RU2164572C1 - Sulfate cellulose bleaching process - Google Patents

Abstract

FIELD: paper-and-pulp industry. SUBSTANCE: cellulose characterized by 84.3 permanganate units is subjected to alternate treatment with hydrogen peroxide in alkali medium and with chlorine dioxide. In the first stage, 10-20% cellulose is treated with hydrogen peroxide (pH 9.0-10.9) at 75-85 C for 60 min with hydrogen peroxide uptake 2% on the weight of absolutely dry cellulose. In the 3rd and 5th stages, cellulose in the same concentration is treated for 120 min at 70-100 C with hydrogen peroxide uptake 0.5 and 1.0%, respectively. The 2nd and 4th stages are carried out at 70 C with chlorine dioxide uptake 0.7-1.0 and 0.3%, respectively, depending on initial hardness of cellulose. Cellulose product is characterized by 86-88% whiteness, which depends on initial hardness of cellulose. EFFECT: enhanced bleaching efficiency. 1 tbl, 10 ex

Description

 The invention relates to the field of pulp production and can be used to produce bleached pulp without the use of molecular chlorine (ECF-cellulose).

A known method of bleaching unbleached pulp, comprising treating unbleached pulp with a hardness of 83 permanganate units by alternating alkaline and acid treatment under predetermined conditions, is carried out. In stage I, pulp with a concentration of 10-20% is treated with H ₂ O ₂ in an alkaline medium (pH 9.5 -10.5) at 70-100 ^o C for 120-180 min at a flow rate of H ₂ O ₂ 2% by weight of absolutely dry cellulose, at stages II and IV, cellulose with a mass concentration of 2-7% is treated with a solution of KMnO ₄ with a flow 0.01-0.8% at 18-25 ^o C until complete absorption of the reagents, stage III and V is carried out under conditions and costs of stage I, given the initial hardness of cellulose (RU patent N 2142529, C1, 03/27/99).

 The objective of this study is to develop a method for producing cellulose, in which hydrogen peroxide is used most effectively at each stage and the whiteness of the pulp increases at the outlet.

The result is achieved by establishing the optimal duration of exposure to H ₂ O ₂ on residual lignin, since for stabilized peroxide bleaching (P) equilibrium processes between chromophores and their leukoforms are possible, which leads to a decrease in the brightness of cellulose, its consumption at each stage of bleaching, taking into account structural changes in the residual lignin after treatment with bleaching reagents of various nature.

The proposed method involves the treatment of cellulose with hydrogen peroxide in the presence of a stabilizer in stage I for 60 minutes at a temperature of 75-85 ^o C (temperature increase at this stage does not give a positive effect), with a duration of treatment with hydrogen peroxide in stages III and V of bleaching 120 minutes, a temperature of 70-100 ^o C and costs of H ₂ O ₂ at which the pulp whiteness at these stages of bleaching is maximum (0.5 and 1%, respectively), at stages II and IV of bleaching, the pulp is treated with chlorine dioxide at a mass concentration of 2-10% in for 90-120 min at 70 ^o C, with its total consumption of 1-1.3% by weight of absolutely dry cellulose. With a total consumption of H ₂ O _{2 of} 2.5% by weight of absolutely dry cellulose (with four-stage bleaching P-D-P-D), the whiteness of cellulose is 84-86%, with a total consumption of 3.5% (bleaching in five stages P -D-P-D-P) whiteness reaches 86-88%, with a consumption of chlorine dioxide of 1.0 and 1.3% by weight of absolutely dry cellulose, respectively. Reducing the stiffness of the original pulp can increase the whiteness of the pulp up to 90%. At the same time, if there is no stabilizer during peroxide bleaching at stages I and III of peroxide bleaching, then the whiteness of cellulose is only 76-80% (depending on the consumption of chlorine dioxide) and 84-85% when bleaching in four and five steps, respectively.

 Thus, the proposed bleaching method takes into account that the parameters of peroxide bleaching cannot be unambiguous at its various stages, due to various structural changes occurring in lignin.

 The technical result, which is in causal connection with the essential features of the invention, is to increase the brightness of the pulp at the output by 3-5%, depending on the rigidity of the pulp.

Salient features of the invention: a method of bleaching cellulose, comprising treating cellulose with a mass concentration of 10-20% hydrogen peroxide in an alkaline medium (pH 9.0-10.9) in the presence of a stabilizer (sodium silicate) and maintaining the cellulosic suspension at 80 ^o C within 60 minutes (the consumption of hydrogen peroxide is 2.0%, sodium silicate 2.0-2.5%, and the consumption of caustic soda - 1.2-1.3%), the separation of the mass from the solution, its neutralization and subsequent processing of cellulose chlorine dioxide with a flow rate of 0.7-1.1% by weight of absolutely dry cellulose (at 70 ^o C, mass concentration 5-7%, processing time 90-120 min), separation and washing of the mass and again treatment with hydrogen peroxide at a temperature of 80-90 ^o C for 120 minutes (consumption of H ₂ O ₂ 0.5%) and chlorine dioxide under the same conditions (consumption of 0.2-0.3%), the fifth stage of completion with hydrogen peroxide is carried out at a temperature of 80-100 ^o C, mass concentration and duration, which and for stage III, at a flow rate of H ₂ O _{2 of} 0.5-1.0% by weight of absolutely dry cellulose. The bleached mass is separated and washed thoroughly.

Example 1
Unbleached hardwood pulp with a hardness of 84.3 permanganate units and a viscosity of 30 cPs is subjected to peroxidation, including treatment of cellulose with a mass concentration of 10% hydrogen peroxide in an alkaline medium (pH 10.9) with a consumption of H ₂ O ₂ 2% in the presence of a silicate stabilizer sodium (2.5%) and caustic soda, the consumption of which is 1.3%, while maintaining the cellulose suspension at 80 ^o C for 60 minutes Then the pulp is thoroughly washed and subjected to treatment with chlorine dioxide at a mass concentration of 7%, a temperature of 70 ^o C, for 120 min and a flow rate of ClO ₂ equal to 1.0% by weight of absolutely dry cellulose (pH 3.5), after which the treatment is repeated hydrogen peroxide at the same mass concentration and temperature as for the first stage, with a H ₂ O ₂ flow rate of 0.5% (NaOH consumption is 1%, Na ₂ SiO ₃ consumption is 2.5%, pH 10.6 ), for 120 min and chlorine dioxide under the same conditions as for the second stage, with a consumption of ClO ₂ equal to 0.3% by weight of absolutely dry cellulose (pH 5.4). After washing, the cellulose is dried.

 Cellulose whiteness 86%, viscosity 26.4 cps, yield 98.2% (table. 1, p. 1).

Example 2
Unbleached cellulose is treated according to example 1 with a consumption of chlorine dioxide in the second stage of bleaching equal to 0.7%.

 The cellulose whiteness was 84.0%, the viscosity was 26.0 cPs, and the yield was 98.6% (Table 1, p. 2).

Example 3
Unbleached pulp is treated according to example 1, including the fifth stage of peroxide bleaching at the same mass concentration as in example 1, at a temperature of 80 ^o C for 120 min and a flow rate of H ₂ O _{2 of} 1.0% by weight of absolutely dry cellulose (pH 0.9). After washing, the cellulose is dried.

 Cellulose whiteness 88.0%, viscosity 16.4 cps, yield 96.5% (table. 1, p. 3).

Example 4
Unbleached pulp is treated according to example 3 at a flow rate of ClO ₂ in the second stage of bleaching of 0.7%. After washing, the cellulose is dried.

 Cellulose whiteness 86.0%, viscosity 19.1 cps, yield 97.5% (table 1, p. 4).

Example 5
Unbleached pulp is treated according to example 3 without the use of a peroxide bleaching stabilizer (sodium silicate), ceteris paribus bleaching. After washing, the cellulose is dried.

 Cellulose whiteness is 85.0%, viscosity 17 cps, yield 95.3% (Table 1, p. 5).

Example 6
Unbleached pulp is treated according to example 4 without the use of a peroxide bleaching stabilizer (sodium silicate), ceteris paribus bleaching. After washing, the cellulose is dried.

 The cellulose whiteness is 84.3%, the viscosity is 19.8 cps, the yield is 97.7% (Table 1, p. 6).

Example 7
Unbleached cellulose is treated according to example 4, changing the duration of treatment with hydrogen peroxide (I stage - 180, II and III stage - 120 minutes). After washing, the cellulose is dried.

 Cellulose whiteness is 83.0%, viscosity is 24 cps, yield is 98.0% (Table 1, p. 7).

Example 8
Unbleached cellulose is treated according to example 6, changing the duration of treatment with hydrogen peroxide (I stage - 180, II and III stage - 120 minutes). After washing, the cellulose is dried.

 Cellulose whiteness is 80%, viscosity is 22.5 cps, yield is 98.4% (Table 1, p. 8).

Example 9
The unbleached pulp is treated in accordance with Example 1 at a temperature in the first stage of peroxide bleaching of 90 ^° C. After washing, the pulp is dried.

 Cellulose whiteness 86%, viscosity 20.2 cps, yield 98.4% (Table 1, p. 9).

Example 10
Unbleached pulp is treated according to example 4 without the use of a sodium silicate step in the fifth stage of peroxide bleaching. After washing, the cellulose is dried.

 Cellulose whiteness 86%, viscosity 20 cps, yield 97% (Table 1, p. 10).

References
1. Fedorova E.I., Smoleva L.L., Shubakov A.A., Yachmeneva S.A., Milenin D.O. Patent for invention No. 2142529 of 05.17.99.

Claims (1)

A method of bleaching pulp, including a five-stage treatment of unbleached pulp by alternating alkaline and acid treatments, in the first stage, the pulp with a concentration of 10-20% is treated with hydrogen peroxide at a rate of 2% by weight of absolutely dry cellulose in an alkaline medium and a temperature of 75 - 85 ^o C for a predetermined time, and in the third and fifth stages, the cellulose is treated with hydrogen peroxide at the same mass concentration for 120 minutes and a temperature of 70 - 100 ^o C, characterized in that in the second and fourth stages of cellulose the vine is treated at a temperature of 70 ^o C with chlorine dioxide with a flow rate of 0.7 - 1.0% and 0.3%, respectively, depending on the initial hardness of the pulp, in the first stage, hydrogen peroxide is treated at pH 9.0 - 10.9 for 60 minutes, and in the third and fifth stages with a consumption of hydrogen peroxide of 0.5% and 1.0%, respectively.

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