RU2045597C1 - Method for production of cellulose - Google Patents

Abstract

FIELD: production of paper and chemical processing. SUBSTANCE: wood chips are impregnated with water or aqueous solution of sodium hydroxide and/or sodium sulfite in amount of 0.5-10.0% of mass of absolutely dry wood chips. Moistening solution is withdrawn. Impregnated wood chips are subjected to prehydrolysis at temperature of 190-230 C for 0.5-10.0 min. Mass is subjected to alkali cooking with sulfate or soda lye. Prior to cooking, pressure may be instantaneously released down to atmospheric. EFFECT: higher efficiency. 4 cl, 5 tbl

Description

 The invention relates to the pulp and paper industry, and in particular to a technology for producing pulp for paper and chemical processing.

A known method of producing cellulose by impregnating wood chips, removing the impregnating solution, prehydrolysis of the impregnated wood chips at elevated temperature and pressure and subsequent alkaline cooking. In this case the chips are impregnated with water at a temperature of 110-130 ^{° C} for 30-60 min and impregnated chips prehydrolysis is performed at 170 ^C for 120 min.

 This method allows to obtain viscose pulp of the desired quality. However, this process is long and environmentally harmful due to the high consumption of sulfur-containing reagents.

 The technical result of the invention is the intensification of the process while maintaining the quality indicators of cellulose, as well as improving the environmental friendliness of the process.

Technical result is achieved by the method for producing cellulose by impregnating wood chips, removing the impregnating solution prehydrolysis impregnated wood chips at elevated temperature and pressure and subsequent alkaline pulping process according to the invention, the impregnated chips prehydrolysis performed at a temperature of 190-230 ^{° C} for 0.5 -10 minutes.

 In this case, the chips are impregnated with water or an aqueous solution of sodium hydroxide and / or sodium sulfite at a flow rate of these reagents of 0.5-10% by weight of absolutely dry wood chips, alkaline cooking is carried out with sulfate or soda liquor. At the end of prehydrolysis, an instantaneous pressure release to atmospheric pressure can be performed.

In the case of short-term high-temperature hydrolysis of pre-impregnated wood chips, hydrolytic destruction of the polymer components of wood occurs, with the lignin and ligno-carbohydrate matrix being degraded to a much greater extent than cellulose and other high molecular weight polysaccharides. This facilitates the subsequent removal of lignin at the cooking stage. Thus, depending on the conditions of high-temperature hydrolysis, i.e. the degree of degradation of lignin and the ligno-carbohydrate matrix, and the cooking conditions, it is possible to obtain both paper pulp and chemical processing. In this limits the temperature ^of 190-230 C and the duration of prehydrolysis 0.5-10 min are optimal, since at a temperature below 190 ^C and greater process intensification process duration is not reached, while the output of the upper limit of the temperature drop occurs and cellulose degradation quality indicators of cellulose.

 Instantaneous pressure relief to atmospheric pressure (decompression) at the end of prehydrolysis can further increase the intensification of the process and improve the lignin content in the target product.

 The method is as follows.

The chips are impregnated with an impregnating solution at a hydraulic module of 1: 3, temperature, mainly 100 ^about C, for 15 minutes

As an impregnating solution, water or an aqueous solution of sodium hydroxide and / or sodium sulfite is used. Then the impregnation solution is removed by extraction and the impregnated chips are subjected to prehydrolysis with water or steam at a water module ^of 1: 2 and a temperature of 190-230 ° C for 0.5-10 minutes. At the end of prehydrolysis, an instantaneous pressure release to atmospheric pressure (decompression) can be performed.

The waste thus is cooked chips with soda or sulphate liquor at liquor ratio of 1: 4, raising the temperature to 170 ^{° C} for 90 min, parking on said final temperature for 30-60 min.

 The proposed method was tested in laboratory conditions using chips from birch and spruce wood and in the factory using technological chips (from a mixture of aspen and birch).

 The process mode for specific parameters and indicators of the resulting pulp are presented in tables.

 Table 1-2 shows the process conditions and indicators of cellulose obtained for chemical processing. Moreover, in examples 1-6 (table 1) use chips from birch, in examples 8-10 (table 2) technological chips from a mixture of aspen and birch.

 Table 3-5 shows examples illustrating a method for producing pulp intended for the manufacture of paper. In examples 12-14 (table 3) use chips from birch, in examples 16-20 (table 4) chips from spruce, and in examples 22-25 (table 5) technological chips from a mixture of aspen and birch.

 For comparison, the tables show examples 7, 11, 15, 21, 26 of obtaining cellulose from the same wood chips, but by the prototype method.

 From these tables it can be seen that the proposed method allows to intensify the process of obtaining cellulose; reducing the duration of impregnation by 2 times, prehydrolysis by 9-180 times, cooking by 1.5-3 times while maintaining the quality indicators of the target product (when carrying out prehydrolysis with instant pressure relief, this effect is even more significant examples 23, 24, 25).

 The proposed method allows to increase the environmental friendliness of the process by reducing or eliminating the consumption of sulfur-containing reagents.

 In addition, the proposed method allows to obtain cellulose, the bleaching of which can be carried out without the use of active chlorine and with a significant reduction in chlorine-containing reagents.

Claims (4)

1. METHOD FOR PRODUCING CELLULOSE by impregnating wood chips, removing the impregnating solution, prehydrolyzing the impregnated chips at elevated temperature and pressure and subsequent alkaline cooking, characterized in that the prehydrolysis of the impregnated chips is carried out at 190-230 ^o C for 0.5-10.0 min .  2. The method according to claim 1, characterized in that the impregnation of the chips is carried out with water or an aqueous solution of sodium hydroxide and / or sodium sulfite at a flow rate of these reagents of 0.5-10% by weight of absolutely dry wood chips.  3. The method according to PP.1 and 2, characterized in that the alkaline cooking is carried out with sulfate or soda liquor.  4. The method according to claims 1 to 3, characterized in that at the end of the pre-hydrolysis, an instant pressure release to atmospheric is performed.

Images