SU861447A1 - Method of bleaching cellulose for chemical processing - Google Patents

Description

one .

The invention relates to the pulp and paper industry and relates to a process for the production of native and sulphate pulp for chemical processing from softwood and hardwood.

A known method of bleaching sulphate prehydrolysis cellulose for chemical processing includes steps for chlorination, alkali, bleaching with hypochlorite, cold refining, hot refining and subsequent finishing with chlorine dioxide in two stages with intermediate alkali 15 and hypochlorite sodium l. The yield of unbleached prehydrolyzed cellulose averages 35%, and after bleaching it does not exceed 32% of the mass of absolutely dry wood.

A method of bleaching sulphate cellulose is also known, which consists in the fact that cellulose of conventional sulphate pulping is subject to bleaching and cold-hot refining according to the scheme described above: chlorination, alkalization, hypochlorite bleaching, and boat refining (concentration of sodium hydroxide in the mass 80-100 g / l units N32.0), hot refinement from 30

Subsequent dobrakoy lime lime reagents f2.

However, the high concentration of cellulose treated with alkaline solutions changes its internal structure, the cellulose content in cold pulp increases, and as a result, it has a low reactivity, therefore, additional treatment of cold pulp with surfactants is required.

If solid wood is used after chlorination of unbleached pulp due to the addition of chlorine to extractive substances, resinous difficulties arise in unsaturated bonds, resulting in the deposition of resin on the processing equipment and resinous pulping of cellulose.

However, in the case of treatment of sulphate cellulose according to a known method, difficulties arise when using spent liquor after a cold refining stage due to the presence of sllorides in it.

The purpose of the invention is to increase the reactivity of cellulose, to prevent gumming difficulties during bleaching, to reduce the consumption of chemicals. This goal is achieved by the fact that operations of cold or hot refining are carried out before chlorination. Cold refining is carried out at an alkali concentration in the mass of 30-70 g / l in units. and a temperature of 15-35 ° C for 5-60 Min, and hot beating is carried out at a mass concentration of 10-12%, a temperature of 90-100 ° C for 1.5-2 hours. The proposed method of producing soda or sulfate pulp. The chemical processing is carried out as follows. Unbleached pulp, for example, sulphate foliar or softwood, is treated with sodium hydroxide solution or white liquor. The treatment conditions are as follows: the concentration of alkali in a mass of 30-70 g / l in units, a temperature of 15-35 ° C, a mass concentration of 7-10%, a treatment time of 5-60 minutes. After the cold refining stage, the pulp is washed and with a residual alkalinity of 0.5-10 g / l of NaOH units subjected to hot refining at a mass concentration of 1012%, a temperature of 90-100 ° C for 1.5-2 hours. The refined pulp is subjected to chlorination at a mass concentration of 3.0-4.0% for 30-6Q minutes Further, the finishing of the cellulose is carried out with chlorine-containing reagents, for example, according to the following schemes: hypochlorite bleaching - hypochlorite bleaching - acid or bleaching with chlorine dioxide g. Hypochlorite bleaching - hypochlorite bleaching-sour. After each bleaching stage, the pulp is washed. Example. Chips of hardwood species of wood (a mixture of aspen and birch was loaded into an autoclave, poured with lye having an active alkali concentration of 97.5 g / l Na2.0 units, and cooked cello-olose. The consumption of Na, jO for cooking is 19% by weight absolute dry wood, hydronic module of cooking 1: 4. In m stands at a temperature of 90 minutes, rise to 170s -90 minutes, from an ash at a temperature of 170s - 120 m. The obtained cellulose had the following quality indicators Delignification degree 57.8 n. e Viscosity 1% copper-ammonia solution 43, bMpa Content of JC-cell1% 89%, Output of unbleached pulp50 , 4% After the separation of fine fiber, atron cellulose with a degree of deligification of 58 p.u., a viscosity of 1% of a media ammonia solution of 46.4 mPa.s, a degree of polymerization (SP) - 1012, and with a cellulose 90.5% was subjected to cold refining with white lye at a mass concentration of 8%, alkali mass concentration of 40 g / l NaOH units (31 g / l NaaO units) and temperature for 60 minutes. After cold refining, the pulp was washed to a residual alkalinity of 1.8 g / l NaOH units and subjected hot beating at a temperature of 10% by mass concentration of 120 min. The refined cellulose, after spilling, was chlorinated at a mass concentration of 3.5% for 60 minutes. Chlorine consumption for chlorination 10 kg / t pulp. Next, the pulp mass was made with sodium hypochlorite in 2 steps. The first stage of hypochlorite bleaching was carried out at a mass concentration of 10%, a temperature of 38-42 ° C for 120-180 minutes. The consumption of hypochlorite in active chlorine was equal to 17 kg / ton of cellulose, the pH of bleaching was 11.9-11.3. The second stage of hypochlorite bleaching was carried out at a mass concentration of 8%, temperature 40-45 0 and consumption of hypo, chlorite 14 kg / t pulp, bleaching pH - 11.9-11.7, duration 240 minutes :. The bleached pulp was treated with sulfuric acid solution to neutralize residual hypochlorite, stabilize whiteness and reduce the ash residue of cellulose. The mass concentration at an acid content is 3.5%, the pH is 2.7, the time is 120 min. In parallel, under similar conditions, for the purpose of comparison, this cellulose was bleached according to the following scheme: chlorination (X) - alkalization (III) - hypochlorite bleaching (g) - cold enrichment (XO) - hot upgrading (go) - hypochlorite bleaching (g) hypochlorite bleaching - kislovka (k) (known method). The data obtained are given in table. one.

Table

 From tab. As can be seen in Figure 1, the proposed bleaching method makes it possible to obtain bleached pulp from cellulose soda pulp that meets the requirements of cellulose for chemical processing with a lower consumption of chlorine and caustic, with a higher yield of bleached pulp compared to the known bleaching method. Example 2. Cellulose sulphate unblena with a yield of 48.6% was obtained from hardwood chips (a mixture of birch and aspen) in an autoclave, when alkali was used for cooking 22% of N32.0 units and the weight of absolutely dry wood in a water ratio of 1: 4 ( white alkali: total alkali content 113 g / l N32.0 units, active alkali content 95.8 g / l Na2.0 units, sulphidity 22%) according to the mode described in example 1. After boiling and separating 4% fine cellulose fibers had the following quality indicators: Delignification degree 50 p.e. Viscosity 1% copper ammonium solution 36.5 mPa s Polymerization degree 1004 Cellosa content 90 $ This cellulose was bleached according to the proposed and well-known method according to the mode described in example 1. The consumption of hypochlorite and hypochlorite tiioio was made up of active chlorine: the level of the hypochlorite was given to hypochlorite and hypochlorite; kg / ton of pulp, for the second stage of hypochlorite dodelki II kg / ton of pulp. In parallel, under analogous conditions for comparison, this cellulose was bleached by a known method. The results are given in Table. 2

The data obtained show that the proposed bleaching method makes it possible to obtain bleached sulphate pulp for chemical processing of a higher yield with lower costs of chemicals, water, steam, and electric power.

Example 3. Hardwood chips (a mixture of aspen and birch) were loaded into a laboratory autoclave, and the evaporated liquor from the cold refining stage was poured. Characteristics of one stripped off liquor: total alkali content 115, 3 g / l units. N320, the content of active alkali - 99.4 g / l units. , degree of sulphidity - 25.7%.

Viscosity, 1% copper-ammonia solution, mPa o

SP

Content with cellulose,%

table 2

The cooking conditions are the same as in example 2. Alkali consumption for cooking is 22% by weight of absolutely dry wood.

The resulting unbleached pulp had the following quality indicators:

Delignifi degree 60 pu cations

Viscosity 1% copper48, 8 mpa s. c1Mmium solution Polymerization degree (cn). 10/0 Contents about -cell88, 4% vine

The bleaching of this cellulose was carried out. According to the schemes and mode described in Example 2, the results are shown in Table. 3

.Table 3

9.4 516

92.3 The obtained results show that with full use of the spent liquor from the cold stage for sulphate cooking, the proposed bleaching method allows to obtain a finished product that meets the requirements of cellulose for chemical processing with significantly lower chemical consumption. Compared with the known method of screening with a higher yield of pulp from wood. Example 4. Prehydrolysis sulfate cellulose (from pine wood) with delignification degree of 84 p.u., viscosity 1% m.a; a solution of 24.3 MPa s, SP-870, content of ci-cellulose 95.9% was bleached according to the scheme: XO-GO-X-DK-K (proposed method). Cold refining was carried out at a mass concentration of 8%, temperature, alkali concentration in the mass of 31 g / l units. within 60 min. After washing the cellulose with a residual alkalinity of 0.8 g / l. N320 at a mass concentration of 10% was subjected to hot beating for 120 min at a temperature of 95 C. Then the cellulose was chlorinated at a mass concentration of 3.5% temperatura 20 ° C for 60 min. Chlorine consumption - 30 kg / t pulp. The first stage of bleaching with sodium hypochlorite was carried out at a mass concentration of 10% at a temperature of 40–42 s, pH - 11.5 for 120–180 min. The consumption of hypochlorite for active chlorine is 15 - kg / t of whole lulose.

Continued table. 3 The second stage of hypochlorite bleaching was carried out at a mass concentration of 8%, temperature, pH - 11.6, consumption of hypochlorite for active chlorine 15 kg / ton of cellulose for 180,240 minutes to a viscosity of 1% cellulose solution of 10 mPa s. The bleached pulp was treated with sulfur dioxide solution at a mass concentration of 3.5%, temperature, pH - 2.7 for 120 minutes. After each step of bleaching, the cellulose was sprinkled with water. In parallel, for comparison, unbleached pulp was bleached according to the following scheme: X-Shch-GHO-GO-G-G-K (according to a known method) -. Unbleached pulp was chlorinated at a mass concentration of 3%, temperature for 60 minutes. Chlorine consumption for chlorination .27 kg / t pulp. Alkalization of chlorinated cellulose was carried out at a mass concentration of 12%, temperature, and consumption of caustic natrium and 15 kg / ton of cellulose for 120. The third stage of treatment, hypochlorite bleaching, was carried out at a mass concentration of 12%, a temperature of 38-40 ° C, and sodium hypochlorite consumption for active chlorine of 20 kg / ton of cellulose for 180 minutes. Cold pulp upgrading was performed with a solution of white liquor at a mass concentration of 8%, alkali concentration in the mass of 31 g / l units. , temperature 20 C for 60 min. Cold pulp was distributed to alkalinity of 1.86 g / l unit. NajO and at

mass concentration 1.0%, temperature

 they performed hot refining for 120 min.

Make up the pulp to a viscosity of 1% ma.a. 10 mPa.s solution was performed with sodium hypochlorite in two steps. The mode I and II stages of the hypochlorite dressing room are the same: concentration

Bleaching under the scheme:

. Cellulose XO-GO-XGGK method)

Viscosity 1% m.a. solution, mPa s.

SP

Content with cellulose,%

Content of pitch,% Whiteness,% white.

Reaction ability of CS / NaOH 80/11, s

The yield of pulp after cooking; %

The yield of pulp after bleaching,%

The output of bleached pulp from wood,%

Consumption of total chlorine for bleaching chlorine kg Kg / t celulose

Consumption of caustic gustics on chlorite bleaching, kg / t pulp

The obtained data confirm the ecological advantages of the proposed method of bleaching with prehydrolysis. Hwy sulphate pulp in obtaining the same quality indicators of the finished product. Example 5. Chain of hardwood species (a mixture of aspen and birch) were loaded into an autoclave and water prehydrolysis was performed. The temperature rise to –– for 125 min at 165 was carried out for 90 min, the hydraulic module was 1: 4.

Then sulphate cooking was performed at hydromodule II4. Alkali consumption

mass - 8-10%, temperature. 38-42 "С, hypochlorite consumption for active chlorine, b kg / ton of cellulose, pH - 11.8-11.5 processing time 120180 min. The bleached pulp was worked out with a solution of sulfur dioxide at a mass concentration of 3%, pH - 2.7 for 120 minutes. The results are shown in Table. four.

Table 4

Bleaching according to the following scheme: X-Shch-G-HO-GO-G-GK (proposed (known method)

10.2 491

95.1

0.14 90

2

33 94.7

31.2 61

32,5 74

43.8

cooking amounted to 19.5% of the units. . Indicators of white liquor: total alkali - 132 g / l units. . Alkali is active - 110 g / l units. The sulfide content is 22.9%.

- Raising the temperature up to 135c for 40 min, standing at for 40 min, rising to –60 min, cooking for 100 min.

the resulting unbleached pulp with a delignification degree of 44 ps., a viscosity of 19.6 MPa, with SP 815 and a content of c6-cellulose 94.4%

Table 5

Claims (2)

Claim 1. The method of bleaching soda or sulfate pulp for chemical. VNIIIPI Order 6467/9 25.6 ------- processing, including the operations of chlorination, cold refining, hot refining, finishing with chlorine-containing reagents and acidification of the pulp, characterized in that, in order to increase the reactivity of the target product, reduce the consumption of Chemicals and prevent tar. bleaching, cold and hot refinement operations are carried out before chlorination ... 2. The method of pop. 1, characterized in that the cold refinement is carried out at a concentration of alkali in the mass of 30-70 g / l in units 'Na ^ O and a temperature of 15-15 ° C for 5-60 minutes, and hot refinement is carried out at a mass concentration of 10-12%> temperature 90-100 ° C for 1.5-2 hours