RU2674198C1 - Method of preparation of cellulose for nitration - Google Patents

Abstract

FIELD: chemical industry.

SUBSTANCE: invention relates to the production of cellulose for chemical processing and can be used in the pulp and paper industry. Process for the production of cellulose for nitration, comprising acidifying a cellulose-containing raw material with a sulphite cooking liquor, neutralization of the spent acid brewing solution with the spent alkaline solution, hot refining of the sodium hydroxide cooking product and subsequent multistage bleaching, as an alkaline solution to neutralize the spent acidic cooking liquor use a mixture of spent alkaline solution from the previous stage of peroxide bleaching and desalinizing agent, taken in the amount of 0.015–0.020 % of the mass of the as. fibers, while the product is cooked for 20–30 minutes at a temperature of 70–80 °C, after this, the spent solution is removed for neutralization and hot refinement is carried out with sodium hydroxide in the presence of a desiccator, taken in an amount of 0.010–0.015 % by weight of the fibers. As a desalinator, a mixture containing anionic, non-ionic and amphoteric surfactant components, as well as a salt or salts from the group, including phosphates and sodium carbonates, disilicate and sodium sulfate. Refinement of the cooking product is carried out at a temperature of 95–99 °C, the duration of 40–60 minutes and the consumption of sodium hydroxide 4.0–4.5 % to the mass of absolutely dry fiber.

EFFECT: process for the production of cellulose for nitration, comprising acidifying a pulp containing a raw material with a sulphite cooking liquor, neutralization of the spent acid cooking liquor with the spent alkaline solution, hot refinement of the sodium hydroxide cooking product and subsequent multi-stage bleaching.

3 cl, 1 tbl

Description

The invention relates to the production of cellulose for chemical processing and can be used in the pulp and paper industry.

Sulphite cellulose after wood chips has a wide molecular weight distribution, that is, it contains macromolecules of various lengths. To align the average length of the macromolecules, a special technological technique is used - alkaline refinement. The refinement process is based on the treatment of cellulose with an alkali solution. Sulphite cellulose after cooking contains about 86-88% of the mass fractions with the length of the macromolecules significantly higher than 250 units, this is the so-called α-cellulose.

For the production of paper and paperboard of most varieties, pulp with an α-cellulose content of not more than 85% is quite suitable. For chemical processing into cellulose ethers, cellulose is used with an α-cellulose content of at least 92%. In the refinement process, hemicelluloses, lignin, resins and fats are removed from the fiber. After refinement, the chemical purity of cellulose reaches 99.0-99.8%, which favorably affects its chemical processing, mainly in the production of esters.

Depending on the technological features of production, it uses two refinement methods: cold and hot. The hot method is carried out at a temperature of 95-130 ° C and an alkali concentration of 0.5-2.0% sodium hydroxide. The duration of the process is 2-3 hours, the concentration of cellulose is 8-10%. This method contributes to a more uniform removal of low molecular weight fractions of cellulose. After refinement, the effluents can be reused for the refinement of cellulose and for the preparation of cooking solutions when cooking pulp from technical wood chips and other materials

A known method of producing cellulose for chemical processing, including cooking spruce chips with sulphite solution in a cooking apparatus, selecting spent cooking liquor and hot refinement of the cooking product with sodium hydroxide in the cooking apparatus immediately after selecting the spent liquor (ed. St. SU No. 1379381, D21C 3/06 , published on March 7, 1988). In this case, sulphite cooking is carried out at a total SO ₂ content _of 7.0-7.5% and 0.9-1.1 Na ₂ O and a temperature of 105-145 ° C, and after selection of a free-flowing spent cooking liquor, chemical refinement is carried out at a temperature 140 ° C by introducing into the cooking apparatus a solution of sodium hydroxide in an amount of 11.0-13.8% by weight of cellulose. The duration of the ennoblement is 0.5-1.0 hours.

The disadvantage of this method is that the indicators of cellulose in the content of resins and fats do not meet the technical requirements for softwood sulphite pulp for chemical processing.

A known method of producing cellulose for chemical processing, including acid cooking in the cooking apparatus of a cellulose-containing raw material with a bisulfite solution on a sodium base, containing, in mass. %: Na ₂ O 1.43-3.14, total SO ₂ 5.5-7.5, with pH 1.6-2.1, at a temperature of 147-152 ° C, in the presence of a degreasing agent in a cooking solution in the form “Vikus” detergent in the amount of 0.04-0.05% based on the weight of absolutely dry raw materials, hot refinement of the cooking product with sodium hydroxide is carried out at a temperature of 95-100 ° C, its duration is 60-90 minutes and the consumption of sodium hydroxide 7, 5-8.0% based on the weight of dry fiber and with the addition of oxygen to the mass in an amount of 0.7-0.8% based on the weight of the fiber, pulp bleaching. The bleaching of the enriched fiber is carried out according to the scheme: chelation (Q) - oxygen alkalization (oxidative alkali) with the addition of hydrogen peroxide (ASC) - bleaching with hydrogen peroxide (P) - acid (K). (Application No. 2012142263, D21C 3/00, publ. 04/10/2014).

In the known method, the “Vikus” demineralizer is used, containing sodium alkylbenzenesulfonate as anionic surfactant, non-ionic ethoxylates of natural higher alcohols of the C ₁₂ -C ₁₄ fraction and / or ethoxylated mono-alkyl phenol based on polypropylene trimers, in as amphoteric - alkylamidopropyl betaine, as phosphates - hexametaphosphate and / or polyphosphate and / or trisodium phosphate, as carbonates - sodium carbonate or bicarbonate.

The use of a demineralizer has a positive effect on the cooking process, and at the end of cooking, when washing the cooked pulp, some of the resins and fats are removed from the pulp with washing water. This method allows to some extent reduce the resin content in the pulp already at the cooking stage and thereby reduce resin difficulties at the stages of pulp processing. However, this technological technique does not provide a sufficiently necessary anti-aging effect at the final stage of pulp processing.

The closest analogue of the invention is a method (SU 1730299, D21C 3/06, publ. 04/30/1992) for the production of cellulose for chemical processing, including acid cooking of cellulose-containing raw materials with a sulphite solution on a sodium base, containing, in mass. %: Na ₂ O 0.7-0.75, total SO ₂ 7-7.5, at a temperature of 150 ° C and a hydraulic module of 1: 4. After cooking, the neutralization and removal of the spent cooking liquor is carried out by displacing it with the spent solution from the alkaline treatment of the previous cooking, having strengthened the latter with a fresh alkaline solution. Alkaline treatment is carried out with a mixture of spent alkaline solution and fresh in a ratio of 50:50 at a temperature of 100 ° C for 2 hours. After completion of the cooking and enrichment cycle, the free-flowing alkaline solution is selected for reuse in the subsequent cooking-enrichment cycle.

To enhance the effect of delignification during the alkaline treatment, hydrogen peroxide is introduced under certain conditions in an amount of 2.0-2.5% by weight of A. with. substances. Next, the mass is washed, sorted and bleached.

In the known method for producing cellulose, the use of a portion of the spent alkaline solution for the refinement process from the previous step is aimed at saving fresh alkaline reagent and reducing waste. However, during the refinement of cellulose, the low molecular weight part of it passes into the solution, therefore, accumulation in the spent alkaline solution proceeds from the refinement of the dissolved organic substances. With each repeated cooking cycle, their refinement in the solution becomes larger and larger, and in this connection, the reactivity of fresh alkali may be lost during the refinement process.

The disadvantages of this method are as follows:

- accumulation in spent alkaline solution from the refinement of dissolved organic substances;

- in this regard, the loss of reactivity of fresh alkali in the process of upgrading.

Signs of the prototype, which are common with the claimed technical solution, include cooking wood chips with sulphite cooking solution, neutralization of spent acidic cooking solution with spent alkaline solution, refinement of cellulose with sodium hydroxide and bleaching.

The aim of the invention is to increase the content of α-cellulose in the finished product, increase the efficiency of reducing the resin and lignin while reducing the consumption of starting reagents when refining cellulose.

This goal is achieved by the fact that in the method of producing cellulose for nitration, including acid cooking of cellulose-containing raw materials with sulphite cooking liquor, neutralizing the spent acid cooking liquor with spent alkaline solution, hot refinement of the cooking product with sodium hydroxide and subsequent multi-stage bleaching, according to the invention, as an alkaline solution for to neutralize the spent acid cooking liquor use a mixture of spent alkaline solution from the previous penalties for peroxide bleaching and deresinuator taken in an amount of 0.015-0.020% by weight fiber, while the cooking product is incubated for 20-30 minutes at a temperature of 70-80 ° C, after which the spent solution is removed to neutralize and hot refinement is carried out with sodium hydroxide in the presence of a de-resin, taken in an amount of 0.010-0.015% by weight of a.s . fiber.

A mixture containing anionic, nonionic and amphoteric surface-active components, as well as a salt or salts from the group consisting of sodium phosphates and carbonates, disilicate and sodium sulfate, is used as a deminegative.

Refining of the cooking product is carried out at a temperature of 95-99 ° C, a duration of 40-60 minutes and a consumption of sodium hydroxide 4.0-4.5% by weight of absolutely dry fiber.

The bleaching of the enriched fiber is carried out according to the scheme: chelation (Q) - oxygen alkalization (oxidative alkali) with the addition of hydrogen peroxide (ASC) - bleaching with hydrogen peroxide (P) - acid (K).

Signs that distinguish it from the prototype are the use of a mixture of spent alkaline solution from the previous stage of peroxide bleaching and a demarcation agent as an alkaline solution to neutralize the spent acidic cooking liquor, as well as the process of enrichment with sodium hydroxide in the presence of a decolorizer. Distinctive features, in combination with the known ones, provide an increase in the content of α-cellulose in the finished product, a decrease in resin and lignin, while reducing the consumption of starting reagents during cellulose enrichment.

The method of producing cellulose for nitration is carried out in the following sequence: load spruce chips into the digester, fill it with a bisulfite solution on a sodium base, containing, in mass. %: Na ₂ O 1.4-2.1, total SO ₂ 7.0-7.5, with pH 1.6-2.1, the contents of the boiler are heated to a temperature of 147-150 ° C and maintained for 7-8 hours.

After the specified time, free-flowing spent sulfite liquor is taken for further processing. The cooked pulp is saturated with spent acidic cooking liquor. To neutralize the spent acid solution from cooking, the spent alkaline peroxide solution from the pulp bleaching stage is fed into the boiler with the following characteristic: residual alkali content, g / dm ³ in units NaOH 0.8-1.0; the content of residual hydrogen peroxide, g / DM ³ in units H ₂ O ₂ 0.10-0.15; The pH of the solution is 9.5-10.5 and the demineralizer pre-mixed with the solution is taken in an amount of 0.015-0.020% by weight of the cooked cellulose. The temperature in the boiler is maintained at a level of 70-80 ° C and maintained for 20-30 minutes.

After removal of the spent alkaline-peroxide solution from the boiler, sodium hydroxide solution is introduced in it in an amount of 4.0-4.5% by weight of cellulose and a demineralizer, taken in an amount of 0.010-0.015% by weight of cooked cellulose, maintain the temperature in the boiler at 95 -99 ° C and withstand 40-60 minutes.

In the process of cooking, the bulk of lignin, low molecular weight fractions of carbohydrate composition and related substances in the form of resins and fats pass from chips to the solution. The other part of these components is retained by cellulose fibers both on the surface and inside the fibers themselves.

The spent alkaline peroxide solution from the bleaching stage in a mixture with a demineralizer is used as a reagent for the neutralization and pretreatment of cellulose in order to ensure the best conditions for removing related components from cellulose. This is achieved by the fact that:

- under the influence of this mixture, the remaining free part of the spent acidic cooking solution is neutralized;

- at the liquid – cellulose fiber interface, due to diffusion processes, the concentration of the cooking solution decreases and it is replaced in the cellulose fibers with an alkaline peroxide solution, and there is no problem removing impurities from the deep layers of the fiber;

- the presence in the alkaline solution of a small amount of residual hydrogen peroxide causes the intensification of the process of extracting lignin from cellulose fibers;

- the presence of a demarcation promotes an increase in surface activity, as a result of which the surface tension at the cellulose-alkaline-peroxide solution interface decreases, and therefore, the resin is more efficiently extracted from the cellulose, and in addition, a more stable emulsion of the resin in the alkaline-peroxide solution is formed.

- pretreatment of the pulp with an alkaline peroxide solution in a mixture with a degreasing agent increases the rate of lignin oxidation to a greater extent than the rate of oxidation of cellulose, increasing the selectivity of delignification and reducing the destruction of cellulose.

The presence of a deminegative in the sodium hydroxide solution used to refine cellulose is aimed at consolidating the achieved results on the demineralization during the pretreatment of cellulose with an alkaline peroxide solution.

Example 1. 1000 g of absolutely dry spruce chips are loaded into a cooker equipped with a circulating device and washed down with a sulphite cooking solution on a sodium base having a pH of 1.7 and containing only 6.5% SO ₂ with a 1: 4 hydromodule. The temperature is raised to 115 ° C for 2.5 hours, this temperature is maintained for 1.5 hours to complete the impregnation, then the temperature is raised for 1.5 hours to 149 ° C and cooking is carried out for 2.5 hours. After the specified time, the spent acidic cooking solution is removed, the apparatus is filled with an alkaline peroxide solution containing sodium hydroxide at a concentration of 1.0 g / dm ³ , hydrogen peroxide at a concentration of 0.15 g / dm ³ , with a pH of solution 10, pre-mixed with a solution of deminegative taken in an amount of 0.015% by weight of the cooked pulp. At the same time maintain the contents of the apparatus for 20 minutes at a temperature of 80 ° C. At the same time, neutralization of acid residues and, so to speak, pretreatment of cellulose are carried out. After the pretreatment is completed, the spent alkaline peroxide solution is removed by displacing it with a fresh sodium hydroxide solution, taken in an amount of 4.5% by weight of absolutely dry fiber, pre-mixed with a de-resin, taken in an amount of 0.01% by weight of absolutely dry fiber at a temperature of 98 ° C for 1.5 hours and a mass concentration of 12%. Subsequent bleaching is carried out according to the scheme: chelation (Q) - oxygen alkalization (oxidative alkali) with the addition of hydrogen peroxide (ASC) - bleaching with hydrogen peroxide (P) - acid (K).

We will consider in more detail one of the stages of bleaching, after which the spent alkaline peroxide solution is used to pretreat the pulp. Cellulose is bleached with an alkaline solution of hydrogen peroxide at a temperature of at least 80 ° C for 120 minutes. The consumption of bleaching reagents, kg / t mass: sodium hydroxide - 12, hydrogen peroxide - 4.5. One of the main conditions for terminating the reaction of hydrogen peroxide and cellulose is that part of the alkaline reagent and hydrogen peroxide should remain unused for the reaction, since only in this case does not reverse the color of the cellulose. After the exposure time, the alkaline peroxide solution is separated from the cellulose and used for other purposes. The spent alkaline peroxide solution from the bleaching stage is characterized by the following quality indicators: residual alkali content, g / dm ³ in units NaOH 0.8-1.0; the content of residual hydrogen peroxide, g / DM ³ in units H ₂ O ₂ 0.10 - 0.15; pH of the solution 9.5-10.5

Example 2. The process conditions and the sequence of operations of cooking, neutralization, alkaline refinement and bleaching are the same as in example 1.

The differences are that the neutralization of the acidic residue and the pretreatment of cellulose with an alkaline peroxide solution is carried out at a temperature of 70 ° C for 30 minutes with a flow rate of the de-grinder of 0.017% by weight of the cellulose.

Alkaline refinement is carried out with sodium hydroxide at a flow rate of 4.0% at a temperature of 90 ° C for 60 minutes with a consumption of de-grinding agent of 0.010%.

Example 3. The process conditions and the sequence of operations of cooking, neutralization, alkaline refinement and bleaching are the same as in example 1.

The differences are that the neutralization of the acidic residue and the pretreatment of cellulose with an alkaline peroxide solution is carried out at a temperature of 75 ° C for 25 minutes with a consumption of de-grinder 0, 020% of the mass of cellulose.

Alkaline refinement is carried out with sodium hydroxide at a flow rate of 4.3% at a temperature of 99 ° C for 60 minutes with a consumption of de-grinding agent of 0.015%.

Example 4 (analogue). The process conditions and the sequence of operations of cooking, alkaline refinement and bleaching are the same as in example 1.

The differences are that the cooking is carried out in the presence of a de-grinder with a flow rate of 0.045%, and alkaline refinement is carried out with sodium hydroxide at a flow rate of 7.5% at a temperature of 100 ° C for 90 minutes in the presence of oxygen with a flow rate of 0.75% by weight of fiber .

Example 5 (prototype). The process conditions and the sequence of operations of cooking, alkaline refinement and bleaching are the same as in example 1.

The differences are that alkaline enrichment is carried out with sodium hydroxide in a mixture with spent liquor from the previous enrichment stage at a ratio of 50:50 at a temperature of 100 ° C for 120 minutes.

The table presents comparative data on the quality of the pulp obtained by the present method, the method is similar and the prototype method.

From the data in the table it is seen that the proposed method allows to reduce the content of resin and lignin in the finished cellulose, while maintaining a high level of α-cellulose.

Claims (3)

1. A method of producing cellulose for nitration, including acid cooking of cellulose-containing raw materials with a sulfite cooking liquor, neutralizing the spent acid cooking liquor with an spent alkaline solution, hot refining the cooking product with sodium hydroxide and subsequent multi-stage bleaching, characterized in that as an alkaline solution for neutralizing the spent acid cooking the solution using a mixture of spent alkaline solution from the previous stage of peroxide bleaching and demolition la, taken in an amount of 0,015-0,020% by weight of AS fiber, while the cooking product is incubated for 20-30 minutes at a temperature of 70-80 ° C, after which the spent solution is removed to neutralize and hot refinement is carried out with sodium hydroxide in the presence of a de-resin, taken in an amount of 0.010-0.015% by weight of a.s . fiber. 2. The method according to p. 1, characterized in that the mixture containing anionic, nonionic and amphoteric surface-active components, as well as a salt or salts from the group consisting of sodium phosphates and carbonates, disilicate and sodium sulfate, is used as a de-grinding agent. 3. The method according to p. 1, characterized in that the refinement of the cooking product is carried out at a temperature of 95-99 ° C, a duration of 40-60 minutes and a flow of sodium hydroxide of 4.0-4.5% by weight of absolutely dry fiber.