Catalytic manufacture of vinyl fluoride

Details Catalytic manufacture of vinyl fluoride Catalytic manufacture of vinyl fluoride

1999-05-18

2001-07-17

Siegel, Alan (Department: 1621)

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

Organic compounds

Halogen containing

C570S156000

Reexamination Certificate

active

06262321

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to processes for the production of vinyl fluoride, and more particularly, to catalysts and to a catalytic process for the dehydrofluorination of 1,1-difluoroethane to vinyl fluoride.
BACKGROUND
Vinyl fluoride is a useful monomer for the preparation of fluorocarbon polymers which have excellent weathering and chemical resistance properties.
Vinyl fluoride can be produced from acetylene and hydrogen fluoride using mercury catalysts. It can also be produced by the dehydrofluorination of 1,1-difluoroethane. The dehydrofluorination of 1,1-difluoroethane to vinyl fluoride and hydrogen fluoride is an equilibrium reaction. According to published literature the following equilibrium concentrations of vinyl fluoride (VF), based on the moles of VF divided by the moles of HFC-152a +VF, have been determined; about 13% VF at 227° C., about 40% VF at 327° C. and about 99% VF at 427° C.
U.S. Pat. No. 2.599,631 discloses a process for the manufacture of vinyl fluoride by the dehydrofluorination of HFC-152a The dehydrofluorination is done in the presence or absence of a catalyst. The dehydrofluorination catalysts disclosed include oxygen, charcoal, and the free metals, salts and oxides of the elements of Groups IA, IB, IIA, IIB, VB and VIII of the periodic table. In an example using the divalent Group II metal compound calcium fluoride as a catalyst (at about 500° C.), the conversion of HFC-1 52a to vinyl fluoride was 66% (i.e., about 66% of equilibrium). There is an ongoing interest in developing more efficient catalysts for the conversion of HFC- 152a to VF.
SUMMARY OF THE INVENTION
A process is provided for the manufacture of vinyl fluoride (i.e., CH
2
═CHF, VF or 1141) from 1,1-difluoroethane (i.e., CH
3
CHF
2
, F152a or HFC-152a) which comprises contacting said, 1,1-difluoroethane at an elevated temperature with a catalyst containing at least one divalent Group II metal compound. The process of this invention is characterized by contacting said 1,1-difluoroethane at a temperature of from about 200° C. to 400° C. with a catalyst containing (a) at least one compound selected from the oxides, fluorides and oxyfluorides of magnesium, zinc and mixtures of magnesium and zinc, and optionally (b) at least one compound selected from the oxides, fluorides and oxyfluorides of aluminum; provided that the atomic ratio of any metals other than magnesium and zinc (e.g., aluminum) in total, to the total of magnesium and zinc in said catalyst is about 1:4. or less (e.g., 1:9).
DETAILED DISCUSSION
The present invention provides a process for the manufacture of vinyl fluoride by contacting 1,1-difluoroethane in the vapor phase in the presence of catalysts selected from the group consisting of oxides, fluorides and oxyfluorides of magnesium, zinc and mixtures of magnesium and zinc. The catalysts may also contain metals other than magnesium and/or zinc provided that the atomic ratio of metals other than magnesium and zinc to the total of magnesium and zinc is about 1:4, or less. Of note are embodiments which contain in addition to the oxides, fluorides and/or oxyfluorides of magnesium and zinc, at least one compound selected from the oxides, fluorides and oxyfluorides of aluminum; provided that the atomic ratio of aluminum to the total of magnesium and zinc in said catalyst is about 1:4, or less (e.g., about 1:9). Preferred catalysts include catalysts consisting essentially of magnesium fluoride, and catalysts consisting essentially of magnesium fluoride and at least one compound selected from the oxides, fluorides and oxyfluorides of aluminum.
A suitable catalyst may be prepared, for example, as follows:
Magnesium oxide is dried until essentially all water is removed, e.g., for about 18 hours at about 100° C. The dried material is then transferred to the reactor to be used. The temperature is then gradually increased to about 400° C. while maintaining a flow of nitrogen through the reactor to remove any remaining traces of moisture from the magnesium oxide and the reactor. The temperature is then lowered to about 200° C. and a fluoriding agent such as HF or other vaporizable fluorine containing compounds such as SF
4
, CCl
3
F, CCl
2
F
2
, CHF
3
or CCl
2
FCClF
2
, diluted with nitrogen is passed through the reactor. The nitrogen can be gradually reduced until only HF or other vaporizable fluorine containing compounds is being passed through the reactor. At this point the temperature can be increased to about 450° C. and held at that temperature for a time sufficient (depending on the fluoriding agent flowrate and the catalyst volume) to convert the magnesium oxide to a fluoride content corresponding to at least 40% by weight (e.g., for from 15 to 300 minutes). The fluorides are in the form of magnesium fluoride or magnesium oxyfluoride; the remainder of the catalyst is magnesium oxide. It is understood in the art that fluoriding conditions such as time and temperature can be adjusted to provide higher than 40 weight % fluoride-containing material.
Another suitable procedure for the catalyst preparation is to add ammonium hydroxide to a solution of magnesium nitrate and (if present) zinc nitrate and/or aluminum nitrate. The ammonium hydroxide is added to the nitrate solution to a pH of about 8.8. At the end of the addition, the solution is filtered, the solid obtained is washed with water, dried and slowly heated to 500° C., where it is calcined. The calcined product is then treated with a suitable fluorine-containing compound as described above.
The physical shape of the catalyst is not critical and may, for example, include pellets, powders or granules. Although not necessary, catalysts which have not been fluorided can be treated with HF before use. It is thought that this converts some of the surface oxides to oxyfluorides. This pretreatment can be accomplished by placing the catalyst in a suitable container (which can be the reactor to be used to perform the reaction of the instant invention) and thereafter, passing HF over the dried catalyst so as to partially saturate the catalyst with HF. This is conveniently carried out by passing HF over the catalyst for a period of time (e.g., about 15 to 300 minutes) at a temperature of, for example, about 200° C. to about 450° C. Nevertheless, this HF treatment is not essential.
The reaction temperature will normally be within the range from about 200° C. to about 400° C., preferably about 225° C. to 375° C. To provide for low acetylene by-product formation and to enhance catalyst life, the temperature is preferably kept within the range of from about 250° C. to about 300° C., more preferably, from about 250° C. to about 280° C.
The 1,1-difluoroethane is typically passed over the catalyst at a rate of about 60 volumes to about 3600 volumes per volume of catalyst per hour; preferably 120 volumes to 720 volumes per volume of catalyst per hour. These volumes correspond to a contact time of about 60 seconds to about 1 second and preferably about 30 seconds to about 5 seconds. Normally a contact time is employed which is sufficient to provide a dehydrofluorination of HFC- 152a equal to at least 50% of the equilibrium value for conversion of 1,1-difluoroethane to vinyl fluoride at the temperature employed; preferably at least 80%, and more preferably at least 90% of the equilibrium value at a given reaction temperature.
The reaction pressure can be subatmospheric, atmospheric or superatmospheric. Generally, near atmospheric pressures are preferred.
Unreacted starting material can be recycled to the reactor for the production of additional CH
2
═CHF. Vinyl fluoride (b.p. −72° C.) may be recovered from the reaction product and any unreacted 1,1-difluoroethane (b.p. −25° C.) by conventional procedures such as distillation.
The process of this invention can be carried out readily in the vapor phase using well known chemical engineering practice.
The reaction zone and its associated feed lines, effluent lines and associated units should be constructed of materials resistant to hydrogen fluoride. Typic

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