1,1,1,3,3,3-hexafluoropropane purification with photochlorination equipment

Abstract

A continuous, vapor phase method for purifying a crude mixture of 1,1,1,3,3,3-hexafluoropropane and one or more unsaturated fluorocarbon compounds, the process comprising: a) providing a photochlorinator vessel comprising: 1) a UV lamp unit comprising a UV lamp located in a transparent inner well, the transparent inner well being located within a transparent outer well, the outer well being provided with material for cooling walls of the inner and outer wells; the inner well and the outer well defining separate chambers isolated from each other; and 2) a reaction vessel into which the UV lamp unit has been inserted; b) introducing into the reaction vessel a gaseous mixture of Cl2 and a distillation inseparable mixture of 1,1,1,3,3,3-hexafluoropropane and one or more unsaturated fluorocarbon compounds; c) reacting, in the gaseous state and in the presence of UV light from the photochlorinator, the mixture with Cl2 with the distillation inseparable mixture of 1,1,1,3,3,3-hexafluoropropane and one or more unsaturated compounds to saturate unsaturated fluorocarbons into a reacted mixture, and d) separating a purified 1,1,1,3,3,3-hexafluoropropane product containing less than 1000 ppm, most preferably less than 100 ppm unsaturated fluorocarbons.

Description

FIELD OF THE INVENTION [0001] This invention relates to a continuous, vapor phase process for purifying 1,1,1,3,3,3-hexafluoropropane (HFC-236fa) to a level of <1000 ppm, preferably <500 ppm, and more preferably <100 ppm, total unsaturates using a UV photochlorinator. BACKGROUND OF THE INVENTION [0002] Due to their stability, relatively low toxicity, compatibility with numerous substances, and low vaporization points, short chain fluorocarbons have been found to have utility or potential utility in industry for many purposes. Such short chain fluorocarbons (about 1 to about 5 carbon atoms) have, for example, been used as propellants, refrigerants, and solvents. [0003] It has been asserted that certain fluorocarbons, especially chlorofluorocarbons, unfortunately may be hazardous to the environment, especially to the ozone layer. Further, impurities in certain fluorocarbons have been found to be troublesome. Unsaturated fluorocarbons are especially undesirable since many of t...

AI Technical Summary

Benefits of technology

The invention provides a continuous, vapor phase method for purifying 1,1,1,3,3,3-hexafluoropropane from distillation inseparable mixtures of 1,1,1,3,3,3-hexafluoropropane and unsaturated fluorocarbon compounds. The method involves reacting the mixture with chlorine in the presence of UV light to saturate the unsaturated fluorocarbons, and then separating the purified 1,1,1,3,3,3-hexafluoropropane product containing less than 1000 ppm, preferably less than 500 ppm, and more preferably less than 100 ppm unsaturated fluorocarbons. The method can also include steps to remove residual HCl and chlorine from the 1,1,1,3,3,3-hexafluoropropane.

Problems solved by technology

It has been asserted that certain fluorocarbons, especially chlorofluorocarbons, unfortunately may be hazardous to the environment, especially to the ozone layer.

Further, impurities in certain fluorocarbons have been found to be troublesome.

Unsaturated fluorocarbons are especially undesirable since many of them are toxic and are also often unstable.

Such unstable unsaturated fluorocarbons can decompose into even more undesirable products which can be corrosive.

Unfortunately, the outcome of such a chlorination technique is not predictable from one fluorocarbon to another, especially when hydrogen is present in the fluorocarbon being purified.

This is because hydrogen is frequently replaced by chlorine which reduces yield of the desired product and results in yet further impurities.

1,1,1,3,3,3-hexafluoropropane might be an excellent replacement for CFC-114, except that pure 1,1,1,3,3,3-hexafluoropropane has not been obtainable by known methods of preparation.

This due to the fact that most known methods for the preparation of 1,1,1,3,3,3-hexafluoropropane result in residual impurities of other fluorocarbons.

Unfortunately, some of the fluorocarbon impurities form low boiling azeotropes with 1,1,1,3,3,3-hexafluoropropane or are close boiling with 1,1,1,3,3,3-hexafluoropropane, which prevents separation by conventional distillation methods (“distillation inseparable mixtures”).

This is especially troublesome since some of the impurities which form azeotropes or close boiling mixtures are unsaturated and cannot be tolerated to any significant extent in refrigerants in certain applications.

However, the patents do not disclose any specific UV photochlorination equipment suitable for use in accomplishing the objective of those patents, nor do patents disclose any photochlorination reaction equipment suitable for conducting the purification reaction in a continuous and vapor phase reaction while still being able to obtain a purified HFC-236fa product containing <100 ppm fluorocarbon unsaturates.

Images