparatively small volume of this reaction mixture, enables economically viable reuse (recycling) of the heterogeneous catalyst used, and avoids the use of two or more different solvent systems and/or different catalysts, in particular when an oxidation step is followed by a hydrogenation step conducted in order to purify the product mixture.

According to a first important aspect, this object is achieved by a process according to the invention for preparation of furan-2,5-dicarboxylic acid (FDCA), comprising the following steps:

A) in an aqueous reactant mixture, catalytically converting one or more organic reactant compounds by means of at least one heterogeneous catalyst, so as to form a first product suspension comprising furan-2,5-dicarboxylic acid in solid form and the heterogeneous catalyst in solid form, preferably by preparing furan-2,5-dicarboxylic acid from the organic reactant compound, or one, more than one or all of the plurality of organic reactant compounds and precipitating it in solid form,

B) heating under pressure

1. this first product suspension, or

2. a second product suspension prepared therefrom by further treatment, each comprising furan-2,5-dicarboxylic acid in solid form and the heterogeneous catalyst in solid form, such that furan-2,5-dicarboxylic acid dissolves fully or partly, resulting in a first aqueous product phase comprising dissolved furan-2,5-dicarboxylic acid, and then

C) separating the heterogeneous catalyst from this first aqueous product phase comprising dissolved furan-2,5-dicarboxylic acid, or from a second product phase which results therefrom through further treatment and comprising dissolved furan-2,5-dicarboxylic acid.

Throughout the present text, the expression "according to the invention" generally relates to a technical teaching as disclosed in the present text (description/specification and I BASF SE I 0000077070 | 0000077070WO01 | claims). The subject matter of the present invention is exclusively defined in the claims. The technical teaching of the subject matter of the present invention as defined in the claims and the technical teaching of further aspects as disclosed in the present text are relevant both in combination with each other and indepently of each other. Preferably, organic reactant compounds comprise any one, two, three, four or five of the compounds shown above as (II) to (VI) or any combinations thereof. More preferably, the most abundant organic reactant compound in the aqueous reactant mixture of step A) is HMF. The aqueous reactant mixture used in the process according to the invention in step A) may comprise a comparatively high total concentration of reactant compound(s). This regularly leads to precipitation of FDCA during the catalytic conversion in step A) and hence to said first product suspension containing (comprising) FDCA in solid form and the heterogeneous catalyst in solid form. In this case, the FDCA prepared in the catalytic conversion in step A), depending on the conditions selected, may precipitate immediately in solid form (i.e. FDCA is formed at the time at which a saturated aqueous phase is already present) or only after it was present in dissolved form at first (i.e. FDCA formed is at first present in dissolved form, but precipitates out at a later juncture because the solubility product is exceeded). Depending on the pH-value, the first and/or second product suspension may additionally contain salts of furan-2,5-dicarboxylic acid. The precipitation of FDCA allows use of a comparatively small volume of aqueous reactant mixture in the process according to the invention. In this way, a high economic viability of the process according to the invention is achieved, since relatively large amounts of FDCA can be produced based on the volume of the reactant mixture. At the same time, the material requirement for building process plants for production of FDCA is thus reduced because the dimensions of respective process plants can be minimized. The effect of a comparatively small volume of the aqueous reactant mixture used in the process according to the invention is that the size of the reaction vessels can be drastically reduced and after performing the process, comparatively small volumes of solvent (especially water) are regularly also obtained, which subsequently, for example, may either (i) be reused as solvent after proper treatment or (ii) first have to be treated and then disposed of in an environmentally compliant manner. The process according to the invention thus utilizes the precipitation of FDCA, which has been regarded as disadvantageous to date, in an advantageous manner. Preferably, the first product suspension arises in step A) with formation of FDCA from the organic reactant compound, or one, more than one or all of the organic reactant compounds, and by precipitation of FDCA thus formed out of the aqueous mixture. Preferably, the aqueous reactant mixture used in step A) does not comprise any significant amounts of FDCA in solid form; in some cases, particular preference is given to the use of an aqueous reactant mixture which does not comprise any FDCA at all.

In the process according to the invention, in the first product suspension which results in step A), both the heterogeneous catalyst and FDCA are in solid form; preferably, the predominant portion of the FDCA formed by catalytic conversion of the organic reactant compounds is in solid form. A heterogeneous catalyst used in step A) may be part of a mixture of two, three or more than three heterogeneous catalysts which may be totally different in nature (catalyst mixture) which together catalyze the conversion and are preferably each in solid form. The first product suspension formed in step A) of a process according to the invention comprises, as well as the solids mentioned, an aqueous phase too, and is thus a solid/liquid mixture. The proportion of the dissolved FDCA in the aqueous phase is low because of the low solubility product of FDCA in aqueous solutions and because of the reaction conditions selected; preferably, the aqueous phase is a saturated solution with respect to FDCA. In step B) of the process according to the invention, the first product suspension or a second product suspension prepared therefrom by further treatment is heated under pressure, such that FDCA dissolves fully or partly, resulting in an aqueous first product phase comprising dissolved FDCA. The term "dissolved furan-2,5-dicarboxylic acid" identifies the amount of FDCA which is part of the aqueous product phase but that was present in solid form beforehand in the first product suspension in step A) or in the second product suspension. Preferably the dissolved FDCA has precipitated out beforehand in step A). In step B) of the process according to the invention, the total amount of FDCA in solution is thus increased compared to the aqueous phase of the first or second product suspension. The international patent application published as WO 2013/191944 A1 discloses that, under pressure and at a temperature in the range of 120°C to 240°C, FDCA in solid form is dissolved in an appropriate aqueous solvent. At appropriate temperature and appropriate pressure, an overheated aqueous solution may comprise a total proportion of dissolved FDCA in the range from 10 to 20% by weight, based on the total amount of aqueous solution.

The expression "heating under pressure" in step B) means that at least a measurable pressure is always present in the apparatus in which step B) of the process according to the invention is performed, preferably a pressure of 1 bar or more. Particularly preferred pressures for dissolution of the FDCA in step B) of a process according to the invention are at an inherent-pressure (which is established in a closed reactor) in the range from 1 to 100 bar, preferably in the range from 1 to 50 bar optionally adding to a pressure from one or more other gases. If not other gas is present in Step B, preferably 1 to 25 bar, more preferably 1 to 15 bar. Particular preference is given to working at the pressure which is established in a closed reactor (inherent pressure), which depends on the temperature and the composition of the liquid phase. In some cases, the inherent pressure is supplemented with an outside pressure which results from the presence of additional gases and increases the total pressure. Preferred additional gases are air, oxygen, nitrogen, carbon dioxide, steam, small hydrocarbons and other gases known to the expert skilled in the art. It is in particular preferred that in a process according to the invention in step B) a pressure is applied such that no boiling of liquids occurs in the first or second product suspension, respectively.

In step B) of the process according to the invention, the first product suspension or the second product suspension prepared by further treatment, each comprising FDCA in solid form and the heterogeneous catalyst in solid form, is heated under pressure, such that FDCA dissolves fully or partly, resulting in an aqueous first product phase. This is advantageous because FDCA precipitated in step A) is frequently also deposited on the surface of the heterogeneous catalyst used in step A) in the process according to the invention.

Heating under pressure of the first product suspension, or the second product suspension prepared by further treatment, each comprising both FDCA in solid form and the heterogeneous catalyst in solid form, regularly dissolves not just all or some of the FDCA in solid form, but also at least some of the FDCA deposited on or within the pore-system of the heterogeneous catalyst (e.g. the pore-system of the support material). The effect of this is that at least part of the internal and external surface area, preferably at least 50% or more of the surface area, more preferably 75% or more of the surface area and especially preferably 99% or more of the surface area of the heterogeneous catalyst becomes available again for further catalysis reaction and therefore enables reusability of the heterogeneous catalyst (recycling). In a preferred process according to the invention, the activity of the heterogeneous catalyst after step C) of a process cycle n comprising steps A), B), and C) is at least 59 %, preferably 70 %, more preferably 90 %, most preferably 99 % of the initial activity of the heterogeneous catalyst immediately before step A). Herein, n refers to the first or any subsequent cycle of the process of the present invention. In some cases a process according to the present invention is preferred wherein additional steps are conducted after step C) in order to further increase the catalytic activity of the heterogeneous catalyst immediately resulting after step C) (for those additional steps after step C) see below). Such process is particularly advantageous if the activity of the heterogeneous catalyst after step C) is rather low, e.g. in the range of 59 to 70 % of the initial activity of the heterogeneous catalyst immediately before step A).

In preferred processes according to the invention (as defined above), heating under pressure is effected such that FDCA in solid form at first dissolves completely, and the resulting aqueous first product phase comprises the dissolved FDCA. In some cases, it is preferable, in a process according to the invention (as defined above, preferably as described above as preferred), to prepare a second product suspension by further treatment of the first product suspension. For example, in such cases, after step A), the first product suspension is separated by mechanical separation processes such that solid constituents are separated from liquid constituents. Subsequently, the solid constituents are subjected, for example, to a washing step and the (washed) solid constituents are subsequently resuspended in an aqueous solution, so as to result in a second product suspension prepared by further treatment.

After step B) of the process according to the invention (as defined above, preferably as described above as preferred), in step C), the heterogeneous catalyst is separated from this aqueous first product phase comprising dissolved FDCA, or from a second product phase resulting therefrom through further treatment, comprising dissolved FDCA. Step C) of the process according to the invention allows separation of the heterogeneous catalyst which has been fully or at least partly freed of solid FDCA. Typically the heterogeneous catalyst is only slightly contaminated or deactivated by the solid FDCA or other products of the reaction.

It has been found that, surprisingly, the heating under pressure in step B) and the separation of the heterogeneous catalyst in step C) lead to a good separation of the heterogeneous catalyst from the other constituents of the first or second product suspension. Preferably, in step C), the amount of all the heterogeneous catalysts used (if a catalyst mixture has been used) is fully or at least partly separated off. It is likewise surprising that the heterogeneous catalysts separated off can be reused, preferably without additional processing or after treatment of the heterogeneous catalysts separated off. This is of particular significance especially when costly, high-value, noble metal- containing heterogeneous catalysts are used in the process according to the invention.

The process according to the invention enables excellent separation of the heterogeneous catalyst from FDCA. The international patent application published as WO 2013/191944 A1 discloses, for example, that a homogeneous catalyst can be separated from FDCA by the precipitation of the latter; in this case, the homogeneous catalyst is separated from the precipitated FDCA, for example, by one or more wash steps. The process according to the invention, in contrast, unlike the process disclosed in WO 2013/191944 A1 , relates to the separation of a heterogeneous catalyst in solid form from FDCA in solid form.

In addition, the process according to the invention can be used for decontamination and / or cleaning and / or reactivation of a heterogeneous catalyst which has been used during the catalytic conversion of one or more organic reactant compounds to FDCA in solid form and contaminated (deactivated) in the process. The process according to the invention (as described above) typically comprises further process steps in addition to process steps A), B) and C).

Preference is given to a process according to the invention (as defined above, preferably as described above as preferred), comprising the additional step of:

(after the separation in step C)) reusing the separated heterogeneous catalyst in the catalytic conversion of one or more organic reactant compounds to furan-2,5-dicarboxylic acid.

Preference is given to a process according to the invention (as defined above, preferably as described above as preferred), wherein the additional step of reusing the heterogeneous catalyst separated off in step C) in the catalytic conversion of one or more organic reactant compounds to furan-2,5-dicarboxylic acid is effected in a process step comprising the above-defined features of step A).

It is possible in a step A) conducted in accordance with the invention as a subsequent cycle, to use separated heterogeneous catalyst which has been separated off in a step C) (of a cycle preceding the subsequent cycle) as defined above. In some cases a process according to the invention (as defined above, preferably as described above as preferred) is preferred, comprising an optional reduction (e.g. hydrogenation) step after step A) and before step C) or more preferably after step B) and before step C). This optional reduction (e.g. hydrogenation) step is intended to convert compounds (e.g. impurities and/or by-products), preferably compounds causing discoloration of the (i) first aqueous product phase or (ii) the second product phase or (iii) the prepared FDCA product, into reduced (e.g. hydrogenated) compounds, preferably into reduced compounds not causing discoloration. In this optional reduction (e.g. hydrogenation) step, the FDCA (primarily in a solid form or in a dissolved form), the compounds to be treated (e.g. impurities and/or by-products) and the heterogeneous catalyst are present and are subjected to conditions suitable for reduction processes, preferably subjected to a hydrogen atmosphere and appropriate reaction (hydrogenation) temperatures. Suitable conditions for such an optional step are known in the art, for example from the international patent application published as WO 2013/191944 A1. It is of advantage to use the heterogeneous catalyst used in step A) of the process according to the invention also to catalyze the conversion of compounds like impurities and/or byproducts, in particular compounds causing said discoloration into reduced (e.g. hydrogenated) compounds, preferably into reduced compounds not causing discoloration. A hydrogenation step is an important feature of the invention as defined in the present claims. Preferably, as discussed in more detail below with reference to the invention as defined in the claims, no substance from the product mixture resulting from the oxidation step is removed before the hydrogenation step.

In some cases a process according to the invention is preferred (as defined above, preferably as described above as preferred), wherein this optional step is carried out after step A) by using the first product suspension. In order to carry out this optional step, the first product suspension is e.g. treated such that the solid parts (furan-2,5-dicarboxylic acid in solid form and the heterogeneous catalyst in solid form) of the first product suspension are separated from the liquid constituents and subsequently mixed with a suitable hydrogenation solvent. Thus, a second product suspension for the optional step is obtained from the first product suspension by further treatment. The separated liquid constituents can be used in a new cycle of the process of the invention starting with step A).

Since, in step C) of a process according to the invention, the heterogeneous catalyst has been separated from the aqueous first product phase comprising dissolved FDCA, or from the second product phase resulting therefrom through further treatment and comprising dissolved FDCA, it is possible in an additional step to separate off the desired FDCA product from further (liquid) constituents of the first or second product phase such as but not limited to by reducing the temperature of the respective solution and therefore reducing the solubility of FDCA in the solution. This ultimately leads to the precipitation of FDCA. Preference is therefore given to a process according to the invention (as defined above, preferably as described above as preferred), comprising the additional step of: after the separation of the heterogeneous catalyst, separating furan-2,5- dicarboxylic acid from further constituents of the first or second product phase. Preferably, the majority of the FDCA is separated off in this way, more preferably at least 60% (w/w), 70% (w/w), 80% (w/w), 90% (w/w), 95% (w/w), 96 % (w/w), 97 % (w/w), 98 % (w/w), 99% (w/w) or 100% (w/w) of the FDCA is separated, based on the total weight of FDCA in the first or second product phase (which is already free of the heterogeneous catalyst). The separation of FDCA from further (liquid) constituents of the first or second product phase is preferably effected in solid form, preferably by crystallization out of the first or second product phase after the heterogeneous catalyst has been separated off beforehand. Preference is given to effecting the crystallization in an apparatus suitable for that purpose, more preferably in a flash crystallizer, in a vacuum crystallizer and/or a simple heat exchanger. A majority of the FDCA dissolved beforehand in step B) precipitates out again here in solid form and can be separated off by means of mechanical separation processes. Preferably, step C) and the additional step of separating furan-2,5-dicarboxylic acid from further (liquid) constituents of the first or second product phase are performed at a temperature and/or under a pressure that will result in gaining an optimum amount of solid FDCA in relation to solid other constituents. Preferred mechanical separation processes for separation of FDCA in solid form are selected from the group consisting of filtration, sedimentation, centrifugation and combinations thereof, the mechanical separation process preferably being or comprising a filtration.

After the precipitated FDCA has been separated off, what remains is an aqueous residual solution which is virtually completely free both of the heterogeneous catalyst and precipitated FDCA. This residual solution frequently comprises unconverted organic reactant compounds, for example selected from the group consisting of compounds of the formulae (II), (III), (IV), (V) and (VI), and/or reaction products which have formed as a consequence of side reactions.

In some cases, preference is given to a process according to the invention (as defined above, preferably as described above as preferred), comprising the additional step of: - mixing the aqueous residual solution or a portion thereof with further constituents, so as to result in an aqueous reactant mixture as defined for step A) of the process according to the invention.

Advantageously, the process according to the invention (as defined above, preferably as referred to above or below as preferred) is then conducted (again). In some cases, the volume of the residual solution is preferably concentrated, for example by distillation, before said mixing of the residual solution or of the portion thereof with the further constituents.

As already stated above, in step C), the heterogeneous catalyst is separated off. Preference is given to a process according to the invention (as defined above, preferably as described above as preferred) wherein, in step C), the heterogeneous catalyst is separated from the first or second product phase by means of a mechanical separation process. Particular preference is given in this respect to a process according to the invention (as defined above, preferably as described above as preferred and especially as defined above as preferred) wherein the mechanical separation process is selected from the group consisting of filtration, sedimentation, centrifugation, magnetic separation and combinations thereof, the mechanical separation process preferably being or comprising a filtration. These are mechanical separation processes that are simple to conduct, and which can also be conducted under pressure and with heating. As mentioned above, in certain cases a magnetic separation of a catalyst having a magnetic core is preferably included in Step C).

The temperature and pressure in step B) of the process according to the invention (as defined above, preferably as described above as preferred) are preferably selected such that the heterogeneous catalyst can be separated off under these conditions, preferably as explained by means of one or more mechanical separation processes, for example filtration, sedimentation, centrifugation and combinations thereof. The present process according to the invention (as defined above, preferably as described above as preferred) allows separation of a heterogeneous catalyst from FDCA which is in solid form in the first or second product phase. It does not necessarily matter here what kind of reaction led to the formation of FDCA. What is important is that both a heterogeneous catalyst and FDCA are each in solid form.

Preference is given to a process according to the invention (as defined above, preferably as described above as preferred) wherein the catalytic conversion in step A) is a catalytic oxidation of the one or more organic reactant compounds by an oxidizing agent. Preferred organic reactant compounds for oxidative conversion are specified above, compounds (II), (III), (IV), (V) and (VI). Compound (II) (HMF) is preferred as reactant.

Preference is given to a process according to the invention for preparing FDCA from one or more organic reactant compounds (e.g. HMF and/or HMF derivatives, compounds (II) to (VI)), which comprises, in step (A), a catalytic oxidation of these one or more reactant compounds by an oxidizing agent. These oxidizing agents may be selected from a variety of compounds. Preference is given to a process according to the invention of this kind (as defined above, preferably as described above as preferred) wherein the oxidizing agent is selected from the group consisting of oxygen, oxygen-containing gases (preferably air, or mixtures of oxygen and nitrogen containing more or less oxygen compared to air), and oxygen releasing compounds (e.g. H ₂ 0 ₂ , other peroxides, nitrogen oxides, KMn0 ₄ , ozone).

Especially oxygen or oxygen-containing gases such as air are particularly preferred in this context (e.g. synthetic air). The particular advantage of air is that it is available in a sufficient amount and inexpensively, and has sufficient oxidizing power in combination with a suitable heterogeneous catalyst. Mixtures of oxygen and air, in which the oxygen content is adjusted either to a level of more oxygen than in air (higher than 21 % in volume), or to less oxygen than in air (lower than 21 % in volume) are specifically disclosed as useful for the purposes of the present invention. The use of gaseous oxidizing agents leads quite generally to the additional advantage that barely any excess oxidizing agent, if any, remains in the first or second product suspension after de- pressurization, whereas liquid oxidizing agents like hydrogen peroxide would have to be removed in a complex manner.

The use of oxygen in the form of oxygen of technical grade purity, air, mixtures of nitrogen and oxygen of varying contents or optionally oxygen-releasing compounds is also frequently advantageous over other oxidizing agents (additionally) comprising nitrogen or sulfur atoms (as, for example, in nitric acid, dinitrogen tetroxide and dimethyl sulfoxide), since no unwanted by-products, for example nitrous gases or sulfur compounds, which firstly may have to be removed and disposed of in an environmentally compliant manner and secondly can additionally lead to contamination of the heterogeneous catalyst, in the case of use thereof.

Typical apparatus for carrying out the oxidation reaction between a gaseous oxidant like oxygen or oxygen containing gases are known to experts skilled in the art and include apparatus which ensure via good mixing of gaseous, liquid and solid reactants sufficient supply of the oxidant (oxidizing agent) in the reaction solution. Typical apparatus in the process of the invention include stirred tank reactors, bubble columns, hexer reactors or other reactors, microreactors being preferred in the process of the invention. Also included in the invention is a series of two or more reactors (reactors as described before), known to the expert skilled in the field as "reactor cascade". Such reactors (such a cascade, respectively) allow conducting reactions (catalytically converting according to step A)) in a more controlled manner by fine adjustment of the reaction conditions (parameters) in each vessel, such conditions (parameters) may for example be temperature, oxygen (or oxidizing agent) concentration or other parameters.

Also explicitly included in the invention is the use of a fixed bed reactor using a heterogeneous catalyst in step A).

Particular preference is given to a process according to the invention (as defined above, preferably as described above as preferred) wherein one, more than one or all of the one or more organic reactant compounds in step A) are selected from the group consisting of 5-hydroxymethylfurfural (HMF, compound of the formula (II)), 2,5-diformylfuran (DFF, compound of the formula (III)), 5-hydroxymethylfuran-2-carboxylic acid (HMFCA, compound of the formula (IV)), 5-formylfuran-2-carboxylic acid (FFCA, compound of the formula (V)), and 2,5-bishydroxymethylfuran (BHMF, compound of the formula (VI)).

The organic reactant compounds enumerated in the group above, especially HMF, are particularly suitable and preferred organic reactant compounds for the aqueous reactant mixture in a process according to the invention (as defined above, preferably as described above as preferred). HMF is a compound which can be obtained from hexose- containing biomass, and corresponding processes are already being conducted on the industrial scale. In some cases, preference is given to a process according to the invention (as defined above, preferably as described above as preferred) wherein a product mixture which comprises HMF and has been obtained from a process for preparing HMF is fed directly to a process according to the invention (process coupling). In this case, this product mixture comprising HMF corresponds to the aqueous reaction mixture in step A) of the process according to the invention (as defined above, preferably as described above as preferred).

Particular preference is given to a process according to the invention (as defined above, preferably as described above as preferred) wherein

- the aqueous reactant mixture comprises one, two or more than two organic reactant compounds selected from the group consisting of 5-hydroxymethylfurfural

(HMF, compound of the formula (II)), 2,5-diformylfuran (DFF, compound of the formula (III)), 5-hydroxymethylfuran-2-carboxylic acid (HMFCA, compound of the formula (IV)), 5-formylfuran-2-carboxylic acid (FFCA, compound of the formula (V)), and 2,5-bishydroxymethylfuran (BHMF, compound of the formula (VI)) and - the catalytic conversion in step A) is a catalytic oxidation of the one or more organic reactant compounds by an oxidizing agent, the oxidizing agent preferably being selected from the group consisting of oxygen, oxygen-containing gases (preferably air, or mixtures of oxygen and nitrogen containing more or less oxygen compared to air), and oxygen-releasing compounds (e.g. H ₂ 0 ₂ , other peroxides, nitrogen oxides, KMn0 ₄ , ozone).

Particular preference is given to a process according to the invention (as defined above, preferably as described above as preferred) wherein the catalytic conversion in step A) is conducted at a pressure in the range from 1 to 200 bar and a temperature in the range from 20 to 140°C, preferably 40 to 130°C, more preferably 60 to 120°C. Temperatures and pressures in the range from 20 to 140°C and 1 to 200 bar are especially preferred since, under these conditions, a good catalytic conversion of the organic reactant compounds (especially of the organic reactant compounds which are referred to above as preferred) is achieved. Temperatures below 20°C regularly lead to only a low catalytic conversion and hence to an uneconomic process regime. Temperatures of (well) above 140°C can lead to considerable thermal decomposition of the organic reactant compound(s). Especially when the reactant mixture comprises HMF, preference is given to a process according to the invention in which the catalytic conversion in step A) is conducted at a temperature in the range from 20 to 140°C and a pressure in the range from 1 to 200 bar.

Temperatures of (well) above 140°C can additionally lead, in the presence of an oxidizing agent, to unwanted side reactions. The by-product compounds formed here may need to be removed again in a complex manner and are therefore undesirable.

Particular preference is given to a process according to the invention (as defined above, preferably as described above as preferred) wherein

1. the first product suspension, or

2. the second product suspension prepared therefrom by further treatment is heated in step B), for dissolution of the furan-2,5-dicarboxylic acid, to a temperature in the range from 120 to 190°C, preferably greater than 120°C to 190°C, more preferably 140°C to 190°C or greater than 140°C to 190°C, especially preferably 150°C to 190°C, in each case at an inherent-pressure in the range from 1 to 100 bar optionally adding to a pressure from one or more other gases. Typically, in step B) the temperature achieved by heating is higher than the temperature in step A) when the first product suspension is formed. Thus, a process according to the invention (as defined above, preferably as described above as preferred) is preferred, wherein in step B) the temperature achieved by heating is higher than the temperature in step A) when the first product suspension is formed.

The following combinations of temperature ranges for steps A) and B) are particularly preferred:

Temperature range in step A) when Temperature range in step B) the first product suspension is formed achieved by heating

i 20 to 140°C 120 to 190°C

ii 20 to 140°C greater than 120°C to 190°C iii 20 to 140°C 140°C to 190°C

iv 20 to 140°C greater than 140°C to 190°C

V 20 to 140°C 150°C to 190°C Preferably, in a process according to the invention, the aforementioned combinations of temperature ranges are combined with a pressure in the range from 1 to 200 bar in step A) and a pressure in the range from 1 to 100 bar in step B). More preferably, the aforementioned combinations of temperature ranges are combined with a pressure in the range from 1 to 200 bar in step A) and a pressure in the range from 1 to 50 bar in step B). Very particular preference is given to the combination of 1 to 200 bar in step A) and 1 to 25 bar in step B); especially preferred is the combination of 1 to 200 bar in step A) and 1 to 15 bar in step B). A temperature in the range from 120 to 190°C at a pressure of 1 to 100 bar is frequently necessary in order to dissolve FDCA again in an economically relevant amount. The dissolution process can be accelerated correspondingly by a high temperature within the temperature range from 120 to 190°C. The person skilled in the art can find out through simple laboratory experiments what temperatures, pressures and amounts of FDCA should be selected in his system in order to achieve dissolution within an acceptable time.

Preferred pressures for dissolution of the FDCA in a process according to the invention are within the range from 1 to 50 bar, preferably 1 to 25 bar, more preferably 1 to 15 bar. Preferably, in step B) the inherent pressure is within the range from 1 to 100 bar, preferably 1 to 25 bar and most preferably is about the same pressure as used in step A). Particular preference is given to working at the pressure which is established in a closed reactor (inherent pressure), which depends on the temperature and the composition of the liquid phase. In some cases, the inherent pressure is supplemented with an outside pressure which results from the presence of additional gases and increases the total pressure. The person skilled in the art will preferably select, in step B), a temperature and a pressure such that the risk of elimination of carbon dioxide out of the FDCA (decarboxylation) does not occur at all, or is preferably low. Preference is given to a process according to the invention (as defined above, preferably as described above as preferred) wherein the total amount of furan-2-carboxylic acid which forms through decarboxylation in the aqueous first product phase is 10% by weight or less, preferably 5% by weight or less, more preferably 2% by weight or less, especially preferably 0.5% by weight or less, based on the total amount of FDCA and furan-2-carboxylic acid in the aqueous first product phase.

Particular preference is given to a process according to the invention (as defined above, preferably as described above as preferred) wherein the aqueous reactant mixture in the conversion in step A) has a pH of < 7.5 and preferably at least intermittently, more preferably for most of the time, has a pH in the range from 0.5 to 5.5 (based on the total duration of process step A)), preferably 1.5 to 5.5, based on the total duration of process step A), more preferably a pH in the range from 1.5 to 3.5, based on the total duration of process step A).

The process according to the invention (as defined above, preferably as described above as preferred) allows to do without the recurrent addition of a base, especially when the abovementioned preferred organic reactant compounds are used. The pH of the aqueous reactant mixture regularly falls in the course of the catalytic conversion until it preferably attains a pH around about pH 2 (intrinsic pH). The lowering of the pH arises through the formation of FDCA, which is itself a diprotic dicarboxylic acid which dissociates in aqueous solution. The aqueous reactant mixture preferably for most of the time has a pH of about pH 2. Preferably, the aqueous reactant mixture has a pH in the range from 6.5 to 7.5 only on commencement of the catalytic conversion and in the case of a correspondingly high concentration of HMF and correspondingly low concentration of FDCA.

Since, in the process according to the invention (as defined above, preferably as described above as preferred), the aqueous reactant mixture preferably has a pH < 7.5 (and a basic pH is not necessarily required either), preference is given to dispensing with the provision and recurrent addition of a base and the continuous monitoring of the pH. At a pH < 7.5, in many cases, the catalytic activity of the heterogeneous catalyst decreases. The process according to the invention, however, allows the heterogeneous catalyst to be separated off and reused in a subsequent cycle of the process according to the invention. The recycling thus permits, on the one hand, toleration of comparatively low catalytic activities and, on the other hand, economic performance of the process according to the invention nonetheless.

Particular preference is given to a process according to the invention (as defined above, preferably as described above as preferred) wherein the heterogeneous catalyst used in step A) is a metal on a support material, a metal oxide on a support material or another metal-containing compound having catalytic activity on a support material. The catalyst optionally comprises one or more than one promotors.

Preferably, the total amount of the catalytically active metal on the support material (loading) is in the range from 0.01 % to below 20% by weight, preferably in the range from 0.02 % to 10% by weight, based on the total weight of the heterogeneous catalyst including the support and any solid material affixed thereto. More preferably, the total amount of the catalytically active metal on the support material is below 10% by weight and even more preferably the total amount is no more than 7% by weight, based on the total weight of the heterogeneous catalyst including the support and any solid material affixed thereto.

Suitable support materials are such known to experts skilled in the art and serve as media for ensuring high dispersity of the catalytically active metal or catalytically active metals and include oxides, nitrides, carbides or other carbon containing support materials which display stability in the respective reaction medium (in the first product suspension according to step A) of the present invention). A preferred support material is a carbon containing support material with at least 10% by weight of carbon, preferably with at least 50% by weight of carbon, more preferred with at least 90% by weight of carbon, based on the total weight of the support material. Preferably the support material is selected from the group of support materials consisting of carbon (preferably activated carbon), graphite, graphene and carbon nanotubes. The examples listed here are not limiting and especially included are also such materials wherein carbon is used as a coating or wherein carbon is coated with another material. Preference is given to one, two or more than two metals selected from the group consisting of Pt, Pd, Au, Re, Rh, Ir, Ru, V, Mn, Cr and W, particular preference being given to noble metals. Preferred support materials are selected from the group consisting of activated carbon, Zr0 ₂ , Ti0 ₂ , Ce0 ₂ , Al ₂ 0 ₃ , Si0 ₂ and zeolites (e.g. hydrotalcites). Particularly preferred catalysts are selected from the group consisting of Pt on carbon containing support materials (preferably on activated carbon) and gold on carbon containing support materials (preferably on activated carbon).

In the selection of suitable heterogeneous catalysts, the person skilled in the art will ensure that they have a high stability/service life in aqueous solutions. Heterogeneous catalysts which, because of their nature, lose activity in aqueous solutions are less preferred for a process according to the invention.

Particular preference is given to a process according to the invention (as defined above, preferably as described above as preferred) wherein the total amount of organic reactant compounds in the aqueous reactant mixture in step A) is 5% by weight or greater, preferably 10% by weight or greater, more preferably 15% by weight or greater, based on the total mass of the aqueous reactant mixture in step A). Preferably, the total amount of compounds (II), (III), (IV), (V) and (VI) in the aqueous reactant mixture in step A) is 5% by weight or greater, preferably 10% by weight or greater, more preferably 15% by weight or greater, based on the total mass of the aqueous reactant mixture in step A). Most preferably, the total amount of compound (I) (HMF) in the aqueous reactant mixture in step A) is 5% by weight or greater, preferably 10% by weight or greater, more preferably 15% by weight or greater, based on the total mass of the aqueous reactant mixture in step A). Herein, "in step A)" preferably means (i) at the start of step A), i.e. at the point in time immediately before the catalytic conversion in step A) is started or (ii) during the catalytic conversion is conducted, wherein preferably for 90% or more of the period in which the catalytic conversion according to step A) is carried out the total amount of organic reactant compounds (preferably HMF) in the aqueous reactant mixture in step A) does not fall below said aforementioned concentrations, based on the total time while the catalytic conversion is carried out. The aforementioned (preferred) total amounts apply preferably in some cases to a continuous process according to the invention (as defined above, preferably as described above as preferred), and in other cases preferably to a process according to the invention (as defined above, preferably as described above as preferred) which is conducted batchwise. More preferred is a process according to the invention (as defined above, preferably as described above as preferred), wherein the aforementioned (preferred) total amounts apply to a process, which is conducted batchwise. Thus, in summary, a process according to the invention (as defined above, preferably as described above as preferred) is preferred, which is conducted batchwise, wherein the total amount of organic reactant compounds in the aqueous reactant mixture at least at the start of step A) is 5% by weight or greater, preferably 10% by weight or greater, more preferably 15% by weight or greater, based on the total mass of the aqueous reactant mixture at the start of step A).

It is particularly advantageous that, in a process according to the invention (as defined above, preferably as described above as preferred), a comparatively high total amount of organic reactant compounds can be initially charged in the aqueous reactant mixture, without any relevant process disadvantages being linked thereto. This is of significance especially in the case of a continuous process regime, since comparatively high FDCA concentrations in the first product suspension can be achieved thereby. For comparison: the international patent application published as WO 2008/054804 A2 discloses that, in a "packed bed up-flow" reactor, an HMF concentration of less than or equal to 3% by weight can be fed in the reactant feed (at a neutral or acidic pH and without precipitation of FDCA).

Preference is given to a process according to the invention (as defined above, preferably as described above as preferred) which is conducted continuously or batchwise. Preference is given here to a continuous process regime. The process according to the invention (as defined above, preferably as described above as preferred) allows a good separation of the heterogeneous catalyst, such that reuse of the heterogeneous catalyst separated off becomes possible. Thus, the process according to the invention is suitable for feeding the catalyst separated off back to a continuous process according to the invention. This leads to a very effective and economic process regime and is therefore particularly preferred. Preference is given to a process according to the invention (as defined above, preferably as described above as preferred) which is performed continuously and using recycled catalyst.

In certain cases the heterogeneous catalyst according to step A) of the process of the present invention degrades due to catalyst ageing. This catalyst ageing can have various reasons, for example:

- sintering, I BASF SE I 0000077070 | 0000077070WO01 |

- formation of deposits of organic materials on the internal and/or external catalyst surface, in particular formation of deposits of specific catalyst poisons, especially catalyst poisons comprising chemical compounds containing (i) heteroatoms like nitrogen, sulfur or (ii) other elements known to dampen catalytic activity of platinum group metal catalysts,

- changes in the oxidation state of the active metal,

- and other effects known to experts skilled in the art.

In the process of the present invention it is very desirable to maintain an acceptable catalytic activity of the heterogeneous catalyst. Thus, the catalytic activity of the heterogeneous catalyst is in many cases almost fully restored by steps B) and C) of the process according to the present invention. In some cases a process according to the present invention is preferred, including additional steps after step C) and prior to re-use in order to further increase the catalytic activity of the heterogeneous catalyst achieved by steps B) and C). Preferably, the catalyst is treated with one or more washing steps before re-use including washing with aqueous and/or organic solvents in the presence of acids or bases. Suitable organic solvents include alcohols, ethers, esters, ketones, amines, and mixtures thereof. Included are also mixtures of aqueous and organic solvents, or the sequential use of such compounds or mixtures. Suitable acids include mineral acids like sulfuric, methanesulfonic or nitric acid or organic acids like acetic or formic acids or mixtures of mineral acids and organic acids. Acids or mixtures of acids can be used as solutions in water or organic solvents. Suitable bases include inorganic bases like ammonia, sodium hydroxide, sodium carbonate or organic bases like amines, alkoxides or phenolates or mixtures of inorganic bases and organic bases. Bases or mixtures of bases can be used as solutions in water or organic solvents. In many cases, within the general concept of the present invention, suitable steps for restoring catalytic activity of the spent catalyst are performed before re-use (preferably after step C) of the process according to the invention) of the catalyst and these include treatment under oxidative conditions, in particularly in the presence of oxygen, hydrogen peroxide and / or ozone in an aqueous environment at elevated temperatures. Also included are treatments under reductive conditions, explicitly the treatment with hydrogen in an aqueous environment at elevated temperatures. I BASF SE I 0000077070 | 0000077070WO01 |

In many cases, within the general concept of the present invention, it is preferred to combine steps described herein as being useful for activity restoration, such as but not limited to the combination of first a washing step and then a reductive treatment, or first an oxidative and then a reductive treatment, In many cases, within the general concept of the present invention, a step is included of removing a portion of the total amount of used catalyst and replacing this portion by a respective portion of fresh catalyst. With this additional step it is ensured that a total amount of a catalyst mixture of sufficient activity is present in the target reaction as defined in step A). The process according to the invention (as defined above, preferably as described above as preferred) allows, especially in the case of a continuous process regime, exceedance of a concentration of organic reactant compounds in the aqueous reactant mixture which typically leads to precipitation of the FDCA formed in correspondingly high concentration. According to the invention, however, what is important is not to prevent the precipitation of the FDCA formed; in fact, such a precipitation is actually desirable, since this can keep the volume of the aqueous reactant mixture (or of a reaction mixture) comparatively low.

As already explained above, in a process according to the invention (as defined above, preferably as described above as preferred), it is possible to use product mixtures from HMF preparation processes as aqueous reactant mixtures in the context of step A) (process coupling). These product mixtures frequently comprise additional constituents and compounds.

As likewise explained above, in a process according to the invention (as defined above, preferably as described above as preferred), an aqueous residual solution from step C can be recycled. Such a residual solution is the result after the heterogeneous catalyst and the FDCA have been separated off, and comprises unconverted reactant compounds in particular. In addition, additional constituents and compounds formed, for example, through side reactions may be present in the aqueous residual solution.

In some cases, preference is therefore given to a process according to the invention (as defined above, preferably as described above as preferred) wherein the aqueous reactant mixture additionally comprises one, more than one or all the compounds selected from the group consisting of: - furan-2,5-dicarboxylic acid in solid form,

- humins (i.e. oligomers of HMF, i.e. oligomers of compound of formula (II)),

- acids, preferably selected from the group consisting of levulinic acid, formic acid, hydrochloric acid, H ₂ S0 ₄ , CH ₃ S0 ₃ H, para-toluenesulfonic acid, H ₃ P0 ₄ , and combinations thereof,

- furan dimers and

- furan oligomers.

Particular preference is given to a process according to the invention (as defined above, preferably as described above as preferred) wherein, in step B), at least 80% by weight, preferably 90% by weight, more preferably 95%, of the furan-2,5-dicarboxylic acid in solid form is dissolved in the first product suspension or in the second product suspension prepared by further treatment, based on the total amount of furan-2,5-dicarboxylic acid in solid form in the first product suspension or in the second product suspension prepared by further treatment. The person skilled in the art is aware, for example, of optical methods with which the degree of dissolution can be determined by means of simple experiments. The person skilled in the art can additionally conduct simple solubility experiments either on individual compounds or on the first or second product suspension and/or on the aqueous first product phase.

As defined in the claims and according to a further important aspect, which is preferably combined with the first aspect as discussed hereinabove, the object as stated above is achieved by a process of making (i.e. by a process for preparing) furan-2,5-dicarboxylic acid, comprising the following steps:

(a) subjecting a starting mixture comprising 5-(hydroxymethyl)furfural and water to oxidation conditions in the presence of a heterogeneous oxidation catalyst and an oxygen-containing gas so that a first product mixture results comprising furan-2,5- dicarboxylic acid, water and by-products,

(b) subjecting a mixture comprising water, said furan-2,5-dicarboxylic acid and said by-products to hydrogenation conditions in the presence of a heterogeneous hydrogenation catalyst so that a second product mixture results comprising furan- 2,5-dicarboxylic acid, water and hydrogenated by-products, and subsequently

(c) separating said furan-2,5-dicarboxylic acid from said hydrogenated by-products so that isolated furan-2,5-dicarboxylic acid results, wherein said first product mixture resulting from step (a) is heated and/or diluted with water to give said mixture subjected to hydrogenation conditions in step (b).

When conducting step (a) of the process of the invention (as defined in the claims) the skilled person will preferably proceed according to steps (A) and, optionally, (B) of the first important aspect of the invention (as defined above). In many cases however it is preferred that in the process of the invention (as defined in the claims), there is no step of heating under pressure a product suspension (in particular a product suspension as defined above) comprising furan-2,5-dicarboxylic acid in solid form and the heterogeneous catalyst in solid form, such that furan-2,5-dicarboxylic acid dissolves fully or partly. In many cases, in a process of the invention (as defined in the claims) it is preferred that furan-2,5-dicarboxylic acid as prepared in step (a) is not precipitated in solid form from the first product mixture comprising furan-2,5-dicarboxylic acid, water and by-products. Correspondingly, in many cases it is preferred that in step (b) the mixture comprising water, said furan-2,5-dicarboxylic acid and said by-products does not comprise any furan-2,5-dicarboxylic acid in solid form or does not comprise more furan- 2,5-dicarboxylic acid in solid form than in the dissolved form.

According to the feature "wherein said first product mixture resulting from step (a) is heated and/or diluted with water to give said mixture subjected to hydrogenation conditions in step (b)" no substance from the product mixture resulting from step (a) is removed between steps (a) and (b). Preferably, said first product mixture resulting from step (a) is heated and/or is diluted with water to give said mixture subjected to hydrogenation conditions in step (b) by addition of (pure) water or by addition of an aqueous mixture comprising more than 50 % by weight water. Said first product mixture resulting from step (a) is heated and/or diluted with water preferably so that any furan-2,5-dicarboxylic acid present after step (a) in the solid form is completely dissolved, so that said mixture subjected to hydrogenation conditions in step (b) does not comprise any furan-2,5-dicarboxylic acid in the solid form. In oxidation step (a) the oxidation can be conducted in one or more sub-steps using suitable reactor types and combinations thereof. Suitable reactor types include batch- and semi-batch-reactors, continuous stirred tank reactors, fixed-bed and trickle-bed reactors or bubble columns and combinations thereof. Further preferred apparatus for use in the process of the invention are stated above.

With respect to step (b) the term "hydrogenated by-products" designates substances obtained by hydrogenating the by-products obtained in step (a).

E.g., in step (b) intermediate FFCA (which is present as a by-product in the first product mixture obtained in step (a)) is converted to 5-hydroxymethylfurane-2-carboxylic acid (HMFCA), 5-methylfurane-2-carboxylic acid (MFCA), furane-2-carboxylic acid (FCA) and other hydrogenated products, which are water soluble and can be readily separated from FDCA through numerous techniques, such as crystallization. In addition, unsaturated colored compounds (which are present as a by-product in the first product mixture obtained in step (a)) are converted to hydrogenated, i.e. saturated, colorless compounds (i.e. specific hydrogenated by-products), and these hydrogenated colorless products are removed from the product FDCA in step (c).

In comparison with processes of the type as disclosed in patent documents as US 2013/0345451 and US 2013/0345452, the present invention is advantageous. In processes of the type disclosed in said patent documents the oxidation step is conducted using a homogeneous catalyst system and using acetic acid as a solvent. Thereafter, in the hydrogenation step, a different solvent system (water) is used. Consequently, between the oxidation step and the hydrogenation step, the solvent system has to be replaced. The acetic acid used in the oxidation step cannot simply be discarded but for economic reasons should be recovered, purified and recycled. Thus, corresponding costs are incurred for energy and corresponding apparatus. Furthermore, the solvent used in the oxidation step, in particular due to the presence of halides, is very corrosive so that the reaction apparatus used must be made from costly corrosion resistant materials as titanium plated or coated steel or nickel-based alloys which are resistant against many aggressive chemicals (e.g. alloys of the 'Hastelloy' type). These disadvantages are overcome by the present invention.

Preferably, in a process according to the invention as defined in the claims the heterogeneous oxidation catalyst is a heterogeneous oxidation catalyst containing a platinum group metal, preferably a heterogeneous oxidation catalyst containing a platinum group metal selected from the group consisting of palladium and platinum. The heterogeneous oxidation catalyst catalyzes the oxidation of 5-(hydroxymethyl)furfural to furan-2,5-dicarboxylic acid.

The heterogeneous oxidation catalyst more preferably is a heterogeneous oxidation catalyst containing Pt, even more preferably a heterogeneous oxidation catalyst containing Pt on carbon.

In processes of the type disclosed in documents as US 2013/0345451 and US 2013/0345452 typically halide anions or halogen as well as cobalt and manganese are present as a catalyst component. In contrast thereto, when using a heterogeneous oxidation catalyst containing a platinum group metal, there is no need for the presence of such halide anions or halogen. Preferably, the starting mixture subjected to oxidation conditions in step (a) and/or the mixture subjected to hydrogenation conditions in step (b) of the process according to the present invention does not comprise any catalytically effective amounts of cobalt, bromine and manganese compounds or admixtures thereof. Even more preferably, said starting mixture subjected to oxidation conditions and/or said mixture subjected to hydrogenation conditions in step (b) of the process of the present invention does not comprise any bromine or bromide in a catalytically effective amount, and more preferably does not comprise any halide anions or halogen in a catalytically effective amount. Furthermore, the use of a heterogeneous catalyst simplifies work-up as heterogeneous catalysts can be more easily separated from a reaction mixture than homogeneous catalysts dissolved in the liquid phase of a reaction mixture.

Preferably, in a process according to the invention as defined in the claims the heterogeneous hydrogenation catalyst is a heterogeneous hydrogenation catalyst containing a metal, preferably a metal selected from the group of transition metals (e.g., but not limited to, Cu and platinum metals like Pt and Pd), preferably a metal selected from the group of platinum metals, preferably a platinum group metal, preferably a heterogeneous hydrogenation catalyst containing a platinum group metal selected from the group consisting of palladium and platinum. The heterogeneous hydrogenation catalyst catalyzes the hydrogenation of oxidation by-products from step (a) of the process according to the invention as defined in the claims.

The heterogeneous hydrogenation catalyst more preferably is a heterogeneous hydrogenation catalyst containing Pt, even more preferably a heterogeneous catalyst containing Pt on carbon. Even more preferably, in a process according to the invention as defined in the claims the heterogeneous oxidation catalyst and the heterogeneous hydrogenation catalyst are both heterogeneous catalysts containing a platinum group metal, wherein preferably the heterogeneous oxidation catalyst and the heterogeneous hydrogenation catalyst are the same.

Preferably the heterogeneous oxidation catalyst and the heterogeneous hydrogenation catalyst are the same heterogeneous catalyst, preferably the same heterogeneous catalyst containing a platinum group metal, preferably the same heterogeneous catalyst containing a platinum group metal selected from the group consisting of palladium and platinum, more preferably the same heterogeneous catalyst containing Pt, even more preferably the same heterogeneous catalyst containing Pt on carbon.

If the heterogeneous oxidation catalyst and heterogeneous hydrogenation catalyst are the same heterogeneous catalyst only a single catalyst system has to be provided and stored for conducting the two-step oxidation/hydrogenation process, and correspondingly the storage costs and the costs for preparing the catalyst system are significantly reduced. Furthermore, both the oxidation and the hydrogenation step can be conducted in the same reactor, or if the oxidation step and the hydrogenation step are conducted in different reactors there is no need for clearly separating these reactors. Furthermore, in a situation where the heterogeneous catalysts used in the process of the present invention need to be replaced it is far simpler for the skilled person if there is only a single heterogeneous catalyst system to be replaced in comparison with the situation where two heterogeneous catalyst systems in separate parts of the reaction apparatus need to be replaced separately and without any cross-contamination.

In other preferred embodiments the heterogeneous oxidation catalyst and the heterogeneous hydrogenation catalyst are not the same heterogeneous catalyst.

Preferred is a process according to the invention as defined in the claims, wherein the first product mixture resulting from step (a) comprises one or more mono-carboxylic acid oxidation products of 5-(hydroxymethyl)furfural, and the second product mixture resulting from step (b) comprises one or more hydrogenated by-products which are hydrogenation products of at least one of said mono-carboxylic acid oxidation products of 5-(hydroxy- methyl)furfural. A typical mono-carboxylic acid oxidation product of 5-(hydroxymethyl)furfural is, for example,

FFCA: 5-Formylfurane-2-carboxylic acid

Typical hydrogenated by-products which are hydrogenation products of at least one of said mono-carboxylic acid oxidation products of 5-(hydroxymethyl)furfural correspondingly are:

HMFCA: 5-(Hydroxymethyl)furane-2-carboxylic acid

5-Methylfurane-2-carboxylic acid

Furane-2-carboxylic acid

Oxidation products as FFCA possess a low solubility in water, and their separation from the reaction mixture (in particular FDCA) and the heterogeneous catalysts used according to the present invention is technically challenging. Thus, it is a major advantage of the present invention that such mono-carboxylic acid oxidation products as I BASF SE I 0000077070 | 0000077070WO01 |

FFCA in the hydrogenation step (b) of the process of the present invention are transferred into hydrogenation products which are more easily separable from both the reaction mixture and the heterogeneous catalysts used. In the process according to the present invention, the mono-carboxylic acid oxidation products of 5- (hydroxymethyl)furfural as comprised in the first product mixture are not separated from the other constituents of said first product mixture before hydrogenation step (b) is conducted. If, in the process of the present invention in step (a), a mono-carboxylic acid oxidation product of 5-(hydroxymethyl)furfural contaminates the heterogeneous oxidation catalyst used in step (a), it is particularly preferable that said contaminated heterogeneous oxidation catalyst is present in step (b) of the process of the present invention. In this case, under hydrogenation conditions of step (b), the contaminant contaminating the heterogeneous oxidation catalyst is removed so that the heterogeneous oxidation catalyst can be used again in an oxidation step (a), or act as a heterogeneous hydrogenation (co-)catalyst in step (b). Correspondingly, it is preferable to conduct both steps (a) and (b) of the process of the present invention consecutively in the same reaction vessel without removal of the heterogeneous oxidation catalyst before hydrogenation.

Step (c) of the process according to the present invention in many cases comprises filtration of (i) the second product mixture comprising furan-2,5-dicarboxylic acid, water and hydrogenated by-products, or (ii) a mixture obtained from the second product mixture by additional treatment steps, to give a filtration residue comprising furan-2,5-dicarboxylic acid, and drying of this filtration residue.

Preferred is a process according to the invention as defined in the claims, wherein step (c) comprises the selective crystallization of furan-2,5-dicarboxylic acid from an aqueous phase, so that hydrogenated by-products remain in the aqueous phase. Herein, the aqueous phase is preferably a mixture obtained from the second product mixture by additional treatment steps, e.g. by adding organic solvents supporting (re-)crystallization. If furan-2,5-dicarboxylic acid is selectively crystallized from an aqueous phase, so that hydrogenated by-products remain in the aqueous phase, the furan-2,5-dicarboxylic acid can be easily separated from said hydrogenated by-products. Surprisingly, furan-2,5- dicarboxylic acid can be selectively crystallized from an aqueous phase so that the hydrogenated by-products (e.g., HMFCA, 5-methylfurane-2-carboxylic acid (MFCA) and furane-2-carboxylic acid (FCA)) remain in the aqueous phase. Thus, the separation of furan-2,5-dicarboxylic acid from said hydrogenated by-products can be accomplished in a straightforward manner. Preferred is a process according to the invention as defined in the claims, wherein in said mixture subjected to hydrogenation conditions in step (b) the furan-2,5-dicarboxylic acid is completely dissolved.

As a heterogeneous hydrogenation catalyst is used in step (b) any furan-2,5-dicarboxylic acid which is not dissolved might contribute to contamination of the heterogeneous hydrogenation catalyst. Thus, it is preferred and particularly advantageous to adjust the reaction conditions so that all of said furan-2,5-dicarboxylic acid (as produced in step (a)) is dissolved in said mixture subjected to hydrogenation conditions in step (b). Preferably, even at the end of the hydrogenation step (b) all of said furan-2,5-dicarboxylic acid is completely dissolved in the product mixture. In this case separation of the target product furan-2,5-dicarboxylic acid from the heterogeneous hydrogenation catalyst is particularly simple.

Preferred is a process according to the invention as defined in the claims, wherein the pH of said starting mixture in step (a) is 7 or below 7, preferably in the range of from 4 to 7 and/or wherein the pH of said first product mixture in step (a) is below 3, more preferably below 2.

When the pH of said starting mixture in step (a) is 7 or below 7, and preferably is in the range of from 4 to 7, the reaction product furan-2,5-dicarboxylic acid is produced without having the opportunity to react with basic compounds to give the corresponding salt of the furan-2,5-dicarboxylic acid. If no significant amounts of pH-modifying additives (i.e. buffers or the like) are present in the starting mixture according to step (a) of the process of the present invention, due to the formation of furan-2,5-dicarboxylic acid the pH in the reaction mixture decreases, and finally the pH of the first product mixture in step (a) is below 3, more preferably below 2. No salt of the reaction product furan-2,5-dicarboxylic acid is formed, or at least no significant amounts of such salt. Correspondingly, in the following step (b) furan-2,5-dicarboxylic acid can be employed without transforming its salt into its acidic form.

Preferred is a process according to the invention as defined in the claims, comprising before step (a) the step (pre-a) preparing the starting mixture of step (a) in a pre-process comprising the production of 5-(hydroxymethyl)furfural by dehydration of sugar.

Preferably, if step (pre-a) is conducted before step (a), preferably in all steps (pre-a), (a), and (b), the respective reaction mixture (in step (pre-a) this is the mixture subjected to dehydration conditions, in step (a) this is the mixture subjected to oxidation conditions, and in step (b) this is the mixture subjected to hydrogenation conditions) is an aqueous mixture comprising water as its main ingredient (i.e. the respective mixture comprises more than 50 wt.% water), and preferably between steps (pre-a) and (a) as well as between steps (a) and (b) there is no solvent replacement step. Thus, the water present in step (pre-a) is present also in step (a) and in step (b), or, if the removal of water from the process cannot completely be avoided, at least 90% by weight of the water employed in step (pre-a) is transferred into step (a) and present therein, and at least 90% of the water present in step (a) is transferred into step (b) and present therein.

Preferably, in the process according to the present invention a crude aqueous HMF- solution from fructose dehydration (conducted as step (pre-a)) is directly used in the oxidation (step (a)). Thus troublesome separation of HMF from an aqueous solution is avoided.

Preferred is a process according to the invention as defined in the claims, wherein said isolated furan-2,5-dicarboxylic acid has a b* of 10 or less, preferably 5 or less. The b* is one of the three-color attributes measured on a spectroscopic reflectance- based instrument. As already stated in US 20130345451 , the color can be measured by any device known in the art. A Hunter Ultrascan XE instrument is typically the measuring device. Positive readings signify the degree of yellow (or absorbance of blue), while negative readings signify the degree of blue (or absorbance absorbance of yellow). Solid samples of FDCA can be analyzed using a Hunter Lab UltraScan Pro spectrophotometer with an integrating light sphere. Per manufacturer recommendation the spectrophotometer should be set to the CIELAB color scale with the D65 illuminate and 10' observer. The spectrophotometer is standardized in total reflectance mode. For further instructions regarding the measurement of b* reference is made to US 20130345451 , paragraphs [0160] to [0177]. Preferred is a process according to the invention as defined in the claims, wherein said isolated furan-2,5-dicarboxylic acid comprises mono-carboxylic acids in an amount of less than 200 ppm preferably in an amount of less than 50 ppm.

The term "isolated furan-2,5-dicarboxylic acid" designates a composition comprising more than 99.8 wt-% furan-2,5-dicarboxylic acid.

Preferred is a process according to the invention as defined in the claims, wherein the molar ratio of isolated furan-2,5-dicarboxylic acid resulting in step (c) to 5-(hydroxy- methyl)furfural present in the starting mixture of step (a) is 0,8 or higher, preferably 0,9 or higher. Preferred is a process according to the invention as defined in the claims, wherein in said starting mixture the amount of 5-(hydroxymethyl)furfural is in the range of from 1 to 40 % by weight, based on the total amount of the starting mixture.

Preferred is a process according to the invention as defined in the claims, wherein said first product mixture resulting from step (a) is separated from said heterogeneous oxidation catalyst before or during said step of heating and/or diluting with water.

Preferred is a process according to the invention as defined in the claims, wherein said steps (a) and (b) are conducted in separate reactors or in separate reaction spaces of the same reactor.

Preferred is a process according to the invention as defined in the claims, comprising the following steps:

(a) subjecting a starting mixture comprising 5-(hydroxymethyl)furfural and water to oxidation conditions in the presence of a heterogeneous oxidation catalyst and an oxygen-containing gas so that a first product mixture results comprising furan-2,5- dicarboxylic acid, water and by-products, (b) subjecting a mixture comprising water, said furan-2,5-dicarboxylic acid and said by-products to hydrogenation conditions in the presence of a heterogeneous hydrogenation catalyst so that a second product mixture results comprising furan- 2,5-dicarboxylic acid, water and hydrogenated by-products, and subsequently

(c) separating said furan-2,5-dicarboxylic acid from said hydrogenated by-products so that isolated furan-2,5-dicarboxylic acid results, wherein said first product mixture resulting from step (a) is heated and/or diluted with water to give said mixture subjected to hydrogenation conditions in step (b), wherein said first product mixture resulting from step (a) before or during said step of heating and/or diluting with water is separated from said heterogeneous oxidation catalyst, wherein in said starting mixture the amount of 5-(hydroxymethyl)furfural is in the range of from 1 to 30 % by weight, based on the total amount of the starting mixture, and wherein step (c) comprises the selective crystallization of furan-2,5-dicarboxylic acid from an aqueous phase, so that hydrogenated by-products remain in the aqueous phase.

The present invention correspondingly also relates to the use of a catalyst for both

(a-u) oxidizing 5-(hydroxymethyl)furfural in a starting mixture comprising 5- (hydroxymethyl)furfural and water so that a first product mixture results comprising furan-2,5-dicarboxylic acid, water and by-products, and subsequently

(b-u) hydrogenating at least part of said by-products in a mixture comprising water and at least a fraction of said furan-2,5-dicarboxylic acid and said by-products.

Herein, the catalyst preferably is a heterogeneous catalyst, preferably containing a platinum group metal, preferably a heterogeneous catalyst containing a platinum group metal selected from the group consisting of palladium and platinum.

The invention as defined in the claims is based on the surprising finding that isolated furan-2,5-dicarboxylic acid (as defined above) can be produced by means of an oxidation/hydrogenation sequence without the need for solvent switches. This can be achieved by conducting the oxidation of HMF to a first product mixture ("crude FDCA") comprising furan-2,5-dicarboxylic acid, water and by-products in water at a pH <7 using a heterogeneous Pt-based catalyst. The oxidation step (step (a) of the process as defined in the claims) can be conducted in one or more steps using suitable reactor types and combinations thereof. Suitable reactor types include batch- and semi-batch-reactors, continuous stirred tank reactors, fixed-bed and trickle-bed reactors or bubble columns and combinations thereof. Optionally, a crude aqueous HMF-solution from fructose dehydration can be used directly in the oxidation thus avoiding troublesome separation of HMF from an aqueous solution. The oxidation step typically yields as the first product mixture a solution or slurry of crude-FDCA. If a slurry is obtained, the temperature may be increased or additional water may be added in order to completely dissolve all solid products of the oxidation reaction of step (a). The thus obtained mixture comprising water, said furan-2,5-dicarboxylic acid and said by-products (crude-FDCA solution) is then typically subjected to hydrogenation (step (b) of the process as defined in the claims) using standard hydrogenation catalysts. Optionally, the catalyst used in the hydrogenation (step (b) of the process as defined in the claims) is the same catalyst type of catalyst used in the oxidation (step (a) of the process as defined in the claims). The obtained composition can then be fitrated and dried using standard unit operations, for separating said furan-2,5-dicarboxylic acid from said hydrogenated by-products so that isolated furan-2,5-dicarboxylic acid results according to step (c) of the process as defined in the claims.

The invention is illustrated in detail hereinafter by examples.

Examples:

Example 1 : Catalyst screening: l-a Catalysts used in catalyst screening:

For the process of the present invention the following heterogeneous catalysts (see Table 1 ) were used in catalytically converting one or more organic reactant compounds according to step A). The heterogeneous catalysts listed in Table 1 are platinum on carbon containing support materials-catalysts, each exhibiting a platinum loading of 5 % by weight, based on the total weight of the dry catalyst. "Humidity" refers to the total amount of water in % by weight, based on the total weight of the catalyst. Table 1 : Heterogeneous catalysts used in the catalyst screening experiments for a catalytic conversion as defined in step A) in the process of the present invention. The asterisks have the following meaning: * abcr GmbH & Co. KG, Im Schlehert 10, 76187 Karlsruhe, Germany, ** Sigma-Aldrich Chemie GmbH, Riedst^e 2, D-89555 Steinheim, Germany. l-b Catalyst screening experiments:

Catalyst screening was carried out in a series of single experiments designated "Screen 1 " to "Screen 7". In each single experiment "Screen 1 " to "Screen 7" the organic reactant compound HMF (compound of Formula (II)) was in parts catalytically converted by means of at least one heterogeneous platinum catalyst (see Tables 1 and 2, below) into FDCA (compound of formula (I)). The general experimental procedure for each screening experiment of "Screen 1 " to "Screen 7" was as follows:

In a first step, an aqueous reactant mixture was prepared by filling a specific amount of deuterated water (D ₂ 0, 99,9 atom%, Sigma Aldrich (151882)) and a specific amount of HMF (99+%, Sigma Aldrich (W501808)) into a steel autoclave reactor (inner volume 60 ml or 90 ml, respectively, for exact information see Table 2, below). In case a steel autoclave reactor with an inner volume of 60 ml was used the amounts of HMF and D ₂ 0 were as follows: D ₂ 0: 18,0 g, HMF: 2,0 g (corresponding to 15,9 mmol as starting amount of HMF). In case a steel autoclave reactor with an inner volume of 90 ml was used the amounts of HMF and D ₂ 0 were as follows: D ₂ 0: 27,0 g, HMF: 3,0 g (corresponding to 23,8 mmol as starting amount of HMF). The starting concentration C ₀ [HMF _] of HMF in each aqueous reactant mixture was 10 % by weight, based on the total mass of the aqueous reactant mixture (total mass of deuterated water and HMF).

The respective amount of solid heterogeneous catalyst as stated in Table 2 was added to the respective aqueous reactant mixture and, thus, a reaction mixture comprising deuterated water, HMF, and the heterogeneous catalyst was obtained. After adding the specific amount of heterogeneous catalyst the obtained reaction mixture appeared as a deep black slurry, the black color apparently caused by the black solid particles of the heterogeneous catalyst. The molar ratio of substrate to metal of the heterogeneous catalyst (HMF : Pt) was approximately 100 : 1.

In a second step, the filled reactor was tightly sealed and pressurized with synthetic air (total pressure 100 bar, Oxygen (as part of the synthetic air) : HMF ratio is approximately 2,25 : 1 ) to obtain conditions for catalytic conversion. The present reaction mixture was heated to a temperature of 100°C while stirring at 2000 rpm. After reaching 100°C this temperature was maintained for 4 or 20 hours, respectively, (see Table 2 "Reaction time" for exact information) while continuing stirring the heated and pressurized reaction mixture during the reaction time. As a result, a first product suspension comprising FDCA in solid form and the heterogeneous catalyst in solid form was formed.

In a third step, after the respective time of 4 or 20 hours, respectively, the steel autoclave reactor was (i) allowed to cool down to room temperature (approximately 22 °C), (ii) the pressure was released and (iii) the steel autoclave reactor was opened. In the steel autoclave reactor a gray slurry was identified, apparently corresponding to a first product suspension comprising FDCA in solid form (off- white particles) and the heterogeneous catalyst in solid form (black particles). For further analysis of the first product suspension a solution of deuterated sodium hydroxide (NaOD, 40 wt.-% in D ₂ 0, 99.5 atom% D, Sigma Aldrich (372072)) was carefully added to the first product suspension until the pH-value was adjusted to a pH in the range of from 9 to 10. As a result, a treated first product suspension resulted comprising the completely dissolved disodium salt of FDCA and the heterogeneous catalyst in solid form. The treated first product suspension appeared black, the black color apparently caused by the black solid particles of the heterogeneous catalyst.

In a fourth step, the heterogeneous catalyst in the treated first product suspension was separated from the dissolved FDCA by syringe filtration and the filtrate was subsequently analyzed by NMR spectroscopy. NMR spectroscopy was used to determine the concentration of compounds of formulae (I) (FDCA), (II) (HMF), (III) (DFF), (IV) (HMFCA), and (V) (FFCA), in particular to determine the HMF concentration C _[H MF _] in the filtrate in order to calculate the HMF conversion in molar%. Furthermore, the total amount of carbon in substances with organic constituents (TOC) of the filtrate was determined by a combustion method.

The type and amount of heterogeneous catalyst used, the reaction time, HMF- conversion, yield and TOC for each single experiment is summarized in Table 2 under item l-e.

A comparison experiment was conducted under the same conditions, with the only exception that no catalyst was used. No FDCA was formed in this comparison experiment. l-c NMR analysis:

1-C.1 NMR sample preparation and NMR measurements:

3-(Trimethylsilyl)propionic-d ₄ acid sodium salt (Standard 1 , 68,39 mg, corresponding to 0,397 mmol, 98+ atom% D, Alfa Aesar (A14489)) and Tetramethylammonium iodide (Me ₄ N ⁺ l ^~ , Standard 2, 80,62 mg, corresponding to 0,397 mmol, 99%, Alfa Aesar (A1281 1 )) were added as internal standards to 5,0 g of a pH-adjusted sample, exhibiting a pH value in the range of from 9 to 10 (such samples are for example filtrates obtained as described in the fourth step according to item l-b above or liquids/filtrates obtained after the sixth step as described below in items ll-a and lll-a, respectively). As a result, a prepared sample liquid resulted.

Finally, 0,7 ml of this prepared sample liquid were transferred into a NMR tube for H NMR quantification experiments. NMR-spectra were recorded in D ₂ 0 at 299 K using a Bruker-DRX 500 spectrometer with a 5mm DUL 13-1 H/19F Z-GRD Z564401/1 1 probe, measuring frequency 499,87 MHz. Recorded Data were processed with the software Topspin 2.1 , Patchlevel 6 (Supplier: Bruker BioSpin GmbH, Silberstreifen 4, 76287 Rheinstetten, Germany).

1-c2 Interpretation of NMR spectra:

Interpretation of NMR spectra is based on published reference data. disodium salt of FDCA (disodium salt of compound of formula (I)): H NMR (500 MHz, D ₂ 0, 299 K): 6.97 ppm (2H, s, furan-H); ³ C{ H} NMR: 166.1 ppm (-COO), 150.0 ppm (furan C atoms), 1 15.8 ppm (furan C atoms).

Reference: J. Ma, Y. Pang, M. Wang, J. Xu, H. Ma and X. Nie, J. Mater. Chem., 2012, 22, 3457-3461. sodium salt of FFCA (sodium salt of compound of formula (V)): H NMR (500 MHz, D ₂ 0, 299 K): 9.49 ppm (1 H, s, -CHO); 7.42 ppm (1 H, d, ³ J= 3.67 Hz, furan-H); 7.03 ppm (1 H, d, ³ J= 3.67 Hz, furan-H).

Reference: A. J. Carpenter, D. J. Chadwick; Tetrahedron 1985, 41 (18), 3803-3812. sodium salt of HMFCA (sodium salt of compound of formula (IV)): H NMR (500 MHz, D ₂ 0, 299 K): 6.89 ppm (1 H, d, ³ J= 3.38 Hz, furan-H); 6.40 ppm (1 H, d, ³ J= 3.38 Hz, furan-H), 4.55 ppm (1 H, s, -CH ₂ OH, methylene H);

Reference: T. Matsui, A. Kudo, S.Tokuda, K. Matsumoto, H. Hosoyama, J. Agric. Food Chem. 2010, 58(20), 10876-10879. 1 D- H-NMR spectra:

In figures 1A, 1 B, and 1 C 1 D- H-NMR spectra are shown. In each figure identified signals are assigned to protons of r the respective compound. The respective compounds are depicted in the spectrum.

Fig. 1A is a 1 D-1 H-NMR spectrum of a sample obtained from the filtrate of the treated first product suspension (see item l-b, third and fourth step) of experiment "Screen 5" (i.e. the catalyst with the catalyst number 5 was used). The signal with the chemical shift of 3, 1 1 ppm belongs to Tetramethylammonium iodide (standard 2). The signal with the chemical shift of -0,08 ppm belongs to 3- (Trimethylsilyl)propionic-d ₄ acid sodium salt (standard 1 ).

Fig. 1 B is an excerpt of the spectrum of Fig. 1A, magnifying the spectral range from 7,5 ppm to 6,3 ppm.

Fig. 1 C is a 1 D-1 H-NMR spectrum of a sample obtained from the filtrate of the treated first product suspension (see item l-b, third and fourth step) of experiment "Screen 7" (i.e. the catalyst with the catalyst number 1 was used). The signal with the chemical shift of 3,07 ppm belongs to Tetramethylammonium iodide (standard 2). The signal with the chemical shift of -0,10 ppm belongs to 3- (Trimethylsilyl)propionic-d ₄ acid sodium salt (standard 1 ).

TOC analysis:

The total amount of carbon in substances with organic constituents (TOC) was determined as follows:

A respective sample was weighed into a tin capsule and combusted in a tube oven in an oxygen atmosphere. The resulting combustion gases (comprising carbon) were converted by catalysts into detectable compounds (e.g. C0 ₂ ) which were subsequently detected.

Carbon: detection and quantification as C0 ₂ by means of TCD- detection,

Sample take-in: 1 - 10 mg, Limit of Determination: w(C) = 0,5 g/100 g

Precision: +/- 0.1 g/100 g

Apparatus: CHN-Analyser Micro Cube, (Supplier: Elementar)

Detection and quantification was carried out based on the following Literature: F. Ehrenberger "Quantitative organische Elementaranalyse" (ISBN 3-527-28056-1 ). l-e Results and analysis of the catalyst screening experiments:

In each single experiment a treated first product suspension comprising FDCA in solid form and a heterogeneous catalyst in solid form was obtained. As shown in Table 2, a variety of heterogeneous platinum catalysts on carbon containing support materials is suited to catalytically convert HMF into FDCA by oxidation reaction. HMF conversion in molar%, yield in molar% and TOC are summarized in Table 2. In Table 2 "Catalyst number" refers to the specific number for each catalyst as assigned in Table 1. "Inner volume" refers to the volume of the steel autoclave reactor. "Reaction time" refers to the time period as described above in item l-b, second step. Reaction conditions have not been optimized to necessarily afford full conversion of HMF to FDCA.

Inner HMF (II) Yield [molar%]

Cat. Cat. volume Reaction Conv. TOC

Experiment

No. [%]

[g] [ml] time [h]

(IV) (Ill) (V) (I)

[molar%]

Screen 1 1 0.936 90 4 100 - - 35.9 53.3 96.4

Screen 2 2 1.239 60 4 100 - - 27.9 60.2 84.8

Screen 3 3 1.238 60 4 100 1.7 - 36.7 42.2 85.3

Screen 4 4 0.620 60 4 100 1.5 - 24.3 65.2 95.4

Screen 5 5 0.620 60 4 100 1.7 - 31.4 55.6 94.5

Screen 6 6 1.548 60 4 100 2.5 - 31.4 39.0 77.7

Screen 7 1 0.620 60 20 100 - - 1.9 95.2 99.2 Table 2: Relevant parameters of catalyst screening experiments. Roman numerals refer to the compounds of the respective formulae used above in the present text: (II) refers to HMF, (IV) refers to HMFCA, (III) refers to DFF, (V) refers to FFCA, and (I) refers to FDCA. HMF conversion in molar% was calculated as follows: HMF Conversion [molar%] = [1-(C[HMF]/CO[HMF] ₎ )]*100, wherein C[HMF] and CO[HMF] are the respective concentrations in % by weight. Yield in molar% was calculated as follows: Yield [molar%] = [(C _[ p _r oduct Mp _ro duct) (Co[HMF] MHMF)]*100, wherein C _[pro duct] is the respective product concentration in % by weight, C ₀ [HMF _] is the HMF starting concentration in % by weight, Mproduct and M _H MF are the respective molecular weights in gram/mol. "Conversion [molar%]" and "yield [molar%]" are average values calculated from a first value based on internal standard 1 and a second value based on internal standard 2 (general deviation is less than 5 %) (for standard 1 and standard 2 see above in item l-c).

In the international patent application with the publication number WO 2013/191944 A1 it is disclosed that the solubility of FDCA in water at a temperature up to 100°C is in the range of from 1 ,0 to 2,0 % by weight. As shown above in item l-b the starting concentration C ₀ [HMF _] of HMF in the aqueous reactant mixture in each single experiment was approximately 10 % by weight, based on the total mass of the aqueous reactant mixture. As shown in Table 2, the yield of FDCA in molar% is in the range of from approximately 39 to 95 %. This corresponds to a FDCA concentration in the first product suspension of at least 5 % by weight, based on the total weight of the first product suspension. The concentration of FDCA in the product suspension can be calculated with the following equation:

C[FDCA] = CO[HMF]/M _[H MF]*M _[F DCA _] *(FDCA yield), wherein C _[F DCA] is the FDCA concentration in % by weight, C ₀ [HMF] is the HMF starting concentration in % by weight, M _[H MF _] is the molecular weight of HMF in gram/mol, M _[FDC A _] is the molecular weight of FDCA in gram/mol, and FDCA yield is the yield in molar% as stated in Table 2 in the column labelled with (I).

For example, a FDCA yield of 40 % corresponds to a FDCA concentration of approximately 5 % by weight, based on the total weight of the first product suspension and based on a HMF starting concentration of 10 % by weight. Thus, the amount of FDCA in the first product suspension exceeds the solubility limit as disclosed in WO 2013/191944 A1. As a consequence, the first product suspension comprises FDCA in solid form, which is confirmed by the presence of the gray- slurry observed in the third step discussed in item l-b.

Further Experiments:

Catalyst screening experiments according to item l-b, above, were repeated with alternative heterogeneous solid catalysts. The alternative heterogeneous solid catalysts exhibited (i) other support materials, including silica or a zeolite and/or (ii) other catalytic metals and mixtures of catalytic metals such as mixtures of platinum and gold.

These further experiments as expected also showed a catalytic conversion of HMF into FDCA.

Example 2: Dissolving solid FDCA and separating dissolved FDCA from heterogeneous catalysts:

Dissolving solid FDCA and separating from the catalyst:

Dissolving solid FDCA and subseguent separation of dissolved FDCA from a heterogeneous catalyst was carried out using an apparatus as described in Fig. 2.

Fig. 2 is a schematic drawing of an apparatus for (i) dissolving solid FDCA in a first product suspension and (ii) subseguent separating of the dissolved FDCA from a heterogeneous catalyst.

The apparatus according to Fig. 2 consists of a first steel autoclave reactor 201 with an inner volume of 90 ml, a second steel autoclave reactor 210 with an inner volume of 90 ml and a transfer line 220 connecting the first steel autoclave reactor 201 with the second steel autoclave reactor 210. The transfer line 220 is heatable and includes a valve 221 in order to control the transfer of material between the autoclave reactors 201 and 210. The transfer line 220 also includes a filter unit 222, wherein the filter unit 222 includes a 2 μητι filter. The filter unit 222 is located near the bottom of the first steel autoclave reactor 201. The first autoclave reactor 201 comprises an overhead stirrer 202 and a thermocouple sensor 203. Both steel autoclave reactors 201 and 210 include a gas inlet 204 and 214, respectively, and an exhaust valve 205 and 215, respectively.

The apparatus according to Fig. 2 was used in the following way: In a first step, a first product suspension, comprising FDCA (ITIOIFDCA _] = 3,7g, corresponding to 23,8 mmol, Sigma Aldrich (722081 )), D ₂ 0 (27 g, Sigma Aldrich (151882)) and a solid heterogeneous catalyst (0.463 g of the catalyst with the catalyst number 1 ) was filled into the first steel autoclave reactor 201 at room temperature, and the reactor 201 was then closed. In a second step, the first steel autoclave reactor 201 was tightly sealed and pressurized with synthetic air to 100 bar. Afterwards, the first product suspension in autoclave reactor 201 was stirred at 2000 rpm while heated to 180°C. As a result, a first aqueous product phase comprising dissolved FDCA was obtained.

The second steel autoclave reactor 210 was pressurized with synthetic air to 10 bar. Then, the transfer line 220 and the second steel autoclave reactor 210 were heated to 185°C.

In a subsequent third step, i.e. after the set temperatures in the first steel autoclave reactor 201 , the transfer line 220 and the second steel autoclave reactor 210 were reached, valve 221 was opened in order to separate the heterogeneous catalyst from the first aqueous product phase by means of filter unit 222 and to transfer the dissolved (and catalyst free) FDCA through transfer line 220 into the second steel autoclave reactor 210. The transfer was accomplished within one minute, then pressure equilibrium between the first autoclave reactor 201 and the second autoclave reactor 210 was achieved. In a fourth step, after the solution including dissolved FDCA was transferred, valve

221 was closed and the apparatus was allowed to cool down to room temperature (approximately 22°C). After cooling down, the apparatus was completely depressurized.

In a fifth step, the first autoclave reactor 201 and the second autoclave reactor 210 were opened. In the second autoclave reactor 210 a white suspension was present, corresponding to the first aqueous product phase without the solid heterogeneous catalyst. In the first autoclave reactor 201 a black residue was present.

In a sixth step, samples for qualitative and quantitative analysis were prepared from the white suspension, as present in the opened second autoclave reactor 210. Sample preparation was carried out as follows: A solution of deuterated Sodium hydroxide (NaOD, 40 wt.-% in D ₂ 0, Sigma Aldrich (372072)) was carefully added to said white suspension until a pH-value was reached in the range of from 9 to 10. As a result, a treated liquid resulted comprising completely dissolved disodium salt of FDCA. The treated liquid was investigated by NMR spectroscopy as described above in item 1 -c.1.

A total volume of 5 ml D ₂ 0 (99,9 atom%, Sigma Aldrich (151882)) was added to the black residue present in the first autoclave reactor 201 . Afterwards, a solution of deuterated Sodium hydroxide (NaOD, 40 wt.-% in D ₂ 0, Sigma Aldrich (372072)) was additionally added until a pH in the range of from 9 to 10 was obtained. The resulting slurry with a pH in the range of from 9 to 10 was subsequently filtered by syringe filtration and the obtained filtrate was also analyzed by NMR spectroscopy as described above in item 1-c.1.

In a seventh step, Data obtained by NMR analysis were compared in order to calculate a filtration efficiency.

Il-b Results and filtration efficiency:

As determined by NMR spectroscopy a total amount of 0,07 g FDCA (m _[FDC A in 201]) was determined in the first autoclave reactor 201 and a total amount of 3, 10 g FDCA (m _[FDC A in 2io]) was determined in the second autoclave reactor 210. Thus, the filtration efficiency was 83.8%, based on the following equation: filtration efficiency in % = (m _[FDC A in 2io] / m _0[ FDCA])*100, wherein m _[FDC A in 2io] is the total amount of FDCA in the second steel autoclave reactor 210 in gram and m ₀ [FDCA] is the total (starting) amount of FDCA in the first product suspension in gram. III Example 3: Oxidation of HMF to FDCA over a Pt/C-heteroqeneous catalyst and subsequent separation of dissolved FDCA from the heterogeneous catalyst: lll-a Oxidation of HMF to FDCA, dissolving FDCA and separating the catalyst:

Experiment 3 combines elements of Examples 1 and 2 and was carried out in the apparatus according to Fig. 2 (for more details about the apparatus see above item ll-a). In Experiment 3 the oxidation of HMF to FDCA as described with respect to various catalyst screening experiments according to Experiment 1 was combined with the mechanical separation (filtration) of dissolved FDCA under heat and pressure from a heterogeneous catalyst as carried out in Experiment 2.

In a first step, an agueous reactant mixture was prepared by filling 27,0 g deuterated water (D ₂ 0, Sigma Aldrich (151882)) and 3,0 g HMF (corresponding to 23.8 mmol = n _0[H MF] = 0,0238 mol, Sigma Aldrich (W501808)) into the first steel autoclave reactor 201 . The starting concentration C ₀ [HMF _] of HMF in the agueous reactant mixture was 10 % by weight, based on the total mass of the agueous reactant mixture (total mass of deuterated water and HMF).

Analogous to experiment "Screen 7" but scaled up to a reactor with an inner volume of 90 ml, a total amount of 0.925 g (corresponding to 0.238 mmol) of the solid heterogeneous catalyst with catalyst number 1 (see Table 1 and Table 2) was added to the agueous reactant mixture resulting in a reaction mixture comprising deuterated water, HMF, and the heterogeneous catalyst. The molar ratio of substrate to metal of the heterogeneous catalyst (HMF : Pt) was approximately 100 : 1.

In a second step, the filled first steel autoclave reactor 201 was tightly sealed and pressurized with synthetic air (total pressure 100 bar, Oxygen (as part of the synthetic air) : HMF ratio is approximately 2,25 : 1 ) to obtain conditions for catalytic conversion. Valve 221 of the transfer line 220 was in a closed state. The reaction mixture present in the first autoclave reactor 201 was heated to a temperature of 100°C while stirring at 2000 rpm. After reaching 100°C this temperature was maintained for 20 hours while continuing stirring the heated and pressurized reaction mixture. After 20 hours, a first product suspension comprising FDCA in solid form and the heterogeneous catalyst in solid form was formed according to step A) of the process of the present invention. As stated in Table 2, experiment "Screen 7", under the experimental conditions selected, HMF conversion was 100% and FDCA yield was more than 95 % (see "95,2 %" in Table 2). Scale-up is considered to have no significant influence. As already stated in item l-e the concentration of FDCA (in % by weight) in the first product suspension can be calculated with the equation:

C[FDCA] = CO[HMF]/M _[H MF]*M _[F DCA _] *(FDCA yield).

According to this equation, the concentration of FDCA (in % by weight) was 1 1 ,7 % by weight, based on the total weight of the first product suspension. This value largely exceeds the solubility limit of FDCA in water at 100°C, which is approximately 1 to 2 % by weight.

In a third step, first steel autoclave reactor 201 was heated to 180°C to obtain a first aqueous product phase comprising dissolved FDCA, according to step B) of the process of the present invention. In addition, second steel autoclave reactor 210 was pressurized with synthetic air (total pressure: 10 bar). Then, the transfer line 220 and the second steel autoclave reactor 210 were heated to 185°C.

In a subsequent fourth step, i.e. after the set temperatures in the first steel autoclave reactor 201 , in the transfer line 220 and in the second steel autoclave reactor 210 were reached, valve 221 was opened in order to separate (see step C) in the process of the present invention) the heterogeneous catalyst from the first aqueous product phase by means of filter unit 222 and to transfer the dissolved

(and catalyst free) FDCA through transfer line 220 into the second steel autoclave reactor 210. The transfer was accomplished within one minute, then pressure equilibrium between the first autoclave reactor 201 and the second autoclave reactor 210 was achieved. In a fifth step, after the solution including dissolved FDCA was transferred, valve

221 was closed and the whole apparatus was allowed to cool down to room temperature (approximately 22°C). After cooling down, the apparatus was completely depressurized.

In a sixth step, both autoclave reactors were opened and samples for further NMR analysis were collected in the same manner as described above in item ll-a, sixth step. Afterwards, NMR analysis was carried out as described above in item 1 -c.1. l l l-b Results, filtration efficiency and FDCA yield:

As determined by NMR spectroscopy a total amount of 0, 13 g FDCA (m _[FDC A in 201]) was determined in the first autoclave reactor 201 and a total amount of 2,78 g FDCA (m _[FDC A in 2io]) was determined in the second autoclave reactor 210.

The FDCA yield is approximately 78 % according to the following equation:

FDCA Yield in molar% = [(m _[FDCA in 201] + m _[FDC A in 210]) / M _[FDCA ]] / n _0[H MF]*100, wherein m _[FDC A in 201] is the total amount of FDCA in the first steel autoclave reactor 201 in gram, m _[FDC A in 210] is the total amount of FDCA in the second steel autoclave reactor 210 in gram, M _[FDC A _] is the molecular weight of FDCA in gram/mol, and n ₀ [HMF] is the total molar amount of HMF in mol used in the aqueous reactant mixture.

Based on the experimental values, the filtration efficiency was 95.5 %, based on the following equation: filtration efficiency in % = (m _[FDCA in 210] / [m _[FDC A in 201] + m _[FDC A in 2io]])*100, wherein m _[FDC A in 210] is the total amount of FDCA in the second steel autoclave reactor 210 in gram and m _[FDC A in 2oi] is the total amount of FDCA in the first steel autoclave reactor 201 in gram.

Example 4: Process of making furan-2,5-dicarboxylic acid by oxidation of HMF to FDCA (and FFCA as a by-product) over a Pt C-heterogeneous catalyst, subsequent hydrogenation of FFCA and other by-products, and separation of FDCA

Example 4 uses elements of Example 1 and was carried out in a steel autoclave reactor with an inner volume of 300 ml. In Experiment 4 the oxidation of HMF to FDCA and FFCA as described with respect to various catalyst screening experiments according to Experiment 1 was combined with the subsequent hydrogenation of FFCA,

Firstly, an aqueous reactant mixture was prepared by filling 90,0 g deuterated water (D ₂ 0, Sigma Aldrich (151882)) and 10,0 g HMF (corresponding to 79.3 mmol = n ₀ [HMF] = 0,0793 mol, Sigma Aldrich (W501808)) into the steel autoclave reactor. The starting concentration C ₀ [HMF] of HMF in the aqueous reactant mixture was 10 % by weight, based on the total mass of the aqueous reactant mixture (total mass of deuterated water and HMF).

Analogous to experiments "Screen 1-6" but scaled up to a reactor with an inner volume of 300 ml, a total amount of 6.190 g (corresponding to 0.800 mmol) of the solid heterogeneous catalyst (5%Pt/C) was added to the aqueous reactant mixture resulting in a reaction mixture comprising deuterated water, HMF, and the heterogeneous catalyst. The molar ratio of substrate (HMF) to metal of the heterogeneous catalyst (HMF : Pt) was approximately 100 : 1.

Secondly, the filled steel autoclave reactor was tightly sealed and pressurized with synthetic air (total pressure 100 bar) to obtain conditions for catalytic oxidation according to step (a) of the process of the present invention as defined in the claims. The starting mixture present in the autoclave reactor was heated to a temperature of 100°C while stirring at 2000 rpm. After reaching 100°C, this temperature was maintained for 4 hours while continuing stirring the heated and pressurized reaction mixture. After 4 hours, the autoclave reactor was opened and a sample for further NMR analysis was collected in the same manner as described above. FDCA and FFCA in a molar ratio 42.8 (FDCA) : 57.2 (FFCA) was obtained without traces of HMF.

Thirdly, the steel autoclave reactor was tightly sealed and pressurized with hydrogen (total pressure 10 bar) to obtain conditions for catalytic hydrogenation according to step (b) of the process of the present invention as defined in the claims. The reaction mixture present in the autoclave reactor was heated to a temperature of 100°C while stirring at 2000 rpm. After reaching 100°C, this temperature was maintained for 4 hours while continuing stirring the heated and pressurized reaction mixture. After 4 hours, the autoclave reactor was opened and a sample for further NMR analysis was collected in the same manner as described above. FDCA and FFCA in a molar ratio 53.4 (FDCA) : 46.6 (FFCA) was obtained without traces of HMF.

Finally, FDCA was separated by chromatography from FFCA and hydrogenated by-products to give isolated furan-2,5-dicarboxylic acid.

In Example 4 the same catalyst was used for oxidation and hydrogenation. I BASF SE I 0000077070 | 0000077070WO01 |

The Example illustrates the concept of the present invention as defined in the claims, and specifically shows that hydrogenation step (b) reduces the amount of oxidation by-products (as FFCA) which result from the oxidation step.

The invention will be explained in more detail below with reference to various specific aspects.

1. Process for preparing furan-2,5-dicarboxylic acid, comprising the following steps:

A) in an aqueous reactant mixture, catalytically converting one or more organic reactant compounds by means of at least one heterogeneous catalyst, so as to form a first product suspension comprising furan-2,5-dicarboxylic acid in solid form and the heterogeneous catalyst in solid form,

B) heating under pressure

1. this first product suspension, or

2. a second product suspension prepared therefrom by further treatment, each comprising furan-2,5-dicarboxylic acid in solid form and the heterogeneous catalyst in solid form, such that furan-2,5-dicarboxylic acid dissolves fully or partly, resulting in a first aqueous product phase comprising dissolved furan-2,5-dicarboxylic acid, and then

C) separating the heterogeneous catalyst from this first aqueous product phase comprising dissolved furan-2,5-dicarboxylic acid, or from a second product phase which results therefrom through further treatment and comprising dissolved furan-2,5-dicarboxylic acid.

2. The process according to aspect 1 , comprising the additional step of: after the separation of the heterogeneous catalyst, separating furan- 2,5-dicarboxylic acid from further constituents of the first or second product phase. I BASF SE I 0000077070 | 0000077070WO01 |

3. The process according to either of the preceding aspects, comprising the additional step of: reusing the separated heterogeneous catalyst in the catalytic conversion of one or more organic reactant compounds to furan-2,5- dicarboxylic acid.

4. The process according to any of the preceding aspects, wherein the heterogeneous catalyst is separated in step C) from the first or second product phase by means of a mechanical separation process.

5. The process according to aspect 4, wherein the mechanical separation process is selected from the group consisting of filtration, sedimentation, centrifugation, magnetic separation and combinations thereof, the mechanical separation process preferably being or comprising a filtration.

6. The process according to any of the preceding aspects, wherein the catalytic conversion in step A) is a catalytic oxidation of the one or more organic reactant compounds by an oxidizing agent.

7. The process according to aspect 6, wherein the oxidizing agent is selected from the group consisting of oxygen, oxygen-containing gases, and oxygen- releasing compounds.

8. The process according to any of the preceding aspects, wherein one, more than one or all of the one or more organic reactant compounds in step A) are selected from the group consisting of 5-hydroxymethylfurfural, 2,5- diformylfuran, 5-formylfuran-2-carboxylic acid, 5-hydroxymethylfuran-2- carboxylic acid and 2,5-bishydroxymethylfuran.

9. The process according to any of the preceding aspects, wherein the catalytic conversion in step A) is conducted at a pressure in the range from 1 to 200 bar and a temperature in the range from 20 to 140°C, preferably 40 to 130°C, more preferably 60 to 120°C .

10. The process according to any of the preceding aspects, wherein 1. the first product suspension, or

2. the second product suspension prepared therefrom by further treatment is heated in step B), for dissolution of the furan-2,5-dicarboxylic acid, to a temperature in the range from 120 to 190°C, preferably greater than 120°C to 190°C, more preferably 140°C to 190°C or greater than 140°C to 190°C, especially preferably 150°C to 190°C, in each case at an inherent pressure in the range from 1 to 100 bar optionally adding to a pressure from one or more other gases. 1 1. The process according to any of the preceding aspects, wherein the aqueous reactant mixture in the conversion in step A) has a pH of < 7.5 and preferably at least intermittently, more preferably for most of the time, has a pH in the range from 0.5 to 5.5, preferably 1.5 to 5.5, more preferably a pH in the range from 1.5 to 3.5, based on the total duration of process step A). 12. The process according to any of the preceding aspects, wherein the heterogeneous catalyst used in step A) is a metal on a support material, a metal oxide on a support material or another metal-containing compound having catalytic activity on a support material.

13. The process according to any of the preceding aspects, which is conducted continuously or batchwise.

14. The process according to any of the preceding aspects, which is conducted batchwise, wherein the total amount of organic reactant compounds in the aqueous reactant mixture at least at the start of step A) is 5% by weight or greater, preferably 10% by weight or greater, more preferably 15% by weight or greater, based on the total mass of the aqueous reactant mixture at the start of step A).

15. The process according to any of the preceding aspects, wherein the aqueous reactant mixture additionally comprises one, more than one or all the compounds selected from the group consisting of: furan-2,5-dicarboxylic acid in solid form, humins, acids, preferably selected from the group consisting of levulinic acid, formic acid, hydrochloric acid, H ₂ S0 ₄ , CH ₃ S0 ₃ H, para-toluenesulfonic acid,H ₃ P0 ₄ , and combinations thereof, furan dimers and furan oligomers.