RU2091363C1 - Method of purification of halohydrocarbons of ethane series - Google Patents

Abstract

FIELD: chemical industry. SUBSTANCE: chemical industry, more particularly purification of ozone-nondestructive halohydrocarbons which should replace use of the chlorofluorohydrocarbons which destruct ozone layer of atmosphere. The claimed method of removing halogen containing impurities are inorganic acids is carried out by passing the product to be purified through carbon sorbent with volumetric sorption space of 0.7-0.9 cubic cm/g followed by rectification of the resulting product and passing the rectificate through sorbent over contact period of less than 20 minutes. EFFECT: more efficient purification method.

Description

 The invention relates to the field of production of ethanol-halogenated hydrocarbons, in particular the purification of raw materials from halogen-containing impurities.

 Currently developed ozone-depleting halogenated hydrocarbons of the ethane series, used as alternative chladones. These include 1-fluoro-1,1-dichloroethane (HFC 141c), 1,1,1,2-tetrafluoroethane (HFC 134a), 1,1-difluoro-1,2,2-trichloroethane (HFC 122) and others .

 Freon obtained in industry with the existing fluorination technology of the initial chlorine-containing compound contains halogen-containing aliphatic unsaturated (unsaturated) organic impurities and inorganic acids that degrade the quality of the target product.

 In the process of primary purification by rectification, it is possible to partially reduce the content of these impurities. However, it is not possible to achieve complete purification from acids and halogen-containing organic impurities and to obtain a marketable product that meets the requirements of TU.

 One of the possible methods of deep purification of chladones and obtaining the target product that meets the technical conditions is the adsorption method of purification.

In the patent of the Russian Federation N 2030379 with the date of publ. 03/10/95, which was chosen as a prototype, a method for purifying ethane freons from ethylene halogen derivatives was proposed, including adsorption of impurities while passing the purified freon through a fixed layer of carbon adsorbent having a maximum adsorption space volume of 0.5-0.9 cm ³ / g at a temperature not exceeding 323 K, at a mass velocity of not more than 0.3 mg / m ² • s, followed by complete desorption. During the cleaning process, adsorption of unsaturated impurities occurs. However, the efficiency of purification of freons by this method, in particular from unsaturated compounds, depends on the specific composition of the impurities, which have a mutual effect when separated by the adsorption method.

These impurities in various freons of the ethane series can be divided into three groups:
1 group of inorganic acids: hydrogen chloride and fluoride;
Group 2 halogen-containing organic impurities are more strongly sorbed than the target product. These include compounds having a greater number of chlorine atoms than in the molecule of the target product.

 Group 3 halogen-containing organic impurities having similar sorption properties with respect to the target product, these include, in particular, unsaturated compounds.

 For 1-fluoro-1,1-dichloroethane (freon 141c), the I group of impurities includes hydrogen chloride and fluoride, the 2 group 1,1,1-trichloroethane, and the 3 group 1,1-dichloroethylene and 1,1-difluoro -1-chloroethane.

 In 1,1-difluoro-1,2,2-trichloroethane (chladone 122), hydrogen chloride and fluoride are included in the 1st group of impurities, 1,2,2-trifluoro-1,2-dichloroethane in the 2nd group; 1,2-difluorotetrachloroethane, tetrachlorethylene and in the 3rd group - 1,2,2-trifluorotrichloroethane, 1,2-difluoro-2,2-dichloroethylene.

 In the presence of amounts commensurate with unsaturated compounds of amounts of more sorbed compounds of groups 1 and 2, the process of purification of the prototype from unsaturated halogenated compounds becomes impossible (see table 1).

 The objective of the invention is to develop a method for purification of ethanol-halogenated hydrocarbons from organic halogen-containing impurities and inorganic acids.

To solve this problem, raw ethanol-halogenated hydrocarbons containing all three groups of the above impurities are passed through a fixed bed of regenerated activated carbon with a total porosity of 0.70-0.9 cm ³ / g at a rate of 0.05-6 m ³ / m ² • hours As a result of the primary treatment of raw coal with the mixture, the mixture is freed from acidic impurities of the 1st group: hydrogen chloride and fluoride. Then the raw material is subjected to rectification to separate halogen-containing impurities of group 2. The absence of acidic impurities allows purification at 2 stages from impurities of group 2 and eliminates the resinification of halogen-containing organic compounds during their heat treatment at 2 stages. After that, the rectified product is passed through a layer of activated carbon obtained from peat by potassium sulphide activation with a total porosity of ≥ 0.70 cm ³ / g. The contact time of raw freon with coal in 3 stages is not less than 30 minutes. The absence of acidic impurities and compounds of the 2 group of impurities allows you to clean at the 3 stage of the target product from compounds of 3 groups, including unsaturated compounds.

 Thanks to this combination and sequence of operations, a marketable product is obtained that meets the technical requirements for quality.

 Example 1

 Purification of 1-fluoro-1,1-dichloroethane (Chl. 141c) was carried out in 3 stages. The composition of the products before cleaning and after is presented in table 1.

At stage 1, the purification was carried out on activated carbon AR-B. The length of the coal layer is 16 cm, the diameter of the column is 1.2 cm. The mass of coal is 7.1 g. The transmission rate (0.36 m ³ / m ² • h). The adsorption temperature is 20 ^o C. Purified from acidic impurities (1 group of impurities) 1-fluoro-1,1-dichloroethane was directed to rectification (2 stage). In the process of rectification, the target product was separated from 1,1,1-trichloroethane (2 group of impurities). Operating mode: pressure 0-1 kgf / cm ² , cube temperature 70-94 ^o C, column top temperature 31-54 ^o C. The vapor-gas mixture from the top of the column through the reflux condenser, cooled by brine with a temperature of minus 15 ^o C, condenses and passed through a layer of activated carbon SKT-2. The mass of coal is 24.62 g, the height of the coal layer is 47 cm, the diameter is 1.2 cm. The adsorption temperature is 20 ^o C. The transmission rate is 0.36 m ³ / m ² • h. Comparison of the cleaning efficiency of 1-fluoro-1,1-dichloroethane by the proposed method and prototype is presented in table 1.

 The purification results of 1,1-difluoro-1,2,2-trichloroethane are presented in example 2 and are summarized in table 2.

 It was experimentally established that the minimum permissible content of acidic products, not preventing the release of impurity compounds of groups 2 and 3 by the proposed method, is equal to 0.002 wt. as confirmed by examples 5 and 6, are given in table 1 and 2.

 Example 7 shows that the cleaning of the prototype with a content of acidic impurities of 0.002 wt. does not lead to the desired result.

 Example 2

Purification of 1,1-difluoro-1,2,2-trichloroethane (freon 122) was carried out similarly to the conditions of example 1. The length of the coal layer was 16 cm, the diameter of the column was 1.2 cm. The mass of coal was 7.1 g. Transmission rate 1.4 ml / min (0.84 m ³ / m ² • h). The adsorption temperature is 21 ^o C. The raw material purified from acidic impurities was sent for rectification. The obtained rectification was passed through a layer of activated carbon SKT. The mass of coal is 24.0 g, the height of the coal layer is 46.5 cm, the diameter is 1.2 cm. The adsorption temperature is 21 ^o C. The transmission rate is 1.4 ml / min. The compositions of the products before and after cleaning are presented in table.2.

 A comparative analysis of the methods of purification of raw freons shows that the proposed method of purification in comparison with the existing one provides purification from impurity halogen-containing aliphatic, unsaturated (unsaturated) and inorganic acids, and provides the target product that meets the technical requirements for the content of impurity components, as well as including the content of the main substance is not less than 99.5 wt.

 Example 3

Purification of 1,1-difluoro-1,2-2-trichloroethane was carried out similarly to the conditions of example 2. The composition of the products is presented in table.3. In contrast to example 2, the acid content is reduced to 0.002%
From table 3 it follows that when the content of acidic impurities of 0.002 weight. the latter reduce the degree of purification by halogen-containing organic impurities according to the method proposed by the prototype. Deterioration is due to the presence of both limiting and unsaturated organic compounds. Thus, the lower concentration limit of the work we offer the method can be taken equal to 0.002 weight.

It was found that the lower limit on the load of 0.05 m ³ / m ² • h is determined by the transition of the process of adsorption of hydrogen chloride and fluoride to the diffusion region, that is, the limiting (determining) stage of the process is the stage of diffusion of hydrogen chloride and fluoride to the surface of the adsorbent, while there is a sharp inhibition of the process as a whole. So at a load of 0.045 m ³ / m ² • h under conditions similar to examples 1 and 3, the content of hydrogen chloride and fluoride in total is 0.02 and 0.07 wt. accordingly, which makes it impossible to clean at subsequent stages, as shown in examples 3 and 4. At loads of 0.05 m ³ / m ² • h or more, such braking is not observed and the cleaning process proceeds according to its performance similarly to that described in examples 1 and 3.

The upper limit on the load is determined by technical and economic considerations, because at loads of more than 6 m ³ / m ² • h high resistance is observed in the adsorbent layer, which leads to excessive energy costs.

The experimentally established maximum capacity of the sorption space for hydrogen chloride and hydrogen fluoride is equal to 0.7 • 0.9 cm ³ / g (first stage).

The study of kinetic characteristics at 20 ^o C for the sorption of impurities belonging to the third group with an acid impurity content of not more than 0.002 wt. showed that the minimum adsorption time is the time corresponding to the contact time equal to the ratio of the sorbent volume to the volumetric feed rate of the components, not less than 20 minutes This means that with a shorter contact time, a breakdown of the adsorbed components is observed at the outlet of the adsorption layer.

Claims (1)

The method of purification of ethanol-halogenated hydrocarbons from organic halogen derivatives of impurities and inorganic acids, including adsorption of impurities by a carbon sorbent, characterized in that the product to be purified is passed through a carbon sorbent with a maximum volume of sorption space of 0.7 0.9 cm ³ / g at a rate of 0.05 6 m ³ / m ² • h, after which it is subjected to rectification, the obtained rectification is passed through sorbent carbon of potassium sulphide activation at a contact time of at least 20 minutes.

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