BY DISTILLATION AND PERMEATION

Field of the invention

The present invention relates a process for the separation of a bio-based product.

Background of the invention

A problem associated with the production of bio-based products such as levulinic acid, 2,5(hydroxymethyl)furfuraldehyde (HMF), and 5-methoxymethyl furfuraldehyde (MMF) by acid hydrolysis of carbohydrates is formation of tar or humins, which can be produced in amounts up to 10 to 50% w/w of the total reaction mixture, creating a high overall purification and separation effort.

Tar and char represent organic material which is insoluble in water, which is dark in colour and which tends to become viscous and very dark to almost black when concentrated. Tar can be formed during heating of organic material, for example by pyrolysis, but is also formed when carbohydrates are subjected to acid hydrolysis, particularly when done at high temperatures. Char usually refers to solid material, for example the remains of solid biomass that has been incompletely combusted, such as charcoal if wood is incompletely burned. Tar usually refers (viscous) liquid, e.g. derived from the destructive distillation of organic matter.

The presence of tar is undesired for a number of reasons. Firstly, its dark colour makes the product unattractive from the perspective of the user or customer. Secondly, the tar may negatively affect the performance of the bio-based product in the application. For this reason tar should be removed from the desired product.

Humins may also be produced by acid hydrolysis of carbohydrates. Yang and Sen (Chem. Sus. Chem. 2010, vol. 3, 597-603) report the formation of humins during production of fuels from carbohydrates such as fructose. They speculate that the humins are formed by acid-catalyzed dehydration. According to US7,896,944 the molecular weight of humins ranges from 2.5 to 300 kDa. Although distillation, which usually consists of one or more distillation steps (units), is normally an efficient process to separate a bio-based product form other components, the presence of tar in distillation presents a problem, because it will end up in the distillation residue as a darkly-coloured, viscous mass which is a mixture of high boiling components.

If the distillation process consists of more than one unit, which is usually the case, the tar will accumulate in the later distillation units and will be even more viscous and darkly-coloured, and will also be more concentrated in the bottom, because products exit the "train" via the top sections. Because of the accumulated tar, the eventual distillation residue may become even darker to almost black and solid and it becomes more difficult to process the distillation unit in terms of flowing and pumping. Moreover, it tends to stick very strongly to the distillation units and will be very difficult to remove. To make things worse, tar can also be formed during the distillation process itself: products such as HMF and furfuraldehyde can degrade to form humins and tar.

The formation of tar is discussed e.g. by WO2010/138957, which describes the formation of a hard dark distillation residue consisting of solid tar (referred to as "char"), and by US2009/0281338, wherein a dark brown residue is formed.

Tar formation and accumulation during distillation is also described e.g. by Hayes et al. (The Biofine Process - Production of Levulinic Acid, Furfuraldehyde, and Formic Acid from Lignocellulosic Feedstocks. D. J . Hayes, S. Fitzpatrick, M. H . B. Hayes, J. R. H. Ross, in Biorefineries-lndustrial Processes and Products, Status Quo and Future Directions, B. Kamm, PR. Gruber, M. Kamm, eds., Wiley-VCH, Weinheim, Germany, 2010, p139-164) who report the formation of acid-resistant tar during the distillation of levulinic acid and 2,5(hydroxymethyl)furfuraldehyde obtained by acid hydrolysis of lignocellulosic feedstocks. They described the tar as the cross-reacted and coalesced product from intermediates of the conversion process, and report that these intermediates tend to cross-react and coalesce to form an acid-resistant tar which incorporates many insoluble residues such as humins.

Any tar present or formed in the distillation residue is normally discarded in the art. For example, US2010/0312028 which relates to the production of fuel components from lignocellulose suggests dewatering the insoluble char and tar and thermally converting it in a recovery boiler to provide process heat, or to feed it to a power plant.

In order to maintain a workable and processable distillation unit, some bio-based product is usually allowed to remain in the distillation residue so as to prevent it from becoming too viscous enabling removal from the distillation unit. However, together with the removal of the distillation residue, also bio-based product is discarded, resulting in a lower yield and increase of waste. Increasing the overall yield of a bio-based product, in a process generating 10-50% tar/humins, becomes particularly important at industrial scale.

In "The Biofine technology - a bio-refinery concept based on thermochemical conversion of Lignocellulosic Feedstocks" (S. Fitzpatrick, in: Feedstocks for the Future, 2006, chapter 20, pp 271-287) it is explained that undesirable side reactions that form tar have inhibited commercial success of the Biofine process.

It is an aim of the invention to overcome the problem of tar accumulation in distillation of bio-based products.

It is another aim of the invention to increase the yield in the separation of a bio- based product.

It is another aim to provide a separation process for a bio-based product which results in a purer and/or clearer product.

Detailed description of the invention

Therefore, the invention provides a process to separate a bio-based product from a composition obtained from a process to convert carbohydrates to a bio-based product by acid hydrolysis said process comprising membrane separation using a membrane which is impermeable for molecules having a molecular weight of 100 kDa or more.

The membrane separation involves separation of one or more dissolved components from one or more other dissolved components. Membrane separation is to be distinguished from filtration. Filtration is a form of solid/liquid separation and involves particles having a size larger than 5 micron. Membrane separation, on the other hand, relates to particles < 5 micron and dissolved particles. From suspended particles of 5 micron down to about 0.1 micron the process is termed microfiltration, while below that the term ultrafiltration applies. Ultrafiltration covers the finest distinct particles (such as colloids), but its lower limits is usually set in molecular weight terms, measured in Daltons. Below ultrafiltration (UF) comes nanofiltration (NF) and reverse osmosis (RO). (Filters and Filtration Handbook, Ken Sutherland, 2008, published by Elsevier, Amsterdam). In membrane separation the fraction passing through the membrane is referred to as "permeate". The trans membrane pressure in the membrane separation process is preferably 5-60 bar, the crossflow velocity is preferably 0.1 -10 m/s, and the temperature is preferably in the range of 25-100°C.

The membrane which is impermeable for molecules having a molecular weight of 100 kDa or more can be easily selected by the skilled person based on the molecular weight cut off (MWCO). The membrane which is impermeable for molecules having a molecular weight of 100 kDa are generally classified as ultrafiltration (UF) or nanofiltration (NF) membranes. NF membranes have a lower MWCO than UF membranes. The MWCO, Molecular Weight Cut Off, describes the retention performance of a membrane. Cut off is defined as that molecular weight which is 90% rejected by the membrane. The retention or rejection, R, is defined as R=100%(1 - Cp/Cf). Wherein Cp is the permeate concentration and Cf is the feed concentration of the membrane. In a continuous system, the feed concentration will be more or less constant, whereas in a batch-system the feed-concentration will increase. A suitable hand book for membrane separation is "Basic principles of membrane technology by Marcel Mulder, published 1991 by Kluwer Academic in Dordrecht, Netherlands).

In the context of the invention "impermeable for molecules having a molecular weight of 100 kDa or more" does not necessarily mean that all molecules having a molecular weight of 100 kDa or more are retained by the membrane. "Impermeable for molecules having a molecular weight of X kDa or more" means that at least 90 wt% of an X kDa solute is retained by the membrane (wherein "X" refers to the molecular weight). Preferably the membrane is impermeable for molecules having a molecular weight of 50 kDa or more, more preferably of 10 kDa or more, 5 kDa or more, even more preferably 2 kDa or more, 1 kDa or more, even more preferably 500 Da or more, even more preferably 300 Da or more.

The membrane is preferably permeable to molecules having a molecular weight of 400 Da or less. "Permeable to molecules having a molecular weight of 400 Da or less" does not necessarily mean that all molecules having a molecular weight of 400 Da or less will end up in the permeate. "Permeable for molecules having a molecular weight of X Da or less" therefore means that at least 90 wt% of an X Da solute will end up in the permeate. More preferably the membrane is permeable to molecules having a molecular weight of 200 Da or less, even more preferably to molecules having a molecular weight of 100 Da or less. The membrane is preferably a nanofiltration membrane. Nanofiltration membranes are commercially available and well described in Nanofiltration: Principles and Applications by Anthony Gordon Fane et al. 2005, published by Elsevier, Oxford. Well known nanofiltration membranes for acid separation in aqueous media are for example Koch MPS34 (pH 0-14), Nadir NP30 (pH 0-14) and GE-Osmonics KH. Nanofilter membrane separation is preferably conducted as crossflow nanofiltration which may be performed using a nanofiltration material having a cut off for normal alkanes dissolved in toluene giving 90% rejection at 300 Da.

The membrane separation may comprise diafiltration. In the diafiltration the retentate obtained by the membrane separation is washed by adding a solvent and subjected to a subsequent membrane separation. This may be repeated several times. Diafiltration may result in higher yield.

The membrane separation is preferably done in the presence of a solvent. Therefore, the process of the invention preferably comprises the step of adding a solvent. The solvent may be water. Alternatively the solvent is an organic solvent. Suitable organic solvents include alcohols, such as methanol, ethanol, propanol, butanol; ketones, such as for example methylbutylketone; ethers, such as for example anisole (methyl phenyl ether), 2,5,8-trioxanonane (diglyme), diethylether, tetrahydrofuran, 2-methyl-tetrahydrofuran, diphenylether, diisopropylether and the dimethylether of di-ethyleneglycol; esters, such as for example ethyl acetate, methyl acetate, dimethyl adipate and butyrolactone; amides, such as for example dimethylacetamide and N-methylpyrrolidone; sulfoxides and sulphones, such as for example dimethylsulphoxide, di-isopropylsulphone, sulfolane (tetrahydrothiophene-2,2- dioxide) 2-methylsulfolane and 2-methyl-4-ethylsulfolane. Other organic solvents may also advantageously be used such as DCM (dicholoromethane), DCE (dichloroethene), toluene, benzene, 2-Heptanone, Butyl acetate, 1 ,2-Dichloroethane, Methyl isobutyl ketone, Dichloromethane, Ethyl propionate, 2-Pentanone, Diethyl ether, t-Amyl alcohol, Butanol, Cyclohexanone, Ethyl acetate, Pyridine, Tetrahydrofuran, 2-Butanone, Acetone, Dioxane, Acetonitrile, Methanol, N,N-Dimethylformamide, Dimethyl sulfoxide, Formamide, Ethylene glycol, 2-ME-THF (2-methyl tetrahydrofuran), MTBE (methyl-ter- butylether), MiBK (methyl isobutylketone), HOAc (acetic acid), CPMe (cyclopentyl methylether), heptane, DMF (dimethyl formamide), NMP (N-methylpyrrolidone), 2-sec- butylphenol (SBP), 4-n-pentylphenol (NPP), 4-n-hexylphenol (NHP), THF (tetrahydrofuran), MTHF (methyl-tetrahydrofuran) and DEGDME (diethyleneglycol dimethylether).

The amount of solvent is not critical. It may not be important to keep the amount of solvent to a minimum, because the permeate including any bio-based product can be fed back to a distillation. In fact, it may be preferred to add more solvent since this may facilitate the membrane separation.

The membrane is preferably a solvent-resistant membrane, more preferably a solvent-resistant nanofiltration membrane. Particularly, the membrane is resistant to organic solvents. Solvent-resistant membranes are known in the field and are commercially available. The preparation of solvent-resistant membranes is known and is described e.g. by P. Vandezande et al., Chem. Soc. Rev., 2008, vol 37, 365-405. Peeva et al. [Nanofiltration Operations in Nonaqueous Systems, Comprehensive Membrane Science and Engineering, 2010, Chapter 2.05, Pages 91 -1 13, L.G. Peeva, M. Sairam, A.G. Livingston] describe the characteristics of a number of solvent-resistant nanofiltration membranes to be used in non-aqueous systems. Suitable solvent- resistant nanofiltration membranes include STARMEM(TM) nanofiltration membranes, produced by UOP ((MET-Evonik, UK), or other polyimide based membranes. These may be employed in spiral wound modules, typically using pressure in the region of 60 bar. They preferably consist of hydrophobic integrally skinned asymmetric membranes with active surfaces manufactured from polyimides. An active skin layer of preferably less than 0.2mm in thickness with a pore size of preferably less than 5 nm covers the PI membrane body. Examples of suitable STARMEM nanofiltration membranes are StarmemTM-122, which has an MWCO of 220 g/mol, StarmemTM 120 having a MWCO of 200 g/mol, and StarmemTM 240 having a MWCO of 400 g/mol. Suitable membranes are stable in alcohols (e.g., butanol, ethanol, and iso-propanol); in alkanes (e.g., hexane and heptane); in aromatics (e.g., toluene and xylene); in ethers (e.g., methyl- tert-butyl-ether); in ketones (e.g., methyl-ethyl-ketone and methyl-isobutyl-ketone); or in other organic solvents (e.g., butyl acetate and ethyl acetate).

The process can be carried out using one, two or more membrane(s) or using one, two or more membrane module(s). Depending on the separation power of the membrane and the desired retention, the desired retention can be achieved by connecting a plurality of membranes or membrane modules in series. The arrangement in series can be effected so that either the retentate or the permeate, preferably the permeate, of a first membrane separation is passed as feed to a further membrane separation. Any further membrane separation(s) following the first membrane separation can be carried out under the same conditions as the first membrane separation or under different conditions, in particular different temperatures or pressures. Also membrane cascade systems comprising ultrafiltration, nanofiltration and reverse osmosis could be used in the invention.

Membrane separation may comprise one or more membranes. If it comprises multiple membranes, said membranes are preferably used in the form of membrane modules. In these modules, the membranes are arranged so that liquid flows over the retentate side of the membranes in such a way that the concentration polarization of the components separated off (the enrichment of the components separated off at the membrane) can be countered and, in addition, the necessary driving force (pressure) can be applied. The permeate can be collected in the permeate collection space on the permeate side of the membranes and discharged from the module. Customary membrane modules for polymer membranes have the membranes in the form of membrane disks, membrane cushions or membrane pockets. Customary membrane modules for membranes based on ceramic supports have these in the form of tubular modules. The membrane modules preferably have open-channel cushion module systems in which the membranes are thermally welded or adhesively bonded to form membrane pockets or cushions or open-channel (wide-spacer) rolled modules in which the membranes are adhesively bonded or welded to form membrane pockets or membrane cushions and rolled up together with spacers to form a permeate collection tube or have the membrane modules in tubular modules. Membrane modules which have open-channel inflow systems in which the membranes are thermally welded or adhesively bonded to form membrane pockets or membrane cushions can be procured from, for example, Solsep (The Netherlands), Borsig/GMT (Germany) Bio Pure Technology (Israel), Koch Membrane (USA) and Evonik-MET Duramem, Puramem, UOP-MET, Starmem (United Kingdom). Membrane modules which have the tubular membranes on a ceramic support can be procured from, for example, Inopor (Germany) membranes, a spin-off company of HITK (Germany) / FraunhoferJKTS (Germany).

To avoid deposits on the membrane, the process is preferably carried out so that the membrane separation, or, if the process comprises more than one membrane separation step, the first membrane separation step, is carried out at a flow velocity at the membrane ranging from 0.1 to 15 m/sec, preferably from 0.2 to 4 m/sec, more preferably from 0.3 to 1 m/sec.

The composition from which the bio-based compound is to be separated is obtained from a process to convert carbohydrates to said bio-based product by acid hydrolysis and comprises said bio-based product, tar, and/or humins. It may be the reaction mixture of the acid hydrolysis process. The composition may also be a permeate after subjecting said reaction mixture to solid liquid fractionation filtration, or the liquid supernatant fraction after centrifugation. The composition may also be a concentrated reaction mixture, e.g. by evaporation. A combination of concentration and solid-liquid fractionation is also possible. The composition is usually aqueous and may for example be in the form of a solution or a suspension.

The conditions of the acid hydrolysis process to convert carbohydrates to a bio- based product are such that they may result in the formation of a bio-based product. Tar and/or humins may also be formed. The composition may therefore also comprise tar and/or humins. Except when stated otherwise, in the context of the invention "tar" is understood to include char. Suitable acids in the acid hydrolysis process are sulphuric acid, hydrochloric acid, and phosphoric acid. A preferred acid is sulphuric acid, preferably diluted sulphuric acid, for example at a concentration between 1 .5 - 3%. The temperature in the acid hydrolysis process may depend on the source of carbohydrates, and may range between 150-250°C, preferably between 170-240°C, more preferably between 190-230°C, even more preferably between 200 and 220°C. Said process may comprise one, two, or more stages. The pressure may also depend on the source of carbohydrates, as well as on the temperature, and may be anywhere between 1 and 50 bar, preferably between 5 and 40 bar, even more preferably between 10 and 30 bar. Suitable reactors include plugflow reactors, backmix reactors, and CSTR reactors. Different reactors for different stages may be used. The skilled person will understand that the reaction time in the process to convert a carbohydrate to a bio- based product depends on the reaction temperature, the pressure, as well as the source of carbohydrate and the concentration of the acid. At higher reaction temperatures the reaction time may be shorter in order to obtain the desired bio-based product, whereas at lower reaction temperatures the reaction time may be longer in order to obtain the desired bio-based product. Likewise, at lower pressure, the reaction time may be longer whereas at higher pressure the reaction time may be shorter. The skilled person may therefore, without undue burden, establish suitable conditions with respect to temperature, reaction time, and pressure in order to obtain the desired bio- based product. The reaction time may vary between one second and one day, preferably between 10 seconds and one hour.

A carbohydrate is an organic compound with the empirical formula Cm(H20)n (where m can be the same as n or different from n); that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 (as in water). Carbohydrates can be viewed as hydrates of carbon, hence their name.

Suitable carbohydrates include sugar, such as glucose and fructose, disaccharides such as saccharose and lactose; polysaccharides such as cellulose and starch; wood; lumber processing side products such as saw dust, wood chippings and wood shavings; cellulosic material e.g. from lignocellulosic feedstock; grass; cereal; starch; algae; tree bark; hay; straw; leaves; paper pulp, and dung, particularly herbivore dung. Paper pulp, or simply pulp, is a lignocellulosic fibrous material obtained by prepared by chemically or mechanically separating cellulose from wood, fibre crops or waste paper. Pulp is rich in cellulose and other carbohydrates. The carbohydrates may be bound to a component, such as to lignin. Lignocellulosic feedstock typically has a fibrous nature and comprises a bran fraction that contains the majority of lignocellulosic (bran) fibers. As an example, corn fiber is a heterogeneous complex of carbohydrate polymers and lignin. It is primarily composed of the outer kernel covering or seed pericarp, along with 10-25% adherent starch. Carbohydrate analyses of corn fiber vary considerably according to the source of the material.

The carbohydrate may be in the form of a composition comprising other components such as water, fat, protein, lignin, and inorganic material such as salts or metals. Said composition comprising carbohydrates may be solid or liquid, or for example in the form of a suspension, sludge, brine, or broth. The amount of the carbohydrate in such composition preferably at least 1 % w/w, at least 2%, at least 5% w/w, more preferably at least 10% w/w, at least 20% w/w, 30% w/w, more preferably at least 50% w/w, at least 70 % w/w, even more preferably at least 90% relative to the total dry weight of the composition.

In an embodiment the bio-based product is separated from one or more other components such as tar or humins.

The bio-based product may be separated from colour. The colour may be present in the composition. Colour of the composition may be for example yellow to brown to black. Colour may be indicative of the presence of contaminants such as tar o r h u m i n s

The bio-based product is preferably selected from the group consisting of levulinic acid, ethyl levulinate, 2,5(hydroxymethyl)furfuraldehyde, alkoxymethylfurfuraldehydes, s u c h a s m et h oxy m et h y l f u rf u ra l d e h y d e a n d ethoxymethylfurfuraldehyde, furfuraldehyde, organic acids such as formic acid and acetic acid, 4,4-bis-(4'-hydroxyphenyl)pentanoic acid, succinic acid, methyltetrahydrofuran, and valerolactone. The composition may comprise one, two, three or more bio-based products. For example, in the "Biofine process", as described by Hayes et al. levulinic acid, furfuraldehyde and formic acid can all be produced by acid hydrolysis of lignocellulosic feedstocks. The process of the invention is particularly suitable for the separation of two or more bio-based products. By way of example, a first bio-based product, such as furfuraldehyde or formic acid, may be separated from the composition as a first distillate ("distillate 1 "). A second, third etc. bio-based product, such as levulinic acid, may be separated as a second, third etc. distillate ("distillate 2", "distillate 3") or it may be present in a distillation residue.

Alkoxymethyl furfuraldehydes are used to synthesize furan-2,5-dicarboxylic acid among others, but can also directly be used as fuel additive.

Furfuraldehyde can be used as solvent but also as intermediate for the synthesis of furfurylalcohol. Both can be applied in resins synthesis but also as foundry sand linker in the oil refining industry.

Formic acid has many applications among them uses in agriculture and clothing.

Hydroxymethyl furfuraldehyde can be used to make among others 2,5- bis(hydromethyl)furan, 2,5-bis(aminomethyl)furan and furan-2,5-dicarboxylic acid which are all used as intermediates to synthesize polyesters and polyamides.

Levulinic acid can be produced by acid hydrolysis of lignocellulosic feedstocks, as described for example by Hayes et al. Levulinic acid can be used for the synthesis of esters known as fuel additive and known to be useful as plasticisers and solvents. Levulinic acid can be used to synthesize methyl tetrahydrofuran (MTHF), used as a solvent. Other applications of levulinic acid are for the synthesis of delta-amino levulinic acid used as herbicides and pesticides, diphenolic acid used to synthesize polycarbonates and succinic acid used to make polyesters. Levulinic acid can also be used to produce gamma-valerolactone (5-methylbutyrolactone), which in turn can be used for production of adipic acid (1 ,6-hexanedioic acid). Adipic acid is an important precursor for inter alia the production of polyamides such as Nylon 6,6. The most important process to produce adipic acid is based on oil and starts from benzene. A disadvantage of this process is that it is based on fossil derived oil. Another disadvantage is the evolution of NOx during the oxidation step, which either is vented to the air, which is highly undesirable as it is a greenhouse gas, or its catalytically destroyed, which is an expensive process. New processes for the production of adipic acid have been developed based on butadiene. However, such processes are also environmentally unfavourable. A third production route to produce adipic acid involves the use of levulinic acid via the following reaction sequence: levulinic acid; gamma- valerolactone; methylpentenoate; dimethyladipate, adipic acid. It is highly desirable to produce polymers such as nylon-6,6 from renewable resources. Such a process reduces the total amount of C0 ₂ emitted for its production and thus helps to mitigate against global warming. In addition, it helps to slow down the depletion of fossil resources. Levulinic acid may be produced from agricultural waste products or waste from the paper industry or municipal waste and therefore constitutes a renewable source of a C-5 fragment.

In an embodiment, the invention provides a process to separate a compound selected from levulinic acid or esters thereof, 2,5(hydroxymethyl)furfuraldehyde, methoxymethylfurfuraldehyde, furfuraldehyde, formic acid, acetic acid, angelica lactone, and valerolactone from a composition obtained from a process to convert carbohydrates to said compound by acid hydrolysis said process comprising subjecting said composition to membrane separation in the presence of an organic solvent using a nanofiltration membrane to yield a retentate and a permeate and recovering the permeate comprising the compound.

In the membrane separation the yield of the bio-based product in the permeate is preferably at least 50% w/w relative to the amount of compound in the composition prior to the membrane separation, preferably the yield is at least 60% w/w, more preferably at least 70% w/w, more preferably at least 80% w/w, 90% w/w, even more preferably at least 95% w/w.

In the membrane separation preferably at least 50% w/w, more preferably at least 70% w/w, more preferably at least 80% w/w, 90% w/w, even more preferably at least 95% w/w of any tar and/or humins in the composition is retained in the retentate.

Preferably at least 50% w/w, more preferably at least 70% w/w, more preferably at least 80% w/w, 90% w/w, even more preferably at least 95% w/w of colour of the composition is retained in the retentate. The permeate preferably has little colour. Preferably the permeate is yellow to colourless; more preferably light-yellow to colourless. The amount of colour of the composition or the retentate or the composition can be quantitatively determined by absorption or extinction spectrometry. Any simple spectrophotometer is su itable wh ich is able to measu re wavelengths anywhere between 400 and 800 nanometres.

The process may further comprise distillation. Therefore, the invention provides a process to separate a bio-based product from a composition obtained from a process to convert carbohydrates to a bio-based product by acid hydrolysis, said process comprising d istillation to yield a d istillate and a distillation residue, and further comprising membrane separation using a membrane which is impermeable for molecules having a molecular weight of 100 kDa or more, wherein said distillation residue is subjected to said membrane separation. Siad permeate comprises the bio- based product. Therefore, the process optionally comprises recovering the permeate.

The distillation yields a distillate and a distillation residue. The distillation residue does not necessarily have to be subjected directly to the membrane separation. The distillation residue may be subjected directly to the membrane separation. Alternatively, the distillation residue may be treated before subjecting it to the membrane separation, for example the distillation residue may be subjected first to solid/liquid separation and then to mem bra ne sepa ration . Alternatively, the d isti l lation resid u e may be concentrated or diluted before subjecting it to the membrane separation.

Depending on such other components and their boiling points several distillation units (a so-called "train") may be required. If there is more than one distillation unit, the process of the invention will comprise more than one distillate; within the context of the invention "a distillate" is understood to include the two or more distillates. The bio-based product will normally be driven off and condensed in one or more of the distillates. The composition will typically comprise water.

The process may comprise one, two, or more distillations and/or one, two, or more membrane separations. In the context of the invention, the term "the distillation" does not necessarily mean that there is only one distillation. Likewise, "the composition is subjected to the distillation" does not necessarily mean that there is only one distillation. The process may comprise other, previous and/or subsequent distillation steps. Similarly, "the membrane separation" does not necessarily mean that there is only one membrane separation; the process may comprise other, previous and/or subsequent membrane separation steps.

The process may be carried out in a continuous way. Thus, distillation and membrane separation may be repeatedly carried out.

The composition may be subjected to the distillation. The composition can be subjected to the distillation directly, i.e. without any intermediate steps, or it may be treated before subjecting it to the distillation, for example the composition may first be concentrated, diluted, and/or fractionated before subjecting it to the distillation.

The permeate obtained by the membrane separation may be subjected to a subsequent distillation. This may be a second, third etc. distillation, e.g. where the composition is subjected to a first distillation. Said process is preferably a continuous process Thus, the composition may be subjected to a (first) distillation to yield a (first) distillate and a (first) distillation residue. Said (first) distillation residue may be subjected to a (first) membrane separation to yield a (first) permeate and a (first) retentate. The (first) permeate may be subjected to a distillation (a second distillation) to yield a (second) distillate and a (second) distillation residue. Said (second) distillation residue can be subjected again to a (second) membrane separation. This may be repeated many times.

The distillation residue preferably comprises the bio-based product, tar, and/or humins. If the distillation residue comprises tar and/or humins, the bio-based product may be dissolved in said tar and/or humins present in said distillation residue and/or composition. The distillation residue may be viscous. The viscosity may depend on the concentration of the distillation residue and/or the concentration of tar and/or humins therein, and may be anywhere from slightly viscous to solid. It may have the consistency of syrup, or a gum. It may even be very hard, almost glass-like.

The distillation may yield one, two, three, four, or more distillates, depending on the number of bio-based products in the composition and their boiling points. The concentration % (w/w) of bio-based product in the distillate is preferably higher than the concentration % (w/w) of said bio-based product in the distillation residue, both based on total dry weight. Preferably the ratio of the concentration % (w/w) of bio-based product in the distillate over the concentration of bio-based product in the distillation residue is at least 2, more preferably at least 4.

The distillation residue may be diluted with a solvent prior to subjecting the distillation residue to the membrane separation, preferably using a solvent which is suitable for dilution of the distillation residue. Preferably such solvent is also suitable to be used in the distillation process. The way in which the distillation residue is diluted is not critical. An easy way of diluting the distillation residue is to simply add the solvent to the distillation residue and mix. It may be preferred to stir so as to ensure that the solvent and the distillation residue are well mixed. Diluting the distillation residue with the solvent may reduce the viscosity of said distillation residue. This may facilitate removal of the distillation residue from the distillation unit. The viscosity of the diluted distillation residue is such that it can be applied to membrane filtration.

To a skilled person it would not be obvious to add a solvent to a distillation residue. Normally distillation is used to remove components from the desired product. Adding a component after distillation would seem to be incompatible with the aim to remove any components from the desired product.

In a preferred embodiment the permeate obtained by the membrane separation is fed (back) to the distillation. This advantageously allows for process to be operated in a continuous mode, i.e. the process is preferably a continuous process. Components in the permeate can be separated from each other or from the bio-based product during this (subsequent) distillation. Because most, if not all tar and/or humins are retained by the membrane separation, feeding said permeate to distillation may not cause any problems that are normally encountered in the art, or to a lesser extent. It may not even be very important that the bio-based product in the permeate is very pure, as long as it comprises little or no tar and/or humins. The process of the invention can thus be repeated many times without the need to remove the tar and/or humins from a distillation unit or bio-based product losses: the bio-based product can easily be separated and collected in the distillate, whilst a small amount is used to remove the distillation residue. Said small amount is then col lected as the permeate after membrane separation and fed back in a subsequent distillation process.

Subjecting the distillation residue to the membrane separation advantageously allows for lower distillation temperatures. High distillation temperatures, which are commonly used in the art, may not be required in order to recover as much as possible from the bio-based product. Instead, the presence of bio-based prod uct in the distillation residue is not a problem and may actually be favoured since it may facilitate the membrane separation, whilst said bio-based product can easily be collected in the permeate. Lower distillation temperatures may also be advantageous from a cost (energy) perspective, they may be environmentally beneficial, safe in operation to personnel, and may require less stringent distillation equipment. Lower distillation temperatures may also be desired to prevent deterioration or degradation of the bio- based product. For example, US5, 189,215 describes that high distillation temperatures may negatively affect storage stability of levulinic acid and may result to browning of the product. The distillation may be done using smaller distillation columns, requiring less vacuum requirements, meaning lower energy costs, lower installation costs, and less waste (less product may be degraded into waste), contributing to sustainability. It also leads to less fouling of the distillation columns and/or less downtime of the process.

The process may comprise a first membrane separation and a second membrane separation, wherein the first membrane separation is done prior to the distillation, and wherein the distillation residue is subjected to a second membrane separation. It follows that the second membrane separation is carried out after the distillation. The "first membrane separation" may comprise more than one membrane separation steps, as long as there is at least one membrane separation step prior to the distillation. Similarly, the "second membrane separation" may comprise more than one membrane separation steps, as long as there is at least one membrane separation after the distillation. As an example, the composition in the process of the invention may be subjected to a (first) membrane separation to yield a (first) retentate and a (first) permeate, whereby said (first) permeate may be subjected to the distillation. Said distillation results in a distillate and distillation residue, and said distillation residue may be subjected to a (second) membrane separation. This advantageously allows for a continuous process.

Subjecting the composition to membrane separation prior to distillation may advantageously remove most or all of the tar and/or humins from said composition, as a result of which no or less tar and/or humins containing the bio-based product may be present in the distillation residue. This in turn may reduce the need for adding the bio- based product in the residue to keep it liquid and may result in higher yields of the bio- based product.

Prior to the membrane separation, the composition may be diluted with a solvent. For example, instead of diluting the distillation residue with the solvent prior to subjecting said residue to the membrane separation, the composition can be diluted with the solvent before subjecting it to the membrane separation. The way in which the composition is diluted is not critical. An easy way of diluting the composition is to simply add the solvent to the composition and mix. It may be preferred to stir so as to ensure that the solvent and the composition are well mixed. Diluting the composition the composition with the solvent may reduce the viscosity of said composition and facilitate a subsequent membrane separation. It also can contribute to dissolve fouling (e.g. of tar or humins) on the membrane and act as a "cleaning agent". This may result in better fluxes, a longer lifetime of the membranes, lower energy consumption and installation foot print and less waste, contributing to sustainability.

Subjecting the composition to membrane separation in the presence of a solvent, to yield a retentate and a permeate, and subjecting said permeate to distillation, advantageously allows a simple recycle to the membrane separation, because less, or even no additional solvent may have to be added prior to the subsequent membrane separation step.

Subjecting the composition to the membrane separation to yield a retentate and a permeate and subjecting said permeate to the distillation also may allow the use of less strict distillation conditions: since most of the tar and/or humins will have been removed by the membrane separation, the temperature during the subsequent distillation is less critical, and may be somewhat lower or higher than used in the art. Also, said process may result in less fouling of the distillation units as compared to a process not comprising said membrane separation.

In an embodiment, prior to membrane separation and distillation, the composition is subjected to a solid / liquid separation. Any solids which may be present in the composition obtained from a process to convert carbohydrates to a bio-based product may hamper the membrane separation or the distillation, so they are preferably removed prior to the subsequent step. Solid-liquid separation is concerned with mechanical processes for the separation of liquids and finely divided insoluble. The solid / liquid separation results in concentrated solids and a clearer solution. The solids may be discarded as co-product and the liquid can be subjected to the membrane separation or the distillation. Examples of suitable solid / liquid separation are filtration, centrifugation, sedimentation, hydrocyclone and flotation.

Compositions obtained from a process to convert carbohydrates to a bio-based product by acid hydrolysis are known to comprise dissolved tar or humins. When such compositions are subjected to distillation, tar and/or humins are known to accumulate in the distillation residue. Tar and humins are generally considered to be a mixture of high-molecular cross-reacted components having a high boiling point. Without wishing to speculate on the mechanism of tar or humin formation, it is assumed that their high molecular weight is the reason why tar and humins may end up in the distillation residue. The skilled person would expect that membrane separation in the presence of tar or humins will cause fouling and/or clogging of the membrane.

Removal of tar and humins by membrane separation is particularly advantageous in a continuous process.

In one embodiment the organic phase, which comprises the bio-based product, and optionally any remaining tar and/or humins, is subjected to distillation to yield a residue and a distillate. Although most of the compound may the in the distillate, some remaining compound may end up in the distillation residue. Therefore, the distillation residue can subsequently be subjected to membrane separation. The permeate may be diafiltrated at least once, or may be recycled to the distillation.

The bio-based product will predominantly be in the organic phase. Tar and humins however may be distributed between the aqueous and the organic phase. These tar and humins may cause problems, such as fouling, in subsequent separation steps, particularly in a later distillation step. Therefore, the organic phase can be subjected to membrane separation in order to remove some or all of any tar and/or humins. This is particularly advantageous if the membrane separation is done in the presence of a solvent e.g. using a solvent-resistant membrane, because the organic phase may act as the solvent. Thus, less, or even no separate solvent needs to be added prior to the membrane separation. To facilitate the membrane separation, a solvent as defined above may be added to the organic phase.

In an embodiment said organic phase is subjected to membrane separation to yield a permeate and a retentate. The permeate, comprising the bio-based product and optionally any tar and/or humins, can be subjected to distillation to yield a distillate and a distillation residue. Said distillation residue, comprising the compound and possible and remaining tar and/or humins, may subsequently be subjected to a second membrane separation.

The permeate resulting from the membrane separation may subsequently be subjected to distillation.

In a further aspect the invention provides the use of membrane filtration for the separation of a bio-based product. The bio-based product is preferably separated from tar and/or humins.

In another aspect the invention provides a process for the separation of a bio- based product from tar and/or humins, said process comprising distillation, characterized in that said process further comprises membrane separation using a membrane which is impermeable for molecules having a molecular weight of 100 kDa or more.

FIGURES

Fig. 1 . A reactor effluent comprising a bio-based product, tar, and/or humins, obtained from a process to convert carbohydrates to a bio-based product by acid hydrolysis, is subjected to solid-liquid separation, e.g. filtration. The solids are discarded (bottom arrow) and the liquid fraction enters a separation train including distillation. One or more bio-based products (such as for example formic acid, furfural, levulinic acid) are recovered as distillates (products 1 -4). The distillation residue, which comprises tar and/or humins, and possibly some desired bio-based product such as levulinic acid, is not discarded, but instead is subjected to membrane separation. A solvent (preferably an organic solvent) can optionally be added to dilute the distillation residue, to make it less viscous). The retentate comprising the humins and tar are discarded and may be used e.g. as fuel. The permeate comprising the bio-based products are recycled to the solid/liquid separation and can be recovered in a subsequent distillation. In such continuous process the valuable bio-based products are not lost in the distillation residue whilst tar and humins do not accumulate in the distillation.

Fig. 2. A reactor effluent comprising a bio-based product, tar, and/or humins, obtained from a process to convert carbohydrates to a bio-based product by acid hydrolysis, is subjected to solid-liquid separation, e.g. filtration. The solids are discarded (bottom arrow) and the liquid fraction comprising the bio-based products (such as for example formic acid, furfural, levulinic acid), and tar and/or humins is subjected to membrane separation. The retentate comprising the humins and tar are discarded and may be used e.g. as fuel. The permeate comprising the bio-based products, and which is low in tar and/or humins, or even free of tar and/or humins, is subjected to distillation. Solvent may be optionally added to wash the retentate by diafiltration. One or more bio- based products (such as for example formic acid, furfural, levulinic acid) are recovered as distillates (products 1 -4). If all tar and/or humins were removed by the membrane separation, the distillation residue, which may comprise some remaining bio-based products, can be recycled to the distillation without causing fouling or other problems (arrow not shown). If the distillation residue still contains some tar and/or humins (in addition to any remaining bio-based products) it can be recycled to the membrane separation, be optionally diafiltrated, and the permeate can be subjected to a subsequent distillation. In such continuous process the valuable bio-based products are not lost in the distillation residue whilst tar and humins do not accumulate in the distillation.

EXAMPLES Example 1

A reaction mixture was obtained via acid hydrolysis of a carbohydrate. Levulinic Acid (LA), Furfuraldehyde (F), 5-methoxymethyl furfuraldehyde (MMF) and 2,5(hydroxymethyl)furfuraldehyde (HMF) were measured with GC-FID analysis in the resulting mixture. Presence of humins and dissolved tar was indicated by a strong dark brown color of the solution and indirectly via a mass balance. An amount of 501 gram of this reaction mixture was nanofiltrated on a laboratory crossflow membrane test unit, type CM Celfa P28. Pressure was set on 28 bars and temperature kept on 40°C. The tested membrane was a flatsheet membrane (28 cm2), Starmem 122 solvent resistant nano filtration membrane, produced by UOP ((MET-Evonik, UK). An amount of 204 grams permeate was produced. The color of the clear permeate was light yellow. At a concentration factor of 2, the flux was of 22 l/m ² .h. The flux at concentration factor 1 .4, 2.5, 4, 6, 9 was respectively 24, 17, 1 1 , 6 and 3 l/m ² .h. The permeate, at a concentration factor 9, and the feed were analysed. The calculated retention (1 - Cpermeate Cfeed) for LA, F, MMF and HMF were respectively -12%, 3%, 3% and -10%. Subsequently, 400 gram of solvent was added to 100 gram retentate and nano-filtrated again . This diafiltration step is repeated 4 times in total, allowing more than 98% recovery of the products for LA, F, MMF and HMF and full retention of the humins and dissolved tar. In total 2000 g of permeate was distilled via two falling film distillation units to remove the solvent. The first falling film distillation unit was operating at 90°C and atmospheric pressure. A second falling film distillation unit was operated at 50°C and 200 mbars. 80% of furfuraldehyde, 90% of MMF 100% of H MF and 100% of LA was recovered in the bottom of the second falling film evaporator and the solvent level was reduced to less than 1 %. Subsequently the furfuraldehyde, LA, MMF and HMF mixture was distilled in a batch distillation column operated with a top pressure of 20 mbars to separate and purify the components. Example 2

A reaction mixture is obtained via acid hydrolysis of a carbohydrate. Presence of humins and dissolved tar is indicated by a strong dark brown color of the solution and indirectly via a mass balance. In total 10 kg of the reaction mixture is flashed to ambient pressure to remove water and furfuraldehyde. The bottom stream of the flasher is fed a series of vacuum distillation columns, operated at a top pressure of respectively 500 mbars, 200 mbars, 50 mbars and 20 mbars to remove the furfuraldehyde, MMF, HMF and LA as topproducts. 2500 g is left in the residue of the final column, containing the humins and dissolved tars. The pressure in the distillation is set on 30 bars and temperature is kept on 40°C. An amount of 100 gram of a distillation residue is mixed with 500 gram of solvent and then nanofiltrated on a laboratory crossflow membrane test unit, type CM Celfa P28. The tested membrane is a flatsheet membrane (28 cm2), Starmem 122 solvent resistant nano filtration membrane, produced by UOP ((MET- Evonik, UK). An amount of 200 gram permeate is produced. The color of the clear obtained permeate is light yellow. The flux at concentration factor 1 .5 is 12 l/m ² .h. The permeate and the feed are analysed. The calculated retention (1 -C _P ermeate Cf _e ed) for LA, F, MMF and HMF range from -12 to 3%. Subsequently, 200 gram of solvent is added to 400 gram retentate and nano-filtrated again. This diafiltration step is repeated 9 times in total, allowing more than 95% recovery of the products for LA, F, MMF and HMF and full retention of the humins and dissolved tar.

Example 3

A reaction mixture was obtained via acid hydrolysis of a carbohydrate. Levulinic Acid (LA), Formic Acid (FA) and Acetic Acid (AA) were measured with HPLC analysis in the resulting mixture. Presence of humins and dissolved tar was indicated by brown color of the solution and via UV-VIS spectrophotometry. The absorption of a dilute sample was measured at 425 nm. The samples were diluted with solvent (15 g Sample + 85 g water). The feed had a pH of 0.89 and a conductivity of 174 mS/cm. An amount of 485.2 gram of this reaction mixture was nanofiltrated on a laboratory crossflow membrane test unit, type CM Celfa P28. Pressure was set up to 9 bars and temperature constant kept on 40°C. The six tested flatsheet membranes had a surface area of 28 cm2. MPF-34, MPF-36 were obtained from Koch, DL from GE, TS80 from Trisep and the NP-010 and UH-004P from Nadir. Results in Table 1 . Table 1

The flux at concentration factor (CF) 1 .6, was between 5 and 48 l/m ² .h. The permeate and retentate, at a concentration factor 1 .6, were analysed. The retention (1 - Cpermeate Cretentate) for LA, FA, AA and humins were calculated and presented in Table 2.

Table 2.

The color of all permeates were light yellow and absorption analysis confirms the good color/humin retention. However, the permeabilities for LA are poor with these

"water/acid" membranes, requiring high concentration factor or membrane cascade constructions. Example 4

A reaction mixture was obtained via acid hydrolysis of a carbohydrate. Levulinic Acid (LA), Furfuraldehyde (F), 5-methoxymethyl furfuraldehyde (MMF) and 2,5(hydroxymethyl)furfuraldehyde (HMF) were measured with GC-FI D analysis in the resulting mixture. Presence of humins and dissolved tar was indicated by a strong dark brown color of the solution. An amount of 501 gram of this reaction mixture was nanofiltrated on a laboratory crossflow membrane test unit, type CM Celfa P28. Pressure was set on 28 bars and temperature kept on 40°C. The tested membrane was a flatsheet membrane (28 cm2), Starmem 1 22 solvent resistant nano filtration membrane, produced by UOP ((MET-Evonik, UK). An amount of 204 grams permeate was produced. The color of the clear permeate was light yellow. At a concentration factor of 2, the flux was of 22 l/m ² .h. The flux at concentration factor 1 .4, 2.5, 4, 6, 9 was respectively 24, 17, 1 1 , 6 and 3 l/m ² .h. The permeate, at a concentration factor 9, and the feed were analysed. The calculated retention (1 -C _P ermeate/C _re tentate) for LA, F, MMF and HMF were respectively -12%, 3%, 3% and -10%. Subsequently, 400 gram of solvent was added to 100 gram retentate and nano-filtrated again. This diafiltration step is repeated 4 times in total, allowing more than 98% recovery of the products for LA, F, MMF and HMF and full retention of the humins and dissolved tar. In total 2000 g of permeate was distilled via two falling film distillation units to remove the solvent. The first falling film distillation unit was operating at 90°C and atmospheric pressure. A second falling film distillation unit was operated at 120°C and 100 mbars. 80% of furfuraldehyde, 90% of MMF 100% of HMF and 100% of LA was recovered in the bottom of the second falling film evaporator and the solvent level was reduced to less than 1 %. Subsequently the furfuraldehyde, LA, MMF and HMF mixture was distilled in a batch distillation column operated with a top pressure of 20 mbars to separate and purify the components. No fouling in the distillation occurred.

Example 5

A reaction mixture is obtained via acid hydrolysis of a carbohydrate. Presence of humins and dissolved tar is indicated by a strong dark brown color of the solution and indirectly via a mass balance. In total 10 kg of the reaction mixture is flashed to ambient pressure to remove water and furfuraldehyde. The bottom stream of the flasher is fed a series of vacuum distillation columns, operated at a top pressure of respectively 500 mbars, 200 mbars, 50 mbars and 20 mbars to remove the furfuraldehyde, MMF, HMF and LA as topproducts. 2500 g is left in the residue of the final column, containing the humins and dissolved tars. An amount of 100 gram of a distillation residue is mixed with 500 gram of solvent and then nanofiltrated on a laboratory crossflow membrane test unit, type CM Celfa P28. The tested membrane is a flatsheet membrane (28 cm2), Starmem 122 solvent resistant nano filtration membrane, produced by UOP ((MET- Evonik, UK). An amount of 200 gram permeate is produced. The color of the clear obtained permeate is light yellow. The flux at concentration factor 1 .5 is 12 l/m ² .h. The permeate and the feed are analysed. The calculated retention (1 -C _P ermeate/C _re tentate) for LA, F, MMF and HMF range from -12 to 3%. Subsequently, 200 gram of solvent is added to 400 gram retentate and nano-filtrated again. This diafiltration step is repeated 9 times in total, allowing more than 95% recovery of the products for LA, F, MMF and HMF and full retention of the humins and dissolved tar.