FI76845C - Process for preparing cellulose pulp and sugar from hardwood chips. - Google Patents

Description

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The present invention relates to a process for the production of pulp and / or sugars from hardwood chips by treating the chips with formic acid and an organic solvent such as a ketone or alcohol.

The extraction of wood material with formic acid in the presence of a surfactant has been studied e.g. Bucholtz, M.

10 and Jordan, R. K. (Pulp and Paper, 1983 (September) 102-104) and Jordan, R.K. (PCT Application US 81/01627). Peroxumartic acid or acetic acid have been used by Poppius, K., Laamanen, L., Sundqvist, J., Wartiovaara, J. and Kauliomäki, S. (Paperi ja Puu 2 (1986) 87-92). Acetic acid-ethyl-15 acetate extraction has been studied e.g. Young, R. (Int. Symp.

Wood and Pulping Chem., Vancouver 1985 Proc., 169-172, and Pulp and Paper, 1986 (February) 33) and Haggin, J., C & EN 1986 (January) 25-26). Alcohols have been used as cooking solvents, e.g. In the APR method (Lora, JH and Azis, S; TAPPI 20 1984 Conference Appleton WI Sept. 30, 215-221) and in the MD method (Baumeister, M and Edel, E; Das Papier 34 (1980) 10A V9- 18 and FI patent 71360). The alcohol-metal salt method has been used by Paszner, L. and Chang, P-C (FI patent 71781).

25 The disadvantage of these prior organosolv processes is the high process temperature (170-240 °) and high pressure (1000-3000 kPa). Only the formic acid and peroxyacid methods work in 100 ° C steps. According to Example 30 describing the Jordan formic acid-surfactant method, 42 g of a pulp of 13 grams (dry matter) are obtained with a pulp number of 13 and a wood / liquid ratio of 1/10 at 100 ° C for 4 hours. The mixture contained a large amount (40 g) of surfactant.

In addition, previous organosolv methods have the disadvantage that the amount of solvent is very large. The wood / solvent ratio is usually 1/10 to 1/20, which results in a high need for solvent regeneration.

It has now been found that by adding a lignin-dissolving organic solvent, 2,768,445 such as a low molecular weight aliphatic ketone or alcohol, to the pulp production step, the quality of the pulp can be improved to obtain a bleachable pulp which is very suitable for papermaking. If desired, lignin can also be recovered, as well as dissolved sugars from the wood.

The process according to the invention makes it possible to produce benign and easily bleached pulp under mild process conditions. The method does not use surfactants or oxidants. The method is different for hardwood, but is applicable to all lignocellulosic materials.

The organic solvents to be added to the cooking solution are aliphatic ketones having 3 to 6 carbon atoms, in particular acetone, and alcohols having 1 to 5 carbon atoms, in particular methanol or ethanol. With the formic acid-acetone mixture, the cooking is most preferably carried out under a slight overpressure (150 to 400 kPa) at a temperature of 100 to 130 ° C, the operating time being 1.5 to 4 hours. Cooking can also be carried out at normal pressure and at a temperature of 90 to 110 ° C, but the cooking time is then longer, about 5 hours.

The process according to the invention makes it possible to produce unbleached paper pulp and / or sugars from wood. By varying the process conditions, the interrelationships of the products are affected. The process does not dissolve or hydrolyze cellulose. However, when up to about 20% of the wood is recovered, depending on the conditions, only less than one-tenth of the sugars are glucose.

The pulp obtained by the process according to the invention is very easy to bleach because the lignin is dissolved out in the cooking and washing. If desired, lignin can be precipitated from solution by adding water. The sugars, on the other hand, are recovered from the water filtrate. Used solvents are recovered by distillation or recycled to the process.

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In the method, the cooking chemicals do not react chemically with the lignin, so they can be recycled or recovered. The process is therefore easy to implement as a continuous countercurrent extraction. The spent broth can be re-used for pre-cooking the fresh chips up to the saturation point, whereby the pre-cooked chips can be very easily and quickly cooked with the fresh cooking solution. In a continuous process, the solvent requirement is reduced even to the wood / solution ratio = 1: 1.

10 The total water content of the mixture must not be so high that lignin precipitates. Water enters the process from technical solvents as well as wet chips.

For the process to work effectively, the total amount of water must be less than 40% of the amount of solvent mixture, less than 15%.

process alternatives

Figures 1 to 3 show block diagrams for a few different process options. If desired, the conditions of the different steps can also be combined in other ways, depending on the desired end result.

The process uses conventional equipment from the wood processing industry. The process can be performed as a batch process or continuously. The process steps, i.e. cooking, defibering, filtering, pulping and solvent recovery, are all methods known per se commonly used in the wood processing industry.

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Option 1, Figure 1

Formic acid and solvent (ketone or alcohol) are added to the chips in a kitchen or pressure vessel equipped with a condenser. Cooking takes place either at atmospheric pressure at a temperature of 70 to 110 ° C, or at an overpressure at a temperature of 70 to 150 ° C. The cooked pulp is defibered (hot or cooled) in the cooking solution with a defibrator and filtered through a pressure and vacuum filter and washed with ketone or alcohol to obtain a bleachable pulp.

10 The cooking solution can be returned to the next soup or combined with the washing solutions. If necessary, the solvents are regenerated by distillation. Lignin is recovered from the concentrated cooking solution by adding water. The sugars are recovered from the filtrate.

Option 2, Figure 2 15 As in Option 1, but the pulp cooked with a mixture of formic acid and solvent is separated from the cooking solution and defibered in an aqueous, acetone or alcohol suspension. The pulp is then separated and treated as in Option 1. Most of the sugars are recovered from the aqueous filtrate.

20 Option 3, Figure 3

Formic acid is added to the chips as in option 1, but the solvent (ketone or alcohol) is only added after the initial cooking or in the defibering / washing step. The solution separated from the cooking mass is returned as it is to the next soup or it is regenerated together with the washing solutions. The pulp is defibered in acetone or alcohol, or water, separated from the broth and washed with ketone or alcohol to give a light bleachable pulp. Lignin precipitates when water is added to the concentrated residue, and sugars are recovered from the aqueous filtrate.

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The invention is described in more detail in the following examples.

Example 1 (Figure 2) 25 g (calculated as dry matter) of air-dried birch chips 5 were treated in a pressure vessel with a solvent mixture of 100 ml of 85% formic acid and 30 ml of acetone. The temperature was 100 ° C and the treatment time was 4 hours. The mixture contained about 12% water.

The pulp was separated from the broth and defibered in water (Top Drive Macerator, Townson & Mercer Ltd). The broth pa-10 was returned to the next broth, or subjected to concentration / regeneration. The pulp was screened and filtered through a Biichner filter and washed several times. 13.6 g or 52.5% of light brown pulp were recovered. The number of pieces was 51. The combined organic solutions were fractionated by distillation. From the Sii-15 rapeseed residue, lignin was precipitated by the addition of water. Of the evaporation residue of the filtrate, 2.5 g or 9.8% of wood was xylose. Other sugars accounted for a total of 1.9% of wood, of which glucose 0.3%.

Example 2 (Figure 1) 20 250 g (calculated as dry matter) of air-dried birch chips were boiled in a Parr pressure vessel in a solution of 850 ml of formic acid and 300 ml of acetone at 105 ° C under an overpressure of 138 kPa for 3 hours. The pulp was defibered in broth, then filtered and washed with acetone. The yield of the pulp of Seu-25 was 136.9 or 54.8% of wood, the number of pieces was 54. 15.8 g of pentose sugars were recovered, of which 12.5 g or 5.0% of wood was xylose.

Example 3 (Figure 2) 50 g (calculated as dry matter) of fresh birch chips 30 (dry matter 57%) were boiled in a Parr pressure vessel in a solution of 170 ml of formic acid and 50 ml of acetone at 130 ° C for 2 hours at 400 kPa. The mass was separated from the broth and defibered in an acetone suspension, after which it was filtered and washed with acetone. The pulp yield 35 was 30.3 g or 60.1% of wood, the number of pieces was 54. Xylose from 0.6% of wood was recovered from the cooking and washing solutions.

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Example 4 (comparative example)

The procedure was as in Example 3, but using acetic acid instead of formic acid, and the cooking time was 3 hours. The yield of pulp was 33.4 g or 66% and the kappa-5 number was 60.

Example 5 (comparative example)

The procedure was as in Example 3, but the pressure was increased so that cooking took place at 150 ° C and 550 kPa for 1.5 hours. 23.8 g of a dark brittle 10 pulp with a number of pieces of 70 were obtained.

Example 6 (comparative example)

The procedure was as in Example 3, but pine wood was used instead of birch chips; boiled for 3.5 hours. A pulp was obtained which was harder and of lower quality than the birch-15 pulp.

Example 7 (Fig. 3) 50 g of dried birch chips were boiled in 170 ml of formic acid at 105 ° C, 105 kPa for 4 hours. The pulp was separated from the broth and defibered from the acetone-20 suspension, after which it was filtered, washed with acetone and screened. The method gave a relatively coarse mass of 21.5 g or 43.0% of wood, the number of pieces was 52.

Example 8 (Figure 3)

The procedure was as in Example 7, but the chips were boiled first for 2 hours in formic acid and then for 2 hours in a mixture of formic acid and acetone (170 ml of formic acid and 30 ml of acetone). The result was similar to Example 7.

Example 9 (Figure 2)

Otherwise, the conditions were the same as in Example 3, 30, but countercurrent extraction was simulated in the cooking. The same chips were boiled twice in fresh solution for 1 hour at 105 ° C. The pulp yield was 61.0% of wood and the number of pieces was 54.

When the same cooking solution filtered from the pulp cooked at 105 ° C for 3 hours in a pressure vessel was used to cook two more fresh batches of birch chips, in the second batch for 5 hours and in the third for 2 hours, a total of 54.9% of wood was obtained, 98 in the combined batch. The wood / broth ratio was 1: 2.2.

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Example 10 (Figure 2) 50 g of dry birch chips were boiled in a Parr pressure vessel in a solution of 170 ml of formic acid and 60 ml of 96% ethanol at 130 ° C at 450 kPa for 5 hours, after which the pulp was treated as in Example 2. except that ethanol was used for washing. The pulp yield was 21.6, or 43.2% of the wood, and the number of chips was 74. Xylose was recovered from 2.8% of the wood.

Claims (10)

A process for preparing cellulose pulp and sugar from hardwood chips by boiling with formic acid, characterized in that the delignification is intensified with the aid of an organic solvent. Process according to claim 1, characterized in that the organic solvent 10 is a ketone or an alcohol. Method according to claims 1 and 2, characterized in that the cooking is carried out at normal pressure and a temperature of 70 - 110 ° C and that the ratio of wood to boiling solution is 1: 1 - 1:10, advantageously 1: 2 - 1: 5, and the ratio of organic solvent to formic acid in the boil is 1:10 - 1: 1, advantageously 0.15 - 0.5. Method according to claims 1 and 2, characterized in that the water content of the boiling solution added to the tile is below 25% by weight. 5. A process according to claims 1 and 2, characterized in that at least at the initial stage the boiling takes place with only formic acid, and only at a later stage of the boiling is organic solvent added or the treatment with organic solvent is carried out after the boiling step. 6. A process according to claims 1-5, characterized in that in the cooking and / or subsequent washing, a 1-6 carbon atoms containing ketone, advantageous acetone, or an alcohol containing 1-5 carbon atoms are used. preferably methanol or ethanol. Process according to claims 1 - 6, characterized in that the cooking takes place at a temperature of 80 - 130 ° C and the cooking time is 1 - 7 tin hours, preferably 2-5 hours, at either normal pressure or 100 - 500 kPa: s overpressure.