EP2417293A1

EP2417293A1 - Method for obtaining cellulose from biomass comprising lignocellulose

Info

Publication number: EP2417293A1
Application number: EP10707821A
Authority: EP
Inventors: Rudolf Patt; Andreas Kreipl
Original assignee: Zylum Beteiligungs GmbH and Co Patente II KG
Current assignee: Zylum Beteiligungs GmbH and Co Patente II KG
Priority date: 2009-04-09
Filing date: 2010-02-25
Publication date: 2012-02-15
Also published as: US9011640B2; NZ595745A; CN102449232A; CA2758038C; RU2534067C2; AU2010234084B8; AU2010234084A1; CL2011002521A1; UA107076C2; ZA201107860B; US20120132379A1; WO2010115488A1; MX2011010552A; CO6450643A2; CA2758038A1; CN102449232B; BRPI1006671A2; AU2010234084B2; RU2011143465A; DE102009017051A1

Abstract

The invention relates to a method for obtaining cellulose by separating lignin from a biomass comprising lignocellulose in the form of plants or plant parts, wherein the biomass comprising lignocellulose is solubilized in a boiler in an alkaline medium comprising alkanol amine, and dissolved lignin is separated from the resulting raw cellulose. Said method is characterized in that the biomass comprising lignocellulose is not from a wood source, and is solubilized at a temperature of less than approximately 170°C in a solubilizing agent based on alkanol amine and water, wherein the weight ratio of alkanol amine to water is set to 80:20 to 20:80, and raw cellulose thus produced is separated from the waste lye using a typical method. Said method is particularly advantageous for obtaining cellulose from annual plants, particularly wheat straw. The method is advantageously improved in that the solubilization takes place in the presence of a catalyst, particularly of anthrachinon. An advantageous bleaching process may be performed subsequently. Said method is characterized by great economic efficiency, particularly due to the high reclamation rates of the alkanol amine used, and leads to lower environmental impact in wastewater, and to reduced disposal costs. The design of the method leads to a greater yield of cellulose and largely prevents degradation of alkanol amine, particularly monoethanol amine (MEA).

Description

Process for obtaining pulp from Liqnocellulose-containing biomass

The invention relates to a process for the recovery of pulp by separating lignin from a lignocellulosic biomass, in particular from straw and other fibers supplying non-woody plants, wherein the lignocellulosic biomass digested in an alkaline medium containing alkanolamine in a digester and dissolved lignin and low molecular weight carbohydrates are separated from the obtained raw pulp.

During the last 30 years, the worldwide production of pulp from biomass other than wood has been steadily increasing. The share of non-wood based fibrous materials is nearly 12% worldwide. Wheat is cultivated on all continents, so that its straw could be extensively used for the production of pulp. According to United Nations FAO statistics (from 2007), world wheat production exceeds 600 million tons. 15 million tons of it were produced in Iran alone. About half of the resulting wheat straw is used in farms. The other half is either burned or plowed into the ground. Based on this data, it can be concluded that the amount of wheat straw available for pulp production could be used to produce 100 million tonnes of pulp per year. In fact, only 4.5 million wheat straw pulp is produced. The digestion with caustic soda is a predominant process for the production of pulp from annual plants. This shows serious disadvantages. Strongly alkaline Aufschiussiaugeπ solve carbohydrates to a considerable extent, which affects the yield of pulp. Most annual plants have a high content of silicates, which are dissolved in the strongly alkaline digestion solutions to a considerable extent, which leads to serious problems in the evaporation plants and the recovery boilers. These are the main reasons why Handling of leaching of the soda process and the recovery of the digestion chemicals continue to be problematic.

Theoretically, organic solvents alone or in admixture with water can overcome the problems of chemical recovery associated with conventional annual plant pulp production. In particular, low boiling alcohols or organic acids can be easily recovered by distillation and recycled to a subsequent cooking process. Dissolved organic material can either be incinerated for energy production or fed to various applications, such as alcohol or yeast production, or as a chemical feedstock. However, no commercial pulping process uses organic solvents.

Monoethanolamine (MEA) has been known for a long time as a very selective delignifying agent and for isolating holocellulose and for determining its content in wood (see Harlow, WM, Wise, LE, Am J. Botany 25 (1938): 217-219 ). Thereafter, there have been many studies on the use of MEA for the production of pulp. Mainly this research concerns the use of wood as raw material. MEA was used in alkaline pulping to aid in the delignification process. Extensive studies have been conducted by Wallis on the use of MEA as the sole delignifying agent in cooking hardwood (Eucalyptus grandis) and softwood (Pinus elliotti) (see, Wallis, Cellulose Chemistry and Technology, 10 (3) (1976), 345- 355). The assumed reactions that occur during MEA delignification of wood are described in the literature (supra).

The outstanding feature of pulp extraction with MEA is the exceptionally good protection of hemicelluloses, which leads to an unusually high yield of pulp. On the other hand, the maximum degree of delignification obtained with MEA as the sole delignifying agent is limited, especially in the case of softwood. Therefore, harsh cooking conditions, especially high temperatures, must be used to obtain sufficient delignification in the production of a pulp suitable for bleaching. In this regard, it must be remembered that MEA decomposes at a boiling point of about 171 °. Therefore, the temperature of about 171 ⁰ C should be below the Biomass digestion to avoid excessive losses of MEA. Furthermore, it should be noted that MEA can be consumed in reactions with lignin and, consequently, the MEA losses are high, when the raw material used for pulp production has a high content of lignin, which is difficult to degrade due to its structure.

Based on these facts, it can be concluded that MEA should not be used for pulpwood pulp production. MEA can generally be used for pulp production from hardwood. It seems doubtful that this is a practically valuable alternative as the temperatures to be applied must be high. Even small losses of MEA make this process uncompetitive to conventional Kraft pulping processes with their highly effective inorganic chemical recovery system.

The situation is completely different when annual plants, such as wheat straw, are used as raw material for the production of pulp after the soda production process. Due to the problem associated with the high silicate content in alkaline digestions, most straw pulp production plants do not have a chemical recovery system. All sodium hydroxide used in digestion must be supplemented. In addition, wheat straw has a low lignin content, can be easily digested under mild conditions, and requires a relatively small amount of chemicals to dissolve lignin. The major advantage of digesting annual plants with MEA is the direct recovery by distillation of MEA. After the distillation of MEA, the residual organic material can be used either as a chemical feedstock or as a nitrogenous organic fertilizer which, unlike mineral nitrogen fertilizer, acts long term as nitrogen is gradually released by microbial degradation of the carrier material.

To complete the above-described relevant prior art, the following patent literature should also be discussed: US Pat. No. 4,597,830 deals with the digestion of lignocellulose in an aqueous solution containing a catalyst, such as anthraquinone, wherein Favoring the digestion of lignoceliulose an Aikohoi / amine mixture is used. US Pat. No. 4,178,861 likewise describes the digestion of lignocellulose-containing materials and proposes the use of, inter alia, anhydrous monoethanolamine with simultaneous addition of catalysts, such as anthraquinone. The EP-BO 149 753 is concerned with the digestion of wood under heat and pressure by impregnation and boiling of chips or shavings in an aqueous digestion solution, the a short-chain alkanolamine, such as monoethanolamine, in addition to ammonium hydroxide as a catalyst. DE-A-26 40 027 relates to a further development of the classical soda digestion process, wherein, inter alia, anthraquinone is used.

The above statements on the prior art show that there are many tasks of improvement. This also applies to digestion processes in which alkanolamines, in particular monoethanolamine, are used. Thus, the loss of spent alkanolamine in the described digestion processes is very high and the achievable delignification is limited. It would be desirable to process cereal straw, in particular wheat straw, which is available in large quantities economically with alkanolamine into pulp, thereby excluding or at least reducing degradation of the pulp and decomposition of alkanolamine during the digestion. It would also be desirable to largely recover the alkanolamine from the process and recycle it to the process. In a further development of such a desirable technical proposal, an environmentally friendly bleaching of the pulp should be additionally connected so that the overall process of pulp production can be adapted to the technological and economic needs of a modern pulp production process. The present invention is therefore based on the object to meet the requirements listed above.

The solution of the object addressed here, of which the present invention proceeds, turns out in a development of the above-described prior art in that the lignocellulosic biomass is not due to wood and at a temperature of less than about 170 ⁰ C in is decomposed to an alkanolamine-based and water-based disintegrating agent in which the weight ratio of alkanolamine to water is adjusted to 80:20 to 20:80, and resulting raw pulp is separated from the waste liquor by conventional methods.

The essence of the invention is therefore that not any lignocellulosic biomass can be used for the designated method, but it is limited in particular to straw and other fibers supplying non-woody plants. In addition, it has surprisingly been found that alkanolamine in combination with water while maintaining a certain weight ratio of alkanolamine to water as a digestion agent is particularly suitable, and in addition the limitation of the maximum temperature must be considered in the process control. Through the use of the digestion agent alkanola- Min / water are surprising advantages, which will be discussed in detail later. First, the invention-relevant features and preferred embodiments of the invention are shown in more detail:

The method according to the invention is expressly directed to lignin and other accompanying substances, including hemicelluloses (polyoses), being separated as far as possible from the pulp. As has been shown above, the term lignocellulose-containing biomass is subject to a relevant restriction in that the lignocellulose-containing biomass should not be derived from wood, since the desired separation of lignin under advantageous conditions is thus not possible to any appreciable extent. Therefore come within the scope of the invention, in particular plants and plant parts of annual plants, in particular straw of cereals such as wheat, barley, oats, rye, corn and rice, and dried grasses, reeds, sugar cane bagasse and bamboo in question. Among the above-mentioned annual plants, wheat straw is particularly preferable. These annual plants usually have a comparatively high silicate content, which may be significant for the success of the invention, without being construed as limiting. In principle, it is possible to use such biomasses, which are comparable in their chemical and morphological composition with the materials derived from annual plants. It should be noted here that the processing of wood to pulp is solved in the prior art, wherein the sulfate process is particularly economical.

In general, the biomass before it is fed to the process according to the invention, sufficiently comminuted, for example by shredding and in individual cases by further crushing. It may also be expedient to dry the biomass before the beginning of the process, where too extensive drying is not meaningful, since the amount of water which brings the biomass into the process according to the invention and that which is contained in the digestion system, the above-mentioned conditions Ratio of alkanolamine to water.

In principle, it is possible to pre-treat the biomass, before it is fed to the process according to the invention, by known processes of the prior art in order, for example, to achieve a preliminary softening of the fiber composite. So this could be done by the starting material of a known steam or ammonia treatment is subjected to. However, it has been shown that such measures usually offer no advantages.

With respect to the term alkanolamine, the invention is not subject to any relevant restrictions. It is preferred that the alkanolamine used is a short-chain alkanolamine, in particular an alkanolamine having 1 to 8 carbon atoms, in particular 1 to 4 carbon atoms. Among these alkanolamines, monoethanolamine, monopropanolamine, monobutanolamine and / or diglycolamine, in particular monoethanolamine, are to be regarded as preferred. The digestion agent monoethanolamine (MEA) / water has several advantages. When digested MEA protects the cellulose from degradation and also preserves the hemicelluoses. At the same time it is delignifying. In the digestion of ügnocellulose-containing biomass or in the extraction of lignin, it may be advantageous to additionally use a further solvent for lignin, in particular with swelling action for the cellulose and hemicellulose.

The basic conditions to be observed for the alkanolamine to water ratio are 80:20 to 20:80. It is preferred if the ratio of alkanolamine to water is adjusted to 70:30 to 30:70, in particular to 60:40 to 40:60. It is very particularly preferred if the ratio of alkanolamine to water is 53 to 57 to 57 to 53. The amount of water involved, as already stated, refers not only to the water content of the mixture alkanol / water, which represents the digestion agent in the digester or used autoclave, but also to the proportion of water, by more or less moist Biomass is registered in the digestion system. So you could specify as a preferred rule that a biomass is set to high water content expediently by drying to a water content of about 10 to 30%, in particular about 15 to 25%. Further drainage would require more energy and would not be beneficial.

For the invention, it is very important that the temperature of about 170 ⁰ C is not exceeded in the process for obtaining pulp from the biomass within the digester or autoclave, in which the mentioned digestion agent of alkanolamine and water is. It has been found by the inventors that exceeding this temperature would lead to a degradation and loss of alkanolamine used, in particular monoethanolamine. On the other hand, higher temperatures could lead to undesirable pulping. Therefore, it is particularly advantageous to increase the temperature during Final set to less than about 165 ° C, in particular less than 15O ⁰ C. The preferred lowest temperature of the digestion is about 12O ⁰ C, in particular about 14O ⁰ C indicate. The temperature range of 140 to 16O ⁰ C is considered to be particularly preferred, since this is the above-formulated object of the invention is achieved particularly advantageous.

When carrying out the process according to the invention, as a rule, an alkaline medium is produced by the chemicals introduced. Accordingly, the pH is above 7, especially at more than 10 and also at about 12. This is evident from the following examples.

In principle, it is possible to repeat the process described above to obtain further delignification and a cleaner pulp product. Here additionally known measures of the prior art can be used.

After the digestion stage carried out according to the invention, the cellulose raw material (cellulose / hemicellulose) is obtained in a customary manner. Thus, the strongly dark brown to black colored Abyaugensubstanzen of the pulp fibers can be separated in a skilled artisan manner, for example by the usual methods for solid / liquid separation, in particular by filtration, pressing or by centrifuging.

The digestion of the lignocellulose-containing biomass is preferably carried out within a period of 15 minutes to 4 hours, in particular from 1 to 3 hours, calculated from the end of the heating. Particularly preferred is a period of 2 to 3 hours. To optimize the process according to the invention, it is expedient to advantageously adjust the liquor ratio of lignocellulose-containing biomass (dry substance) and digestion mixture alkanolamine / water, in particular to about 8: 1 to 2: 1, the range from about 5: 1 to 3: 1 is particularly preferred.

Finally, the digestion of the lignocellulosic biomass or the extraction of lignin in the presence of suitable catalysts is accelerated. These are, in particular, catalytically active quinones, in particular in the form of naphthoquinone, anthraquinone, anthrone, phenanthrenequinone. Anthraquinone has been found to be particularly advantageous, but also alkyl-substituted derivatives thereof, such as 2-methyl-anthraquinone, 2-ethyl-anthraquinone, 2,6-dimethyl-anthraquinone, 2,7-dimethyl-anthraquinone and the like. On- Final reactions are promoted in the presence of the catalyst and side reactions are strongly suppressed. In addition, advantageously low kappa numbers are obtained.

The process according to the invention can be carried out both continuously and batchwise. In a batch mode, e.g. the comminuted lignocellulose-containing biomass with the water still contained therein, in particular in an autoclave, with the digestion agent alkanol / water and optionally and preferably with one of the designated catalysts. In this case, the described mandatory features of the method according to the invention are observed. The continuous digestion is preferably carried out by allowing the lignocellulose-containing biomass charged in a reactor to flow through the optionally preheated digestion agent or, in countercurrent, to the lignocellulose-containing biomass to be extracted or digested. Here is the advantage compared to the batch operation, ie the stationary operation, that due to the removal of the degradation products with the digestion center! Side reactions are largely excluded. In addition, with the same digestion effect, a lower liquor ratio of digestion agent to lignocellulose-containing biomass and also at a lower temperature can be used. In another preferred embodiment, the digestion is multi-stage, i. in at least two successive digestions or extractions with the respective mixture alkanolamine / water performed.

The process according to the invention can be advantageously configured in that the liginin-containing liquid phase which has been obtained after separation of the raw pulp or after separation of the delignified and / or bleached pulp, in particular by centrifuging, pressing or filtering and washing, and in addition Lignin and carbohydrates further biomass extractives, and optionally contains the mentioned catalyst, treated as follows: The waste liquor is evaporated in a thin film evaporator, film evaporator or tube evaporator, wherein alkanolamine and water are separated. The distillation residue is fed to a further utilization for energy production, as a chemical raw material or as an N-deposit fertilizer, the latter utilization can also be carried out with additives. In order to obtain a pulp with higher purity and also with a low lignin content, it is preferred that the raw pulp be bleached after removal of the waste liquor and optionally additional washing. It is appropriate to make the bleaching so that this is carried out as part of an alkanolamine / oxygen stage (with alkanolamine as alkali source) for further delignification and then the bleached pulp of adhering liquid portions in which alkanolamine is still contained, separated, in particular pressed and filtered to obtain thereon an alkanolamine-enriched liquid phase, which is fed as filtrate back to the digester, optionally with intervening measures, such as the washing of the raw pulp , In order to further enrich the liquid phase of alkanolamine, evaporation can be carried out with low thermal stress, as already mentioned above, which is carried out in particular in a thin film evaporator, falling film evaporator or tubular evaporator. It is particularly preferred that the filtrate obtained after the measure of bleaching by, for example, pressing off recovered pulp, which also contains, inter alia, alkanolamine, in particular MEA, is used as a washing solution for washing the pulp separated from the spent liquor of the digester. In principle, it may be expedient to subject the pulp obtained after bleaching with the alkanolamine / oxygen stage to further bleaching in customary ECF and TCF sequences, especially under the action of oxygen / and hydrogen peroxide, hydrogen peroxide in the presence of NaOH, O ₃ , CiO ₂ or formamidinesulfinic acid (FAS).

The above-described inventive approach after seizure of the raw pulp or the pure pulp will be described in more detail below:

It has thus been found that the pulp (cellulose / hemicellulose mixture) obtained according to the invention or obtained after delignification and / or bleaching does not become valuable products in all desirable secondary reactions, in particular because of the adhering alkanolamine, such as in particular for the pyrolytic production of wood gas for the production of fuel , suitable is. It is advisable to treat the raw pulp or cellulose to separate the still adhering alkanolamine a) with a non-aqueous solvent which dissolves the alkanolamine and to separate the alkanolamine-containing nonaqueous solvent and / or b) the raw pulp / pulp with a to treat the solvent which does not dissolve the alkanolamine, it being possible to carry out the treatment both before and after the separation of the solution of lignin, and to separate the alkanolamine phase from the resulting two-phase mixture. In measure a), the separated alkanolamine-containing solvent mixture is separated by distillation in order to recycle the alkanolamine into the process. It is preferred in this case for the residual alkanolamine to be separated off by the formation of azeotrope by addition of the alkanolamine-dissolving nonaqueous solvent towards the end of the distillation. As a non-aqueous solvent is preferably ethanol, Methanol, DMF, toluene and / or acetone or an alkanolamine solvent used. Preferably, the solvent-moist pulp obtained according to measure a) is reacted directly in a pyrolysis process to form a gas mixture suitable for the production of fuel.

In the described measure b), the procedure is preferably such that the solvent which does not dissolve the alkanolamine is an alkane, in particular petroleum ether, pentane, hexane, alkane, diesel and / or biodiesel, or a solvent which does not dissolve the alkanolamine. Preferably, the biphasic mixture obtained after measure b) (after removal of the crude pulp) is separated and the resulting alkanolamine fraction is then separated by distillation.

By means of the above-described measures, the alkanolamine is largely isolated in the sense of the invention, in order to then expediently recycle it to the beginning of the process. In addition, remaining residues of lignin are removed or processes with quantified ligin are added together with hemicelluloses (polyoses). In principle, expert measures can still be included between the extraction of the raw pulp and the pulp.

The preferred measures according to which the lignin is separated from the various waste liquors are to be shown more specifically below: Thus, water and the alkanolamine used are separated off by distillation, preferably by vacuum distillation. Other separation processes that lead to the desired concentration of lignin extract (in the limit to dry matter), are suitable. Separation of the lignin also succeeds by adding a non-solvent to the solution of lignin in alkanolamine. The lignin precipitates in the form of solid particles and can be separated from the alkanolamine by a suitable solid / liquid separation process, such as filtration, centrifugation, thin-layer evaporation or membrane. The separation of the lignin can be carried out, for example, by introducing carbon dioxide into the lignin / alkanolamine extract, optionally concentrated with water or, better, with the washing after the alkanolamine extraction. By concentrating by means of a thin film evaporation or other suitable distillation means, much of the alkanolamine is recovered in pure form and can be recycled to the process. The remainder of the alkanolamine is distilled after the water has been distilled off from the precipitating liquid after separation of the lignin, likewise in vacuo. The precipitation of lignin is thus achieved by introducing carbon dioxide and centrifuging. The addition compound alkanola- forming with the carbon dioxide min * Carbon dioxide can be completely decomposed thermally or by injecting steam back into alkanolamine and carbon dioxide. The residue consists of a degraded, reactive lignin. This can be supplied as a chemical raw material diverse applications, such as the production of thermosets of polyurethanes or binders. Accordingly, falls through the above-described measures a) and b), in particular in its advantageous embodiments, a lignin-containing, water or solvent-rich fraction, which can be used multiple times, the lignin is concentrated and a strong lignin containing and alkanolamine-rich fraction is obtained. From the alkanolamine-rich and low-water fraction, only a small amount of water needs to be distilled off, in order then to be able to recover the largest amount of alkanolamine, for example by thin-film evaporation.

The advantages achieved with the present invention are obvious. All the compounds introduced into the reaction mechanisms are either largely recovered, such as the alkanolamine contained in the digestion agent, or are put to useful uses after economic work-up. This applies in particular to the lignin and the carbohydrates dissolved in the digestion. The inventively obtained pulp shows a surprisingly high purity and exceptionally favorable reactivity. It has a favorable kappa number of less than 20, sometimes less than 15. The pulp obtained can be used with advantage for the production of paper and chemical pulp as well as for energy (bioethanol).

In view of the fact that the pulping agent used is a mixture of alkanolamine and water with a high water content, the consumption of alkanolamine is greatly reduced. Since digestion with a decomposition agent alkanolamine / water in an amount ratio of about 50:50 takes place advantageously, in particular with addition of catalyst, considerable amounts of alkanolamine, in particular monoethanolamine, can be saved, which leads to a significant increase in profitability. The alkanolamine has the advantage of recovery in a simple vacuum distillation. The invention allows the digestion or extraction at a favorable liquor ratio (about 8: 1 to 2: 1), especially in continuous operation. This has a positive effect on the steam consumption during digestion in comparison to classical digestion processes.

The inventive method can be integrated with minor modifications in existing systems, with only investment costs incurred for an additional distillation unit. In Neuaniagen the time-consuming chemical recovery is replaced by a simpler and cost-effective distillation. According to the invention, the lignocellulosic containing biomass to be processed into a pulp with particularly favorable reactivity. This can be expertly converted into sugars, for example, and fermented to bioethanol. The alkanolamine obtained after the separation of the lignin has further value and can be recycled to the process according to the invention. Finally, it is possible to separate the raw pulp (also according to the state of the art) into celluloses and hemicelluloses and in this way to obtain a chemical pulp. The use of the product obtained according to the invention, if appropriate after the alkanolamine recovery, in particular the monoethanolamine recovery, as a paper, energy and chemical raw material or as an N-deposit fertilizer, is particularly preferred.

As already stated, particular advantages are achieved with the monoethanolamine in the context of the invention. In addition, the following should be noted: It results for the particular monoalkanolamine used, in particular monoethanolamine, a very high recovery rate, which is of great economic importance, especially in view of the high cost of monoethanolamine at about EUR 1,400 .- / t. A viable process is possible using the alkanolamine in the invention by: mild conditions, since in the digestion a comparatively low temperature can be selected so that MEA is not decomposed (boiling point 17O ⁰ C), and lower use of monoalkanolamine, in particular MEA, by dilution with water, preferably in the ratio of about 1: 1 (Note: Because of the mild conditions of dilution, the method is preferably limited to annual plants.) With wood, harsher conditions must be chosen which lead to the decomposition of MEA).

The invention will be explained in more detail below with reference to examples, wherein it should also be shown which individual parameters are of particular relevance for the invention:

Examples

In the experiments described below, wheat straw from the 2008 harvest of a farm in Schleswig-Holstein was used for all digestions. The straw was crushed in a shredder, the fine material separated and used in this form for the digestions in a 15 l rotary autoclave with external shell heating and a process control system. The straw had a solids content of 90.3%. For all cookings, 400 g of dry straw were used uniformly. The heating time to a maximum temperature for all digestions was 60 min. example 1

In the overall process is used as the alkanolamine monoethanolamine (MEA). From the following overall consideration, it follows that it is an essential aspect that the monoethanolamine is used in a mixture with water as a digestion agent and recycled after recovering the raw pulp or pulp into the system. In detail, the procedure is as follows, reference being made to the attached flow diagram (FIG. 1).

A plant for carrying out the method according to the invention comprises, according to a preferred embodiment, a digester 2, a separator 8, a delignification unit 10 and a bleaching unit 13. Further, the plant comprises a distillation device 11, a water tank 5 and an MEA tank 4. The individual Components of the system are coupled together by cables. The arrangement and connection of the individual components with one another is explained in more detail in the following process description:

The cooker 2 has a biomass feed line 1 and a catalyst feed line 3, whereby the digester 2 biomass and catalyst is fed. The biomass preferably comprises wheat straw as a one-year-old plant. Monoethanolamine (MEA) is also fed to digester 2 through a first M EA return 4.2 and water via a digester feed line 5.4. The biomass is digested in the digester 2 with a digestion solution of MEA and water in the presence of the catalyst. Preferably the pulping is conducted at a kettle temperature of between 130 ⁰ C and 170 ⁰ C, in particular between 140 ⁰ C and 160 ⁰ C, particularly at about 150 ⁰ C. The digestion time is preferably from 130 min to 170 min, in particular from 140 min to 160 min, in particular about 150 min.

The biomass digestion is subsequently fed to the separating device 8 via a biomass digestion line 6.1. The separator 8 is further supplied via a first water line 5.1 water from the water tank 5. In the separating device 8, a gradual separation of the Zeiistoffs from the biomass digestion takes place. The water supplied via the first water line 5.1 is used as washing water. In the separation of the pulp waste liquor arrives, which comprises the dissolved biomass and the digester 2 supplied digestion chemicals, in particular MEA. The waste liquor is supplied from the separator 8 via a Ablaugeableitung 7.1 of the distillation device 11, whose operation will be discussed in more detail later. The separated in the separator 8 green pulp is fed via a pulp forwarding 6.2 delignification unit 10. The delignification unit 10 furthermore comprises an oxygen feed line 10.1 and an MEA feed in the form of a second MEA feed back 4.3. Via the second MEA feedback 4.3, MEA is supplied from the MEA container 4 to the delignification process in the delignification unit 10. Furthermore, the delignification unit 10 is connected by a second water line 5.2 to the water tank 5, so that water can be supplied to the delignification process. In the delignification unit 10, an MEA-O ₂ bleach is carried out, wherein in particular lignin is separated off. The separated lignin filtrate is returned via the Ligninableitung 9 to the separator 8 and used for carried out in the separator 8 pulp washing.

After the MEA / O ₂ bleach in the delignification unit 10, the bleached pulp is fed to the bleach unit 13 via a pulp feed line 6.3. The bleaching unit 13 further comprises a bleach supply 13.1, whereby bleaching agents, for example O / P, O ₃ , P, CIO ₂ and / or FAS, can be fed. The bleaching process in the bleaching unit 13 may include elemental chlorine free (ECF) or totally chlorine free (TCF) sequences. The pulp is lightened in the bleaching unit 13 to higher whiteness levels. Further, the bleaching unit 13 is supplied with water from the water tank 5 through a third water pipe 5.5, so that the pulp in the bleaching unit 13 is washed. The bleach filtrate is separated from the pulp and discharged via a Filtratab- line 14. The recovered pulp is derived from the bleaching unit 13 via a pulp discharge 6.4.

The separated in the separator 8 and the Ablaugeableitung 7.1 the distillation device 11 supplied waste liquor is further separated in the distillation device 11. By the separation or distillation in the distillation device 11, a recovery of water and MEA is achieved. The recovered water or wastewater is fed via a sewer line 5.3 the water tank 5 and is the process for the recovery of pulp again available. The recovery of the MEA takes place analogously, the MEA being supplied to the MEA container 4 via an MEA feed line 4.1. The MEA container 4 further includes an MEA Introduction 4.4, via which MEA can be externally fed or refilled. This may be useful if MEA losses occur during the extraction process. The distillation device 11 further comprises a solids discharge 12, are discharged via the after the water and MEA separation remaining Ablaugesubstanzen, especially dry Ablaugesubstanzen. Example 2 (influence of temperature in MEA digestion of wheat straw)

The essential prerequisite for a reduction in MEA decomposition during digestion is the lowering of the cooking temperature. Therefore, the digestion temperature between 165 ⁰ C and 130 ⁰ C was varied. The conditions and results otherwise used are listed in Table 1. For comparison, soda and soda / anthraquinone (AQ) digestions have been used, which are the standard method for digesting straw on an industrial scale. It was found that a lowering of the digestion temperature up to 150 ⁰ C (WS 10, WS 3-5) is possible without the delignification of the system decreases (Kappa number) and the yields are at a high level. Compared to conventional soda or soda / AQ outcrops, they are up to 12% higher in raw material, which means about a quarter more pulp production from the same amount of raw material. The M EA ZeI Istoffe had very low whiteness levels (15% ISO to 28% ISO) compared to the soda. A pretreatment of the digestion material with ammonia did not bring any advantages here (WS7-WS9).

Table 1 (digestion of wheat straw in the 15 liter MK cooker)

(Continued from Table 1) Remarks:

* MEA digestions = MEA / straw ratio, adding 250 ml of water for lossless flushing of the MEA, actual liquor ratio: 4.77

** A-MEA: with ammonia pretreatment: 10% / dry straw, liquor 3: 1, 33 min heating time to 120 ^° C.,

10 min at 120 ⁰ C, then exhaust gases

*** Cooking material was additionally pitched before being whipped in the pulper with an Ultra-Turrax

(Preliminary test for MEA balancing), resulting in fewer splinters and higher acceptances

Example 3 (replacement of a part of the MEA in the digestion with water)

In order to further reduce the specific MEA consumption in the digestion stepwise MEA was replaced by water. The results are summarized in Table 2 below. A reduction of the MEA fraction in the digestion solution to 50% had hardly any negative influence on the digestion. The kappa number increased under otherwise constant conditions only by 2.5 units (WS6, WS16, 17). When the MEA content of the digestion solution was reduced to 37.5%, the kappa number increased by one more unit (WS23), while at 25% MEA fraction it jumped by 16 units, which was not sufficient for defibration digested straw portion in the form of splinters (WS18). Based on these results, standard cookages with MEA-H ₂ O ratios of 50:50 were used.

Table 2

( ^" Continued from Table 2 :) Remarks:

W = water

O = oxygen

For MEAS 11 use of oxygen after cooking or during the cooling phase

In MEAS 12 use of oxygen one hour before the end of the cooking

* Pouring bleach

Example 4 (Use of catalysts in the digestion system MEA-H ₂ O)

Since MEA digestion takes place under alkaline conditions and is used in known alkaline digestion processes such as the soda and force processes, AQ has been used as a catalyst to accelerate digestion and to stabilize the carbohydrates against chain-end degradation, also in MEA digestion this catalyst is used. Quantities of 0.05-0.1% / raw material accelerate the digestion significantly. The kappa number is additionally reduced by 4-5 units (WS19-21, WS24, 25). This makes it possible, with an MEA / H ₂ 0 ratio of 37.5: 62.5, to achieve the same delignification as in a pure MEA digestion. In contrast, the use of DMAP (4-dimethylaminophenol hydrochloride) as catalyst did not affect the digestion (WS22, WS28-31).

Example 5 (Use of MEA as an alkali source in the oxygen delignification of MEA pulps)

To activate oxygen in the further delignification of pulps, NaOH is usually used as the alkali source. It has been investigated whether MEA can substitute NaOH as an alkali source, as it is advantageous for the closure of the pulp manufacturing process if the same base is used in the cooking and the oxygen delignification. Table 3 summarizes oxygen delignification results using both NaOH and MEA as the alkali source. The NaOH amount was 2 and 3% while 10-160% MEA / pulp was used. The reaction temperature was varied between 90 and HO ⁰ C while the reaction time was kept constant at 90 min. With a Ausgangsskappazahl in the unbleached pulp of 19.5 this could be lowered depending on temperature and amount of alkali up to half. Here, MEA proved to be very effective, although 20% MEA / pulp was needed to reach a kappa number of 10,9 at 9O ⁰ C, which is suitable for further bleaching of the pulp (high O stage). The resulting bleach liquor can be separated in a wash and used to wash the Kocherstoffes. It can then be worked up together with the digestion solution (chemical recovery).

Table 3

Remarks:

In all O tests consistency 20%, O-pressure 6 bar, yield after O-stage: 97.2%

Example 6 (Bleaching of MEA pulps)

The oxygen delignified 10.5 kappa pulp was bleached in a totally chlorine-free bleaching sequence (TCF) and a bleaching sequence using small amounts of chlorine dioxide (D). Each bleaching stage was optimized and the optimized conditions in the overall sequence were used to bleach a larger quantity of pulp to determine the papermaking properties of the pulps.

After the oxygen stage, the fabric was treated in a complexing step (Q) to remove heavy metals. Various complexing agents or complexing agent combinations were used (see Table 4). To improve the solubility of the heavy metals, the substance was adjusted to pH values between 4 and 2.5 with sulfuric acid. After 30 minutes of treatment at 60 ^° C., the complexed metals were removed in a wash. Subsequently, the fabrics were bleached in a peroxide-enhanced oxygen (OP) stage and alternatively only peroxide. The conditions of these stages were varied to find optimal conditions (see Table 4). The results show that a greater decrease in pH in the Q-stage improves the efficiency of the subsequent bleaching stage. With respect to the bleaching effect, the OP level was superior to the P-level taking into account the peroxide use. For this reason, the OP stage was used in the further bleaching sequences.

As already mentioned, both chlorine dioxide (D) and ozone (Z) were used in the final bleaching of the pulps (see Table 5). In these steps, complexing agents were added again to make the ozone stage and the final peroxide stage (P) more selective.

The chlorine dioxide stage was again optimized with regard to the chemical use and set a quantity of 0.2% chlorine dioxide / cellulose for the bleaching of the large batch. In the ozone treatment a constant 0.35% ozone was used. For both bleaching variants, a peroxide stage was finally used, which was further optimized with regard to the use of chemicals. In the final bleaching of the large batches, 2% H ₂ O ₂ and 2% NaOH were used. The final whiteness reached in the sequence 0-OP- (DQ) -P was 79.8% ISO while in the sequence 0-OP- (ZQ) -P a whiteness of 80.1% ISO was achieved (Table 5). This is a sufficient degree of whiteness for most uses of straw pulp.

Table 4

Remarks:

Q *: pH beginning 4 - pH end 4.5 Q **: pH beginning 2.8 - end 3.2 Q ***: pH beginning 2.5 - pH end 3 Table 5

Example 7 (Technological properties of MEA pulps)

Tables 6 to 8 contain technological and optical values of an unbleached and the same pulp bleached in the two different sequences. The values obtained are very good for wheat straw pulps, especially considering the high yields of the pulps. Strength values even increase after bleaching, which is not the case for pulps made in conventional processes. This may also be due to the gentle digestion conditions of the MEA method. The bleaching slightly reduces the high hemicellulose content of the M EA-ZeI Istoffe, which has a positive effect on the strengths. Comparisons between wheat straw pulps produced in the MEA process and in the conventional soda / AQ process have shown that MEA pulps are technologically superior to the corresponding soda pulps.

Table 6

Remarks:

Paper Wheat straw MEA32-34 unbleached (15.10.2008) 150 ⁰ C, 150 min, starting material for bleaching tests Substance name WS 32-34; MEAS 17-19 Table 7

Remarks:

Wheat straw MEA32-34 OQ (OP) (ZQ) PI (15.10.2008) 150 ⁰ C, 150 min, bleached Substance name WS 32-34; MEAS 17-19 Table 8

Remarks:

Wheat straw MEA32-34 OQ (OP) (DQ) P (15.10.2008) 150 ⁰ C, 150 min, bleached Substance name WS 32-34; MEAS 17-19

Example 8 (Elemental analysis of the digestion solution dissolved in the digest after the recovery of the MEA)

The use of low-boiling organic solvents for pulp production enables the separation of the solvent and the components of the solution which have gone into solution Digestion by distillation. While the solvent is being reused, a use has to be found for the solutes. In conventional processes, this is the energetic use associated with the recovery of the inorganic digestion chemicals.

In the case of MEA digestion, in addition to the combustion of the concentrated abhesive substance after distilling off the MEA, it is also conceivable to use the dissolved lignocelluloses as a chemical raw material or as an organic fertilizer with a long-term effect. The latter utilization requires the highest possible nitrogen content. This nitrogen, unlike inorganically bound nitrogen, is slowly released to the soil by microbial decomposition of the substrate. Lignocelluloses also have a high water absorption and water binding capacity and increase the pore volume of soils. As shown in Table 9, approximately 6% organically bound nitrogen was detected in MEA-free waste liquors.

Table 9

(Elemental analysis) ThermoQuest EA 1112

*) somewhat inhomogeneous **) inhomogeneous ***) very inhomogeneous

* * * LIST OF REFERENCES

1 biomass feed

2 cookers

3 catalyst feed

4 MEA containers

4.1 MEA supply line

4.2 first MEA feedback

4.3 second MEA feedback

4.4 MEA Introduction

5 water tanks

5.1 first water pipe

5.2 second water pipe

5.3 Sewer pipe

5.4 Cooker supply

5.5 third water pipe

6.1 Biomass digestion line

6.2 Pulp forwarding

6.3 Pulp feed

6.4 Pulp discharge

7.1 Leakage removal

8 separating device

9 Lignin derivative

10 delignification unit

10.1 oxygen supply

11 Distillation device

12 solids discharge

13 bleaching unit

13.1 bleach supply

14 filtrate discharge

* * *

Claims

claims

Anspruch [en] A process for recovering pulp by separating lignin from a lignocellulosic biomass in the form of plants or plant parts, wherein the lignocellulosic biomass in an alkaline medium containing alkanolamine is digested in a digester and dissolved lignin from the resulting lignin Raw pulp is separated, characterized in that the lignocellulosic biomass is not due to wood and digested at a temperature of less than about 170 ⁰ C in a based on alkanolamine and water disintegrating agent in which the weight ratio of alkanolamine to water to 80: 20 to 20:80 is set, and resulting raw pulp is separated from the spent liquor by conventional methods.

2. Method according to claim 1, characterized in that the lignocellulose-containing biomass is annual plants.

3. The method according to claim 1 or 2, characterized in that is treated as lignocellulosic biomass grain straw, in particular wheat straw.

4. The method according to any one of claims 1 to 3, characterized in that as alkanolamine, a short-chain alkanolamine, in particular an alkanolamine having 1 to 4 carbon atoms is used.

5. The method according to claim 4, characterized in that are used as the alkanolamine monoethanolamine, monopropanolamine and / or monobutanolamine, in particular monoethanolamine.

6. The method according to at least one of the preceding claims, characterized in that the ratio of alkanolamine to water to 70:30 to 30: 70, - is set to 60:40 to 40:60 in particular.

7. The method according to claim 6, characterized in that the ratio of alkanolamine to water is adjusted to 53:57 to 57:53.

8. The method according to at least one of the preceding claims, characterized in that the digestion temperature is set to less than about 165 ⁰ C, in particular to less than 15O ⁰ C.

9. The method according to at least one of the preceding claims, characterized in that the digestion temperature to more than about 120 ⁰ C, in particular more than about 14O ⁰ C is set.

10. The method according to claim 8 or 9, characterized in that the digestion temperature is adjusted to 140 to 160 ⁰ C.

11. The method according to at least one of the preceding claims, characterized in that the digestion is carried out after heating for a period of 15 min to 4 h, in particular from 1 h to 3 h.

12. The method according to claim 11, characterized in that the digestion is carried out for a period of 2 to 3 hours.

13. The method according to at least one of the preceding claims, characterized in that the liquor ratio of aufzuschließender biomass (dry matter) and digesting agent alkanolamine / water to about 8: 1 to 2: 1, in particular about 5: 1 to 3: 1, is set ,

14. The method according to at least one of the preceding claims, characterized in that the digestion in the digester is carried out continuously.

15. The method according to at least one of the preceding claims, characterized in that the digestion is carried out in the presence of a catalyst, in particular in the form of a quinone.

16. The method according to claim 15, characterized in that is chosen as the catalyst anthraquinone.

17. The method according to at least one of the preceding claims, characterized in that the raw pulp from the waste liquor of the digester by solid / liquid separation, in particular filtration, pressing or centrifuging, is separated and the resulting waste liquor filtrate, optionally after evaporation, enriched in alkanolamine and returned to the digester.

18. The method according to claim 17, characterized in that the resulting raw pulp is washed and the resulting wash liquor is combined with the cooking liquor.

19. The method according to at least one of the preceding claims, characterized in that the raw pulp, separated from the cooking liquor and optionally washed, is bleached.

20. The method according to claim 19, characterized in that the bleaching is carried out in the context of an alkanolamine / oxygen stage, with alkanolamine as alkali source, for further delignification tion, the bleached pulp of adhering liquid fractions, which still contain alkanolamine, separated, in particular pressed or filtered to supply the alkanolamine-enriched liquid phase, in particular the filtrate, back to the digester.

21. The method according to at least one of the preceding claims, characterized in that a vaporization, which is optionally carried out at different process steps, is carried out with low thermal stress, in particular in a thin-film evaporator, falling film evaporator or tube evaporator.

22. The method according to at least one of the preceding claims, characterized in that the delignification is carried out repeatedly in a digester.

23. The method according to any one of claims 19 to 22, characterized in that the filtrate, which has been obtained after the measure of bleaching, is used as a washing solution for washing the unbleached raw pulp.

24. The method according to at least one of the preceding claims, characterized in that the raw pulp or after bleaching with the alkanol with the min / oxygen stage pulp is subjected to further bleaching in standard ECF and TCF sequences.

25. The method according to at least one of claims 19 to 24, characterized in that the bleaching, in particular the further bleaching of the pulp, by the action of oxygen / hydrogen peroxide, hydrogen peroxide in the presence of NaOH, O ₃ , CIO ₂ and / or formamidinesulfinic acid (FAS ) is carried out.

26. Use of the product obtained by the process according to at least one of the preceding claims, optionally after the alkanolamine recovery, in particular the monoethanolamine recovery, as a paper, energy and chemical raw material or as organic N-Depotdünger.