PROCESS FOR PURIFICATION OF 2,2,3,3-TETRAFLUOROOXETANE

Abstract: A process for purifying 2,2,3,3-tetrafluorooxetane which contains at least one impurity compound selected from the group consisting of hydrogen fluoride and trifluoropropionylfluoride, which process comprises contacting 2,2,3,3-tetrafluorooxetane with at least one adsorbent selected from the group consisting of silica gel and alumina and causing said impurity to be adsorbed on said particles to remove it from 2,2,3,3-tetrafluorooxetane.

Description: The present invention relates to a process for purification of a mixture comprising 2,2,3,3-tetrafluorooxetane (hereinafter referred to as "tetrafluorooxetane"). Particularly, the present invention relates to a process for purification of tetrafluorooxetane containing hydrogen fluoride and/or trifluoropropionylfluoride, especially in a small amount. Tetrafluorooxetane is useful as a solvent or a raw material in the production of linear ethers, and can be commercially produced through a reaction of tetrafluoroethylene and paraformaldehyde in anhydrous hydrogen fluoride. The product produced through the above reaction should be purified since it contains not only tetrafluorooxetane but also, as impurities, hydrogen fluoride and trifluoropropionylfluoride. In order to purify such product to obtain tetrafluorooxetane without impurities, a distillation process may be generally employed. However, in view of the fact that hydrogen fluoride has the boiling point of 20 °C, trifluoropropionylfluoride has the boiling point of 27 °C, and tetrafluorooxetane has the boiling point of 28 °C, it is very difficult to remove hydrogen fluoride and trifluoropropionylfluoride from tetrafluorooxetane with a distillation process. In particular, when amounts of hydrogen fluoride and/or trifluoropropionylfluoride are very small, for example when the amount thereof is from 500 to 1000 ppm, it becomes more difficult to remove these impurities from tetrafluorooxetane. In order to overcome the problem described above, it is proposed to remove hydrogen fluoride in the reaction product by neutralizing it with aqueous ammonia. However, with the proposed process, additional problems arise in operations of separation and drying after neutralization. Therefore, it is difficult to adopt such the proposed process in commercial scale. It is, therefore, an object of the present invention to provide a novel process for purification of a mixture comprising tetrafluorooxetane with overcoming the problems described above. According to the present invention, there is provided a process for purification of tetrafluorooxetane which contains at least one impurity compound selected from hydrogen fluoride and trifluoropropionylfluoride, especially in a small amount thereof, which process comprises contacting continuously said tetrafluorooxetane with at least one adsorbent selected from silica gel and alumina, whereby said impurity compound is adsorbed on the adsorbent and in turn tetrafluorooxetane is purified. In one preferred embodiment of the the present invention, the process comprises forming tetrafluorooxetane, which contains, as an impurity, a small amount of hydrogen fluoride and/or trifluoropropionylfluoride, for example in the order of a few hundreds or thousands of ppm, such as in an amount of from 500 to 1000 ppm each, into a gaseous form, and then contacting it continuously with at least one adsorbent selected from the group consisting of silica gel and alumina, whereby the impurity compound is adsorbed on the adsorbent and removed it from tetrafluorooxetane. The temperature at which tetrafluorooxetane containing the impurity compound is formed into the gaseous form is higher than the boiling point of the system to be purified and it is preferably not lower than 30 °C. However, it is not suitable to form the mixture into the gaseous form at a temperature higher than 100 °C since tetrafluorooxetane is decomposed at such a high temperature. Therefore, it is preferred to form the mixture to be purified into the gaseous form in the temperature range between 30 and 70 °C. In addition, the process according to the present invention may be applied to any system in which a mixture is present comprising tetrafluorooxetane as one of main components. One example of such a mixture is one containing tetrafluorooxetane and 1,1,2-trichloro-1,2,2-trifluoroethane, for example, in a weight ratio of 85:15. When such the mixture is purified with the process of the present invention, it is also possible to obtain the similar result to cases wherein tetrafluorooxetane containing a small amount of the impurities is purified according to the present invention. The silica gel or alumina used as the adsorbent in the process of the present invention may be any one which is commercially available. Adsorbent particles having a mean diameter of from 4 to 8 mm and a void on filling of from 50 to 60 % are most preferable. The relation between the amount of tetrafluorooxetane to be treated and that of the adsorbent particles may be determined depending on the amounts of impurities contained in tetrafluorooxetane, the characteristics of the adsorbent and the adsorbing apparatus and so on. For example, when an adsorption column of 35 cm in diameter filled with the particles of silica gel or alumina, of which mean diameter is from 4 to 8 mm and void on filling is from 50 to 60 %, is used with an effective filling height of from 380 to 450 cm, gaseous tetrafluorooxetane containing hydrogen fluoride of from 100 to 500 ppm and trifluoropropionylfluoride of from 500 to 1000 ppm can be treated at a rate of from 10 to 20 l/hr, whereby, as an effluent, tetrafluorooxetane containing impurities of less than 10 ppm is obtained. Example 1 A column of 35 cm in diameter was filled with particles of silica gel to form a adsorption column with an effective filling height of 400 cm. A mean diameter of the silica gel was 6 mm and a void on filling was 60 %. Under a pressure of 0.8 kg/cm²G, a mixture of tetrafluorooxetane and 1,1,2-trichloro-1,2,2-trifluoroethane in the weight ratio of 85:15 containing, as impurity compounds, 500 ppm of hydrogen fluoride and 1000 ppm of trifluoropropionylfluoride was supplied to the adsorption column to remove the impurities. The mixture was preheated to 50-70 °C and supplied continuously in the gaseous form into the adsorption column which had been preheated to 50-70 °C at a rate of 20 l/hr for 170 hours. During the above absorption operation, the effluent mixture of tetrafluorooxetane and 1,1,2-trichloro-1,2,2-trifluoroethane from the column contained constantly hydrogen fluoride and tetrafluorooxetane in an amount of less than 10 ppm respectively. An yield of tetrafluorooxetane was 98 % by weight. Example 2 The same mixture as used in Example 1 was purified with the same apparatus under the same conditions as described in Example 1 except that particles of alumina were used in place of the silica gel particles. The particles of alumina had a mean diameter of 6 mm, and a void on filling was 60 %. In this example, during the operation, the effluent mixture from the adsorption column contained constantly hydrogen fluoride and trifluoropropionylfluoride in an amount of less than 10 ppm respectively. An yield of tetrafluorooxetane was 98 % by weight.

Claims: 1. A process for purifying 2,2,3,3-tetrafluorooxetane which contains at least one impurity compound selected from hydrogen fluoride and trifluoropropionylfluoride, which process comprises contacting 2,2,3,3-tetrafluorooxetane with at least one adsorbent selected from silica gel and alumina and causing said impurity to be adsorbed on said adsorbent to remove it from 2,2,3,3-tetrafluorooxetane. 2. The process according to claim 1, which further comprises forming 2,2,3,3-tetrafluorooxetane into a gaseous form before the contacting it with said adsorbent. 3. The process according to claim 1, in which 2,2,3,3-tetrafluorooxetane before treatment contains hydrogen fluoride and trifluoropropionylfluoride in an amount of from 500 to 1000 ppm respectively. 4. The process according to claim 2, in which the 2,2,3,3-tetrafluorooxetane is formed into the gaseous form at 30-70 °C. 5. The process according to claim 1, in which said adsorbent has a mean diameter of from 4 to 8 mm and a void on filling is from 50 to 60 %.

Inventors: OHSAKA, YOHNOSUKE, Takaki, Shoji
Applicants: DAIKIN INDUSTRIES, LIMITED
Application year: 1989
Main classification: C07D305
IPC codes: C07D305