Preparation of levulinic acid

Background of the invention

[0001] The invention relates to a formic acid-based process for the preparation of levulinic acid from biomass while simultaneously producing formic acid and, if desired, cellulose, sugars (glucose) and bioethanol.

[0002] Today, there is an increasing need to produce glucose and further bioethanol from lignocellulose-containing raw material for biofuel applications. Formic acid-based cooking processes are one alternative to producing glucose. In these processes, the lignocellulose-containing raw material is first cooked in formic acid, and the thus obtained cellulose is hydrolysed enzymati- cally into glucose. Problems in the preparation of glucose include formic acid losses in cooking and high enzyme dosages related to the enzymatic hydrolysis especially when striving at a high glucose yield.

[0003] In formic acid-containing biomass cooking processes, the aim is to regenerate the cooking acid as efficiently as possible, and after regeneration the cooking acid is returned to the process. Regeneration processes of cooking acid are known per se (evaporation, distillation, etc.). Because some of the formic acid is consumed in the process, the regenerated formic acid is not necessarily enough and extra formic acid needs to be added to compensate for the loss. Thus, there is also a need to provide processes, in which the process itself produces more formic acid.

[0004] Levulinic acid is a valuable raw material in the chemical industry, and its preparation from biomass has lately aroused a great deal of interest. Producing levulinic acid from the cellulose in biomass simultaneously produces formic acid according to the following reaction:

[0005] The reaction produces glucose and 5-hydroxy methyl furfural as intermediate products.

[0006] Dissertation Girisuta B, Levulinic Acid from Lignocellulosic Biomass, University of Groningen, 5 November 2007, pages 7 to 13, describes several known processes for preparing levulinic acid from biomass. The prepa- ration is usually done by acid catalysis. The acid used is typically a mineral acid, such as sulphuric acid, hydrochloric acid or hydrobromic acid.

[0007] Page 11 , second paragraph, of the dissertation describes a process, in which corn cob residue obtained from the production of furfural is used as raw material. Sulphuric acid and water are added to the residue stream (amount of raw material 21 % by weight and acid content 3% by weight). The reaction temperature is 169°C and a typical reaction time is 2 h. Non-dissolved humines are filtered and the levulinic acid extracted with methyl isobutyl ketone. After this, the water-acid mixture is recirculated to the reactor, levulinic acid and methyl isobutyl ketone separated, the latter returned to extraction and levulinic acid concentrated and purified by vacuum distillation. The levulinic acid yield is 19.9 % of the dry raw material.

[0008] Page 11 , second paragraph, and page 12 of the dissertation describes the preparation of levulinic acid from corn starch by adding sulphuric acid and water and passing the thus obtained pulp through a double-screw extruder (temperature profile 80 to 100°C, 120 to 150°C and 50°C). After this, the humines are filtered and levulinic acid recovered from the filtrate in the same manner as described above. The levulinic acid yield is approximately 48% by weight.

[0009] Pages 12 and 13 of the dissertation describe processes based on "Biofine technology" for the preparation of levulinic acid from different wood-based raw materials, such as bleached or unbleached Kraft paper pulp by using a sulphuric acid catalyst. The reaction takes place in a tube reactor (temperature 210 to 220°C, reaction time 12 s), in which carbohydrates are hydrolysed into soluble monomers (hexoses and pentoses). After the tube reactor, the product is fed into a continuous mixing reactor (190 to 200°C, 20 min). Levulinic acid is recovered from the liquid stream exiting the tube reactor and the formed formic acid and furfural are recovered as condensate (volatile products).

[0010] Compilation article Rackemann, D, W. & Doherty, O S., The conversion of lignocellulosics to levulinic acid, Biofuels, Bioprodud. Bioref. 5: 198-214 (2011 ) discusses the production of levulinic acid from lignocellulose- based materials. This publication, too, refers to mineral acid-catalysed processes (HBr, HCI and H2SO4). It also mentions fluorated solvents/acids (trifluo- ro acetic acid), solid catalysts (e.g. zeolites), supercritical fluids and ionic fluids. [0011] Producing levulinic acid by mineral acid-catalysed processes from biomass has the disadvantage, for instance, that acid concentrations are low and, correspondingly, water amounts are large. The amount of water to be separated is thus large. The recovery of the formic acid formed in the reaction from the product stream of the mineral acid-catalysed levulinic acid is also expensive and requires several process steps.

[0012] One process for recovering formic acid from such a product stream of levulinic acid is described in published US application 2011/0137051 (Kemira Oyj). The publication relates to a process for recovering concentrated formic acid from a solution that is obtained from cooking biomass and contains formic acid, levulinic acid and possibly furfural. The solution is liquid-liquid extracted with an extraction agent (e.g. octanol or tris-2-ethyl hexyl phosphate), whereby an organic phase (containing an extraction agent, formic acid, levulinic acid and possibly furfural) and a water phase are obtained. The organic phase and water phase are separated, formic acid is separated as an at least 50% solution from the organic phase by distillation and levulinic acid (or le- vunate salt) is separated from the organic phase. In addition, furfural is separated from the organic phase, if desired.

[0013] The prior art does not disclose processes in which levulinic acid is produced from biomass through the catalysis of organic acids, such as formic acid.

Brief description of the invention

[0014] It is thus an object of the invention to develop a process for the preparation of levulinic acid in a formic acid-based cooking process of biomass, in which the separation of a separate catalyst, such as mineral acids that are difficult to recover, from the reaction product is avoided. Another object of the invention is to aim at a process, in which the necessity of separating water is minimized in the production of levulinic acid. Yet another object of the invention is to aim at a cooking process that would be as self-supporting as possible in relation to cooking chemicals, especially formic acid. One object of the invention is also to combine the preparation of glucose and levulinic acid in an advantageous manner in a formic acid-based cooking process of biomass, in which the above-mentioned disadvantages that relate to the preparation of levulinic acid and glucose in known processes are avoided. These objects of the invention are achieved by a process which is characterised by what is dis- closed in the independent claims. Preferred embodiments of the invention are disclosed in the dependent claims.

[0015] The invention is based on producing levulinic acid in a formic acid-based cooking process of biomass through a formic acid catalysis at formic acid contents that are advantageous for water separation. In levulinic acid production, a molecularly equivalent amount of formic acid is formed and can be utilized as cooking chemical in the process.

[0016] The process of the invention provides the advantage that the use of extra inorganic catalysts and extraction agents is avoided in the production of levulinic acid. In addition, formic acid is produced, whereby extra formic acid does not need to be added to the process. Because it is possible to use high acid contents in comparison with inorganic acid catalysts, the need for water separation is also reduced.

[0017] In an embodiment of the invention, the cellulose obtained in a formic acid-based cooking process of biomass is only partially hydrolysed into glucose, and the non-hydrolysed cellulose is led to the preparation of levulinic acid. It was found that most of the cellulose can be hydrolysed with only a small proportion of the enzyme requirement needed for a complete hydrolysis. Levulinic acid is prepared through a formic acid catalysis at formic acid contents that are advantageous for water separation. In levulinic acid production, a molecularly equivalent amount of formic acid is formed and can be utilized as cooking chemical in the process. This way, in the process of the invention, both high enzyme dosages in the enzymatic hydrolysis and formic acid losses in formic acid cooking are avoided. At the same time, levulinic acid is produced.

Brief description of the figures

[0018] Figure 1 shows an embodiment of the invention as a process chart (process chart 1 ) for the production of levulinic acid and, at the same time, formic acid from biomass in a formic acid-based cooking process. In the embodiment of Figure 1 , sugars (glucose) are also produced as well as bio- ethanol from them.

[0019] Figure 2 shows another embodiment of the invention as a process chart (process chart 2) for the production of glucose, levulinic acid and, at the same time, formic acid from biomass in a formic acid-based cooking process. [0020] Figure 3 is a graphical representation of the effect of the enzyme dosage on the glucose yield in the embodiment of example 2.

[0021] Figure 4 is a graphical representation of the effect of the enzyme dosage on the glucose yield in the embodiment of example 3.

Detailed description of the invention

[0022] The invention relates to a process for the production of le- vulinic acid and formic acid and, if desired, cellulose, a sugar product and/or bioethanol from biomass in a formic acid-based cooking process. The process is characterised in that it comprises the following steps:

(a) cooking the biomass in formic acid and thereafter washing it with formic acid and, if desired, washing it with water and then de-esterifying it,

(b) reacting at least part of the thus obtained cellulose pulp in a formic acid solution to produce levulinic acid and formic acid under the following conditions:

- pulp consistency 15 to 330 g, preferably 15 to 250 g dry pulp / litre of formic acid solution,

- formic acid content of the solution 10 to 90%, preferably 20 to 60%, especially 30 to 60% of dry pulp,

- temperature 160 to 220°C,

- reaction time 2 to 7 hours,

(c) separating levulinic acid and formic acid,

(d) recovering levulinic acid,

(e) returning at least part of the formic acid to cooking, and

(f) if desired, recovering part of the cellulose pulp obtained in step (a) or leading it to enzymatic hydrolysis to produce a sugar product and to fermentation to produce bioethanol.

[0023] In an embodiment of the invention, the invention relates to a process for the preparation of cellulose, a sugar product and/or bioethanol from biomass in a formic acid-based cooking process, while simultaneously producing levulinic acid and formic acid and wherein the process contains the following steps:

(a) cooking the biomass in formic acid and thereafter washing it with formic acid and, if desired, washing it with water and then de-esterifying it,

(b) reacting at least part of the thus obtained cellulose pulp in a formic acid solution to produce levulinic acid and formic acid under the following conditions: - pulp consistency 15 to 330 g, preferably 15 to 250 g dry pulp / litre of formic acid solution,

- formic acid content of the solution 10 to 90%, preferably 20 to 60%, especially 30 to 60% of dry pulp,

- temperature 60 to 220°C,

- reaction time 2 to 7 hours,

(c) separating levulinic acid and formic acid,

(d) recovering levulinic acid,

(e) returning at least part of the formic acid to cooking, and

(f) washing a second part of the cellulose pulp obtained in step (a) with water and recovering it or, if desired, leading it to enzymatic hydrolysis to produce a sugar product and to fermentation to produce bioethanol.

[0024] In an embodiment of the invention, the preparation step (b) of levulinic acid is performed in one step under the following conditions:

- pulp consistency 5 to 330 g, preferably 15 to 250 g dry pulp / litre of formic acid solution, especially 30 to 250 g dry pulp / litre of formic acid solution,

- formic acid content of the solution 10 to 90% by weight, preferably 20 to 60% by weight, especially 30 to 60% by weight per dry pulp,

- temperature 160 to 190°C, preferably 175 to 185°C,

- reaction time 2 to 7 h.

[0025] In another embodiment of the invention, the preparation step (b) of levulinic acid is performed in two steps,

with the first step under the following conditions:

- pulp consistency 15 to 330 g, preferably 5 to 250 g dry pulp / litre of formic acid solution,

- formic acid content of the solution 10 to 90% by weight, preferably 20 to 60% by weight, especially 30 to 60% by weight per dry pulp,

- temperature 200 to 240°C,

- reaction time 1 to 10 min, preferably 2 to 6 min,

and the second step under the following conditions: ^;

- pulp consistency 5 to 330 g, preferably 15 to 250 g dry pulp / litre of formic acid solution,

- formic acid content of the solution 10 to 90% by weight, preferably 20 to 60% by weight, especially 30 to 60% by weight per dry pulp,

- temperature 180 to 200°C, - reaction time 0.5 to 3 h, preferably 1 to 2 h.

[0026] The process of the invention may also contain between steps (a) and (b) a step (aO), in which the cellulose pulp intended for step (b) is washed with water or a formic acid solution so that the formic acid content of the cellulose pulp is 20 to 60% of dry pulp.

[0027] One embodiment of the invention relates to a process, in which from the water wash of step (f) a formic acid solution is recovered as a washing filtrate and used in step (aO) to wash the cellulose pulp.

[0028] In an embodiment of the invention, molecularly the same amount of levulinic acid is formed as the amount of make-up formic acid returned to the process.

[0029] In an embodiment of the invention, the formic acid used in the cooking step (a) may also contain acetic acid.

[0030] In an embodiment of the invention, a formic acid solution is recovered as a wash filtrate from step (aO), formic acid is then separated from it and returned to the cooking step (a).

[0031] In an embodiment of the invention, the invention relates to a process for producing glucose, levulinic acid and formic acid from biomass in a formic acid-based cooking process, the process comprising the following steps:

(a) cooking the biomass in formic acid and washing the thus obtained cellulose pulp with formic acid,

(a') washing the cellulose pulp with water and de-esterifying it, (a") performing a partial enzymatic hydrolysis on the thus obtained cellulose to produce glucose,

(b) reacting the non-hydrolysed cellulose pulp from step (a") in a formic acid solution to produce levulinic acid and formic acid under the following conditions:

- pulp consistency 15 to 330 g, preferably 15 to 250 g dry pulp / litre of formic acid solution,

- formic acid content of the solution 10 to 90% by weight, preferably 20 to 60%, especially 30 to 60% of dry pulp,

- temperature 160 to 220°C,

- reaction time 2 to 7 hours,

(e) separating levulinic acid and formic acid,

(f) recovering levulinic acid, and (g) returning at least part of the formic acid to cooking.

[0032] The preparation step (b) of levulinic acid can be implemented in one or two steps in the manner described above.

[0033] From step (a"), a levulinic acid solution can be recovered as a wash filtrate and used in the preparation of levulinic acid in step (b) to adjust the formic acid content to be suitable for the preparation of levulinic acid. A suitable formic acid content for the levulinic acid reactions is 20 to 60% of dry pulp. From the acid wash of step (a), a formic acid solution can be recovered as a wash filtrate, from which formic acid is separated and returned to the cooking of step (a).

[0034] In an embodiment of the invention, in step (a") 30 to 70% of the cellulose is hydrolysed into glucose, and the non-hydrolysed cellulose is led to step (b) for the preparation of levulinic acid.

Cooking and acid wash step (a)

[0035] The formic acid cooking of the cooking step (a) is performed by using cooking acid with a formic acid content in the range of 50 to 98%, preferably 70 to 98% (the rest is water). The cooking acid may also contain acetic acid, the amount being typically less than 30%, preferably less than 15%, particularly preferably less than 1 %, as calculated from the weight of the total cooking reagent. In an embodiment of the invention, the amounts of formic acid and acetic acid are essentially equal.

[0036] The cooking is performed at a temperature of 60 to 220°C, preferably 00 to 180°C, for example 130 to 170°C.

[0037] In an embodiment of the invention, peracid treatment can also be added to the cooking. In this case, the cellulose pulp obtained from the formic acid cooking, which has been concentrated to a consistency of 10 to 40% and washed, is treated at 50 to 90°C with perform ic acid that is made by adding to the formic acid hydrogen peroxide at an amount of 0.5 to 3% of dry pulp, allowing the formic acid and hydrogen peroxide to react into performic acid during 1 to 10 minutes before the performic acid is added to the concentrated and washed pulp, and the performic acid treatment of the cellulose pulp is continued until the performic acid has essentially run out, and the treatment is continued thereafter by allowing the reaction mixture to react at the same temperature.

[0038] Cooking produces cellulose pulp that is washed with formic acid. The formic acid used in washing may be the same in consistency and concentration as that used in cooking. Components dissolved from the cellulose pulp, i.e. mainly lignin and hemicellulose, are removed in the acid wash. Cellulose pulp with a dry matter content of 20 to 30% is obtained, with the rest being a concentrated acid solution. Acids and lignin are separated from the wash filtrate. Acids are returned to cooking and/or acid wash.

[0039] The acid solution used in cooking and washing is typically acid recovered from later steps of the process that has been returned to the process.

[0040] In an embodiment of the invention, the cellulose pulp obtained from step (a) is used in its entirety in the preparation of levulinic acid. In another embodiment, part of the pulp is used in the preparation of levulinic acid and part in the preparation of a sugar product (glucose), bioethanol or alternatively dissolving pulp, for instance.

[0041] The pulp used in the preparation of levulinic acid typically contains less than 10% of hemicellulose (as xylan).

Water washing step (aO)

[0042] In an embodiment of the invention, the process may also have after step (a) and before step (b) a step (aO), in which the cellulose pulp entering step (b) is washed with water or a formic acid solution (typical content 30 to 60%). The pulp is typically washed in steps and the amount of washing solution is adjusted so that a formic acid content of approximately 20 to 60% per dry pulp is obtained in the pulp. This has been found a suitable content for the following preparation reaction of levulinic acid.

[0043] In an embodiment of the invention, a formic acid-containing wash filtrate (content typically 30 to 60%) obtained from the water wash of the cellulose pulp of step (f) and intended for the preparation of bioethanol is used in the washing (aO).

[0044] In step (aO), the formic acid-content of the pulp is adjusted so that it is suitable for the preparation of levulinic acid.

[0045] Step (aO) is advantageous when the cooking reagent contains only formic acid as the acid.

[0046] When the cooking reagent contains acetic acid in addition to formic acid (preferably the same amounts of both), the water washing (aO) of the pulp is not needed, and the pulp can be led from step (a) acid wash directly to the preparation of levulinic acid. Water washing and de-esterification step (a') in an embodiment of the invention where a partial enzymatic hydrolysis into glucose is performed

[0047] The cellulose pulp entering step (a") is washed with water and de-esterified to remove formic acid and other acids (acetic acid) formed during cooking or to reduce their amount to a suitable level for enzymatic hydrolysis. De-esterification is performed by treating the pulp with dilute formic acid (content 5 to 20%, preferably 10 to 15%) at low consistency (3 to 15%, preferably 5 to 10%) at a temperature of 70 to 90°C (preferably 85°C). The treatment time is 0.5 to 24 h, preferably 4 to 12 h. De-esterification takes place during the water washing of the pulp. During de-esterification, organic acids which were bound to the pulp in a chemically esterified form in the cooking step are released from the cellulose pulp.

[0048] The formic acid-containing wash filtrate obtained during the water washing and de-esterification step and having a typical content of 30 to 60% is led to the preparation reaction of levulinic acid.

[0049] The wash filtrate is used in the preparation step (b) of levulinic acid to adjust the formic acid content of the non-hydrolysed piilp to suit the preparation reactions of levulinic acid.

Preparation of glucose (a")

[0050] A partial enzymatic hydrolysis is performed on the cellulose pulp obtained from step (a') for the production of glucose in step (a").

[0051] In the partial hydrolysis, 30 to 70% of the cellulose is typically hydrolysed into glucose. This is typically done with an enzyme dosage that is 20 to 50% of the enzyme dosage required for an approximately 90% hydrolysis. It was found that an essentially lower enzyme cost per produced glucose was reached when only a partial hydrolysis was performed by using a significantly smaller enzyme dose.

[0052] The glucose (liquid hydrolysis product) obtained from the hydrolysis is separated from the hydrolysis residue (solid non-hydrolysed cellulose) and led to fermentation, for example the preparation of bioethanol, if desired.

[0053] The solid cellulose obtained as hydrolysis residue is led to the preparation of levulinic acid. Preparation step (b) of levulinic acid

[0054] In step (b), at least part of the cellulose pulp obtained in step (a) is allowed to react in a formic acid solution to produce levulinic acid and formic acid under the following conditions:

- pulp consistency 5 to 330 g, preferably 15 to 250 g dry pulp / litre of formic acid solution,

- formic acid content of the solution 10% to 90%, preferably 20% to 60%, especially 30% to 60% of dry pulp,

- temperature 60 to 220°C,

- reaction time 2 to 7 hours.

[0055] The preparation of levulinic acid is performed in the presence of formic acid in the formic acid-content defined above, whereby the formic acid catalyses the formation of levulinic acid, and at the same time molecularly the same amount of formic acid is formed. The formic acid content of the reaction solution can be adjusted to the desired range in the manner described in step (aO) above, for example.

[0056] The preparation of levulinic acid can be implemented in a one- or two-step process described above.

Separation of levulinic acid and formic acid (c)

[0057] From the reaction solution obtained in step (b), the solid matter (typically lignin-containing residue) is separated by filtration, for example, whereby a solution containing levulinic acid and formic acid is obtained. Levulinic acid and formic acid as well as possibly other components (acetic acid, furfural, water) are separated by distillation, for instance.

Recovery of levulinic acid and return of formic acid to cooking (d)

[0058] The separated levulinic acid is recovered and sold as a commercial product. At least part of the formic acid formed in the levulinic acid reaction is returned as a make-up cooking chemical (a chemical replacing the formic acid loss) in the process, and the rest may be sold as a commercial product. This way, the process can be kept self-sufficient in terms of formic acid, and extra formic acid need not be acquired.

[0059] Because in the levulinic acid reaction, molecularly the same amounts of levulinic acid and formic acid are formed, the production of levulinic acid and formic acid can, if desired, be adjusted so that only the amount of formic acid is produced that is required as make-up chemical in the process (a molecularly equivalent amount of levulinic acid is obtained). The amount of formed levulinic acid can be calculated, when the required amount of formic acid per ton of cellulose and the total yield of cellulose or ethanol (in tons) are known. Molecularly the same amount of levulinic acid is then formed as the amount of make-up formic acid returned to the process. This provides an advantage in the economy of the total process.

Preparation of a sugar product (glucose) and bioethanol (f)

[0060] In an embodiment of the invention, part of the cellulose pulp obtained in step (a) is used in the preparation of a sugar product (glucose) and, if desired, further in the preparation of bioethanol. The pulp is then first led to enzymatic hydrolysis to produce glucose and, if desired, on to fermentation to prepare bioethanol. Alternatively, the pulp may also be used in the preparation of dissolving pulp, for example.

Raw material

[0061] The biomass used as the starting material in the process is typically lignocellulosic material that may be any lignocellulosic plant material. It may be wood material, such as softwood or hardwood, such as eucalyptus or acacia. It may also be non-wood material based on herbaceous plants, bast fibres, leaf fibres or fruit seed fibres. Examples of usable materials based on herbaceous plants include straw, such as cereal straw (wheat, rye, oat, barley, rice), reeds, such as reed canary grass, common reed, papyrus, sugar cane, i.e. bagasse, and bamboo, as well as grasses, such as esparto, sabai and lemon grass and sorghum. Examples of bast fibres include flax, such as stalks of common flax and stalks of oil flax, stalks of cassava, hemp, East Indian hemp, kenaf, jute, ramie, paper mulberry, gampi fibre and mitsumata fibre. Examples of leaf fibres include abaca and sisal. Examples of fruit seed fibres include cottonseed hairs and cotton linter fibres, kapok and coir fibre.

[0062] Herbaceous plants growing in Finland and usable in the present invention include common reed, reed canary grass, timothy, cocksfoot, yellow sweet clover, smooth brome, red fescue, white sweet clover, red clover, goat's rue and alfalfa.

[0063] Particularly preferably, biomass based on herbaceous plants, such as cereal straw, is used. In an embodiment, biomass based on annual herbaceous plants is used. In another embodiment, biomass based on perennial non-wood plants is used. In accordance with the invention, lignocellulose- containing waste material from industry or agriculture, including empty fruit bunch of oil palm and the above-mentioned cereal straw, may also be used.

Figure 1

[0064] The process of the invention may be included as part of a formic acid-based total process, in which bioethanol, levulinic acid and, if desired, other chemicals are produced from biomass and in which the formic acid formed in the preparation of levulinic acid is utilized as make-up chemical in biomass cooking.

[0065] As shown in Figure 1 , the biomass 1 is fed to cooking 120 together with cooking acid 21 ,32. Cooking acid 21 ,32 is an acid mixture originating from the formic acid recovered from the evaporation 190 of cooking acid and distillation 240 of levulinic acid. The cellulose pulp 7 obtained from cooking is led to acid washing 130, where the pulp is washed with the same acid mixture 21 ,32 as that used in cooking. The acid-containing wash filtrate from the acid wash is led to evaporation 190.

[0066] The acid-washed cellulose pulp 8 is divided into two parts, of which one continues to water wash 140 and the other to water wash 210. The washed pulp 11 from water wash 140 is led on to enzymatic hydrolysis 150 and the thus obtained hydrolysis product (glucose) 14 is led to the preparation 160 of bioethanol. The second part continues to water wash 210. In water wash 210, a filtrate 17 from water wash 140 is used, whereby the formic acid content of the pulp 18 obtained from water wash 140 is made suitable for the preparation 220 of levulinic acid.

[0067] The preparation 220 of levulinic acid is performed formic acid-catalysed at an acid concentration adjusted with the wash filtrate 17. A stream 24 that contains levulinic acid and formic acid is obtained and led to separation, for instance filtration 230. Filtration 230 separates a lignin- containing residue 26 and a filtrate 27 containing levulinic acid and formic acid that is led to the distillery 240. In the distillery 240, acetic acid 28, furfural 29, levulinic acid 30, water 31 and formic acid-containing cooking acid 32 are separated. This is returned as make-up acid to cooking 120.

[0068] The filtrate 19 from water wash 210 is led to evaporation 190, where the cooking acid 21 is separated and led back to biomass cooking 120. The concentrated cooking acid 20 obtained from evaporation 190 is led to the preparation 180 of furfural. The stream 22 obtained therefrom is led to lig- nin drying 200, from which lignin is obtained as a dry product 34, and a stream 33 containing furfural and acids is also obtained. The furfural and acid stream 33 is led to the distillery 240.

Figure 2

[0069] The process of the invention may also be included as part of a formic acid-based total process, in which glucose, bioethanol, levulinic acid and, if desired, other chemicals are produced from biomass and in which the formic acid formed in the preparation of levulinic acid is utilized as make-up chemical in biomass cooking.

[0070] As in Figure 1 , the biomass 1 is fed to cooking 120 together with cooking acid 21 ,32. Cooking acid 21 ,32 is an acid mixture originating from the formic acid recovered from the evaporation 190 of cooking acid and distillation 240 of levulinic acid. The cellulose pulp 7 obtained from cooking is led to;ac- id washing 130, where the pulp is washed with the same acid mixture 21 ,32 as that used in cooking. The acid-containing wash filtrate from the acid wash is led to evaporation 190.

[0071] The acid-washed cellulose pulp 8 continues to water wash and de-esterification 140. The obtained washed pulp 11 is led to enzymatic hydrolysis 150 performed with enzymes 13. In step 170, a liquid fraction 14 (glucose) and a solid hydrolysis residue 36 (non-hydrolysed cellulose) are separated from the hydrolysis product 35. The glucose is led to fermentation, for instance the preparation 160 of bioethanol. The solid cellulose is led to the preparation 220 of levulinic acid. In the preparation of levulinic acid, the filtrate 17 from water wash 140 is used to adjust the formic acid content, whereby the formic acid content of the cellulose pulp 36 is made suitable for the preparation 220 of levulinic acid.

[0072] The preparation 220 of levulinic acid is performed formic acid-catalysed at an acid concentration adjusted with the wash filtrate 17. A stream 24 that contains levulinic acid and formic acid is obtained and led to separation, for instance filtration 230. Filtration 230 separates a lignin- containing residue 26 and a filtrate 27 containing levulinic acid and formic acid that is led to the distillery 240. In the distillery 240, acetic acid 28, furfural 29, levulinic acid 30, water 31 and formic acid-containing cooking acid 32 are separated. This is returned as make-up acid to cooking 120.

[0073] The filtrate 9 from acid wash 130 is led to evaporation 190, where the cooking acid 21 is separated and led back to biomass cooking 120. The concentrated cooking acid 20 obtained from evaporation 190 is led to the preparation 180 of furfural. The stream 22 obtained therefrom is led to lignin drying 200, from which lignin is obtained as a dry product 34, and a stream 33 containing furfural and acids is also obtained. The furfural and acid stream 33 is led to the distillery 240.

Examples

[0074] In the following, the invention will be described with reference to illustrating but non-restrictive examples.

Example 1

Cooking and acid wash

[0075] Cellulose pulp was prepared by cooking wheat straw in 83% formic acid (cooking temperature approximately 140°C, liquid ratio approximately 5 and cooking time approximately 35 minutes). The formic acid used in cooking is typically acid regenerated from the total process supplemented by make-up formic acid obtained from the later levulinic acid preparation step. After this, the pulp was washed with approximately 82% formic acid in several steps. The formic acid used in washing pulp is also typically acid regenerated from the total process supplemented by formic acid obtained from the levulinic acid preparation step. After the acid wash, the obtained pulp may be used in its entirety to prepare levulinic acid, or it may be divided into two parts, of which one is used in the preparation of bioethanol and the other in the preparation of levulinic acid.

Water wash

[0076] The pulp intended for the preparation of levulinic acid was washed with water (which may be a water wash filtrate of pulp intended for the preparation of bioethanol) so that the pulp contained approximately 20 to 30% of formic acid (calculated as percentage by weight of dry pulp). The acid- containing filtrate from the water wash is typically led to evaporation, where acid is separated and returned as cooking chemical to cooking.

Preparation of levulinic acid

[0077] The pulp that has been washed with water and contains 20 to 30% formic acid (properties shown in table 1 ) was led to the preparation of levulinic acid. . Table 1. Properties of cellulose pulp prior to the preparation of levulinic acid

[0078]

One-step process

[0079] The preparation of levulinic acid was performed in one step under the conditions shown in table 2:

Table 2

Xpuip, % = cellulose conversion

Ygiuc/puip, % by weight = glucose yield from cellulose

Y , % by weight = 5-hydroxy methyl furfural HMF (intermediate product) yield from cellulose

Yuvpuip, % by weight = levulinic acid yield from cellulose [0080] The maximum yield of levulinic acid in the tests was approximately 18 g of levulinic acid per dry cellulose pulp (Y _LA/PU I _p )- This was achieved under the following conditions:

- 40 g/l cellulose pulp

- 80°C, 20% HCOOH, 6 h and

- 180°C, 30% HCOOH, < 4 h.

[0081] Molecularly the same amount of formic acid was also formed in the preparation of levulinic acid.

Separation of levulinic acid and formic acid

[0082] From the reaction mixture containing levulinic acid and formic acid, lignin was filtered and the filtrate led to a distillery, where the levulinic acid and formic acid were separated. Furfural and acetic acid are also typically obtained as distillation products. Formic acid was led as a make-up chemical to the cooking of biomass. Levulinic acid was recovered.

Two-step process

[0083] An acid- and water-washed cellulose pulp was prepared as described above. Levulinic acid was prepared of the thus obtained cellulose pulp with a two-step process under the conditions described in the following table 3.

Table 3

[0084]

Xpuip, % = cellulose conversion

Ygiuc/puip, % by weight = glucose yield from cellulose

H F/P _U IP, % by weight = 5-hydroxy methyl furfural HMF (intermediate product) yield from cellulose

Y /puip, % by weight = levulinic acid yield from cellulose [0085] It was found that the first step mainly accelerated the degradation of cellulose into glucose and the second step accelerated the reaction of cellulose into 5-hydroxy methyl furfural (HMF) and on to levulinic acid and formic acid.

[0086] The results show that the conversion of cellulose and production of levulinic acid can be improved by using a two-step process. It was also found that by lengthening the reaction time, the production of levulinic acid can be improved even more.

Example 2 (hydrolysis of cellulose prepared from sweet sorghum bagasse)

[0087] Cellulose pulp was prepared by cooking sweet sorghum bagasse in 82% formic acid (cooking temperature 140°C and cooking time 12 minutes). The formic acid used in cooking is typically acid regenerated from the total process supplemented by make-up formic acid obtained from the later levulinic acid preparation step. After cooking, peracid treatment with 1.9% per- acid was performed for 180 minutes. After this, the pulp was washed with the same 82% formic acid and then with water so that the acid content was reduced to be suitable for enzymatic hydrolysis.

[0088] The enzymatic hydrolysis was performed with different enzyme dosages. After the hydrolysis, solid matter (non-hydrolysed cellulose) was separated by filtration. Glucose yields (as calculated from dry cellulose) with different enzyme dosages are shown in Figure 3. The enzyme dosages are given per dry cellulose.

[0089] The results show that a 94% hydrolysis into glucose is achieved with an enzyme dosage of 3.8% and, correspondingly, a 65% hydrolysis yield is achieved with an enzyme dosage of 2%.

[0090] The reduction of the enzyme dosage in a partial hydrolysis can be illustrated by examining the enzyme consumption per produced glucose unit. On the basis of the results of Figure 3, a 2% enzyme dosage (per dry cellulose) thus produces a 65% hydrolysis degree, whereby the production of a glucose unit consumes 3.1 % [2%/65%] of enzyme and as calculated to a hydrolysis degree of 94%, 3.0% [2%/65% ^* 94%] of enzyme. The difference (as calculated from dry cellulose) in enzyme consumption in a partial hydrolysis (65%) and a nearly complete hydrolysis (94%) is 1.8% [3.8-2.0%], and the difference has consumed 6.9% [1.8%/(94%-65%)] of enzyme. Thus, the final hydrolysis (from 65% to 94%) consumes approximately a twofold amount of enzyme per produced glucose unit in comparison with a partial hydrolysis.

[0091] When performing only a partial hydrolysis, the enzyme dosage and the related costs were significantly reduced.

[0092] The hydrolysis residue (non-hydrolysed cellulose) was led to the preparation of levulinic acid.

Example 3 (hydrolysis of cellulose prepared from wheat straw)

[0093] Cellulose pulp was prepared by cooking wheat straw in 82% formic acid (cooking temperature 138°C and cooking time 35 minutes). The formic acid used in cooking is typically acid regenerated from the total process supplemented by make-up formic acid obtained from a later levulinic acid preparation step. After cooking, peracid treatment with 1.9% peracid was performed for 240 minutes. After this, the pulp was washed with the same 82% formic acid and then with water so that the acid content was reduced to be suitable for enzymatic hydrolysis.

[0094] The enzymatic hydrolysis was performed with different enzyme dosages. After the hydrolysis, solid matter (non-hydrolysed cellulose) was separated by filtration. Glucose yields (as calculated from dry cellulose) with different enzyme dosages are shown in Figure 4. The enzyme dosages are given per dry cellulose.

[0095] The results show that a 97% hydrolysis into glucose is achieved with an enzyme dosage of 5.2% and, correspondingly, a 37% hydrolysis yield is achieved with an enzyme dosage of only 1.1%.

[0096] On the basis of the results of Figure 4, an enzyme dosage of 1.1 % (per dry cellulose) produces a hydrolysis degree of 37%, whereby the production of a glucose unit consumes 2.9% [1.1%/37%] of enzyme, and as calculated to a hydrolysis degree of 97%, 2.8% [1.1%/37%*97%] of enzyme. The difference (as calculated from dry cellulose) between a partial hydrolysis (37%) and a nearly complete hydrolysis (97%) is 4.1 % [5 2-1.1 %], and the difference has consumed 6.9% [4.1 %/(97%-37%)] of enzyme. Thus, the final hydrolysis (from 37% to 97%) consumes a nearly 2.5fold amount of enzyme per produced glucose unit in comparison with a partial hydrolysis.

[0097] When performing only a partial hydrolysis, the enzyme dosage was significantly reduced. Example 4 (preparation of levulinic acid)

[0098] The hydrolysis residue (non-hydrolysed cellulose) obtained from the enzymatic hydrolysis of examples 2 and 3 was led to the preparation of levulinic acid. The formic acid content of the cellulose pulp was adjusted with the formic acid-containing wash filtrate obtained from the water wash to a value of 20 to 30%.

[0099] It was unexpectedly found that the non-hydrolysed cellulose pulp obtained as hydrolysis residue was well suited for raw material in the preparation of levulinic acid.

[0100] It will be apparent to a person skilled in the art that as technology advances, the basic idea of the invention may be implemented in many different ways. The invention and its embodiments are thus not restricted to the examples described above but may vary within the scope of the claims.