RU2133755C1 - Method of preparing carboxyalkyl cellulose salt - Google Patents

Abstract

FIELD: chemical industry. SUBSTANCE: method comprises activation of cellulose vegetable stock by stirring with aqueous alkali solution in the presence of hydrogen peroxide, esterification with chlorosubstituted alkylcarboxylic acid and drying. Stock includes unpurified lint and flax waste and this makes it possible to reduce cost. EFFECT: more efficient preparation method. 3 cl, 15 ex, 2 tbl

Description

The invention relates to the field of technology of cellulose ethers, in particular, it is a method for producing salts of carboxyalkyl cellulose or, in other words, salts of cellulose ether and hydroxycarboxylic acid of the formula
[C ₆ H ₇ O ₂ (OH) _3-x (OC _n H _2n COOMe) _x ] _m ,
where x is the degree of substitution on carboxyalkyl groups;
n is the number of carbon atoms in the alkyl radical of the oxycarboxylic acid residue;
m is the degree of polymerization of carboxyalkyl cellulose or its salt;
Me is an alkali metal.

Currently, the most practical application is found in the sodium salt of the simplest representative of the homologous series of carboxyalkyl celluloses - carboxymethyl cellulose [C ₆ H ₇ O ₂ (OH) _3-x (OCH ₂ COOMNa) _x ] _m . The sodium salt of craboxymethyl cellulose is used as a protective colloid to increase the stability of clay solutions when drilling oil and gas wells, a thickener for suspensions and binders in the construction, paper, textile, match, food industry, medicine, pharmaceuticals and the production of synthetic detergents (V.M. Nikitin, Chemistry of Wood and Cellulose, M.-L.: Goslesbumizdat, 1960, p. 325, 326; Z. A. Rogovin, Chemical Transformations and Modification of Cellulose, M., Chemistry, 1967, pp. 83-87; Chemistry and production technology pulp production, edited by ZA Rogovin, Upper Volga Book Publishing House, 1964, pp. 119-120, 133-140).

Known methods for producing the sodium salt of carboxymethyl cellulose using cellulose, sodium hydroxide and monochloracetic acid or sodium monochloracetate as starting materials, comprising the following steps:
- activation of cellulose with sodium hydroxide;
- esterification of activated cellulose with monochloracetic acid or sodium monochloracetate;
- removal of excess water from the product by drying (Chemistry and technology of cellulose derivatives. Edited by ZA Rogovin. Upper Volga Book Publishing House, 1964, p. 115, 125-131).

According to the method (US Pat. No. 2001040 of Russia, MKI C 08 B 11/12, decl. 4.02.91, publ. 15.10.93), the sodium salt of carboxymethyl cellulose is obtained by successive operations of activating cellulose with sodium hydroxide in an aqueous organic solvent and addition of monochloracetic acid (MCA) during fractional introduction of reagents, moreover, sodium hydroxide in the second and last additions is introduced in solid form to a molar ratio of sodium hydroxide-cellulose (1-2): 1 in the reaction mixture pre-cooled to 25-35 ^o C, and monochloracetic acid is introduced into the form e solution in an organic solvent to a molar ratio of sodium hydroxide - MHUK in the first stage of 2.1: 1, and in the second and subsequent 2: 1.

 In the method (U.S. Pat. No. 1131251, MKI C 08 B 11/12, claimed 29.09.65, publ. 23.10.68), the carboxymethyl cellulose salt is prepared by esterifying alkaline cellulose in a two-phase liquid system containing a water-soluble aliphatic alcohol, moreover, one phase contains an aqueous solution of alcohol, and the other contains a solution of alcohol in an inert solvent, and the resulting carboxymethyl cellulose is further treated with a bleaching agent in order to reduce the viscosity of carboxymethyl cellulose and increase its whiteness. As the bleaching agent in the method (US Pat. UK N 1131251) using hydrogen peroxide, perborates, periodates or hypochlorites of alkali metals.

 The disadvantages of these methods are associated with the use of expensive organic solvents, their irretrievable losses and the cost of catching solvent vapors during drying of the carboxymethyl cellulose salt.

 There is a known industrial-scale method for producing sodium salt of carboxymethyl cellulose, according to which cellulose is activated by stirring with a solution of sodium hydroxide, the resulting activated cellulose is mixed with sodium monochloracetate until the esterification reaction is completed, after which the product (sodium salt of carboxymethyl cellulose) is dried in a stream of hot air (B.I. Bytensky, EP Kuznetsova. Production of cellulose ethers. L., Chemistry, 1974, see 166-168).

 Closest to the invention is a method of producing a salt of carboxymethyl cellulose (US Pat. UK N 1108282, MKI C 08 B 11/10, decl. 04/23/65, publ. 3.04.68,), in which as a cellulosic material for salt synthesis carboxymethyl cellulose uses purified cotton lint (see page 3, lines 40-44 and page 7, line 5 of the patent description), i.e. cotton cellulose purified from non-cellulosic impurities, similar in purity to domestic cotton cellulose (GOST 595) with the following indicators: the content of waxes and fats - no more than 0 , 1%, ash content - 0.1 - 0.2%, lignin content not more than 0.1%, as well as wood pulp (page 2, lines 25-27 of the patent description).

 In the method (UK patent N 1108282), purified cotton lint or wood pulp is activated with aqueous alkali in a two-phase liquid system consisting of an aqueous solution of alcohol in one phase and a solution of alcohol in an aromatic hydrocarbon in another phase, after which the alkaline cellulose is mixed with monochloracetic acid or its with salt. The disadvantage of this method is also associated with the use of expensive organic solvents.

 It should be noted that in the known methods as cellulose raw materials for the production of carboxymethyl cellulose and its salts, specially purified, impurity-free cellulose (most often sulphite, as well as sulphate and peeled cotton lint) is used (V.Ya. Bytensky, E.P. Kuznetsova Production of cellulose ethers. L., Chemistry, 1974, p. 161; Chemistry and technology of cellulose derivatives. Edited by ZA Rogovin, Upper Volga Book Publishing House, 1964, p. 18; V.M Nikitin, Chemistry of Wood and Cellulose, M.-L .; Goslesbumizdat, 1960, pp. 207-215; L.V. Zabelin, A.P. Zakoshchikov, V.K. Postnikov, Cotton Cellulose, M., Central Scientific Research Institute of Informatics, 1976, pp. 119-145; 199-265).

 The technical task of the invention is to reduce the costs associated with obtaining salts of carboxymethyl cellulose, through the use of cheaper cellulose-containing raw materials: raw cotton lint or linen tow.

 Crude cotton lint is based on fibers remaining on cotton seeds after textile fibers have been removed. Lint fibers include cellulose (up to 94% by weight of fibers) and small amounts of non-cellulosic substances (waxes and fats, proteinaceous, water-soluble and coloring substances), and waxes and fats cover the cotton fibers with a thin protective layer from the outside (P. P. Shorygin Cellulose Chemistry. M., ONTI, 1936, p. 67). Lint infestation is caused by whole seeds and the remains of cotton stalks, seed husks, bunches, and all these impurities differ from cotton fiber in a much higher content of non-cellulosic components (lignin, protein and dye substances) (L.V. Zabelin et al. Cotton cellulose, S. 92-107, 189-194).

 Flax tow is formed when flax fibers are processed on carding machines and are fibers coated with a thin layer of fats and waxes, the main component of which is cellulose, mixed with fires, bast fibers, weeds (L.A. Birman, K.G. Bus, U .D. Harrison et al. Cellulose bleaching. M.-L.: Goslesbumizdat, 1957, p. 198).

 The main quality indicators that determine the practical value of the carboxyalkyl cellulose salt and the field of its use are the degree of substitution for carboxy groups and the degree of polymerization (V.Ya. Bytensky et al. Production of cellulose ethers, pp. 172-174; Technical sodium carboxymethyl cellulose. Technical conditions 6- 55-40-90). For example, the degree of substitution with respect to carboxymethyl groups, affecting such an important property of the carboxymethyl cellulose salt as its solubility in water, should be at least 45. The degree of polymerization of macromolecules of carboxymethyl cellulose, the lower limit of which is 200, determines the viscosity of solutions of its salts.

The problem is achieved in that as the cellulosic raw materials in the proposed method use unrefined cotton lint or flax tow, and when alkaline activation is introduced into the reaction mass of hydrogen peroxide in an amount of not more than 0.1 kg of hydrogen peroxide per 1 kg of cellulosic raw materials or cellulosic raw materials before alkaline activation is sequentially treated with an aqueous solution containing alkali (sodium or potassium hydroxide) at a concentration of 0.02-0.3 mol / l at a temperature of at least 75 ^o C and an aqueous solution containing hydrogen peroxide ode concentration of 1-8 g / l at a temperature not lower than 50 ^o C.

 In the proposed method, the introduction of hydrogen peroxide in the reaction mass during alkaline activation of cellulose raw materials is due to the need for destruction of fats and waxes covering the fibers of raw cotton and flax and preventing the effective activation of cellulose with alkali and subsequent esterification of alkaline cellulose with chlorine-substituted alkylcarboxylic acid or its salt.

The task of cleaning cotton lint and linen tows from fats and waxes covering the fibers in the proposed method is also solved by sequentially treating cellulosic raw materials with an aqueous alkali solution at a concentration of 0.02-0.3 mol / l at a temperature of at least 75 ^o C and an aqueous solution of peroxide hydrogen concentration 1-8 g / l at a temperature not lower than 50 ^o C. In this case, along with the destruction fats and waxes, coating fibers occur non-cellulosic hydrolysis and oxidation of constituents (lignin, proteins and dyes) impurities linter linters and flax (intact seeds, seed husks, flaps bolls, fires, bast fibers, residual stems). The resulting degradation products of non-cellulosic constituents pass into the cooking solution, and the cellulosic product after washing is separated from the excess water (for example, by centrifugation) and then subsequently subjected to alkaline activation and esterification by known methods.

 It should be noted that the introduction of hydrogen peroxide into the reaction mass at the stage of alkaline activation of the cellulosic product is expediently used for raw materials (unpeeled cotton lint, linen flax) with a relatively low content of impurities.

 For cellulosic raw materials with a higher content of impurities, it becomes preferable that the proposed method involves sequential processing of the raw materials with solutions of alkali and hydrogen peroxide, since the non-cellulosic components of the impurities are decomposed with the formation of water-soluble compounds, due to which the content of the useful substance, the carboxyalkyl cellulose salt, in the final product increases.

 The proposed method is illustrated by examples 1-15.

 When introducing hydrogen peroxide into the reaction mass at the stage of alkaline activation of cellulosic raw materials according to the proposed method, the amount of hydrogen peroxide should be no more than 0.1 kg per 1 kg of raw material. When the amount of hydrogen peroxide is more than 0.1 kg per 1 kg of cellulosic raw materials, along with the destruction of fats and waxes, excessive depolymerization of cellulose macromolecules occurs, which, with subsequent esterification, leads to the formation of low-viscosity carboxyalkyl cellulose, which has no practical value (examples 4, 5, 8 )

The sequential treatment of cellulose raw materials with solutions of sodium hydroxide and hydrogen peroxide should be carried out at an alkali concentration of 0.02-0.3 mol / l and a temperature of at least 75 ^o C and at a concentration of hydrogen peroxide of 1-8 g / l and a temperature of at least 50 ^o C .

When the concentration of sodium hydroxide in the aqueous solution is less than 0.02 mol / L and the processing temperature of the cellulosic raw materials with a solution below 75 ^o C, when the concentration of hydrogen peroxide in the aqueous solution is less than 1 g / L and the temperature of the treatment with this solution below 50 ^o C, the destruction of fats and waxes coating fibers is not efficient enough and the resulting carboxyalkyl cellulose has a low degree of substitution (examples 10, 11). When the concentration of sodium hydroxide is more than 0.3 mol / l and the concentration of hydrogen peroxide is more than 8 g / l, along with the destruction of fats and waxes on the surface of the fibers, as well as non-cellulosic constituents of the raw material impurities, excessive depolymerization of cellulose macromolecules occurs, which leads to the formation of esterification low viscosity carboxylalkyl cellulose, not having practical value (examples 12, 13).

 To implement the proposed method, you can use a mixer with paddle working bodies, for example, a Werner-Pfleiderer mixer (L. Venen, E. Burlo, A. Lekorshe. Production of gunpowder. M., ONTI, 1936) with the following characteristics: working volume 500 l, the rotation frequency of the horizontal blades is 22-25 rpm and 10-12 rpm.

Example 1. The Werner-Pfleiderer mixer was loaded with 34.5 kg of air-dried raw cotton lint (humidity 9 wt.%, Fat and wax content of 0.74 wt.%, Weediness of 2.5 wt.%, Including the content of whole seed 0.3 wt.%). Then 68.5 l of an aqueous solution of sodium hydroxide with a concentration of 19.6 wt.% Was poured into the mixer and after stirring for 15 minutes 2 l of perhydrol was poured into the mixer (an aqueous solution of hydrogen peroxide of a concentration of 34 wt.%, I.e. 0.76 kg of peroxide hydrogen), after its contents the mixer was stirred for 180 minutes. Then, 46.0 kg of sodium monochloracetate was loaded into the mixer, and, after stirring the mass for 80 minutes while continuing stirring, the temperature of the mass was raised to 70 ^° C. by supplying steam to the mixer jacket. After 60 minutes of stirring at 70 ^° C, the mass was unloaded from the mixer and dried at 110 ^° C as a layer 80 mm high to a moisture content of 9.5 wt.%. After drying, a loose gray-brown fibrous product was obtained with the following characteristics: degree of substitution for carboxymethyl groups 56, degree of polymerization 320.

 In examples 2 to 6, 8, the same sequence of operations was used to implement the proposed method as in example 1. In example 7, after loading 34.5 kg of air-dried linen tows into a mixer, 72.6 l of an aqueous solution of potassium hydroxide was poured into the mixer concentration of 25.4 wt.%, after which the same sequence of operations was used as in example 1. The characteristics of the raw materials and reagents used and the properties of the product obtained with this are shown in table 1.

 In examples 9 to 15 used a variant of the proposed method, including sequential processing of cellulosic raw materials with solutions of alkali and hydrogen peroxide.

Example 9. In this example, as a cellulosic raw material used crude cotton lint with the following characteristics: humidity 9 wt. %, the content of fats and waxes 1.4 wt.%, weediness 11.5 wt.%, including the content of whole seeds 6.5 wt.%. Cotton lint was loaded into an aqueous solution of sodium hydroxide at a concentration of 0.1 mol / L, the resulting suspension with a solids content of 9.5 wt.% Was heated to 98 ^° C and held at this temperature for 8 hours. Then, the temperature of the suspension of the cellulosic product was lowered to 85 ^o C, perhydrol was introduced (an aqueous solution of hydrogen peroxide with a concentration of 34 wt.%) Until the concentration of hydrogen peroxide in the aqueous solution was 4 g / l and the suspension was kept at 85 ^o C for 6 hours. Next, the cooking solution was drained from the cellulosic product, the product washed by irrigation , Pressed in a centrifuge to a moisture content of 55.5 wt.%, And was loaded into a Werner & Pfleiderer mixer, 70.5 kg of the product (i.e., 34.5 kg based on cellulosic product with a moisture content 9 wt.%). Then, 33.6 l of an aqueous solution of sodium hydroxide with a concentration of 36.1 wt.% Was poured into the mixer, after stirring the mass for 180 minutes, 46.0 kg of sodium monochloracetate was loaded into the mixer and after stirring the mass for 80 minutes, stirring continued, the temperature of the mass raised to 70 ^o C by feeding steam into the jacket of the mixer. After 60 minutes of stirring at 70 ^° C, the mass was unloaded from the mixer and dried, as in Example 1. After drying, a loose fibrous white product was obtained with the following characteristics: degree of substitution for carboxymethyl groups 72, degree of polymerization 420.

 In examples 10-13, 15, the same sequence of operations was used to implement the proposed method as in example 9. In example 14, after loading a humid cellulose product into the mixer, as in example 9, 36.1 l of an aqueous solution of potassium hydroxide were poured into the mixer concentration of 44 wt. %, after which the same sequence of operations was used as in example 9. The characteristics of the raw materials and reagents used and the properties of the resulting product are shown in table 2.

Claims (2)

 1. A method of producing a salt of carboxyalkyl cellulose, including activation of cellulosic plant material by mixing it with an aqueous alkali solution, esterification with a chlorine-substituted alkyl carboxylic acid salt and drying, characterized in that raw cotton linters or linen tows are used as raw materials and the raw materials are activated in the presence of hydrogen peroxide in the amount of not more than 0.1 kg of hydrogen peroxide per 1 kg of raw materials. 2. A method of producing a salt of carboxyalkyl cellulose, including activation of cellulosic plant material by mixing it with an aqueous alkali solution, esterification with a chlorine-substituted alkyl carboxylic acid salt and drying, characterized in that raw cotton lint or linen tows are used as raw materials and the raw materials are first treated with an alkali concentration solution before activation 0.02 - 0.3 mol / l at a temperature of not lower than 75 ^o C, and then with a solution of hydrogen peroxide concentration of 1 - 8 g / l at a temperature of not lower than 50 ^o C.

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