RU2039032C1 - Process for cleaning 1,1,1,2-tetrafluoroethane from unsaturated halogenated impurities - Google Patents

Abstract

FIELD: in the production of flurochlorosubstituted hydrocarbons. SUBSTANCE: R-134a is cleaned from unsaturated halogenated impurities (R-1113, R-1123, R-1243 and R-1225) by passing contaminated R-134a with the total amount of the impurities mentioned above of not greater than 10,000 ppm through a layer of carbon at 253-323 K at a pressure not greater than the pressure of saturated R-124a vapors at the given temperature. The specific flow rate of the gas being cleaned is not greater than 0,35 kg/(mm²·s). The total amount of impurities after the cleaning operation does not exceed 10 ppm. To make the process more efficient, before absorption begins R-134a which contains no impurities of unsaturated halogen hydrocarbons is passed through a layer or adsorbent. The absorbent is carbon of sulfur-potassium activation with an ultimate volume of sorption space of 0,50-0,80 cm³/g. The adsorbent is regenerated at 473 to 523 K and at a pressure of 2·10^-4 to 0.15 MPa. In this case, the absorbed products become completely desorbed. The number of sorption cycles is determined by mechanical strength of carbons. EFFECT: more efficient cleaning process. 2 tbl

Description

 The invention relates to the production of ethanol-halogenated hydrocarbons, in particular to methods for the purification of ozone-safe refrigerants.

 The purification process of 1,1,1,2-tetrafluoroethane (R-134a) is of significant interest due to the promise of its use as an ozone-safe refrigerant substitute for difluorodichloromethane (R-12).

 During the synthesis of R-134a by catalytic hydrofluorination of 1,1,1-trifluoroethane (R-133a) or trichlorethylene, a reaction mixture is formed containing, in addition to the target product, hydrogen fluoride and R-133a, also pentafluoroethane (R-125), 1,1, 1-trifluoroethane (R-143a), 1,1-difluoroethane (R-152a), 1,1,1,2-tetrafluorochloroethane (R-124a), significant amount of unsaturated compounds: trifluorochlorethylene (R-1113), 1,1 di-fluoro-2-chloroethylene (R-1122), trifluoroethylene (R-1123), 1,1,1-trifluoropropylene (R-1243), 1,1,1,3,3-pentafluoropropylene (R-1225) 1,1,1,2,3-pentafluoropropylene and a number of other products.

 During the initial purification of this mixture, the target product, R-134a, is separated from most impurities. However, at this stage of purification, impurities of unsaturated compounds cannot be completely removed from the reaction mixture. Due to the toxicity of the latter, the use of R-134a contaminated with them is not possible. Additional measures are required for the post-treatment of R-134a.

US Pat. No. 3,819,493 proposes a method for purifying R-134a by extractive distillation using C ₄ -C ₁₀ paraffins as a separating agent. However, this method requires complex hardware design and high energy costs. The method is ineffective when cleaning from the entire gamut of unsaturated impurities.

 Du Pont de Nemours (US application CH-1539) has proposed a method for oxidizing unsaturated impurities on hopcalite. This method is highly effective, however, its use is associated with irretrievable losses of the oxidizing agent and its high environmental hazard.

 Offered by Allied Signal Inc. US Pat. US N 4906796, the adsorption method of purification of R-134a is the absorption of 1,1-difluoro-2-chloroethylene (R-1122) by zeolites or carbon molecular sieves with an average pore size of 0.38-0.48 nm. Removal of R-1122 from R-134a occurs through the use of molecular sieve properties of the proposed adsorbents, selectively absorbing those components whose molecular size corresponds to or slightly less than the pore size of the adsorbent. Since the size of the molecules of R-1243 and R-1225 exceeds the average pore size of the proposed adsorbents, their removal from R-134a does not occur. Thus, this method cannot be applied to clean R-134a from R-1243, R-1225 and R-1113.

 In US Pat. EP 0389334 (Atochem, prototype) a method for purifying R-134a from R-1122 using a number of industrial activated carbons as an adsorbent is proposed. Due to the significantly greater proximity of the adsorption properties of a number of unsaturated compounds to R-134a compared to R-1122, the removal of the entire gamut of unsaturated halogenated impurities on most coals is ineffective. It is necessary to use special, highly efficient brands of coal, as well as increasing the efficiency of adsorption using additional measures.

The purification of R-134a from unsaturated halogenated impurities consists in passing contaminated R-134a with the content of the listed impurities up to 10,000 ppm through a fixed layer of activated carbon at a temperature of 253 to 323 K and a pressure not exceeding the saturated vapor pressure of R-134a at a given temperature. The specific consumption of the purified gas is not more than 0.35 kg / (m ² .s). In this case, selective adsorption of unsaturated halogenated impurities occurs, the total content of which in the purified freon does not exceed 10 ppm.

 To increase the efficiency of the adsorption process, R-134a, in which there are no impurities of unsaturated halogenated hydrocarbons, is passed through the adsorbent layer before it begins. This significantly increases the time of the protective effect of the adsorbent.

It is proposed to use potassium sulphide activation coals with a limiting volume of sorption space of 0.50-0.80 cm ³ / g as an adsorbent. Coals are characterized by developed micro- and mesoporosity. Before use, the adsorbent is subjected to heat treatment under vacuum or in a stream of inert gas until the adsorbed moisture is completely removed. The adsorbent is regenerated at a temperature of 473-523K and a pressure of 2˙10 ^-4 -0.15 MPa, while the complete desorption of the adsorbed products occurs. The number of sorption cycles is determined by the mechanical strength of the coals.

PRI me R 1. 100 g of pre-prepared coal grade SKT is placed in an adsorber with a diameter of 25 mm, made of stainless steel. Freon R-134a, containing impurities of pentafluoroethane (R-125), trifluoroethane (R-143a), trifluorochloroethane (R-133a), trifluoroethylene (R-1123), trifluorochloroethylene (R-1113), difluorochlorethylene (R-1122 ), trifluoropropylene (R-1243), pentafluoropropylene (R-1225), is passed through an adsorbent bed with a volume flow of 200 normal ml / min under the following conditions:
1 pressure 0.1 MPa, temperature 298 K;
2 pressure 0.1 MPa, temperature 263 K;
3 pressure 0.35 MPa, temperature 298 K.

 The outgoing gas stream is analyzed by gas chromatography on a packed column 6 m long and 2 mm in diameter, filled with silochrome (0.16-0.20 mm fraction) modified with potassium, at 296 K, using a flame ionization detector.

 The results of the experiment are given in table. 1 and 2.

 Analysis of the outgoing gas stream shows the absence of unsaturated halogenated hydrocarbons and a slight increase in the content of other products associated with the adsorption of R-134a itself and, possibly, with the catalytic disproportionation of this product in micro quantities.

 SKT coal almost completely sorb R-1123, R-1113, R-1122, R-1243 and R-1225 and does not sorb other impurity components.

 PRI me R 2. 100 g of pre-prepared coal grade SKT is placed in an adsorber with a diameter of 25 mm, made of stainless steel. Freon R-134a with a low content of possible impurities (see example 1, table. 1) is passed through an adsorbent bed with a volume flow of 200 norms. ml / min at atmospheric pressure and a temperature of 298 K for 3 hours. After 1.5 hours, the gas leaving the adsorber is analyzed. After completion of the adsorption, the amount of absorbed product is determined by the weight gain of the adsorbent.

 Desorption is carried out at atmospheric pressure and a temperature of 500 K for 3 hours, after which the amount of desorbed product is determined by the decrease in the weight of the adsorbent.

 The adsorption-desorption cycle is repeated as many times as necessary.

 The results are shown in table. 3.

 The experimental results show that long-term cyclic work leads to a deterioration in the adsorption properties of coal. The service life of the sorbent, therefore, is determined by its mechanical strength.

 PRI me R 3. Two identical adsorbers with a diameter of 25 mm and a height of 500 mm are filled with activated carbon SKT. At the input of the first adsorber, R-134a, contaminated with impurities, the composition and concentration of which is indicated in Example 1, table. 1, with a volume flow of 200 norms. ml / min The olefin-free R-134a is fed to the inlet of the second adsorber until the coal is completely saturated, and then the R-134a to be cleaned begins to be fed at the same rate as the first adsorber. The time of the protective action of the adsorbers is determined until the total olefin concentration 1ppm appears at the output.

 As a result of the experiment, it was found that the time of the protective action of the second adsorber is 155 minutes, which exceeds the time of the protective action of the first adsorber (99 minutes) by 1.6 times.

Claims (1)

METHOD FOR CLEANING 1,1,1,2-TETRAFLUOROETHANE FROM UNSATURATED HALOGENO-DERIVATED IMPURITIES, consisting in the adsorption of these impurities by a carbon adsorbent, characterized in that the product to be purified is passed through potassium sulphide activated sorbent activated carbon 1,1,1,2-tetrafluoroethane with a maximum volume of sorption space of 0.50 0.80 cm ³ / g in the temperature range of 253 323 K at a pressure of up to 1.3 MPa, with a gas flow rate of up to 0.35 kg / (m ² · s) with subsequent complete desorption.

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