RU2513387C2 - Production of cellulosed semi-finished product - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to production of cellulose of wood and can be used in pulp-and-paper industries for production of paper and cardboard. Proposed method comprises impregnation of wood ships with water solution of sodium hydroxide or potassium hydroxide with concentration of 80…180 g/l in units Na₂O, containing hydrazine in amount of 20…25% of dry wood weight at 20…40°C for 6…24 h. Dripping liquid phase is extracted. Isobutyl alcohol is added to said mass, temperature is increased to 120…150°C and boiled thereat for 1…4 h.

EFFECT: higher yield of cellulose, decreased consumption of hydrazine, alkalis, energy, simplified process.

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Description

The invention relates to the field of production of cellulose from plant materials, in particular to methods for producing a cellulosic semi-finished product using alkalis and alcohols for the manufacture of paper and paperboard for various purposes, and may find application in the pulp and paper industry.

A known method of producing cellulose from a cellulose-containing material by cooking with ethanol-alkali mixture at elevated temperatures and pressure (Marton R., Crenzow S. Ethanol alkaline pulping. TAPPI Journal, 1981, 65, No. 6, pp. 103-106). The delignification process by this method occurs more quickly and efficiently than by the soda method, and is comparable to sulfate cooking. The cellulose obtained by this method has a higher yield than sodar cooking, but lower mechanical strength, especially tensile length.

Also known is a cooking solution for producing cellulose, which consists of sodium hydroxide, methanol, hydrazine and water (Kiryushina M.F., Zarubin M.Ya., Oparin V.N., Troitsky V.V., Chirkin G.S. AS SU 1060729 A, 12.15.83, BI No. 46). Using this solution, cellulose of higher yield with a lower lignin content can be obtained compared to cooking in a solution containing sodium hydroxide, methanol and water. However, the use of an extremely toxic and volatile reagent - methanol - in the composition of the cooking solution will require increased safety measures, and to achieve additional acceleration of the delignification process and increase the yield of cellulose, a high consumption of hydrazine for cooking is required.

The closest in technical essence and purpose to the present invention is a method for producing cellulose by cooking wood chips with an aqueous solution containing sodium hydroxide, hydrazine and ethyl alcohol with a content of the latter in a solution of 30 ... 50 vol.% (Pazukhina G.A., Dao Shi Shan. Auth. USSR Certificate No. 1542983 02/15/90 BI No. 6). Pine wood chips are loaded into an autoclave, an aqueous solution containing a predetermined amount of ethyl alcohol, hydrazine and sodium hydroxide is poured, the consumption of the latter is 15 and 17% of the weight of wood chips, respectively. The temperature was raised to 170 ° C in 2 hours and cooking was carried out at this temperature for 55 and 75 minutes. The cellulose yield of this method is 52 ... 54%.

The disadvantages of this method are the high energy costs of the cooking process and the regeneration of ethyl alcohol (distillation), high consumption of hydrazine and alkali and low yield of cellulose prefabricated fiber.

New positive results of the proposed method are reducing energy costs for the cooking process and the regeneration of alcohol, reducing the consumption of hydrazine and alkali, expanding the range of yields of the target product in the direction of its increase.

These results are achieved by the fact that in the proposed method, the wood chips are impregnated with an aqueous solution of sodium hydroxide or potassium hydroxide containing hydrazine, the solution remaining after impregnation is drained, partially replaced with isobutyl alcohol and cooking is carried out. According to the invention, an aqueous solution of sodium hydroxide or potassium hydroxide with a concentration of 80 ... 180 g / l in units is used as an impregnating solution. Na ₂ O containing hydrazine in an amount of 20 ... 25% by weight of dry wood. The chips are kept in an impregnating solution with natural impregnation at a temperature of 20 ... 40 ° C for 6 ... 24 hours, and with forced impregnation - 30 ... 60 minutes At the end of the impregnation and selection of the liquid phase, isobutanol is added in an amount up to 40% of the volume of the selected liquid phase, the mass temperature is quickly increased to 120 ... 150 ° C and cooking is carried out at this temperature for 1 ... 4 hours depending on the desired degree of cellulose delignification. The solution selected after the impregnation is reused. Isobutyl alcohol is limitedly mixed with water, does not dissolve hydrazine and alkali, its consumption is practically absent, since it easily exfoliates from aqueous solutions and is reused. The increase in the yield of cellulose prefabricated occurs both due to a shift in the separation point of wood chips into fibers towards a high lignin content, and as a result of better preservation of carbohydrate components.

Testing of the proposed method on the example of processing wood chips of pine and birch was carried out in laboratory conditions using autoclaves heated in a glycerin bath with a high temperature rise rate. In all examples of the method, 30 g of air-dried wood chips are taken, loaded into a 400 ml autoclave, 150 ml of an aqueous solution of sodium hydroxide or potassium hydroxide of a given concentration with a hydrazine content of 30 g / l are poured, the autoclave is closed and kept at room temperature for 18 h. At the end of the impregnation, 100 ml of the impregnation solution are taken from the autoclave and 75 ml of isobutyl alcohol is added. The autoclave is hermetically sealed, placed in a glycerin bath, heated to a final temperature for 30 minutes. Cooking at the final temperature is carried out for 1 ... 4 hours. In the examples, the following parameters are changed: the type of alkali and its concentration in the impregnating solution, the final temperature and the cooking time at the final temperature.

The product yield and lignin content and mechanical strength are measured.

Example 1. In an autoclave, load 30 g of air-dried pine wood, pour 150 ml of a solution of potassium hydroxide with a concentration of 140 g / l in units Na ₂ O containing hydrazine in an amount of 30 g / l, the autoclave is closed with a lid and kept at room temperature for 18 hours. At the end of the impregnation, the autoclave is opened, poured out 100 ml of the spent impregnating solution, pour 75 ml of isobutyl alcohol, the autoclave is sealed, placed, placed in a rapidly heated glycerin bath, over 30 minutes the temperature is raised to 140 ° C and cooking is carried out at this temperature for 2 hours. The cellulose yield is 60.2%, the lignin content is 12.8%.

Example 2. Cooking is carried out in the same way as in example 1, but the final temperature is increased to 145 ° C and the autoclave is kept at this temperature for 3 hours. Cellulose yield 52.5%, lignin content 6.4%.

Example 3. Cooking is carried out in the same way as in example 2, replacing the potassium hydroxide solution used for impregnation with sodium hydroxide of equal concentration. The cellulose yield of 52.0%, the lignin content of 6.9%.

Example 4. For cooking using birch wood. Cooking is carried out as in example 1, with the only difference being that a potassium hydroxide solution with a concentration of 110 g / l in units of Na ₂ O is used for impregnation, and cooking at a temperature of 140 ° C is continued for 2 hours. Cellulose yield 49.0 %, lignin content of 3.5%.

Example 5. Cooking is carried out in the same way as in example 4, lowering only the cooking temperature to 130 ° C and increasing the cooking time at this temperature to 3 hours. Cellulose yield 49.3, lignin content 4.2%.

Example 6. Cooking is carried out under the same conditions as in example 5, but the concentration of the potassium hydroxide solution is reduced to 80 g / l in units. Na ₂ O and increase the cooking time at the final temperature up to 4 hours. Cellulose yield 53.8%, lignin content 6.4%.

Example 7 (prototype). 30 g of pine wood chips are loaded into an autoclave, and 134 ml of an aqueous solution containing 40 vol.% Ethyl alcohol and sodium hydroxide and hydrazine are poured, the consumption of which is respectively 17 and 15% by weight of wood chips. The temperature was raised to 170 ° C in 2 hours and cooking was carried out at this temperature for 75 minutes. The cellulose yield of 52.2%, the lignin content of 6.2%.

The obtained data on the efficiency of the process are summarized in table.

The proposed method allows to reduce the cooking temperature, lower the consumption of hydrazine and alkali, to expand the range of pulp yields upward, to reuse isobutyl alcohol without distillation.

No. p / p Process conditions and pulp quality indicators Known method The proposed method one. Cooking temperature, ° С 170 120 ... 150 2. Cooking time, h 3 1,5 ... 4,5 3. The consumption of hydrazine for cooking,% fifteen 5 ... 8 four. The yield of cellulose,% 52 ... 54 47 ... 64 5. The lignin content,% 3 ... 5 1 ... 14 6. Breaking length, km 9 ... 10 7 ... 10 7. Bursting Resistance, kPa 450 ... 500 300 ... 500 8. Tear resistance, mN 800 ... 850 500 ... 900

Claims (1)

A method of producing a cellulosic semi-finished product, comprising boiling wood with an aqueous alkali solution in the presence of hydrazine and isobutyl alcohol, characterized in that the cooking is carried out in two stages, the first stage being impregnated with an aqueous alkali solution with a concentration of 80 ... 180 g / l in units. Na ₂ O containing hydrazine in an amount of 15 ... 25% by weight of abs. dry wood, at a temperature of 20 ... 50 ° C for 6-24 hours, isobutyl alcohol is added to the mass after selection of the flowing liquid phase, the mass temperature is increased to 120 ... 145 ° C and cooking at this temperature is carried out for 1 ... 4 hours.