SU555190A1 - Cellulose Bleaching Method - Google Patents

Description

(54) METHOD OF BLEACHING CELLSHEU

The invention relates to the bleaching of cellulose and can be used in pulp and paper production.

Widely known is the multi-stage cellulose bleaching method, in which the bleaching agents and oxides are consistently C1,, NaCfO, CIO ,. The whole bleaching process takes about 18 hours, this consumes a very large volume of water {1}.

Izvesgo also has an electrochemical method for chlorine and insoluble anodes (olsha, graphite) C2.

The more bliss of the invention is the method of electrolytic bleaching of celpiso, in which an oily skin is subjected to dignification and followed by bleaching with active chlorine evolved during the electrolysis of the chloride role (e.g., sea water) in a salt% 2.5%, color of 2.5%, color of a salt, 2.5%, color. 3%, pH of solution 63, current density 0.03 A / cm, temperature 20 ° С, total time for delvfing and bleaching up to 6.5 hours and changing the electrolyte solution after the process of delignification 3.

The disadvantage of these methods is that at b very low current densities (in the prototype.

0.03 A / cm), corresponding to a potential range of 0.8-1.3 V, 5-o the oxygen will be emitted at a low speed of the anode. When the equilibrium potential of chlorine release (1gSv) is reached, the joint selection of the X) and then chlorine button begins. In time the VIAH offered in the prototype takes 5 hours to start the release of chlorine. And since the density of the anode current remains low, it takes about 1.5 more hours for tar and bleaching and after bleaching to release chlorine. I

In addition, a reduced salt content in the electrolyte (2.50%) increases the resistivity of the solution and thereby consumes electric power due to ohmic losses.

The purpose of the invention is. process and its simpler process.

This is achieved by the fact that the electrolysis is carried out at an electrogas concentration of 6%, starting at pH 2.0-2.5 and at an anode current density of 0.20-0.24 a / cm. Conducting the bleaching process at a higher current density as a result of electrochemical and chemical reactions. In solution, it is possible to obtain oxidants of such oxidants as О ,, С | ,, jVaClO ,, CiO, possessing at the moment of preparation.

activity and thereby accelerate the process of bleaching unbleached pulp.

The proposed method noiiu.isei process / chelifi- cation and bleaching of the weights in one stage, in one and the same electrolyte solution. In this case, the ratio of the anode area and the cathode Sa: Sk is 1: 2. Under their conditions, a decrease in the cathode current density and cathode potential is possible. For such undesirable processes on the cathode, such as, for example, the recovery process

NaCIO + H, 0 + 2e - jNaCt + 2OH Using a 6% aqueous solution of NaCf reduces ohmic sweat {I1 voltage and thus energy consumption and provides such a presence of chlorine and other oxidants in the electrolyte, which promotes rapid bleaching.

All this allows one to shorten the pulping time, which depends on the required bleaching degree of the MOCT1I, to reduce the number of bleaching stages — and thereby reduce water consumption during the bleaching process.

During electrolysis, the pH of the solution rises to 12.0-12.3 during the electrolysis. At the same time, depending on the time of electrolysis, the temperature rises.

The quality of the original bleached pulp is assessed by whiteness and hardness (permanganate method).

Whiteness (%) was determined according to GOST 7690-66, SB rigidity) according to GOST 6845-54.

Example 1. Source pulp -) ebene cellulose, obtained by sulphate is is cooking from 50% pine and 50% larch

Stiffness vshg d a 87 be

Whiteness source, 56%

2 wt.% Suspension cellulose: in 6% aqueous solution of sodium chloride, pre-diluted) with hydrochloric acid to a pH of 2.4 and an initial temperature of 18 ° C. The graphite electrodes are immersed in the suspension (the ratio Sa-Sk ll: 2, and pass a constant current at a current density of 0.22 A / cm. The electrolysis is carried out for 20 minutes with periodic stirring 1 (mass = 50 mm).

final pH12

T ° C is finite 45

3.7 ° Be

75%

Example. The outcome of cellulose is unbleached sulphate) Lg ;.)

Initial stiffness 109Be

Whiteness of the original 53% Condition bleaching:

Cellulose concentration 2 wt.%

NaC26% concentration

pH of initial 2

 source 15

Pro: Sk.1: 2

Current density: 0.24 A / cm

Electrolysis time30 min

12.3 (when periorN is the end of wild mixing) T ° C is finite 50

Bleaching performance:

 Hardness1,2 ° Be

Whiteness87%

The use of electrochemical bleaching of sulphate pulp under the proposed conditions at high bleaching rates makes it possible to reduce the bleaching time to 30-40 minutes, reduce the number of stages and significantly reduce water consumption for bleaching pulp. Form m at I and inventions

The method of cellulose bleaching by suspending cellulose in an aqueous solution of sodium chloride followed by electrolysis of the electrolyte thus obtained, characterized in that, with an intensification of the process and its simplification, the electrolysis is carried out by an npi electrolyte concentration of 5, anode pH Current Current 0.20-0.24 a / y.

Sources of information taken into account in the examination:

1. Nepenin Yu.N. Pulp technology, Part 2, Forest industry, 1963.

2. Fedotyev N.P. Applied electrochemistry. Leningrad, GNTI chemical literature, 1962.

3. Japan patent G 47-3881, class 39 A 481.

1972 (prototype).