SU952285A1 - Method for desublimitation of organic synthesis products from gas-vapour mixture - Google Patents

Description

The invention relates to desublimation processes that are used in the isolation of organic-synthesis products from vapor-gas mixtures, such as phthalic and maleic anhydrides, anthraquinone, phthalonitrile, etc.

. Methods are known for the desublimation of organic synthesis products by mixing the vapor-gas mixture with a cold gas or by contacting the vapor-gas mixture with a cooled surface l.

However, in the volume of the desublimator apparatus, sublimate crystals are formed, which limits the linear velocity of the mixture and, consequently, the specific productivity of the apparatus, which is approximately 0.2 kg / m. hour.

There is also known a method according to which the method of alternately cooling and heating the gas stream to a temperature below and above the dew point 2 is used to prevent desublimation in the volume of the apparatus.

However, a large number (up to 18) of cooling and heating equipment is required for carrying out this method.

There is also known a method of forest sublimation of products from a steam-gas mixture.

by its thermal contact simultaneously with two heat exchange surfaces, one of which is cooled below the point or the desublimation product, and the other is heated above the point of not the product. It is proposed to maintain the temperature of the cooling surface by extruding any point of impurities, which allows

10 to obtain a pure product 3}.

However, this also does not exclude desublimation in volume.

The aim of the invention is to intensify the process by preventing product desublimation in the vapor-gas stream.

The goal is achieved by the fact that, according to the method, the temperature of the vapor-gas mixture between the heat exchanging surfaces is maintained above the point of no desublimating product.

For this, the gas-vapor mixture is heated simultaneously with the formation of a sublimate layer on the cooled surface. This prevents desublimation in the volume, crystals form only on the cooled surface, the density increases and

30 thermal conductivity of the sublimate layer and

conditions are met to significantly increase the velocity of the vapor-gas mixture and the performance of the apparatus

In order to implement the method, a steam-gas mixture (for example, a mixture of phthalic anhydride vapor and air) is passed between the cooling and heating surfaces. The dimensions of the surfaces, the temperature between them: the refrigerant and the coolant are calculated from the dependences of the vapor pressure of the released substance on the temperature and the corresponding heat and mass transfer formulas so that the vapor-gas mixture temperature in the volume is higher than the point of the separated product.

The heating and cooling surfaces can be coaxially arranged tubes of a shell-and-tube heat exchanger, in the annular spaces of which coolant is fed, and in. internal tubes - the heat carrier. Gas-vapor mixture is passed through the annular gaps between the tubes.

For phthalic anhydride with its initial concentration in air of 1% by volume, the temperature of the vapor-gas mixture above the ine point can be achieved, for example, with a ratio of heating and cooling tube diameters of 1: 2, inlet coolant temperatures of 140-1bO, outlet 70 100 ° С, coolant temperature 40-50 ° С.

: It is also possible to pass the vapor-gas mixture through a plate heat exchanger - desublator with slit channels, one of the flat walls of which is heated and the other

cools down. For phthalic acid; Because of the above mentioned initial concentration, the required temperature is achieved, for example, at a ratio of heating and cooling surfaces of 1: 1, refrigerant temperatures of 40-50 ° C, heat carrier 120-14 ° C at the inlet and 60-90 ° C at the outlet.

Example 1. A phthalodiscular mixture with an initial concentration of 1% by volume and a temperature is supplied to an annular gap formed by two tubes: diameter 22x1 mm and 10 mm. The first tube is cooled with water at a temperature, the second is heated with oil at a temperature of 140 s. The length of both tubes of the 4th, l-line speed of the vapor-gas mixture in the annular gap between the tubes is 7-12 m / s. Phthalic anhydride in the form of a dense layer of fine crystals is released on the inner surface of the cooled outer tube.

Etc. and measure 2. At the same installation, male-air mixture is desublimated with an initial Concentration of 1.2 vol.% and temperature. The outer tube is cooled with water at a temperature, internally heated with water at a temperature of 80 ° C; the linear velocity of the vapor – gas mixture in the annular gap is 10–15 m / s.

 The main results of these experiments and their comparison with a known method are presented in the table.

Thus, the proposed method allows to intensify the process, increasing the specific productivity of desublimators by 2.5-5 times in comparison with the known methods.

The degree of excretion of the product,%

phthalic anhydride

maleic anhydride Density of the sublimate layer, kg / m

about

Thermal conductivity of the layer, W / m gra

Linear steam-gas velocity. Mixture, m / s

Heat transfer coefficient,

Specific capacity, kg / m h

98

98 90

90

00-200

500-800

700-1000 0.04 0.1-0.3 0.2-0.4

7-12

0.3

10-15 5. 18

22 0.6-1.0 0.2

0.6-0.9

59522856

Claims (3)

The invention of the product in the vapor-gas flow, -IC-MS, the method of desublimation of products between the heat exchange of organic synthesis of steam and gas, is maintained above the point of the mixture by its thermal contact-and-de-dubbing product, which simultaneously with two heat exchange-5 MIs, one of which is taken into account by expert examination, is cooled below point or subli-1. Turevich D.A. Phthalic anhydrating product, and another heating. M., Himi, 1968, p. 125. above the point of this product, 2. USSR author's certificate characterized by the fact that 10 No. 363501, cl. At 01 O 5/00, 1973. in order to intensify the process of 3. Patent of Great Britain to prevent desublimation No. 1075594, cl. B 1 B, 1967. perraturu steam-gas mixture,;;;: -: