RU2312945C1 - Cellulose production process - Google Patents

Abstract

FIELD: paper-and-pulp industry.

SUBSTANCE: invention relates to production of fibrous intermediate products from rice straw. The latter is first treated with NaOH solution, 20-60 g/L, in presence of anthraquinone at temperature not lower than 70°C for at least 20 min in order to remove silica. Anthraquinone is added in amount at least 0.01% based on dry weight of cellulose-containing raw material. Resulting pulp is separated from alkali solution and subjected to alkali digestion in NaOH solution ensuring uptake of 8-14% of dry raw material for at least 60 min.

EFFECT: increased yield of desired product, reduced consumption of reagents in digestion operation, and improved quality of product due to retention of hemicellulose complex as well as partial removal of lignin.

2 cl, 3 tbl

Description

The invention relates to the field of pulp and paper production, can be used to obtain fibrous semi-finished products from annual plants, in particular from rice straw.

A widely known method of producing cellulose from annual plants by alkaline cooking in an aqueous solution of sodium hydroxide and sodium sulfide at a temperature of 150 ... 160 ° C under pressure in one stage [Yu.N. Nepenin. Pulp technology. T.2. M .: Forest industry, 1990].

There is also known a method for producing cellulosic material, according to which the cooking process is carried out by alkaline treatment of crushed plant materials at elevated temperatures in two stages at different pH [G. Pazukhina Stepwise pulp production methods. M .: Forest industry, 1990, 216 p.].

Closest to the proposed is a two-stage method for producing cellulose by alkaline cooking of the feedstock in a sodium hydroxide solution by heating with preliminary prehydrolysis of the feedstock, while the prehydrolysis is carried out with diluted mineral acid or boiling water [Yu.N. Nepenin. Pulp technology. T.2. M .: Forestry industry, 1990, p.229], while reed is used as feedstock, and processing is carried out with sulfuric acid [Yu.N. Nepenin. Pulp technology. T.3. M .: Forest industry, 1990, p.444].

Known processes do not allow to process cellulose-containing raw materials with a high content of mineral components (SiO ₂ ). This is due to the fact that during cooking SiO ₂ passes into the solution in the form of poorly soluble silicates by reaction (1), which leads to a significant decrease in the yield and quality of the product (deterioration of lignin removal), as well as to the appearance of silicate deposits on the surfaces of technological equipment by reaction (2).

In addition, when implementing the known method, hemicelluloses are removed, and the associated decrease in silicate ash is due to the destruction of the covering tissue. This leads to the fact that the resulting cellulose is suitable only for chemical processing.

The objective of the invention is to improve the quality of the resulting cellulosic material while increasing the yield of the target product.

The problem is solved in that the process of producing cellulose is carried out by alkaline cooking of cellulose-containing raw materials at elevated temperatures, while rice straw, previously subjected to desalination by treatment with a NaOH solution of a concentration of 20-60 g / l at a temperature of at least 70 ° C, is used as a cellulose-containing raw material. and a duration of at least 20 minutes in the presence of anthraquinone, followed by separation of the cellulose-containing feed from the alkaline solution. Anthraquinone is administered in an amount of at least 0.01% by weight of A. with. cellulose-containing raw materials.

The alkaline cooking of cellulose-containing raw materials is carried out in a known manner in a NaOH solution at a rate of 8-14% of a.a. cellulose-containing raw materials for at least 60 minutes

The inventive method allows to increase the yield of the target product, to reduce the consumption of chemicals for cooking by removing silicon-containing compounds at the stage of alkaline processing of plant materials. The inventive method of processing cellulose-containing raw materials provides desiliconization only through the process of extraction, but not the destruction of the membranes and hemicelluloses. The implemented processing mechanism of the feedstock allows to improve the quality of the target product by preserving the hemicellulose complex, as well as partial removal of lignin.

The claimed method is illustrated by examples.

Removal of silicon-containing compounds from feedstock without catalyst

Rice straw (SiO ₂ content _of 11.5%) was treated with alkali with a concentration of 10 ... 60 g / l at 50 ... 100 ° C for 20 ... 120 minutes, a water module of 10: 1 (examples 1-24).

The content of SiO ₂ in the raw material after processing was determined according to the standard method by the gravimetric method according to GOST 9428. Reagents: silicon (IV) oxide. The results are presented in table 1.

From the data presented in table 1, it can be seen that the essential conditions under which the removal of silicon dioxide from rice straw (more than 90%) is an alkali content of 20 ... 60 g / l, a temperature of at least 70 ° C, a duration of less than 20 min (example 13, 14, 16, 17, 19, 21, 23, 24).

It is widely known to specialists that during alkaline treatment of plant materials, hemicelluloses undergo significant destruction, the destruction of which leads to a significant decrease in the yield of technical cellulose [Nepenin Yu.N. Pulp technology. T.2. M .: Forest industry, 1990]. If rice straw containing up to 35% hemicelluloses is used as plant material, the percentage of losses during their destruction can reach more than half of their content. To reduce the loss of hemicelluloses from their destruction during alkaline treatment, an anthraquinone catalyst was introduced into the process. For the established optimal modes of removal of silicon dioxide (example 13, 14, 16, 17, 19, 21, 23, 24), alkaline treatments were performed in the presence of anthraquinone.

Table 1 The influence of processing conditions on the content of SiO ₂ in rice straw Example No. The concentration of NaOH, g / l Duration min Temperature ° C The extraction of SiO ₂ from raw materials,% one. 10 twenty fifty twenty 2. twenty 35 3. 40 40 four. 60 fifty 5. 10 twenty 70 35 6. twenty 40 7. 40 45 8. 60 75 9. 10 twenty 90 40 10. twenty 45 eleven. 40 58 12. 60 85 13. 40 one hundred 95 fourteen. 60 98 fifteen. twenty thirty 70 85 16. 40 95 17. 60 98 eighteen. twenty 60 90 85 19. 40 > 99 twenty. twenty 60 one hundred 85 21. 40 > 99 22. twenty 120 90 85 23. 40 > 99 24. 60 > 99

Removal of silicon-containing compounds from feedstock under optimal conditions (removal of more than 95%) in the presence of anthraquinone

Rice straw (SiO ₂ content _of 11.5%, lignin 22.3% by weight of raw material, hemicellulose 20.0% by weight of raw material) was treated with 40 g / l alkali at 90 ° C for 60 min ( example 19) in the presence of 0.005 ... 0.1% anthraquinone to A. with. raw materials and a hydraulic module 10: 1.

The content of SiO ₂ in the feedstock and after processing was determined according to the standard method by the gravimetric method according to GOST 9428. Reagents: silicon (IV) oxide. The content of hemicelluloses according to GOST 9002, lignin GOST 10070.

The results are presented in table.2.

table 2 The effect of anthraquinone consumption on the results of pre-treatment of rice straw (SiO ₂ recovery _of more than 99%) Example No. The consumption of anthraquinone,% to A.S. raw materials The content of components in the processed raw materials,% of A. with. raw materials Hemicellulose Residual lignin 25. - 5,0 15,2 26. 0.005 6.5 10,4 27. 0.01 17.6 6.5 28. 0.05 18.2 6.0 29. 0.10 18.5 6.0

From the data presented in table 2, it can be seen that the essential conditions under which there is less destruction of hemicelluloses with simultaneous selective removal of silicon dioxide from rice straw, is the consumption of anthraquinone at least 0.01% by weight of A. with. raw materials (example 27-29). So, if in the feedstock the proportion of hemicelluloses soluble in an aqueous solution of sodium hydroxide (5%) is 20%, after the stage of desiliconization their content decreases by 4 times (Example 25), then when using anthraquinone at the stage of desiliconization, it almost completely preserves them content (examples 27-29).

To establish optimal conditions corresponding to the removal of more than 99% SiO ₂ and better preservation of hemicelluloses, cellulose was cooked. Silicon dioxide is removed at a concentration of 40 g / l, the flow rate of 0.05% by weight of A. with. raw materials, temperature 90 ° C and a duration of 60 minutes

Cooking Sintered Material

After the pretreatment stage, the siliceous raw material is separated from the alkaline solution and used in the cooking process in a NaOH solution at a rate of 8 ... 14% by as raw materials, temperature 160 °, hydraulic module 10: 1. The cooking results are presented in table.3.

Table 3 The influence of cooking conditions on the quality of the obtained rice straw pulp No. The consumption of active alkali,% to A.S. raw materials Preliminary processing The yield of cellulose,% Residual lignin,% thirty. 12 no 39.1 * 5.3 31. 8 there is 49.2 5.2 32. 10 there is 45.6 2,5 33. 12 there is 44.6 2.2 34. fourteen there is 43.5 1.7 * yield of technical pulp without ash residue

As can be seen from the presented data (table. 3), preliminary removal of silicon dioxide from the feedstock with an alkaline solution in the presence of AX leads to an increase in the yield of cellulose due to stored hemicelluloses, while at the same time there is a significant decrease in the content of residual lignin (examples 30, 33), except Moreover, the implementation of the inventive method will reduce the consumption of active alkali during cooking (examples 31-34).

Using the proposed method in the pulp and paper industry will expand the raw material base to produce high-quality pulp suitable for the manufacture of paper.

Claims (2)

1. The method of producing cellulose by chemical treatment of cellulose-containing raw materials with its subsequent alkaline cooking when heated, characterized in that rice pulp is used as cellulose-containing raw materials, previously subjected to desalination by treatment with a concentration of 20-60 g / l NaOH solution at a temperature of at least 70 ° C and a duration of at least 20 minutes, in the presence of anthraquinone, followed by separation of the cellulose-containing raw material from the alkaline solution. 2. The method according to claim 1. characterized in that anthraquinone is administered in an amount of not less than 0.01% by weight of absolutely dry cellulose-containing raw materials.