EP2844796A1

EP2844796A1 - Method for producing pulp having low lignin content from lignocellulosic material

Info

Publication number: EP2844796A1
Application number: EP13723025.6A
Authority: EP
Inventors: Alexander DYBOV; Florian Boeck
Original assignee: Annikki GmbH
Current assignee: Annikki GmbH
Priority date: 2012-05-03
Filing date: 2013-04-24
Publication date: 2015-03-11
Anticipated expiration: 2033-04-24
Also published as: EP2844796B1; WO2013164234A1; AR091998A1; US20150122429A1

Abstract

The invention relates to a method for obtaining pulp having low lignin content, characterized by a combination of the measures in which a) lignocellulosic material is treated with an aqueous solution, which contains a C_1-6 alcohol and has a pH value of 10 to 14, at a temperature below 100°C, whereupon the aqueous solution, in which lignin that was cleaved from the lignocellulose is dissolved, is separated from the solid, which is a material enriched with cellulose and hemicellulose, b) hemicellulose is removed from the material enriched with cellulose and hemicellulose from a), c) the material obtained in b), which is depleted of hemicellulose, is treated in aqueous alkaline solution with an alkali, alkaline-earth, or ammonium sulfite, in particular Na₂SO₃, and/or with oxygen, wherein lignin goes into solution and pulp having low lignin content is obtained; and pulp that can be produced by means of the method.

Description

Process for the production of low lignin pulp from lignocellulosic material

The present invention relates to a process for the production of low lignin pulp from lignocellulosic material.

The conversion of lignocellulose can be done in two fundamentally different ways:

1) With the help of the so-called "Thermochemical Platform", in which the lignocellulose is first gasified and the synthesis gases are converted to desired products, and

2) with the aid of the so-called "Sugar Platform", in which the main interest in the use of the bound in the polymers cellulose and hemicellulose sugars,

or in the use of the polymers themselves.

The present invention follows the second route: The polymeric components (cellulose and lignin) are to be separated from lignocellulose, with as few changes as possible in the said components after the separation process.

In classical wood pulping pulps, unselective pulping processes are generally used in which lignin and xylan are simultaneously removed at high temperatures in the presence of sulfur-containing reagents from the

Lignocellulosematerial be removed. The removed lignin is greatly altered in its structure by ring condensation and attack of the sulfur-containing reagents and can usually be used only as a fuel. In addition, high temperature processes can lead to the formation of heterocyclic substances (e.g., furfural) from sugars, requiring elaborate recycling processes.

A technological improvement in this area would be the development of

Low-temperature process (ie at a temperature of below 100 ° C and below), all substances are obtained in the highest possible purity and the material yield is maximized. This would mean a significant advance, since lignocellulosic material in successive digestions at low temperatures (<100 ° C) separated into the individual pure substance classes lignin, xylan and pulp and then to

higher value products can be implemented. In addition, such processes can be an energetically economical process due to the low temperatures.

Various processes for producing delignified pulp are known in the literature. The following describes those methods that have found industrial application, namely, "soda pulping processes", "force pulping processes", and "sulfite pulping processes." Many examples and Detailed descriptions of the techniques can be found in the Handbook for Pulp & Paper Technologies, 2nd Edition, GA Smook, Angus Wilde Publications (1992). Here, the prior art will be described in terms of publications which each represent the most recent improvements and modifications of said processes.

To the "soda process"

The soda process was developed in 1851 by Burgess and Watts and dispenses with the use of environmentally hazardous sulfur compounds. Only sodium hydroxide is used as the digestive chemical, which is why the process must be carried out for sufficient delignification at high temperatures. In comparison with other processes, a high degradation of carbohydrates takes place, so that a lower degree of polymerization and a lower tear strength in the cellulose is obtained. In addition, the method is only suitable for slightly bleachable materials. In some cases, anthraquinone is added to stabilize carbohydrates and for better delignification (soda-anthraquinone method).

US 6,946,057 B2 describes an environmentally friendly process in which

lignocellulosic material in several stages with an alkaline buffer solution containing Metaborate and sodium carbonate as main components. The process is carried out at a temperature of 160 ° C. A major aspect of the process described in the patent is effective recovery of the digestion chemicals. From US 3,954,553 a process is known in which hardwood is treated with an alkaline solution containing sodium hydroxide and sodium carbonate at a temperature of 340 ° F to 376 ° F (from 171 ° C to 191 ° C) for one hour. The combination of the two chemicals describes efficiencies and selectivities comparable to those of Kraft processes.

The soda process offers a way to obtain lignin without or with very low sulfur content compared to the kraft process. In order to obtain the same delignification effect as in the force process, however, the lignin removal must be at even higher

Temperatures are performed as in the Kraft process, whereby more condensed lignin is obtained. In addition, when carbohydrates are heated at soda-process temperatures, heterocyclic substances such as furfural are formed, which must be separated in a complicated manner.

The "sulphite process"

The sulfite process was first patented by Benjamin Tilghman in 1867. The first industrial process using this process started in 1874 in Sweden. In this process, mixtures of various salts of sulfurous acid are usually added as active reagents. The most widespread are the calcium and

Magnesium salts. By suitable choice of counterions, the process can be operated from the strongly acidic to the basic environment. A two-step combination of both has also proven useful in some cases. Classic methods work in strongly acidic (calcium, pH = l-2) or weakly acidic (magnesium, pH = 3-4) medium. The sulfite chemically modifies the lignin and makes it more soluble in water. Due to the environmental harmfulness of the process, it has today a minor importance, but is often used for the production of chemical pulp, since this easily bleachable cellulose is produced.

In US 8,038,842 a method for the fractionation of lignocellulosic material in cellulose, hemicellulose and lignin is described. In this case, in a continuous or stepwise process, a treatment with a vaporous mixture of aliphatic alcohol, S0 ₂ , ammonia and water, wherein the concentration of S0 ₂ between 10 parts by weight and 50 parts by weight in the solution. After direct contact of said vaporous mixture with lignocellulosic material for between 5 minutes and 3 hours at a temperature between 115 ° C and 150 ° C, a mixture of cellulose, hemicellulose and lignin is formed, from which cellulose can be removed.

From US 3,630,832 a controlled process for sulfite pulp production is known wherein the use of sodium sulfide is avoided. The process is carried out at a temperature above 145 ° C and a pH between 8 and 11. By means of online analytics, the pH value is monitored and readjusted accordingly.

From EP 1 375 734 a process for the production of cellulose is known wherein lignocellulosic material is treated with magnesium bisulfite, optionally with SO ₂ excess, at a temperature between 130 ° C and 165 ° C to remove lignin. The method also includes a combination with a bleaching sequence after removal of the lignin, which is performed exclusively with chlorine-free reagents.

DE 103 23 376 describes a process for delignifying lignocellulosic raw materials, wherein the lignin is removed by using sulfites in the presence of an alkaline component, in particular sodium hydroxide or sodium carbonate, or a mixture thereof, in aqueous solution using elevated temperature and elevated pressure , At the beginning of a digestion aqueous sulfite solution is used and the temperature is increased up to the maximum reaction temperature. The alkaline component is added only after the beginning of the digestion.

Although both the molecular mass of cellulose is largely retained in these sulfite processes, and a lignin degradation is avoided, they have the great disadvantage that the lignin obtained may contain a sulfur content of about 5% (S. Brudin, P. Schoenmaker, J. Sep. Sci. 2010, 33, 439-452), what its possible

Restricts applications very much. The "kraft process"

The Kraft process was developed by Carl Ferdinand Dahl in Gdansk in 1884 (see, for example, US 296,935) and involves a process of leaching lignin from the pulp using a mixture of sodium sulfate, sodium carbonate, sodium hydroxide and sodium sulfide under an overpressure of 5 to 14 atmospheres. The lignin is obtained as a soluble alkali metal in the black liquor and has a high sulfur content. Lignin by force process contains between 1.5 and 3.0% sulfur (Marton J. "Lignins;

Occurrence, formation, structure and reactions ", 1971, Wiley-Interscience, Eds. Sarkanen KV and Ludwig CH, USA, p 666) It is burned in most cases as an energy source for generating the heat demand for the process currently represents the most common process for the production of paper pulp.

US 2011/0073264 A1 discloses a method for increasing kraft pulp yield and increasing the viscosity of the resulting pulp. This is achieved by pre-treating lignocellulosic material with hot water or steam at a temperature of 160 ° C. Remaining lignin is then removed by treatment with Na ₂ S and NaOH under force conditions.

In US 2011/0067829 AI an optimization of the power process is described, in which the sulfur concentration is kept constant by an optimized process for chemical recirculation during the pulping.

From US 6,613,192 Bl a modification of the force process is known in which

Eucalyptus shavings are fermented by inoculation with white rot fungi, whereby lignin is modified and thus more readily degradable in the process force.

From US 7,824,521 B2 an optimization of the force process is known, wherein

lignocellulosic material with aqueous solution containing another base is treated to extract acidic material from lignocellulosic material. This extracts a fraction of the hemicellulose, making the actual force process more effective. From US 7,520,958 B2, a method of producing a modified pulp is known wherein wood chips are treated with peroxides in an acidic solution to remove 5-20% of the hemicellulose. With this pretreated wood, a kraft pulp can be produced which contains only between 5% and 9% hemicellulose in dry matter.

In US 6,153,052 A and US 7,828,930 B2 improved pulp processes are described in which polysulfides are used, whereby the yield of the pulp can be increased. The polysulfides act primarily as reducing agents that inhibit unwanted "peeling" - reactions.

In US 7 828 930 B2 and US 6 143 130 a modified method of the Kraft process is described wherein polysulfides are used as active delignification component. This procedure results in a higher yield of pulp and allows lignin to be removed at lower temperatures (100 ° C to 160 ° C) than in the classical kraft process.

From EP 0 468 016 a process for kraft pulp production is known, wherein

Lignocellulosic material is pretreated with loaded cooking liquor at a temperature between 20 ° C and 100 ° C. The pretreated lignocellulosic material is heated at a temperature between 135 ° C and 155 ° C and delignified.

No. 6,576,084 B1 discloses a process for increasing the yield and viscosity of the pulp. The technique is based on the pretreatment of lignocellulosic material with anthraquinone or polysulfides at a temperature of 80 ° C to 130 ° C. By this measure, a decomposition of cellulose is avoided. Subsequently, the pretreated material is reacted with cooking liquor at a temperature of more than 130 ° C.

An advantage of the Kraft process described above is the relatively easy way to produce delignified, readily further bleachable cellulose. A major disadvantage of this is that the potentially high-quality lignin is suitable for further application only limited, since it is separated from the other raw material components by

High-temperature condensation reactions is greatly altered in its structure. In addition, the lignin is strongly modified with sulfur by the reaction with sulfide. Other delignification methods

As relatively new concepts, organosolv processes have recently been taken up again. These were first described in the 1970s. At that time were

Strategies for "extended cooking" based essentially on increasing the degree of delignification and reducing bleaching have been used as solvents, predominantly alcohols, such as ethanol or methanol, which should primarily increase the solubility of lignin, while being the actual digestion chemicals acids, alkalis, sulphite or sulphide or oxidative reagents (H.

Hergert, 1998, Developments in organosolv pulping; In: R.A. Young and M. Akhtar, Environmental Friendly Technologies for the pulp and paper industry; John Wiley & Sons Inc., New York, 5-68).

Fundamentally, organosolv processes can be subdivided into acidic and basic variants. An acidic process is e.g. The Allcell process, which was acquired and further developed by LIGNOL (C. Arato, E.K. Pye, G. Gjennestad, 2005, The Lignol approach to biorefining of woody biomass to produce ethanol and chemicals; Appl. Biochem.

Biotechnol., Vol. 121-124, p. 871-882). Wood, straw or bagasse are used as substrates. The underlying chemical reaction is the autohydrolytic cleavage of hemicelluose at a pH of 2.0 to 3.8, which results from the cleaved by xylan acetic acid (conditions: 180 ° C to 195 ° C, ethanol concentration: 35 wt. % to 70% by weight, liquid to solid ratio: from 4: 1 to 10: 1, reaction time 30 to 90 minutes). This is partly cellulose in the form of insoluble

Oligosaccharides and much of the hemicellulose to soluble oligo- and

Cleaved monosaccharides. Part of the pentoses is oxidized to furfural under the reaction conditions. Lignin is also partially hydrolyzed and falls together with the other degradation products in the cooking liquor, from which the degradation products are then recovered. The other, unhydrolyzed part, remains in the solid and can, for example, be hydrolyzed enzymatically to sugars and fermented to ethanol. The lignin remaining in the solid (20% to 25% of the original) falls as

Fermentation residue on and can only be burned. It can be said that in acidic processes, on the one hand, the amount of lignin obtained is relatively low and lignin degradation can not be decoupled from hemicellulose degradation. Due to the relatively poor lignin degradation results in a pulp with a residual lignin content, which would require a considerable bleaching effort in the case of use as a chemical raw material and is unsuitable for this use. It is therefore primarily intended to be used as a raw material for the production of bio-alcohol, although there are reports which show that the accessibility of the residual lignin in the pulp is relatively high (EK Pye, JH Lora, 1991, The All Cell Process - A Proven Alternative to Kraft Pulping, TAPPI Journal March 1991, 113-117).

In the past, basic organosolv processes have been investigated much less than acid, since high technical requirements for the recovery of caustic soda are required for high sodium hydroxide use, especially when using straw as substrate (Marton & Granzow 1982, Use of ethanol in alkaline pulping WO82 / 01568).

In Germany, the organocell process for pulp cooking was developed in industrial applications until the 1990s (N. Zier, 1996, Structural Characteristics of Organosolv Lignin with Variation of Parameters, Dissertation, Dresden University of Technology). The process is carried out in two stages, starting with an alcohol-water impregnation (ratio: 3 parts alcohol: 7 parts water) at 110 ° C to 140 ° C and subsequent boiling at 165 ° C to 170 ° C with the addition of 30% sodium hydroxide solution and 0.1% anthraquinone, based on the dry weight of the substrate. The process is suitable for the decomposition of deciduous and coniferous wood, as well as for annual plants. The pulp quality is comparable to kraft pulp and bleached with chlorine-free oxygen. According to various sources, the plant was closed soon after commissioning due to technical problems related in part to the recovery of the high level of caustic soda (El-Sakhawy et al., 1996: Organosolv pulping, (3), ethanol pulping of wheat straw Cellul Chem., Technol. 30, 281-296).

For a profitable biorefinery process that is not based on the extraction of bio-alcohol, but the use of all the main components of lignocellulose as a chemical or Material raw material, the extraction of the highest possible proportion of the existing lignin is required. This should be in a consistent product stream with low

Contaminated by degradation products from other components.

WO 2011/014894 and WO 2012/027767 describe low-temperature processes for

Separation of the said lignin from lignocellulosic material such as straw, bagasse, energy grasses and or husks known. The digestion process sees one

Low-temperature process for delignification at below 100 ° C, after which the resulting enriched with cellulose and hemicellulose material with at least one

carbohydrate-cleaving enzyme can be treated. One variant is the use of xylanases, which selectively degrades xylan and strongly with cellulose

enriched material is formed. A disadvantage of such a low-temperature process is, compared to pulp from kraft or soda processes, high lignin content in the cellulose.

Xylanabtrennung

WO 2010/124312 describes a method for the separation of hemicellulose from a material enriched with hemicellulose and cellulose, which is produced according to WO 2011/014894. This is the, obtained after digestion

Suspended solid mixture in an acetate buffer and treated with xylanases to selectively depolymerize hemicellose and bring into solution. The highly cellulose-enriched solid obtained after separation can then be used to obtain glucose, for example by reaction with cellulases.

A chemical method for xylan separation from kraft pulp for the production of

Chemical pulp is described in WO 2005/118923 Al. In this case, the pulp obtained is treated with an at least 5%, preferably 9%, sodium hydroxide solution at a temperature of less than 25 ° C. The obtained xylanhhaltige solution can, as in US 2010/0021975 AI concentrated by nanofiltration and precipitated by the addition of mineral acid. As described in AT 503 624, the addition of a monohydric or polyhydric alcohol can promote this precipitation. Removal of (residual) lignin

For the removal of lignin, or for the cleavage of lignin are from the literature

For example, the following methods are known:

EP 1 025 305 discloses a chemical process for lignin depolymerization. It relies on the catalytic action of complexed copper in conjunction with hydrogen peroxide or organic hydroperoxides and is capable of lignin

To cleave temperatures below 100 ° C oxidatively. The complexing agents used are pyridine derivatives. Synthetic lignin models have been used to demonstrate that when von ₂ 0 _{2 is used} as the oxidant, a cleavage occurs in the propyl side chain of the lignin molecule, causing the lignin polymer to break down into oligomeric subunits. When using the copper system with hydroperoxides, it is possible to delignify wood. The system based on H ₂ 0 ₂ seems technically better to implement. It was tested as a bleaching additive in the peroxide bleaching of kraft pulp and resulted in an improved degree of delignification. A disadvantage of such a system is the high consumption of high-priced reagents, such as H ₂ 0 ₂ or pyridine derivatives and the structural change of the lignin.

US Pat. No. 4,560,437 describes that wood pulp may be subjected to a second digestion with sodium sulphite addition before the actual bleaching process, whereby the effectiveness of the following bleaching steps, in particular oxygen bleaching, should be increased and thus costs for bleaching chemicals should be saved. Best results could be achieved using 25 to 30 kg S0 ₂ (in the form of sodium sulfite) per tonne of the unbleached pulp at pH 8.

In addition, "Oxidation of Lignin Using Aqueous Polyoxometalates in the Presence of Alcohols" (ChemSusChem 2008, 1, 763-769) describes that the delignifying effect of polyoxometalates under an oxygen atmosphere in the presence of aliphatic alcohols can be significantly increased. that in the catalytic cycle alkoxy radicals are formed which initiate the lignin cleavage. EP 0 524 127 describes in detail the effect of ethanol as an additive in the oxygen bleaching of pulp. By adding catalytic amounts of ethanol it is shown that the delignification efficiency and selectivity

can be increased equally.

It is also described in US Pat. No. 5,609,723 that a higher efficiency of oxygen bleaching can be achieved with a constant pulp viscosity when polyhydric alcohols are added to the bleaching solution. From US 6,923,887 is also known that the efficiency of the peroxide bleach by the addition of an organic solvent, preferably a Ci-2-alcohol, can be increased.

US 4,004,967 also reports increased bleach selectivity of kraft pulp by the addition of polyols or monohydric alcohols. However, best effects were achieved with the addition of formaldehyde.

In all the methods described, the sole criterion considered is the quality of the cellulose. It is neglected that lignin is also a valuable raw material component.

In contrast to the processes described, it is an object of the present invention to provide a process in which, in addition to isolated lignin, a high cellulosic, low lignin content material (kappa <10) can be obtained without substantial depolymerization of the cellulose.

In one aspect, the present invention provides a process for recovering low lignin pulp, characterized by a combination of the measures

a) lignocellulosic material with an aqueous solution containing a Ci-6-alcohol and having a pH of 10 to 14, is treated at a temperature below 100 ° C, after which the aqueous solution, in the lignin, from the Lignocellulose was cleaved, is present from the solid, the one with cellulose and

Hemicellulose enriched material is separated, b) hemicellulose is removed from the cellulosic and hemicellulose-enriched material from a),

c) the material obtained in b), which has been depleted in hemicellulose, in aqueous

alkaline solution with an alkali, alkaline earth or ammonium sulfite such as Na ₂ S0 ₃ and / or with oxygen, whereby lignin goes into solution and pulp with a low lignin content is obtained.

A method provided in accordance with the present invention is also referred to herein as the "method of (in accordance with) the present invention."

In a process of the present invention, lignin-containing organic material is used as the lignocellulosic material, e.g. Annual plants, such as (dry) grasses, or parts of grasses, preferably grasses, straw, energy grasses, such. B.

Switchgrass, elephant grass or abaca, sisal, bagasse, or atypical

Lignocellulosic substrates such as husks, e.g. Lemmas such as rice husks, more preferably straw, energy grasses bagasse or husks, even more preferably straw or bagasse, e.g. Straw, such as wheat straw.

In a process according to the present invention, the solids content at the beginning of the delignification process according to measure a) is preferably 3 to 30% by weight

lignocellulosic material in the aqueous solution, and is preferably in a consistency of 3 to 30 parts by weight, especially 5 to 20 wt. Before.

In a process according to the present invention, the alcohol used is preferably an aliphatic alcohol, such as a C 1-6 -alcohol, more preferably a C 1-4 -alcohol, such as ethanol or isopropanol, according to measure a) lignin of

Separate lignocellulosic material.

In a process according to the present invention, the pH of the solution according to measure a) can be adjusted with a base, preferably an inorganic base, for example a hydroxide, such as sodium hydroxide solution, potassium hydroxide solution. The lignin digestion according to measure a) in a process according to the present invention is carried out at a temperature of below 100.degree. C., preferably from 40.degree. C. to 90.degree. C., more preferably from 50.degree. C. to 70.degree. It has been found that when using temperatures of more than 100 ° C increased condensation products of lignin occur, for example, condensed, phenolic fragments of the formulas

diphenylmethanes formed by ring condensation reactions. It was found by 2D NMR study that the content of such fragments in lignin isolated according to the present invention is surprisingly much lower than in comparative lignins prepared by high temperature extraction, as shown in Table 1 below:

Table 1

Condensed phenolic fragments in lignin,

Lignin mmol / g

Diphenylmethane 4-0-5 5-5 Total

Lignin obtained after the procedure

according to the present invention 0.02 0.06 0.10 0.18

Soda lignin from wheat straw 0,04 0,09 0,12 0,25

Sarkand Grass soda lignin 0.36 0.21 0.28 0.84

Agricultural fiber soda lignin 0.40 0.25 0.31 0.96

Hardwood organosolv lignin 0.45 0.25 0.27 0.97 In addition, no sulfur-containing reagents must be used in the digestion process according to measure a), so that according to the method according to present

Invention isolated lignin is free of sulfur from sulfur-containing reagents.

In one aspect, the present invention is based on the finding that less strongly condensed lignin is obtained from a lignocellulosic material treated with an aqueous basic solution which comprises an alcohol, in particular a C 1-6 -alcohol and a pH of 10 to 14 can be. In addition, the treated cellulosic and hemicellulose enriched material proves to be a more useful material for enzymatic degradation to carbohydrate cleavage products.

An advantage of the method according to the present invention is that in that

Hemicellulose has a low solubility at higher alcohol concentrations, a selective isolation of pure lignin is possible. Hemicellulose can be in one

Following step (b) of cellulose and hemicellulose-enriched lignocellulosic material as a pure product.

In a process of the present invention about 59% to 92% of the total lignin can be removed. This allows for further enzymatic conversion to separate hemicellulose, preferably xylan, from cellulose. Alternatively, and in one aspect of the present invention, hemicellulose can be separated by a combination of chemical and enzymatic treatment to give as pure a dexylanated as possible

To obtain cellulose.

However, a predominant enzymatic degradation of xylan has been found to be less effective, since the sugars of lignocellulose are present in tightly crosslinked, polymeric, crystalline structures of cellulose and hemicellulose, in addition to a

Ligninmantel are covered, resulting in an extremely dense complex. Direct access to the individual polymer classes is made more difficult. The enzymes, due to their high molecular weight, are unable to penetrate through the narrow pores in the lignocellulose. This means that a first step must be taken, which increases the porosity of the lignocellulose and thereby enables further enzymatic conversion. The depletion and optionally isolation of the hemicellulose in a process according to the present invention according to measure b) can be carried out chemically or enzymatically.

In a further aspect, the present invention provides a method according to the present invention in which according to measure b) either

Hemicellulose from the cellulosic and hemicellulose-enriched material from a) is brought into solution by treatment with at least one carbohydrate-splitting enzyme, or

Hemicellulose from the cellulosic and hemicellulose-enriched material from a) is brought into solution by treatment with aqueous alkaline solution at a temperature of 20 ° C to 50 ° C, preferably from 25 ° C to 35 ° C, or

Hemicellulose from the cellulosic and hemicellulose-enriched material from a) both by treatment with aqueous alkaline solution at a temperature of 20 ° C to 50 ° C, preferably from 25 ° C to 35 ° C, as well as by treatment with at least one carbohydrate-splitting enzyme is brought into solution.

The dissolved hemicellulose can be isolated by separating the solution from the solid from the solution.

The combined measures a) and b) in a process according to the present invention have proven to be particularly suitable for depleting cellulose from a

lignocellulosic material exposed.

Compared with the methods of the prior art, the process of the present invention for producing delignified pulp from lignocellulosic material is a process in which the separate isolation of all streams is made possible to obtain high-grade sulfur-free lignin. An essential advantage of the process according to the present invention is the high delignification with high selectivity. By delignification carried out in the digestion according to measure a), the porosity of the cell walls of the lignocellulosic material is increased, so that

carbohydrate-cleaving enzymes penetrate the straw and the xylan contained

can hydrolyze. In addition, activity losses of the enzymes can be reduced by non-specific binding to the lignin. For the removal of hemicellulose, in particular xylan from the lignocellulosic material with preservation of the cellulose according to measure b) in a method of the present invention, pure endo-l, 4-.beta.-xylanases, e.g. Enzyme preparations with pure endoxylanase activity.

Mixing enzymes with β-xylosidase or α-L-arabinofuranosidase activity also convert too much cellulose and must therefore be excluded. As enzyme preparations with pure endoxylanase activity are, for example, Pentopan BG ™ and Pulpzyme HC ™. Depending on the enzyme, the enzymatic reactions are carried out under the optimum conditions and pH values.

In addition to the enzymatic hydrolysis xylan can also be extracted chemically according to one aspect of the measure b). This exploits the high functionalization with acidic residues compared to cellulose. By using a strongly basic solution, xylan can be selectively extracted from a cellulose and hemicellulose enriched material. In the process according to the invention, the pH according to measure b) is determined by an inorganic base, e.g. a hydroxide, preferably sodium hydroxide, adjusted at a molar amount of 1 to 20 parts by weight based on the amount of liquid. The extraction is preferably carried out at a temperature of 20 ° C to 50 ° C, more preferably from 25 ° C to 35 ° C.

Unless otherwise indicated, pulp is a highly cellulose-fortified material such as, for example, material produced by delignification and dexylanation according to the process described above.

In a process according to the present invention, according to measure c), the material obtained in accordance with measure b), which has been depleted with hemicellulose, removes lignin, namely residual lignin, from the pulp. For this purpose, either a sulfite, in particular an alkali, alkaline earth or ammonium sulfite, preferably sodium sulfite and / or oxygen used to obtain a pulp with a low lignin content. It has been found that the use of a combination of sulfite and oxygen results in a significantly increased delignification efficiency.

The solution obtained after removal of the (residual) lignin also provides opportunities to isolate and utilize the removed lignin.

The delignification efficiency is defined as follows:

(Start value cap; pa- end value kappa) x 100

Delignification efficiency = ^■

Starting value Kappa

The kappa value is a measure of the residual lignin content of the pulp.

The removal of the (residual) lignin in a variant according to measure c) in a process of the present invention using sulfite, e.g. Sodium sulfite, at a temperature of 90 ° C to 150 ° C, preferably from 120 ° C to 140 ° C, performed.

It has surprisingly been found that better delignification occurs under alkaline conditions. Sulphite, such as sodium sulphite, is preferably used in an amount of from 10 to 100% by weight, particularly preferably 20% by weight, based on the dry mass. As the base, an inorganic base, preferably a hydroxide, e.g. Sodium hydroxide, in a concentration of 0.1 to 3.0 parts by weight, based on the

Dry matter, used. Thus, an optimal pH of 9 to 13 can be set. In addition, in one embodiment of the process, an anthraquinone derivative, preferably sodium anthraquinone-2-sulfonate, in an amount of preferably from 0.05 to 5% by weight, more preferably in an amount of 0.1 to 1% by weight, most preferably in in an amount of 0.5% by weight, based on the dry matter, as a mediator to increase delignification efficiency.

In another variant of the method according to the present invention according to measure c), the (residual) lignin can be removed by means of oxygen treatment at a temperature of 60 to 130 ° C, preferably from 80 ° C to 100 ° C, particularly preferably at 90 ° C. become.

In this case, an inorganic base, for example a hydroxide, such as sodium hydroxide, in an amount of 1.0 to 10.0 parts by weight, preferably in an amount of 6 parts by weight, based on the

Dry matter, used. With appropriate oxygen bleaching an oxygen pressure, preferably from 1 to 20 bar, particularly preferably 10 bar, is used. In addition, in one embodiment of this process, an anthraquinone derivative, preferably sodium anthraquinone-2-sulfonate, in an amount of 0.05 to 5% by weight, preferably in an amount of 0.1 and 1% by weight, particularly preferably in one Amount of 0.5 wt. Added to the dry mass as a mediator. Surprisingly, it has been found that an embodiment in which an aqueous solution with 0.1 to 60% by volume of alcohol, preferably 1 to 5% by volume, particularly preferably 3% by volume is used, gives improved delignification efficiency.

In order to achieve a desired delignification efficiency in the removal of residual lignin of the pulp obtained after the separation of hemicellulose and lignin, the respective percentage compositions of all

Delignification components and the reaction parameters temperature, reaction time and solids concentration can be adjusted.

Pulp made in accordance with the present invention, e.g. with the kappa number and viscosity achievable by the process of the present invention is novel and also subject of the present invention.

In another aspect, the present invention provides pulp, preparable, in particular manufactured, by a process of the present invention.

The following examples show the influence of the ethanol and mediator content as well as the reaction time on the delignification efficiency.

In the following examples all temperatures are given in ° C.

example 1

a) digestion Wheat straw (21.0% by weight lignin content, 20.9% by weight xylan content, 36.8% by weight

Cellulo segehalt based on the dry mass) is crushed to a particle size of 2 mm with an ultracentrifugal mill. The crushed straw is suspended in a mixture of water, ethanol (alcohol content 60% by volume) and sodium hydroxide solution (8% by weight, based on dry matter). The mixture is stirred mechanically at a constant temperature of 70 ° C for 18 hours. Subsequently, the resulting solid is squeezed and washed with sufficient water to give a cellulosic and hemicellulose-enriched material. Yield and important parameters of the resulting material are shown in Table 2 below.

Table 2

informative parameters

Solids yield 60.1 + 3.1%

Delignification 78 + 6%

Lignin content of the solid 8.2 + 1.1%

Delignification 75 + 5%

Extracted lignin 15.8 +1.18 g

per 100 g wheat straw

Extracted sugar 1.4 ± 0.4 g

per 100 g wheat straw b) dexylanation (chemical and enzymatic)

Material enriched with cellulose and hemicellulose from a) (about 58.2% by weight cellulose content, about 36.9% by weight xylange content, about 8.2% by weight lignin content) is dexylanized in a two-stage sequence. To this end, the material is first suspended in a 10% sodium hydroxide solution heated to 30 ° C. to a dry mass fraction of 10% by weight and stirred at this temperature for 30 minutes. After this time, the homogeneous mixture is filtered off and washed neutral with dilute hydrochloric acid and water. The filter cake obtained is in a 50 mm acetate buffer solution to a

Solid content of 10% based on the dry mass suspended, whereupon the pH is corrected to 5. To this mixture is added 150 U of pentopane BG ™ per g of pulp, after which the suspension is heated to 50 ° C for 72 hours. After that will the aqueous phase is squeezed out and washed with twice the amount of water, whereby the pulp is obtained. A solids yield of 75% of the dry matter used was obtained. The important parameters of the pulp are summarized in Table 3 below.

Table 3

Parameter composition

Cellulose 80.9%

(Remainder) xylan 2.2%

Ash 1.0%

(Remainder) lignin 10.4%

(Rest) arabinan 0.7%

Other sugars and uronic acids 1.8%

MW cellulose 2200 kDa

Crystal form cellulose I + II

Kappa number 57.6

CuEn viscosity 694 ml / g

Degree of polymerization 1850

Whiteness 32.6% ISO c) delignification

The pulp of b) was suspended in water to a dry weight content of 4% by weight. 7.6% by weight of NaOH and 0.5% by weight of Mg ²⁺ based on the dry weight of the pulp were added to the reaction mixture. The delignification was carried out under 0 ₂ pressure of 10 bar and at a temperature of 90 ° C for 4 hours. Thereafter, the pulp was washed with a sufficient amount of water and dried. Subsequently, the kappa number and viscosity were determined.

Example 2 Digestion and dexylanation were carried out as in Example 1. Carrying out and approach of the delignification correspond to Example la), except that instead of water, a 3% aqueous ethanol solution was used as the reaction medium.

Example 3

Digestion and dexylanation were carried out as in Example 1. Carrying out and approach of the delignification correspond to Example 1, but added during the delignification in addition 6.3 parts by weight anthraquinone-2-sulfonic acid sodium salt monohydrate based on the total dried mass as a mediator.

Example 4

Digestion and dexylanation were carried out as in Example 1. The procedure and approach of delignification correspond to Example 3, except that instead of water, a 3% aqueous ethanol solution was used as the reaction medium.

Example 5

Digestion and dexylanation were carried out as in Example 1. Procedure and approach of (residual) delignification correspond to Example 3, except that the reaction time was extended to 16 hours.

Example 6

Digestion and dexylanation were carried out as in Example 1. The procedure and approach of (residual) delignification correspond to Example 5, except that instead of water, a 3% ethanol-water mixture was used as the reaction medium.

Example 7

Digestion and dexylanation were carried out as in Example 1. The pulp was suspended in the water to delignify to a dry weight level of 4% by weight and was charged with 64% by weight sodium sulfite and 1.5% by weight sodium hydroxide in the presence of 2.0% by weight anthraquinone-2-sulfonic acid sodium salt monohydrate the

Dry mass of pulp reacted. The reaction time was 1 hour at a temperature of 130 ° C. After delignification, the pulp became a sufficient amount Washed water and dried. Subsequently, the kappa number and viscosity were determined.

Example 8

The pulp prepared according to Example 7 was bleached with oxygen and alkali. The reaction procedure and the reaction mixture were as in Example 4 for the

Delignification described.

Example 9

Digestion and dexylanation were carried out as in Example 1. The procedure and approach of delignification are the same as Example 7, except that the reaction was carried out at a temperature of 140 ° C for 3 hours.

Example 10

The pulp prepared according to Example 9 was bleached with oxygen and alkali. The reaction procedure and the reaction batch corresponded to the information described in Example 4 with respect to the delignification.

The kappa numbers and viscosity results of the individual delignification methods are shown in Table 4 below.

The kappa value is determined according to DIN 54357 and is a measure of the (residual) lignin content of the pulp. The viscosity was determined in a 0.5 m aqueous copper ethylenediamine solution (CuEn) using a Ubbelohde capillary viscometer after a simplified

The same capillary was used for sample and blank (SCAN-C 15:62, SCAN-C 16:62 and SCAN-CM 15:88).

As can be seen from Table 4 below, a significantly greater reduction in kappa number could be achieved in the experiments in which EtOH was added from the beginning. The delignification efficiency here is surprisingly much stronger than in comparable bleaching processes of kraft pulp.

Table 4 Kappa, delignification efficiency, viscosity,

mL% mL / L

Example 1 31.8 44.5 699

Example 2 27.8 51.5 740

Example 3 28.3 50.6 717

Example 4 24.7 56.9 758

Example 5 18.1 68.4 715

Example 6 14.6 74.5 736

Example 7 29.7 48.2 915

Example 8 9.7 83.1 809

Example 9 19.4 66.3 971

Example 10 7.7 86.6 843

When the pulp was additionally delignified with Na ₂ S0 ₃ prior to oxygen bleaching, surprisingly, a significantly lower kappa number of 7.7 ml could be obtained after two

Bleaching steps are achieved, which corresponds to a total delignification of 86.6%. Compared to pulp bleached only with oxygen (example 6), there is a kappa number difference of about 6.9 ml. This difference is significant in terms of industrial application, considering that, in general, at low kappa number

Lignin removal is more difficult and expensive selective delignification reagents are needed. In addition, the viscosity of in a two-stage process

delignified pulp higher than that of pulp bleached with oxygen only. For example, the pulp produced according to Example 10 was further used with

Peroxyacetic acid bleached. Peroxyacetic acid was used in an amount of 10% by weight, based on dry matter. The consistency was 4%, the temperature 70 ° C. After a reaction time of 3 hours, the pulp was washed with a sufficient amount of water and dried. Subsequently, a kappa number of 1.2 ml was measured.

Claims

claims

1. A process for the production of low lignin pulp characterized by a combination of the measures

a) lignocellulosic material with an aqueous solution containing a C _1-6 - alcohol and having a pH of 10 to 14, is treated at a temperature below 100 ° C, whereupon the aqueous solution, in the lignin, the the lignocellulose is cleaved, separated from the solid, which is a material enriched with cellulose and hemicellulose, b) hemicellulose is removed from the cellulosic and hemicellulose-enriched material from a),

c) the material obtained in b), which is depleted in hemicellulose, in aqueous alkaline solution with an alkali, alkaline earth or ammonium sulfite, in particular Na ₂ S0 ₃ , and / or treated with oxygen, wherein lignin goes into solution and Pulp with low lignin content is obtained.

2. The method according to claim 1, characterized in that in b) hemicellulose from the cellulosic and hemicellulose-enriched material from a) by

Treatment with at least one carbohydrate-cleaving enzyme is brought into solution.

3. The method according to claim 1, characterized in that in b) hemicellulose from the cellulosic and hemicellulose-enriched material from a) by

Treatment with aqueous alkaline solution at a temperature of 20 ° C to 50 ° C, preferably from 25 ° C to 35 ° C, brought into solution.

4. The method according to claim 1, characterized in that in b) hemicellulose from the cellulosic and hemicellulose-enriched material from a) both by treatment with aqueous alkaline solution at a temperature of 20 ° C to 50 ° C, preferably from 25 ° C. to 35 ° C, as is brought into solution by treatment with at least one carbohydrate-splitting enzyme.

5. The method according to claim any one of claims 1 to 4, characterized in that in c) a temperature of 90 ° C to 150 ° C, preferably from 120 ° C to 140 ° C is used when alkali, alkaline earth or ammonium sulfite is used.

6. The method according to any one of claims 1 to 4, characterized in that in C) a temperature of 60 ° C to 130 ° C, preferably from 80 ° C to 100 ° C is used when oxygen is used.

7. The method according to any one of claims 1 to 6, characterized in that as

lignocellulosic material straw, bagasse, energy grasses, in particular

Elephant grass, switch grass, and / or husks, especially lobes, is used.

8. The method according to any one of claims 1 to 7, characterized in that the lignocellulosic material in the aqueous solution in a consistency of 3 to 30 wt .- based on the dry mass.

9. The method according to one of claims 1 to 8, characterized in that in c) an anthraquinone derivative, preferably sodium anthraquinone-2-sulfonate, in an amount of 0.05 to 5 parts by weight, preferably in an amount of 0.1 to 1 wt .-, particularly preferably in an amount of 0.5% by weight based on the dry mass as

Mediator is added.

10. Pulp, producible, in particular produced according to one of claims 1 to 9.