RU2423570C1 - Method to produce cellulose from straw - Google Patents

Abstract

FIELD: textile, paper.

SUBSTANCE: method includes chopped straw impregnation in a reactor and maceration with aqueous solutions of sodium hydroxide with concentration of 20-30 g/l in a unit of Na₂O at the temperature of 30-80°C. The method is carried out at the ratio of the solution weight to the dry chopped straw equal to 7:1. The impregnated chopped straw is maintained at the specified temperature for 30 min. The leaking liquid phase is extracted. Heated water is added to the mass, the mass temperature is increased up to 96°C, and boiling is executed at this temperature for 2 hours and 30 min.

EFFECT: higher yield of cellulose, reduced duration of process, its simplification and reduction of power inputs.

1 dwg, 1 tbl

Description

The invention relates to the production of cellulose from plant materials, in particular rice straw, and may find application in the pulp and paper industry.

A known method of oxidative-organosolvent cooking of cellulose from rice straw and husks (Vurasko A.V. et al., J. Cellulose. Paper. Cardboard. 2007, No. 1, pp. 16-19). By this method, only technical pulp can be produced.

There is also a known method of producing cellulose by cooking rice straw and / or husk with a mixture of glacial acetic acid and hydrogen peroxide in the presence of a catalyst when heated, and the straw and / or husk is preliminarily chemically treated with a NaOH solution with a concentration of 20-60 g / l at a temperature of at least 70 ° C for at least 20 minutes and then washed with water until neutral (RU 2312946, IPC D21C 1/06, D21C 3/04 dated 03/31/2006). The disadvantages of the method are the complexity of its execution, the consumption of expensive chemicals, the need to use combined methods of wastewater treatment process.

The closest in technical essence and purpose to the proposed invention is a method of cooking a section of rice straw by processing it in two steps (Handbook of a wallet (technologist) vol. 1. M.-L .: Goslesbumizdat, 1955, pp. 566-588) . In the first stage, the cross-section is impregnated in the reactor with sulfate liquor at a temperature of 20-80 ° C with a ratio of the mass of liquor to the mass of cross-section 7: 1. The concentration of active alkali in liquor is 25 g / l. The impregnated mass is maintained depending on the temperature of the liquor for 8-1.5 hours. During this period, the process of maceration, i.e. the separation of cells in plant tissues as a result of dissolution of the intercellular substance. Next, the impregnating solution is separated from the mass. The mass after complete draining of the liquid phase is loaded into a digester, in which at a temperature of 160-175 ° C for 15-40 minutes it is cooked with dissolution of lignin components and hemicelluloses and razvolnenie straw material. The cellulose yield according to the method is from 47.4 to 50.2% with permanganate stiffness values from 51.2 to 63.7 units. The liquor obtained by draining from the mass at the end of the first stage of the process is again used with the addition of fresh white liquor to impregnate the straw section.

The duration of the rotation of the digester taking into account the time for heating the mass to 160-175 ° C, cooking, pressure relief, unloading the mass is 3 hours 45 minutes.

The disadvantage of this method is the high consumption of thermal energy, the need to use complex sealing systems for a high-temperature cooking reactor, the long duration of the process of producing cellulose.

The new positive results of using the proposed method are reducing energy costs, metal consumption of equipment, eliminating the need to use complex protective equipment of the digester, reducing the duration of the process, making it possible to obtain cellulosic material in a wider range of its output.

These results are achieved by the fact that in the method of producing cellulose from straw, which includes impregnation in a reactor and maceration of a straw section with an aqueous solution containing sodium hydroxide at a temperature of 30-80 ° C and a ratio of the mass of the solution to the mass of dry section is 7: 1, the exposure of the impregnated section in the specified temperature range for a predetermined time, the selection of the entire flowing liquid phase, heating the mass, cooking it in a digester, according to the invention, a solution of sodium hydroxide with a concentration of 20- is used as an impregnating solution 30 g / l in units Na ₂ O, the impregnated cross-section is kept at a given temperature for 30 minutes, water is added to the mass after selection of the falling liquid phase in an amount of 35% of the volume of the glass phase, the mass temperature is increased to 96 ° C and cooking at this temperature is carried out for 2 hours 30 minutes .

The method is carried out using the installation, the scheme of which is shown in the drawing, in which 1 is a tank for a fresh solution of NaOH; 2 - tank for a circulating solution of NaOH after maceration; 3 - tank for a mixed (working) NaOH solution; 4 - tank for heating a mixed solution of NaOH; 5 - a supply tank of a heated mixed solution of NaOH; 6 - a hopper for chopping straw; 7 - auger mixer conveyor with an adjustable mass feed rate; 8 - macerator; 9 - mesh for draining; 10 - funnel; 11 - pump for pumping a circulating solution; 12 - mass screw pump; 13 - a cooking boiler. In the diagram, the ratio of the scale of the installation elements is not observed.

A NaOH solution of the given concentration is prepared and poured into the tank 1, the straw cross-section is fed into the hopper 6. When the installation is started, the NaOH solution from the tank 1 is fed through the tank 3 to the solution heating tank 4, from which it enters the consumable tank 5. The cross-section from the hopper 6 and the solution from the tank 5 is fed into the screw mixer-conveyor 7, in which the cross-section is mixed with the solution and impregnated with it. The mixture is fed into a macerator 8, in which it is held for 30 minutes. The required temperature of the mixture in the macerator is maintained by supplying steam to it. After 30 minutes, the mixture is quickly heated to 96 ° C and passed with the help of a mass screw pump 12 into the digester 13. During bypass, the mass passes over the net 9 through which excess NaOH solution flows into the funnel 10. The mass in front of the digester is supplied with water heated to 95 ° C in an amount of 33-35 vol.% Of the volume of the glass solution. In a digester, the mass is kept for 2 hours 30 minutes. The temperature at a predetermined level is maintained by supplying steam to the boiler. The finished pulp is removed from the digester and sent for washing and further processing.

The NaOH solution that has flowed through the mesh 9 is pumped by pump 11 into the tank 2 for the NaOH working solution, then it is mixed in the tank 3 with a fresh NaOH solution, the mixture is sent for heating, then into the supply tank 5, mixed with the cross-section, i.e. higher solution is reused.

To obtain cellulose according to the described technology in a steady-state continuous mode, the feed rate of the impregnated section with a screw mixer-conveyor 7 into the macerator 8 is selected such that the duration of the passage of the mass through the macerator is, for example, 30 minutes. The same speed of mass transfer is selected for the mass screw pump 12, which feeds the mass into the digester 13, while the volume of the boiler is selected so that the duration of the passage of mass through it, i.e. the duration of cooking, is, for example, 2 hours 30 minutes.

Tests of the proposed method on the example of rice straw processing were carried out in laboratory conditions using a flask equipped with a reflux condenser and a thermostat with a high rate of temperature rise. In all examples of the method, 50 g of air-dried cross-section of rice straw is taken, loaded into a 500 ml Erlenmeyer conical flask equipped with a reflux condenser, 340 ml of a NaOH solution of a given concentration and heated to the desired temperature are poured, the flask is placed in a thermostat, heated to the solution temperature NaOH in each specific example, and incubated for 30 minutes During this period, the processes of impregnation and maceration of the cross-section proceed. At the end of this treatment, 225 ml of the impregnation solution are taken from the flask. This is the entire volume of the free-flowing liquid phase. Add 80 ml of water heated to 95 ° C to the flask, place it in a heated thermostat and quickly the contents of the flask are heated to 96 ° C. Cooking at this temperature is carried out for 2 hours 30 minutes. In the examples, the following parameters are changed: the temperature of the mixture of cross-section and the solution in the stage of impregnation and maceration of raw materials, the concentration of the solution for impregnation and maceration in units Na ₂ O. Measure the yield of product, the degree of penetration in permanganate units, the ash content.

These details are shown in Table 1.

Table 1
Characteristics of NaOH and Rice Straw Cellulose No. of examples The concentration of the impregnating solution, g / l in units Na ₂ O The temperature of the impregnation solution, ° C The yield of cellulose,% by weight A.S. straw The degree of penetration, in permanganate units Ash content in cellulose one 25 thirty 58 67 5.8 2 25 fifty 54 65 4.8 3 25 70 52 62 3.8 four twenty 70 54 64 5,0 5 thirty 80 49 57 2.9

In two-stage methods with high-temperature cooking, the pulp yield (including lack of fusion) does not exceed 51.3% (see the link to the prototype, page 588). In the technology of the proposed method, the temperature of the mass at all stages of the processing of raw materials does not exceed 96 ° C and, accordingly, at a pressure almost equal to atmospheric, there is no need to seal the units of the installation. This makes it possible to use lightweight apparatus designs.

Thus, in the method all the goals are achieved.

Claims (1)

A method of producing cellulose from straw, including impregnation in a reactor and maceration of a straw section with an aqueous solution containing sodium hydroxide at a temperature of 30-80 ° C and a ratio of the mass of the solution to the mass of dry section 7: 1, holding the impregnated section at a given temperature for a given time, the selection of the entire flowing liquid phase, heating the mass, its cooking in a digester, characterized in that a solution of sodium hydroxide with a concentration of 20-30 g / l in units is used as an impregnating solution. Na ₂ O, the impregnated cross-section is maintained at a predetermined temperature for 30 minutes, heated water is added to the mass after selection of the flowing liquid phase, the mass temperature is increased to 96 ° C and cooking at this temperature is carried out for 2 hours and 30 minutes.

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