Wood digestion process

Abstract

The present invention relates to a process for digesting biogenic lignin-containing material, e.g. in the form of wood, in which the biogenic material, in paste or particulate form, is first impregnated with an excess of water-miscible organic solvent having a boiling point of < 110°C, this solvent is then separated out and the product obtained in this way is subsequently treated with a digestion reagent for lignin, in order to separate the biogenic material into its component parts (e.g. in particular lignin, cellulose and hemicellulose). The water content in the biogenic material is significantly reduced through the pre-treatment with the water-miscible organic solvent, thus reducing the energy requirement of the digestive process.

Description

Wood pulping process DESCRIPTION The present invention relates to a digestion process for biogenic lignocellulosic material, e.g. in the form of wood, in which the biogenic material in pasty or particle form is first impregnated with an excess of water-miscible organic solvent having a boiling point of < 110°C, this solvent is then separated off, and the product thus obtained is subsequently treated with a digestion reagent in order to separate the biogenic material into its components (i.e. in particular lignin, cellulose and hemicellulose). By pretreatment with the water-miscible organic solvent, the water content in the biogenic material is significantly reduced, and a product is obtained which has a lower water absorption capacity than wood conventionally dried at elevated temperature. State of the art The structural substances of plants consist essentially of cellulose, hemicelluloses, and lignin (e.g., 16-29% in hardwoods and 27-37% in softwoods). Tree bark also contains tannin. To date, cellulose is predominantly obtained from wood, with two main processes being used technically: So-called sulfate pulping is used worldwide to obtain cellulose, but only a few companies use it to produce lignin. In this process, sodium sulfide / NaOH is allowed to act on wood particles, partially demethylating the lignin and splitting it into smaller phenolic units. The phenols and the partial phenol ethers are dissolved in the lye. Byproducts are foul-smelling compounds such as methyl mercaptan and dimethyl sulfide. The partially demethylated lignin can be precipitated from the resulting, dark-colored solutions using sulfuric acid, hydrochloric acid, or CO2.The lignin obtained in this way is called kraft lignin and is primarily used as fuel. In sulfite digestion, sodium sulfite is the digesting agent. When exposed to wood, dehydration presumably occurs, forming quinoid systems to which sulfite attaches, and lignin sulfonates dissolved in water are formed. Lignosulfonates or ligninsulfonic acids are used as auxiliary materials in a wide variety of areas, e.g. as dispersants in cement and gypsum mortar, or as flotation aids in fluorspar extraction, molding sand binders, or foundries. Chemically "unaltered" lignin suitable for scientific purposes can be obtained by extracting wood flour with organic solvents, which may be diluted with water. For example, so-called milled-wood lignin, which is extracted using acetone / water (9:4) after milling the wood under toluene, is distinguished from dioxane lignin, which uses dioxane / water (9:1) as the extraction agent. In another method, the lignin contained in the wood is extracted from the wood using ethanol / water mixtures, optionally with the addition of acids (e.g., oxalic acid), at temperatures between 150 and 200°C. For example, poplar and beech wood can be digested in the presence of acid at 160-200°C under a pressure of 15-20 bar within 1-2 hours, during which the hemicelluloses and the majority of the lignin dissolve. However, due to partial hydrolysis, the remaining cellulose is no longer suitable for the production of cellulosic products and is therefore enzymatically broken down into sugars, which are then fermented to produce ethanol. Another problem with this process is that the precipitation of lignin from the solvent mixture is only possible incompletely. EP 2 611 820 B1 describes a process for producing lignin from lignocellulosic material, in which the material is treated with a mixture of a C1-C4 alcohol, water, and NaOH or KOH at temperatures below 100°C, and the base is applied to the lignocellulosic material in specific amounts. However, in this process, only lignin and xylose were isolated from the reaction mixture. Comparative studies have also been conducted on digestion processes using ionic liquids, such as boiling, ultrasonic irradiation, or microwave irradiation. However, due to their comparatively high costs, these processes are not yet economically viable. WO 2005 / 017252A1 describes the separation of lignin from lignin-containing natural sources using ionic liquids, optionally in combination with water, organic solvents, and acids. This process is carried out at temperatures between 50 and 200°C. The cationic part of the ionic liquids used consists of substituted or unsubstituted heterocyclic cations such as imidazolium, triazolium, pyrazolium, pyridinium, pyrolidinium, piperidinium, as well as ammonium, phosphonium, or sulfonium ions. The anions used are alkyl or arylsulfonates, alkyl sulfates, carboxylates, phosphinates, or phosphates. DE 10 2010 048 614 A1 describes a process for the extraction of cellulose, hemicelluloses, and lignin, or lignin and tannin. In this process, a particle-processed wood material is treated with iminium salts or zwitterionic iminium salts to extract cellulose and hemicellulose. Subsequently, the cellulose or hemicelluloses are precipitated and separated from the iminium salt solution. This process has achieved lignin yields of up to 30%, although the isolated lignin was still heavily contaminated with hemicelluloses (hemicellulose content in lignin approximately 30%). DE 10 2015 006 926 A1 describes a similar process in which lignin, hemicellulose, tannin and resins are dissolved from the treated biomass using mixtures of alcohol solvents such as tetrahydrofurfural and an ionic liquid formed from dimethylformamide or N-methylpyrrolidone and sulfuric acid and separated from the remaining cellulose. A major problem in wood pulping processes is the water content of the wood, which must be removed from the wood before extraction with lignin-dissolving solvents. Today, this is usually done by drying, e.g. previously produced wood chips, which are treated in a furnace with heat. Since water has a very high heat capacity (about 4.19 kJ- kg'^K -1) very large amounts of energy are required for this, which is particularly disadvantageous in view of the recent sharp increase in energy costs. Drying at elevated temperatures also leads to an irreversible reduction in the water absorption capacity of the wood and a corresponding reduction in its swelling capacity, e.g. through pre-horning (see e.g. E. Roffael, P. Kraft, Eur. J. Wood Prod. 2012, 70, 393-395), which makes it more difficult to dissolve cellulose and lignin from the material. Although air drying can significantly reduce the amount of energy required for drying, in this case the wood must be stored for a long time, which requires corresponding storage capacity. Even with this type of drying, a reduction in the water absorption capacity, e.g. cornification of the wood, cannot be avoided. Against this background, there is a need for a more economical process for biomass and, in particular, wood pulping, in which more cellulose, hemicellulose and lignin can be obtained from the wood with the same amount of energy used. The present invention addresses this need. Description of the invention In the investigations underlying this invention, it was surprisingly found that a significant reduction in the water content in wood or other lignin-based cellulosic biomass can be achieved by treatment with an excess of water-miscible organic solvent. During this treatment, an equilibrium is established in the wood between the solvent used and water, so that, depending on the amount of solvent added, the water content in the wood can be reduced. Since the treatment requires little to no energy input (it is usually sufficient to just stir the mixture), and the majority of the solvent can be separated from the wood by filtration, the majority of the energy required for the treatment of the wood is used for the preparation of the water-miscible organic solvent. For this purpose, if the solvent is not added after each treatment of wood, but only After multiple treatments, less energy is required than for reducing the water content in the wood by drying. The treatment also has the advantage that, as a result of the swelling of the wood through the solvent treatment, the pulping time for dissolving the lignin, hemicellulose, and possibly tannin can be reduced, which also contributes to lower energy consumption and lower costs of the pulping process. Without relying on any particular theory, it is assumed that the swelling facilitates the subsequent penetration of the lignin extraction solvent into the wood and the dissolution of the lignin. Furthermore, the reduction in the water absorption capacity of the wood is suppressed by the fact that the water is not removed but replaced by the organic solvent. Accordingly, the present invention relates in a first aspect to a digestion process for biogenic lignocellulosic material for obtaining cellulose, hemicelluloses and lignin or lignin and tannin, in which a pasty or particulate biogenic material is subjected to the following steps: i) treating the biogenic lignocellulosic material with an excess of water-miscible organic solvent having a boiling point of < 110°C, preferably < 100°C, wherein the biogenic I ignocellulose-containing material is impregnated with the water-miscible organic solvent, ii) mechanically separating the water-miscible organic solvent from the biogenic I lignin-containing material, iii) treating the biogenic I lignin-containing material obtained in ii) with a lignin-dissolving digestion reagent which preferably contains an acidic ionic liquid dissolved in an ether, alcohol, ether alcohol, acetal, ketal or mixtures thereof, and separating the solution from the undissolved residue. An "acidic ionic liquid" in the context of the invention described here is an ionic liquid which, when added in an amount of 1 g per 100 ml of neutral water, produces an acidic pH. Acidic ionic liquids are, for example, the adduct of Dimethylformamide and sulfuric acid, and the ionic liquids specified in DE 10 2015 006 926 Al. Cellulose does not dissolve to any significant extent in such acidic ionic liquids. If the process according to the invention is designed as a process for obtaining cellulose, hemicelluloses, and lignin, the starting material used is a material that contains these components, e.g., wood chips or wood flour. If the process according to the invention is designed as a process for obtaining lignin and tannin, the starting material used is a material that has high proportions of lignin and tannin, e.g., tree bark. In step i) of the process, the solvent penetrates the intracellular space and preferably also the cellular space of the biogenic material. There, an equilibrium can be established between the existing water and the water-miscible organic solvent, whereby water is displaced from the intracellular and, if applicable, also from the cellular space of the biogenic material and dissolves in the organic solvent. The biogenic lignocellulosic material to which the process is applied is a plant-derived lignocellulosic material, preferably derived from hardwood, softwood, bamboo, hemp, plant residues such as corn stalks, cereal straw, rice straw, sugar cane, hay, or waste materials such as residues from biogas plants, residues from fermentation and digestion processes, or similar waste products. The hay can, in particular, originate from fast-growing grasses such as buffalo grass, elephant grass, or fast-growing plants such as Nacandia or Jacaranda. The biogenic lignocellulosic material is particularly preferably based on softwood or hardwood.Most preferably, the biogenic lignocellulose-containing material is derived from hardwood, as this generally has a higher density than softwood and therefore the swelling caused by the solvent treatment has a particularly beneficial effect on the extraction time. The biogenic lignocellulose-containing material is incorporated into the process as a paste-like material or in the form of particles. A suitable paste-like material is, for example, fermentation residues from biogas production. If a biogenic If lignocellulosic material in the form of particles is incorporated into the process, it is advantageous to use particles in the form of wood chips, wood shavings or wood flour which have a size of no more than 6 cm (obtainable, for example, via an appropriate sieve), in particular no more than 2 cm, more preferably no more than 1 cm and even more preferably no more than 0.5 cm. A particle size of no more than 0.5 mm and preferably no more than 1 mm can be specified as a lower limit, although this value is not due to impregnation reasons, but rather to the greater effort required to produce such small particles. Smaller particle sizes therefore do not impair the efficiency of the digestion process, but they can have an adverse effect on the economic viability of the process, and mechanical separation of the organic solvent in step ii) of the process can be made more difficult. The size, e.g."1 cm" here indicates the mesh size of a sieve used to remove larger particles. Such particles can be crushed using a suitable process and recycled back into the process. As an alternative to wood chips, wood shavings, or wood flour, groundwood with a grain size of 4.5 mm to 0.001 mm, such as groundwood for the production of very short-fiber pulp, can also be used. Since there is no comminution of wood particles, but rather the starting material (tree) is directly "ground," the inventive process still achieves high economic efficiency. The biogenic lignocellulosic material is treated by combining the material with the solvent. The mixture can be agitated, for example, using a stirrer to bring all of the lignocellulosic material into contact with the solvent. This treatment can be carried out in a suitable reactor. The treatment can be carried out at ambient temperature (20 to 28°C) or at elevated temperatures, e.g., in the range of 30 to 80°C or 35 to 50°C. Treatment at ambient temperature is preferred for energy reasons. It is also possible to promote the treatment by carrying it out at increased pressure or by first subjecting the biogenic lignocellulosic material to a vacuum and then adding the solvent under vacuum. The biogenic lignocellulose-containing material used in the process according to the invention preferably has a residual moisture content in the range of 3 to 65 wt.% and preferably 5 to 20 wt.%, in particular 10 wt.% + / - 3 wt.%. A residual moisture content of less than 3 wt.% can only be achieved through more complex drying processes and would also counteract the purpose of reducing the water content of the material through the treatment according to the invention. In addition, with materials with a water content in the range of 3% or below, there is a risk that the water absorption capacity of the material will be reduced, for example by "hornification," which makes it more difficult to dissolve cellulose and lignin from the material. Material with a residual moisture content of more than 65 wt.%, on the other hand, is very wet, and the cost-benefit ratio here is more on the side of drying, e.g., in air, where the residual moisture content of the wood can be reduced comparatively quickly to less than 65 wt.%.-%. The weight percentages refer to absolutely dry wood. The treatment period is not subject to any relevant restrictions and can, for example, be set in the range from 0.5 h to 48 h. In general, the period should be long enough to achieve equilibrium between the water contained in the biogenic lignocellulosic material and the solvent used for treatment. A treatment period of 2 h to 30 h is preferred, in particular from 12 h to 24 h, such as about 20 h or about 24 h. The time required to achieve equilibrium between the water contained in the biogenic lignocellulosic material and the solvent is usually shorter for smaller particle sizes than for larger particle sizes, since in such particles the diffusion path for the water out of the particle is shorter. The following treatment conditions can be given as examples: - A wood starting material with a particle size of 2cm + / - 1cm is treated in the solvent for 0.5h under vacuum of approx. 80 Torr at room temperature; - A wood raw material with a particle size of 2cm + / - 1cm is treated for 24h at 40°C under normal pressure in the solvent. The treatment temperature is also not subject to any significant restrictions; although higher treatment temperatures are possible, they are rather unfavorable due to cost considerations. The treatment temperature is preferably between approximately 0 and approximately 50°C, more preferably between 15°C and 35°C, and even more preferably between approximately 20°C and 28°C (ambient temperature), since in this case, no energy is required to heat or cool the solvent. The solvent used for treatment is, as mentioned above, a water-miscible organic solvent with a boiling point of < 110°C. Its miscibility with water ensures that an equilibrium can be established between the solvent and the water, in which the water content of the solvent not contained in the biogenic lignocellulosic material is approximately equal to the water content of the solvent contained therein. The efficiency of the process is enhanced by the fact that less energy is required for subsequent evaporation of the solvent than for evaporation of the water during further processing. This means that if the solvent has a boiling point above 100°C, its heat capacity should be significantly lower than the heat capacity of water. Suitable solvents for this purpose include C1-C4 alcohols, C1-C2 carboxylic acids, C3-C5 ketones or diketones, C2-C3 nitriles, acetaldehyde, mixtures of these solvents, or mixtures of one or more of the aforementioned solvents with dimethyl or diethyl acetals of formaldehyde or acetaldehyde. Particularly preferred C1-C4 alcohols are methanol, ethanol, n- or isopropanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, or allyl alcohol. Suitable C1-C2 carboxylic acids are formic or acetic acid. Suitable ketones and diketones are acetone, ethyl methyl ketone, 2,3-butanedione, or diethyl ketone. A preferred nitrile is acetonitrile. Of these solvents, dimethyl or diethyl acetals of formaldehyde or acetaldehyde form a reactive solvent that reacts with water to form the aldehyde and the corresponding alcohols. If the water content in the biogenic material is less than about 65%, the treated biogenic material can swell during the digestion process according to the invention, so that after the treatment less solvent can be separated from the material by mechanical processes than added In such a case, the solvent is preferably used in excess of the biogenic lignocellulose-containing material. The solvent is preferably included in the digestion process according to the invention in such a proportion that the weight ratio of water-miscible organic solvent to the biogenic lignocellulose-containing material is in the range from 2:1 to 10:1 and in particular 3:1 to 6:1. It is obvious to the person skilled in the art that a higher weight ratio allows more water to be removed from the biogenic lignocellulose-containing material, but more energy must be expended for processing the solvent, which reduces the efficiency of the process. This disadvantage can, however, be partially compensated for by repeated use of the solvent without intermediate processing. As mentioned above, the treatment with the water-miscible organic solvent in the process according to the invention can be carried out at atmospheric pressure (approximately 1000 hPa), or under positive or negative pressure. If the process is carried out under positive pressure, this should preferably be set in a range from 0.5 to 5 bar (above atmospheric pressure) and in particular 1 to 2 bar. If the treatment is carried out under negative pressure, this should preferably be set to 10 to 200 mbar and in particular 20 to 100 mbar. The biogenic lignocellulosic material is expediently exposed to the stated negative pressure and the solvent is then added under vacuum. For cost reasons, however, treatment of the biogenic lignocellulosic material at atmospheric pressure is usually preferred, since in this case no additional energy needs to be expended to provide the positive or negative pressure. After treating the biogenic lignocellulosic material with solvent, it is separated as far as possible from the biogenic lignocellulosic material by mechanical separation. Generally, all mechanical processes for separating solid and liquid components are suitable for the separation, with centrifugation and filtration or sieving (or a combination of these processes) being particularly suitable. It will be apparent to those skilled in the art that, as a result of swelling processes during treatment with the water-miscible organic solvent, the solvent is partially absorbed into the treated material, so that normally a smaller amount of solvent can be removed by mechanical separation than was added for the treatment. By treating the biogenic lignocellulose-containing material with the solvent, a product is obtained after separation thereof which has a lower water content than the starting material used in the process. Preferably, the biogenic lignocellulose-containing material after step ii) has a water content of less than 10 wt. %, particularly preferably less than 5 wt. % and even more preferably less than 2 wt. % (the water content is determined according to the invention by means of the xylene method or Karl Fischer titration). Alternatively or additionally, it is preferred if the water content of the biogenic lignocellulose-containing material after steps i) and ii) is in the range from 10 to 50% and in particular 15 to 30 wt. % of the water content of the biogenic lignocellulose-containing material before step i). The aqueous organic solvent obtained from step ii) of the process according to the invention can be treated with any suitable purification method to purify the solvent. Preferably, the water content of the solvent is reduced by the purification, e.g., by fractional distillation. It is not always necessary to recycle the water-containing organic solvent after treatment, e.g., if the treated biogenic material has only a low water content or if a relatively large excess of the water-containing organic solvent was used for the treatment. In this case, the water content of the water-containing organic solvent is only slightly higher than that of corresponding fresh solvent. In a preferred embodiment of the process according to the invention, solvent is therefore only recycle if it has a water content of at least 30%. In another preferred embodiment, solvent is therefore only recycle if it has a water content of at least 20%. In step iii), the biogenic lignocellulosic material is treated with a digestion reagent, which is a chemical substance that dissolves lignin and preferably also hemicelluloses. This treatment is carried out analogously to procedures described in the prior art (such as DE 10 2015 006 926 A1), i.e., by adding a digestion reagent consisting of an organic solvent and an acidic ionic liquid to the biogenic lignocellulosic material, and the material is treated under suitable temperature and pressure conditions to extract and dissolve lignin and optionally hemicellulose from the biogenic lignocellulosic material. For example, a temperature in the range of 40°C to 200°C, in particular in the range of 100°C to 200°C, preferably in the range of 125°C to 165°C and particularly preferably in the range of 150°C + / - 10°C can be set for the treatment. The treatment time can be set between 0.5 h and 24 h and is preferably (by setting a suitable treatment temperature) kept in the range of 1 h to 12 h, more preferably 1 h to 8 h, even more preferably 1 h to 6 h and even more preferably 1 h to 5 h. Depending on the temperature used for the treatment, a comparatively short treatment time, e.g. in the range of 0.5 h to 4 h or 0.5 h to 2 h, may be advantageous, e.g. in order to only partially delignify the lignocellulosic material. It is obvious to the skilled person that higher treatment temperatures lead to an increased formation of degradation products, but can dissolve more lignin in a shorter time than when the reaction is conducted at lower temperatures. The skilled person also recognizes that at lower reaction temperatures, a longer reaction time is required to dissolve a comparable amount of lignin from the biogenic lignocellulose-containing material. The ratio of material to be extracted and digestion reagent (based on their mass) used for the treatment can vary within a wide range, e.g. between 1:1.5 and 1:60, whereby it is preferred if the ratio is in the range of 1:5 to 1:10. For an organic solvent used in the digestion reagent, it is preferred if it has a boiling point of 110°C or more. This ensures a sufficient difference between the boiling points of the solvent used in step i) of the process and the solvent in the digestion reagent, so that the solvent from the treatment in i) can be distilled off from the digestion mixture during heating of the lignocellulosic material obtained from step ii), together with any residual water still present. Particularly suitable organic solvents for the digestion reagent in this context are alcohol, ether, ether alcohol, acetal, or ketal co-solvents. Suitable alcohol co-solvents are, for example, 2-methoxyethanol, 2-methoxy-l-propanol, 3-methoxy-2-propanol, glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, glycerol, tetrahydrofurfuryl alcohol, 4-hydroxyethyl-l,3-dioxolane, 5-hydroxy-l,3- dioxane, 4-hydroxyethyl-2,2-dimethyl-1,3-dioxolane, or benzyl alcohol. Suitable ether co-solvents are 4-(te / t-butoxymethyl)-l,3-dioxolane, 2-(te / t-butoxymethyl)tetrahydrofuran, 5-(te / t-buoxy)-l,3-dioxane, glycol di(te / t-butyl)ether, l,3-propanediol-di(te / t-butyl)ether, l,4-butanediol di(tert-butyl)ether, l-tert-(butoxy)-2-methoxyethane or l-te / t-(butoxy)-2-methoxypropane. Other suitable cosolvents that are not based on alcohols or ethers include l,4-dioxa-spiro[4,5]-decane (cyclohexanone ethylene acetal), l,5-dioxa-spiro[5,5]-undecane, butyrolactone, or valerolactone. These cosolvents can be used alone or as mixtures of several of the solvents together with the ionic liquid. As mentioned, the digestion reagent contains, in addition to the solvent, an ionic liquid that does not dissolve cellulose (i.e., it is an acidic ionic liquid). The proportion of this ionic liquid is preferably less than 15 wt.%, based on the total weight of ionic liquid and solvent in the digestion reagent. A proportion of 1 to 10 wt.% is particularly preferred, and in particular 2 to 8 wt.%. The ionic liquid can, in principle, be any ionic liquid that does not dissolve cellulose to a relevant extent. However, it is preferred to use an iminium salt as the ionic liquid, and particularly preferably a zwitterionic iminium salt. Such iminium salts are, for example, the iminium salts specified in DE 10 2015 006 926 A1, which, in addition to an imine function, also have a sulfone group (-SCh'), in particular in

[0012] of this application. Very particularly preferred ionic liquids are the addition salt of methylformamide and sulfuric acid, the addition salt of dimethylformamide and sulfuric acid, and the addition salt of oxalic acid bis(dimethylamide) and sulfuric acid. In a further embodiment, the ionic liquid is an ionic liquid based on imidazolium cations. As the water content is already significantly reduced in step i) of the process according to the invention, ionic liquids that are sensitive to hydrolysis can be used without any problems in the digestion of the wood in step iii) (this effect is described, for example, in “Final report on the BMBF joint project - A new process for the production of hemicellulose from biogenic material using novel ionic liquids", 2016, available at https: / / edocs.tib.eu / files / e01fbl6 / 872500748.pdf). Examples of such ionic liquids are adducts of dimethylformamide and dialkyl sulfates, from which the alcohol (e.g. methanol) and protonated dimethylformamide are formed in contact with water, or the already mentioned adduct of dimethylformamide and sulfuric acid. During treatment with the digestion reagent in step iii), it is advantageous for the digestion mixture to be agitated, which can be achieved by techniques known to those skilled in the art. Suitable techniques include, for example, stirring, agitation, or pressure wave treatment. Further processing of the solution obtained in step iii) (which primarily contains lignin, but also hemicelluloses and possibly tannin) and the undissolved residue (which primarily contains cellulose) is conveniently carried out using known and established methods. In a first step, the undissolved residue can be separated from the dissolved lignin by mechanical separation, for example, by filtering the mixture through a suitable filter or centrifuging it. This produces a filter cake and a filtrate. To isolate the lignin from the resulting filtrate, the filtrate can be neutralized in a next step (i.e., the pH of the filtrate is adjusted to a range of 5.5 to 8.5). The organic solvent of the digestion reagent can then be removed from the neutralized filtrate, e.g., by distillation, which can be assisted by applying a vacuum if necessary. In this case, the distillation also removes residual traces of the solvent used in step i) and water that was not removed from the biogenic lignin-containing material in steps i) and ii). The residue remaining after distillation contains primarily lignin and hemicelluloses, as well as possibly tannin. The lignin can then be precipitated by adding a solvent, particularly water or a water-alcohol mixture, and separated from the dissolved residue, e.g., hemicellulose. This is conveniently done by filtration or centrifugation. It is also possible to use the digestion reagent multiple times in the described process without intermediately isolating the lignin and other dissolved components of the biogenic, cellulose-containing material. For this purpose, the filtrate obtained after an initial treatment according to step iii) and filtering off the cellulose is used directly as a digestion reagent for a further batch of biogenic, cellulose-containing material to be processed. This can be repeated multiple times, but this leads to a decrease in the purity of the cellulose obtained by the process, as the delignifying effect of the digestion reagent is reduced. From the repeatedly used filtrate obtained in this way, the total lignin can be precipitated according to the water addition described above. The undissolved residue obtained in step iii) (primarily cellulose) can be further purified, for example, by washing with a suitable solvent, e.g., water or alcohol, especially ethanol. This yields relatively clean and intact cellulose that can be used for common applications.

Claims

Claims 1. A digestion process for biogenic lignocellulosic material for obtaining cellulose, hemicelluloses and lignin or lignin and tannin, characterized in that a pasty or particulate biogenic lignocellulosic material is subjected to the following steps: i) treating the biogenic lignocellulosic material with an excess of water-miscible organic solvent having a boiling point of < 110°C, preferably < 100°C, wherein the biogenic lignocellulosic material is impregnated with the water-miscible organic solvent, ii) mechanically separating the water-miscible organic solvent from the biogenic lignocellulosic material, iii) treating the biogenic lignocellulosic material obtained in ii) with a lignin-dissolving digestion reagent and separating the solution from the undissolved residue.

2. The digestion process according to claim 1, characterized in that the biogenic lignocellulose-containing material included in step i) of the process has a residual moisture content in the range of 3 to 65 wt.% and preferably 5 to 20 wt.%.

3. The digestion process according to claim 1 or 2, characterized in that the biogenic lignocellulose-containing material included in step i) of the process has a particle size in the range of 0.5 mm to 6 cm, and preferably 1 mm to 2 cm.

4. The pulping process according to at least one of claims 1 to 3, characterized in that the biogenic lignocellulose-containing material included in step i) of the process is based on coniferous or hardwood, preferably hardwood.

5. The digestion process according to at least one of the preceding claims, wherein the treatment of the biogenic lignocellulose-containing material in step i) is carried out for a period in the range of 0.5 to 48 h and preferably 2 to 30 h, and at a temperature in the range of 0 to 50°C, preferably 15 to 35°C.

6. Digestion process according to at least one of the preceding claims, characterized in that the water-miscible organic solvent is selected from C1-C4 alcohols, C1-C2 carboxylic acids, C3-C5 ketones or diketones, C2-C3 nitriles, or a mixture of the aforementioned solvents or a mixture of the aforementioned solvents with and dimethyl or diethyl acetals of formaldehyde or acetaldehyde, wherein methanol is preferably used as solvent.

7. Digestion process according to at least one of the preceding claims, characterized in that the water-miscible organic solvent is used in step i) in a weight ratio of 2: 1 to 10: 1 and preferably 3: 1 to 6: 1 to the biogenic lignocellulose-containing material.

8. Digestion process according to at least one of the preceding claims, characterized in that the treatment with the water-miscible organic solvent is carried out at overpressure or underpressure, preferably at an overpressure in the range of 1 to 5 bar or a underpressure of 20 to 200 mbar and preferably 30 to 100 mbar.

9. Digestion process according to at least one of the preceding claims, characterized in that the organic solvent in ii) is separated from the biogenic lignocellulose-containing material by centrifugation and / or sieving.

10. Digestion process according to at least one of the preceding claims, characterized in that the biogenic 10% cellulose-containing material after step ii) has a residual water content of less than 10% by weight, preferably less than 5% by weight and more preferably less than 2% by weight.

11. Digestion process according to at least one of the preceding claims, characterized in that the digestion reagent in step iii) is an acidic ionic liquid and optionally additionally a co-solvent selected from alcohol, ether, ether alcohol, acetal, ketal or mixture thereof.

12. Digestion process according to at least one of the preceding claims, characterized in that the digestion reagent in step iii) contains a proportion of an ionic liquid or a mixture of several ionic liquids of 1 to 10 wt.% and preferably 2 to 8 wt.%, based on the total amount of digestion reagent.

13. The digestion process according to claim 11 or 12, characterized in that an iminium salt, a zwitterionic iminium salt or an imidazolium salt is used as the ionic liquid.

14. Digestion process according to at least one of the preceding claims, characterized in that the biogenic 11 nitrocellulose-containing material is treated with the digestion reagent in step iii) at a temperature in the range of 20 to 160°C and preferably 60 to 150°C and / or for a period of 1 to 10 h and preferably 2 to 5 h.

15. The digestion process according to at least one of the preceding claims, characterized in that the residue not dissolved in step iii) is separated from the dissolved lignin by filtration and / or centrifugation.

16. Digestion process according to claim 15, characterized in that the dissolved lignin is precipitated from the distillation residue after neutralizing the solution, distilling off organic solvents, and adding a solvent, preferably water.

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