Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
1997-06-30
2001-10-23
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C570S168000
Reexamination Certificate
active
06307114
ABSTRACT:
The present invention relates to an improvement in the preparation of 1,1,1-trifluoro-2-chloroethane (hereinafter referred to as HCFC 133a), carried out by hydrofluorination of trichloroethylene (TCE) in the gas phase, in the presence of chrome oxide and/or chrome oxyfluorides or fluorides as catalysts.
Preparations of HCFC 133a according to such method are broadly described in the art; in this connection, reference should be made to patents: U.S. Pat. Nos. 3,752,850; 2,637,747; 2,885,427; 3,755,477; GB 1,000,485; DE 1,104,496.
A serious drawback affecting the preparation of HCFC 133a according to the abovesaid method is represented by the decay of the catalyst activity during the reaction.
So, for examples, if a mixture of trichloroethylene and anhydrous HF in a 1/6 molar ratio is conveyed onto a catalyst based on chrome oxide and/or chrome oxyfluoride or fluoride carried on fluorinated alumina, with a contact time of 5 seconds, the starting conversion of trichloroethylene is very high (typically of 90-95%), which, however, gradually decreases at a rate which is depending on temperature. For example, at 300° C. the conversion begins to decrease after 25 hours and sinks to 80%, within 90 hours, while at 350° C. the conversion sinks to 70-75% in 50 hours.
To overcome this drawback it was suggested to add air or oxygen to the reagent mixture.
Such method, however, is affected by the serious drawback of promoting dismutation reactions of the reaction intermediate products, giving rise to great amounts of undesired products. For example, maintaining the abovesaid conditions, with the exception of the addition of air in a O
2
/trichloroethylene molar ratio equal to 1/6, about 6% by weight of dismutation products form, while in the absence of air such products form only in amounts of 0.5-0.6% by weight.
Furthermore, if it is operated in the presence of oxygen, the amount of 1,1-difluoro-2-chloroethylene (undesired product owing to its toxicity) rises from 0.02-0.03% to 0.250-0.30% by weight.
Lastly, operating in the presence of oxygen, the trichloroethylene conversion is slightly lower (88-90%) as compared with the cases when it is operated in the absence of oxygen.
It has now surprisingly been found by the Applicant that it is possible to maintain for a long period of time the catalyst activity and selectivity by adding to the reaction mixture, composed of trichloroethylene and of hydrofluoric acid, little amounts of HCFC 133a, what, in terms of plant engineering, is equivalent to recycle to the reactor a little part of the reaction product, optionally comprising the unreacted trichloroethylene and hydrofluoric acid.
A further advantage of this operating method resides in the fact that the formation of by-products decreases instead of increasing, as conversely happens when it is operated in the presence of oxygen.
The amount of HCFC 133a to be added to the reagent mixture sent to the reactor shall be at least of 7 mols %, and preferably of at least 10 mols %, referred to the mixture with trichloroethylene.
Generally, HCFC 133a amounts ranging from 7 to 25 mols % and preferably from 10 to 20 mols %, calculated on its mixture with trichloroethylene, can be considered as suitable for the purposes of the invention.
The reaction temperature suitably ranges from 250° to 330° C., preferably from 280° to 300° C.
From European patent application 449,614 it is known a process for preparing 1,1,1-trifluoro-2-fluoroethane by hydrofluorination of trichloroethylene, which process comprises a step of preparing 1,1,1-trifluoro-2-chloroethane (step D) via hydrofluorination of mixtures of said 1,1,1-trifluoro-2-chloroethane with trichloroethylene.
In such step, however, the amount of 1,1,1-trifluoro-2-chloroethane in the mixture is always by far prevailing on the amount of trichloroethylene (which, according to the examples, is of about 15 mols %), wherefore the conditions of the present invention do not exist in such process, nor the advantages are inferable therefrom.
Thus, it is an object of the present invention to provide a process for preparing HCFC 133a by hydrofluorination of trichloroethylene with hydrofluoric acid in the gas phase, in the presence of catalysts composed of chrome oxide and/or chrome oxyfluorides or fluorides and carried on at least partially fluorinated alumina, carried out under the above-described conditions.
The catalyst can be prepared according to any method of the art.
Preferably it is prepared by impregnating an alumina carrier, which had been at least partially previously fluorinated, with an aqueous solution of a trivalent chrome salt, by drying the whole and activating with air or nitrogen, either or not in the presence of water and/or crystallization water which can act as an oxidizer, at temperatures ranging from 200° to 600° C., but preferably from 350° to 500° l C., in order to convert chrome into Cr
2
O
3
.
Preferably, but not necessarily, the catalyst is then treated, prior to the use, with gaseous HF, at a temperature from 200° to 450° C., optionally in the same reactor to be used for the reaction of trichloroethylene and HF.
By at least partially fluorinated alumina is meant herein the alumina comprising at least 50%, but preferably at least 90% by weight of AlF
3
.
Such a fluorinated alumina is preparable by hydrofluorination of alumina according to what is described in FR patent No. 1,383,927.
The chrome amount on the carrier preferably ranges from 1 to 15% by weight calculated on the total weight of the catalyst.
The carrier can be in the form of a powder having particle size from 20 to 200 microns, or in the form of pellets.
The at least partially fluorinated alumina used as a carrier comprises AlF
3
mainly in the gamma and/or beta forms; however also the delta form can be present up to amounts of 30% by weight.
Also AlF
3
in the alpha form can be present, however in little amounts.
Another method of preparing the catalyst comprises soaking the alumina with an aqueous solution of a chrome salt, drying and then, optionally, subjecting the resulting product to fluorination with HF till obtaining a fluorination of the alumina for at least 50% and preferably for at least 90%.
A further method comprises coprecipitating the aluminium and chrome hydroxides, drying them, subjecting them to calcination in order to convert them into mixed oxides and, lastly, treating them with HF till obtaining the desired alumina fluorination degree.
In the trichloroethylene hydrofluorination reaction it is preferably operated with HF/trichloroethylene molar ratios higher than 3/1. Generally, ratios between 5/1 and 10/1 are utilized.
The pressure is not critical; generally it is operated at atmospheric pressure.
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patent: 2637747 (1953-05-01), McBee
patent: 2885427 (1959-05-01), Ruh et al.
patent: 3752850 (1973-08-01), Scherer et al.
patent: 3755477 (1973-08-01), Firth et al.
patent: 4967023 (1990-10-01), Carmello et al.
patent: 5185482 (1993-02-01), Manzer
patent: 5334786 (1994-08-01), Koyama et al.
patent: 1104496 (1959-04-01), None
patent: 1246703 (1967-08-01), None
patent: 408005 (1991-01-01), None
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patent: A-449614 (1991-10-01), None
patent: 449614 (1991-10-01), None
patent: 1383927 (1963-11-01), None
patent: 1000485 (1962-02-01), None
patent: PCT/EP 90/08755 (1990-08-01), None
European Search Report for EP-A-93 11 2630.
Ausimont S.p.A.
Cave LLP Bryan
Siegel Alan
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