Method of bleaching of sulphate pulp

 

(57) Abstract:

The method relates to the field of pulp and can be used to produce bleached pulp without the use of molecular chlorine. Cellulose rigidity of 84.3 permanganate units subject alternating treatment with hydrogen peroxide in alkaline medium and chlorine dioxide. At stage I the cellulose concentration of 10-20 mass% is treated with hydrogen peroxide (H2O2) for 60 min in an alkaline medium (pH from 9.0 to 10.9) at a temperature of 75-85°C and the flow rate of H2O22% of the mass of absolutely dry pulp. On the third and fifth stages of the pulp treated with the same concentration of mass within 120 min at a temperature of 70-100°C with a flow rate of H2O20.5% and 1.0%, II and stage IV is carried out at a temperature of 70°With chlorine dioxide at a flow rate of 0.7-1.0% and 0.3%, respectively, depending on the initial stiffness of the cellulose. The technical result consists in obtaining the white pulp 86-88% and higher depending on the stiffness of the original cellulose. table 1.

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

Iatneh units by alternating alkaline and acidic treatment under specified modes, at stage I, the cellulose concentration of 10-20 mass% process H2O2in an alkaline environment (pH of 9.5 to 10.5) at 70-100oC for 120-180 min at a flow rate H2O22% of the mass of absolutely dry pulp, II and IV stages cellulose concentration mass 2-7% is treated with a solution of KMnO4with a flow rate of 0.01 to 0.8% in the 18-25oC until complete absorption of reagents, III and V stage is carried out at conditions and costs stage I, given the initial stiffness of cellulose (RU patent N 2142529, C1, 27.03.99).

The goal of this research is to develop a method of producing pulp, which is most effectively used hydrogen peroxide at each stage and increases the whiteness of the pulp at the outlet.

The result is achieved by setting the optimum exposure time, H2O2the residual lignin, because stable peroxide bleaching (P) possible equilibrium processes between the chromophores and their leucovorine, which leads to reduction of the white pulp consumption at each stage of bleaching, taking into account the structural changes of the residual lignin after treatment, bleaching agents of different nature.

The proposed method includes both 75-85oC (temperature rise at this stage does not give a positive effect), when the duration of treatment with hydrogen peroxide in the third and fifth stages of bleaching 120 min, a temperature of 70-100oC and expenditures of H2O2when the white pulp at these stages of the bleaching maximum (0.5 and 1%, respectively), II and IV stages of bleaching pulp is treated with chlorine dioxide at a concentration of 2-10 mass% for 90-120 min at 70oC, when its total consumption, 1-1,3% of the mass of absolutely dry pulp. When the total consumption of H2O22.5% of the mass of absolutely dry pulp (with a four-stage bleaching P-D-P-D) white pulp is 84-86%, when the total flow rate of 3.5% (bleaching in five stages P-D-P-D-P) white reaches 86-88 %, at a flow rate of chlorine dioxide 1.0 and 1.3% of the mass of absolutely dry pulp, respectively. The lowering of the rigidity of the original cellulose can increase the whiteness of the pulp up to 90%. However, if the peroxide bleaching there is no stabilizer on the first and third stages of peroxide bleaching, the white pulp is only 76 - 80% (depending on the flow rate of chlorine dioxide) and 84-85% when bleaching in four and five steps, respectively.

Thus, the proposed method of bleaching uchityvaem structural changes what is happening in lignin.

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

The essential features of the invention: method of bleaching pulp, comprising the treatment of pulp with a concentration of 10-20 mass% hydrogen peroxide in alkaline medium (pH from 9.0 to 10.9) in the presence of a stabilizer (sodium silicate) and maintaining the pulp slurry at 80oC for 60 min (the flow rate of the hydrogen peroxide is 2.0%, sodium silicate 2.0 to 2.5%, while the consumption of caustic soda is 1.2-1.3%), separation from the solution, the neutralization and subsequent treatment of pulp with chlorine dioxide at a flow rate of 0.7-1.1% of the mass of absolutely dry pulp (70oC, concentration of mass of 5-7%, the processing time 90-120 min), separation and washing of the masses and again treatment with hydrogen peroxide at a temperature of 80-90oC for 120 minutes (flow H2O20.5%) and chlorine dioxide under the same conditions (flow rate of 0.2-0.3%), a fifth step of dobelli hydrogen peroxide is carried out at a temperature of 80-100oC, concentration, mass and duration for stage III, H2O21

Unbleached pulp from hardwood rigidity of 84.3 permanganate units, with a viscosity of 30 centipoise subjected to peroxide treatment, including the treatment of pulp with a consistency of 10 % hydrogen peroxide in alkaline medium (pH 10,9) with the consumption of H2O22% in the presence of the stabilizer of sodium silicate (2.5%) and caustic soda consumption, which is 1.3%, while maintaining the pulp slurry at 80oC for 60 minutes Then the pulp is thoroughly washed, and processed chlorine dioxide at a concentration of mass to 7%, a temperature of 70oC for 120 min and the flow ClO2equal to 1.0% of the mass of absolutely dry pulp (pH 3.5), and then repeat the treatment with hydrogen peroxide at the same concentration of mass and temperature, as for the first stage, with the consumption of H2O20.5% (consumption of NaOH is 1%, the consumption of Na2SiO32.5%, and a pH of 10.6), for 120 min and chlorine dioxide under the same conditions as for the second phase, with a flow rate of ClO2equal to 0.3% of the mass of absolutely dry cellulose (pH of 5.4). After washing, the pulp is dried.

White pulp 86%, the viscosity of 26.4 SDR, the yield of 98.2% (table. 1, p. 1).

Example 2

Unbleached pulp is treated as in example 1 with rashood to 98.6% (table. 1, p. 2).

Example 3

Unbleached pulp is treated as in example 1, to include a fifth stage peroxide bleaching at the same concentration of mass as in example 1, at a temperature of 80oC for 120 min and the flow rate of H2O21.0% of the mass of absolutely dry pulp (pH of 0.9). After washing, the pulp is dried.

White pulp 88,0%, the viscosity of 16.4 SDR, the yield of 96.5% (table. 1, p. 3).

Example 4

Unbleached pulp is treated according to example 3 at a flow rate ClO2on the second bleaching stage of 0.7%. After washing, the pulp is dried.

White pulp 86,0%, the viscosity of 19.1 SDR, the yield of 97.5% (table. 1, p. 4).

Example 5

Unbleached pulp is treated according to example 3 without using stabilizer, peroxide bleaching (sodium silicate) ceteris paribus bleaching. After washing, the pulp is dried.

White pulp 85,0%, a viscosity of 17 SDR output to 95.3% (table. 1, p. 5).

Example 6

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

The white pulp of 84.3%, viscosity 19,8 SDR, the yield of 97.7% (table. 1, p. 6).

White pulp 83,0%, a viscosity of 24 SDR output 98,0% (table. 1, p. 7).

Example 8

Unbleached pulp is treated according to example 6, by changing the duration of the treatment with hydrogen peroxide (grade I - 180, II and III stage - 120 min). After washing, the pulp is dried.

White pulp 80%, the viscosity of 22.5 SDR output to 98.4% (table. 1, p. 8).

Example 9

Unbleached pulp is treated as in example 1 at a temperature in the first stage peroxide bleaching 90oC. After washing, the pulp is dried.

White pulp 86%, viscosity 20,2 SDR output to 98.4% (table. 1, p. 9).

Example 10

Unbleached pulp is treated according to example 4 without using the fifth stage peroxide bleaching stage of sodium silicate. After washing, the pulp is dried.

White pulp 86 %, a viscosity of 20 centipoise, yield 97% (table. 1, p. 10).

Bibliography

1. Fedorova, E. I., Smolev L. L., Chubakov A. A., yachmenyov S. A., Milenin D. O. Patent N 2142529 from 17.05.99.

Method of bleaching pulp, comprising platitudinous processing unbleached pulp by alternating alkaline and acidic on the consumption and 2% of the mass of absolutely dry pulp in an alkaline medium and a temperature of 75 85oC for a specified time, and on the third and fifth stages of the cellulose is treated with hydrogen peroxide at the same concentration of mass within 120 min and a temperature of 70 - 100oC, characterized in that on the second and fourth stages, the pulp is treated at a temperature of 70oC chlorine dioxide with a flow rate of 0.7 - 1.0% and 0.3%, respectively, depending on the initial stiffness of the cellulose, in the first stage treatment with hydrogen peroxide is carried out at a pH of from 9.0 to 10.9 for 60 min, while the third and fifth stages of the consumption of hydrogen peroxide 0.5% and 1.0%.

 

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