RU2283909C1 - Cellulose bleaching process - Google Patents

Abstract

FIELD: pulp-and-paper industry.

SUBSTANCE: unbleached sulfate cellulose obtained from hardwood is subjected oxygen-alkali delignification, after which treated with chlorine dioxide in presence of oxyethylidenediphosphonic acid and then consecutively hydrogen peroxide and chlorine dioxide solutions. Process may be used in production of bleached fibrous intermediates.

EFFECT: increased whiteness and strength characteristics of cellulose and improved environmental safety of bleaching process.

2 cl, 1 tbl

Description

The invention relates to methods for bleaching pulp and can be used in the pulp and paper industry in the production of bleached fibrous semi-finished products.

A known method of bleaching cellulose, including stages of oxygen-alkaline delignification (KShD), treatment of cellulose with Trilon B or other complexing agents, treatment of cellulose with hydrogen peroxide and chlorine dioxide (Meller L. Possibilities of reducing AOX in the effluent. Cellulose bleaching without elemental chlorine and completely chlorine-free bleaching PAPFOR - 93. Plenary reports of the International Scientific and Technical Conference, St. Petersburg, October 4-6, 1993, p.186-208.)

However, the known method has several significant disadvantages. To process cellulose with Trilon B or another complexing agent, additional equipment is required (tower, wash filter, pumps, mixers). In addition, to achieve the required level of pulp whiteness (88-90%), an increased consumption of chemicals (chlorine dioxide or hydrogen peroxide) is required.

Closest to the technical nature of the proposed method is a method of bleaching cellulose, including the stage KShD, combined treatment of cellulose with chlorine dioxide and complexing agents (trilon B), treatment with solutions of hydrogen peroxide and chlorine dioxide (RU 2123552, CL D 21 C 9/10, op .2001.)

However, this method has significant disadvantages. Upon receipt of cellulose with a high level of whiteness (88-90%), the strength characteristics of cellulose (breaking length) are reduced and an increased consumption of hydrogen peroxide or chlorine dioxide is required.

The technical result is to increase the whiteness and strength characteristics of cellulose with environmentally friendly bleaching technology without the use of molecular chlorine.

This technical result is achieved by the fact that in the method of bleaching cellulose, including oxygen-alkaline delignification, combined treatment of cellulose with chlorine dioxide and a complexing agent, treatment of cellulose with a solution of hydrogen peroxide and chlorine dioxide, according to the invention, after oxygen-alkaline delignification, the cellulose is treated with chlorine dioxide in the presence of 1-hydroxyethylidene diphosphonic acid (OEC). This acid is added in an amount of 1-7 kg / ton of cellulose.

Example 1

After oxygen-alkaline delignification (KShD), unbleached sulfate cellulose from hardwood wood is treated sequentially with chlorine dioxide in the presence of Trilon B complexing agent, an alkaline solution of hydrogen peroxide and oxygen. The bleaching conditions and pulp indices are presented in table 1 (experiment 1).

Example 2

After unrefined hardwood sulfate pulp from hardwood, after treatment with chlorine dioxide, it is treated sequentially with chlorine dioxide in the presence of an ODK complexing agent with a flow rate of 0.5-9.0 kg / t cellulose, an alkaline solution of hydrogen peroxide and oxygen. The processing conditions and quality indicators of cellulose are presented in table 1 (experiments 2-7).

A comparison of the results of laboratory experiments (table 1) shows that the cellulose obtained after bleaching according to the proposed method compared to the prototype with the same complexing agent consumption (2.0 kg / t cellulose) has a higher brightness level (respectively: 87.4 and 88 , 8%) and discontinuous length (respectively: 8.4 and 8.8 km). In addition, to maintain the pH (2.8-3.0), the use of OEC compared with the prototype can reduce the consumption of sulfuric acid by 2.0 kg / t of cellulose (40%).

The results presented in table 1 show that when DCE is added at the stage of cellulose treatment with chlorine dioxide in the range of 1.0-7.0 kg / t cellulose, the whiteness and breaking length of bleached fibrous prefabricated are increased. With an OEC consumption of less than 1.0 kg / t of pulp and more than 7.0 kg / t, there is no improvement in these indicators of pulp quality.

Thus, the proposed method allows to obtain cellulose with a high (compared with the prototype) level of whiteness and breaking length.

Table 1
Changes in the quality indicators of cellulose when using complexing agents (ODK) at the stage chlorine dioxide cellulose bleaching. Indicators of unbleached hardwood pulp: the degree of delignification - 16.3 units. Kappa; breaking length - 10.1 km. Bleaching stage, indicators Experience Number one 2 3 four 5 6 7 one 2 3 four 5 6 7 8 KShchD step
Temperature - 95 ° C; mass concentration - 8.0%; time 90 min .; NaOH consumption, kg / t 18.0 18.0 18.0 18.0 18.0 18.0 18.0 Oxygen pressure, MPa
- at the beginning of the reaction 0.8 0.8 0.8 0.8 0.8 0.8 0.8 - at the end of the reaction 0.4 0.4 0.4 0.4 0.4 0.4 0.4 The degree of delignification, units Kappa 8.4 8.4 8.4 8.4 8.4 8.4 8.4 Breaking length, km 9.5 9.5 9.5 9.5 9.5 9.5 9.5 Stage D / Q Temperature 90 ° C; mass concentration 10%; time 120 minutes ClO ₂ consumption, kg / t (in units of act. Chlorine) 26.3 26.3 26.3 26.3 26.3 26.3 26.3 Consumption of H ₂ SO ₄ , kg / t 5,0 3.0 3.0 3.0 3.0 3.0 3.0 UEC consumption, kg / t 0 0.5 1,0 2.0 5,0 7.0 9.0 Trilon B consumption, kg / t 2.0 0,0 0,0 0,0 0,0 0,0 0,0 pH at the end of bleaching 3.0 3.0 3.0 3.0 2,8 2,8 2.7 The remainder. chlorine content, g / dm ³ no no no no no no no The degree of delignification, units Kappa 3.2 2.7 2.7 2,8 2.7 2.9 3.0 White,% 75,2 75.0 75.6 76.3 75.5 75.6 75.3

Continuation of table 1 one 2 3 four 5 6 7 8 Step SCHP Temperature 90 ° C; time 120 min., cm = 8% NaOH consumption, kg / t 12.0 12.0 12.0 12.0 12.0 12.0 12.0 Consumption of N ₂ About ₂ , kg / t 20,0 20,0 20,0 20,0 20,0 20,0 20,0 Oxygen pressure, MPa 0.2 0.2 0.2 0.2 0.2 0.2 0.2 PH at the end of bleaching 11.9 11.6 11.3 11.7 11.6 11.2 11.2 The remainder. The content of NaOH, g / DM ³ 0.43 0.50 0.54 0.56 0.46 0.49 0.47 Pulp indicators: White,% 87.7 87.7 89.1 88.8 88.7 88.9 88.7 Breaking length, km 8.4 8.4 8.7 8.8 8.8 9.0 8.8

Claims (2)

1. The method of bleaching cellulose, including oxygen-alkaline delignification, combined treatment of cellulose with chlorine dioxide and a complexing agent, treatment of cellulose with solutions of hydrogen peroxide and chlorine dioxide, characterized in that after oxygen-alkaline delignification, the cellulose is treated with chlorine dioxide in the presence of 1-hydroxyethylidene diphosphonic acid. 2. The method according to claim 1, characterized in that 1-hydroxyethylidene diphosphonic acid is added in an amount of 1-7 kg / t cellulose.