SU874811A1 - Continuous pulp-bleaching method - Google Patents

Description

(54) METHOD FOR CONTINUOUS CLEARING OF CELLULOSE

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The present invention relates to methods for continuous bleaching of pulp and can be used in the pulp and paper industry.

There is a known method of bleaching pulp, including dilution of pulp, treatment with a mixture of chlorine and chlorine dioxide, first washing, separating the filtrate and using its JQ to wash unbleached pulp after sorting, diluting cellulose mass and ejecting chlorine, alkaline extraction, second pouring, separating filtrate partial use calling it for the first, according to the following pulp processing.

According to this method, the filtrate from cellulose spillage after sorting and excess filtrates from the first 20 and second washes are discharged into

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The main disadvantage of this method is the partial use of filtrates, which requires an additional 25 consumption of fresh water.

The closest to the invention is a method of continuous bleaching of cellulose, including dilution of pulp, treatment with a mixture of 30

chlorine and chlorine dioxide, first flushing, separating the resulting filter. rata, cleaning and feeding it to the pulp dilution, alkaline extraction, second washing with water, separating the filtrate and feeding it to the first washing.

According to this method, the filtrate obtained after the first and the second line is subjected to purification on an ion exchange resin 2.

The disadvantage of this method is the need to use two stages of purification using expensive 1-to-1 X ion-exchange resins.

The purpose of the invention is to increase the efficiency of the process by eliminating the operation of cleaning the filtrate from the pro-cessing of the pulp after alkaline extraction.

The goal is achieved by the fact that in the method of continuous bleaching of cellulose, which includes dilution of the pulp, treatment with a mixture of chlorine and chlorine dioxide, first, “Separating the filtrate, cleaning and feeding it to the pulp dilution, alkaline extraction, second watering .

separating the filtrate and feeding it to the first rinsing, cleaning the filtrate after the first procuring is carried out by electro-sorption on activated carbon at a current of 0.015-0.1 A and a voltage of 4-10.5 V.

The filtrate is not cleaned from the second wash before it is used in the first wash.

The use of electrosorption cleaning on activated carbon filtrate from the first npoNUBKH ensures the preservation of pulp quality indicators at the required level without cleaning the filtrate from the second finish, which reduces the cost of cleaning.

Example. Sulfate softwood pulp with a hardness of 27.2 units of Kappa and a viscosity of 1% copper ammonia 1370 MP solution is diluted, treated with a mixture of chlorine and chlorine dioxide, washed, subjected to alkaline extraction, again washed with hot water.

The filtrate from the second wash is used to pitch the wash.

In a series of experiments A, the filtrate from the first washing is purified by electrosorption on activated carbon; in a series of experiments, this filtrate is not subjected to purification. In both series, the filtrate is used to dilute the pulp before being treated with chlorine and chlorine dioxide (chlorination). In the first experience of both Series A and Series B | Fresh water is used instead of filtrates. Notice not.

Chlorination of cellulose is carried out as follows.

Consumption of active chlorine 0,22% to absolutely dry cellulose for 1 unit; Kappa, with 70% of active chlorine being given, in the form of chlorine dioxide, a mass concentration of 3%, a temperature of 60 ° C, a treatment time of 30 minutes. Alkaline extraction is carried out at a mass concentration of 12% and a temperature of 65 ° C for 120 minutes with a consumption of caustic soda 3% of the weight of absolutely dry unbleached pulp. For the second npoivuBKH, water is used with a temperature of 9.5 ml / g of absolutely dry cellulose.

Electro-sorption of the filtrate from the first industrial flow in the experiments of series A is carried out in the anode space of a diaphragm two-chamber electrolyzer on a bulk electrode from a sulfone angle. The cathode is granular graphite. The voltage on the electrolysis cell is from 4 to 10.5 V, current is 0.1 A. Overlap of current Increases the cleaning efficiency of the filtrate in color by 30%, permanganate oxidation by 17% compared to cleaning it on a sulfone without current.

in tab. 1 shows the results of experiments characterizing the quality of cellulose and filtrate during chlorination and alkaline extraction; series A, and the same, series B.

Table 1 In table. 1 fraction shows the characteristics of the filtrates before cleaning (in the numerator) and after cleaning (in the denominator). As follows from the table. 1 and 2 ten times the use of filtrates in the presence of purification of the electrolyte from the first finish (series A) under the same bleaching conditions does not practically degrade the quality of the cellulose after alkaline extraction. If the filtrate is not cleaned from the first washing, the series cellulose is increased by up to 50% compared with treatment. in pure water. PRI mme R 2. Cellulose samples after chlorination and alkaline extraction using pure water (AO experience), purified (A-10 experiment) and unpurified (B-9 experiment), the filtrate from the first washing is added with chlorine dioxide in two stages with intermediate extraction. The consumption of chlorine dioxide (by active chlorine) in both stages is 2% to absolutely dry cellulose, the consumption of caustic natran intermediate alkaline extraction 2% to absolutely dry cellulose; KOHI mass concentration at all steps of the additional treatment 10%, temperature at the steps, chlorine dioxide 70 ° С, at the chain extraction stage, processing time at the first stage of chlorine dioxide 240 min, intermediate alkaline extraction 120 min, second stage chlorine dioxide 180 min. As a result of bleaching, cellulose is obtained (respectively, experiments AO, A-.10, and B-9) with whiteness of 88.0%, 88.3%, 86.0% and a breaking length of 8500 m, 8100 m, 7900 m.

Table 2 From the data presented, it is clear that bleaching with countercurrent use of filtrates of chlorination and alkaline extraction stages and one step of purifying the filtrate from the first npONEiBKH by electroplating on activated carbon before re-using provides pulp with the required quality indicators. Example 3. Purification of the filtrate from the first flushing by electrosorption is carried out in the anode space of a double-chamber diaphragm electrolyzer at the anode from the sulfougl. In tab. 3 you will give the results of experiments on the purification of the filtrate from the first washing with electrosorption when it is used again. Table 3

The magnitude of the voltage is determined in this case by the content of various ions in the filtrate. As salt accumulates in the filtrate, a current of 0.1 amps is reached with less voltage. An increase in current of more than 0.1 A leads to the electrolysis of water and salt, and a decrease in the strength of the current decreases the cleaning efficiency. For example, at a current of 0/015 A, the degree of purification of the filtrate is 30%.

Thus, the proposed continuous pulp bleaching method allows to ensure the required pulp quality when reusing the filtrates of bleaching stages with lower cleaning costs due to the use of electro-sorption cleaning on activated carbon, which is more accessible and detail than ion-exchange resins.

Claims (2)

1. TAPPI, 197, 59, 3, p. 75-77 2. US patent number 4070234 / kl.210-31 1978 (prototype).