EP1190137A1

EP1190137A1 - Method for separating lignocellulose-containing biomass

Info

Publication number: EP1190137A1
Application number: EP00925193A
Authority: EP
Inventors: Ties Karstens
Original assignee: Rhodia Acetow GmbH
Current assignee: Cerdia Produktions GmbH
Priority date: 1999-04-12
Filing date: 2000-04-11
Publication date: 2002-03-27
Anticipated expiration: 2020-04-11
Also published as: NO20014939D0; CA2368872A1; EP1190137B1; SK14392001A3; NO20014939L; BR0011169A; RU2220245C2; AU4399500A; CN1352716A; WO2000061858A1; CN1208514C; NZ515051A; JP2002541355A; CZ20013627A3; PL351393A1; ES2213011T3; PT1190137E; BR0011169B1; CA2368872C; DE19916347C1

Abstract

The invention relates to a method for separating lignocellulose-containing biomass, especially wood, into the essential components in the form of lignin, hemicellulose and cellulose, with the following steps: a) pre-hydrolyzing the lignocellulose-containing biomass by treating it with water or steam; b) extracting the hydrolyzed hemicellulose obtained by pre-hydrolyzation with an aqueous medium; c) extracting the process-modified lignin that remains in the residue with an alkanolamine, isolating the lignin, recovering the alkanolamine, whereby the alkanolamine is not substituted by alkyl groups at the nitrogen atom, and d) obtaining a cellulose raw material. The inventive method is characterized in that hemicelluloses and lignin can be specifically separated from the cellulose in two different process steps. For this purpose, simple and commercially available system components can be used that facilitate an economical operation also with small installations.

Description

Process for separating biomass containing lignocellulose

The present invention relates to a process for separating lignocellulose-containing biomass, in particular wood or grain straw, into the essential components in the form of lignin, hemicellulose and cellulose.

The disadvantages of classic pulp processes are mainly the high water requirement, the high content of organic substances in the wastewater and the relatively high operating costs. The latter are not least due to the secondary operations for processing the lye and the waste water or waste streams. The conventional processes do not remove the lignin without the use of sulfur-containing compounds; this is associated with odor nuisance. The classic wood pulping processes (sulphate, sulphite, Milox) are among the processes that chemically break down lignin and mainly break down the breakdown products (lignin sulphonic acids).

From an economic point of view, plants using conventional methods can only be operated from annual capacities of more than 200,000 tons. Overall, chemical pulp production only accounts for a small share of around 4% of the capacity. On the other hand, every chemical pulp processor wants tailor-made pulps for his needs - and if possible in different grades of quality.

In the newer processes, the Formacell process is a process that mainly dissolves the lignin and only slightly breaks it down. ASAM and Organocell are combined processes. The ASAM process in particular requires a complicated chemical recovery system. A method of dissolving the lignin would have the advantage that the lignin and other by-products could easily be separated.

Unlike paper pulp (paper, cardboard, fluff), the chemical properties and not the physical properties of the cellulose fibers are decisive for the chemical cellulose, since the structure of the fibers is broken in the process of chemical cellulose processing. The following criteria play a role here: degree of polymerization and distribution, degree of whiteness and solubility in NaOH.

A disadvantage of the industrially introduced pulp processes is definitely the loss of reactivity due to drying. So-called never-dried pulp (after pulping and bleaching not less than 30% moist dried pulp) is highly reactive. Sheet formation on a paper machine and drying are required to transport the pulp. This involves considerable technical effort, which is counterproductive, at least for the processing of the pulp into derivatives, since this incurs high costs for the reactivation of the chemical pulp. The fiber form after digestion - undried - would be much more suitable for further chemical processing.

In the case of steam explosion processes, pressures above 20 bar are customary in accordance with the prior art to exceed the softening temperatures of the lignin and the polyoses. The high steam temperatures of over 200 ° C associated with these high pressures on the one hand cause a strong chain breakdown of the cellulose, on the other hand they lead to condensation of the lignin - with the result that it is difficult to extract. The steam is unlikely to penetrate into crystalline areas of the lignocellulosic structure; in this respect, modifications are not possible there.

The state of the art in the steam explosion is recorded in a large number of patents, which primarily relate to the technical design and the basic procedures. Most of the studies were done with wood as the raw material. In the majority of cases, the focus was on optimizing ranked the severity factor (integral of the product of steam temperature and exposure time).

A disadvantage of using steam is that additives cannot be added to the steam, or only with great technical effort. Rather, the biomass must be brought into contact with the substances to be used before the steam explosion, which is generally associated with poor distribution or with a higher dosage. This also applies analogously to the steam refming process (steam digestion process with subsequent mechanical fibering), which works with less high-tension steam (10 - 15 bar) and uses mechanical devices for fibering.

The only fully continuously operable pulping process that is implemented on an industrial scale is the steam explosion of wood chips or other biomass with the Stake System II from StakeTech Stake Technology.

The removal of the lignin poses the greatest challenge in all wood digestion processes. Alcoholic extraction of the lignin from wood was published as early as the end of the 19th century. At that time there was a different objective than today for the development of environmentally friendly wood digestion processes. Growing criticism of the effects of traditional wood digestion processes on the environment, stricter legal regulations on wastewater loads, emissions into the air and on the handling of waste, but also efforts to make better use of the wood substance can be seen as the main reasons for the increased efforts in the past 20 years, to develop new environmentally friendly wood digestion processes. Since chemical pulps play a subordinate role (share of world pulp production only about 4%), research and development work focuses on wood pulping processes for the production of paper pulps. However, the chemical removal of lignin is more important than that of paper pulp. High levels of lignin are found in the central lamella of the wood. This causes the stiffness of wood. The maximum permissible content of lignin after pulping before the bleach is introduced on an industrial scale is given as a number of 40.

Cereal straw is also of particular interest as a raw material, since 125 million tons of wheat straw are produced annually in the USA and even 170 million tons in Europe. In many countries - especially in Asia (e.g. China) and in Africa - there is a lack of wood as a raw material for the production of pulp, so that one has to rely on the use of straw. Known processing methods are, for example, the steam explosion or soda pulping (pulping) of straw. The former method is a relatively complex mechanical construction and does not solve the problem of the clean separation of cellulose and lignin. The fiberization is never completely complete, which makes it necessary to add refiners, but above all a high dilution of the fiber suspension down to 2%. Sodium hydroxide solution must still be used for the separation of lignin. The latter method represents a high environmental impact due to "straw pulp" mills and / or high costs of waste water treatment in the case of alkali delignification. In "non-woody" mills the technological effort is often not made as is the case with pulping processes of wood is now state of the art. Today, wood digestion works with almost closed cycles and effective recovery of the cooking chemicals. When digestion of "non-woody" fibers, such as straw, the plants are often too small to operate with the same high technological expenditure. Even if the plant size would economically justify the recovery of the cooking chemicals, there are

Problems, because the high silicon content is difficult to cope with in traditional digestion processes. You can help yourself by simply releasing most of the used digestion chemicals into the environment. For example, win Pulp factories based on straw only return 60% of the cooking chemicals.

In connection with pulping (pulping), two different uses of ammonia are state of the art: defibrating lignocellulosic material using ammonia to plasticize at higher temperatures by means of an explosion-like expansion (JJ O'Connor Tappi 55 (3), (1972) 353-358) and plasticizing wood chips in an Asplund refiner under pressure with ammonia: the wood was subjected to stress a significantly lower energy input (RC Peterson and RW Strauss J. Polymer Sci. C36 (1971) 241-250). In both

In cases, lignin could not be largely removed.

The use of alkanolamines to remove lignin from lignocelluloses was first developed by Elton Fisher and R.S. Bower (J. Am. Chem. Soc. 63 (1941) 1881-1883). In the 1970s, monoethanolamine was processed as an additive to caustic soda for wood pulping (keywords: alkaline pulping in aqueous alcohols and amines, acceleration of soda delignification, sulfür free de-lignification). This should make it possible to reduce or even replace sulfur-containing chemicals.

The processing of the digestion chemicals sodium hydroxide solution and efhanolamine and the separation of the lignin were probably a problem. Lignin is usually obtained from sodium hydroxide solution by precipitation with the addition of acid. Obtaining lignin from the sodium hydroxide / alkanolamine solution in this way would certainly not have facilitated the processing and recovery of the digestion chemicals. The usual combustion of the lignin in the NaOH after thickening as the first step of the NaOH recovery would also lead to the loss of the alkanolamine, which would entail considerable costs.

Presumably because of this, the use of monoethanolamine as an additive to NaOH for the production of high-yielding substances was given up again. In no case was the goal to produce chemical pulp. Monoethanolamine was used in all cases on fresh wood - mostly softwood. Cooking was carried out in pressure vessels in batch mode.

The use of very little monoethanolamine as an additive to aqueous ammonia solution is also described (patents: CA 1232109 Kauppi, Peter K. "Alkanol- amine and NH OH in high-yield pulping "and EP 149 753 Gordy, John" Nonsulftir chemomechanical pulping "). When wood chips are treated at temperatures of 120 ° C and higher, the monoethanolamine in these dilute aqueous, ammoniacal solutions acts as a plasticizer, which the subsequent mechanical pulping of the wood for cardboard or paper production is easier.

According to the disclosure of US Pat. No. 2,192,202, a process for pulping raw lignocellulosic materials, in particular for the production of alpha-cellulose and other valuable products, is described, at least 70% by weight alkylolamine being used as the treatment agent. The treatment is carried out by boiling under pressure between room temperature and 200 ° C for 4 to 20 hours. NaOH can optionally be used. The treatment agent is then separated off, the pulp obtained is washed with dilute inorganic acid and bleached. However, the separation into the individual constituents of the pulp achieved thereby is completely inadequate and the quality obtained is unsatisfactory.

The invention is therefore based on the object of providing a method for fractionating biomass containing lignocellulose, in which the disadvantages of the prior art which have been mentioned are largely eliminated. The wood components hemicellulose, lignin and cellulose are to be obtained separately from one another in the least contaminated form in order to make these raw materials available to further processors. In this case, a sulfur and chlorine-free wood digestion process is to be provided which also works without sodium hydroxide solution and can therefore dispense with complex recovery, exhaust air and wastewater treatment processes. In particular, chemical pulp production should be able to be carried out in a small, decentralized unit in a way that saves time, chemicals and energy. Cellulose should be processed as never-dried pulp, ie with high accessibility, directly to cellulose derivatives. The aim of this is to produce pulp tailored to the criteria of the individual chemical pulp processor at low cost and also in the state of the highest reactivity. vity for further processing are made possible with an integrated processing chain from wood to cellulose derivative.

According to the invention, the above object is achieved by a method for separating lignocellulose-containing biomass, in particular wood, into the essential constituents in the form of lignin, hemicellulose and cellulose, with the following steps: a) pre-hydrolyzing the lignocellulose-containing biomass by treatment with water or steam; b) extracting the hydrolyzed hemellulose formed by prehydrolysis with an aqueous medium; c) extracting the process-modified lignin remaining in the residue with an alkanolamine, isolating the lignin, recovering the alkanolamine, the alkanolamine not being substituted by alkyl groups on the nitrogen, and d) obtaining a cellulose raw material.

The method according to the invention enables lignocelluloses to be broken down and broken down into their components by first subjecting them to a pre-hydrolysis by treatment with water or steam, then extracting the hydrolyzed hemicelluloses formed with aqueous media and then extracting the residue with alkanolamine to obtain a Cellulose raw material is subjected.

All types of lignocellulose can be used for the teaching according to the invention, namely the fractionation into the essential components cellulose, polyoses and lignin. Plant growth materials of various types, such as wood, oat husks, maize and grain stalks, bagasse, straw of all kinds, such as wheat straw, rice straw and oat straw, are suitable as lignocellulose-containing biomass. In the case of wood, it is common to use logs or industrial waste wood, preferably in comminuted form, for example in the form of wood chips. In the case of fibrous raw materials, such as annual plants, fibers cut up by cutting are suitable. It is preferred to shredded or shredded wood, used in the form of hardwood, beech or softwood.

The water content of the lignocellulose-containing biomass can be between the typical content for freshly harvested lignocelluloses of about 80% by mass, in particular 50%

% By mass, and after intensive drying are also close to 0%.

The initial step of the method according to the invention comprises the pre-hydrolysis of the lignocellulose-containing biomass by treatment with water or steam. The mass ratio of water vapor to biomass (based on

Dry matter) to about 1: 1 to 3: 1, from water to biomass to about 3: 1 to 10: 1, in particular about 6: 1. The biomass can be subjected to a so-called steam explosion process, and the steam refining process can also be used. It is preferred to carry out the pre-hydrolysis of the biomass under mild conditions, the aim being this

The process step is to break down the hemicelluloses to such an extent that their subsequent separation as oligosaccharides is easily possible by extraction with aqueous media, such as washing with water. Pre-hydrolysis is a well-known process step in the pulp industry, which need not be discussed in more detail here. Cellulose and lignin should be attacked as little as possible.

According to the invention, the entire breakdown of the hemicelluloses can take place in the first step of the process, ie the prehydrolysis, since the alkanolamine in the extraction step does not attack cellulose or the hemicellulose, but rather stabilizes them. The pre-hydrolysis according to step a) can, however, also be carried out to a small extent. It is then pre-hydrolyzed to such an extent that the acids bound to the hemicelluloses can be split off and the split off acids are washed out in accordance with step b). This is particularly important for the production of high-yield pulp. Excess acids would react with the alkanolamine to be used subsequently and thus lead to losses. A minimum pre-hydrolysis may therefore already be sufficient. To improve the effectiveness of the pre-hydrolysis, a two-stage pre-hydrolysis can also be carried out at the same temperature and the same cooking conditions, but with greater effectiveness, ie first steam and then hot water.

If straw is used as biomass, for example, the pre-hydrolysis can be carried out according to

Steps a) and b) are omitted and an immediate extraction according to step c) is carried out at an elevated temperature below about 170 ° C., preferably below about 160 ° C., in particular at about 115 to 135 ° C., in order to obtain paper pulp. As an alternative to this, the straw can also be prehydrolyzed at about 150 ° C. to 190 ° C., in particular about 170 ° C., and then extracted according to step c) at an elevated temperature below about 170 ° C., preferably below about 160 ° C., in particular at about 115 to 135 ° C to obtain chemical pulp. Sugar is obtained here by concentrating the pre-hydrolyzate, which can be followed by suitable further processing. The appropriate variant can be selected depending on the desired pulp quality.

If necessary, stabilizers can be added to avoid the condensation of lignin components. Furthermore, the lignocellulose-containing biomass can be carried out before carrying out step a), i.e. the pre-hydrolysis, an acidic or alkaline pretreatment. This means a further increase in the yield of the desired products.

After the steam explosion or steam refining process used, for example, the raw material, which is generally already well-fibrated, can be treated with hot water in order to dissolve and separate the majority of the degraded hemicellulose. The pre-hydrolyzed and softened biomass is thus freed from the hydrolyzed hemicelluloses formed by extraction with an aqueous medium. For this purpose, excess water is preferably pressed off and washed hot. This can be followed by mechanical fibering of the biomass, for example crushing in a refiner to the desired degree of division, which can be of great importance depending on the desired quality. This can be followed by an optional treatment with ammonia. This can be carried out at any suitable point, after washing step b), with aqueous ammonia solution, with ammonia gas or with liquid ammonia.

The mass ratio of the liquid ammonia to the mass to be treated (based on dry substance) is preferably set to approximately 0.1: 1 to 4: 1.

This is followed by extraction of the biomass already freed from the hemicelluloses of the process-modified lignin remaining in the residue with an alkanolamine to obtain a cellulose raw material. All alkanolamines which are not substituted by alkyl groups on the nitrogen are particularly suitable as alkanolamines. For example, from: N-methyl-monoethanolamine and N, N-dimethyl-monoethanolamine, since these have no effect on the extraction of the lignin from the wood.

Monoethanolamine is preferably used as the extracting agent, which can be used in preheated form, in particular at least at about 80 ° C. It has been shown here that the extraction effect in the series of non-pretreated biomass, via prehydrolysed biomass to biomass pretreated with ammonia, clearly increases. The lignin content of the extract is about 60% higher under ammonia-treated biomass under the same extraction conditions than with only prehydrolyzed biomass.

The extraction according to the invention is preferably carried out under pressure, i.e. in a suitable autoclave or a continuous extractor. By extraction under atmospheric pressure, e.g. with straw, equally good results can be achieved.

In batch operation, ie in an autoclave, the biomass washed free from the hemicelluloses, if necessary comminuted and appropriately pretreated with ammonia, with the water, the extractant (s), contained therein, for at least about 1 hour a temperature between about 80 and 220 ° C heated. It solvents for the resulting lignin degradation components may already be present.

A continuous extraction is preferred over a batch mode of operation. This can be carried out by letting the preheated extractant flow through the biomass filled into a pressure reactor or by leading the material to be extracted, the biomass, to the extractant in countercurrent. Both variants have the advantage over the autoclave, ie stationary operation, that secondary reactions are largely excluded as a result of the removal of the degradation products with the extractant. In addition, with the same extraction effect, a lower liquor ratio of extractant to chips and at a lower temperature can be used. The solubility of Organosolv lignin in monoethanolamine is relatively high (250 g / liter).

In a preferred embodiment of the invention, the extraction is multi-stage, i.e. carried out in at least two successive extractions with alkanolamine. Here, the same total amount of alkanolamine is preferably used as in a one-step extraction. In this case, countercurrent extraction can be carried out effectively, since the shortest extraction times are realized here.

If, for example, a two-stage pre-hydrolysis is carried out, then this can be very well reconciled with the technologies introduced for the production of chemomechanical pulp ("chemical mechanical pulp" == cmp) if the steam treatment of the best is additionally carried out beforehand with dilute acetic acid impregnated wood chips in a so-called "inclined screw reactor" (actual pre-hydrolysis) and then the extraction of the sugar under fibrillation is carried out according to the countercurrent principle.

Monoethanolamine (hereinafter abbreviated as: MEA) as an extractant has several advantages. In the pulping process, MEA prevents lignin condensation and grafting on cellulose, it protects the cellulose from DP degradation, improves delignification and reduces the need for bleaching chemicals.

The alkanolamine extraction can be carried out at lower temperatures (about 100 to 120 ° C) if an ammonia pretreatment is carried out.

Despite the low temperatures, low kappa numbers are then obtained. In addition, side reactions are strongly suppressed.

After the extraction stage, the cellulose raw material is obtained. For this purpose, the strongly dark brown to black colored lignin extract is separated from the raw cellulose fibers in a suitable manner by the methods customary for solid / liquid separation. If complete removal of the process-modified lignin remaining in the raw pulp is desired, this can be extracted with a suitable solvent by washing or countercurrent washing. The solvent used here is then separated from the lignin and the extracting agent by distillation, is recovered in this way and is thus available again.

The residue after distilling off the solvent can also be combined with the extract separated from the fibers. This turns into water and that as

Extracting alkanolamine separated by distillation, preferably vacuum distillation. Other separation processes which, as desired, lead to the concentration of the lignin extract - in extreme cases to dry matter - are also suitable here. The lignin can also be separated off by adding a non-solvent to the solution of the lignin in alkanolamine. The lignin precipitates in the form of solid particles and can be separated from the extraction agent alkanolamine by a suitable solid / liquid separation process, such as filtration, centrifugation, thin-layer evaporation or membrane separation processes. The lignin can be separated off, for example, by introducing CO2 into the lignin / alk-molamine extract, which is optionally concentrated and diluted with water or better with the washing water after the alkanolamine extraction. By concentrating using thin film evaporation or another suitable distillation method most of the alkanolamine is recovered in pure form. The rest of the alkanolamine is distilled after the water has been distilled off from the precipitation liquid after the lignin has been separated off, likewise in vacuo. Lignin precipitation is thus achieved by introducing CO2 and centrifuging. The alkanolamine * CO 2 addition compound that forms with the CO2 can be completely decomposed into alkanolamine and CO2 again thermally or by injecting steam. The residue consists of lignin, which is greatly degraded in its molecular weight and not chemically modified. This can therefore be used as a chemical raw material, eg for the production of thermosets or polyurethanes.

The degraded hemicelluloses are in aqueous solution or suspension and can also be used again.

The raw pulp has a kappa number of at most about 20, preferably below about 10. This corresponds to a lignin content of <3 or <1.5 mass% and represents an advantageous entry into bleaching.

In practice, a so-called "included screw reactor" can be used for the pre-hydrolysis, which is followed by a fiberization and washing-out customary in the production of "cmp" (see above). For example, the use of an "included screw" is preferred reactors "for the pretreatment with NH ₄ OH / alkanolamine, then an above-mentioned fibrillation for the thorough ligin extraction in the form of countercurrent extraction. In the first case, these two steps result in a weakly lignin-containing, water-rich fraction, which can be used several times, the lignin being concentrated, and in the second case, a high-lignin-containing and alkanolamine-rich fraction. The combination of the two fractions in the ratio water-rich / alkanolamine-rich - 2/1 enables the lignin to be precipitated by CO2 at elevated temperature. Only a little water needs to be distilled off from the alkanolamine-rich and low-water fraction in order to then be able to recover most of the alkanolamine, for example by thin-layer evaporation, and at the same time increase the lignin concentration by more than 20%. To illustrate the method according to the invention, various variants of the method for separating lignocellulose-containing biomass in the form of flow diagrams are shown in the attached FIGS. 1 and 2. 1 shows the so-called pre-hydrolysis, for example in the form of the steam explosion or steam refming process, which, after extraction with an aqueous medium, leads to the separation of the hemicelluloses. A refining is carried out on this in a refiner, which influences the execution of the further process. This is followed by an optional ammonia treatment. This can be a so-called ammonia explosion, for example. This can then be followed by fiberization in a refiner, after which the extraction with an alkanolamine, in particular monoethanolamine, leads to the separation of lignin and cellulose in batch or continuous mode. It is not absolutely necessary to carry out an ammonia treatment; after prehydrolysis or after a steam explosion or steam refming process, extraction with an alkanolamine can be carried out directly.

A variant of the alkanolamine extraction is shown in detail in FIG. 2. A recycling circuit is shown here, which represents the recovery of the solvent or the extraction agent used. This variant allows an extremely economical mode of operation.

A number of advantages are associated with the invention. One advantage is that no sulfur-containing chemicals are used for the wood digestion. Furthermore, chlorine-containing chemicals do not have to be used for bleaching.

In the case of pure steam treatment (steam refining, steam explosion), in contrast to the present invention, the so-called severity factor, that is to say the integral of the steam temperature and the duration of action, must be chosen so high that both the hemicelluloses and the lignin can be successfully mined, however under these drastic conditions, the molecular weight of the cellulose also drops sharply and the lignin fragments tend to condense. The advantages of this one-step process have to be bought with compromises in the quality of the fractional components.

One of the advantages of the process according to the invention is that hemicelluloses and lignin are separated from the cellulose in two different process steps, accordingly appropriately and in a targeted manner. This also means that the molecular weight of the cellulose does not decrease so much and that the lignin content before bleaching is significantly lower than in the processes mentioned above and also in the industrially introduced processes (sulfate and sulfite processes).

Furthermore, the steam used for the prehydrolysis of the hemicelluloses can serve to preheat the extractor. It is used twice. The energy to be used for the unraveling is also due to the strong softening of the

Biomass very low after extraction. The fibrillation mostly takes place after the pre-hydrolysis, in individual cases after the extraction step, without having to accept any significant input of mechanical energy.

Another advantage lies in the avoidance of sodium hydroxide solution as an extracting agent for lignin, as is customary after the steam explosion or the steam refming process. The use of sodium hydroxide solution in particular requires the construction and operation of so-called recovery systems (recovery) in the pulp mills. Their size is primarily due to the economically sensible operation of these ancillary systems only to a certain extent.

If cereal straw is used as the starting material, there is no need for the classic, multi-stage, time-consuming recovery or wet oxidation process. The recovery of alkanolamine is a simple vacuum distillation. The alkanolamine * CO 2 addition compound that forms with the CO2 can be completely decomposed into alkanolamine and CO2 again thermally or by injecting steam. There is no need to recover sodium salts. With a simple one Prehydroylysis with water makes the alkanolamine extraction so effective that the raw pulp already has an ISO brightness of approx. 50%. The alkanolamine extraction can also be carried out without pressure given the low water content of the straw, which allows the use of simple apparatus.

The so-called "white liquor", ie the mixture of at least 20% sodium hydroxide solution and sodium sulfide in the sulfate (power) process, is applied to the biomass in a relatively high liquor ratio of 10: 1 (for example in the form of wood chips) . The biomass must also be of relatively the same size within relatively narrow limits, since otherwise e.g. larger chips are not sufficiently penetrated by the white liquor during the cooking time. In contrast, the invention allows extraction with an alkanolamine at significantly lower liquor ratios (approximately 3: 1) - especially in continuous operation. This has a positive effect on the steam consumption during extraction and recovery.

In the process of the invention, the biomass is advantageously machined with steam with little mechanical energy expenditure in suitable refers or defibrators after the pre-hydrolysis with steam, so that the effective duration is not influenced by diffusion processes in the subsequent extraction with alkanolamine.

Small decentralized units for the production of chemical pulp cannot be operated under optimal economic conditions if the sodium hydroxide solution has to be recovered. The use of alkanolamines as extractants is therefore advantageous in two respects: recovery by distillation is not energy-intensive with the heat of vaporization inherent in these substances. The separation of the lignin can be carried out without the use of acids, which also avoids complex work-up processes and protects the environment.

Additives to prevent the condensation of the lignin are also not required, which saves costs. As a pretreatment with chemicals, as required when using only the steam explosion and steam refining process is eliminated, there are no problems with their distribution. As a result, the process according to the invention has a very low reject rate (coarse wood components which are not sufficiently frayed due to a lack of distribution).

In addition, after extraction with alkanolamine, the pulps show increased decrystallization compared to other processes. This is undoubtedly very cheap for use as chemical pulp, since it provides uniform access to chemicals for the production of cellulose derivatives. The possibility of using ammonia in a much smaller amount than with the pure ammonia explosion of wood also has a favorable effect on operating costs. There is no need for time-consuming recovery of liquid ammonia.

Since the expenditure for bleaching is naturally lower, the lower the kappa numbers (the lignin contents) after the extraction, there are also favorable conditions in the process of the invention. As a result of a fully continuous operation, the specific investments are therefore low and the space / time yields are high. Simple, commercially available plant components can be used. This allows economical operation even with small system sizes (factor 10 smaller than the systems currently in use). The alkanolamine recovery can also be closed. As a result, there is less effort in concentrating, less water consumption and less energy costs in distillation.

According to the invention, the pre-hydrolysis can be used either for total degradation or to a lesser extent, which results in a further possibility of variation. If a multi-stage alkanolamine extraction is selected instead of a single stage in the process according to the invention, this alternative offers further advantages with regard to efficiency and performance of the process control.

The process according to the invention furthermore improves the sugar separation by fiberization before or after the pre-hydrolysis. In addition, to improve the effectiveness of pre-hydrolysis is a two-stage pre-hydrolysis possible. Short dwell times and effective extraction of the broken down sugars also lead to less furfural formation

Continuous process control also has advantages: there is no need to displace one process liquid with another, as is necessary with classic pulping technology in stoves. The exchange and washing processes in stoves are less effective and take a relatively long time. In addition, the discriminatory power when displaced in practice is such that undesired mixing or blurred transitions occur, which means that additional effort in the recovery process is required. With a continuous process, the use of apparatus that does not have to be designed for high pressures is possible.

There is no need in conventional stoves to expel the air from the chips by means of water / steam (otherwise there is a risk that the pre-hydrolysis will not run homogeneously and evenly); because in the fibering according to the invention, such as, for example, using the technologies customary in the production of "cmp", homogeneous conditions exist. There is also no risk of acid residues remaining in the chips after the pre-hydrolysis and the washing (as is unavoidable in the conventional method) with the fiberization carried out within the scope of the invention.

Drying can be omitted if small, decentralized units work economically; this is possible with the method according to the invention. This significantly reduces the specific investment and operating costs. The process according to the invention also delivers higher yields than other chemical pulp processes; cold alkali extraction to achieve low hemicellulose residues is also not necessary.

The bleaching of the product obtained is possible, for example, with peracetic acid, which allows a subsequent acetylation without changing the solvent and represents a high cost saving. The invention is described in detail below with the aid of examples, which are not intended to restrict the teaching according to the invention. Further exemplary embodiments are obvious to the person skilled in the art in the context of the disclosure according to the invention.

Examples

The following analytical methods were used in the examples:

a. Kappa number determination / lignin content

This was done according to Zellcheming Leaflet IN / 37/80. It is titrated with 0.1 N potassium permanganate solution (3.161 g / 1). The number of ml per gram of pulp used in the titration is equal to the kappa number. The lignin content can be estimated from the kappa number by multiplying by 0.15.

b. Optical density of the MEA extract as a measure of the lignin concentration

In a 1 mm quartz cuvette, the extract diluted by a factor of 100 with MEA at the wavelength λ = 281 nm was the absorption maximum of the lignin

(cf. Fengel, Wegener "Wood", p. 159, Tab. 6-5 Extinction coefficients of lignin: for organosolvlignin, ε = 24 - 26 [1 / g * cm]) the measurement was carried out.

The extinction coefficient of ε = 26 [1 / g * cm]) was determined from the optical density at λ = 281 nm from our own measurements of UV spectra (concentration series with organosolvlignin in monoethanolamine). This was used to calculate the concentration of the lignin extracted by MEA.

c. DP determination

The DP determination was carried out using the known Cuoxam method. The procedure was as follows:

1. Pre-hydrolysis:

Without added acid:

The chips were heated in a cooker to 160 ° C with steam, then left at 160 ° C for one hour. The condensate had a pH of 4.6.

With added acid: The pre-shredded wood chips were heated in a 10 liter autoclave with the addition of sulfuric acid or hydrochloric acid to the final temperature of the pre-hydrolysis in 20-30 minutes. The mass ratio of steam to wood chips (with 50 mass% moisture) was in the range 1: 1 to 3: 1. The final temperature was between 120 ° C and 180 ° C. The residence times were a maximum of 60 minutes.

Pretreatment with ammonia:

The pre-shredded wood chips were treated in a pressure-resistant reactor with liquid ammonia under pressure at a mass ratio in the range from 0.1: 1 to 4: 1 for a few minutes at temperatures of 80 <T <125 ° C, then the contents of the Suddenly discharge the pressure reactor. The wood chips that still contain ammonia were then subjected to additional treatment.

In an alternative treatment, the pre-shredded wood chips were soaked with ammonia in the form of commercially available ammonia water (25% by mass) at room temperature, then filtered off and extracted from the ammonia water.

Example 1 (comparative example)

Crushed and pre-hydrolyzed (160 ° C, 1 hour) wood chips (40 g) were treated with liquid ammonia from the pressure reactor by sudden discharge removed and then whipped into individual fibers in a kitchen mixer. The Kappa number was found to be 142. After an alkaline extraction (8% by mass NaOH or wood chips based on oven-dry) at 90 ° C for one hour, an extensive wash with about 50 times the amount of distilled water and centrifuging in a laundry drum to a solids content of 30 - 40% the kappa number was determined to be 131.

Example 2 (comparative example)

Crushed and pre-hydrolyzed (160 ° C, 1 hour) wood chips (40 g) were boiled in a mixture consisting of liquid ammonia, monoethanolamine and water (80 g ^• 40 g: 20 g) in a drain reactor at 140 ° C, then suddenly from the Unload reactor, washed and dried. The kappa number was 143, after the alkaline extraction of example 1 the kappa number was 129.

Example 3:

Influence of pressure during extraction with monoethanolamine

10 g of shredded, pre-hydrolyzed and ammonia-exploded wood chips were extracted with 110 ml MEA for two hours once under atmospheric conditions (refluxing) and the other under the pressure in the autoclave of 3 bar at 180 ° C. The optical densities (measured at λ = 281 nm) were 0.25 and 0.55, respectively. This shows that pressure is an important parameter in the extraction.

Example 4:

Influence of the amount of extractant monoethanolamine

10 g of shredded and pre-hydrolyzed wood chips were extracted with the amounts of MEA given below for three hours under the pressure in the autoclave at 155 ° C. The results are shown in Figure 3. These show that the amount of lignin extracted does not largely depend on the amount of monoethanolamine used based on 10 g of wood chips of natural moisture (50% by mass).

Example 5:

Influence of temperature

10 g of shredded and prehydrolyzed wood chips were extracted with 110 ml of MEA for two hours under the pressure in the autoclave at various temperatures.

Table 1

Temperatures far above the boiling point of MEA (170 ° C) obviously do not bring any further increase in lignin extraction; this may be related to the decomposition of the MEA into acetaldehyde and ammonia which begins above the boiling point.

Example 6:

Influence of the extraction time

10 g of shredded and pre-hydrolyzed wood chips were extracted with 110 ml of MEA for the times indicated under the pressure at 155 ° C. which resulted in the autoclave. A duration of two hours of extraction in an autoclave appears to be necessary at 155 ° C in order to achieve stable conditions. Table 2

Example 7: Extraction with derivatives of monoethanolamine

N-methylmonoethanolamm and N, N-dimethylmonoethanolamine, have no effect on the extraction, since the nitrogen is substituted by alkyl groups.

Example 8:

Influence of the pretreatment of the wood chips

After various pretreatments, 10 g of shredded wood chips were extracted at 155 ° C. under the pressure resulting in the autoclave. It turned out that the pretreatment has a great influence on the extraction result.

a) With 110 ml MEA, duration 3 hours

Table 3

b) With 30 ml MEA and three hours duration

Table 4

c) With 110 ml MEA, duration 1 hour

Table 5

The lignin extraction is therefore significantly improved if an ammonia explosion has occurred. On the other hand, adding MEA with the ammonia to the chips before the explosion does not have a positive effect on the NH ₃ explosion without adding MEA. Example 9:

Influence of multiple extraction treatments on the same sample

This is intended to demonstrate the efficiency of the extraction treatment. 10 g of shredded and prehydrolyzed wood chips were extracted at 155 ° C. under the pressure resulting in the autoclave.

Table 6

The wood chips had already largely lost the lignin in the first run.

Table 7

Even with a small amount of MEA, the lignin content can be reduced to less than 10% of the original (comparison of the optical densities) in the first pass. Table 8

Even with an extraction time of only 45 minutes and a small amount of monoethanolamine, the lignin content can be gradually reduced.

Example 10:

Continuous extraction

The results of the continuous extraction are explained on the basis of FIG.

The cumulative extracted amounts of lignin, expressed in% of the absolute lignin content, are plotted for row 1 (100 ° C.), row 2 (140 ° C.) and row 3 (170 ° C.). The extraction rate is about 45 ml per hour. Crushed and prehydrolyzed wood chips (40 g) were used.

The apparatus used is a pressure-resistant chromatography column that was filled with the wood chips. This was brought to the specified temperatures using electric heating tapes; the temperatures were kept constant by an electronic control. The monoethanolamine was preheated and pumped through the wood chips using a high pressure pump (HPLC). Fractions of 25 ml each were collected, of which the optical densities were measured after being diluted by a factor of 100.

In FIG. 4, the relative percentage of lignin extracted from the wood is plotted on the ordinate. Here, 100% of extracted lignin corresponds to the amount of lignin originally contained in the wood. When using 40 g of wood with a moisture content of 50% by mass, the proportion of wood is 20 g. With a lignin content of 22% by mass typical for beech wood, 4.4 g of lignin are contained. This 4.4 g of lignin corresponds to the ordinate value of 100 in FIG. 4, ie all the lignin contained in the wood has been extracted. The same applies to smaller ordinate values:

Table 9

* absolute percentage of the lignin contained in the wood

** the kappa number is a standard used in the pulp industry; it is calculated from the absolute lignin content by going through it

0, 15 divided.

It is therefore given here, by way of example, for row 2 in FIG. 4, that is to say the dark column, that in the fourth fraction the dark column reaches almost 80%. Since the ordinate shows the amount of extracted lignin as a percentage of the original lignin content of the wood, it follows that after the 4th fraction only 20% of the lignin originally contained in the wood has not yet been extracted. As is extracted at an extraction rate of 45 ml / hour and each fraction

25 ml, it can be seen that after 4 fractions = 100 ml extract the extraction time was a little over 2 hours. Example 11:

The method according to the invention was carried out with Eucalypms Urograndis. The following determinations were carried out:

a) Cellulose yield and xylose content for Eucalyptus Urograndis:

Table 10

* H.Sixta, A. Borgards, "Das Papier" 4 (1999), pp. 220 ff.

b) Xylose content and DP for Eucalyptus Urograndis:

Table 11

c) Acetic acid retention:

Table 12

d) The X-ray diffraction diagram obtained can be seen from FIG. 5. The peaks found were as follows:

Table 13

Underground = 47.7 + 2.61 * 20 Table 14

Peak 1: 20 = 15,540 ° ß = 3,885 ° INT = 304 c / s = 69%

Peak 2: 20 = 20.901 ° ß = 7.808 ° INT = 204 c / s = 93%

Peak 3: 20 = 22.266 ° ß = 2.418 ° INT = 707 c / s = 100%

Peak 4: 20 = 34,372 ° ß = 2,668 ° INT = 72 c / s = 11%

Example 12:

Pre-hydrolysis of Eucalypms

A pre-hydrolysis of eucalyptus was carried out using the method according to the invention. Table 15 below shows a mass balance taking into account the influence of size reduction by a disc refiner:

Table 15

= not detectable

+ = below the detection limit (0.3 mg / 100 mg) Example 13:

Influence of pretreatment with ammonia water

a) For the pretreatment at room temperature for 30 minutes, 25% ammonia water was used in an amount such that 7 g of pure NH 2 were added to 30 g of beech chips with a water content of 70% by mass. The lignin was extracted from the wood chips impregnated with the ammonia water using 60 g of MEA at 140 ° C. over a period of two hours. A kappa number of 10 was obtained.

b) The comparison test (without impregnation) gave a kappa number of 18 under otherwise identical test conditions.

The influence of the temperature on the lignin extraction using MEA with and without pretreatment by ammonia water is shown in FIG. 6.

It becomes clear that the kappa number can be reduced after a previous treatment with ammonia water at the same extraction temperature. To achieve a certain kappa number, one can work with appropriate pretreatment at an extraction temperature approx. 15 to 20 ° C lower. From the extrapolation of the curves kappa = f (extraction temperature) towards lower temperatures it can be seen that the extraction temperature could be reduced to 100 to 110 ° C by impregnation with ammonia water. A low extraction temperature means that side reactions also take place to a lesser extent. The ratio of the activation energies of the extraction with / without pretreatment with / without ammonia water can be determined from the inclinations of the straight line ln (kappa) vs. Determine 1 / T as 0.87.

Example 14:

Influence of a multi-stage extraction

When using the same total amount of monoethanolamine for the lignin extraction, the lowering of the kappa number is greater if the monoetha- nolamine amount is divided into two successive extractions. This is shown in FIG. 7, in which the kappa number of eucalyptus pulp is shown after one- and two-stage extraction with monoethanolamine (30-1 stove; T = 160 ° C., ti. Stage = 90 min, ü.s-stage = 120 min) .

Example 15:

Influence of the pressure prevailing during the extraction:

This is shown in FIG. 8, the kappa number of eucalyptus pulp being shown after two-stage extraction with monoethanolamine (parameters: with and without pressure, laboratory autoclave, T = 160 ° C., t = 2x60 min).

Example 16:

Influence of water content during the MEA extraction of the lignin:

With a mass ratio of MEA / water = 4.9 / 1 and a wood moisture content of 50% (total water content in the system during the extraction ~ 17%), there is no difference for extraction conditions of 2 mouths at 160 ° C compared to an extraction of these wood chips with pure MEA (Total water content in the system during the extraction ~ 8%) found. In contrast, the extraction effect diminishes when the mass ratio of MEA / water = 2.6 / 1 (total water content in the system during the extraction ~ 26%).

Example 17: Influence of the hemicellulose content on the extractability of the lignin

The degree of pre-hydrolysis was very different for the substances previously used for MEA extraction. The residual hemicellulose content accordingly varied from 1.5 to 16% by mass. A noticeable influence on the extractability of the lignin by monoethanolamine could not be found. Example 18:

The yield in the course of the process steps "pre-hydrolysis - washing - MEA extraction - washing"'is significantly higher using the same wood type than with conventional pulping processes and also higher than with newer pulping methods. Eucalypms pulping with a lower xylose content (acetate grade) can be achieved with a much higher yield than with a modern pre-hydrolysis-sulfate process, as shown in the following table:

Table 16

4--

*): Composition of eucalyptus (O. Kordsachia, R. Patt, H. Sixta Das Papier 2 (1999). 96: 52% cellulose, 20% gliicuronoxylan, 2% gluconianiian and 23% lignin **): for example Bacell Process ( H. Sixta, A. Borgard's "Das Papier" 4 (1999), p. 220 ff.)

Example 19:

Variation of the pre-hydrolysis conditions

Depending on the type of wood, the pre-hydrolysis conditions (heating-up time, duration, temperamr, type and concentration of acid) can be adjusted in order to achieve the desired residual hemicellulose content. The following table shows the status achieved in autoclave tests in the laboratory (heating-up time approx. 30 minutes):

Table 17

Acetic acid is not sufficient for the complete pre-hydrolysis of hemicellulose in beech wood. A hemicellulose content of ~ 3% by mass can be achieved for beech chips without the addition of acid in the pre-hydrolysis. The mannose content under these conditions is <1%. The α-cellulose content is thus> 96%, which is sufficient for chemical pulp - except for acetylating cellulose. However, the low xylose content <2% by mass required for acetylation pulp could be achieved in beech wood with sharper digestion conditions and in eucalyptus with less harsh conditions. A deterioration in the target sizes when switching to original size wood chips was not found. The results were even better in larger autoclaves. Example 20:

A pre-hydrolysis was carried out, the hydrolysis temperature being modified as shown in FIG. 9. It can be seen from FIG. 9 that the residual xylose content can be significantly reduced with increasing sulfuric acid concentration.

Example 21: Straw as biomass

Straw was roughly crushed with scissors and prehydrolyzed with water at a liquor ratio of 10: 1 in a small laboratory autoclave (capacity 300 ml) at a temperature of 170 ° C and a pressure of about 7 bar, which took about 30 minutes to heat up Minutes and a holding time of 120 min. After removal of the pre-hydrolyzate and after a water rinse, MEA was added to the moist pre-hydrolyzed straw in a ratio of 1: 6.5. The mixture was heated again to 160 ° C. for 30 minutes and held at this temperature and a pressure of 3 bar for three hours.

As a result, the analysis showed the following composition: cellulose (as glucose) 93.7%

Xylose 6.1%

Mannose 0.2%

The yield was 40%, the whiteness 50%.

Example 22:

Example 21 was repeated, but there was no prehydrolysis. The whiteness obtained was 22%. Example 23:

An experiment was carried out with the autoclave open to the atmosphere. For this purpose, shredded straw was directly subjected to an MEA extraction. The conditions were 160 ° C, liquor ratio 10: 1 = MEA / straw and 180 minutes cooking time. Contrary to expectations, no unpleasant smell developed during the cooking of the non-pre-hydrolyzed straw with MEA, nor did steam escape from the autoclave. The whiteness was 29%.

Example 24:

The products obtained from the preceding examples were each examined for by-products of the monoethanolamine. It was found that the by-products of monoethanolamine, such as N-methyl-monoethanolamine, N, N-dimethyl-monoethanolamine, N-acetyl-monoethanolamine and N-formyl-monoethanolamine, did not occur or were used in one case of N-methyl-monoethanolamine was only present in a proportion of 0.3% (based on the analyzed MEA-lignin extract). So-called head space gas chromatography was used as the analysis method.

* * *

Claims

claims

1. Process for the separation of lignocellulose-containing biomass, in particular of

Wood, in the essential components in the form of lignin, hemicellulose and cellulose, with the following steps: a) pre-hydrolyzing the lignocellulose-containing biomass by treatment with water or steam; b) extracting the hydrolyzed hemicellulose formed by prehydrolyzing with an aqueous medium; c) extracting the process-modified lignin remaining in the residue with an alkanolamine, isolating the lignin, recovering the alkanolamine, the alkanolamine not being substituted by alkyl groups on the nitrogen, and d) obtaining a cellulose raw material.

2. The method according to claim 1, characterized in that the pre-hydrolysis according to step a) is carried out only to such an extent that the acids bound to hemicelluloses can be split off, and according to step b) the split-off acids are washed out.

3. The method according to claim 1 or 2, characterized in that shredded or shredded wood, in particular hardwood, beech or softwood, is used as lignocellulose-containing biomass.

4. The method according to at least one of claims 1 to 3, characterized in that cereal straw is used as biomass.

5. The method according to claim 4, characterized in that without pre-hydrolysis according to step a) and b) immediately an extraction according to step c) with increased Temperamr below about 170 ° C, preferably below about 160 ° C, in particular at about 115 to 135 ° C is carried out to obtain paper pulp.

6. The method according to claim 4, characterized in that at about 150 to 190 ° C, in particular about 170 ° C, pre-hydrolyzed and then an extraction according to

Step c) is carried out at an elevated temperature below approximately 170 ° C., preferably below approximately 160 ° C., in particular at approximately 115 to 135 ° C., in order to obtain chemical pulp.

7. The method according to at least one of the preceding claims, characterized in that the prehydrolyzed lignocellulose-containing biomass is mechanically fiberized before step b) is carried out.

8. The method according to at least one of the preceding claims, characterized in that an additional acidic or alkaline pretreatment is carried out before the steam treatment of step a).

9. The method according to at least one of the preceding claims, characterized in that the pre-hydrolysis according to step a) is carried out in the form of a steam explosion or a steam refining process.

10. The method according to at least one of the preceding claims, characterized in that after step b) (a) solvent for lignin is (is) added.

11. The method according to at least one of the preceding claims, characterized in that the mass ratio of water to biomass (based on dry matter) to about 3: 1 to 10: 1, in particular 6: 1, and the mass ratio of water vapor to biomass to about 1 : 1 to 3: 1 is set.

12. The method according to at least one of the preceding claims, characterized in that the water is pressed before step b) from the mass obtained and this is then mechanically fiberized.

13. The method according to claim 12, characterized in that the frayed

The mass is also washed with hot water.

14. The method according to at least one of the preceding claims, characterized in that after step b) an additional treatment with aqueous ammonia solution, with ammonia gas or with liquid ammonia is carried out.

15. The method according to claim 14, characterized in that one works with liquid ammonia at an increased outlet pressure compared to atmospheric pressure.

16. The method according to claim 15, characterized in that the mass obtained is still hot from the previous steam treatment and washing and with the liquid ammonia the volume available to the treated, hemicellulose-free mass by relaxing while lowering the pressure by at least 5 bar is increased explosively.

17. The method according to claim 16, characterized in that the mass ratio of liquid ammonia to the mass to be treated (based on dry matter) is set to about 0.1: 1 to 4: 1.

18. The method according to at least one of the preceding claims, characterized in that in step c) at least two successive extractions are carried out with alkanolamine.

19. The method according to at least one of the preceding claims, characterized in that the extraction is carried out for at least about 1 hour at a temperature of about 80 to 220 ° C.

20. The method according to at least one of the preceding claims, characterized in that the extractant is preheated in step c), in particular to at least about 80 ° C.

21. The method according to at least one of the preceding claims, characterized in that monoethanolamine is used as the extraction agent.

22. The method according to at least one of the preceding claims, characterized in that after extraction of the residues adhering to the raw pulp in one

Process-modified lignin dissolved in alkanolamine can be completely removed by a solvent.

23. The method according to claim 22, characterized in that the residue of process-modified lignin and alkanolamine in the raw pulp is removed with the solvent by washing or countercurrent washing and then the solvent is separated by distillation of lignin and the extracting agent alkanolamine and recovered for reuse can be.

24. The method according to at least one of the preceding claims, characterized in that the removal of the alkanolamine with the process-modified lignin dissolved therein from the raw pulp is carried out by pressing or centrifuging.

25. The method according to at least one of the preceding claims, characterized in that the process-modified lignin is precipitated from the alkanolamine by adding a non-solvent and is separated off by solid / liquid separation processes.

26. The method according to claim 25, characterized in that the precipitated lignin is separated from the alkanolamine by filtration or centrifugation.

27. The method according to claim 25, characterized in that the process-modified lignin is separated from the alkanolamine in a thin-film evaporator or by a membrane process.

* * *