RU2177481C1 - Method of preparing carboxymethyl cellulose - Google Patents

Abstract

FIELD: preparation of high-molecular compounds, particularly, ethers of carboxymethyl cellulose used as semifinished product for preparing purified salts of carboxymethyl cellulose as thickeners, emulsifiers, stabilizers of aqueous solutions, suspensions and emulsions. SUBSTANCE: in order to carry method into effect Na- carboxymethyl cellulose is successively converted into acid with aqueous solution of orthophosphoric acid having concentration of at least 10% and not higher than 20% for 15-30 min. Treatment with cross- linking aldehyde is combined with first washing operation and carried out for 15-30 min. Aldehyde is a aqueous solution containing 1.5-20 wt.pts of aldehyde per 100 wt.pts of sodium salt of carboxymethyl cellulose. Invention makes it possible to cut down total duration of process and individual stages, thereof, retain degree of polymerization of carboxy methyl cellulose, increase yield, reduce consumption of cross-linking agent, lower ecological hazard due to absence of organic solvents. EFFECT: more efficient preparation method. 1 tbl

Description

 The invention relates to the field of producing macromolecular compounds, namely, to methods for producing carboxymethyl cellulose (hereinafter - CMC), also referred to in the scientific literature as cellulose glycolic acid and N-CMC. CMC as a commercial product is relatively unknown, despite its undeniable advantage over other products of this class: it is non-hygroscopic, and this is important during its transportation, storage and use, especially in wet conditions. Mainly CMC is used as an intermediate to obtain purified water-soluble or water-swelling salts of various metals: sodium, calcium and lithium, mainly sodium, which are widely used as thickeners, emulsifiers, stabilizers of aqueous solutions, suspensions and emulsions in the battery industry, in production welding electrodes, in the production of heat-resistant and moisture-resistant papers, in the textile, pharmaceutical, cosmetic, food industries and a number of other industries.

 CMC technical salts contain sodium chloride and glycolate as the main impurities, and sodium hydroxide, carbonate and sodium bicarbonate are also possible. The presence of such impurities degrades the properties of CMC salts or makes it impossible to use them in some industries, therefore, the washing stage is of particular importance in such methods.

 The known methods for producing CMC are based on the extraction of impurities from Na-CMC by converting Na-CMC into a water-insoluble acid form by treatment with strong inorganic or organic acids and then washing it from impurities with water [Goloshchanova IS, Dalabaev UD, Dkharyal I .D. Obtaining pure carboxymethyl ethers of cellulose.// Petrochemistry, chemical processes and oil refining, - M .: Chemistry, 1964 - p. 228-230].

 The disadvantage of this method of producing CMC is the need to maintain harsh conditions (the use of strong acids, high concentrations and temperatures of solutions, processing time) to complete the conversion of Na-CMC to an acid form in order to prevent the production of a highly swelling or soluble product and complicate the subsequent process of washing impurities. A significant disadvantage of this method is the high catalytic activity of sulfuric and hydrochloric acids in the hydrolysis of cellulose derivatives, leading to a decrease in the degree of polymerization of the starting polymer and the yield of the product. In addition, the use of strong acids at the stage of conversion of Na-CMC into an acidic form requires the use of corrosion-resistant equipment.

 A known method of producing CMC in the form of an acid, as claimed by Nippon Seisy K.K. (Japanese Accepted Application No. 6-81762), in which Na-CMC is dispersed in an aqueous-alcoholic solution, then inorganic calcium and aluminum salts (chlorides, acetates or hydroxides) are simultaneously or separately introduced into the solution, mixed, the product is separated from the solution and dried . The dried product is treated with an aqueous solution of an inorganic acid (sulfuric, hydrochloric, nitric or phosphoric), stirred and the CMC is separated from the solution. The extraction of impurities is carried out with water. The disadvantages of this method are the need for the introduction of additional stages of processing Na-CMC with calcium and aluminum salts and drying the product before acid treatment, regeneration of the organic solvent from a solution containing acid and water. In addition, the introduction of significant quantities of inorganic salts of calcium and aluminum leads to a decrease in the purity of the product.

The closest technical solution to the claimed method is a method for producing CMC, described in Japanese Patent Laid-open No. 11-49920, which aims to purify Na-CMC by converting Na-CMC to CMC and washing with water. The method is as follows: technical Na-CMC is dispersed in an organic or aqueous-organic solvent containing 3-100 wt.h. aldehyde per 100 parts by weight Na-CMC at a pH of 3-6, treated at a temperature of 40-80 ^o C for 0.5-2.0 hours, removed the solvent, dried, treated with aqueous solutions of inorganic acids (sulfuric, hydrochloric, nitric, phosphoric) with a concentration of 1 -20 wt. % at a temperature of 5-50 ^o C for 30-60 minutes to obtain CMC, CMC is separated from the acid solution and washed with water.

 The sequence of stages declared in the prototype, namely, preliminary treatment of Na-CMC with a cross-linking agent, an aldehyde in an alcohol or water-alcohol solution, necessitates drying the product before converting the Na-CMC into an acid form, which significantly increases the duration of the process, and this is especially important in conditions large-scale industries, which include the receipt of CMC. The presence of an organic solvent for the crosslinking agent makes the process non-ecological and obliges the introduction of an additional stage of regeneration of the spent solvent. In addition, the processing of crosslinked Na-CMC with a solution of strong inorganic acids under prolonged exposure at elevated temperatures necessary to ensure the exchange reaction between the carboxyl groups of Na-CMC and phosphoric acid simultaneously enhances the activity of acids in the processes of destruction of cellulosic materials [Rogovin 3.A . Cellulose Chemistry. - M.: Chemistry, 1972, p. 173].

 The result of degradation is a rupture of polymer chains, leading, firstly, to a decrease in the degree of polymerization, which determines the quality of the CMC obtained, and, secondly, to the formation of low molecular weight water-soluble fractions, leaving the washing stage, and, as a result, to a decrease in the yield of CMC . The claimed method cannot ultimately provide CMC of high quality, determined by a high degree of polymerization and a low amount of impurities, with a high yield of the target product.

 In addition, the use of acidic solutions, which are strong corrosive substances, at elevated temperatures and for a long time requires the use of more expensive corrosion-resistant equipment [Sukhotin AM Corrosion and protection of chemical equipment. / Reference manual / - L .: Chemistry, 1972 - v. 6, p. 7].

 The technical problem to which the claimed technical solution is directed is to refine the conditions for the implementation of the method for producing CMC in the form of a water-insoluble product in order to be able to rinse it with water from water-soluble salts, to create "gentle", mild conditions for the conversion of Na-CMC to the acid form - CMC. The technical result of the proposed solution was to reduce the overall duration of the process and individual stages, maintaining the degree of polymerization of CMC, increasing the yield of CMC, increasing the environmental friendliness of the process due to the absence of organic solvents.

The specified technical problem in the prototype is achieved by the fact that CMC is produced by treating Na-CMC with aldehydes in an organic or aqueous-organic solvent in an acidic medium at a temperature of 40-80 ^o C for 0.5-2.0 hours, isolation and drying of the product followed by treatment with an inorganic acid of 1-20% concentration for 30-60 minutes, at a temperature of 5-50 ^o C. The amount of aldehyde introduced is 3-100 parts by weight. per 100 parts by weight Na-CMC.

A feature of the proposed method is that Na-CMC is treated with an aqueous solution of phosphoric acid at a concentration of not less than 10% and not more than 20% for 15-30 minutes, after which they are treated with a crosslinking agent, combining it with the first washing stage of the CMC. The treatment is carried out with an aqueous solution of aldehyde containing 1.5-20 wt.h. per 100 parts by weight Na-CMC for 15-30 minutes at 40-60 ^o C, after which an additional washing of the CMC with water is carried out and dried.

The transfer of Na-CMC to CMC occurs as a result of the exchange reaction between the carboxyl groups of Na-CMC and phosphoric acid to form the actual CMC. The rate constant of the hydrolysis of cellulose derivatives with inorganic acid solutions increases sharply with increasing temperature [Zabelin L.V., Zakoshchikov A.P., Postnikov V.K. Cotton cellulose - M.: TSNIINTI, 1976 - p. 79]. Processing Na-CMC with an aqueous solution of phosphoric acid for 15-30 minutes at a temperature of not more than 25 ^o C allows to reduce the destruction of the polymer at the stage of inorganic acid conversion of Na-CMC to CMC and thus preserve the molecular weight (degree of polymerization) and, as a result , increase the yield of the target product - CMC. The mild conditions for the conversion of Na-CMC to the acidic form, which allows maintaining the degree of polymerization and the quality of CMC, inevitably lead to the presence of a small amount of carboxyl groups in the Na form, which can lead to undesirable swelling of the polymer and complicate the washing process. The introduction of a crosslinking agent in the wash water at the first stage of washing allows to avoid swelling due to crosslinking of CMC with aldehyde groups and to exclude a separate stage of treatment with a crosslinking agent. The proposed sequence of stages and modes of conversion of Na - CMC into an acid form, treatment with a crosslinking agent and washing can significantly reduce the duration of the process, the consumption of a crosslinking agent, avoid the use of organic solvents and their regeneration, maintain the degree of polymerization of CMC, increase its yield.

 The method is as follows.

 In a vertical apparatus equipped with a heating jacket and an anchor stirrer, water and phosphoric acid are poured, after which the solution is mixed. Technical Na-CMC is loaded into the prepared solution and mixed until a uniform suspension is formed. After processing, the suspension is discharged into a centrifuge, where the product is pressed. At the same time, water and an aqueous aldehyde solution are poured into the vertical apparatus, after which the solution is mixed and heated. Pressed CMC is loaded into the prepared solution. After processing, the suspension is discharged into a centrifuge, where the product is pressed. After extraction, the distillate is fed into the centrifuge and an additional product washing is carried out.

The obtained CMC is a white coarse product with a bulk density of 420-450 kg / m ³ insoluble in water, with a basic substance content of 99.1-99.6% in the finished product. The yield of the target product - CMC - 98.5-99.0% of theoretical.

 To implement the method, the following substances and materials were used.

KMTs sodium salt (Na-KMTs) technical grade 7H, grade 9H - TU 6-55-221-1453-96
Technical phosphoric acid - GOST 10678-76
Glyoxal - TU 6-09-3530-74
Water (distillate) - GOST 6709-72
The possibility of implementing the method is illustrated by the following examples.

 Example 1

In a device with a capacity of 0.3 m ³ , a 10% phosphoric acid solution is prepared: 88.24 kg of water (distillate) and 11.76 kg of phosphoric acid are poured and mixed for 5 minutes. 20 kg of technical Na-CMC (degree of polymerization of Na-CMC 660) are fed into the prepared solution and stirred for 15 minutes at 20 ^° C. Then the suspension is discharged into a centrifuge and the product is squeezed to a squeeze ratio of 1.8. 200 kg of water (distillate) and 0.75 kg of a 40% aqueous solution of glyoxal are poured into the apparatus, stirred for 5 minutes and heated to 40 ^° C. The CMC pressed in a centrifuge is fed into the prepared solution and stirred for 15 minutes at 40 ^° C. Then the suspension is discharged into a centrifuge and the product is squeezed to a spin ratio of 1.8. After extraction, 2 rinses are carried out with the obtained CMC water (distillate). The resulting product has a basic substance content of 99.1%, a degree of polymerization of 640, a yield of 99.0% of theory.

 Data on technological modes and characteristics of the finished product are given in the table.

 Example 2

 The sequence of stages is the same as in example 1.

A 15% phosphoric acid solution is prepared in the apparatus: 82.35 kg of water and 17.65 kg of phosphoric acid are poured. 20 kg of Na-CMC are added to the prepared solution and stirred for 20 minutes at a temperature of 22 ^o C. The suspension is discharged into a centrifuge, and 200 kg of water and 5 kg of a 40% aqueous glyoxal solution are poured into the apparatus, mixed and heated to 50 ^o C. the solution is fed squeezed in the CMC centrifuge and stirred for 20 minutes at 50 ^o C, after which the washing is carried out.

 Example 3

The sequence of steps is the same as in example 1. A 20% phosphoric acid solution is prepared in the apparatus: 76.5 kg of water (distillate) and 23.5 kg of phosphoric acid are poured. 20 kg of Na-CMC are added to the prepared solution and stirred for 30 minutes at a temperature of 25 ^o C. The suspension is discharged into a centrifuge, and 200 kg of water and 10 kg of a 40% aqueous glyoxal solution are poured into the apparatus, mixed and heated to 60 ^o C. the solution is fed squeezed in a CMC centrifuge and stirred for 30 minutes at 60 ° C., followed by washing.

 Example 4

 The sequence of stages is the same as in example 1.

To the prepared 15% aqueous solution of phosphoric acid in an amount of 100 kg add 20 kg of Na-CMC and mix for 15 minutes at a temperature of 25 ^o C. The suspension is discharged into a centrifuge, and 200 kg of water and 0.75 kg of 40% aqueous formaldehyde solution are poured into the apparatus , stirred and heated to 40 ^o C. In the prepared solution serves squeezed in a centrifuge CMC and stirred for 15 minutes at 40 ^o C, after which washing is carried out.

 Example 5

 The sequence of stages is the same as in example 1.

To the prepared 15% aqueous solution of phosphoric acid in an amount of 100 kg add 20 kg of Na-CMC and mix for 20 minutes at a temperature of 25 ^o C. The suspension is discharged into a centrifuge, and 200 kg of water and 5 kg of 40% aqueous solution of acetaldehyde are poured into the apparatus, mixed and heated to 50 ^° C. The CMC pressed in a centrifuge is fed into the prepared solution and stirred for 20 minutes at 50 ^° C., followed by washing.

 Example 6

 The sequence of stages is the same as in example 1.

To the prepared 15% aqueous solution of phosphoric acid in an amount of 100 kg add 20 kg of Na-CMC and mix for 30 minutes at a temperature of 20 ^o C. The suspension is discharged into a centrifuge, and 200 kg of water and 10 kg of a 40% aqueous solution of benzaldehyde are poured into the apparatus, mixed and heated to 60 ^o C. In the prepared solution served pressed in a centrifuge CMC and stirred for 30 minutes at 60 ^o C, followed by washing.

 Example 7

The sequence of steps is the same as in example 1. In the prepared 15% aqueous solution of phosphoric acid in an amount of 100 kg add 20 kg of Na-CMC and mix for 20 minutes at a temperature of 20 ^o C. the Suspension is discharged into a centrifuge, and 200 kg of water is poured into the apparatus and 5 kg of a 40% aqueous solution of α-, β-naphthaldehyde, stirred and heated to 50 ^o C. Into the prepared solution served CMC pressed in a centrifuge and stirred for 20 minutes at 50 ^o C, after which washing is carried out.

Example 8 (prototype). 20 kg of isopropanol (80%) and 20 kg of Na-CMC were charged into the mixer and stirred for 30 minutes at a temperature of 50 ^° C. A 10% aqueous solution of H ₂ SO _{4 was} then added until a pH of 3.5 was obtained. To the prepared solution was added 11.7 kg of a 40% aqueous glyoxal solution. The suspension was stirred for 60 minutes at a temperature of 50 ^o C, the solvent was drained, and the product was dried for 5 hours at a temperature of 80 ^o C. The dried product was introduced into 300 kg of a 15% aqueous solution of sulfuric acid and after acid treatment for 1.0 hour at 50 ^° C. the CMC was washed with water. The test results are shown in the table.

 As can be seen from the table, the inventive method provides CMC with a higher degree of polymerization of 620-640 (prototype 450), increasing the yield of the product from 80% to 98.5-99.0%. The combination of the washing and aldehyde treatment stages allows avoiding the use of organic solvents and their regeneration, reducing the aldehyde consumption, eliminating additional stages of crosslinking, squeezing the product and drying it, shortening the stage of conversion to acid form and lowering its temperature, which significantly reduces the overall duration of the process maintaining the purity of the CMC.

Claims (1)

 A method for producing carboxymethyl cellulose, comprising converting the sodium salt of carboxymethyl cellulose into an acid form by treating an aqueous solution of phosphoric acid with a concentration of not less than 10% and not more than 20%, crosslinking with aldehyde, pressing, washing and drying, characterized in that the carboxymethyl cellulose sodium salt is first converted into acid form for 15-30 minutes, and then crosslinking, which is carried out by treatment with an aqueous solution of aldehyde containing 1.5-20 wt.h. aldehyde per 100 parts by weight sodium salt of carboxymethyl cellulose simultaneously with the first washing for 15-30 minutes

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