GB2040332A - Pulping of lignocellulose with aqueous alcohol/catalyst mixture. - Google Patents

Abstract

Lignocellulosic plant materials are treated with a catalyst containing an aqueous lower alcohol solution and converted into fibre possessing superior pulp characteristics. The preferred organic solvent is methanol and the catalyst is supplied in the form of an aqueous alcohol-soluble metal salt, with or without a minor quantity of strong mineral acid in a pressure vessel at temperatures between 130 to 210 DEG C, preferably between 190 DEG C to 200 DEG C for durations from 15 minutes to over one hour. The catalyst salt is a chloride, sulphate, or nitrate of calcium, magnesium or barium, and is used in concentrations between 0.005 to 1.0 molar. A pulp yield of 54 to 56% is easily obtained for a softwood having a Kappa number 35 and a TAPPI (0.5g) viscosity of 20 cP within 45 minutes of cooking whereas aspen can be cooked to a pulp yield of 62% with TAPPI viscosity 22 cP at a Kappa number 25 in less than 30 min.

Description

SPECIFICATION Pulping of lignocellulose with aqueous alcoholic catalyst mixture This invention is in a novel process for treating lignocellulose with a solvent mixture comprised of water and the lower aliphatic alcohols of three carbon atoms and less, and a dissolved proton generating salt catalyst under conditions of elevated temperature in the range 130"C to 21000 to produce a fibrous chemical pulp by preferably and at least partially depolymerizing and dissolving the lignin and hemicellulose materials of plant cell walls.

The process is particularly successful in producing pulps having low Kappa or Roe number, high fibre strength with the cellulose retaining nearly its natural undegraded state. Significantly, the invention is equally efficient on both gymnosperm and angiosperm wood species as well as the lignocellulosic agricultural residues, when carefully cooked under the above mentioned conditions.

With today's energy and chemicals shortages the accent should be on efficiency of cooking and completeness of chemical recoveries. The new pulping method should be efficient in lignin removal to allow short cooking times and at the same time mild enough to allow nearly theoretical fibre yields and quantative recovery of the dissolved by products. Delignification must be as complete as possible to avoid low bonding strength of the fibres and to reduce bleaching chemical requirements when fully bleached paper grades are required. It is further a requirement of a good pulping process that fibre liberation be as complete as possible. Thus delignification must extend to both the fibre cementing layers (middle lamella), composed of lignin-carbohydrate matrix, as well as the cell wall matrices containing lignin and hemicelluloses in various proportions.Such efficient delignification will lead to low screened rejects and the cooked chips will require little if any mechanical action for full defiberization which preserves process energy as well as fibre iength.

Heretofore in processes where wood is subjected to hydrolysis in aqueous or aqueous-organic solvent mixtures containing unbuffered or unmoderated acid catalysts at a temperature say between 1 65 C to 21000 the cellulose is also attacked so rapidly that before the lignin and hermicellulose constituents of the cell wall are dissolved, extensive degradation of the cellulose has occured, as well. Even when relatively weak acid, such as dicarboxylic organic acid, was used as catalyst, the fibres when liberated had a degree of polymerization of their cellulose below that found in their natural condition so that paper sheets made from such pulps lacked high tear strength, burst strength, and breaking length desirable for industrial uses.

While known processes have advantages of requiring very short cooking times and yield a soluble lignin and dissolved sugars having considerable value, it has remained a desirable objective that liberation of cellulosic fibres should preserve almost the entire polyglucan fraction and retain the native strength of cellulose fibres when acceptably low lignin content of the pulp is attained. A further object of the present invention was to produce high yield, low residual lignin content pulp to improve fibre bonding and conformation in the paper web and reduce the bleaching chemicals requirement when fully bleached grades are made.A further desirable objective is to avoid damage to the cellulose through attack by acids and especially the water-miscible organic solvents used in the present invention which show marked consistency in their delignification specificity and lack of attack on the carbohydrates. Another major improvement of the present invention accrues from the selection of inexpensive mild salt catalysts which possess the unique property that they form weakly acidic solutions in aqueous alcohols, contribute to generation of acidic protons to the system through cation exchange with functional groups on the lignin and carbohydrates and protect the cellulose from attack by acidic protons at high temperature. The substantially lowered acidity further eliminates the necessity for providing highly acid resistant cooking hardware.

Another objective of the present invention is to provide a pulping process essentially free of water and air pollution.

Other objectives of the present invention should become evident during the course of the following description of teachings concerning the process.

Aqueous solvent pulping processes are described e.g. in U.S. Patent No.3.585.184 and most recently U.S.

Patent No. 4.100.016. The present invention overcomes the major deficiencies of these and other known chemical pulping processes, by employing a method which essentially consists in treating lignocellulose materials with a solvent mixture of at least four times the weight of lignocellulose to be pulped, with the solvent made up of methanol, ethanol or n-propanol, or mixtures thereof, in proportion of 20 to 80 to 80 to 20 per cent mixture with water and containing from 0.005 to 1.0 moles of a metal salt soluble in water and alcohol selected from salt chlorides, sulphates or nitrates of the metals magnesium, calcium or barium, or mixtures thereof, at a temperature of 13000 to 210 C, preferably 17000 to 20000 for a time generally between 15 and about 90 minutes.For lignocellulosics which are generally delignified with difficulty, and salts having low catalystic effect as is the case with magnesium sulphate, incorporation of small quantities of a strong acid, with the corresponding anion preferred, to make the solution 0.0005 to 0.008 N with respect to the strong acid in said solution in addition to the salt catalyst used, greatly improves the degree of delignification without appreciably affecting the polydispersity of the recovered cellulose. The process thus described provides high specificity in delignification and recovers cellulosic fibres with high degree of polymerization and high glucan content.

The method is particularly effective when the salt is magnesium or calcium chloride or nitrate at a molar concentration between 0.02 molar fo 0.05 molar and the ratio, by volume, of water to methanol of the solvent mixture is about 30 to 70, and the cooking is carried out at a temperature between 190"C and 200 C. When coniferous woods, such as spruce is cooked by the novel process a pulp is obtained which retains appreciable amounts of hemicelluloses yet has low residual lignin content and a degree of polymerization (DP) higher than most pulps obtainable by the kraft process; the cooking time need be only 30 to 45 min to yield a pulp with Kappa number 33, TAPPI viscosity of 0.5g of 20 centipoise, or a degree of polymerization of 1320.The cooked chips are separated into individual fibres by merely being slurried with water and the resulting pulp is readily bleachable from its as-cooked brightness of 50 % GE to the desired 80 % and higher brightness than is kraft spruce pulp of comparable residual lignin content with a much lower starting brightness, typically 35 % GE.

Pulping processes presently in use further suffer from the disadvantage that by-product recovery greatly upsets cooking chemical recoveries making such efforts economically less attractive. Further, in the kraft process for example the dissolved sugars are largely converted to saccharinic acid salts having only limited usefulness as industrial chemicals. Similarly, lignin is converted to sulphur derivatives in order to attain the degree of solubility needed to isolate a low lignincontent fibre, a fact which converts the otherwise partially solvent soluble lignin into one which can be dispersed only in alkali.In contrast to these above difficulties with by-product recovery from the cooking of lignocellulosics, the present method requires recovery of the dissolved lignin and sugars as they are normally separated in the course of cooking solvent recovery by flash evaporation leaving relatively concentrated aqueous sugar solutions in which the otherwise solvent soluble lignin appears as a powderous precipitate. Separation of the lignin from sugars occurs by centrifuging or simple fiitration.

The recovered sugar solution is found to be rich in xylane and other hemicelluloses with relatively low yields of glucan. Most of the sugars occur as dimers and low molecular weight oligomers which can be readily degraded to simple sugars by a secondary hydrolysis, in nearly quantitative yield. The fact that the sugars appear as low molecular weight sugar polymers preserves them from dehydration during the high temperature cooking and allows higher dissolved sugar recoveries.

The precipitated lignin, following removal of the solvent, retains its solvent solubility, a property highly desirable when chemical processing is contemplated. Molecular weight of such solvent soluble lignin was determined by gel permeation-chromatography and high pressure-liquid chromatography to fall between 300 to 12,000 with an average molecular weight calculated around 3,000. The lignin thus obtained can be readily purified by redissolution in acetone, filtering the acetone solution to remove the insolubles and repeated reprecipitation into water or a non-polar solvent such as diethyl ether, benzene and n-hexane.

Other solvents such as dichloro methane can also be used as precipitating agents whereas tetrahydrofuran, dimethyl sulphoxide, furfural, methyl cellosolve, dioxane ethanol and acrylonitrile are excellent solvents for the lignin. The most attractive energy saving technique for recovery of the precipitated lignin is by way of spray drying from acetone solutions under 65"C temperature. The lignin thus obtained is usually light in color and in the form of a free flowing powder.

The fully cooked chips are readily separated into free fibres on slurrying them into a good lignin solvent which removes large amounts of lignin from the fibre. Usually a simple wash with hot methanol-water or with aceton is sufficient to remove the bulk of the dissolved lignin which was lodged within the fibres.

Subsequent washing with water has no adverse effect on bleachability of the fibres. It is a further characteristic of the fibres thus produced that the freeness normally desirable of paper-making pulps can be reached with substantially less energy during the beating process. The original freeness of 750 obtained with spruce pulp requires only 4,000 revolutions on a PFI beater to obtain a freeness of 300 in comparison to kraft pulps of the same initial freeness which require between 7,000 to 9,000 revolutions to the same freeness, typically 300.

The invention will be more particularly described in and by the following examples and statements of preferred modes of carrying into effect the said method.

Example 1 A study of the delignification and cellulose polydispersity was undertaken using 0.16 molar concentration of CaCI2 in 30:70 mixtures of water with methanol, ethanol, or n-propanol. The cooks were carried out in 3 laboratory scale stainless steel pressure vessel measuring about 20 cm height and 8 cm in diameter. Air dry wood chips at 8 % moisture content of the species spruce were placed in the digester in 10 gram batches along with 100 grams of the previously prepared cooking solution. The sealed bombs were heated to 200"C in an oil bath and held at the cooking temperature for the predetermined time. The cooking time was so selected as to give a free pulp after slurrying the cooked chips into 500 ml of acetone and stirring the solution at less than 800 rpm. At the end of the cook the vessels were chilled and the liquor decanted. The pulp was washed with acetone followed by water and air-dried until constant weight was obtained. Samples were reserved for Kappa number and viscosity determinations were upon the final moisture content of the residual pulp was determined to allow calculation of the pulp yield. For all analyses TAPPI standard test methods were used. All the test data from this series of cooks are summarized in TABLE 1. The date clearly indicate the superior selectivity of methanol as delignifying agent as indicated by the high viscosity of the isolated cellulosic pulp.

TABLE 1 Cooking liquor CaCI2 Cooking Cond. Pulp TAPPI Catalyst Time Temp Yield K. No. Viscosity Composition Vol.Ratio Mole Min "C % 0.59 80:20 0.16 30 200 58 63 18 MeOH:H2O 70:30 0.16 30 200 53 55 20.5 60:40 0.16 30 200 51 44 14 80:20 0.16 30 200 54 66 12.5 EtOH:H2O 70:30 0.16 30 200 50 59 8 60:40 0.16 30 200 46 27 5 70:30 0.10 25 200 52 75 8 n-Propanol: 70:30 0.10 35 200 48 48 6 H2O 70:30 0.10 45 200 46 32 5 Example 71 The process exhibits a high tolerance to large variation in the molar concentration of the metal salt used, under otherwise constant cooking conditions.Hardwoods generally may be cooked with lower salt concentrations of any of the preferred salt catalysts than softwoods; for example aspen wood cooks with calcium or magnesium chloride or nitrate in less than min at salt concentrations of 0.025 to 0.10 molar whereas with magnesium sulphate of the same concentration 45 min is required. Softwoods such as spruce will generally require a higher salt concentration between 0.05 to 0.20 molar, and in certain instances improved fibre separation may be gained with concentrations approaching 0.5 molar or higher. The preferred salts are the chlorides of magnesium and calcium, which have the advantages of lowest cost in addition to being well tolerated in fermentation processes to which the aqueous sugar residue may be fed to convert the sugars to ethyl alcohol, yeast or other fermentable products.Magnesium sulphate has limited solubility in alcohols and hence the salt concentration which can be entered into solution may often be limited. To compensate for the lower salt concentration of MgSO4 cooking times in excess of those deemed acceptable are required.

Table II shows representative data on pulp yield and properties for one hardwood, aspen, and one softwood, spruce, when cooked with aqueous methanol at 200"C with a constant wood: liquor ratio of 1:10 (water: methanol ratio is 30:70).

TABLE II Catalyst Cooking Pulp Kappa TAPPI D.P.

Wood Salt Moles Time Yield Number Viscosity Min. % o.5g Oo MgC12 0.01 30 62 27 20 1320 o MgSO4 0.05 60 64 35 23 1410 CaCI2 0.01 30 63 30 21 1360 Z CaCI2 0.10 25 61 16 18.7 1280 (X) MgCI2 0.10 25 59 15 19 1300 < BaCI2 0.01 30 69 46 Poor fibre separation MgCI2 0.05 30 59 51 17 1200 MgCl2 0.10 30 54 29 18 1270 MgSO4 0.05 60 78 95 Poor fibre separation w CaCI2 0.05 30 66 60 20 1320 @ CaCI2 0.10 30 54 35 19 1300 @ Mg(NO3)2. 10 45 57 55 23 1410 @ Ca(N03)2. 10 45 58 62 29 1570 In Table II the DP values are derived from TAPPI Standard viscosity measurements and use of the nomogram published by Rydholm on page 1120.

Example III Further cooks were carried out according to wood and liquor charges as described in the previous example. The liquor consisted of 30:70 mixture of water and methanol containing 0.10 moles of CaCI2 as catalyst. Both cooking time and temperature were varied as recorded in TABLE III.

TABLE Ill Species Cooking Pulp Kappa TAPPI (0.5g) D.P.

Time Temp. Yield Number Viscosity min. "C % cP 15 200 72 103 No Fibre Separation 25 200 62 63 28 1550 35 200 56 46 18 1275 SPRUCE 45 200 52 42 15 1160 50 190 63 61 28 1500 80 190 56 40 23 1410 10 200 90 99 No fibre separation 15 200 73 61 25 1450 20 200 63 22 21 1360 ASPEN 25 200 61 16 19 1300 40 180 63 48 41 1750 40 190 57 9 21 1360 TABLE IV A Pulp properties for wood cooks in H2O-methanol3:7, wood:liquorratio 1:10, varying temp. and CACTI2 Species CaCI2 Temp.Time Pulp Yield KAPPA TAPPI (0.5) DP Mols "C Min. Weight% Number Visc., cp ASPEN 0.10 190 40 57 9.4 21 1360 SUGARCANE RIND 0.05 190 30 58 12.0 22.5 1390 WHEAT STRAW 0.10 190 35 55 14 21.5 1365 BIRCH 0.10 190 40 56 20 21 1360 SPRUCE 0.10 200 30 54 35 19 1300 WESTERN HEMLOCK 0.05 200 30 59 30 21 1360 DOUGLAS FIR 0.10 200 30 54 35 20.5 1340 TABLE IV B Handsheet properties for washed pulp not bleached, beaten 300 Csf Species Pulp Beater Breaking Tear Burst O-Span Freeness Revs length m ASPEN 715 2,300 8,800 73 65 16000 SUGARCANERIND 500 1,300 8,600 66 50 15100 WHEAT STRAW 478 970 9,600 62 52 20050 BIRCH 680 1,800 10,700 71 62 18900 SPRUCE 750 4,000 10,800 87 76 19250 WESTERN HEMLOCK DOUGLAS-FIR Because each lignocellulosic material represents a different composition and character of its lignin carbohydrate matrix as it occurs in naturally grown plant materials, the practice of the invention will necessarily require some experimentation with a given material to obtain the optimum pulp properties.

Some guidance may be obtained from TABLE IV A, B which records pulp analysis for some seven different species all of which yielded high quaiity pulps. The pulps were produced under conditions described above.

It is to be understood that these conditions are illustrative of good practice rather than optimal conditions.

The table includes handsheet properties of interest after the pulps were beaten to 300 Canadian Standard Freeness, sheet testing being carried out according to prescribed TAPPI standards. The pulps were treated only by an acetone wash to wash out the dissolved lignin and suspended in water before screening and handsheet formation.

A summative analysis for sugars, lignin and wood pulp was carried for the aspen and spruce cooks described in TABLE IV A, B and presented in TABLE V.

TABLE V Species Substrate Pulp Res. TAPPl Carbohydrate composition Total sugars Yield Lign. Visco. Gluc. Xyl. Gal Arab. Mann. Glac % % cP % % % % % % % WOOD 77.41 19.72 223 57.9 13 0.5 0.2 3.4 1.0 67.0 PULP 61.0 21 19 53.1 3 0.1 Trace 2.2 0.06 58.26 LIQU. - 16.3 - 0.4 7 0.5 Trace 0.8 0.2 9.1 WOOD 72.3 26.5 21 49.9 6 1.8 1.1 11.9 0.8 71.5 PULP 52 2.9 19 43.1 2 - - 2.5 Trace 47.6 LIQU. - 23.0 - 1.7 1.4 1 0.6 4.7 0.1 8.9 1. Holocellulose (lignin-free); 2. Klason Lignin; 3. FeTNa viscosity according to Jayme.

The high glucose content in the pulps indicates little if any degradation of the wood cellulose.

Example IV Since the salts were suspected to enter into cation exchange type of reaction with the wood it was expected that some of the salt would be retained in the pulp fibres. For this reason pulps were prepared according to EXAMPLE Ill and subjected to digestion in a strong oxidizing agent and followed by dilution with demineralized water. The resulting solutions were then analysed for Ca++ and Mg++ by atomic absorption spectrophotometry. The data obtained are presented in TABLE VI.

TABLE VI Cation Species % in Wood % in Pulp Species Mg++ 0.0215 0.0107 Ca++ 0.1086 0.0009 ASPEN WOOD Mg++ 0.0052 0.0077 Ca++ 0.0651 0.0012 SPRUCE WOOD Mg++ 0.0151 0.0015 BIRCH WOOD Ca++ 0.0712 0.0453 All cooks were made with 70:30 methanol water containing 0.05 M of MgCl2 or CaCI2 the temperature being maintained for 30 min. The pulps were washed once with acetone and with two portions of 500 ml distilled water before air drying and analysis.

It is quite evident from TABLE VI that the pulps contained far less cations as were originally present in the respective woods.

Example V It is known that for rapid bulk delignification in acid catalysed aqueous organic solvent mixtures relatively large initial proton concentrations are required to cause rapid delignification. Metal salt catalysts as disclosed herein seem to lack the capability for in situ generation of such high proton concentrations, on the average a pH drop of from 5.8 for 70:30 methanol: water mixtures containing 0.05 moles of CaCI2 to 4.2 was observed only when the cooking solution was added to the wood chips. Development of such weak acid character in salt solutions when added to wood chips is well known from the literature. At times, especially with the gymnosperm species the rate of delignification may be too slow and non-selective enough so that pulps with low residual lignin content are difficult to produce.In such cases it was found that the initial proton concentration can be effectively boosted with small concentrations of mineral acid, usually of the same anion type as found with the metal salt. Such acid additions usually enhance the bulk delignification and hydrolysis of the hemicelluloses at a time when the cellulose is still well protected from the protons by the encrusted lignin since in its native structural environment cellulose is less accessible to acids when swelling by solvents is restricted by the lignin-hemicellulose matrix. The function and effects metal salt catalysts remain unchanged from that experienced in the absence of the mineral acid, i.e., the metal salt serves both as proton generating agent as well as provides important protection to the cellulose especially at the later stages of the cook against the ensuing hydrolytic solvolysis.Evidence for such synergistic effect is presented in TABLE VII. The higher acid concentrations are found to be most effective in reduction of residual lignin in the pulp. This is achieved at the expense of a slight reduction in pulp yield without significant drop in cellulose viscosity.

Thus air-dry spruce wood chips were cooked at a wood:liquor ratio of 1:10 with 70:30 mixture of methanol :water doped with the indicated amount of acid/salt/catalyst. The temperature was 200 C and the heating-up time, included in the time recorded, was 7 minutes for each cook.

TABLE VII Catalyst Cooking Pulp KAPPA TAPPI D.P.

acid n Time Yield Number Viscosity salt m min. % cP H2SO4 0.00375 40 45.8 39 3.7 460 MgSO4 0.05 60 78 105 No fibre separation H2SO4/MgSO4 40 51 36 9.5 910 HCI 0.002 40 70 - No fibre separation CaCI2 0.05 40 54 44 20 1320 HCI/CaC12 40 56 58 30 1600 HCI 0.002/CaCI2 35 58 57 24 1440 HCI 0.004/CaCI2 40 53 37 23 1420 HCI 0.0025/MgSO4 40 56 51 19.2 1310 HNO3 0.004 45 48 50 4.0 470 Ca(NO3)2 0.10 45 58 62 29 1570 HNO3 0.004/Ca,NO3)2 45 55 37 23 1420 HNO30.002/Mg(NO3)2 45 56 39 25 1450 ASPEN HCI 0.002/CaCI2 0.005 25 58 20 25 1450 By way of the foregoing discussions and examples we attempted to describe this invention in as full, clear, concise and exact terms as possible to enable those skilled in the art to practice the same, and having set forth the best mode contemplated for carrying out this invention we regard the invention delineated and distinctly claimed in what follows, and being aware of the fact that equivalents and modifications of, substitutions for parts of the above specification and embodyments of this invention could also be made without substantially departing from the spirit of this invention as set forth in what is claimed. It is intended that the letters patent shall cover, by appropriate expression in the claims, whatever patentable novelty exists in the invention declared hereby.

What we claim is:

Claims (20)

1. A method for chemically converting lignocellulose to the form of separated fibres, characterised in that it comprises heating lignocellulose with an aqueous alcoholic solvent mixture in an amount of at least four times the weight of the lignocellulose, the said mixture comprising from 1 to 4 volumes of a lower aliphatic alcohol per volume of water and a metal salt catalyst in a concentration of from 0.001 molar to 0.1 molar, and with or without a small proportion of added strong acid, heating the mixture to a temperature between 130"C and 210"C, for a time not longer than two hours but sufficient to effect at least partial depolymerisation and dissolution of the lignin, the hemi-celluloses and other cell wall materials which encase the cellulosic fibres, recovering the separated fibres from the liquor residue, and recovering the heating and wash solvents, lignins and sugars from the spent liquor residue.

2. The method of claim 1, further characterised in that the lower aliphatic alcohol is methanol.

3. The method of either of claims 1, or 2 further characterised in that the catalyst is a chloride or nitrate of magnesium, calcium or barium or magnesium sulphate or a mixture thereof.

4. The method of any of claims 1 to 3 further characterised in that said lignocellulose is heated with from 5 to 10 times its weight of said aqueous alcoholic solvent mixture.

5. The method of any of claims 1 to 4 further characterised in that said mixture is heated at 180 to 200"C.

6. The method of any of claims 3 to 5 further characterised in that the strong acid is hydrochloric, sulphuric, nitric or phosphoric acid and the concentration is from 0.0005 N to 0.0008 N.

7. The method of any of claims 3 to 6 further characterised in that the anion of said added strong acid is the same as that of said metal salt.

8. The method of any of claims 1 to 7 further characterised in that the separated fibres are washed with hot methanol-water solution or with acetone and finally with water.

9. The method of any of claims 1 to 8 further characterised in that it includes the step of volatilising the organic solvents from the combined heating and wash liquor residues and fractionally condensing the volatile material to recover methanol and/or acetone therefrom.

10. The method of any of claims 1 to 9 further characterised in that the remaining aqueous solution is cooled to complete precipitation of the lignin and the lignin precipitate is separated from the solution in acetone to produce a saturated solution, the solution filtered to remove undissolved materials and the lignin reprecipitated in ten volumes of water, five volumes of a non-polar organic solvent or spray dried at low temperature.

11. The method of claim 10 further characterised in that, the aqueous liquor from the reprecipitation of the lignin is diluted and supplied as an ingredient to a fermentation process to convert sugars in said residue to alcohol or protein.

12. A method for chemically converting lignocellulosic material from a plant belong to the order of Angiosperms to the form of separated fibres, characterised in that it comprises heating fragmented lignocellulosic material from said plant in an aqueous solvent mixture in an amount from 5 to 10 times the weight of lignocellulosic material, the said solvent mixture comprising substantially 3 volumes of water to 7 volumes of methanol and containing a metal salt catalyst which is a chloride or nitrate of magnesium or calcium or magnesium sulphate in a concentration of from 0.025 to 0.10 molar, the heating temperature being from 180"C to 2000C for at least 15 minutes and sufficient to effect at least partial depolymerisation and dissolution of lignin and hemicelluloses and other cell wall materials encasing the cellulosic fibres, recovering the separated fibres from the liquor residue, and recovering from the heating and wash solvents, lignins and sugars from the spent liquor residue.

13. A method for chemically converting lignocellulosic material from a plant belonging to the order of Gymnosperms to the form of separated fibres, characterised in that it comprises, heating fragmented lignocellulosic material from said plant in an aqueous solvent mixture in an amount of from 5 to 10 times the weight of lignocellulosic material, the said solvent mixture comprising substantially 3 volumes of water to 7 volumes of methanol and containing a metal salt catalyst which is a chloride or nitrate of calcium or magnesium in a concentration of from 0.05 to 0.2 molar, the heating temperature being from 1900Cto 2000C for substantially 20 minutes and sufficient to effect at least partial depolymerisation and dissolution of lignin and himicelluloses and other cell wall materials encasing the cellulosic fibres, recovering the separated fibres from the liquor residue, and recovering the methanol, lignin and sugars from the spent liquor.

14. The method of chemically converting lignocellulosic material from a plant belonging to the plant orders of Gymnosperms and Angiosperms to the form of separated fibres, characterised in that it comprises, heating fragmented lignocellulosic material from said plant in an aqueous solvent mixture in an amount of from 5 to 10 times the weight of lignocellulosic material, the said solvent mixture comprising substantially 3 volumes of water to 7 volumes of methanol and containing a metal salt catalyst mixture selected from the chlorides and nitrates of calcium and magnesium and magnesium sulphate in a concentration of from 0.05 molar to 0.2 molar and a strong acid of from 0.0005 to 0.008 normal, the heating temperature being maintained at from 190"C to 200"C for substantially 30 minutes and sufficient to effect at least partial depolymerisation and dissolution of lignin and hemicelluloses and other cell wall materials encasing the cellulosic fibres, recovering the separated fibres from the liquor residue, and recovering the methanol, lignin and sugars from the spent liquor.

15. The method of claim 14furthercharacterised in that the strong acid is hydrochloric, sulphuric, nitric or phosphoric acid.

16. The method of any claims 12 to 15 further characterised in that the recovered separated fibres are washed with hot aqueous methanol or acetone and the washed pulp is rinsed with water.

17. The method of any claims 12 to 16 further characterised in that the volatile organic materials are recovered by voltilisation and condensation of their vapours.

18. The method of any of claims 12 to 17 further characterised in that lignin is recovered in powder form by cooling the aqueous liquor residue and physically separating the lignin solids from the aqueous liquor residue and drying the said solids.

19. The method of any of claims 12 to 18 further characterised in that the aqueous liquor from the separation of the lignin, is diluted and supplied as an ingredient to a fermentation process to convert the sugars in said liquor residue to alcohol or protein.

20. The method of claims 12 to 19 further characterised in that the aqueous organic solvent containing catalyst is admitted to the lignocellulose in a pressure vessel having a plurality of inlet and discharge ports and the said solvent mixture is continuously circulated through the said lignocellulose, and when a continuous process is used, the solvent mixture is moved at a higher rate relative to the lignocellulose towards the discharge port.