RU2572419C2 - Method of obtaining cellulose nitrates - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of obtaining cellulose nitrates in water-free medium by processing cellulose by nitrating agent, which represents mixture of concentrated nitric acid and acetic anhydride with molar ratio of nitric acid to acetic anhydride from 1:1 to 1:5, in carbon dioxide solvent, which is in sub-critical or super-critical condition at pressure not less than 50 atm, temperature of reaction mixture from 10 to 60°C for 10-240 minutes with the following washing of cellulose nitrate with carbon dioxide, which is in sub- or super-critical condition at pressure from 60 to 250 atm, and temperature from 40 to 80°C. Method makes it possible to produce any grades of cellulose nitrates from any kind of cellulose.

EFFECT: method makes it possible to improve ecological situation near the enterprises- producers of cellulose nitrates due to elimination of considerable quantities of concentrated mineral acids from technological cycle.

2 cl, 2 tbl

Description

The invention relates to the chemical industry, namely to the production of cellulose nitrates, and can be used in their production by continuous and combined technologies.

A known method of producing cellulose nitrate, according to which cellulose is treated with a nitrating mixture of nitric and trifluoroacetic acids in a ratio of 1.0-1.4: 1.0-0.6, followed by stabilization of the obtained cellulose nitrate [AS N883057, USSR, IPC С08В 5 / 02, 1981].

The disadvantages of this method are the use of large quantities of nitrating mixture containing trifluoroacetic acid, a significant duration of the process, the formation of a large number of acid-containing effluents, the need to stabilize the resulting cellulose nitrates.

A known method for producing pyroxylins by a continuous technological scheme, which has found wide application in industry, in which nitration is carried out with a mixture of concentrated nitric and sulfuric acids in two stages in order to remove waste acids. The technology provides for the stage of decomposition of cellulose sulfates by hot washing with soda solution [Gindich V.I. Cellulose nitrate production. Technology and equipment. TSNIINTI, 1984, pp. 59-62].

The disadvantages of this method are the use of large quantities of nitrating mixture, the formation of a large number of acid-containing effluents, the need to stabilize the resulting cellulose nitrates, and the overall complexity of the process.

The closest analogue of the proposed invention can be recognized as a method of producing cellulose nitrates, used in industry for the production of high nitrogen materials - pyroxylins. Nitration is carried out with a mixture of concentrated nitric and sulfuric acids. The technology provides for the stage of decomposition of cellulose sulfates by hot washing with soda solution [Gindich V.I. Cellulose nitrate production. Technology and equipment. TSNIINTI, 1984, pp. 55-59]. This decision was made as a prototype.

The disadvantage of this method is the use of large quantities of nitrating mixture, a significant duration of the process, the formation of a large number of acid-containing effluents, the need to stabilize the resulting cellulose nitrates, the overall complexity of the process.

The problem to which the invention is directed is to reduce the consumption of the nitrating mixture and the duration of the process, as well as to improve the environmental situation near enterprises producing nitrocellulose.

This is achieved by the fact that the production of cellulose nitrate is carried out in a carbon dioxide medium in a subcritical or supercritical state.

The method is as follows. Cellulose is treated with a mixture of fuming nitric acid and acetic anhydride (acetyl nitrate, nitrating mixture, HC) in a medium representing carbon dioxide in a sub- or supercritical state. The composition of the nitrating mixture varies from 1: 1 to 1: 5 (mol of nitric acid: mol of acetic anhydride). The consumption of HC 1-4 ml / g of cellulose. The temperature of the experiment is 10-60 ° C.

Overpressure in the system is maintained at a level of 50-400 atm. The processing time at the final temperature is 10-240 minutes. At the end of the process, cellulose nitrate is washed with carbon dioxide. The carbon dioxide feed rate is 1-20 g / min, with varying overpressure and temperature in the ranges of 60-250 atm and 40-80 ° C, respectively. The specific consumption of carbon dioxide is 25-250 g / g of the original cellulose. Carbon dioxide waste solution with the remaining unspent nitrating mixture can be regenerated and reused. The degree of substitution of cellulose is controlled by a change in the nitration time. The resulting cellulose nitrate is washed with carbon dioxide in a subcritical or supercritical state. The resulting cellulose nitrate contains 11-14% of bound nitrogen with a yield of 96-100% of theoretical.

Specific conditions for the implementation of the method (pressure, temperature, time modes, composition of the solution) can vary and are determined based on the characteristics of cellulose.

The chemical composition of cellulose nitrates and their yield were determined by methods known and generally recognized in the art.

Examples confirming the possibility of obtaining cellulose nitrates by the proposed method are shown in table 1. The parameters of the washing regime of cellulose nitrate are presented in table 2.

From the above examples it follows that the samples of cellulose nitrates are obtained homogeneous in nitrogen content and yield.

From the same examples it is seen that according to the proposed method it is possible to obtain cellulose nitrates with a bound nitrogen content in the range of 11-14%

To implement the proposed method can be used standard equipment for conducting supercritical fluid extraction.

The inventive method is environmentally friendly, because nitration does not produce toxic or difficult to recycle waste or by-products.

The inventive method can be used to obtain cellulose nitrates both in laboratory practice and in industry and is suitable for both periodic and continuous technological methods of nitration.

Claims (2)

1. A method of producing cellulose nitrates in an anhydrous medium, treating cellulose with a nitrating agent, which is a mixture of concentrated nitric acid and acetic anhydride with a molar ratio of nitric acid to acetic anhydride of 1: 1 to 1: 5 in a carbon dioxide solvent located in subcritical or supercritical a state at a pressure of at least 50 atm, a temperature of the reaction mixture from 10 to 60 ° C for 10-240 minutes, followed by washing of cellulose nitrate with carbon dioxide in sub- or supercritical condition at a pressure of 60 to 250 atm and a temperature of 40 to 80 ° C. 2. The method according to p. 1, characterized in that technical cellulose can be used as a feedstock: bleached and / or bleached, viscose sulphite.