WO2010111995A2

WO2010111995A2 - Method for the hydrolysis of cellulose raw materials

Info

Publication number: WO2010111995A2
Application number: PCT/DE2010/000320
Authority: WO
Inventors: Ferdi SCHÜTH; Roberto Rinaldi; Philip Engel; Antje Spiess; Jochen Büchs
Original assignee: Studiengesellschaft Kohle Mbh; Rheinisch-Westfälische Technische Hochschule Aachen
Priority date: 2009-04-02
Filing date: 2010-03-23
Publication date: 2010-10-07
Also published as: WO2010111995A3; DE102009016001A1

Abstract

A method for the depolymerization of cellulose is claimed, wherein a solution made of cellulose is brought in contact with a solid acid catalyst in an ionic fluid and in a subsequent step, the depolymerized cellulose obtained in this way is subjected to enzymatic hydrolysis.

Description

Process for the hydrolysis of cellulose raw materials

The present invention relates to a process for the degradation of cellulose-based materials in which the cellulose is first depolymerized in an ionic liquid in the presence of catalysts and subsequently converted into fermentable sugars.

Lignocellulosic materials such as crop residues, straw and wood are renewable and spread all over the world materials that are promising raw materials for the chemical industry and energy generation in the 21st century. These materials are complex mixtures of natural polymers, namely cellulose, hemicelluloses and lignin, which are bound together by physical and chemical interactions.

Chemically, the cellulose is an unbranched polysaccharide consisting of several hundred to ten thousand / 3-D glucose molecules. The number of / 3-D-glucose units is defined as the degree of polymerization of the cellulose (P _w - weight average of the degree of polymerization, P _n - number average of the degree of polymerization). It is an important technical raw material used as a raw material in the paper industry or in the clothing industry as viscose, cotton fiber or linen. Another important field of application is the building materials industry, where cellulose derivatives such as methyl cellulose are used as flow improvers, etc. Further fields of application are the production of cellophane or the development of regenerative car fuels, such as cellulose ethanol, which is produced from vegetable biomass. Furthermore, cellulose derivatives are used as additives in the food and pharmaceutical industries.

Cellulose is a very stable material, which is also stable to chemical and biological agents, so that direct processing of cellulose-based materials is not possible. Various pretreatment methods have been developed to circumvent the stability of cellulose to biological transformations. These pretreatments utilize physical, chemical and / or biological processes to remove lignin and reduce the degree of crystallinity of the cellulose. Even if While these pretreatment processes result in better cellulase processability of cellulose, the yield of glucose is still far from quantitative conversion. Some pretreatment steps have been developed to allow for substantially quantitative conversion of cellulose to glucose. The disadvantages of these known methods are a high energy requirement, expensive and / or toxic reagents and the formation of toxic reaction products that affect the subsequent fermentation reaction.

Cellulose is insoluble in water and in most organic solvents. It has some solubility in toxic solvents such as CS ₂ , amines, dimethylacetamide / LiCl morpholines, etc., concentrated mineral acids, molten salts, and copper ammonia. Currently commercially used solvents are, for example, N-methylmorpholine-N-oxide and CS ₂ .

Furthermore, it is possible to physically dissolve cellulose in an ionic liquid. With the cellulose thus dissolved, chemical syntheses can be carried out which are not possible in other solvents.

Ionic liquids are liquid salts which are liquid at temperatures below 100 ^° C. Examples of cations used are alkylated imidazolium, pyridinium, ammonium or phosphonium ions. As anions, a wide variety of ions can be used, ranging from simple halides over more complex inorganic ions such as tetrafluoroborates to large organic ions such as trifluoromethanesulfonamide. Examples of suitable ionic liquids are described in patents US-A1, 943,176, WO03 / 029329 and WO07 / 057235.

International patent applications WO2008 / 090156 and WO2008 / 090155 disclose processes for producing glucose products from a lignocellulosic material. In the disclosed methods, the lignocellulosic starting material is treated with an ionic liquid which isolates enriched cellulosic material and then subjected to enzymatic hydrolysis. The separation of the resulting cellulose products via precipitation, separation and enrichment steps.

A disadvantage of the process described in the prior art is that in the treatment of cellulose in ionic liquids no depolymerization takes place, the

Hydrogen bonds are merely broken, ie the crystalline structure of the cellulose is degraded. The enzymatic step lasts because of the high Degree of polymerization of the cellulose usually many hours to achieve a quantitative conversion of cellulose into glucose.

Accordingly, it was an object of the present invention to provide a more efficient process for the depolymerization of cellulose which does not have the disadvantages known from the prior art and gives as quantitative a yield as possible of low molecular weight glucose units up to monomolecular glucose.

The present invention accordingly provides a process for the depolymerization of cellulose in which a solution of cellulose in an ionic liquid is contacted with a solid acid catalyst and in a subsequent step the resulting depolymerized cellulose is subjected to enzymatic hydrolysis.

By pretreating the cellulose in an ionic liquid with a solid acid catalyst, a low molecular weight or oligomeric reaction mixture having a narrow molecular weight distribution can be obtained within a short time. These low molecular weight or oligomeric structures can be converted very rapidly by cellulase and cellulase preparations almost quantitatively into glucose and cellulase within a short time. In the first reaction step, a depolymerized cellulose is obtained whose polymer degree P "is preferably between 1000 and 20 AGU.

As starting materials for the process according to the invention, any cellulose-based materials can be used, such as. Microcrystalline cellulose, σ-cellulose, mechanically treated cellulose or wood pulp. Also, the origin may be arbitrary, the cellulosic material may consist of wood, oilseeds, beans, cereals and cereal fibers, cotton, sugarcane, all parts can be used, i. Leaves, stems, stems, shells, pods and flower parts etc.

In the first process step, the cellulosic material is contacted with an acid catalyst in an ionic liquid.

In the context of the present application, ionic liquids refer to organic salts whose melting point is below 180 ^° C., that is, which are liquid at temperatures below 180 ^° C. Preferably, the melting point is in a range from -50 ⁰ C to 150 ⁰ C, more preferably in the range of -20 ⁰ C to 120 ⁰ C and in particular below 100 ⁰ C. Ionic liquids, which are already in room temperature in liquid Aggregate state are described, for example, by KN Marsh et al., Fluid Phase Equilibria 219 (2004), 93-98 and JG Huddieston et al., Green Chemistry 2001, 3, 156-164.

Cations and anions are present in the ionic liquid. In this case, within the ionic liquid from the cation, a proton or an alkyl radical can be transferred to the anion, resulting in two neutral molecules. In the ionic liquid used according to the invention, therefore, there can be an equilibrium of anions, cations and neutral molecules formed therefrom.

In the method according to the invention suitable ionic liquids are preferably as cations

DIalkylfmidazolium, alkylpyridine, tetraalkylammonium, tetraalkylphosphonium

on. The anions are preferably selected from chloride, bromide, nitrate, sulfate, phosphate, tetrafluoroborate, tetrachloroaluminate; Tetrachloroferrate (III), hexafluorophosphate, hexafluoroantimonate, carboxylic anions, trifluoromethanesulfonate, alkyl phosphate, alkylsulfate, alkylsulfonate, benzenesulfonate, bis (trifluoromethylsulfonyl) imide,

Trifluoromethansulfonamid. The cations and anions can be combined as desired.

Particularly suitable ionic liquids have proven to be alkylated imidazolium, pyridinium, ammonium or phosphonium radicals and as anions halides, inorganic, complex anions such as tetrafluoroborates, or organic ions such as Trifluoromethansulfonamide.

As catalysts solid acid catalysts are used according to the invention. These have the advantage that they are active in solid form, and can be separated from the reaction products after completion of the reaction. In a preferred embodiment, acidic catalysts used are acidic ion exchangers or acidic inorganic metal oxides. Acid ion exchangers are, for example, macroporous or mesoporous crosslinked polymers which have acidic groups on their surface. Other suitable catalysts are inorganic materials, eg. Example, silica, alumina, aluminosilicates and zirconia whose surface can be modified by acidic groups. As suitable modifications on the surface come z. B. -SO ₃ H or -OSO ₃ H-functionalization or phosphoric surface modifications into consideration.

As particularly preferred catalysts serve ion exchange resins, with a surface area of 1 to 41 m ² g ^{'1 is} advantageous. Preferably, these ion exchange resins have a pore volume of 0.002 to 0.220 cm ³ g ^"1 and an average pore diameter of 24 to 30 nm and an ion exchange capacity of 2.5 to 5.4 mmol g ^'1 .

The reaction can be carried out at relatively low temperatures as compared with the prior art. Depolymerization results at a relatively short reaction time are obtained in a temperature range between 80 and 13O ⁰ C. By targeted modification of the ionic liquid used but also reactions in the range of room temperature to 8O ⁰ C are conceivable.

The oligomers obtained from the oligomers obtained in the first process step can be separated from the ionic liquid before the further treatment and optionally washed with water to remove the ionic liquid. The degree of polymerization P _{w of} the depolymerized cellulose obtained is preferably between 20 and 100.

In a subsequent step, the aqueous suspension of cellulose oligomers is subjected to enzymatic hydrolysis in which the oligomers are hydrolyzed almost quantitatively in glucose and cellulase.

Suitable enzymes for use in the process according to the invention are the cellulases belonging to the category of the hydrolases (1,4- (1,3,1,4) -β-D-glucan-4-glucanohydrolases). The EC number is 3.2.1.4., The CAS number 9012-54-8. The cellulase enzyme complex consists of three different types of enzymes: endoglucanases break the compounds within the cellulose to dissolve the crystalline structure, exoglucanases separate smaller oligosaccharide units, usually disaccharide and tetrasaccharide units (cellobiose, cetotetrose units) from the ends of the smaller chains producing the endoglucanase. Cellobiases or β-glucosidases cleave the bond between the glucose molecules in the oligosaccharides. Suitable z. Cellulases from Trichoderma reesei (ATCC # 26799), commercially available from Worthington Biochemical Corporation. Also suitable are the cellulase mixtures, Celluclast 1, 5 L with Novozym 188 (Novozymes, Denmark) or Spezyme CP (Genencor International Inc., Rochester, USA) with Novozym 188 (Novozymes, Denmark).

The concentration of enzyme is between 0.1 and 2.0 v / v%, ie about 500 to 20,000 I U / L, with an IU corresponding to the cleavage of 1 μmol bonds per min.

The enzymatic hydrolysis is preferably carried out in an aqueous medium. The aqueous medium used is essentially free of ionic liquids. The term "essentially free of ionic liquids" in the context of the application means a content of less than 1% by volume, preferably less than 0.1% by volume, based on the total volume of the liquid reaction medium used for the hydrolysis.

The enzymatic hydrolysis takes place at a pH suitable for the enzymes used, generally between 3.5 and 8. An advantageous pH range for many of the enzymes usable in the context of the present invention is about 4 to 5.5. Of course, working at a higher or lower pH is also possible in detail, as long as the enzyme used permits this. The adjustment of the pH can be carried out by customary, known to those skilled buffer systems. These include acetate buffer, Tris buffer, etc.

The enzymatic hydrolysis is preferably carried out at a temperature of 0 to 80 ° C, more preferably at 20 to 60 ⁰ C.

The reaction product obtained, the depolymerized cellulose, can be isolated from the reaction mixture in a manner known per se. In one possible embodiment, the glucose is precipitated by the addition of water, lower aliphatic alcohols, lower ketones or protic low boiling solvents.

In a preferred embodiment of the process according to the invention, the material and / or energy flows are integrated so that the ionic liquid used is substantially completely recycled and / or the amount of heat required in the process (eg for the separation of ionic liquid and precipitant) is used at least partially in another step of the method. EXAMPLES

The invention will be explained in more detail with reference to the following examples:

example 1

5 g of σ-cellulose were dissolved in 100 g of 1-butyl-3-methylimidazolium chloride at 100 ⁰ C. After dissolving the cellulose, 2 ml of distilled water was added. The solution was stirred for a further 15 min, then 1 g of Amberlyst 15 DRY (commercial product from Rohm & Haas, DE) was added to the solution. The depolymerization of the cellulose was carried out at 100 ^° C. The reaction mixture was sampled every 15 minutes for the first hour and hourly thereafter. 25 ml of water were added to each of the samples. The precipitated cellulose was separated by centrifugation. Table 1 shows the course of the degree of polymerization of the resulting cellulose as a function of the reaction time. The amount of cellulose recovered was determined by weighing the cellulose samples. These samples were derivatized with phenyl isocyanate for GPC analysis.

The isolated cellulose oligomers having a degree of polymerization of 100 anhydroglucose units (AGU) were washed with water to remove the ionic liquid. The aqueous suspension of the cellulose oligomers was treated with a

Acetate buffer (pH 4.8) diluted to a concentration of 10 g / L cellulose oligomers. to

Suspension was a cellulase preparation in a concentration of 0.5 V / V%

(Celluclast 1, 5 L, cellulose from Trichoderma reesei, Novozyme, TK, 700 EGU / ml) at 45 ° C processed. With the hydrolysis, a conversion of 82% was achieved within 4 hours, consisting of 45% Cellubiose and 28% glucose.

Table 1. Depolymerization of α-cellulose with Amberlyst 15DRY.

P _w - weight average of the degree of polymerization; P _n - Number average of the degree of polymerization.

Example 2

5 g or-cellulose were dissolved in 100 g of 1-butyl-3-methylimidazolium chloride at 100 ⁰ C. After dissolving the cellulose, 2 ml of distilled water was added. The solution was stirred for an additional 15 min, then 1 g of Amberlyst 15DRY (commercial product of Rohm & Haas, DE) was added to the solution. The depolymerization of the cellulose was carried out at 100 ^° C. The reaction mixture was sampled every 15 minutes for the first hour and hourly thereafter. 25 ml of water were added to each of the samples. The precipitated cellulose was separated by centrifugation.

The isolated cellulose oligomers were further reacted as in Example 1, except that 2.0 v / v% Celluclast was used. The enzymatic hydrolysis resulted in a turnover of the oligomers of 94%, consisting of 48% Cellubiose and 46% glucose within two hours. Example 3

5 g of microcrystalline cellulose were dissolved in 100 g of i-butyl-3-methylimidazolium chloride at 100 ^° C. After dissolving the cellulose, 2 ml of distilled water was added. The solution was stirred for an additional 15 min, then 1 g of Amberlyst 15DRY (commercial product of Rohm & Haas, DE) was added to the solution. The depolymerization of the cellulose was carried out at 100 ^° C. The reaction mixture was sampled every 15 minutes for the first hour and hourly thereafter. 25 ml of water were added to each of the samples. The precipitated cellulose was separated by centrifugation.

The isolated cellulose oligomers were further reacted as in Example 2, except that the hydrolysis was carried out at 65 ^° C. The enzymatic hydrolysis resulted in a turnover of the oligomers of 94%, consisting of 48% Cellubiose and 46% glucose within two hours.

Example 4

5 g of α-cellulose were dissolved in 100 g of 1-butyl-3-methylimidazolium chloride at 100 ⁰ C. After dissolving the cellulose, 2 mL of distilled water was added. The solution was stirred for an additional 15 min, then 1 g of Amberlyst 15DRY (commercial product of Rohm & Haas, DE) was added to the solution. The depolymerization of the cellulose was carried out at 100 ^° C. The reaction mixture was sampled every 15 minutes for the first hour and hourly thereafter. 25 ml of water were added to each of the samples. The precipitated cellulose was separated by centrifugation.

The isolated cellulose oligomers having a degree of polymerization of 50 anhydroglucose units (AGU) were reacted further as in Example 1. The enzymatic hydrolysis resulted in a turnover of the oligomers of 92%, consisting of 60% Cellubiose and 32% glucose within four hours.

Example 5

5 g of σ-cellulose were dissolved in 100 g of 1-butyl-3-methylimidazolium chloride at 100 ⁰ C. After dissolving the cellulose, 2 mL of distilled water was added. The solution was stirred for an additional 15 min, then 1 g of Amberlyst 15DRY (commercial product of Rohm & Haas, DE) was added to the solution. The depolymerization of the cellulose was carried out at 100 ^° C. The reaction mixture was sampled every 15 minutes for the first hour and hourly thereafter. The resulting depolymerization product was precipitated by the addition of methanol. The ionic liquid was extracted from the precipitate by extraction with methanol and the suspension of cellulose oligomers was washed in water.

The isolated cellulose oligomers having a degree of polymerization of 100 AGU were reacted further as in Example 1. The enzymatic hydrolysis resulted in a turnover of the oligomers of 96%, consisting of 55% Cellubiose and 41% glucose within two hours.

Example 6

5 g of wood were dissolved in 100 g of i-butyl-3-methylimidazolium chloride at 100 ⁰ C. After dissolving the cellulose, 2 mL of distilled water was added. The solution was stirred for an additional 15 min, then 1 g of Amberlyst 15DRY (commercial product of Rohm & Haas, DE) was added to the solution. The depolymerization of the cellulose was carried out at 100 ^° C. The reaction mixture was sampled every 15 minutes for the first hour and hourly thereafter. 25 ml of water were added to each of the samples. The precipitated cellulose was separated by centrifugation. Table 2 shows the course of the degree of polymerization of the resulting cellulose as a function of the reaction time. These samples were derivatized with phenyl isocyanate for GPC analysis.

Table 2. Depolymerization of wood with Amberlyst 15DRY.

Example 7 α-cellulose which had not been pretreated with an acid in ionic liquid according to the present invention was mixed with an acetate buffer (pH 4.8). whereby a suspension of 10 g / L was obtained. The suspension was treated with cellulase as in Example 5 to give a conversion of 35% consisting of 17% cellobiose and 18% glucose within 4 hours.

Example 8 σ-cellulose treated in an ionic liquid but not depolymerized in the presence of a solid acid had a degree of depolymerization between 1,000 and 2,000 AGU. This material was mixed into an acetate buffer (pH 4.8) as in Example 1 to give a suspension of 10 g / L. This suspension was treated with cellulase as in Example 1. The enzymatic hydrolysis of the α-cellulose, which was removed from the ionic liquid, gave a degradation rate of 78%, and consisted 43% of Cellubiose and 35% glucose within 1.5 hours.

Claims

claims

A process for the depolymerization of cellulose in which a solution of cellulose in an ionic liquid is contacted with a solid acid catalyst and in a subsequent step the resulting depolvmerized cellulose is subjected to enzymatic hydrolysis.

2. The method according to claim 1, characterized in that the ionic liquid is selected from alkylated imidazolium, pyridinium, ammonium or phosphonium cations with anions selected from halides, inorganic, complex anions, such as tetrafluoroborates, and organic ions, such as trifluoromethanesulfonamide ,

3. The method according to any one of claims 1 or 2, characterized in that the solid acid catalyst is selected from acidic ion exchangers, metal oxides or zeolitic materials.

4. The method according to claim 3, characterized in that the catalyst is an acidic ion exchanger and / or an inorganic material having on the surface modifications in the form of -SO ₃ H or -OSO ₃ H-functionalization and / or phosphoric surface modifications ,

5. The method according to any one of claims 1 to 4, characterized in that the obtained from the treatment with the solid acid catalyst depolymerized cellulose has a degree of polymerization P _w between 20 and 100.

6. The method according to any one of claims 1 to 5, characterized in that for the enzymatic hydrolysis cellulase or a cellulase preparation is used.

7. The method according to any one of claims 1 to 6, characterized in that the enzymes are present as a whole cell preparation, as a cell extract, or as a mixture of cell extracts, as a purified enzyme preparation, or as immobilized enzyme preparation.

8. The method according to claim 6 or 7, characterized in that the Cellulasepreparation is a mixture of cellobiohydrolases, endoglucanases and beta-glucosidase.

9. The method according to any one of claims 1 to 8, characterized in that the hydrolysis is carried out at a pH between 3.5 and 8.

10. The method according to any one of claims 1 to 9, characterized in that the hydrolysis is carried out at a temperature of between 20 and 80 ⁰ C.

11. The method according to any one of claims 1 to 10, characterized in that the depolymerized cellulose by addition of water, lower aliphatic

Alcohols, lower ketones or protic solvents with a low boiling point is precipitated.