WO2018114905A1

WO2018114905A1 - Two-stage digestion method for chemical fractionation of lignocellulose

Info

Publication number: WO2018114905A1
Application number: PCT/EP2017/083475
Authority: WO
Inventors: Moritz Leschinsky; Michael Buchmann
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2016-12-21
Filing date: 2017-12-19
Publication date: 2018-06-28
Also published as: DE102016225827A1; DE102016225827B4

Abstract

The invention relates to a two-stage digestion method for chemical fractionation of lignocellulose. In a first stage, the lignocellulose is pre-treated with water vapor or water at temperatures above 100 °C and increased pressures. In a second stage, an extraction of the pre-treated lignocellulose occurs by means of an extraction solution, wherein lignin is dissolved from the lignocellulose. A characterizing feature of the method according to the invention is that the temperature is not reduced below 80 °C between the two stages.

Description

Two-stage digestion process for the chemical fractionation of

lignocellulose

The present invention relates to a two-stage digestion process for the chemical fractionation of lignocellulose. Here, in a first stage, the lignocellulose is pretreated with steam or water at temperatures above 100 ° C and elevated pressures (i.e., at pressures greater than 1 bar absolute). In a second stage, an extraction of the pretreated lignocellulose with an extraction solution, whereby lignin is dissolved from the lignocellulose. Characteristic feature of the method according to the invention is that the temperature is not reduced below 80 ° C between the two stages.

In order to dissolve lignocellulose according to the present state of the organosolv process, ie to separate lignin and hemicellulose as defined as possible from the cellulose fiber fraction, temperatures of 150 ° C.-200 ° C., preferably about 170-190 ° C., are usually required. At the same time, the successful extraction of the abovementioned ΟΠΘ concentrations of 50% w / w + - 30% w / w of an organic solvent, usually an aliphatic alcohol used in water. In the first place here are methanol or ethanol used. This applies equally to a batchwise and a continuously operating method.

The usual today water-based alkaline or acid batch or continuously operated digestion processes (sulfate or sulfite process and their modifications) require comparable temperatures and residence times, but come by the absence of relatively low-boiling organic solvents at the same temperature with an approximately half as high design pressure as Organosolv method. There are numerous cost-optimized and risk-minimized technical solutions for all tasks for these procedures.

In the case of biomass digestion, this results in considerable competitive disadvantages for the conventional organosolv process with regard to investment and operating costs (large apparatus wall thicknesses with comparatively expensive construction materials) and a multitude of technical risks which must be absorbed by expensive special solutions. The technical risks relate in particular to shaft feedthroughs of biomass feed and discharge systems in the digester, circulating pumps, heat exchangers and other apparatus. Furthermore, with widespread direct heating of the boiler circuits by means of saturated steam or superheated steam, an approximately twice as high network pressure is required as usual.

Also, the apparatus, which is directly downstream of the cooker and still contains solvents, which, irrespective of the mode of operation of the cooker i. d. R. work continuously, such as. As MC pumps, pressure diffusers, washing presses, etc. are affected by these problems.

Pre-treatment of biomass plays a crucial role in the concept of an integrated lignocellulosic biorefinery for the supply of celluloses, hemicelluloses and lignin and their further processing into pulps,

Chemicals or biofuels. The concept of lignocellulosic biorefinery includes as an integral part a pretreatment of the lignocellulose used. This is by using organic Solvents or in aqueous, acidic or alkaline medium, the lignocellulose with the aim of improved accessibility of the raw material for fermentative or chemical processing open-minded. Basically, it is a question of loosening the fiber composite and achieving a loosening of the structure of the lignocellulose. In the chemical digestion process, in addition, a fractionation of the main constituents is generally also desired, whereby either the lignin or the carbohydrates are dissolved.

In the following, with the purpose of classifying the organosolv digestion, a brief overview of the most important and most promising industrial processes is given. In principle, a distinction can be made between structure-preserving and structure-degrading processes. In structure-preserving processes, the basic structure of the main constituents remains completely or largely preserved by pure component separation. In structure-degrading processes, the basic structure of the main components is not preserved and is degraded by thermochemical or biochemical reactions. In practice, however, there are no completely structure-preserving methods, so that only a grading of "almost completely structure-preserving methods" up to "completely structure-changing methods" can be established.

The Organosolv method is clearly classified in the structure-preserving methods. Other methods in which the structure is largely retained are autohydrolysis / hydrothermolysis, alkaline digestion, sulfite digestion, digestion with other alcohols, organic acids and ionic liquids. In the case of enzymatic saccharification and saccharification with mineral acids, the structure of the cellulose is largely degraded and glucose is obtained, the yields and properties of the products being very different with respect to their further applicability. In the following, the various methods are briefly described.

Autohydrolysis / Hydrothermolysis

There are a variety of processes that operate on the principle of auto-hydrolysis. The basic principle is the treatment of lignocellulose at elevated temperature and elevated pressure in aqueous medium Depolymerization of lignin, Memiceiiuiosen and cellulose comes. As a result, only the degradation products that are soluble in water dissolve. The process of autohydrolysis or hydrothermolysis is simple and robust and the use of chemicals is not absolutely necessary. However, a clean fractionation of the biomass components is only possible with this method approach at a higher cost. Thus, the material use of lignin due to strong impurities is currently difficult to implement. As a rule, lignin, which is very heavily contaminated with carbohydrates, proteins and inorganic components, can not be suitable for material-chemical use or only after extensive purification. According to the principle of autohydrolysis, for example, the processes of Aquasolv hydrothermolysis, prehydrolysis in the two-stage prehydrolysis-kraft pulp process for the production of chemical pulp or the steam explosion process. Alkaline digestion procedures

There are also various processes for the alkaline digestion of lignocellulose, above all the power digestion (sulphate pulping) and the soda digestion. Products are pulp consisting of cellulose and hemicelluloses and the so-called black liquor. The process is established worldwide as part of the kraft process for pulp production. That in the

Black liquor contained lignin can be discharged to certain proportions before the recovery of the digestion chemicals and fed to a material use. The discharge takes place under high technical effort and using considerable amounts of chemicals (for example lignoboost process). The majority of lignin (about 80%) must be in the

Recovery of digestion chemicals are used thermally. However, due to the size and spread of kraft pulp mills, the process is potentially a very important source of lignin recovery. Alkaline pulping is an established and efficient pulp recovery process, despite the mostly sulfur-based and expensive chemical recovery process. The so-called kraft lignin Contains 1-2% organically bound sulfur and higher levels of inorganic components (about 0.5-3%) compared to Organosolv lignin. In addition, it has other properties (eg strong odor due to the sulfur components, other thermoplastic behavior). sulfite pulping

There is also a wide range of process variants in sulfite pulping, with the sulfonation of lignin with SO _{2 being} a central component of the process. Subsequently, a water-soluble, strongly sulfur-containing lignin derivative is obtained. Products are the cellulosic and hemicellulosic pulp and waste liquor, which can either be used energetically as part of the recovery of the pulping chemicals or as material. Large quantities of lignosulfonates are used for energy purposes, mainly to provide the process energy. The main application for the lignosulfonates, some of which are still to be purified, is the

Additization of cement. This is currently the largest industrial application of lignin. In addition, there are quite a few niche applications. Other constituents of the waste liquor are xylose, furfural and acetic acid, which can be obtained as by-products. Disadvantages of the sulfite process are a complex chemical recovery and associated high

Sulfur losses.

Digestion with alcohols and organic acids

For the digestion with alcohols, there are a number of processes in which different alcohols are used and which take place at different temperatures, pressures and pH values. The digestion processes with organic solvents and acids are summarized under the term 0 rga nsoso I v-pro vie rs.

In the digestion process with alcohols are used in most cases methanol, ethanol or propanol as a solvent, often catalysts such as sulfuric acid or sodium hydroxide are added. The

Lignocellulose is treated with a solvent, water and a catalyst in a reactor at 165 - 200 ° C, a pressure of 15 - 35 bar and a pH in the acidic range of 2 - 4 or in the alkaline range of 13 - 14 for 2 - 4 hours open-minded. Three process examples are the EtOH water digestion, the O rga noce Ii process and the

Monoethanolamine method (MEA method). Advantages of the ethanol-water digestion compared to the conventional digestion methods such as force or sulfite are the almost complete and simple recovery of the Digestion chemicals by the destination of the alcohol used, a selective fractionation, the recovery of very pure and reactive lignin and, above all, lower corrosion problems compared with the digestion with organic acids. MEA processes and organocell processes, in contrast to ethanol-water digestion, require complex chemical recovery. Difficulties in the process management form in most digestion processes with organic solvents, the high pressures that make special demands on the digestion apparatus, as well as compared to the previously mentioned digestion significantly higher requirements for explosion protection.

There are also a large number of processes in the field of organic acid digestion processes. These include, for example, the Milox process, the Formacell process, the Acetosolv process and the Acetocell process. In this digestion process lignocellulose is digested with the addition of water, formic acid or acetic acid as a solvent and optionally catalysts (HCl or H ₂ 0 ₂ ). The raw materials are digested at 110-190 ° C, a pressure of 1-13 bar and at a pH of 1-3 for 4-6 h. Products are on the one hand a fraction of cellulose and residual lignin and on the other hand the waste liquor, which consists mainly of hemicelluloses, lignin, by-products and degradation products of lignin and carbohydrates and the corresponding solvents. Advantages of these methods are that both the production of chemical by-products and, in principle, a pressureless digestion is possible. Disadvantages are the corrosion-related high material requirements and the corresponding explosion protection requirements.

Multi-stage digestion with alcohols and organic acids

In autohydrolysis, acetyl groups are split off from the hemicelluloses by an autocatalytic reaction. The concentration of acetic acid in the liquid phase increases with increasing reaction time, which leads to a decrease in the pH. The pH reaches a minimum of about 3-4 after a certain reaction time, which is not undershot. The acetic acid released from the biomass in turn catalyzes the cleavage of the β- (1-4) glycosidic bonds of the hemicelluloses, leading to a reduction in the molecular weight of the hemicelluloses and ultimately to formation of water-soluble oligosaccharides and monosaccharides. In the further course of the autohydrolysis, there are also dehydration reactions of the monosaccharides, which triggers the formation of condensation and degradation products. Products of the autohydrolysis of lignocellulose are a solid fraction with cellulose fibers and lignin, a dissolved fraction with hemicelluloses and soluble extractives, lignin residues and acetic acid, and water vapor-volatile products such as furfural.

The autohydrolysis is used as the first stage of the two-stage prehydrolysis power process for the production of chemical pulps. Pre-hydrolysis is used to decompose the hemicelluloses contained in the wood in order to achieve the required purity levels for the cellulose content in the pulp. In the prehydrolysis-force process, the prehydrolysis can be carried out either at high liquor ratio with mass ratios (water / wood) of e.g. 3/1 to 6/1 be carried out as so-called water pre-hydrolysis or at low liquor ratios of 0.8 / 1 to 2/1 as so-called steam prehydrolysis. In water pre-hydrolysis, a free, aqueous solution is formed in the reactor, which contains a large part of the degraded hemicelluloses and can be utilized as prehydrolysate. During the steam prehydrolysis, so little free water is contained in the reactor that no or only little free prehydrolysate is obtained in the reactor. The prehydrolysate remains in this case largely in the free pore volume of lignocellulose.

In order to achieve high degrees of purity of the cellulose also with a pre-hydrolysis / Kraft hydrolysis process, EP0672207B1 describes a process in which the digestion reactor is filled with hot, strongly alkaline black liquor and possibly white liquor directly after the steam prehydrolysis, so that the Hydrolysis products are neutralized and the resulting neutralization liquor is then at least partially displaced from the reactor with fresh white liquor (Wizani, W., Krotschek, A., Schuster, J., Lackner, K. 1994. Process for the production of viscose pulp, Voest Alpine

Industrieanlagenbau GmbH, Lenzing AG). This method makes it possible to eliminate the disadvantages otherwise caused by carrying out a steam prehydrolysis on the lignin removal during the subsequent force digestion. Sufficiently pure chemical pulps could previously only be produced by means of water prehydrolysis, but with large quantities incurred in prehydrolysates whose tntsorgung or recovery is associated with high costs. On the other hand, no by-products can be obtained from the hydrolyzed hemicelluloses with the process described in EP0672207B1, since these are completely diversified in alkaline power digestion or neutralization with caustic

Hydroxycarboxylic acids are degraded.

In connection with the pulping with organic solvents, also two-stage process concepts were described in which in the first stage, an autohydrolysis was combined with a subsequent solvent extraction as a second stage.

It was found that following autohydrolysis of poplar wood, the lignin could be largely removed by extraction with dioxane-water mixtures or dilute sodium hydroxide solution under atmospheric conditions. It was found that during autohydrolysis a relatively narrow parameter window, characterized by the temperature and residence time of the autohydrolysis, must be observed in order to remove a maximum of lignin during the subsequent solvent extraction. At a liquor ratio of 1: 1, temperatures of 220 ° C and residence times of 8 minutes in the autohydrolysis, more than 80% of the lignin could be removed in the subsequent dioxane-water extraction (Lora, J.H., Wyman,

MN. 1978. DELINACTION OF HARDWOODS BY AUTHYDROLYSIS AND EXTRACTION. Tappi, 61 (6), 47-50).

Based on this finding, various publications on two-step process concepts for organosolv digestion followed. It has been published that a water prehydrolysis of pine wood at 180 ° C or

200 ° C could improve the delignification in a subsequent butanol-water digestion by 2% and 3% respectively (April, G. C, Bharoocha, R., Sheng, J., Hansen, S. 1982. Prehydrolysis achieves higher organosolv delignication Tappi, 65 (2)). Likewise, a process concept was proposed in which steam autohydrolysis is followed by digestion with ethylene glycol

(Thring, RW, Chornet, E., Overend, RP 1993. FRACTIONATION OF WOODMEAL BY PREHYDROLYSIS AND THERMAL ORGANOSOLV PROCESS STRATEGY, RECOVERY OF CONSTITUENTS, AND SOLVENT FRACTIONATION OF LIGNINS SO PRODUCED Canadian Journal of Chemical Engineering, 71 (1), 116 - 123).

In connection with the ethanol-water digestion, however, Peter and Höglinger (Peter, W., Höglinger, 1986, Production of Synthetic Pulp According to the Organosolv Dissolution Process, Lenzinger Berichte (61), 2626-2641) was unable to improve the delignification the introduction of a steam prehydrolysis can be found. Instead, after a steam treatment of 30 minutes at 195 ° C and subsequent ethanol-water digestion at 195 ° C a significant deterioration of delignification occurred, which was expressed in a higher kappa and an increased splinter content. This degradation occurred even though the parameter window of autohydrolysis was chosen in the parameter space described by Lora and Wayman (1978) as being optimally described. Due to this publication, it was not expected that a two-stage ethanol-water digestion with steam prehydrolysis could be successful. Numerous further studies on two-stage organosolv process concepts are concerned with prehydrolysis for the separation and recovery of hemicelluloses in the first stage. The aim of these concepts is to obtain the hemicelluloses by their upstream extraction as a separate stream and thus to prevent their degradation in the subsequent Organosolv process. All concepts are the same that after the prehydrolysis, which is usually carried out at high liquor ratio, the reactor cooled and relaxed, the prehydrolysate separated from the wood residue and this is usually washed with water before the second step of Organosolv digestion follows. In this regard, the prehydrolysis of pine and hardwood at liquor ratios of 10: 1 at temperatures of only 130 ° C with the addition of SO 2 as an acid catalyst and subsequent ethanol-water digestion (Aravamuthan, R., Chen, W., Zargarian, K., April, G. 1989. Chemicals from wood: Prehydrolysis / organosolv methods, Biomass, 20 (3), 263-276). Ruiz et al. (Ruiz, H.A., Ruzene, D.S., Silva, D.P., da Silva, F.F.M., Vicente, A.

A., Teixeira, HA 2011. Development and Characterization of Environmentally's Friendly Process Sequence (Autohydrolysis and Organosolv) for Wheat Straav Delignification. Applied Biochemistry and Biotechnology, 164 (5), 629-641) teach water pre-hydrolysis of wheat straw Liquor ratio 10: 1 and 180 ^~ 1 with subsequent alkaline ethanol-water digestion with the addition of 0.1% sodium hydroxide solution.

Huijgen et al. (Huijgen, WJJ, Smit, AT, de Wild, PJ, Uil, H.D. 2012 Fractionation of wheat straw by prehydrolysis, organosolv delignification and enzymatic hydrolysis for production of sugars and lignin, Bioresource Technology, 114, 389-398) in that with a sulfuric acid-catalyzed water prehydrolysis of wheat straw at 175 ° C., liquor ratio 7.5: 1 and 30 minutes residence time the subsequent delignification in the ethanol-water digestion is worsened and this must be compensated by higher temperatures in the second process step.

In contrast, Brosse et al. (Brosse, N., El Hage, R., Sannigrahi, P., Ragauskas, A., 2010. DILUTE SULPHURIC ACID AND ETHANOL ORGANOSOLV PRETREATMENT OF Miscanthus x Giganteus Cellulose Chemistry and Technology 44 (1-3), 71-78; Brosse, N., Sannigrahi, P. Ragauskas, A. 2009. Pretreatment of Miscanthus x giganteus Using the Ethanl Organosolv

Process for Ethanol Production. Ind. Eng. Chem. Res., 48 (18), 8328-8334) conditions for a sulfuric acid-catalyzed prehydrolysis, which led to improved delignification: The atmospheric boiling of Miscanthus flour with dilute sulfuric acid at reflux at liquor ratios of 10: 1, the Delignification during subsequent ethanol-water digestion at 170-180 ° C slightly improve.

Caparros et al. (Caparros, S., Ariza, J., Carrote, G., Lopez, F., Diaz, MJ 2007. Optimization of Paulownia fortune L. autohydrolysis organosolv pulping as a source of xylooligomers and cellulose pulp. Industrial & Engineering Chemistry Research , 46 (2), 623-631) suggested a water pre-hydrolysis organosolvent

Process in which a water prehydrolysis at 190 ° C with an alkaline ethanol-water digestion at 180 ° C with the addition of sodium carbonate and anthraquinone.

Romani et al. (Romani, A., Garrote, G., Lopez, F., Parajo, J.C. 2011. Eucalyptus globulus wood fractionation by autohydrolysis and organosolv delignification.

Bioresource Technology, 102 (10), 5896-5904) studied water pre-hydrolysis of Eucalyptus globulus at 8: 1 liquor ratio and subsequent autocatalytic Organosolv digestion at 175 and 200 ° C. The combination of mild water pre-hydrolysis at temperatures between 130 and 150 ° C with the addition of 2-naphthol and subsequent ethanol-water digestion at 170 ° C was reported by El Hage et al. (El Hage, R., Chrusciel, L, Desharanais, L, Brosse, N., 2010. Effect of autohydrolysis of Miscanthus x giganteus on lignin structure and organosolv delignification., Bioresource Technology, 101 (23), 9321-9329). The addition of 2-naphthol in prehydrolysis partially compensated for the otherwise observed decrease in delignification in organosolv digestion.

As a departure from the process concept of water pre-hydrolysis to remove the hemicelluloses, a steam explosion treatment at about 200 ° C (1.5 MPa) for 4.5 minutes with sudden relaxation, washing and subsequent alkaline ethanol-water digestion with addition of 0.1% caustic soda at 180 ° C (Hongzhang, C, Liying, L., 2007. Unpolluted fractionation of wheat straw by steam explosion and ethanol extraction, Bioresource Technology 98 (3), 666-676).

The combination of water prehydrolysis of rice straw with subsequent atmospheric ethanol-water extraction at 30 ° C was reported by Moniz et al. (Moniz, P., Lino, J., Duarte, L.C., Roseiro, LB, Boeriu, CG, Peerira, H., Carvalheiro, F. 2015. Fractionation of Hemicelluloses and Lignin from Rice Straw by Combining Autohydrolysis and Optimized Mild Organosolv Delignification, Bioresources, 10 (2), 2626-2641). It was possible to extract up to 40% of the lignin contained in the raw material after the water pre-hydrolysis by the ethanolic extraction.

Overall, however, no published process concept has been identified in which steam prehydrolysis succeeds, i. without significant deterioration of delignification, combined with a subsequent particularly mild ethanol-water digestion.

Proceeding from this, it is therefore an object of the present invention to provide a process for the extraction of lignocellulose, which avoids the disadvantages mentioned above, d. H. in which a significant deterioration of the delignification can be avoided.

This method is achieved with the features of claim 1. Respective dependent claims are thereby advantageous developments.

The invention thus relates to a two-stage digestion process for the chemical fractionation of lignocellulose in which a) the lignocellulose is treated in a first stage with steam or water at temperatures above 100 ° C and a pressure of more than 1 bar (absolute), b) subsequently in a second stage the treated in the first stage lignocellulose at temperatures above 80 ° C and a pressure of more than 1 bar (absolute) with an extraction solution containing water and at least one lignin solvent organic solvent with extraction of lignin from the lignocellulose and dissolving the Lignin is treated in the extraction solution and then the lignocellulose is separated from the extraction solution, wherein the temperature is not reduced below 80 ° C between the two stages.

Both essential stages of the process according to the invention are thus carried out at overpressure (i.e., at a pressure of more than 1 bar absolute).

Surprisingly, the method described by Peter et al. The statement made on the digestion in the vapor phase can not be confirmed on a flat-rate basis, even though it is of the opinion that Peter et al. investigated time-temperature window, described by the so-called P-factor, has been shown to be valid. Instead, a time-temperature window could be found, which allows a digestion in the vapor phase meaningful.

The described invention enables a pulping or continuous pulping process using organic solvents, especially aliphatic alcohols, especially ethanol and / or methanol, at system pressures comparable to those of aqueous pulping processes. The space-time yield of the process is not seriously affected compared to the current state of the art. Just- Thus, lactones, in particular (jamma- valerolactone and / or gamma-butyrolactone, ketones, in particular acetone or mixtures of the abovementioned solvents for the purposes of the present invention are suitable.

The digestion in the vapor phase results in a homogeneous temperature distribution which is easier to ensure in the lignocellulose bed and at the same time better heat transfer than in the liquid phase. This results in shorter heating times and a more homogeneous cooking result as well as savings in operating costs. The lignocellulose is already so open to subsequent solvent extraction that, despite comparable low yields, it proceeds at a similar speed to the organosolv process of the prior art at significantly higher temperatures.

In contrast to the state of the art, the new method thus makes it possible to use already commercially available technical solutions for all areas of the digestion apparatus with relatively little technical effort and risk. Even the hitherto unthinkable conversion of existing pulp plants to the new process is now possible.

Overall, the mentioned disadvantages of Organosolv digestion compared to the currently common digestion methods are largely neutralized in terms of higher investment costs and greater technical risks. The new digestion process enables high yields of pulp, pure lignin and hemicellulose-based products for the fiber industry and for chemical purposes, which can be represented relatively easily from the obtained streams. This results in a greatly improved competitiveness compared to the established digestion processes of the pulp industry and, moreover, an ideal use in biorefineries.

According to a preferred embodiment, the pressure between stages a) and b) of the process according to the invention is not reduced below 1 bar (absolute). In particular, stage Ό immediately follows, ie without interruption, directly at stage a).

The treatment of the lignocellulose with water vapor (vapor state when added overheated, saturated or wet), or water in the first stage a) can at temperatures of 110 to 250 ° C, preferably 120 to 220 ° C, in particular from 160 to 190 ° C,

over a period of 20 to 240 minutes, preferably from 20 to 120 minutes, particularly preferably from 30 to 90 minutes and / or

at pressures of 1.4 to 40 bar (absolute), preferably 2 to 23.2 bar (absolute), more preferably 6.2 to 11.6 bar (absolute).

be performed.

Alternatively or additionally, it is possible that the treatment of the lignocellulose with the extraction solution in the second stage b)

at temperatures of the extraction solution of 80 to 240 ° C, preferably from 100 to 200 ° C, in particular from 140 to 160 ° C,

over a period of 1 to 480 minutes, preferably from 30 to 240 minutes, more preferably from 60 to 180 minutes and / or

at pressures of 2 to 20 bar (absolute), preferably 6 to 18 bar (absolute), more preferably 10 to 14 bar (absolute) is performed.

Between the individual stages, it is preferred if the temperature is not reduced below 80 ° C., preferably not below 140 ° C., and the pressure is not below 1 bar (absolute), preferably not below 6 bar (absolute), more preferably not below 10 relaxed (absolutely).

The respective preferred temperatures thus presuppose that correspondingly high temperatures or pressures already prevail in the first stage.

A preferred embodiment provides that at least one lignin-dissolving organic solvent is selected from the group consisting of aliphatic alcohols, in particular ethanol, methanol or mixtures thereof. Further, it is advantageous that the extraction solution contains water and the at least one lignin-dissolving organic solvent in a mass fraction of 80% to 20%, preferably from 70% to 30%, particularly preferably from 60% to 40%.

Optionally, the extraction solution may additionally contain catalysts, e.g. affect the pH of the extraction solution. Possible catalysts are, for example, inorganic acids, in particular sulfuric acid. This allows the pH of the extraction solution to be adjusted to e.g. 1 to 6, preferably 1.5 to 5, in particular 2 to 4 are set. Alternatively, the extraction solution as catalyst may also include inorganic bases, especially sodium hydroxide, whereby the pH of the extraction solution can be adjusted to 5-14, preferably 7-14, especially 8-13. It is particularly preferred if the lignocellulose is fiberized before and / or during and / or after the first stage a) and / or the second stage b) by mechanical action and / or by means of a pressure gradient.

For example, it can be provided that, before the preparation in stage a), the lignocellulose is mechanically shredded in particular, or during one or both stages a) (or b)), the lignocellulose is modified by varying the pressure, ie. H. is shredded by a pressure gradient.

A particularly economical process results when the extracted lignin is recovered from the separated extraction solution and thereby the extraction solution is regenerated. The extraction solution may optionally further work-up steps

(eg, distillation), especially after carrying out these further purification steps, the extraction solution can be used again in the process in step b).

Further preferably, the separated lignocellulose is washed with a washing solution containing water and at least one lignin-dissolving organic

Solvent, for which purpose, preferably as described above, regenerated extraction solution is used. Alternatively or additionally, it may be that the separated lignocellulose is washed with water, preferably the washing step with water followed by the washing step with a washing solution according to the preceding claim.

In the aforementioned embodiment, it is advantageous if the water is treated after the washing step, wherein in particular solvent contained in the washing water is recovered.

In addition, it is advantageous if, during the washing process with washing solution and / or water, the lignocellulose is treated in countercurrent and / or crossflow with the washing solution and / or the water.

In particular, the lignocellulose is selected from the group consisting of woody plant parts, in particular wood chips from hardwood or softwoods and / or parts of annual plants such as miscanthus or straw.

The process can be carried out continuously or batchwise.

The treatment of the lignocellulose with water vapor or water and the treatment with extraction solution can be carried out in the same apparatus or in separate apparatuses connected in series.

Both in batchwise, as well as in the continuous process, both process steps a) and b) can be carried out in the same apparatus. In the case of a continuous process, the apparatus then has several zones which are successively passed through by the lignocellulose to be treated.

Particularly preferably, the treatment of the lignocellulose with washing solution and / or water is carried out in separate apparatus, i. H. Final treatment steps such as washing are carried out in separate apparatuses separated from stages a) and b).

The application of hot steam or water to the lignocellulose, on the one hand, causes an inerting of the treatment system and, on the other hand, a displacement of air from the lignocellulose to be treated. In particular, when carrying out both stages of the process in a closed The apparatus defines step a), the boiling point of the hot water vapor or water being the later operating pressure of the digestion apparatus used for the process.

The second stage b) can be referred to as reactive extraction. In this case, in particular lignin, but also dissolved sugars are extracted from the lignocellulose. The extract formed in stage b) can be displaced, for example, with a fresh aqueous solvent mixture or a solvent-containing wash filtrate which is obtained in a subsequent washing step of the extracted lignocellulose (see detailed description below). This allows almost complete extract extraction, post-extraction and cooling of the lignocellulose before the optionally occurring subsequent treatment steps, in particular washing steps.

The defibration of the lignocellulose can take place in particular by means of a device suitable for this purpose (batchwise method) or by means of a pressure gradient, in particular via blow valves (particularly preferably in the case of continuous process control).

The present invention will be explained in more detail with reference to the following embodiments, without limiting the invention thereto.

Each 70 kg (atro) beech chips were digested on a pilot scale in a 400 liter reactor (working volume) under various conditions with and without steam prehydrolysis by boiling the woodchips with ethanol-water mixtures. The digestion was in all cases at a starting concentration of 50% (w / w) ethanol in the cooking liquor, a liquor ratio of 3.2 to 1 (mass wood atro to mass ethanol-water mixture) using 1.1% sulfuric acid based on the wood dry matter. In the tests without steam prehydrolysis, the wood chips were steamed with steam at a maximum of 100 ° C. under atmospheric conditions; in the tests with steam prehydrolysis, the steam treatment for a certain P-factor (calculated in Table 1) was then additionally carried out at higher pressure and higher temperature according to Sixta et al 1992 (Sixta H., Schild G., Baldinger T .: Water Pre-hydrolysis of Beech Wood (1992): 9,527-539), 2006 (Sixta, H. (2006) Multistage force pulping. In: HancmooK οτ ulp. Ed. Sixta, H. Wiley-VCH. Weinheim. Pp. 325-365)).

Table 1: Experimental conditions and important parameters of organosolv digestion experiments without (comparative example) and with (examples 1 and 2) steam prehydrolysis

Digestion No. Comparative Example Example 1 Example 2

Maximum temperature 100 ° C 173 ° C 176 ° C

Steam treatment (° C)

Maximum pressure water1 12.2 12.0 steam treatment (bar

absolutely)

Fleet ratio pre 1.1 1.0

hydrolysis

Minimum temperature 121 143 between prehydrolysis

and digestion (° C)

P-factor prehydrolysis 0 2116 965

Fleet ratio to 3.2 3.2 3.2

Enough

Temperature up170 140 155 final solution before adding cooker (° C)

Temperature digestion 170 150 155

Pressure digestion (bar 21 13 13

absolutely)

Duration of digestion (Mi83 30 134 minutes at Tmax) H-factor (calculated 1000 123 435 with EA 125.6 kJ / mol)

After completion of the damping or after reaching the respective P-factor, the ethanol-water mixture already preheated to the desired digestion temperature was pumped into the digester. By circulating the cooking liquor via a heat exchanger connected to the digestion vessel and through the woodchip bed, the actual organosolv digestion took place. This enriches the digestion solution, which is also referred to as cooking liquor, with lignin and hemicelluloses. From the cooking liquor circulation samples were taken regularly over the time course of the digestion and analyzed with regard to the lignin and hemicellulose content. The experimental setup is shown in simplified form in FIG. 1 and in this case comprises a digester 1 with a working volume of 400 l. The solution contained therein is circulated and kept at temperature by means of a heat exchanger 2. In the digester wood chips 3, 4 steam and an ethanol-water mixture 5 are abandoned. Samples of the resulting cooking liquor 6 can be taken at a suitable location.

The determination of the lignin content in the cooking liquor samples was carried out by addition of water, centrifugation of the resulting precipitate and its gravimetric determination. The xylan content was determined from the supernatant remaining after lignin precipitation and centrifugation by chromatographic determination of the xylose content after analytical total hydrolysis.

FIG. 2 shows the course of the lignin concentration in the cooking liquor over the digestion time. It becomes clear that the prehydrolysis has a significant influence on the subsequent delignification. Depending on the selected experimental conditions, the prehydrolysis can have a positive (Example 2) or negative (Example 1) effect on the delignification with ethanol-water compared to the comparative example without prehydrolysis. In any case, according to Table 1, in the tests with steam prehydrolysis, the system pressure was lowered when digesting to a maximum of 12 bar over 20 bar at the reference digestion and the wood could be delignified in the subsequent organosolv digestion. In the right choice of Vorhydrolysis and Aufschlußbeamgungen and thus the particularly preferred process variant could also be significantly increased Deligninfizierungsgeschwindigkeit compared to the comparative example. In addition to the influence on the delignification, it was possible to observe a positive influence on the solution of xylan from wood for the particularly preferred process variant according to the invention (Example 2). Due to the suitable combination of prehydrolysis conditions and digestion conditions, higher concentrations of monomeric and oligomeric xylose could be released in the cooking liquor than in the comparative example (FIG. 3).

Claims

claims

Two-stage digestion process for the chemical fractionation of lignocellulose in the

a) the lignocellulose is treated in a first stage with steam or water at temperatures above 100 ° C and a pressure of more than 1 bar (absolute),

b) then in a second stage, the treated in the first stage lignocellulose at temperatures above 80 ° C and a pressure of more than 1 bar (absolute) with an extraction solution containing water and at least one lignin-dissolving organic solvent with extraction of lignin from the Treated lignocellulose and dissolving the lignin in the extraction solution and then the lignocellulose is separated from the extraction solution, between the two stages, the temperature is not reduced below 80 ° C.

A method according to claim 1, characterized in that between stages a) and b) of the inventive method is not under 1 bar (absolute) is relaxed.

Method according to one of the preceding claims, characterized in that the treatment of the lignocellulose with water vapor or water in the first stage a)

at temperatures of 110 to 250 ° C, preferably 120 to 220 ° C, in particular from 160 to 190 ° C,

at pressures of 1.4 to 40 bar (absolute), preferably 2.0 to 23.2 bar (absolute), more preferably 6.2 to 11.6 bar (absolute) is carried out.

Method according to one of the preceding claims, characterized in that the treatment of the lignocellulose with the extraction solution in the second stage b)

at pressures of 2 to 20 bar (absolute), preferably 6 to 18 bar, particularly preferably 10 to 14 bar (absolute)

is carried out.

Method according to one of the preceding claims, characterized in that between the two stages both the temperature is not below 80 ° C, preferably not reduced below 140 ° C and the pressure not less than 1 bar (absolute), preferably not less than 6 bar (absolute ), more preferably not below 10 bar (absolute).

Method according to one of the preceding claims, characterized in that at least one lignin-dissolving organic solvent is selected from the group consisting of aliphatic alcohols, in particular ethanol, methanol or mixtures thereof.

Method according to one of the preceding claims, characterized in that the extraction solution contains water and the at least one lignin-dissolving organic solvent in a mass fraction of 80% to 20%, preferably from 70% to 30%, particularly preferably from 60% to 40%.

8. The method according to any one of the preceding claims, characterized in that the extraction solution in addition catalysts, in particular catalysts selected from the group consisting of inorganic acids, in particular sulfuric acid, so that the pH of the extraction solution is preferably from 1 to 6, more preferably from 1.5 to 5, in particular from 2 to 4, or

inorganic bases, in particular sodium hydroxide, such that the pH of the extraction solution is preferably from 5-14, more preferably from 7-14, in particular from 8-13,

includes.

Method according to one of the preceding claims, characterized in that the lignocellulose is fiberized before and / or during and / or after the first stage a) and / or the second stage b) by mechanical action and / or by means of a pressure gradient.

Method according to one of the preceding claims, characterized in that the extracted lignin is recovered from the separated extraction solution and thereby the extraction solution is regenerated.

Method according to one of the preceding claims, characterized in that the separated lignocellulose is washed with a washing solution containing water and at least one lignin-dissolving organic solvent, for which purpose preferably a regenerated according to the preceding claim extraction solution is used.

Method according to one of the preceding claims, characterized in that the separated lignocellulose is washed with water, wherein preferably the washing step with water is followed by the washing step with a washing solution according to the preceding claim.

Method according to the preceding claim, characterized in that the water is treated after the washing step, wherein in particular solvent contained in the washing water is recovered.

14. The method according to any one of claims 9 to 12, characterized in that the washing process with washing solution and / or water, the lignocellulose is treated in countercurrent and / or cross-flow with the washing solution and / or the water.

15. The method according to any one of the preceding claims, characterized in that the lignocellulose is selected from the group consisting of woody plant parts, in particular wood chips from deciduous or coniferous wood and / or parts of

Annual plants like miscanthus or straw.

16. The method according to any one of the preceding claims, characterized in that the method is performed continuously or batchwise.

17. The method according to any one of the preceding claims, characterized in that the treatment of the lignocellulose with water vapor and the treatment with extraction solution in the same apparatus or in separate, sequentially switched equipment is performed.

18. The method according to any one of the preceding claims, characterized in that the treatment of the lignocellulose with washing solution and / or water is carried out in separate apparatus.