SU996579A1 - Method of producing pulp - Google Patents

Description

(54) METHOD FOR OBTAINING CELLULOSE

The invention relates to methods for producing cellulose from vegetable raw materials and may find application in the pulp and paper industry in the production of lulosa.

Traditional methods of producing cellulose using nitric acid consist in the two-step treatment of the raw material with chemical solutions — nitric acid in the first stage of cooking and alkali in the second stage. However, it is a process that requires a significant consumption of chemicals. Various methods are being developed to reduce the length of the cooking process.

A method of producing pulp is known, in which vibratory mixing of a mixture of chips and mortar is used to intensify the process at an amplitude of mechanical oscillations of 0.5-2.0 mm and a frequency of 30 Hz. The vibrations arising during vibration intermingling are transmitted to the solution and chips and accelerate the penetration into the capillaries of the wood chips, which makes it possible to shorten the impregnation time from four hours to half an hour and eliminate the damage to the chips 1.

The disadvantage of this method is the slight effect of vibratory mixing on the inner layers of the chips, as well as the need for a second stage of cooking, as a result of which it turned out to be ineffective.

The method of nitrate cooking is known, to intensify the process of which a solution of nitric acid is used.

10 acids 8-20%, and to reduce the consumption of caustic soda, chips after cooking are subjected to drying at a temperature not exceeding 90 ° C for 15,120 minutes C2.

15

The disadvantage of this method is also low efficiency, since the process goes in two stages and requires the use of both acid and alkali.

20

The closest to the invention to the technical essence and the achieved result is a method for producing cellulose by processing the raw cellulose-containing raw material.

25 nitric acid solution with simultaneous multiple mechanical effects on raw materials. The mechanical action consists in cyclic pressing of the raw material, which is 30 at the impregnation and cooking stages under a pressure of 1-10 MPa, and in each pressing cycle the pressure is increased for 0.2-1 min and maintained at a final pressure of 0.51.5 min . During impregnation, 4–6-fold cyclic pressing under pressure of 5.0–10.0 MPa is carried out, and during cooking - 2–4-fold pressing under pressure of 3.0–6.0 MP in initial cycles with a gradual decrease in pressure to 1-2 MPa in the final cycles. After relieving pressure, the cycle is repeated in J1-7 minutes. After the removal of excess acid, the cellulose-containing raw material impregnated with a solution of nitric acid is kept at atmospheric pressure for 30-60 minutes Cs.

The disadvantages of this method are damage to the cellulose fibers as a result of pressing and the high consumption of chemicals and energy for processing. The chips are pressed without prior orientation relative to the pressing surfaces, due to the compression of the chips, kaiK occurs across the fibers and in the most dangerous longitudinal direction of damage to the fibers. Chip damage also occurs as a result of the fact that, in order to ensure uniform impregnation of the chips, with a relatively small number of compression cycles, such high compression is necessary that the cellulose fibers are destroyed, and the process requires a lot of energy.

The purpose of the invention is to reduce the density of cellulose, reducing the consumption of chemicals and the duration of the process.

The goal is achieved by the fact that according to the method of producing cellulose by treating the initial cellulose-containing raw material with a solution of nitric acid with simultaneous multiple mechanical action on the raw material, the mechanical action is performed by compressing the raw material at its multiplicity of 120-150000 and at a frequency of 10-50 oscillations per second.

The treatment is carried out at 60-100 ° C and a concentration of a solution of nitric acid of 12-22% for 0.2-5.0 mi

. The method is carried out as follows.

The plant material and the nitric acid solution are continuously fed into the gap between two metal surfaces, one of which imparts a force forcing it to oscillate at a predetermined frequency. The moving chip layer is repeatedly compressed in a solution of nitric acid. With a frequency of 10-15 mechanical oscillations per second per time

staying in the treatment area Ip300 with the material is subjected to compression 100-15000 times, as a result of which there is a rapid and uniform saturation with its nitric acid, which initiates an intensive chemical interaction of nitric acid with the components of the plant material. Due to the exothermic nature of the oxidation reactions that occur during this process, the reaction mass is self-heating and the additional acceleration associated with it takes place. With this method of processing, not only is the penetration of nitric acid into wood chips, but the mechanical reduction of chips is facilitated by the fact that nitric acid penetrating into wood, being a highly reactive oxidant of lignin, causes its destruction and weakening of interfiber bonds in wood. , increase its plasticity and, therefore, facilitate its machining, i.e. significant reduction in energy consumption for processing. The force exerted on the chips in this case is minimal and, despite repeated repetitions, does not cause significant damage to the cellulose fibers. In this case, the mechanical effect on the chips, carried out with a BS-OO C in a 12-22% solution of nitric acid, is not so much for even impregnation of the inner and outer layers of chips, how much for the sequential separation (peeling) of the delignified and mechanically weakened layers of wood. At the same time, the deeper layers of wood chips, in turn, are exposed to a solution of nitric acid and the process continues until the chips are completely converted into fibrous material. The combined effect of the repeated mechanical forces of the reduction and chemical action of nitric acid leads to the fact that the lignin contained in the plant material is oxidized and dissolves at a faster rate than with the usual material, uniformly saturated with nitric acid.

f.

The rapid dissolution of the intercellular substance and the weakening of interfiber bonds in wood, resulting in this, leads to the separation of chips into fibers without the use of the second stage of cooking — alkaline extraction, i.e. to conduct cooking in one step.

Example. About 5 kg of aspen chips and 4 liters of nitric acid with a concentration of 17.5% are simultaneously fed to the upper part of the hollow body, inside which a rotor is installed with an annular gap of 10 mm, which is given circular oscillatory movements with a frequency of 25 kicks per second . Under the force of gravity, tqena and the solution are moved downward in the annular gap between the outer and inner working surfaces of the apparatus. The rotary oscillating rotary rotor transfers the force to the chips, which is subjected to repeated mechanical compression, is completely and uniformly fed with nitric acid. In this experiment, the processing time of chips was 1.0 min and, therefore, the number of compression cycles was 1500. The processed chips were separated from the excess acid solution and kept for 30 min in a thermally insulated vessel (L thermos) for completion) mass reaches. The irradiated cellulose is separated from the spent acid, which, after freshly consolidated, is used in the next ogalt with KISM1, then the cellulose is washed with {WATER and subjected to sorting on (Scet. Bleaching and sintering the obtained unbleached cellulose) by; soda e for 1 h tfi room temperature. The consumption of chemicals, the yield and indicators of cellulose are presented in Table 1. Example p 2. 0.1 kg of birch chips and 0.2 l of a 12% solution of nitric acid prepared from spent acid, obtained oh in Example 1, and charged with fresh nitric acid in a closed vessel within which is placed ftoroplas .tovy vklgschysh: mp vessel mounted on a knot at the vkladash which due to its inertia moved from inside the vessel with a frequency of 50 cycles per second, the set carried out..

Consumption from the original absolutely dry wood,%:

one . nitric acid

caustic soda dl. "Christmas tree extraction

23

28

thirty

20 times, squeezing chips in acid solution. The processing time of chips in a vessel.5, the total number of cycles 15bOO, and the time of additional soaking in a tank isolated vessel 15 minutes Thereafter, the mass is separated from the excess solution and subjected to washing and sorting. The bleaching and refining of the cellulose are carried out, as in Example 1, with 5% sodium hydroxide solution. Data on chemical consumption, yield and pulp indicators are presented in the table. Example 3. 0.7 kg of aspen wood chips are treated as in Example 1 in a 22% solution of nitric acid at a rotor oscillation frequency of 10 and a sales processing time of 0.2 minutes, which corresponds to a total number of cycles 120. After separating the excess acid chips. process, ak-in example 1. The results of the experiment are placed in the table. Example 4. For comparison, the nitrate cooking of birch chips is known as sporeroma. For this, birch chips are steamed with live steam for 15 minutes and pressed in 14% nitric acid at. Increase the pressing pressure for 30 s to 8 MPa, hold for 1 minute, release pressure and hold for 1 minute. Pressing is tested 5 times during the impregnation of the chips and 3 times at a pressure of 7.5 and 3 MPg during the cooking process of the chips. Then the mass is washed with water and alkaline extraction by extraction with a 2% sodium hydroxide solution at 90-95 ° C for 1 hour. After npoNHB and sorting, the mass is refined with 5% sodium hydroxide solution at room temperature for 1 h .. The results are presented in the table.

caustic soda for refining

The content of alpha-cellulose,%

The yield of refined pulp,

The content of pentoean,%

The total duration of impregnation and cooking, min. As follows from the table, refined cellulose, obtained using multiple mechanical reduction of chips in a solution of azonic acid, is higher in alpha cellulose, lower in pentosans and less. chemical consumption and time consumption

Thus, repeated mechanical compression of plant material in a solution of nitric acid according to the proposed mode makes it possible to provide a fast and uniform impregnation of the material with nitric acid, to increase the reaction capacity of lignin, thereby speeding up the process of lelification, and carry out cooking in one step, eliminate the consumption of caustic soda when cooking, simplify cooking equipment and improve its performance.

The exclusion of the consumption of caustic soda for cooking 1 ton of cellulose minus the cost of increased consumption of nitric acid when cooking by the proposed method with an annual productivity of 15 thousand tons of cellulose provides an economic effect of more than 400 thousand rubles.

Table continuation

20

20

91.7

93,8

41.9 38.6

4.30 5.40

90

thirty

Claims (3)

1. A method of producing cellulose by treating a raw cellulose-containing raw material with a solution of nitric acid with simultaneous multiple mechanical effects on raw materials, characterized in that, in order to reduce cellulose destruction, reduce chemical consumption and process time, the mechanical effect was performed by Q compressing the raw material at its multiplicity 120-15000 and a frequency of 10-50 oscillations per second. 2. A method according to claim 1, characterized in that the treatment is carried out at 60-100 ° C and the concentration of the nitric acid solution is 12-22% for 0.2-5.0 minutes. Sources of information taken into account in the examination 1. Author's certificate of the USSR 690101, cl. D 21 3/16, 1975. 2. USSR author's certificate number 622909, cl. About 21 3/16, 1976. 3. Authors certificate of the USSR 825745, cl. About 21 C, 3/16, 1979, (prototype).