Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Patent
1997-01-28
1998-12-22
Siegel, Alan
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
570177, 570179, 570180, 570176, C07C 1738, C07C 1908
Patent
active
058522239
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/JP95/01488 filed Jul. 25, 1995.
Industrial Fields Where the Invention can be Utilized
This invention relates to purification methods of pentafluoroethane (also referred to as HFC-125), specifically to a method of purification of HFC-125 from a mixture composed of HFC-125 which contains at least chloropentafluoroethane (also referred to as CFC-115) as a component (that is, an unpurified mixture which contains at least CFC-115 and HFC-125).
Conventional Technologies
HFC-125 is a chlorine-free compound and is a useful alternative to flon (chlorofluorocarbons and hydrochlorofluorocarbons). It is used as a refrigerant, a blowing agent and a propellant.
As a method of producing the HFC-125, a method of fluorinating tetrachloroethylene is considered effective.
In this production method, however, CFC-115 is formed as a by-product. Since the boiling point of CFC-115 is -38.7.degree. C., and close to that of the desired product, HFC-125, -48.5.degree. C., and since the relative volatility of CFC-115 to HFC-125 is near 1, it is difficult to separate them by a distillation method.
Thus, it is necessary to remove CFC-115 by another method. One of such method is to remove CFC-115 by converting it to another compound by a reduction.
Such a reduction of CFC-115 is a known reaction. For example, Jap. Unexamined Pat. Publication Nos. 258632/89 and 29941/92, WO 91/05752 and EP 506525 disclose methods of reducing CFC-115 by hydrogen while using mainly noble metals as catalysts. Furthermore, in WO 94/02439, a method of removing CFC-115 by converting it to HFC-125 through hydrogen reduction of HFC-125 which contains CFC-115 at temperatures between 380.degree. C. and 500.degree. C. in the gas phase (that is, the hydrogen reduction of CFC-115), has been disclosed.
However, in such a hydrogen reduction reaction of CFC-115, the amounts of hydrogen generally used is greater than that of CFC-115. In particular, when HFC-125 which contains CFC-115 is reduced (by the method given in WO 94/02439), the amount of hydrogen greatly exceeds that of CFC-115. Hydrogen is very expensive, and the large amount of hydrogen required in the reduction process increases the cost of obtaining the desired product.
Development of the Invention
To resolve the above-mentioned problem, the re-use of hydrogen was considered. Extensive studies of the re-use by the inventors revealed, however, that recycling gas obtained after removal of HFC-125 after reduction reaction reduces reactivity considerably. This necessitates longer reaction times or higher temperatures to sustain reaction with CFC-115 until the target concentration is reached.
At the same time, if the reaction temperature is raised, the amount of multi-reduced products such as R-134a (1,1,1,2-tetrafluoroethane) or R-143a (1,1,1-trifluoroethane) increases when CFC-115 is reduced, resulting in lower yields of HFC-125. If the reaction time is made longer, both the quantity of catalyst and the volume of the reaction vessel increase, resulting in increased costs for catalysts and equipment.
Purpose of the Invention
The purpose of the invention is to provide a purification method for HFC-125, wherein CFC-115 can be exterminated (or removed) cheaply and efficiently without lowering the reactivity (or activity) on recycling hydrogen to produce HFC-125 in high yield, when HFC-125 containing CFC-115 is reduced with hydrogen in the gas phase.
The Structure of the Invention
As a result of intensive studies on the recycle of gas following reduction in the above-mentioned hydrogen reduction, the inventors found that because of the presence of hydrogen chloride which is produced as a by-product during the reduction of CFC-115 in the recycle gas, it's reactivity falls sharply.
The adverse effect of hydrogen chloride was found not to be caused by an equilibrium reaction. (Therefore, even if hydrogen chloride reacts with HFC-125 under the same conditions, CFC-115 will not be produced.) Rather, it is a catalyst poison of reduction catalysts or an obstruction due to adsorption on CFC-1
Kohno Satoru
Shibanuma Takashi
Daikin Industries Ltd.
Siegel Alan
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