CA1150012A - Aqueous catalysed solvent pulping of lignocellulose - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

High quality and high yield of chemical pulp is obtained by cooking fragments of lignocellulose material at up to 250°C with mixture of alcohol-water in volume ratio between 50:50 to virtually anhydrous methyl alcohol having in solution as primary catalyst between 0.001 to 1.0 moles of chloride, nitrate or sulphate salt of magnesium, calcium or barium and an auto-catalytically generated organic acid from 0.0001 to 0.05 Normal; and added strong mineral acid, or weak mineral acid, or organic acid from zero to 0.01 Normal or an acidic metal salt secondary catalyst from zero to 0.01 Molar may be added and aids rapid and early delignification. In addition, pressures substantially higher than normally developed in enclosed spaces of particular solvent compositions used at the particular temperatures aid both delignification and in particular suppression of carbohydrate degradation.
Undegraded depolymerized lignin and carbohydrates are separated from said pulp fibers by straining and washing and are recovered separately on reclaiming the cooking solvent.

Description

z This invention is in improvements of the process described in the patent application filed in the USA Serial Number 126 441 with priority in Canada, Serial Number 316 951 for treating lignocellulose materials with an aqueous solvent mixture comprised of substantially methyl alcohol and up to 50 per cent water and a dissolved neutral alkali earth metal salt catalyst or a mixture thereof as primary catalyst augmented by minor amounts of added acid catal.yst or no such additives at all, at a temperature in the range of 180C to 210C to produce high yields of chemical pulp of strong separated cellulosic fibres.
Now we find that the catalytic system can be extended to numerous auxiliary aci.ds in addition to those autocatalytically generated during the high-tem-perature cooking procedure and that it is particularly advantageous if high pressures are used during the cooking to obtain totally liberated fibers of very high viscosity and low Kappa number without requiring mechanical refining or grinding. Such pulps also have nearly theoretical alpha-cellulose content and retain a high proportion of the hemicelluloses required for forming strong paper webs.
With these improvements the process becomes universially effective in treating both gymonsperm and angiosperm woody materials as well as lignocellulosic plant materials such as bamboo, sugarcane, cerial and grass plant stalks.

DESCRIPTION OF THE PRIOR ART
Much effort was exerted in the past in perfecting the high-temperature alcohol-water extraction process firs-t disclosed by Kleinert and Tayenthal in their Z
patent GB 357 821 in which wood material was exposed to the decomposing action of ethanol-water in roughly equal volumetric ratio in the presence of organic and inroganic acid salts or alkali additives, the additives being acetic and formic acid, sodium bisulphite, bisulphate, sodium carbonate and magnesium carbonate. Investigation of these systems showed that the process described was limited to low-density hardwoods mainly poplars and had ~ither limited delignification power for softwoods or was so destructive that useful pulp fibers could not be recovered.
A further disadvantage of earlier alcohol-water processes exemplified by patents issued to Kleinert US Patent Serial No. 3 535 104 and to Diebold et al. US
Patent Serial No. 4 lO0 016, using no added catalytic agent and using ethanol as the preferred solvent,is the poor solubility in the relatively low alcohol concentration solvent preferred of lignins causing effective blockage of effective micropores in wood and preventing the penet-ration of the cooking ~iquor and allowing early spontaneous precipitation of the dissolved lignin on slight cooling of the spent cooking liquor. This leads to high rejects content from~ disintegrated chips and resulted in the requirements of frequent liquor changes in the digester during cooking. Such lignin solubility problems lead to a substantial slow-dcwn and insufficient delignification of species other than the poplars and due to the uncontrolled action of the autocatalytically generated acids~cellulose degradation cannot be avoided. Further process problems arize on processing of the spent cooking liquor due to precipitation and deposition of lignin solids on the equipment walls~ This precipitate is removed form the piping only with difficulty.

The present improvements on our earlier invention described in Canadian patent application Serial Number 316 951 and further improved in US patent application Serial Number 126 441 eliminates all these disadvantages had with earlier inventions. This invention presents the ideal process by which virtually all the lignin and only a minimum of the cell wall carbohydrate materials are removed within relatively short cooking times while fiber yields almost equal to the total cellulose content,a substantial proportion of the hemicellulose content originally present in the wood,can be obtained. Further,no degradation other than depolymerization of the dissolved lignins and carbo-hydrates occurs duringt~e high temeperature cooking so that these can be quantitatively recovered on reclaiming the `
cooking solvent. The pulp produced is low in residual lignin content and bright in color so that bleach requirement to at~ln a certainibrightness is much reduced. The process uses a solvent combination which is inexpensive, low in specific heat in minimum quantities dictated only by the void colume inside the lignocellulose and around the packed chips. Thus the process maximizes on fiber yield and ~uality, mass recovery per unit weight of lignocellulose pulped and minimizes on energy required for obtaining fully liberated fibers for papermaking and dissolving pulp purposes. The process is particularly efficient in making fibers of extremely high visocisity at high fiber yileds. The spent cooking liquor is stable against lignin precipitation even after cooling to room temperature whereby all pulp washing and di!sinteg~ation can be done in the cooking liquor to remove trapped dissolved lignins. It is the essential combination of high alcohol concentration and high process pressures which allows pro~ection of the carbohydrates 36:1 ~2 and production of pulps with suprer high viscosity.
According to the present invention there is provided a method for pulping lignocellulose plant material ; to separated fibers in which the plant material is digested with an aqueous aliphatic alcohol containing a catalyst compound to aid delignification at elevated temperature, the improvement of which comprises: cooking fragmented lignocellulose material with an aqueous solvent mixture containing a major volume portion of alcohol and water containing an alkali earth metal salt primary catalyst compound and an acid as auxiliary hydrolysing catalyst at elevated temperature in excess of that developed by the vapours at the temperature used, for a time sufficient to effect at least partial depolymerization and dissolution of the lignin and hemicelluloses to render the fibers separable from each other in the liquor residue containing dissolved lignin materials and sugars, recovering the separated fibers from liquor residue, and separating the spent liquor into solvent, lignin and sugars.
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- 3a -c~m~3 The present invention consists in the method for pulping lignocelluloses materials to fully separated fibers by digestion with a solvent mixture at least four times the weight of lignocellulose to be pulped, with the solvent made up of methanol: water in the proportion l:l to 4:1 and substantially anhydrous merely having water which was contained in the lignocellulose and containing from 0.005 to l.0 moles of a metal salt which is a chloride, nitrate of any of the metals magnesium,.. calcium and barium, and mixtures thereof, or magnesium sulphate, with even seawater being effective as a source of catalyst, at 180 to 240C for a time generally from a few minutes to 90 min at pressures normally those generated from the solvent in closed vessels, corresponding to the laws of thermodynamics, and pa~icularly at higher than normal pressures generated and maintained by any means during the cooking process. As will be made evident in the disclosure, the pressure is not applied as a me~ans of furthering liquor penetration as was earlier thought to be required in the prior art (Dreyfus U.S. Patent Serial No. 2,022,654 and Kleinert W. German Patent application Serial No. 26 44 155, 1977) but is applied in order that the ~inetics of carbohydrat.e degradation be favourably altered on account of furthering the selectivity o~ delignification in this process. For .
lignocellulosics which may show particular resistance to delignification even in the presence of the alkali earth metal salt catalyst, incorporation of a secondary acid catalyst in addition to organic acids autocatalytically generated during the cooking process, in amounts between zero to 0.01 Normal or Molar in the form of strong mineral acids as hydrochloric, sulphuric, weak mineral acids such as boric, sulphurous ~,~ CSm/!~', z or phosphorous acids or others with PK values below 4.0, organic acids such as oxalic, maleic and salicilic acids or those having PK values below 4.75 or acid salts such as aluminum chloride or sulphate, ferr.ic or ferrous chloride, or stannic chloride may be used. A more complete list of the preferred catalyst system of our invention is given in TABLE 1. The use of added auxiliary acidic hydrolysing catalyst is optional and serves the function to accelerate the splitting of lignin carbohydrate bonds during the process of delignification. It is particularly important that when auxiliary catalysts are used the effective concentrations of both the pri.mary and auxiliary catalyst is substantially reduced to levels at which none of the individual catalysts would be-effective alone.
The preferred alcohol as cooking medium is methanol at preferred alcohol.~:water ratios of 70:30, 80:20 or 90:10 with higher ratios such as 95:5 and 98:2 also being effective but relatively difficult to achieve with fresh wood due to the natural moisture being sometime in excess of 30 to 200 per cent. At these alcohol-water ratios it is always necessary to calculate the amount of water contributed by the natural moisture content of the chips to arrive at the desired alcohol-water ratio and to proportion the mixture using anhydrous alcohol as stock solvent. At high alcohol-water ratios not only i5 delig~
nification more complete, but carbohydrate degradation is suppressed, especially if also high pressure is allowed generated during the cooking cicle, but the resulting aqueous solution will have improved dissolving power for the dissolved lignin and upon evaporation of the cooking solvent an aqueous solution of sugars is obtained which will have solids in excess of 8 per cent and up to 25 per ~ ~ t~
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cent. Such high sugar concentrations are especially advantageous in further processing of the sugars (ferment-ation) and concentration of the fermentation effluents to eliminate pollution. Further,less water need be heated during stripping of the alcohol during the recovery process.
The process is particularly effective to delignify all lignocellulosis materials rapidly, achieving yields of free-fiber pulps as high as 80 per cent of the wood weight when the neutral salt catalyst is magnesium or calcium chloride or nitrate or magnesium sulphate at a concentration of between 0~002 to 0.1 Moles per liter of cooking mixture and the solvent water mixture proportioned in the range of 70:30 to 90:10. Particularly high fiber yields are obtained when the cooking times are held short by selecting high cooking temperatures in the range of 180 to 230C, with hardwoods usually requiring lower temperatures than the softwoods. In case the digester void volume is reduced to less than the normal expansion of the cooking chemicals plus the chip charge~abnormally high pressures can he generated inside the digester with the benefit of reduced cooking time but most improtantly by obtaining higher selectivity to delignification and virtually no degradation of the native cellulose. Other mean-s of genera~ting these excess pressures such as from compressed inert gases, pressure intensifiers, vibrators are equally effective. In case an auxiliary acid catalyst is also selected the cooking temperature can be lowered but the alcohol concentration is kept as high as possible.
From the wide range of cooking parameters described herein it is intended to show that the process exhihits excellent tolerance to variation in salt concentration, solvent composition and cooking conditions in provi~ing a full array of chemical pulps at exceptionally high yields and of high quality. Thus hardwoods will generally require "milder" cooking conditions, lower temperatures, lower catalyst concentrations and shorter cooking times, whereas most softwoods-should be processed under conditions closer to the upper limits specified. In spite of these differences the process can be adjusted in such a way that both softwoods and hardwoods can be processed in admixtures without degradation of either type of fiber by over-and/or undercooking. The practice of this invention will necessarily require some experimentation to obtain maximum pulp properties since each lignocellulose material presents a different composition and character of lignin carbohydrate matrix, cell wall porousity, sequestered mineral quantity and extractives each individually and in unisome affecting the pulpablitiy of the wood species in question.
As will be made evident from the following examples and data presented in the following it is a truly surprising effect of this invention that a very effective way has been found to preserve the natural high molecular weight structure of cell-ulose on applying the alakali earth metal catalysts in aqueous alcohol solutions at high alcohol concentration and unusually high pressures even at such high process temepartures. This invention removes all restrictions which were imposed on aqueous~-alcohol pulping due to the poor solubility of dissolved lignins in aqueoNs alcohol solutions.
The inventlon will be more particularly revealed in and by the Examples and Tables of data reported from experimental cooks and analyses according to the invention discussed hereinafter.

TABLE 2. AQUEOUS METHANOL COOKING WITH METAL SALT CATALYSTS
MET~ANOL-WATER RATIO 70:30 WOOD/LIQUOR 1:10 UNDER
NORMAL COOKING PRESSURES
; WOOD COOKING PULP KAPPA TAPPI
SPECIEs SALT MOLES TIME TEMP. YIELD NO. (0.5%) D P
PER L. Min.* C WT % Visc.

~ MgC12 0,01 30 200 62 27 20 1320 O " 0,01 25 200 59 15 19 1400 MgSO4 0,05 60 200 64 35 23 1410 3 CaC12 0,01 30 200 63 30 21 1360 " 0,025 35 190 71 46 32 1600 " 0,01 15 200 90 99 No Fiber Separation " 0,01 25 200 63 22 21 1360 " 0,01 30 190 61 25 24 1440 " 0,01 30 200 73 61 25 1450 " 0,01 40 190 57 9 21 1360 BaC12 0,05 30 200 69 46 Poor Fiber Sep'n a MgC12 0,05 30 200 59 51 17 1200 : o " 0,10 30 200 54 29 18 1270 MgSO4 0,05 60 200 78 95 Poor Fiber Sep'n Mg(NO3)2 0,10 45 200 57 53 23 1410 (NO3)2 0,10 45 200 58 62 29 1570 CaC12 0,05 30 200 66 60 28 1500 " 0,10 20 200 72 103 Poor Fiber Sep'n " 0,10 30 200 62 63 24 1440 " 0,10 40 200 56 46 18 1275 " 0,10 50 200 52 42 15 1160 " 0,10 55 190 63 61 28 1500 " 0,10 85 190 56 40 23 1410 * Includes heating-up time of 11 minutes --ol--u~ o g o ~ ~

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., . , _ l2 EXA~PLE I.

To investigate the effectiveness of deligni-fication and yield of fiber when using the novel salt catalysed largely methanol-water solvent mixtures, a number of cooks were carried out in laboratory-scale stainless steel pressure vessels having internal dimensions of 11 cm height and 4.5 cm diameter.
Wood chips in both air-dry and green condition were conditioned to a uniform moisture content before the pulping trials. Batch quantities of commercial size chips were charged into the digester with ten times their weight of coo}cing liquor containing predetermined quantities of the salk catalysts. The volume ratio of methanol to water ranged between 70:30 to 98:2. The sealed stationary vessel was quickly brought to cooking temperature in a thermostatically controlled glycerine bath and the tempe-rature held constant for the cooking interval required.
The reported cooks are those which at the end of the stated period produced a free pulp when slurried in disintegrator at slow stirring speed.
At the end of each cook the digester was rapidly chilled with cold water and the liquor decanted.
After disintegration of the cooked chips in acetone or ¢ooking solvent and final washing in water the pulp was air-dried to constant weight and yield,Kappa number and TAPPI 0.5 per cent viscosity determined in an effort to characterize the pulp. TABLES 2, 3 and 4 indicate the determinations made on the pulp as well as indicate the wide variations in cooking conditions under which such free pulps can be obtained. In TABLE 2 effectiveness of the various alkali metal salt catalysts is demonstrated, whereas in TABLE 3 the effect of various added secondary TABLE 4. COOKING SPRUCE WOOD WITH PRIMARY AND AUXILIARY
ACID HYDROLYZING CATALYSTS

C A T A L Y S T COOKING COOKING PULP KAPPA TAPPI 0.5%
1 2 TIME* TEMP. YIELD NO. VISCOSITY
NORMAL/MOLARmin C % cP

H2SO4 MgCl35 200 58 38 19 0.001 0.0038 SnC12 CaC1255 200 63 77 22 0.0002 0.01 40 200 58 67 24 AlC13 CaC1240 200 60 67 24 0.0003 0.01 E12SO3 CaC12 65 200 67 93 22 0.009 0.003 HCl CaC1245 200 59 56 27 G.002 0.025 .... ~
SALICYLIC MgC12 0.0001 0.005 ... .. . .. _ . _ _ _ OXALIC CaC12 65 200 61 78 27 0.0001 0.005 55 210 63 57 30 ACETIC CaC12 0.0001 0.0~5 * Includes 11 min heating-up time to temperature ~12-z strong mineral acid catalysts are given. TABLE 4 shows the effect of added secondary acid catalysts on delignification of spruce wood whereas in TABLE 5 the effect of varying alcohol-water ratios and the compensating effect of increaesd temperature and prolonged cooking time are demonstrated.
Pulping spruce wood at the high alcohol concentrations indicated in the table shows that in the presence of 0.05 molar salt concentrations,with or without the secondary acid catalysts~free fiber separation is obtained within 15 to 60 min and in spite of the relatively high Kappa number, fiber liberation wa~ obtained at relatively high pulp yield. The pulps had viscosities between 20 to 48 centipoise corresponding to a de~ree of polymerization of 1320 to 1880 (Rydholm, Pulping Processes, p. 1120).
In a number of cooks tnot reported) wherein the cooking interval was not sufficient to render fiber separation, the chips were found to be suEiciently soft so that a semi-mechanical pulp could be prepared on treatment at high speed in a blender. In certain of the reported cooks where "poor fiber separation" was reported after a predetermined cooking time it was found that on high-speed blending acceptable pulps could be produced. It is there-fore to be undesrstood that this invention is not limited to the length of cooking at which a free fiber state is reached but also includes cooks for only a sufficient time at which minimal delignificat:ion and hemicellulose removal took place to produce a semi-chemical pulp product of ultra high yields say about 80 to 90 per cent. Fùlly defiberized pulps can be had at 75 per cent pulp yield.
The process also appears to be quite tolerant to extended cooking times wherein the parameter most affected is residual lignin content.

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TABLE 5. VARIATION OF METHANOL-WAT:ER RATIO, COOKING TEMPERATURE, AND TIME IN CaC12-CATALYSED (0.05 MOLES PER L) PULPING
OF ASPEN AND SPRUCE WOODS

SpEcI~ls ALCOHOL C O O K I N G P U L P TAPPI 0.05% CuEn to WATER TEMP TIME** YIELD KAPPA VISCOSITY, cP.
RATIO* C min. ~ No . _ . ............... .
~ 70:30 190 30 61 25 24 o 80:20 190 42 61 14 32 90:10 190 35 64 20 50 90:10 190 50 63 15 38 Z 95: 5 190 30 67 39 ANHYDR. 190 50 69 37 90:10 200 10 61 19 95: 5 220 8.5 66 33 ================================================================
70:30 200 30 56 47 23 80:20 200 50 59 45 80:20 210 13 70 95 46 80:20 210 25 60 42 37 ~ 90:10 210 20 75 86 48 90:10 210 25 69 70 90:10 220 11 78 112 90:10 220 13 74 99 90:10 220 20 61 59 40 90:10 220 25 59 39 43 95: 5 200 50 66 75 46 95: 5 200 55 63 59 95: 5 210 30 67 73 52 95: 5 220 15 66 60 42 95: 5 220 25 60 51 48 98: 2 220 35 63 52 35 * Wood/Liquor ratio 1:10 ** Cooking time include~ 11 minute heating-up time The pulping li~uor when subjected to vacuum distillation at low temperature yields a flocculated lignin precipitate. After recovery of the lignin by filtration or centrifuging a sugar wort is obtained with solids concentration up to 25 per cent of which 95 per cent is dimeric and oligomeric sugars. Charcoal filtration removes most of the yellow color due to the water soluble lignin depolymerization products. The molecular weight distribution of the lignin shows one major and 2 to 3 minor peaks with the maximum being under 3800. Puri~ication of the crude lignin is most effectively done by redissolution in acetone and spray drying in vaccum at low temperature to avoid melting and resinification. ~ dried solid filt~r cake is easily broken up into a free f]owing tan-colored powder.
Similar pulping data is presented for aspen poplar wood in TABLE 6. The liquor to wood ra~io in all cooks was 10:1.

TABLE 6. COOKING OF ASPEN POPhAR WOOD CHIPS WITH METHANOL-WATER CONTAINING 0.05 MOLES OF CaC12 PRIMARY CATALYST.

ALCOHOL: COOKING COOKING PULP KAPPA TAPPI 0.5 ~
WATERTIME,TEMP. YIELD NUMBER CuEn VISCOSITY
RATIOmin* C ~ cP
__ _ _ . _ . ...... . _ . . .
80:2042 190 61 14 32 _ . . . _ _ . ~
90:1035 190 64 20 50 . . _ _ _ . .
95:5 30 190 67 30 44 ANHYDR. 50 190 69 37 42 90:1010 200 61 19 36 95:58.5 200 66 33 40 * Includes 11 min hea-ting-up tlme to temperature.
Very similar results were obtained with othQr lignocellulosic species whereby sugarcane rind behaved like aspen poplar, jack pine, ponderosa pine, western hemlock and Douglas-fir behaved like spruce wood whereas birch and Eucalyptus species proved to be intermediate species and wheat straw was found to be a more difficult species than spruce requiring lar~r ~ catalyst concentrations than spruce to yield pulps with equal degree of delignification.
Numerous other secondary catalysts listed in TABLE 1 were also tested but their results not reported herein due to the large similarity in results obtainable on applying them. In these cases some adjustments in cooking conditions were necessary to compensate for the variation in acid strength.

EXAMPLE II.

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In a further series of cooks carried out as illustrated in EXA~P~E I the effect of degree of delignification was studied with respect to its influence on the pulp chemical, physical and mechanical properties. All cooks were conducted with CaC12 as the only catalyst and a standard liquor composition of 90:10 alcohol:water mixture containing 0.05 moles of catalyst was used throughout.
The pulping data is summarized in TABLE 7 for both spruce and aspen wood.
The pulp fibers thus produced were first screened through a No 6-cut flat screen and then beaten in various steps to 300 ml Csf (Canadian Standard Freeness, TAPPI T 227 Os-58) in a PFI (Papierindustriens Forsknings-inst~tut)mill and standard handsheets were prepared according to the relevant TAPPI standard procedures. Sheet mechanical properties such as breaking length, tear and burst factor and zero-span tensile strength were also determined according to the relevant TAPPI standard testing procedures. On selected pulps a three-stage bleaching of CEH sequence was also carried and its effect on the pulp properties were also lncluded in TABLE 7.
Several of the higher-yield pulps were also a ~D o u. ~ ~ cn ~
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delignified with sodium chlorite for 5 min according to TAPPI 230-su-66 in preparation for purification to an alpha-cellulose (TAPPI T 429-m-48 gravimetric) to estimate the 17.5 % NaO~-resistant fraction remaining in the pulps.
Spruce pulps averaged between ~3.8 to 45.1 per cent alpha-cellulose based on dessiccated wood as 100, this value showing little if any variation with the actual pulp yield.
Similarly, the TAPPI 0.5 ~ CuEn viscosity (TAPPI T 230 Os-76) was also determined for these pulps to indicate the surpris ingly low carbohydrate degradation by this process. Aspen pulps showed in comparable tests an alpha-cellulose content of 48~ the dessiccated wood taken as 100 per cent. The natural as cooked brightness of the pulps was 55 to 63 ~
brightness GE for spruce and up to 70 % for the low residual lignin content aspen pulps showing very little variation with varying levels of residual lignin.
It can be seen from the data that the intrinsic fiber strength and chemical quality of the fibers surpass those previously published for organosolv pulps and closely approach or exceed th~se reported in the literature for the species.
Some of the pulps were also tested for residual cations of Ca++ and Mg + normally absorbed by cellulose fibers from such solutions through cation type exchange.
Analysis of fully digested pulps by atomic absorption spectrophotometry shows Ca and Mg levels in these pulps to be lower than found in the original wood itself.
In conjunction with these tests summative carbohydrate analyses were also carried out for the original wood of spruce and aspen poplar and the pulps prepared therefrom. Findings of these investigations are summarized in TABLE 8. Sugar composition of alpha-celluloses are o ~ rll ~ ~
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z those prepared from the pulps. The aspen pulp samples were found to be rich in xylan and spruce in mannan with the other less improtant hemicellulose being present in smaller amounts. Retention of these hemicelluloses explain the improvements in sheet strength and higher than usual yield had earlier with this process.
Analysis of the sugar wort showed (data not reported herewith) that the majority of dissolved sugars was present as monomers (about 30 to 50 ~) and the rest as low molecular-weight oligomers. Surprisingly no furfurals were detected in the residual liquors following the cooks done with the alkali earth metal as primary catalysts alone.
In prior organosolv cooking degradation (dehydration) of the xylose and hexose sugars to furfurals is a simultaneous reaction with hydrolysis and delignification and was found to be prevalent at the higher temperatures (above 200C).
In solution these furfurals are very active and condense readily with the dislodged low molecular-weight lignin fragments to form alcohol insoluble products. The absence of furfurals in residual liquors of this invention assures complete solubility of the dissolved lignin and a high degree of sugar recovery as by-product. The sugar solutions are readily fermentable into ethanol,yeast and other fermentation products. The alkali earth metal catalysts do not interfere with such fermentation processes and can also be safely discharged in mill effluents.

EXAMPLE III.
While the examples given before show quite adequate selectivity for delignification at thermodynamically defined conditions, allowing or causing an increase in internal pressures higher than that normally found for enclosed liquids under free expansion conditions, or by --21_ .,L, deliberate application of pressure from a pressure intensifier or through compressed inert gases was found to offset delignification and carbohydrate degradation rates at high alcohol water ratios and high temperatures by shifting the rate constants in a very favourable manner.
In general it was observed, that in order to achieve the same degree of delignification at high alcohol water ratios especially over 85:15 higher temperatures were required.
Thus desired delignification rates could be maintained and cooking times could be held within reasonable limits. It was also found that as the system perssure increased so did the pulp viscosity indicating the beneficial effects of pressure on delignification rates and on lowering the sensitivity of the carbohydrates to increased thermal treatment which normally led to lower viscosities. It was also observed that the pressure effects were not linked to increased penetration into the wood matrix since when air-dry chips are cooked with 90:10 or 95:5 alcohol:water solvent mixtures in the presence of 0.05 moles of CaCl2 at 210C under normal pressure (35 atm and 39 atm, respec-tively) complete penetration of the chips is observed within the first lO min of cooking yet no fiber separation occurs even after prolonged cooking, up to 50 min. Under the same conditions but with added or internally generated overpressure fully cooked chips are obtained which show the same fiber liberation tendencies as chips cooked at lower alcohol concentration (under 80:20) Whle this in itself was surprising effect, analysis of the resulting pulps showed a consistently higher pulp viscosity, in fact the pulp viscosity consistently increased with the level of pressure applied or generated. Some data on high pressure sooks is reproduced in TABLE 9. In comparison to previous test data provided in TABLE 5 wherein the increased selectivity of delignification and the lower carbohydrate degradation (higher pulp viscosity) and a significant reduction in cooking time is clearly evident. Thus the confounded effect of high alcohol concentration and high pressure becomes the most important aspect of this invention in that it allows now the deligni~ication of any wood species to residual lignin content levels whic~ earlier were not possible without considerable losses in cellulose viscosity. The pressure effect somewhat diminishes when solvent compositions lower than 60:40 alcohol:water content are used.

TABLE 9. EFFECT OF INCREASED PRESSURE ON DELIGNIFICATION
RATES AND CARBOHYDRATE DEGRADATION AT VARIOUS
ALCOHOL:WATER RATIOS.ON COOKING SPRUCE WOOD.

_ _ LIQUOR C O O K I N G YIELD KAPPA TAPPI 0.5 COMP.* TEMP. PRESSURE TIME NO. Viscosity C atm min % cP

70:30 190 265 30 72 82 70 _ . _ . . _ . . _ . . _ .. .. .. ...
70:30 190 265 50 64 70 58 . _ . . .
70:30 190 265 70 59 48 53 . . _ . . . _ . _ _ . . _ _ 70:30 190 23 70 64 71 48 .
70:30 190 23 90 61 61 44 . _ . . . ..... . . . _ . . . _ 80:20 210 285 25 60 41 57 .
80:20 210 285 30 57 45 47 _ _ .. _ . . .. _ .. _ _ .
80:20 210 285 35 52 27 26 . .
80:20 210 33 25 61 63 55 . _ .. . _ . . _ _ .
80:20 210 33 30 59 56 40 . _ 80:20 210 33 35 57 45 38 .. . . _ . _ 90:10 210320 20 75 86 62 ~ . .
~0:10 210320 25 69 71 50 ., . _ . . , . , _ , ~
90:10 210 320 35 63 62 ==~ . .. . _ . . . _ . .. _ 90:10 210 320 60 57 36 . . . ~
90:10 210 40 35 59 100 24 ~ . . . ... _ . .. .. . .. _ 90:10 21040 80 52 100 10 , . . .

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Y~2 All cooks were done at a wood:liquor ration of l:lO.
Cooking times include 9 min for heating-up to temperature.
In a similar series of cooks with 90:10 alcohol:water mixture, cooked at 210C and 320 atm it was established that the ratio of lignin to carbohydrate removed can be as high as 9.48 on spruce wood and delignification could be persued to a Kappa number of 14.5 at a residual pulp yield of 49 %. The viscosity dropped from an initial value of 55 cP to 24 on cooking for 50 min under the above conditions. Thus t~e pulp properties generally increase with increased overpressure at the lower temperatures possible. Interestingly, the alpha-cellulose yield of the highly delignified pulp was still 43.2 % based on wood as lO0, representing 88 % of the total pulp mass.

Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for pulping lignocellulose plant material to separated fibers in which the plant material is digested with an aqueous aliphatic alcohol containing a catalyst compound to aid delignification at elevated temperature, the improvement of which comprises:
- cooking fragmented lignocellulose material with an aqueous solvent mixture containing a major volume portion of alcohol and water containing an alkali earth metal salt primary catalyst compound and an acid as auxiliary hydrolysing catalyst at elevated pressures greater than the autogeneous pressure developed by the vapours at the temperature used, for a time sufficient to effect at least partial depolymerization and dissolution of the lignin and hemicelluloses to render the fibers separable from each other in the liquor residue containing dissolved lignin materials and sugars, - recovering the separated fibers from liquor residue, and - separating the spent liquor into solvent, lignin and sugars.

2. The method of Claim 1 wherein the lignocellulose material comprises between 1/6 to 1/100 by weight of the solvent mixture.

3. The method of Claim 1 wherein the alcohol is methanol and the solvent to water ratio is in the range from 50:50 to 98:2 volume per cent.

4. The method of Claim 1 wherein the lignocellulose material comprises between 1/6 to 1/100 by weight of the solvent mixture, the alcohol is methanol and the solvent to water ratio is in the range from 50:50 to 98:2 volume per cent, the primary catalyst compound is a salt or mixture selected from the group consisting of chloride, nitrate and sulphate of divalent neutral alkali earth metal calcium, magnesium and barium and the concentration is at least 0.001 mole per liter solution.

5. The method of Claim 4 wherein the acidic auxiliary secondary hydrolysis catalyst is either autocatalytically generated or added consisting of formic or acetlc acid and mixtures thereof and the concentration being between 0.0001 to 0.05 normal per liter solution.

6. The method of Claim 4 wherein the acidic auxiliary secondary hyrolysis catalyst is either autocatalytically generated or added consisting of formic or acetic acid and mixtures thereof and the concentration being between 0.0001 to 0.05 normal per liter solution, and the added acidic auxiliary hydrolysing catalyst is selected from the groups of strong mineral acids, weak mineral acids, weak organic acids and strongly acidic metal salts.

7. The method of Claim 6 wherein the strong mineral acid is hydrochloric, sulphuric, nitric or phosphoric acid, preferably but not necessarily matching the anion of the primary catalyst in the concentration between zero to 0.01 normal.

8. The method of Claim 6 wherein the weak mineral acid is selected from the group consisting of sulphurous, phosphorous acid and the concentration be between zero to 0.01 normal.

9. The method of Claim 6 wherein the weak organic acid is selected from the group consisting of oxalic, salicilic, maleic, L-malic, succinic, o-phthalic, benzoic and the concentration may be from zero to 0.05 molar.

10. The method of Claim 6 wherein the strongly acidic metal salt is selected from the group consisting of stannic chloride, aluminum chloride or sulphate, ferric or ferrous chloride and the concentration may be from zero to 0.025 molar.

11. The process of Claim 4, 5 or 6 wherein the cooking temperature is between 180 to 240°C.

12. The process of Claim 4, 5 or 6 wherein the pressure during the cook is at least 5 atmospheres higher than that usually developed by vapors at the temperature used.

13. The process of Claim 1 wherein on low temperature vacuum distillation of the spent liquor the lignin precipitates as a filtrable powder.

14. The process of Claim 13 wherein the residual aqueous solution contains at least 6 to 25% dissolved wood sugars.