Fluorocarbon purification process

Details Fluorocarbon purification process Fluorocarbon purification process

1995-08-11

2001-08-28

Siegel, Alan (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Halogen containing

C570S168000, C570S178000

Reexamination Certificate

active

06281396

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a process for the purification of fluorocarbons and the recovery of hydrogen fluoride used in their manufacture.
In many processes for making fluorocarbons in order to obtain an adequate degree of conversion of the starting halocarbon, it is necessary to employ an excess of hydrogen fluoride. It is highly desirable for economic reasons to recover this excess hydrogen fluoride, e.g., so it can be recycled.
Many processes have been developed for this purpose. However, since some of the hydrogen fluoride may be combined with the product as an azeotrope or be present in a slight excess to the product, in many cases it is difficult to remove. Neutralization of such hydrogen fluoride leads to waste disposal problems and environmental concerns. More complicated methods of separation lead to additional capital investment because hydrogen fluoride is a hazardous and difficult to handle material.
Furthermore, the recovery of the hydrogen fluoride is complicated by the unsaturated compounds which may also be present as impurities. These materials are particularly undesirable as contaminants as they may be toxic and for most uses their concentrations in the saturated products must be lowered to as low a level as is practically possible. Distillation and other conventional physical methods which may be used to lower the concentrations of unsaturated products are generally ineffective if the boiling points are too close, and are generally too costly. Therefore, various chemical treatments have been proposed.
None of these prior processes is entirely satisfactory from a commercial viewpoint. The aqueous alkaline metal permanganate treatments of the art require that the halocarbon products exiting the treatment medium be dried (separated from its entrained water) before further refining, which adds to the expense of the treatment. Moreover, where saturated halohydrocarbon products are being treated, the possibility exists that some of the valuable saturated material could be lost to the alkaline oxidative medium along with the unsaturated impurities.
Thus, an effective process must not only recover the combined hydrogen fluoride but must also take care of any unsaturated impurities present.
The process of the invention efficiently utilizes the combined hydrogen fluoride by reacting it with additional starting material or any other suitable halocarbon or halo-olefin and also with the olefin which is in the reaction product that is to be treated.
SUMMARY OF THE INVENTION
This invention provides for a process for the reduction of the hydrogen fluoride content of a halocarbon product made from the reaction of hydrogen fluoride with a halocarbon by reacting the excess hydrogen fluoride, which is substantially combined as an azeotrope, with additional halocarbon or halo-olefin, over a fluorination catalyst under fluorination conditions. The halocarbon product containing the hydrogen fluoride may also contain olefinic impurities which are converted to saturated compounds during the fluorination.
DETAIL OF THE INVENTION
The invention may be applied to the reduction of the hydrogen fluoride content of saturated halocarbon products and mixtures thereof, prepared by reaction with hydrogen fluoride and which contain one or more fluorine atoms in the molecule, and if they contain more than one carbon atom may be contaminated with olefinic impurities. Included are chlorofluoro- and fluorohydrocarbons composed of: carbon, hydrogen, chlorine and fluorine, and carbon, hydrogen and fluorine. The saturated halocarbons and/or mixtures thereof preferably contain 1 to 6 carbon atoms, more preferably 1 to 3, most preferably 1 to 2 because of their greater commercial importance.
The saturated halocarbons and/or mixtures thereof include cyclic as well as acyclic compounds represented by the empirical formula C
a
H
b
Cl
c
F
d
where a is an integer from 1 to 6, b, c and d are integers from 1 to 13, provided that b+c+d equals 2a+2 when the compound is acyclic and equals 2a when the compound is cyclic.
In a preferred embodiment the halocarbons are acyclic chlorofluorohydrocarbons, represented by the above empirical formula where a is 1 to 3, b and c are 1 to 7 and is 1 to 7.
In another preferred embodiment the halocarbons are acyclic fluorohydrocarbons represented by the above empirical formula where a is 1 to 3, b is 1 to 7, c is 0, and d is 1 to 7, and b+d equals 4 when a equals 1, equals 6 when a equals 2, and equals 8 when a equals 3.
Representative saturated halocarbons that can be treated in accordance with the method of the invention include chlorofluorohydrocarbons such as CHClF
2
, CF
3
CHCl
2
and CF
3
CHClF; and fluorohydrocarbons such as CHF
2
CHF
2
and CF
3
CH
2
F.
The above saturated halocarbons are produced by processes that result in the product containing excess hydrogen fluoride, usually combined as an azeotrope. The composition of this azeotrope will vary depending on the product halocarbon. In some embodiments, if the excess hydrogen fluoride is not all combined to form an azeotrope, the product mixture can first be subjected to a conventional separation process to remove the uncombined hydrogen fluoride and other easily separated material. In other embodiments, the product mixture will contain unsaturated impurities. By easily separated materials is meant materials having boiling points sufficiently far apart to make an economic separation feasible, e.g., distillation.
As set forth above, the product mixture contains the excess hydrogen fluoride as an azeotrope. This is an azeotrope of hydrogen fluoride with the halocarbon of the formula C
a
H
b
Cl
c
F
d
where a, b, c and d are as previously defined.
The product mixture after separation of its easily separated components, is then fed into a reactor where it is contacted with additional halocarbon under fluorinating conditions in the presence of a fluorination catalyst.
The additional halocarbon which is reacted with the excess hydrogen fluoride azeotrope can be represented by the empirical formula C
a
H
b
Cl
c
F
d
where a is an integer from 1 to 6, b and a are integers from 0 to 13, and a is an integer from 1 to 13, provided that b+c+d equals 2a+2 when the compound is acyclic and equals 2a when the compound is cyclic.
The additional halo-olefin which is reacted with the excess hydrogen fluoride azeotrope can be represented by the empirical formula C
a
H
b
Cl
c
F
d
where a is an integer from 2 to 6, b and d are integers from 0 to 11, and c is an integer from 1 to 11, provided that b+c+d equals 2a when the compound is acyclic and equals 2a−2 when the compound is cyclic.
Conventional fluorination catalysts and conditions can be used in the process of the invention.
The catalytic systems needed to effect the reaction of the product halocarbon/hydrogen fluoride mixture with an additional halocarbon can employ both vapor and liquid phase approaches. Examples of vapor phase catalysts and procedures for their use in fluorination reactions are described in U.S. Pat. Nos. 4,766,260, 3,258,500, and in the references cited therein. Examples of liquid phase catalysts and procedures for their use in fluorination reactions are described in U.S. Pat. Nos. 4,374,289, 4,258,225, and in the references cited therein.
The reaction vessel is constructed from materials which are resistant to the action of hydrogen halide such as Hastelloy® nickel alloy or Inconel® nickel alloy.
The purified halocarbons are useful as refrigerants, blowing agents and solvents.
A process is provided in accordance with this invention for the reduction of the hydrogen fluoride content of fluorocarbons by reacting excess hydrogen fluoride with a halocarbon comprising: (a) feeding a halocarbon product mixture containing an azeotrope of hydrogen fluoride with at least one compound of the formula C
a
H
b
Cl
c
F
d
, where a is 1 to 6, b is 1 to 13, c is 1 to 13 and d is 1 to 13, provided that b+c+d equals 2a+2 when the compound is acyclic and 2a when it is cyclic, into a reac

Affiliated with

Also associated with

Rating

Fluorocarbon purification process does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Fluorocarbon purification process, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fluorocarbon purification process will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2513732