SU485178A1 - The method of obtaining sulphate pulp - Google Patents

Description

(54) METHOD FOR OBTAINING SULPHATE PULP

one

The invention relates to a method for producing sulphate prehydrolysis cellulose, which is widely used for the production of cord, staple and other types of artificial fibers.

A method of producing cellulose is known by pre-hydrolysis of the starting cellulose-containing raw material at an elevated temperature, followed by sulphate cooking.

There are two methods of preliminary hydrolysis - acid and water. In the first method, the hydrolysis is carried out with dilute solutions of mineral acids. H S Oh, HC1 or aqueous solution of sulfur dioxide at 1OO-130 ° C. In the second method, wood is first treated with water or steamed at a temperature of 160-170 ° C and a water ratio of 2-5. Practical hydrolysis also takes place in an acidic medium due to the separation of various organic acids from wood during this treatment (the pH of the hydrolyzate is 3-4. During the prehydrolysis period, 15–20% of the wood passes into the solution, 75% of which are nutrients. When administering prehydrolysis about 20–30% of the lignin contained in the chips is removed by an aqueous solution of a S ° of the beginning of sulphate pulping, but even in this case there is a danger of lignin condensation.

The known method provides a low yield of sulphate prehydrolysis cellulose - 29-35% by weight of absolutely dry wood for various species. A particularly low yield is characterized by sulphate prehydrolysis of hardwood pulp.

In order to increase the yield of the target product and improve its quality, a method has been proposed for producing sulphate cellulose, which consists in that the detrimental hydrolysis is carried out in the presence of an additive of sodium hypophosphite in an amount of 1-15% by weight of absolutely dry raw material.

When this occurs, pentosans are predominantly dissolved, celluloses and the hexozan part of hemicelluloses are protected from dissolution, and the process of lignin condensation is less developed, which contributes to its complete removal with further sulphate cooking. The addition of sodium hypophosphite additive, prehydrolysis, can be carried out by any of the known methods (acidic, aqueous solution 802, etc.). . The yield of pulp for pine is 36-40.4%, for aspen it is 37.7-41.4%. The degree of delignificik, pntozanov content, alkali resistance of cellulose, and other quality indicators depend on the amount of sodium phosphate phosphate and; Acidity of the hydrolyzing solution. The resulting cellulose contains a smaller amount of extractive pentosan substances, has a lower copper number, i.e. it is less destructed, the base is alkali resistant, and so has a lower solubility in 10% - and alkali. Example 1. The raw material used is cooked pine and aspen chips, which correspond in size to the normal fraction of industrial chips - 20x15x10x2 mm. Chip flow 34-38%. The cooking is carried out in a battery autoclave. Prehydrolysis is carried out with 0.5-0.75% and 1, with a solution of sulfuric acid; an aqueous solution of sulfur dioxide with a content of 5.12% of the whole and also water. In this case, sodium hypophosphite is added to the hydrolyzing solution in an amount of from 1 to 15% by weight of the absolutely dry raw material. Temperature; increase in accordance with the cooking schedule.

Sulfate pine wood cooking with acid prehydrolysis

Indicators

Cooking

Conditions of prehydrolysis Concentration H S О% Temperature - С Duration, hour Hydraulic module Consumption,% by weight of absolutely dry raw material

Table 1.

 five

6

0.75 125

3 1: 5

ten

15 For pine Acid Prehydrolysis Lifting up to 125 ° C Lead at 6 ° 1 tempera2 hour tour Water Prehydrolysis Lifting up to 170 ° C 2 hours 15 minutes Exposure at this 1 hour 30 minutes. temperature (Prethydrolysis with an aqueous solution of $ 0. Rise to 105-110 ° C for 2 hours. Release at this 1 hour and 45 min. temperature. Acidic Prehydrolysis is carried out under the same conditions as for pine. Water Prehydrolysis. The temperature rises to 160 ° C 2 hours 15 min. Exposure at this temperature for 1 hour and 30 minutes After the end of the prehydrolysis, the hydrolyzate is dried for analysis. White liquor is fed into the autoclave and sulphite is continued. In the case of acidic prehydrolysis, it is washed with water for 4 hours in a pesulfate cooking. esu abse lute dry initial chips, liquor fluffiness - 25%, hydromodule. The mode of sulphate cooking does not change when carrying out various types of prerolysis, with the exception of the tempering temperature, which is 170 ° C for pine, and 160 ° C for analyzing results. pulp obtained are abl 1-4.

Pine wood sulphate cooking with water prehydropysis

Content of 0 {-cellulose,% 96,597,497.2

Table 2

485178-.

Pine wood sulphate cooking

with prehydrolysis aqueous solution 3

T a b l and c a -3 Sulfate pulping of the main wood with prehydrol and with additives HH Content, Of-cellulose,% 95,096,2 Table 4 with acid and water PO 96.6. 96.8 94,597,7

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 PRI mme R 2. Pine chips are usually sized with an aqueous solution of sulfur dioxide containing 5% D2%

§0 and 5% sodium hypophosphite by weight of absolutely dry wood at 105-110 C for 3 hours and 45 minutes. Then the hydrolyzate is removed and the chips are poured with white liquor and: sulphate cooking is carried out at a water ratio of 1: 5 for 3 hours at 170 ° C. The consumption of active alkali to the weight of absolutely dry chips is 23% in units. On oh

sulfide liquor - 25%. The yield of cellulose is 40.4%. Similar cooking without the addition of hypophosphite sodium gave cellulose with a yield of 35.5% by weight of absolutely dry. Cellulose indicators

Pine

Preliminary hydrolysis with an aqueous solution

no additives with the addition of 5%. Without additives

Output,% to absolutely bag raw

Incomplete penetration,% to absolutely

sukoyu raw materials

Stiffness be

The content of lignin,%

absolutely dry raw material Pentosan content,%

absolutely dry raw materials

- Content of resins,%

a, absolutely dry raw materials

Copper number,%

Solubility,%:

 in NaOH

in 18% - Noah NaON.

e The addition of sodium hypophosphite to a hydrolysis solution in a relatively small amount is absolutely by weight. dry raw materials (see tab. 3-4) cause. know

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go raw materials. Relatively qualitative indicators of cellulose are presented in table 5.

PRI me R 3. Aspen chips of normal size are subjected to a water prehydrogenolysis at a water ratio of 1: 5 and a temperature of 160 ° C for 3 hours and 45 minutes. Before starting iredhydrolysis, 5% sodium hydrosposphyte sodium is added to the water by weight of the initial absolutely dry wood. At the end of the gi; In the course of the rolling process, the hydrolyzate is retracted and white liquor is poured into the boiler for cooking, which takes place at 1 hour 3 hours at 160 ° C. The pulp yield is 41.4% of the absolutely Dry initial wood .;

Comparative qualitative indicators of cellulose are presented in Table. five,, .,.

Table5

Aspen

Water prehydrolysis

with the addition of 5%. To

Absolutely dry hoi chips, chips

34,8

41.4

Nat

No 125 117

8.51

3.90 6.85 2.85

1.01

0.57 0.33

0.32

4.7O

6.30 4.65 3.85

reading increase in the yield of rulphate prehydrolysis cellulose during cooking of needles and hardwood.

This reduces the stiffness

the maintenance of lignin, gums and pentosans in cellulose (see Table 1-4), the content of D-cellulose increases, the stability of cellulose in relation to alkalis. When sodium hypophosphite is used in prehydrolysis, after cooking, pulp can be obtained with an increased (up to 98, table. 1) content of cellulose.

Action || U | AN2PO is favorable with respect to both carcass and yield of sulfate prehydrolysis cellulose using acidic and aqueous prehydrolysis.

Especially strong production of sulphate prehydrolysis cellulose; observed when cooking hardwood.

 in quantity

When adding

3% of absolutely dry wood pulp yield is increased by 6.5% (see

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tab. 4), the lignin content of pentosans and resins is more than halved, the solubility of cellulose in 10% - and 18% - - NaOH is reduced on average by 1%, the content of SG-cellulose increases by 1.6% (. See table . four).

invented and

PREDEME

The method of obtaining sulphate cellulose by preliminary hydrolysis of the initial cellulose-containing raw material at an increased temperature, followed by boiling according to the sulphate method, characterized in that, in order to increase the yield of the target product and improve its quality, preliminary hydrolysis is carried out in the presence of sodium hypophosphite additive in the amount of 1- 5% by weight is absolutely cyxofo feedstock.