RU2290469C1 - Multistep sulfite cellulose bleaching process - Google Patents

Abstract

FIELD: paper-and-pulp industry.

SUBSTANCE: invention is designed for use in production of bleached sulfite cellulose with reduced level of resins and fats for manufacturing paper and cardboard in multistep bleaching processes. Process according to invention comprises treatment of pulp with sodium hypochlorite solution in presence of chemical additive, bucking and souring of pulp, sad chemical additive being aqueous mixture of ethoxylated fatty alcohols having density 0.99-1.1 g/cm³ in amount 0.04-0.08% of the weight of absolutely dry cellulose. Bucking of pulp is carried out in presence of detergent named VIK-1 used in amount 0.1-0.3% of the weight of absolutely dry cellulose. Souring is carried out in presence of aqueous solution of quaternary polyammonium compound (BZK-2) used in amount 0.4-0.8% of the weight of absolutely dry cellulose.

EFFECT: reduced gumminess of bleached sulfite cellulose and enhanced whiteness at the same cost.

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Description

The invention relates to the pulp and paper industry and can be used in the production of bleached pulp with a reduced content of resins and fats for the manufacture of paper and cardboard in multi-stage bleaching processes.

A known method of multi-stage bleaching of sulphite cellulose, comprising an alkali step in the presence of ethoxylated paranonylphenol with a branched nonyl radical and a degree of ethoxylation of 10-12 (see SU 1527350, A1, D 21 C 9/12, 07/12/89).

In this case, the chemical additive is introduced in an amount of 0.2-0.5% by weight of absolutely dry cellulose.

Bleached cellulose obtained in a known manner is characterized by a reduced resin and fat content (0.39-0.51%) and increased mechanical strength (breaking length - 7800 m, fracture resistance - 1200 ppm).

A known method of reducing the resinity of sulphite cellulose by refinement using surfactants in an alkaline medium (see Ozhichanova VR and others. Reducing the resinity of sulphite viscose pulp using surface-active substances. Summary of information "Cellulose, paper and cardboard" - M. : 1970, No. 18, pp. 7-8).

Moreover, as a surfactant in the known method, a Schkopau detergent of the W-OF brand is used, which is the product of the hydroxyethylation of a mixture of technical fatty alcohols.

Cellulose, ennobled in a known manner, is characterized by the following resin content when using additives in an amount of 0.5% by weight of fiber: the resin content in cellulose is 0.23%; when using additives - 1.0% by weight of fiber, the resin content in cellulose is 0.17%; when using additives - 1.5% by weight of fiber, the resin content in cellulose is 0.07%.

However, the known method does not allow to obtain bleached sulfite cellulose with the required level of quality.

The closest analogue of the claimed invention in technical essence is a method of multi-stage bleaching of cellulose, comprising treating the pulp with a solution of sodium hypochlorite in the presence of a chemical additive, alkalizing the pulp and acidifying it (see SU 1618802 A1, D 21 C 9/08, 04/11/1984). Moreover, as an additive in the known method using sodium hypophosphite or waste products in the amount of 0.005-0.060% by weight of absolutely dry cellulose.

The known method provides an increase in the mechanical strength of cellulose and whiteness, as well as a low mass fraction of resin in the cellulose.

When bleaching cellulose according to the G-G-K scheme, the mass fraction of resin in bleached sulfite cellulose is 0.33-1.05%, when bleaching the cellulose according to the X-SH-X-G-D-G-K scheme, the mass fraction of resin in bleached sulphite pulp is 0.20-0.52%, when bleaching pulp according to the scheme G-X- (D-Shch) -G-G-D-Shch-D-K, the mass fraction of resin in bleached sulphite pulp is 0.17- 0.40%, where G is sodium hypochlorite treatment; K - acidity; X is chlorination; Щ - alkalization; D is chlorine dioxide.

However, the known method does not allow to obtain bleached sulfite cellulose with the required quality level from wood species of high resinity, such as pine, a mixture of aspen and birch.

A new technical result from the use of the proposed technical solution is to reduce the resinity of bleached sulfite cellulose while increasing the whiteness while maintaining its low cost.

This new technical result is achieved by the fact that in the method of multistage bleaching of sulfite pulp, which includes treating the pulp with a solution of sodium hypochlorite in the presence of a chemical additive, alkalizing the pulp and acidifying, an aqueous mixture of ethoxylated is used as a chemical additive at the stage of processing the pulp with a solution of sodium hypochlorite fatty alcohols having a density of 0,99-1,1 g / cm ³ in an amount of 0.04-0.08% by weight of absolutely dry cellulose pulp bucking is carried out in presence ' and detergent VIK-1 in an amount of 0.1-0.3% by weight of absolutely dry cellulose, and acidification is carried out in the presence of an aqueous solution of a Quaternary polyammonium compound BZK-2 in an amount of 0.04-0.08% by weight of absolutely dry cellulose .

Moreover, the used chemical additives at the stages of hypochlorite treatment, alkalization and acidification are obtained industrially according to the following regulatory documents:

- an aqueous mixture of ethoxylated fatty alcohols with a density of 0.99-1.1 g / cm ³ (UMS-1) according to TU 2484-114-05800142-2002;

- detergent VIK-1 according to TU 2381-002-24063040-2002;

- an aqueous solution of a Quaternary polyammonium compound BZK-2 according to TU 2484-073-05800142-2001.

The combination of chemical additives used in the proposed method in the claimed quantitative range allows to obtain bleached sulphite pulp of high whiteness with a reduced content of resins and fats.

It should be noted that the use of these chemical additives changes the cost of bleached cellulose by only 2%, with a significant increase in the quality of cellulose, which eliminates material costs for the further use of cellulose due to the absence of problems with harmful resin. With the proposed multi-stage bleaching, you can use sulfite cellulose obtained by cooking wood of highly resinous species: aspen, birch and pine.

The present invention is illustrated by the following examples:

Example 1. The method of multistage bleaching of sulphite pulp is as follows:

- the mass of sulfite cellulose, characterized by the following quality indicators:

kappa number - 27 tar and fat content - 1.5% breaking length, m - 9100 resistance: - kink, ch.p. - 1500 - tearing, mN - 480 - punching, kPa - 420

bleach according to the scheme: X-SH-G-G-K;

- the stage of alkalization is carried out in the presence of detergent VIK-1 in an amount of 0.3% by weight of absolutely dry cellulose;

- at the stage of hypochlorite bleaching, UMS-1 is introduced into the mass - an aqueous mixture of ethoxylated fatty alcohols with a density of 0.98-1.1 g / cm ³ in an amount of 0.04% by weight of absolutely dry cellulose;

- at the stage of acidification, an aqueous solution of the Quaternary polyammonium compound BZK-2 is introduced into the mass in an amount of 0.04% by weight of absolutely dry cellulose.

The resulting mass is washed and the quality of the obtained bleached sulfite pulp is determined by standard methods.

Quality indicators bleached sulfite pulp are shown in the table.

The sulphite cellulose used in bleaching is obtained by cooking high-resinous wood species (aspen, birch and pine) at a pH of 2.3–2.8 of a cooking solution, SO ₂ concentration _of 4.5–5.5%, and a cooking temperature of 153–156 ° C.

Example 2. The method of multistage bleaching of sulfite pulp is carried out according to the scheme: G-Shch-GK. In this case, sulfite cellulose with quality indicators is used, as in example 1:

- at the stage of hypochlorite bleaching, an aqueous mixture of ethoxylated fatty alcohols is introduced into the mass, as in example 1, in an amount of 0.08% by weight of absolutely dry cellulose;

- at the stage of alkalization, VIK-1 detergent is introduced in an amount of 0.1% by weight of absolutely dry cellulose;

- at the acidification stage, BZK-2 is introduced, as in Example 1, in an amount of 0.08% by weight of absolutely dry cellulose.

The resulting mass is washed and determine the quality indicators of bleached pulp, which are shown in the table.

The sulphite pulp used in bleaching is obtained as in Example 1.

Example 3 (prototype).

Sulphite cellulose from a mixture of spruce, pine and birch, obtained as in example 1, is bleached according to the scheme G-G-K. At the second stage G, the waste product of sodium hypochlorite KSC-1 is introduced into the mass in an amount of 0.005% of the mass of absolutely dry cellulose at a pH of 7.3 for 60 minutes. After acidification, the mass is washed. The quality indicators of bleached pulp are shown in the table.

As can be seen from the table, the proposed method in comparison with the known one provides an increase in the whiteness and mechanical strength of bleached pulp and a decrease in the content of resins and fats in the pulp.

Table Bleached Pulp Quality Indicators Examples one 2 According to the prototype White,% 88.0 87.5 86.6 The content of resins and fats,% 0.17 0.10 0.38 Mechanical strength: - breaking length, m 8200 8500 6800 - resistance: break, ch.p. 1200 1250 700 punching, kPa 370 390 290

Claims (1)

A method of multistage bleaching of sulfite cellulose, comprising treating the pulp with a solution of sodium hypochlorite in the presence of a chemical additive, alkalizing the pulp and acidifying it, characterized in that an aqueous mixture of ethoxylated fatty alcohols with a density of 0 is used as a chemical additive at the stage of processing the pulp with a solution of sodium hypochlorite , 99-1,1 g / cm ³ in an amount of 0.04-0.08% by weight of absolutely dry cellulose pulp bucking conducted in the presence of detergent VIC-1 koliches ve 0.1-0.3% by weight of oven-dry pulp, and Kislovka performed in the presence of an aqueous solution of UPC-2 quaternary polyammonium compound in an amount of 0.04-0.08% by weight of oven-dry pulp.