SU821618A1 - Cellulose pulp bleaching method - Google Patents

Description

(54) PULSE BLEACHING METHOD

This invention relates to a pulp bleaching process and can be used in the pulp and paper industry.

There is a method of bleaching cellulose by treating it with chlorine dioxide and chlorine, followed by washing with water and alkali and subsequent single or multiple treatments with chlorine dioxide and / or hypochlorite 1.

However, such a method, providing a high whiteness to the target product, leads to a significant contamination of wastewater.

There is also known a method of bleaching cellulose, which includes treating it with chlorine, alkali, hypochlorite. Chlorination of cellulose in this method is carried out in the presence of sulfamic acid or urea 2.

However, when chlorinating with the addition of sulfamic acid or urea, there is a slight increase in the whiteness of the pulp and the wastewater is practically not neutralized after the chlorination step.

The closest to the present invention is a bleaching method, which includes a three-stage treatment with chlorine-containing compounds, the first of which is carried out with a mixture of chlorine dioxide and chlorine, the second - chlorine and the third - chlorine dioxide or hypochlorite with consecutive, washing and alkali treatment between steps and the subsequent kislovka. The method allows to radiate cellulose with high whiteness and to maintain physical and mechanical properties 3,

However, this method does not allow to sufficiently reduce the pollution of wastewater. To neutralize chlorine-containing chemical and biological products of lignin decomposition.

The purpose of the invention is to reduce the pollution of wastewater while increasing the physico-mechanical properties and the yield of the target product.

This goal is achieved by the fact that according to the method of pulp bleaching, which includes a three-stage treatment with chlorine-containing compounds, the first of which is carried out with a mixture of chlorine dioxide and chlorine, the second is chlorine and the third .- chlorine dioxide or hypochlorite with a subsequent. In particular, operations of washing and processing with alkali between steps; and subsequent acid treatment, processing cellulose with chlorine for the second. the steps are carried out in the presence of urea in an amount of 0.05-0.5% by weight of absolutely dry fiber. At the same time, chlorine treatment at the second stage is carried out at 20-50 ° C and the concentration of the mass is 3-5% for 30-60 minutes. Example. Take unbleached sulphate pulp with a delignification degree of 90 p. with a hardwood content of 87% and coniferous wood - 13%, viscosity index 276 Mp of copper-ammonia solution, discontinuous with length of 7600 m, number of double kinks 1270. Process with chlorine-chlorine chlorine-dyuoxide mixture with total consumption of active chlorine of 5.1 to dry fiber with mass concentration of 3.5%, at 25 ° C for 45 minutes, washed with water and subjected to alkaline extraction at a rate

Viscosity 0.7%

copper-ammonium

solution, Mp223241

Breaking length, m 7160 7370

1050 1170

144.0 234.13 432 .17 -324.12

93.7 -94.9. -.

As can be seen from the table. 1, in the obtained bleached celscolose with the addition of urea 0.10–0.20% (experiments II-JV), there is an increase in viscosity by 9–11%, a gap of 10%, and the number of double kinks by 13–20% compared to with experience 1, bleached by the BECTHOw method.

276

242246264 7600

744075407580

13001390

79.2

82.08 157.57 163.89

332,77: 95,2

The oxidizability and the COD of the filtrate obtained from cellulose samples with the addition of urea in an amount of 0.15 and 0.5% to the fiber, 5 decreases respectively, 43–45%, 30–32%, the COD of the filtrates of the same samples after the second alkali after treatment chlorine is reduced by 25% compared with the filtrate. caustic soda 2.5 / ,. at 70 ° C, kch) and center of mass 10%, 120 lyiHH. After washing with water, the mass is divided into five parts, each of which is treated with chlorine in an amount of 2% to dry fiber with the addition of different amounts of urea (experiments 1-0; 11-0.10%; 111-0.15%; IV- 0.20%; V-0.50% to dry fiber) at 30 ° C, mass concentration 5%, 45 min. Then, after washing with water, the mass is treated with caustic soda at a rate of 0.5% to the fiber at 70 ° C, mass concentration 10%, 120 minutes. The addition of chlorine dioxide is carried out after washing with water at a flow rate of 0,8% to fiber at 75 ° C, concentration 10%, 210 minutes. The acidity is carried out without prior washing with water with a COj consumption of 1% to the fiber for 30 minutes. at a mass concentration of 5%. In tab. 1 shows the test results (for example I). Table 1

 five

selected from figurative, processed by a known method. The output of celine obtained with the addition of urea 0; 15-0.5%, increased by 1.4-1-1.6 / g compared with chlorine treatment according to a known method.

Moreover, the addition of urea to samples II-IV in an amount of 0.1-0.2%. dry fiber practically does not lead to a decrease in whiteness with respect to sample I, processed by a known method. .

When chlorine interacts with cellulose and ochevina, it obviously acts as an activator of the oxidation of decay products formed by the interaction of cellulose satellites with chlorine containing lignin chromoform groups.

Thus, when bleaching cellulose according to the blend scheme (chlorine dioxide + chlorine - chlorine dioxide, chlorine treatment in the second stage, with the addition of urea, increases cellulose running time, viscosity, physical and mechanical parameters, practically without reducing the whiteness. When

91.59i; 591,391.3-89.4

274 290302314327.

71207360760175907670

13201420158415741690

x

124- 57.1 52.4 37.9

The data given in table. 2, confirm the results of the experiments given in table. one.

Claims (3)

1. A method of bleaching cellulose, which includes a three-stage treatment with chlorine-containing compounds, the first of which is carried out with a mixture of chlorine dioxide and chlorine, the second with chlorine and a third with chlorine dioxide or hypochlorite, with sequential washing and alkaline processing between .6. JTOM results in significant disposal of wastewater after pulp bleaching, which allows to & t reduce the consumption of fresh water for bleaching. Example 2. Sulfite unbleached integer / skid with a delignification degree of 94. p. Units, with a viscosity of 336 Mp copper-alkaline solution, a breaking length of 7744 m and a number of double kinks of 1970, is treated with a mixture of chlorine dioxide and chlorine and then the parameters given in example 1 Treatment with chlorine with urea in the second stage is carried out with the consumption of the latter in experiments -0; 11-0.05%; 111-0.10%; IV-0.15%; V-0.50% by weight of dry fiber at 25 ° C, mass concentration 5%, 50 minutes The treatment is then carried out with caustic soda at 50 ° C. After washing with water, the mass is added with chlorine dioxide 210 minutes. Sulfurous acid sour is carried out without intermediate water washing. In tab. 2 shows the test results (for example 2). ,  Table 2 7744 1970 step by step; This three-stage treatment and subsequent acidification, characterized in that, in order to reduce wastewater pollution while simultaneously increasing the physics-mechanical indicators and the yield of the target product, the second stage treatment of cellulose with chlorine is carried out in the presence of urea, in an amount of 0.05-0, 5% by weight of absolutely dry fiber. 2. The method according to claim 1, wherein the treatment of cellulose with chlorine in the second stage is carried out at 20-50 ° C and at a mass concentration of 3-5% for 30-60 minutes. 7821618.8. Sources of information, 2. Gudivak, R. R., and Amirap, V. R. Inhibitors into consideration by examiners in bleaching pulp. - indian palp 1. The patent of the USSR And 196679, cl. D 21 C 9/10, 3. USSR author's certificate N 583226, 1965.5 cl. D 21 C 9/14, 1976 (prototype). End Pepper, J973. 27.9.