RU2248421C1 - High-refined cellulose production process - Google Patents

Abstract

FIELD: paper-and-pulp industry.

SUBSTANCE: process of producing high-refined cellulose for manufacture of man-made fibers and films comprises water or acid pre-hydrolysis of disintegrated vegetable material followed by delignification of pre-hydrolyzed wood by way of catalyzed peroxide pulping and alkali extraction of oxidized lignin at atmospheric pressure. Final operations are bleaching and alkali refining of cellulose.

EFFECT: improved quality of cellulose, improved environmental safety of process, and reduced power consumption.

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Description

The invention relates to the pulp and paper industry and is intended to produce highly refined pulp used for the production of chemical fibers and films.

Known methods for producing cellulose, including the cooking of crushed plant materials with a solution of hydrogen peroxide in the presence of a multicomponent catalyst (a mixture of tungsten acid or its salts, molybdenum acid or its salts and sulfuric acid with molar fractions of the components in the mixture, respectively, 0.2 ... 0, 4; 0.2 ... 0.4; 0.2 ... 0.6) with subsequent alkaline extraction or without it. In this case, toxic and foul-smelling by-products of cooking are not formed, and hemi-cellulose retains high reactivity due to the absence of stabilization reactions during cooking (RU, No. 2206654, MKI 7 D 21 C 3/04, 3/22, bull. No. 17 , 2003; RU, No. 2212483, MKI 7 D 21 S 3/04, 3/22, bull. No. 26, 2003).

The disadvantages of the known methods are the high content of hemicelluloses and the low mass fraction of alpha cellulose in the resulting peroxide cellulose, which does not allow to obtain highly refined cellulose and use it as a raw material for chemical processing (for the production of chemical fibers and films).

The closest in technical essence is a method of producing highly refined wood pulp, including aqueous or acid prehydrolysis, sulphate cooking, bleaching and alkaline refinement (Cellulose technology. In 3 volumes. T.2 Nepenin Yu.N. Production of sulfate cellulose. M .: Forest industry, 1990. - С 229).

The disadvantage of this method is the use of sodium sulfide for delignification of wood during sulfate cooking, which leads to the formation of toxic and foul-smelling substances (hydrogen sulfide, methyl mercaptan, dimethyl sulfide, etc.) during the process and creates an environmentally unfavorable environment in the vicinity of the enterprise. In addition, during sulfate cooking, both degradation of polysaccharides (peeling process) and their stabilization (stopping process) occur. Both of these processes lead to the accumulation in cellulose of low molecular weight fractions of polysaccharides that are resistant to alkali. As a result, the possibilities of removing hemicelluloses (especially pentazane) during the subsequent alkaline refinement of cellulose are not fully realized.

The invention solves the problem of obtaining highly refined cellulose without the formation of sulfur-containing products, improving the environmental friendliness of the process and reducing energy costs.

To solve this problem, the crushed wood is subjected to aqueous or acid prehydrolysis, the wood residue is delignified with an aqueous solution of hydrogen peroxide in the presence of a catalyst, followed by alkaline extraction, the resulting cellulose is bleached and refined with an alkaline method.

The technical result when using the invention is to obtain high-quality cellulose, the most complete removal of hemicelluloses (including pentosans), improving the technological parameters of production - reducing the cooking temperature and pressure, improving the environmental friendliness of the process - no harmful emissions of toxic and foul-smelling substances while maintaining the high quality obtained pulp, reducing energy costs.

To achieve the specified technical result in a method for producing highly refined cellulose, including acid or water prehydrolysis of chopped wood, delignification of wood residue, bleaching and alkaline refinement of cellulose, according to the invention, wood residue remains delignified by catalytic peroxide cooking followed by alkaline extraction of oxidized lignin at atmospheric pressure below 100 ° C.

The proposed method for producing highly refined cellulose differs from the prototype in that the delignification of prehydrolyzed wood is carried out with hydrogen peroxide in the presence of a catalyst followed by alkaline extraction of oxidized lignin. These features are the basis of the proposed method.

A method of producing highly refined pulp is as follows.

The crushed plant raw materials are subjected to aqueous prehydrolysis at a temperature of 160-170 ° C or acid prehydrolysis at a temperature of 110-120 ° C and cooking with a solution of hydrogen peroxide in the presence of a catalyst, for example a multicomponent mixed catalyst - tungsten acid or its salts (mole fraction in the mixed catalyst 0 , 2 ... 0.4), molybdenum acid or its salts (molar fraction 0.2 ... 0.4) and sulfuric acid (molar fraction 0.2 ... 0.6), at a temperature of 70 .. .95 ° C. The solid residue is washed with water and treated with an alkali solution at a temperature of 60-97 ° C and atmospheric pressure to remove oxidation products. The resulting pulp is bleached and refined according to generally accepted schemes and technological conditions.

Example 1

To carry out water prehydrolysis, spruce wood (100 g) in the form of shavings and 500 g of water are loaded into an autoclave, quickly heated to 160 ° C and maintained at this temperature for 2 hours. The woody residue (84 g) is washed with water, transferred to a glass the flask and treated with a solution of hydrogen peroxide with a catalyst. Processing conditions: hydromodule 4; initial concentration of hydrogen peroxide 17%; the total concentration of the complex catalyst is 0.010 mol / dm ³ (including sulfuric acid 0.0034 mol / dm ³ , sodium tungstate 0.0033 mol / dm ³ , sodium molybdate 0.0033 mol / dm ³ ); temperature 87 ° C; atmospheric pressure; the duration of the process is 2.5 hours. The solid residue is washed with water and treated in a glass flask with sodium hydroxide solution under the following conditions: hydromodule 4; initial concentration of NaOH 4%; temperature 97 ° C; atmospheric pressure; duration 2.5 hours. The resulting cellulose is freed from lignin residues by treatment with sodium hypochlorite solution at a temperature of 23 ° C for 1 hour (the consumption of active chlorine is adjusted depending on the lignin content) and a cold alkaline enrichment is carried out. The conditions for upgrading: the concentration of the fibrous suspension is 5%, the concentration of sodium hydroxide is 9%, the temperature is 15 ° C, the duration of the process is 3 hours. At the end of the process, the cellulose is washed with distilled water, dried in air at room temperature and analyzed by standard methods. The yield of enriched cellulose 32 g. The results of the analyzes are shown in the table.

Example 2

To carry out acid prehydrolysis, 100 g of spruce wood in the form of shavings and 500 g of sulfuric acid with a concentration of 0.3% are loaded into an autoclave, quickly heated to a temperature of 115 ° C and kept at this temperature for 2.5 hours. Woody residue (yield 82 g ) washed with water, transferred to a glass flask and carried out catalyzed peroxide cooking, alkaline extraction, bleaching and enrichment as in Example 1. Cellulose is washed with distilled water, dried in air at room temperature and analyzed by standard methods. The yield of enriched cellulose is 31.0 g. The results of the analyzes are shown in the table.

Example 3. According to the prototype method using aqueous prehydrolysis.

To carry out water prehydrolysis, spruce wood (100 g) in the form of shavings and 500 g of water are loaded into an autoclave, quickly heated to 160 ° C and maintained at this temperature for 2 hours. The woody residue (84 g yield) is washed with water and delignified with isothermal sulfate cooking in an autoclave under the conditions of: hydromodule 4.5; the concentration of NaOH 50 g / DM ³ ; concentration of Na ₂ S g / dm ³ ; temperature 170 ° C; pressure 0.9 MPa; the duration of the process is 2 hours. The bleaching and refinement is carried out analogously to example 1. Cellulose is washed with distilled water, dried in air at room temperature and analyzed by standard methods. The yield of enriched cellulose 29.9 g. The results of the analyzes are shown in the table.

Example 4. According to the prototype method using acid prehydrolysis.

To carry out acid prehydrolysis, 100 g of spruce wood in the form of shavings and 500 g of sulfuric acid with a concentration of 0.3% are loaded into an autoclave, quickly heated to a temperature of 115 ° C and kept at this temperature for 2.5 hours. Woody residue (yield 82 g ) washed with water and carry out sulfate cooking, bleaching and enrichment, as in example 3. Cellulose is washed with distilled water, dried in air at room temperature and analyzed by standard methods. The yield of enriched cellulose is 30.5 g. The results of the analyzes are shown in the table.

Table Refined Pulp Properties Example 1 Example 2 Example 3 Example 4 Mass fraction of alpha cellulose,% 97.5 97.6 97.2 97.4 Mass fraction of pentosans,% 2.1 2.0 2,5 2.2 The average degree of polymerization 780 820 910 890 Reactivity,% CS ₂ / NaOH 110/12 110/12 110/12 110/12

As can be seen from the table, the claimed method has the following advantages over the known:

- lower temperature and pressure during the delignification stage of the process (alkaline extraction);

- less mass fraction of pentosans in cellulose with comparable other properties indicators, which is a prerequisite for better pulp processability by the viscose method;

- sulfur compounds are not used in the pulp production process, which is a prerequisite for reducing the technogenic load on the environment and for improving the quality of life.

The indicated advantages of the proposed method for producing enriched cellulose are achieved by replacing the sulfate method of delignification with a catalyzed peroxide method of delignification.

Claims (1)

A method for producing highly refined cellulose, including aqueous or acidic prehydrolysis of ground plant material, delignification of wood residues, bleaching and alkaline refinement of cellulose, characterized in that delignification of prehydrolyzed wood is carried out by catalytic peroxide cooking and subsequent alkaline extraction of oxidized lignin under pressure.