SU1035030A1 - Process for preparing secondary cellulose acetate - Google Patents

Abstract

METHOD POLUCHENIYA..VTORICHN Yago cellulose acetate cellulose glacial acetic acid activation sposledukitsey esterification of acetic anhydride in an organic stretch voritel in presence of an acidic catalyst and isolating tselevohyu product of l and m h and w and u and so that, with simplicity delyu and intensification of the process, activation is carried out in the presence of 5-10 vol.% liquid nitrogen oxides, and esterification in acetone in the presence of perchloric acid as a catalyst at 15-20 C.

Description

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The invention relates to chemical technology, in particular, to the production of acetone-soluble, partially substituted cellulose acetate (AC widely used in the production of plastics for various purposes, artificial fibers, varnishes, and can be used to significantly intensify the process, reduce its energy intensity, improve the quality of its products. ,

In the technology of production of acetone-soluble ACs (secondary ACs), the process is carried out exclusively by a two-stage process, including cellulose acetylation to triacetate (TAC), followed by saponification of the latter in solution to the degree of substitution (T) 230-240, which ensures good solubility of the product. The feeding step lasts several hours and is very energy intensive. .

A known method for the production of LC, according to which the saponification of TAC, obtained in the first stage using an acetylating mixture containing acetic anhydride, acetic acid, a catalyst (a mixture of perchloric and sulfuric acids), is carried out in a homogeneous medium for 12-18 h at 45-50 ° C eleven.

A known method of direct acetylation of cellulose, the essence of which is that the process is carried out in the presence of large amounts of sulfuric acid (up to 16% by weight of cellulose). A mixed ether sulfoacetate is obtained, from which the sulfo group is boiled away in an aqueous, low concentrated solution of inorganic acid C2.

The complexity of this process lies, firstly, in the need to completely remove sulfo groups to ensure the heat resistance of the product, otherwise a special stabilization step is necessary. Secondly, the usual viscosity control of AC solutions is unacceptable, since the solubility of sulfoacetates and the viscosity of their solutions differ from the corresponding values for AC, and the viscosity of the solutions determined in the acetylation process does not correlate with the viscosity of the final product. Thirdly, the control over the degree of substitution of the ether obtained is too complicated, since it is necessary to preliminarily establish the content of both substituents. These and a number of other reasons prevent the use of a known method in industry.

Closest to the invention is a method for acetylating cellulose in the presence of a large excess of sulfuric acid, according to which

etherification of cellulose, previously activated with glacial acetic acid, is carried out with an acetyl mixture containing 15–25% sulfuric acid by weight of cellulose in dioxane at 38–4 ° C. However, this method also has the considered disadvantages of acetylation processes in the presence of large amounts sulfuric acid. To impart heat resistance to products, a special stabilization stage is required. The degree of substitution of the resulting AC (240260) is slightly higher than that of the standard secondary ACs produced by industry, which impairs their hydrophilic and, accordingly, hygienic properties. The lack of a clearly} correlation between the degree of substitution and the solubility of AC indicates a strong dependence of their properties on the conditions of the process, which are not always fully controlled. The disadvantages of the method include the use in large quantities of expensive and toxic dioxane.

The aim of the invention is to simplify and intensify the process of obtaining secondary cellulose acetate soluble in acetone and other organic solvents.

The goal is achieved by the fact that according to the method of obtaining secondary cellulose acetate, the activation of cellulose with glacial acetic acid followed by esterification with acetic anhydride in an organic solvent medium in the presence of an acid catalyst and release of the target product, is activated in the presence of 5-10% by volume of liquid nitrogen oxides, and esterification in acetone in the presence of perchloric acid as a catalyst at 15–20 ° C.

Use for the esterification of cellulose acetyl mixture with ma-. A clear amount of perchloric acid, taken as a catalyst, eliminates the possibility of side reactions (such as sulfation in known methods), which makes the process technologically advanced, and the final product is sufficiently heat-resistant and requires additional stabilization. Carrying out the reaction in acetone to a pure floor makes it easy to control the completion points of the formation of the acetone-soluble product. In addition, acetone, unlike dioxin, is cheap, is widely used in solvent industry, the maximum allowable concentration of it (200 mg / m) in the air of the working area of industrial premises is 20 times higher than that of disoxane (10 mg / m-2). ). It is experimentally established that for a uniform npoxejcaHHH reaction and to obtain a homogeneous product eto | It is expedient to carry out the testing at relatively low (15–20 ° C) temperatures, which in turn is convenient from a technological and advantageous from an economic point of view. The primary, partially substituted ACs produced by the proposed Moma process are more characterized. Narrow molecular mass distribution compared with a perforated secondary PRI me me R 1. 5 g of air-dry cotton cellulose (SP-2700) or wood floresla schloza (SP-1150} is kept for 5 minutes at 25-30C mixtures of 95 MP glacial acetic acid with 5 ml of liquid nitrogen oxides, after which the material is removed from the activating mixture, squeezed, washed with several portions of glacial acetic acid until the initial white color was obtained by the fibers, pressed again and flashed with a mixture of acetyl mixture The composition of the acetidating mixture: uksu 30% acetic anhydride, acetic acid 10% ice, 60% acetone, perchloric acid, 0% (by weight of cellulose). 1/10 acetylation module. The reaction is carried out in a thermostat at 15–20 ° C and stirring until complete clarification. the reaction mixture with the formation of a clear syrup (to a clean floor). The AC is removed from the solution in the acetylurization mixture by pouring the solution in a thin stream into a large volume of hot water while stirring. The resulting white flakes. The CA is washed until neutral, dried, the yield is determined Product -. Content in A associated respectively with acetic acid and the degree of substitution determined by known alkali saponification. SP is calculated from the characteristic viscosity of the solution in acetone. The results of the acetylation experiments are shown in the table.

Example 2. 5 g of air-dried cotton cellulose (SP-2700) are activated at 26.0 for 5 minutes with a mixture of 90 ml of glacial acetic acid with 10 ml of liquid nitrogen oxides, after which the polymer is drained, washed with glacial acetic acid before purchasing fibers white coloring. Acetylation of the activated cellulose, precipitation and analysis of the AC are carried out as indicated in Example 1. The duration of the acetylation to a bare floor is 25 minutes. The resulting AC contains 52., 3% of bound acetic acid (), characterized by SP-480 and yield 93.5%. From a comparison of these data with the results of the experiments of Example 1, it can be seen that the use of an activating mixture containing 5% by volume of nitrogen oxides is most acceptable both from the point of view of intensifying the esterification process and from the point of view of reducing the consumption of toxic and aggressive reagent. As can be seen from the table, the duration of the reaction of the cellulose within the specified conditions is 25-30 minutes, which is 2-3 times faster than during esterification by a known method. Compared to the industrial secondary AC, the primary ACs obtained by the proposed method are characterized by a somewhat lower degree of substitution {1 218-223), which improves their hydrophilic properties, and a somewhat higher SP, which favorably affects the physicomechanical indicators. In addition, the CO of the target product under the conditions of such a rapid reaction under mild conditions is determined mainly by the JV of the feedstock, which allows one to purposefully produce active sites of various molecular weights. The yield of the final product in the acetylation method is close to theoretical.

The use of the proposed method for the preparation of AC provides, in comparison with the known, the ability to quickly obtain, by direct acetylation, soluble in acetone and other organic solvents of partially-mixed cellulose acetates in catalysts, due to adverse reactions that complicate the process and worsen the quality of the target products; reduction of energy consumption due to the short duration of the process and low temperatures; the possibility of obtaining soluble DCs with an increased JV, as well as JV adjustments, by selecting a raw material, which significantly improves, speeds up the process of cellulose processing and improves the quality of AC-based products.

Claims (1)

METHOD FOR PRODUCING.: SECONDARY CELLULOSE ACETATE by activating cellulose with glacial acetic acid followed by esterification with acetic anhydride in an organic solvent in the presence of an acid catalyst and isolating the target product, which involves activation in order to simplify and intensify the process 5 10 vol.% Liquid · nitrogen oxides, and esterification - using acetone in the presence of perchloric acid as a catalyst at 15-20 ° C.