RU2055962C1 - Method of cellulose producing for chemical processing - Google Patents

Abstract

FIELD: cellulose industry. SUBSTANCE: immediately after leafy wood boiling with oxidized white lye the hot refining of cellulose is carried out at 45-140 C at alkali concentration 20-80 g/l. EFFECT: improved method of cellulose production. 4 tbl

Description

 The invention relates to methods for producing cellulose and can be used in the pulp and paper industry to obtain fibrous semi-finished products intended for chemical processing.

 A known method of producing cellulose for chemical processing by sulphate and soda pulping of hardwood without prior hydrolysis, cold, hot refinement and bleaching.

However, the known method does not allow to achieve a sufficiently high chemical uniformity of cellulose after cooking and requires an additional stage of cold refinement in order to dissolve hemicelluloses. Step cold refinement performed at 15-35 ^{° C} with solutions of active alkali content in weight of 30-70 g / l (u Na ₂ O). Implementation of this process step at a low temperature leads to unavoidable heat losses as pulp after washing has a temperature of 60-80 ^{° C,} and after cold-hot stage upgrading is needed refinement (to restore its reactivity) at 80-90 ° ^C. Moreover, the spent solution after cold upgrading for reuse must be heated and evaporated in order to bring the concentration of active alkali to a level of 100 ± 5 g / l. And finally, to implement the known method, additional equipment is required for a cold improvement tower, washing plants, instrumentation, pumps, etc.

 The closest to the proposed method is a method of producing cellulose from hardwood without prior hydrolysis using oxidized white liquor, cold and hot refinement.

 The use of oxidized white liquor as a cooking reagent can increase the chemical uniformity of cellulose, the criterion of which is the content of α-cellulose, and also prevents the formation of methyl mercaptan and other toxic compounds at the cooking stage.

 However, known methods include cold and hot refinement of cellulose, the disadvantages of which are described above.

 The aim of the invention is to simplify the process of upgrading unbleached pulp, reducing the content of residual lignin in it and, as a result, reducing the discharge of pollutants from waste water.

The goal is achieved in that, after pulping chemical processing oxidized white liquor is carried out at a temperature elevation hot 45-140 ^{° C,} the active alkali concentration of 20-80 g / L (units. Na ₂ O). A comparative analysis of the claimed regime with the known shows that the proposed method is characterized in that after cooking, hot refinement of cellulose is carried out. The exclusion of the stage of cold refinement can significantly simplify the process of refinement of cellulose, reduce the content of residual lignin in it, and reduce the discharge of pollutants from waste water.

 The proposed method for producing cellulose for chemical processing is implemented as follows.

PRI me R 1. The cooking of cellulose from aspen wood is carried out in laboratory rotating autoclaves with a capacity of 800 cm ³ equipped with electric heating.

Cooking mode: temperature increase from 80 to 170 ^{° C} 150 minutes, parking at 170 ° ^C 120 min, liquor ratio 4: 1. For cooking, oxidized white liquor is used with a degree of conversion of sodium sulfide of 99.9% consumption of active alkali (units of Na ₂ O). After cooking, the pulp is washed on laboratory sieves, its yield and quality indicators are determined. Then, cold and hot refinement of unbleached pulp is carried out.

Cold conditioning mode: active alkali concentration 50 g / l (units of Na ₂ O), temperature 20 ^о С, time 60 min, mass concentration 8% Hot upgrading mode: active alkali concentration of 2 g / l (units of Na ₂ O) , temperature 90 ^о С, time 120 min, mass concentration 8%
The results obtained are presented in table 1 (experiment 1).

PRI me R 2. Cooking cellulose for chemical processing is carried out under conditions similar to those described in example 1. After cooking, the pulp is washed on laboratory sieves, analyzed and conduct hot refinement. Hot upgrading mode: active alkali concentration 50 g / l (units Na ₂ O), temperature 45-140 ^о С, time 60 min, mass concentration 8%
The results obtained are presented in table 1 (experiment 2-7).

 PRI me R 3. Cooking pulp was carried out under the conditions described in example 1.

After cooking, the cellulose is washed on laboratory sieves, analyzed and hot refinement is carried out. Hot upgrading mode: concentration of active alkali 10-100 g / l (units Na ₂ O), temperature 120 ^о С, time 60 min, mass concentration 8%
The results obtained are presented in table.2 (experiments 1-6). The results are presented in Table 1 show that increasing the refining temperature in the range 45-140 ^{° C} allows to 42,5-56,1% increase in the degree of delignification of unbleached pulp viscose (from 8.7 to 3,8-5,0 units of Kappa), while according to the known method, the degree of delignification of cellulose is 35.6% (from 8.7 to 5.6 units of Kappa). In this case, the viscosity and cellulose content are almost at the same level. It is advisable to maintain the concentration of active alkali at the stage of hot refinement in the range of 20-80 g / l (depending on the requirements for the quality indicators of cellulose for chemical processing). This is due to the fact that when the alkali concentration is below 20 g / l (Table 2, experiment 1), a significant effect of the refinement and delignification of cellulose after cooking is not achieved. An increase in alkali concentration above 80 g / l is impractical because it does not lead to the additional effect of delignification and refinement of cellulose (Table 1, experiment 6).

PRI me R 4. Cooking cellulose was carried out under conditions similar to those described in example 1. After cooking, the pulp is washed, subjected to cold and hot refinement (conditions are presented in example 2) and bleaching according to a three-stage scheme:
D ₁ SC (O ₂ + P) D ₂ K, where D ₁ I stage of bleaching with chlorine dioxide;
D ₂ 2 stage bleaching with chlorine dioxide;
Щ (О ₂ + П) stage of oxygen delignification with the addition of hydrogen peroxide.

 The bleaching conditions and quality indicators of bleached viscose pulp are presented in table 3.

PRI me R 5. Cooking cellulose was carried out under conditions similar to those presented in example 1. Then, the pulp was washed, subjected to hot dressing and bleaching. Hot upgrading mode: temperature 90 ^о С, active alkali concentration 50 g / l, mass concentration 8%, time 60 min. The bleaching mode is similar to that presented in example 4. The bleaching conditions and pulp quality indicators are presented in table 4.

A comparative analysis of bleached viscose pulp obtained by the known and proposed methods shows that in both cases it meets the requirements of GOST 24299-80. The advantage of the proposed method is that the loss of α-cellulose during bleaching under the same conditions is 1.6% and by a known method 2.0%
Thus, the use of the proposed method for the production of cellulose for chemical processing allows you to completely eliminate the stage of cold refinement and the associated capital, operating costs, additional heat consumption and (compared with the known method) to increase the degree of delignification of pulp coming to bleaching. Reducing the content of residual lignin in the pulp entering the bleach, respectively, reduces the discharge of pollutants and filtrates of the bleaching stages into the environment.

 Bleaching conditions and pulp quality indicators after cold and hot upgrading

Claims (1)

METHOD FOR PRODUCING CELLULOSE FOR CHEMICAL PROCESSING, including cooking hardwood with oxidized white liquor and hot dressing with alkaline solution, characterized in that the hot treatment of cellulose is carried out immediately after cooking at a temperature of 45 - 140 ^o C and an alkali concentration of 20 - 80 g / l.

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