FI71781C - KOKNING AV LIGNOCELLULOSA MED VATTENHALTIG ALKOHOL OCH JORDALKALIMETALLSALTKATALYSATOR. - Google Patents

Description

1 71781

The present invention relates to a process for dissolving a lignocellulosic substance containing a lignocellulosic substance which contains an alkaline earth metal salt, namely magnesium, calcium or barium chloride or magnesium sulphate or a soluble mixture thereof, in a concentration of less than 0.1 molar and optionally in a normal concentration of the acid-reactive substance of less than 0.008 for up to two hours above 130 ° C at a temperature at which the amount of the cooking solution is always at least 4 parts by weight per part by weight of the lignocellulosic substance, recovering the fibers thus liberated from the cooking solution, and separating the remaining cooking waste solution into solvent, lignin and sugars.

Such a method is described in DE-A-20 29 20 731. The main advantages of this known method compared to conventional organosolv cooking methods using mixtures of alcohol and water as a cooking solution without the addition of an alkaline earth metal salt are significantly higher delignification rate and lignin recovery in powder form and not in powder form. as a semi-molten phase which is not easily removed from the equipment and has a low commercial value.

The problem to be solved by the invention is to improve the specificity of delignification with respect to all lignocellulose species and thus to increase the yield of cellulose pulp, to reduce the viscosity losses due to carbohydrate degradation, to improve the quality and stability of raising the temperature stability of substances in high temperature soups.

2,71781 These problems have been solved by the method set out in the claim.

GB patent no. 357 821 (Kleinert) describes a process for the decomposition of vegetable fibers for the recovery of cellulose and peel materials, in which mixtures of alcohol and water with a water content of 20 to 75% by weight are used as a decomposing agent, and on page 1, lines 74-77 it is stated that using 96% alcohol gives a dark brown residue corresponding to 92% of the 10 raw materials. An article by Theodor Kleinert in "Zeitschrift f, angewandte Chemie" 44 (1931), pp. 788-791, on page 789 shows that absolute alcohol dissolves little lignin and hardly any carbohydrates, and in lines 4-2 of the same page, 15 ha, referring to Figure 1, that the maximum dissolution is obtained at an alcoholic strength of 45-50%, and U.S. Patent 3,585,104 (Kleinert) discloses in column 2, lines 42-44, that methanol and ethanol, used at a mean concentration range of about 20-75 % by weight of alcohol, has a stronger delignifying effect on fibrous plant materials than anhydrous alcohols.

Thus, it was surprising that using aqueous methanol or ethanol containing 80-98% by volume of alcohol in the presence of alkaline earth metal salts as defined in the claims and optionally acidic substances can give much better results than using lower alcohol contents in the cooking solution.

It was also surprising that if, in addition to the alkaline earth metal salts, one or more of the specified acid-reactive substances are added to the cooking solution, the additive has a much greater effect than adding either the alkaline earth metal salt or the acid-reactive substances so that the total amount of additives can be substantially reduced.

35 Dissolution of the lignocellulosic substance produces 71781 organic acids, such as formic or acetic acid.

These acids should be taken into account when determining the amount of acidic substance to be added to the cooking solution so that the pH of the reaction mixture remains at a value which is preferably greater than 3.8 and less than 7.0, regardless of the acids added or autocatalytically formed. Such pH adjustment is readily accomplished using mild buffering of alkali metal ion systems, as is the case with the technical grade alkaline earth metal salts used in this invention, or with standard buffer salts for this pH range. Another very important feature of such systems is that the actual cooking pH varies only within relatively small ranges between 3.8 and 5.6, or not at all, depending on the acidity of the wood grade and the buffering effect of the alkali metal ions present or added to the cooking solution.

In the process of the invention, methanol is the most preferred alcohol, but when methanol is not available in sufficient amounts, ethanol may just as well be used.

The alcohol content of the cooking liquor is preferably 80 to 98% by volume, but higher percentages in this range are relatively difficult to achieve due to the moisture content of the lignocellulosic starting material.

The ratio of lignocellulosic agent to cooking solution is preferably 1: 6 to 1:20.

When the required high alcohol-water ratios and additives are used, not only is delignification more complete but the decomposition of carbohydrates is also reduced, especially when using an overpressure of more than 5 bar above which cooking medium vapors develop at the temperature used.

The following Table 1 shows the combinations of alkaline earth metals and acid hydrolysing agents used in the process according to the invention: v 71781

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71781 5

Example 1:

To investigate the efficiency of delignification specificity and fiber yield using a new, mainly methanol-water solvent extraction in the presence of alkaline earth metal salts and additional acid catalysts, a series of soups were performed in stainless steel laboratory pressure vessels with a diameter of 4.5 cm and a diameter of 11 cm.

Both air-dried and fresh wood chips were conditioned to a uniform moisture content of 10 before cooking experiments. Commercially sized chips were charged in batches to the cooking vessel along with ten times the weight of the cooking solution containing predetermined amounts of salt catalysts. The volume ratio of methanol to water ranged from 90:10. The temperature of the closed stationary vessel was rapidly raised to the cooking temperature in a thermostatically controlled glycerin bath and the temperature was kept constant for the required cooking period. The soups reported are those which, after said period, formed a loose mass slurried in a disintegrator using a low stirring speed.

After each cooking, the cooking vessel was rapidly cooled with cold water and the liquid was decanted. After decomposing the cooked chips in acetone or cooking solvent and after final washing with water, the pulp was air dried to constant weight and yield, and the kappa number and TAPPI 0.5% viscosity were determined to characterize the pulp. The results are summarized in Table 2.

Table 2 «71781

Spruce wood soup with primary and additional acid hydrolysing catalysts__

Catalyst Cooking time * Cooking heat Pulp- Kappa TAPPI 0.5% 1 ° 2 ° min C ° yield no. viscosity

normal / mol% Pa * s-J

ri H2S ° 4 070038 40 200 46 39 3.7

MgCl2 0.01 50 200 no fiber separation h2so4 MgCl- 07001 0.0038 35 200 58 38 19

CaCl2 0.01 45,200 no fiber separation

SnCl2 CaCl2 55 200 63 77 22 0.0002 0.01 40 200 58 67 24 ÄlCl3 0.005 70 200 no fiber separation A1C13 CaCl2 40 200 60 67 24 0.0003 0.01 h2so3 0.005 70 200 no fiber separation H2SO3 CaCl2 65 200 67 93 22 0.009 0.003 HCl 0.0025 40 200 no fiber separation HCl CaCl2 45 200 59 56 27 0.002 0.025

Table 2 (continued) 71781

Decoction of spruce with primary and additional acid hydrolysing catalysts_

Catalyst Cooking time1 Cooking heat Pulp- Kappa TAPPI 0.5% 1 ° 2 ° min C ° yield no. viscosity normal / mol% Pa · s ~ 3 ri

Salicylic acid 0.005 70 200 no fiber separation

Salicylic MgCl2 acid 0.0001 0.005 55 200 62 60 28

Oxalic acid 0.005 70 200 no fiber separation

Oxal- CaCl. 65 200 61 78 27 acid 1 85 200 58 67 26 0.0001 0.005 55 210 63 57 30

Acetic acid 0.005 70 200 no fiber separation

Acetic acid CaCl2 ^ 55 200 61 68 34 0.0001 0.005

Includes a heating time of 11 minutes. to a temperature of 71781

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In particular, the results in Table 2 show that effective delignification selectivity and fiber release are obtained at concentrations of alkaline earth metal salts and excess acid catalyst that are normally ineffective under the conditions listed in Table 2. The synergistic additive effect of both catalyst types is all the more surprising, especially in cases where the combined amounts of both catalysts are well below the amount previously considered to be the lowest effective salt concentration required to release the fibers.

Table 3 shows the effect obtained by varying the alcohol-water ratios and the compensating effect of the elevated temperature and the extended cooking time on spruce wood.

When cooking with aspen and spruce using the high alcohol concentrations listed in Table 3, it is seen that in the presence of 0.05 molar salt concentration with or without a secondary acid catalyst, free fiber separation is achieved in 15-60 minutes (including 11 to 20 minutes heating time) and despite relatively high kappa number. fiber release was obtained at relatively high pulp yields. The viscosities of the pulps were 20-52 PsS, corresponding to a degree of polymerization of 1320-2200 (Rydholm, Pulping Processes, p. 1120).

Table 3 9 71781

Variation of cooking temperature and time of methanol-water ratio in CaCl 2 -catalyzed (0.05 mol / l) aspen and spruce wood

Type Alcohol: Pulp soup TAPPI 0.05% CuEn water Temp. Time ** Yield Kappa viscosity, ratio1 2 CC min. % no. Pa1s ~ ^ 70:30 190 30 61 25 24 80:20 190 42 61 14 32 90:10 190 35 64 20 50

Aspen 90:10 190 50 63 15 38 tree 95: 5 190 30 67 39 44

Anhydrase. 190 50 69 37 42 90:10 200 10 61 19 36 95: 5 220 8.5 66 33 40 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

Spruce 90:10 220 13 74 99 tree 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 48 95: 5 220 25 60 51 42 98: 2 220 35 63 52 35 wood / liquid ratio 1:10 2 cooking time includes 11 min heating time 71781 10

It is found that the system follows Arrhenius laws on temperature so that cooking times relative to fiber separation and comparable kappa number decrease with increasing temperature even at an unusually high temperature of 220 ° C, while the effect on viscosity is only negligible or non-existent at such a high temperature. When the broth contains 80% by volume of alcohol or more, the most sensitive parameter is residual lignin, while only small losses in pulp yield occur. Accelerated degradation of carbohydrates is observed in al-10 alcohol: water ratios of 70:30 and below, so the carbohydrate stabilizing effect of a high alcohol broth is a very surprising effect and quite the opposite of the previously reported data. High alcohol solutions allow for more complete delignification at a given cooking time.

It can be seen from the table that a pulp yield of more than 60% can be achieved by boiling spruce in a kappa number of 45 and less than this in a cooking time of 25 (minus 11) minutes.

The process also seems to withstand extended cooking times, with the residual lignin content being the most sensitive parameter.

In some soups (not explained) where the cooking time was not sufficient to effect fiber separation, the chips were found to be soft enough to produce a semi-mechanical pulp 25 by treatment in a high speed mixer. For some soups that had previously reported "No fiber separation" (NFS) after a predetermined cooking time, it was found that acceptable pulps could be prepared using high speed mixing. Thus, it is to be understood that this invention is not limited to the length of cooking time in which free fiber space is reached, but also includes soups that are only long enough to have minimal delignification and hemicellulose removal to produce semi-chemical pulp in very high yields, e.g. % yield. Completely 71781 11 fiber separated pulps can be prepared in 75% pulp yields.

Cooking liquid exposed to vacuum distillation at low temperatures gives a flocculated lignite precipitate. After recovery of the ligig-5, filtration or centrifugation gives a sugar solution with a solids content of up to 25%. Carbon filtration removes most of the yellow color derived from water-soluble lignin depolymerization products. The molecular weight distribution of lignin shows 10 single large and 2 to 3 smaller peaks with a maximum value below 3800. Crude lignin is best purified by redissolving it in acetone and spray drying in vacuo at low temperature to avoid melting and resinization. The dried solid filter cake can be easily broken into a free-flowing light brown powder.

In addition to these experiments, additive carbohydrate analyzes were also performed on the original spruce and aspen wood (Aspen poplar) and the pulps made from them. The findings of these studies are summarized in Chapter 4 of tau-20. The sugar compositions of alpha-cellulose correspond to those obtained from the pulps. Aspen pulp samples were found to be xylan-rich and spruce pulp samples mannan-rich with other minor hemicelluloses present in smaller amounts. The retention of these hemicelluloses explains higher than normal yields previously obtained by this method.

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Analysis of the sugar wort (results not shown here) shows that most of the dissolved sugars were present as monomers (about 30-50%) and the rest as low molecular weight ol-isomers. Surprisingly, no furfurals were observed in the waste solutions of soups made using alkaline earth metal salts alone as primary catalysts. In previously known acid-catalyzed organosolv soups, the decomposition (dehydration) of xylose and hexose sugars to furfural is a reaction that occurs simultaneously with hydrolysis and delignification and was found to be predominant at the highest temperatures (above 200 ° C). In solutions, these furfural are highly active and readily condense with detached low molecular weight lignin fragments to form alcohol-insoluble products. The absence of furfural in the waste solutions of this invention ensures complete solubilization of dissolved lignin and a high degree of sugar recovery as a by-product. Sugar solutions can be easily converted to ethanol, yeast and other fermentation products through fermentation. Ground-alkali-20 metal catalysts do not interfere with these fermentation processes and can also be safely removed with factory sewage.

Very similar results were obtained with other lignocellulosic secrets. Sugar cane shell behaved similarly to 25 aspen, jack-pine, ponderosa-pine, and Western hemlock; Douglas-fir behaved in the same way as spruce, while birch and Eucalyptus species proved to be medium species and wheat straw was harder than spruce, requiring higher catalyst concentrations than spruce to produce pulps with the same degree of delignification. Numerous other secondary catalysts listed in Table 1 were also tested, but their results are not reported here because their results were similar. In these cases, the cooking conditions had to be adjusted to some extent to compensate for variations in acid strength.

14 71 781

Example II

Although the above examples show very good delignification selectivity under thermodynamically defined conditions, it was found that if the internal pressure was allowed to rise or was raised above the values normally found with closed liquids under conditions allowing free expansion, or if the soups were deliberately -10 1a, this affected delignification and carbohydrate degradation rates, especially at high alcohol: water ratios and high temperatures, by shifting the rate constant in a very advantageous manner. It was generally found that higher temperatures were required to achieve the same degree of delignification at high alcohol: water ratios, especially above 85:15. Thus, the desired delignification rates could be maintained and cooking times remained within reasonable limits. It was also found that as the system pressure increased, so did the viscosity of the pulp, indicating a beneficial effect of pressure on delignification rates and a reduction in the sensitivity of carbohydrates to more intense heat treatment, which normally led to lower viscosities. It was also found that the pressure effects were not associated with increased penetration into the wood matrix because when boiling air-dried spruce chips in 90:10 or 95 ^ alcohol: water solvent mixtures using 0.05 moles of CaCl 2 at 210 ° C at normal autogenous pressure (35 atm and 39 atm, respectively) complete penetration of the chips takes place during the first 10 minutes of cooking -30 na but still the separation of the fibers is also minimal after extended cooking, up to 50 minutes. Under the same conditions, but using increased or internally developed overpressure, fully cooked chips are obtained which have the same tendency to release fiber fibers as chips cooked using lower alcohol concentrations (ai 71781 15 le 80:20). Although this in itself is a surprising effect, analyzes of the masses obtained consistently showed a higher mass viscosity. In the case of Tise, the viscosity of the pulp increased uniformly with increasing pressure applied or developed. Table 5 shows some values for high-pressure cookers. For comparison, previous experimental results are shown in Table 5, where increased selectivity of delignification and lower carbohydrate degradation (higher mass viscosity) and a significant reduction in cooking time with increased pressure are clearly observed.

Thus, the combined effect of high alcohol concentration and high pressure is an important feature of this invention because it allows faster delignification of an arbitrary wood species to low residual lignin concentrations without significant cellulose viscosity losses. The pressure effect is somewhat reduced when using solvent compositions with an alcohol: water ratio of less than 80:20.

16 71781

Table 5

Effect of elevated pressure on delignification rates and degradation of carbohydrates at different alcohol and water ratios when boiling spruce wood 5 Solution Soup yield Kappa TAPPI 0.5% composition * temp. pressure time no. viscosity ° C bar% Pa * s 80:20 210 285 25 60 41 57 10 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 15 90:10 210 320 20 75 86 62 90:10 210 320 25 69 71 50 90:10 210 320 35 63 62 43 90:10 210 320 60 57 36 41 90:10 210 40 35 59 100 24 20 90:10 210 40 80 52 100 10

All soups were performed using a wood: solution ratio of 1:10. Cooking times include a heating time of 9 minutes. temperature. In a similar series of soups using 90:10 alcohol: water mixtures at 210 ° C and 320 bar, it was found that the ratio of separated lignin to carbohydrate can be as high as 9.48 for spruce and that delignification could be performed up to a kappa number of 14.5 with a residual mass yield of 49%. The viscosity of 30 decreased from an initial value of 55 Pa * s- ^ to 24 when cooked for 50 minutes under the above conditions. Thus, the properties of the pulp generally improve with increased overpressure at the lowest possible temperatures. It is interesting to note that the yield of highly delignified pulp alpha-cellulose-35 was still 43.2% based on the value of 100 wood, which

II

Claims (8)

17 71 7 81 corresponds to 88% of the total mass. All pulps prepared under these conditions were completely fiberized and did not form any waste materials when screened no. 6 through a cut flat standard laboratory mass sieve. The claims; A process for preparing fibrous cellulose from a lignocellulosic material by dissolving lignin and hemicelluloses from a starting material in a mixture of water and methyl or ethyl alcohol containing an alkaline earth metal salt in solution, namely magnesium, calcium or barium chloride or nitrate or magnesium sulphate or magnesium sulphate thereof or for a maximum of two hours at a temperature of 170 to 240 ° C, the cooking solution being at least 4 parts by weight per part by weight of lignocellulose and separating the cellulose from the resulting solution, characterized in that: 1. aqueous methanol or ethanol has an alcoholic strength of at least 80 and at most 98 volume-%; 2. the pressure during cooking is kept at least 5 bar higher than the vapor pressure of the cooking solution which develops at the cooking temperature; and 3. the alkaline earth metal salt is used in a concentration of 0.001 to 1.0 molar. Process according to Claim 1, characterized in that one or more acid-reactive substances are dissolved in the cooking solution in such a way that their total concentration does not exceed 0.009 N, in order to maintain a pH between 3.8 and 3.6, the acid-reactive substance being a strong mineral acid. weak mineral acid, organic acid or acid-reactive salt ie 717 81 or a mixture thereof. Process according to Claim 2, characterized in that hydrochloric, sulfuric, nitric or phosphoric acid is dissolved in the cooking solution in a concentration of at most 0.001. Process according to Claim 2, characterized in that sulfuric acid, phosphoric acid or boric acid are dissolved in the cooking solution at a maximum concentration of 0.009. Process according to Claim 2, characterized in that formic, acetic, oxalic, salicylic, maleic, 1-malic, succinic, o-phthalic or benzoic acid is dissolved in the cooking solution in a concentration of at most 0.005. Process according to Claim 2, characterized in that one of the following salts is dissolved in the cooking solution at a maximum concentration of 0.0025: SnCl 4, AlCl 3, Al 2 (804) 3, FeCl 2 or FeCl 3 · 1. A composition for the production of cellulose in a fiber form from a lignocellulosic material genome to a lignite and hemicellulosic material from a mixture of water and methyl or ethyl alcohol or a barium-magnesium-magnesium, calibrated and jordalkalimetimetalt, e.g. magnesium sulphate or enriched in a mixture with a temperature of between 170 and 240 ° C, colors within a maximum temperature of 170 to 240 ° C, colors of the stemstone of the stemstone, and the genome at a temperature of 170 to 240 ° C, cellulosa fran the separera Bildad the solution, characterized in that in that of the alkoholhalten vattenhaltiga 1. the methanol was eller ethano-len is at least 80 och volym- no more than 98%; I)