RU2088563C1 - Method of refining 1,1,1,2-tetrafluoroethane from unsaturated halogen-containing impurity - Google Patents

Abstract

FIELD: chemical technology. SUBSTANCE: method involves passing the crude 1,1,1,2-tetrafluoroethane through the layer of dehydrated solid oxidizer that is copper or nickel chromites of the formula Me₂Cr₂O₅ where: Me - copper or nickel at heating. After oxidation of unsaturated compounds their content in 1,1,1,2-tetrafluoroethane is decreased to less 10 ppm Process is carried out to breakthrough olefin concentration appearance at outlet and then oxidizing agent is regenerated with the dried oxygen-containing gaseous mixtures at heating. EFFECT: improved method of refining, enhanced quality of product. 3 cl, 1 tbl

Description

 The invention relates to the field of production of 1,1,1,2-tetrafluoroethane, in particular, to a method for purifying this product from unsaturated halogen-containing impurities associated with 1,1,1,2-tetrafluoroethane during synthesis.

 1,1,1,2-tetrafluoroethane (freon 134a) is a low-toxic ozone-safe product and is used as a refrigerant, propellant, blowing agent, as well as for the production of other halogenated products. 1,1,1,2-tetrafluoroethane is of great interest as a substitute for difluorodichloromethane (HFC 12).

 However, in the process of synthesis of 1,1,1,2-tetrafluoroethane, along with the target product, a number of by-products, both saturated and unsaturated, are formed. Most unsaturated foods are highly toxic and should therefore be reduced to 10ppm or lower. Rectification and other traditional purification methods that can be used to remove them to the required level are in some cases ineffective or too expensive.

 Accordingly, various methods have been proposed for deep cleaning purposes.

Bell [1] found that the content of 1,1-difluoro-2-chloro-ethylene CF ₂ = CHCl in 1,1,1,2-tetrafluoroethane can be reduced by passing the contaminated product through an aqueous solution of alkali metal permanganate at 10 40 ^o C. However, this method does not meet industrial requirements, since the treatment with aqueous solutions of alkali metal permanganates requires a stage of subsequent drying of the product and is associated with its additional losses, which significantly increases the cost of this method.

 A method [2] of adsorption purification of 1,1,1,2-tetrafluoroethane on a carbon adsorbent is proposed, during which selective absorption of unsaturated impurities occurs. The adsorption absorption of unsaturated impurities by a carbon adsorbent is effective for halogen derivatives of ethylene, and for halogen-substituted propylene the protective characteristics of the carbon adsorbent are not high enough, which leads to a low efficiency of the process of purification from the entire gamut of impurities.

Fernandez [3] (prototype) proposes a method of reducing unsaturated impurities in saturated halocarbons and halocarbons by passing a contaminated dried saturated product through a dehydrated composition of amorphous solid metal oxides, consisting mainly of copper oxide, silver oxide, cobalt oxide and manganese dioxide or a mixture of any two or more components, at effective temperatures up to 300 ^o C.

 However, when using the above compositions of metal oxides, unsaturated halogen-containing impurities, reacting with the surface of the oxidizing agent, are destroyed mainly until the formation of carbon dioxide (example 1 of the prototype, p. 8), detected in the output stream, and hydrogen halides irreversibly interacting with the surface of the oxidizing agent ( are not detected in the output stream), which prevents the reuse of these compositions in the cleaning process.

 The task is to create an effective method for deep purification of 1,1,1,2-tetrafluoroethane from unsaturated halogen-containing impurities, allowing multiple use of an absorber of unsaturated impurities.

It is established that the goal is achieved by using an oxidizing agent of unsaturated halogen-containing impurities as the absorber, the active part of which is chromite or gross chromite of the formula Me ₂ Cr ₂ O ₅ , where Me is copper or nickel.

The essence of the proposed method is as follows: dried 1,1,1,2-tetrafluoroethane containing one or more unsaturated impurities is passed through a fixed layer of a dehydrated solid oxidizer, the active part of which is chromite copper or nickel gross formula Me ₂ Cr ₂ O ₅ , where Me is copper or nickel when heated. During the cleaning process, unsaturated compounds are oxidized, as a result of which their total concentration decreases to less than 10 ppm. At temperatures of 250 ^° C. and below, no reactions of 1,1,1,2-tetrafluoroethane with the oxidizing surface occur.

 In the process, the surface of the solid oxidizer is depleted of chemically bound oxygen, and to restore its activity, regeneration is carried out, which consists in passing the dried oxygen-containing gas mixtures through the layers of the oxidizer when heated.

 It was found that the oxidizing agent does not change its activity during 10 cycles of operation.

 A comparative analysis of our proposed method and the method proposed [3] is given in the table.

Example 1. 1,1,1,2-tetrafluoroethane containing 407 ppm unsaturated compounds (150 ppm 1,1-difluoro-2-chloroethylene C ₂ F ₂ HCl, 107 ppm C ₃ F ₅ H and 150 ppm C ₃ F ₃ H ₃ ) pass through 27 g of an oxidizing agent with a grain size of 2 to 4 mm, placed in a glass tube with a diameter of 23 mm, equipped with electric heating, with a speed of 160 170 ml / min at a temperature of 200 ^o C.

An oxidizing agent containing 74.7% Ni ₂ Cr ₂ O ₅ and 25.3% Al ₂ O ₃ is prepared as follows: 301.4 g of nickel chromite Ni ₂ Cr ₂ O ₅ are mixed with 156 g of aluminum trihydrate AL (OH) ₃ , calcined at a temperature of 300 ^o C for 3 hours and molded into granules.

 The analysis of the output stream was carried out in a gas-liquid chromatograph on a capillary column having a detection threshold of the indicated unsaturated compounds of 0.5 ppm each. For 155 minutes no unsaturated compounds were observed in the outlet stream.

The capacity of the oxidizing agent at this temperature was 0.0015 g of unsaturated compounds per 1 cm ^{3 of} oxidizing agent.

Example 2. 1,1,1,2-tetrafluoroethane containing 480 ppm of unsaturated impurities (160 ppm C ₂ F ₂ HCl, 160 ppm C ₃ F ₅ H, 160 ppm C ₃ F ₃ H ₃ ) was passed through 29 g of oxidizing agent of size grain from 2 to 4 mm, placed in a glass tube with a diameter of 23 mm, equipped with electric heating, with a speed of 160 170 ml / min at a temperature of 200 and 250 ^o C.

An oxidizing agent containing 75.3% Cu ₂ Cr ₂ O ₅ and 24.7% Al ₂ O ₃ is prepared as follows: 775 g of copper chromite Cu ₂ Cr ₂ O _{5 is} mixed with 390 g of aluminum trihydrate Al (OH) ₃ , calcined at a temperature of 300 ^o C for 3 hours and formed into granules.

 The output stream is analyzed as described in example 1.

At a temperature of 200 ^o C for 140 min in the output stream was not observed the presence of unsaturated compounds, while the capacity of the oxidizing agent was 0.0013 g of unsaturated compounds per 1 cm ³ .

At a temperature of 250 ^° C. for 315 minutes no unsaturated impurities were observed in the outlet stream, while the oxidizer capacity was 0.0038 g of unsaturated compounds per 1 cm ^{3 of} oxidizing agent.

Example 3. Through a glass tube with a diameter of 23 mm, equipped with electric heating, filled with 46.5 g of a sample of copper chromite prepared according to the method described in example 2, 1,1,1,2-tetrafluoroethane containing 750 ppm of unsaturated impurities was passed (160 ppm C ₂ F ₂ HCl, 250 ppm C ₃ F ₃ H ₃ and 340 ppm C ₃ F ₅ H) at a rate of 300 - 310 ml / min at a temperature of 250 ^o C.

The output stream was analyzed as described in Example 1. After 136 minutes from the passage of the above mixture, 4 ppm unsaturated impurities were detected in the output stream. The capacity of the oxidizing agent was 0.0031 g of unsaturated compounds per 1 cm ^{3 of} oxidizing agent.

The transmission of 1,1,1,2-tetrafluoroethane contaminated with olefins when breakthrough concentrations appeared was stopped, and dried air was passed through an oxidizing tube at a flow rate of 300 ml / min at 350 ^° C for 2 hours.

Then the tube with the oxidizer sample was evacuated to a pressure of 2 • 10 ^-3 MPa.

 As a result of the operations carried out, the oxidizing agent restores its activity at the previous level, as evidenced by experiments conducted repeatedly on the same sample of the oxidizing agent.

When carrying out 10 cycles of “oxidation of olefins, the restoration of the activity of the oxidizing agent”, the capacity of the sample of the oxidizing agent remained unchanged and amounted to 0.0031 + 0.0001 g of unsaturated compounds per 1 cm ^{3 of} oxidizing agent.

Claims (3)

1. The method of purification of 1,1,1,2-tetrafluoroethane from unsaturated halogen-containing impurities by passing the initial dried 1,1,1,2-tetrafluoroethane through a layer of anhydrous solid metal-containing oxidizing agent by heating, characterized in that chromite of the formula is used as an oxidizing agent
Me ₂ Cr ₂ O ₅ ,
where Me is copper or nickel,
and transmission of the starting 1,1,1,2-tetrafluoroethane is carried out to a breakthrough olefin concentration, after which the solid oxidizer is subjected to regeneration by an oxygen-containing gas mixture when heated. 2. The method according to claim 1, characterized in that the process is carried out at 200 ^o With the use of nickel chromite and at 250 ^o With the use of copper chromite, respectively. 3. The method according to claim 1, characterized in that the regeneration of the spent oxidizing agent is carried out with an oxygen-containing gas mixture at 350 ^o C.

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