SU1214809A1 - Pulp bleaching process - Google Patents

Description

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The invention relates to the pulp and paper industry, in particular to the bleaching of fibrous semi-finished products, and can be used in the bleaching of wood pulp, obtained by firearms, thermomechanically and by other methods.

The purpose of the invention is to intensify the process and reduce the weediness of the target product.

The proposed method of bleaching wood pulp provides for the treatment of lignocellulosic material at the same temperature in two stages, while the processing in the second stage is carried out by successively introducing portions of sodium hydrosulfite at intervals of 2– (min at a flow rate of each portion of 0.2–0.4% by weight of absolute dry fiber and an initial wood pulp concentration of 13-17%.

The treatment with sodium hydrosulfite is completed with a pulp concentration of 3-4%.

The proposed method of bleaching wood pulp is carried out as follows.

Wood pulp obtained by one of the known methods - grinded, refiner, thermomechanical or thermochemical is loaded into a bleaching plant, heated to a temperature of 70-90 ° C, and then chemical reagents necessary for the mercury are supplied to the mass: hydrogen peroxide, sodium hydroxide, sodium silicate and complexing agent. The mass is thoroughly mixed and maintained at the same time 60-90 minutes. After the indicated time has elapsed, the mass is treated with an acidic reagent, for example, a solution of sodium bisulfite and sulfuric acid or sulfurous anhydride, pH adjustment, equal to 5.0-5.5.

The second bleaching stage is carried out with sodium hydrosulfite in an acidic medium. Pre-prepared aqueous solution of sodium hydrosulfite is introduced into a suspension of 13-17% wood mass heated to 70-80 0 in an amount of 0.2-0.4% by weight of absolutely dry fiber, after 2-6 minutes the next batch, the total consumption of hydrosulfite up to 0.6-0.8% by weight of absolutely dry fiber. With full dosage

15

20

25

thirty

35

40

45

148092

Rososulphite sodium yassu concentration 3-4% hold 30-4D min. After the specified time, the wood pulp is evaluated according to the indicator of weediness and whiteness.

Example 1. Thermomechanical pulp obtained from a mixture of spruce and pine chips in the first bleaching stage is placed in a bleaching plant and heated to a temperature of 70 C. The mass concentration is 25%. A bleaching solution of hydrogen peroxide is prepared at a rate of 2.0% by weight of absolutely dry fiber; it is introduced into the fibrous suspension and mixed thoroughly for 90 minutes. The mass concentration is 15%. After this time, the mass is diluted with a solution of sodium bisulfite and sulfuric acid to a pH value of 5.0 and a concentration of 2%. To carry out the second stage, the bleaching mass is sorted, concentrated to a concentration of 13% and heated to 80 ° C. An alkaline solution of sodium hydrosulfite is prepared and in parts of 0.2% by weight of absolutely dry fiber is introduced into a pulp suspension. The total consumption of hydrosulfite 0.6% by weight of absolutely dry fiber. The time interval between portions of 2 min. The mass concentration after the introduction of the last portion of hydrosulfite is 3%, the holding time is 30 minutes. At the end of the bleaching, the mass is analyzed for changing the weed and optical properties.

Example 2. The procedure for bleaching wood pulp is the same as in Example 1. The differences are as follows: hydrosulfite is introduced in portions of 0.4% with a total consumption of 0.8% by weight of absolutely dry fiber. The time interval between the inputs of hydrosulfite 6 minutes The mass concentration before the introduction of the sodium hydrosulfite solution is 17% and the temperature is 70 ° C. The mass concentration after the introduction of the last portion of hydrosulfite is 4%, the holding time is 40 minutes.

Example 3. The procedure for carrying out the process is the same as in Example 1. The differences are as follows: hydrosulfite is introduced in portions of 0.3% with a total consumption of 0.6% by weight of absolutely dry fiber. Time interval between entries

50

55

hydrosulfite 4 min. The mass concentration of the start of bleaching is 15%, after the introduction of the last portion of 3.5%, the holding time is 35 minutes.

Example 4. The process is carried out similarly as in example 1. The differences are as follows: hydrosulfite is introduced in portions of 0.2% at a total consumption of 0.8% by weight of absolutely dry fiber. The interval between the inputs of hydrosulfite 3 minutes The mass concentration of the start of bleaching is 15%, after the introduction of the last portion of 4%, the holding time is 30 minutes.

Example 5 (control). The process is conducted in the same way as willows. Example 1. The differences are as follows: Sodium hydrosulfite is introduced in portions of 0.1% at a total consumption of 0.5% by weight of absolutely dry fiber. The time interval between portions of 8 min. The mass concentration at the start of the bleaching was 19%; after the last portion was added 6%, the retention time was 60 minutes.

PRI me R 6 (control). The process is the same as

and in example 1, but its differences are as follows: sodium hydrosulfite is introduced in portions of 0.5% at a total consumption of 1.0% by weight of absolutely dry fiber. The time interval between portions of 1 min. The mass concentration at the start of bleaching was 10%; after the last portion was added 2%, the holding time was 20 minutes.

Example 7 (prototype). The procedure is the same as in Example 1. The differences are as follows: after the first bleaching stage, the pulp is diluted with water to a concentration of 5% and then a solution of sodium hydrosulfite in an amount of 1.0% by weight of absolutely dry is introduced into the fibrous suspension. fibers, with sodium hydrosulfite being added in a single step. The mass concentration after the introduction of the sodium hydrosulfite solution was 3%, and the holding time was 120 minutes. The conditions for the selection of wood pulp and its composition are presented in the table. ,

Table continuation

Claims (2)

1. METHOD FOR BLEACHING WOOD MASS, including processing lignocellulosic material at an elevated temperature in two steps, the first of which is carried out with an alkaline solution of hydrogen peroxide, and the second with sodium hydrosulfite, characterized in that, in order to intensify the process and reduce the degree of debris of the target product, processing on the second step is carried out by sequential administration of sodium hydrosulfite portions at an interval of 2-6 minutes at a flow rate of each portion ab- 0.2-0.4% by weight _of dry fiber and lutely initial concentration ® revesnoy weight of 13-17%. 2. The method of pop. 1, characterized in that the processing of hydrosulfite em sodium is carried out at a final concentration of wood pulp 3-4%.