RU2207416C1 - Cotton cellulose manufacture process - Google Patents

Abstract

FIELD: paper-and-pulp industry. SUBSTANCE: crude cotton cellulose is subjected to hoeing, cleared, and moistened with hot sodium hydroxide solution at 60-80 C. Digestion is carried out in sodium hydroxide solution with sulfanol additive (emulsifier) at modulus 1:13 to 1:8 and temperature 125-160 C during 3-6 h. Cellulose is then bleached for 1.0-2.5 h in sodium hypochlorite at concentration of active chlorine in bleaching solution 0.7-2.0 g/l at temperature 20-40 C. Bleached pulp undergoes sulfuric acid souring involving rinsing with softened water (water hardness no higher than 0.1 equ/l with weight proportion of iron no higher than 0.03 mg/l) followed by pressing, and drying. The latter operation is conducted in two-stage aerofountain drier consisting of several sections with first-section air temperature 160-175 C and 2nd, 3rd, and 4th-section temperatures, 90-100, and 75-80 C, respectively. Drying lowers moisture to 2-10%. Hydrodynamic pulp bleaching process should satisfy following conditions: 19500 </= Re </= 2060 at ratios d_m/D ~0.46, H/D ~1.8 and D/d~2.1, where Re is Reynolds number, d_m agitator diameter, D bleaching tub diameter, and H height of pulp layer in tub. Product can be used for production of nitrocellulose, acetylcellulose, carboxymethylcellulose, microcrystalline cellulose, copper-ammonia fiber, cardboard, and in gun powder production. EFFECT: improved quality of product utilizing environmentally safe process. 1 dwg, 2 tbl

Description

 The invention relates to a method for producing cellulose, in particular to a method for producing cotton cellulose from cotton lint, and can be used in the pulp and paper, chemical industries, for producing nitrocellulose, cellulose acetate, carboxymethyl cellulose, microcrystalline cellulose, copper-ammonia fiber, cardboard and powder industry.

 A known method of producing cotton pulp according to copyright certificate 829750, class. 3 D 21 C 5/00, USSR, 1979

The method includes passing purified nitrogen gas through a 2% sodium hydroxide solution at a temperature of 85 ^{° C.} for 5 hours, cooking cotton lint in a 2% sodium hydroxide solution with the addition of a surfactant (OP-7) at a temperature 140-150 ^o C for 1-4 hours and a pressure of 4 atm with a module of 20: 1.

 The disadvantage of this method is the complex hardware design of the process of producing cotton pulp due to the passage of gaseous nitrogen through a 2% sodium hydroxide solution. In addition, gaseous nitrogen has an irritating effect on the mucous membrane of the respiratory tract of staff. The invention does not indicate further processing of cotton pulp. This method uses cotton lint I, II grade.

 A known method of producing cotton pulp according to the copyright certificate 1251597 A1, class. 6 D 21 C 5/00, USSR, 1984

The method includes pre-wetting cotton lint with water by steaming at a pressure of 0.11-0.13 MPa, treating the ozone-air mixture in the gas phase with vigorous stirring, with an ozone-air mixture flowing 15-20 mg / l for 15- 30 min, boiling in a 2% NaOH solution at a temperature of 95-100 ^o C for 1 h, washing with hot and cold water for 5 minutes, acidification in a 0.3% solution of sulfuric acid for 15 minutes, washing with cold water twice for 5 min to a pH of 6-7, extraction and drying in air.

 The disadvantage of this method is air drying, which leads to a significant increase in time for the technological process, the use of an ozone-air mixture that is harmful to the body, which has an irritating effect on the mucous membranes of the respiratory tract, up to pulmonary edema, causing dizziness, headache. There are no cellulose bleaching operations in the process, so cellulose may have an uneven gray color.

 A known method of producing cotton pulp according to the copyright certificate 308133, class. 6 D 21 C 5/00, USSR, 1976

A method of producing cotton cellulose from cellulose-containing raw materials, such as cotton lint, consists in sequentially double processing the raw material with a hot alkali solution at a temperature of 95-100 ^o C, bleaching by treatment with sodium hypochlorite, subsequent processing with sulfuric acid, washing with the selection of the target product by known methods. To simplify the process, the reaction mass after treatment with a hot alkali solution is sequentially treated with an alkali solution with a concentration of 1.0-1.2% and 0.5-0.7% and hot water, the treatment is carried out by flow-irrigation method. Rinsing with water is carried out until neutral, then spin and drying.

 The disadvantage of this method is the long technological process for the production of cotton cellulose, consisting of a double treatment of cellulose, the absence of an emulsifier that affects the cooking process, contributes to a decrease in the viscosity of the cellulose, ensures uniformity of the cellulose in viscosity in different zones in the digester, and the penetration of reagents into the pores of the cellulose. The specific temperature and drying time of cotton pulp is also not indicated, which is important for the process.

 Closest to the proposed method is a method for producing cotton cellulose (Zabelin L.V., Lawyers A.P., Postnikov V.K. Cotton cellulose. M., TsNIIMTI, 1976, p. 202-252).

The method of producing cotton cellulose from cellulose-containing raw materials includes the following process steps: loosening, cleaning, wetting cotton lint in a solution of caustic soda 1.2-3.8% at a temperature of 60-80 ^o C, cooking in a solution of caustic soda 1.2-3 , 8% for 4-8 hours at a temperature of 130-150 ^o With a module from 1: 8 to 1:11 with the addition of an emulsifier (solution of rosin soap, detergents "Neol", "Progress", Petrova contact) at a working pressure up to 0.7-0.8 MPa, washing twice with hot water with a temperature of 60-80 ^o C, then cold. Each washing is carried out with working mixers for 25-30 minutes. The bleaching is carried out in sodium hypochlorite with a concentration of active chlorine of 0.35 g / l at a temperature of 60-80 ^o With stirring for 0.5-4 hours. Then it is again washed twice with cold water for 1-2 hours and acidified in solution sulfuric acid with a concentration of 0.5-2 g / l for 0.5-2 hours, after which it is washed twice with cold water for 30 minutes with stirring until neutral, the total lots are mixed, squeezed to a moisture content of 55-60%. Drying of cotton pulp to a moisture content of 10-12% is carried out in a three-belt aero-fountain dryer at an air temperature in the first shot glass of the dryer 90-100 ^o C, in the second - 80-100 ^o C, in the third - 60-80 ^o C. Then they are packed and packaged . Rinsing is carried out with process water having a hardness of not more than 2 mg • equiv / l, and the mass fraction of iron is not more than 0.3 mg / l.

 The disadvantage of this method is the long technological process for producing cotton pulp. For washing, process water is used, which has greater rigidity, which affects the quality and time of washing the pulp. The pulp itself is an adsorbent, which affects the whiteness of cotton pulp. Cotton lint is cooked with the addition of an emulsifier (solution of rosin soap, detergents Neol, Progress, Petrov’s contact), which does not sufficiently wet the cotton lint, which lengthens the cooking time and quality.

 The objective of the invention is to obtain cotton cellulose of the required quality using an environmentally friendly method from various varieties of cotton lint at a lower cost in time and simple equipment technology.

The problem is solved due to the fact that in the known method of producing cotton cellulose from cellulose-containing raw materials, including loosening, cleaning, wetting with a hot solution of caustic soda 1.2-3.8% at a temperature of 60-80 ^o C, cooking in a solution of caustic soda 1 , 2-3.8% with the addition of an emulsifier, bleaching in sodium hypochlorite, acidification in a solution of sulfuric acid with washing the mass with water after each operation, pressing and drying, cooking is carried out at a module of 1: 13-1: 8 at a temperature of 125-160 ^o C for 3-6 hours, and a mixture of sodium salts is used as an emulsifier alkylbenzenesulfonic acids (sulfanol), bleaching is carried out at a concentration of active chlorine in a bleaching solution of 0.7-2.0 g / l at a temperature of 20-40 ^o C for 1.0-2.5 hours, and the washing of the mass is carried out with softened water having hardness not more than 0.1 mg • equiv / l, with a mass fraction of iron not more than 0.03 mg / l, drying is carried out in a two-stage aero-fountain dryer, consisting of sections, at an air temperature in the first section of 160-175 ^o C, in the second - 90-100 ^o C, in the third - 90-100 ^o C, in the fourth - 75-80 ^o C to a moisture content of 2-10%, in addition, the hydrodynamic process of bleaching pulp in the vat must satisfy the conditions
19500≤Re≤20600,
in a relationship
d _m / D ~ 0.46;
H / D ~ 1.8;
D / d ~ 2.1,
where Re is the Reynolds number;
d _m - diameter of the mixer;
D is the diameter of the vat;
H is the height of the pulp in the tub.

 Cotton lint (GOST 3818.0-72) is used as raw material.

 The method is as follows.

First, the cotton lint is loosened and cleaned of litter and partially from seeds and foreign impurities, then it is fed into the cyclone hopper 1, where it is wetted with a 1.2-3.8% sodium hydroxide solution at a temperature of 60-80 ^o С , which allows to increase the loading of the digester due to the compaction of the material. A cotton lint moistened with a solution from a cyclone hopper is discharged onto auger 2, then to a digester 3. Lint is cooked at a temperature of 125-160 ^o C in a solution of caustic soda (alkali) with a concentration of 1.2-3.8% with the addition of an emulsifier - sulfanol (a mixture of sodium salts of alkylbenzenesulfonic acids) with a cooking module from 1:13 to 1: 8. During cooking, the cooking solution is continuously circulated in the boiler-heater system to uniformly wet the lint in the caustic soda solution. The cooking time is determined by the grade and viscosity of the pulp produced and ranges from 3 to 6 hours at a working pressure of not more than 0.5 MPa. At the end of cooking, the pulp from the boiler is blown into pump 4 to remove alkali and rinse. In the pump, first the washing is carried out twice with hot softened water with a temperature of 60-90 ^o C for 30 minutes and cold softened water with constant stirring for 10-20 minutes. Rinsing is performed to remove husks, seeds and ash dissolved and emulsified during cooking. After washing, the pulp with a working mixer is fed into the bleaching tank 5 to give the pulp a white color.

 The hydrodynamic process of bleaching pulp is determined by the type of mixing device, the rotational speed of the mixer bleaching vat.

The pulp bleaching is carried out at a temperature of from 20 to 40 ^o With a pH of the solution from 10 to 11 for 1.0 to 2.5 hours with a working mixer. The concentration of active chlorine in the bleaching solution is 0.7-2.0 g / l. The cellulose bleaching process enhances reactivity and decreases viscosity of cotton pulp. Then, the pulp is washed with cold softened water for 15-30 minutes. After draining the wash water, a solution of sulfuric acid with a concentration of 1-4 g / l is loaded into the vat to destroy the sodium hypochlorite and alkali remaining in the cellulose and excess ash. The duration of acidification is 30-60 minutes. After acidification, the pulp is washed twice with cold softened water for 30 minutes until the active chlorine is absent in the wash water and the pH is from 7 to 8. Then, after draining the waste water, the pulp is poured with cold softened water and sent to mixer 6 to mix common batches with the aim of obtaining batches of large volumes and achieving uniformity in physicochemical characteristics. Then the pulp is fed to the squeezing unit 7, where it is squeezed to a moisture content of 50-60% and fed to the dryer. Drying is carried out in a two-stage aero-fountain dryer 8, consisting of two sections each, at an air temperature in the first section of 160-175 ^o С, in the second - 90-100 ^o С, in the third - 90-100 ^o С, in the fourth - 75-80 ^o C.

 The cotton pulp after the squeezing unit is picked up by a hot air stream, passes through two sections of the first air fountain dryer, the intermediate drum is fed into the stream of hot air carrying cotton cellulose to the second air fountain dryer. The moisture content of cotton pulp in the first stage is reached 40-55%, when passing through the second stage is 2-10%.

 The viscosity of cotton pulp depends on the processing regimes of cellulose with a solution of caustic soda in a digester, and the modes of bleaching cellulose. Depending on this, we obtain cellulose of the required brand.

 The proposed method for producing cotton cellulose allows you to get cotton cellulose of the required quality from different varieties of cotton lint at a relatively lower cost in time.

By changing the cooking modes (temperature from 125 to 160 ^o C and cooking time from 3 to 6 hours), it is possible to vary the properties of cotton cellulose depending on the grade and quality of cotton lint, the use of sulfanol in the cooking process improves emulsification of unsaponifiable substances, improves fiber wetting and facilitate the transfer of contaminants from the fiber, and the use of a two-stage aero-fountain dryer, consisting of two sections each, for drying cotton pulp allows uniform drying, thereby eliminating the need for burnt, burnt cellulose, the use of softened water for leaching, contributes to the production of cotton pulp of the required whiteness.

To optimize the bleaching regime, experimental work was carried out. As a generalizing parameter that determines the quality of cotton cellulose, taking into account the hydrodynamics of the technological phase of bleaching, the Reynolds criterion - Re
19500≤Re≤20600,
in a relationship
d _m / D ~ 0.46;
H / D ~ 1.8;
D / d ~ 2.1,
where Re is the Reynolds number;
d _m - diameter of the mixer;
D is the diameter of the vat;
H is the height of the pulp in the tub.

 The use of the above hydrodynamic regimes of pulp bleaching in a bleaching tank contributes to the uniform effect of sodium hypochlorite on cellulose throughout the tank, which facilitates the removal of residues of nitrogen-containing, waxy and other non-cellulose impurities.

 Obtained by this method, cotton cellulose fully meets GOST 595-79.

 Examples of specific performance of the proposed technological operations are given in table. 1 and 2.

 The scheme for producing cotton pulp is shown in the drawing.

Claims (1)

A method of producing cotton cellulose, including loosening, cleaning, wetting with a hot solution of caustic soda at a temperature of 60 - 80 ^o C, cooking in a solution of caustic soda with the addition of an emulsifier, bleaching in sodium hypochlorite, acidification in a solution of sulfuric acid with washing the mass with water after each operation, pressing and drying, characterized in that the cooking is carried out at a module of 1: 13-1: 8, at a temperature of 125-160 ^o C for 3-6 hours, and a mixture of sodium salts of alkylbenzenesulfonic acids - sulfanol is used as an emulsifier, bleaching is carried out at a concentration actively chlorine in a bleaching solution of 0.7-2.0 g / l at a temperature of 20-40 ^o C for 1.0-2.5 hours, and the washing of the mass is carried out with softened water having a hardness of not more than 0.1 mg • equiv / l with a mass fraction of iron of not more than 0.03 mg / l, drying is carried out in a two-stage aero-fountain dryer, consisting of sections, at an air temperature in the first section of 160-175 ^o С, in the second - 90-100 ^o С, in the third - 90-100 ^o C, in the fourth - 75-80 ^o C to a moisture content of 2-10%, in addition, the hydrodynamic process of bleaching pulp in a tub should satisfy the conditions:
19500≤Re≤20600,
in a relationship
d _m / D ~ 0.46,
H / D ~ 1.8,
D / d ~ 2.1,
where Re is the Reynolds number;
d _m - diameter of the mixer;
D is the diameter of the vat;
H is the height of the pulp in the tub.

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