The way chlorine-free bleaching of sulphate pulp

 

(57) Abstract:

The method relates to chlorine-free bleaching of sulphate pulp. It includes two-stage processing nebelenoj sulphate pulp by alternating acid and alkali treatments. In the first stage, the pulp concentration of 5-20 mass% is treated with a solution of ammonium persulfate in 40-50% sulfuric acid at a ratio of from 0.5 to 2 ammonium persulfate per unit mass of absolutely dry pulp at a temperature of about 22-24°C for 1 to 4 hours. In the second stage is conducted in an alkaline processing pulp with a concentration of 5-10% solution of sodium hydroxide or potassium hydroxide with a concentration of 3-4% at a temperature close to the boiling point of water, for 1 hour. The technical result is to eliminate the use of dangerous and expensive hydrogen peroxide, mnogostadiinost process, paired with additional energy, time and material costs while minimizing the process of the decomposition of cellulose fibers and a high yield of bleached pulp. table 2.

The invention relates to the production of cellulose and can be used to produce bleached pulp without using chlorine, response A. C., Politova N. To. Patent N 2164572 from 14.03.2000], including platitudinous processing by alternating alkaline and acid treatments, at the first stage, the pulp concentration of 10-20 mass% is treated with hydrogen peroxide for 1 hour in an alkaline medium (pH from 9.0 to 10.9) at a temperature of 75 to 85°with the consumption of hydrogen peroxide 2% by weight of absolutely dry pulp. On the third and fifth stages of the pulp treated with the same concentration of mass in the course of 2 hours each and a temperature of 70 to 100°with the consumption of hydrogen peroxide 0.5% and 1.0%. The second and fourth stages carried out for 2 hours each at a temperature of 70°With chlorine dioxide at a concentration of 0.7-1.0% and 0.3%, respectively, depending on the initial stiffness of the cellulose. As in the examples (1-10) the timing of stages varies, the total time of the process of bleaching is 7-9 hours. The resulting product has good output for 95.3-98.6% of the values of white 80-88%.

The disadvantages of this method of bleaching can be attributed to the use of chlorine (chlorine dioxide), explosive and expensive (hydrogen peroxide) reagents, as well as a multi-stage process that involves dopolnitvah a multi-step process (from 5 to 8 feet), in which at each stage, and processing of cellulose using various bleaching agents. Between stages of bleaching is used to wash the pulp with water to remove from the mass of waste solutions. In addition, the use of bleaching reagents chlorine and its compounds leads to the appearance in the wastewater, as well as in the production of highly toxic organochlorine compounds (dioxins, chlorophenols). Great resource and energy consumption of traditional technologies is mainly due to the relatively long processes of bleaching, washing, a large volume of water used and high energy costs as the main technological process and wastewater treatment.

The objective of the invention is to develop a method of bleaching of sulphate pulp without using chlorine-containing reagents.

Bleaching is due to oxidation of residual lignin, followed by extraction of the oxidation products of the alkali solution.

Proposed two-stage method of bleaching unbleached sulphate pulp by alternating acid and alkali treatments. In the first stage of unbleached pulp with a concentration by weight of one from 0.5 to 2 per unit mass of absolutely dry pulp at a temperature of about 22-24°C for 1 to 4 hours. In the second stage is conducted in an alkaline processing pulp with a concentration of 5-10% solution of sodium hydroxide or potassium hydroxide with a concentration of 3-4% at a temperature close to the boiling point of water, for 1 hour. After each stage the pulp mass is thoroughly washed with water. The technical result is bleached the pulp with the release of 80-96% and cellulose content 84-94%.

In the proposed oxidative system, consisting of 40-50% sulfuric acid and ammonium persulfate, formed a number of oxidants, the strongest of which is acid Caro [zachys, F., Neubert B. I. effect on the lignin of persulfates. // The chemistry of wood, 1971, No. 9, - S. 109-117]. In the result of the oxidation process in the cellulose fiber formed selfaligning, which is poorly soluble in an oxidizing system and a little better in the wash water. Treatment with hot alkali solution facilitates intense transition of products of interaction of selfaligning with alkali (quinoid structure) in the solution. Liberated from the oxidation products bleached pulp mass is repeatedly washed with water until neutral.

Due to the fact that oxidative system is poorly soluble oxidation products (the ow of fresh ammonium persulfate and sulfuric acid if necessary.

The oxidation process is conducted at a temperature of about 22-24°C with continuous removal of the heat that is necessary, because with the increase of temperature decreases the content of the Caro's acid oxidizing system, which affects the oxidation of lignin. Prevention of heat mass can minimize the process of the decomposition of cellulose fibers.

Received the bleached pulp was analyzed for cellulose, cellulose (as an indicator of destruction) and stiffness. It was investigated the effect of the mass of the oxidizer and the time of oxidation treatment on the process of pulp bleaching. The results obtained are summarized in tables 1, 2.

Example 1

Unbleached sulphate pulp with a hardness of 85 permanganate units with a mass concentration of 10% (10 grams) is treated with a solution of ammonium persulfate in 50% sulfuric acid at a ratio of flow rate of ammonium persulfate and absolutely dry cellulose 1:1 at a temperature of about 22-24°C for 1 hour. Then the pulp is thoroughly washed with water and subjected to alkaline treatment solution of sodium hydroxide with a concentration of 4% and the concentration of pulp 10% at a temperature close to TVsets bleached the pulp with a yield of 96%, the cellulose content of 84.3%, a content of the pulp of 81.5% and a hardness of 53 permanganate units.

Example 2

Unbleached sulphate pulp is treated with a solution of ammonium persulfate in sulfuric acid for 2 hours (the rest as in example 1).

The technical result is bleached the pulp with a yield of 89%, the cellulose content of 87.8%, a content of the pulp of 84.3% and rigidity 39 permanganate units.

Example 3

Unbleached sulphate pulp is treated with a solution of ammonium persulfate in sulfuric acid for 3 hours (the rest as in example 1).

The technical result is bleached the pulp with a yield of 84%, cellulose content is 91.4%, a content of the pulp of 87.5% and a hardness of 26 permanganate units.

Example 4

Unbleached sulphate pulp is treated with a solution of ammonium persulfate in sulfuric acid for 4 hours (the rest as in example 1).

The technical result is bleached the pulp with a yield of 80%, cellulose content 93,7%, a content of the pulp of 89.1% and a hardness of 15 permanganate units.

A positive technical result Cellulosa weight with out 80-96% and cellulose content 84-94%.

The way chlorine-free bleaching of sulphate pulp, including the two-stage processing of unbleached sulphate pulp by alternating acid and alkali treatments, characterized in that in the first stage, the pulp concentration of 5-20 mass% is treated with a solution of ammonium persulfate in 40-50% sulfuric acid at a ratio of flow rate of ammonium persulfate 0.5 to 2 per unit mass of absolutely dry pulp at a temperature of about 22-24°C for 1 to 4 h, the second stage is conducted in an alkaline processing pulp with a concentration of 5-10% solution of sodium hydroxide or potassium hydroxide with a concentration of 3-4% at a temperature close to the boiling point of water within one hour.



 

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FIELD: cellulose production.

SUBSTANCE: invention relates to manufacture of cellulose from cotton lint after alkali pulping or from prehydrolyzed wood cellulose and can be utilized in paper-and-pulp industry or in manufacture of artificial fibers, films, and other cellulose materials. Pulped cotton lint or prehydrolyzed wood cellulose is bleached by sodium hypochlorite at modulus 1:20 to 1:30 and 20-30°C, washed, treated for 50-60 min with 1.0-1.5% sodium hydroxide solution at 80-90°C, and subjected to souring, after which desired product is recovered. More specifically, cotton lint after alkali pulping is bleached in two steps separated by washing. In the first step, bleaching is carried out for 0.5-2.0 h at active chlorine concentration 0.3-2.0 g/L and, in the seconds step, for 0.5-6.0 h with 1.0-6.0 g/L active chlorine concentration. Prehydrolyzed wood cellulose is leached in one step for 0.5-6.0 h with 0.3-6.0 g/L active chlorine concentration.

EFFECT: improved quality of product, reduced average degree of polymerization, and increased reactivity thereof.

2 tbl, 18 ex

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