Drug – bio-affecting and body treating compositions – Designated organic active ingredient containing – Phosphorus containing other than solely as part of an...
Reexamination Certificate
1999-10-21
2002-04-02
Pryor, Alton (Department: 1616)
Drug, bio-affecting and body treating compositions
Designated organic active ingredient containing
Phosphorus containing other than solely as part of an...
C169S060000, C169S060000, C169S060000, C169S060000, C169S060000, C169S060000
Reexamination Certificate
active
06365580
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a vapor phase process for the production of difluoromethane, HFC-32. In particular, this invention provides a process for the preparation of HFC-32 that exhibits good product yield and selectivity.
BACKGROUND OF THE INVENTION
is well known in the art that HFC-32 may be used as a replacement for environmentally disadvantageous chlorofluorocarbon refrigerants, blowing agents, and aerosol propellants. A variety of methods for the vapor phase production of HFC-32 are known.
For example, U.S. Pat. No. 2,745,886 discloses a vapor phase process for fluorinating a variety of halohydrocarbons including methylene chloride, HCC-30, which process utilizes a hydrated chromium fluoride catalyst activated with oxygen. Similarly, U.S. Pat. No. 2,744,148 discloses a halohydrocarbon fluorination process in which an HF-activated alumina catalyst is used.
U.S. Pat. No. 3,862,995 discloses the vapor phase production of HFC-32 by reacting vinyl chloride and HF in the presence of a vanadium derivative catalyst supported on carbon. U.S. Pat. No.4,147,733 discloses a vapor phase reaction for the production of HFC-32 by HCC-30 with HF in the presence of a metal fluoride catalyst.
In practice, these processes for HFC-32 production suffer from a variety of problems including low product yield and selectivity as well as operational difficulties such as feed decomposition. The process of this invention provides for the production of HFC-32 by a process that overcomes some of the disadvantages of the known processes.
DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
The present invention provides a method for HFC-32 production in good yield and selectivity. In general, the process of this invention comprises contacting HCC-30 and HF in the presence of a fluorination catalyst to produce a product stream of difluoromethane, chlorofluoromethane (“HCFC-31”), hydrogen chloride, dichloromethane, and hydrogen fluoride and separating HFC-32 from the product stream. In a preferred embodiment, the invention comprises the steps of:
(A) preheating a composition comprising hydrogen fluoride (“HE”) and HCC-30 and, optionally, HCFC-31, to form a vaporized and superheated composition;
(B) reacting the preheated composition of step (A) in the presence of a fluorination catalyst under conditions suitable to form a product stream comprising HFC-32, HCFC-31 and hydrogen chloride and unreacted HCC-30 and HF;
(C) recovering by distillation from the product stream of step (B) a high boiling fraction comprising HF, HCC-30, and HCFC-31 and a low boiling fraction comprising HFC-32, HCl, HF, and reaction byproducts; and
(D) recovering substantially pure HFC-32 product from the low boiling fraction of step (C).
In step (A) a composition comprising HF and HCC-30 is preheated in at least one vaporizer. By “preheating ” is meant to vaporize and superheat the composition. The composition is heated to a temperature of from about 125° C. to about 400° C., preferably 150° C. to about 300° C., more preferably from about 175° C. to about 275° C. and most preferably 200° C. to about 250° C. The vaporizer, as well as the other vessels used in this process, may be made of any suitable corrosion resistant material.
Although fresh HF and HCC-30 may be used in step (A), preferably the composition of step (A) contains recycled material from step (C) as described below. When the process is run without continuous recycle, the mole ratio of HF to organic, specifically the mole ratio of HF to HCC-30, is from about 1:1 to about 10:1, preferably from about 1:1 to about 4:1. Optionally, fresh HCFC-31 may be added to the composition of step (A).
Alternatively, a continuous recycle stream of the high boiling fraction obtained in step (C) is recycled to step (A) in which case a large excess of HF to organics is used. In the process of this invention, the higher the HF: organics mole ratio, the higher the yield and selectivity for HFC-32. Correspondingly, a large excess of HF will result in the reduction of HCFC-31 produced as well as the concentration of unreacted HCC-30. Additionally, the use of a large excess of HF will decrease catalyst deactivation rates and result in less decomposition in preheaters and vaporizers, especially when the reaction is conducted at pressures in excess of 3 atmospheres. Generally, a ratio of HF to HCFC-31, as measured after separation of HFC-32 from the product stream, of at least about 25:1 to at least about 300:1, preferably at least about 50:1 to at least about 200:1, and more preferably at least about 75:1 to at least about 150:1 is used.
The preheated composition of step (A) is reacted in step (B) in a vapor phase fluorination reaction to form a product stream mixture. The reaction may proceed in one or more isothermal or adiabatic reactors. When more than one reactor is used, the reactor arrangement is not critical, but a sequential arrangement is preferred. Inter-reactor heating or cooling may be used to obtain the best reactor performance.
The reactor or reactors used in this process are filled with a fluorination catalyst and the organic and HF vapor is allowed to contact the catalyst under conditions suitable to form a reaction mixture. The reactor temperature is maintained at from about 125° to about 425° C., preferably 150° C. to about 300° C., more preferably 175° C. to about 275° C. and most preferably 200° C to about 250° C. Reactor pressure may be atmospheric, subatmospheric, or superatmospheric. Preferably reactor pressure is maintained at from about 0 psig to about 250 psig. Contact time, the time required for the reactants to pass through the catalyst bed assuming a 100% void catalyst bed, is typically from about 1 to about 120 seconds, preferably from about 2 to 60 seconds, more preferably from about 4 to about 50 seconds, and most preferably from about 5 to about 30 seconds.
Any known vapor phase fluorination catalyst may be used in the process of this invention. Exemplary catalysts include, without limitation, chromium, copper, aluminum, cobalt, magnesium, manganese, zinc, nickel and iron oxides, hydroxides, halides, oxyhalides and inorganic salts thereof, Cr
2
O
3
/Al
2
O
3
, Cr
2
O
3
/AlF
3
, Cr
2
O
3
/carbon, CoCl
2
/Cr
2
O
3
/Al
2
O
3
, NiCl
2
/Cr
2
O
3
/Al
2
O
3
, CoCl
2
/AlF
3
and NiCl
2
/AlF
3
. Additionally, supported metal catalysts such as nickel, cobalt, zinc, iron, and copper supported on chromia, magnesia, or alumina may be used. Chromium oxide/aluminum oxide catalysts are described in U.S. Pat. No. 5,155,082 which is incorporated herein in its entirety. Preferably, chromium oxide, a commercially available catalyst, is used. The chromium oxide may be crystalline or amorphous. Preferably, amorphous chromium oxide is used. The catalyst is used in an amount effective to drive the reaction.
The fluorination catalyst may be, and is preferably, pretreated prior to the introduction of the reaction feed stock. By “pretreat” is meant to chemically or physically alter the catalyst in order to create active sites on the catalyst at which the reaction may occur. The catalyst is pretreated by calcining under a flow of inert gas such as nitrogen at a temperature from about 200° C. to about 450° C. for at least about 1 hour. The catalyst is then exposed to HF alone or in combination with up to about 5 to about 99 weight percent of an inert gas at a temperature from about 200° C., to about 450° C. for at least about
1
hour. Preferably, the catalyst then undergoes a third pretreatment step in which it is contacted with chlorine gas. Preferably, the chlorine is diluted with from about 60 to about 75% HF and/or from about 20 to about 30% of an inert gas. The chlorine may be passed over the catalyst at a total volume chlorine to total volume catalyst of about 1:3,000 v/v, preferably about 10:1,000 v/v, more preferably about 50:500 v/v. Exposure time may be from about 1 to about 200 hours, preferably 5 to 70 hours, more preferably 10 to 30 hours. The chlorine exposure may be conducted at any temperature and pressure convenient to the fluorination reac
Bass John Stephen
Clemmer Paul Gene
Smith Addison Miles
Tung Hsueh Sung
Allied-Signal Inc.
Pryor Alton
Szuch Colleen D.
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