Preparation process of 227

Details Preparation process of 227 Preparation process of 227

1999-06-16

2001-02-13

Siegel, Alan (Department: 1621)

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

Organic compounds

Halogen containing

C570S168000, C570S169000

Reexamination Certificate

active

06187975

ABSTRACT:

The present invention relates to a process for obtaining CF
3
—CHF—CF
3
(227ea) with high yields and selectivity.
More specifically the present invention relates to a perfluoropropene (PFP) hydrofluorination process in gaseous phase which uses a particular catalyst for obtaining CF
3
—CHF—CF
3
(227ea) with high yields and selectivity, the PFP amount at the end of the reaction being lower than 3% by weight, preferably lower than 0.05% by weight.
More specifically the present invention relates to a process for preparing 227 in the ea form without the presence of 227ca CF
3
—CF
2
—CHF
2
.
It is known that, owing to well known problems of atmospheric ozone layer depletion, the use and production of chlorofluorocarbons (CFC) such as A-11 (CCl
3
F), A-12 (CCl
2
F
2
), A-113 (CCl
2
FCClF
2
), A-114 (CClF
2
CClF
2
), have been banned or limited since they have at least a chlorine atom in their structure. Compounds not containing chlorine atoms in their molecule such as for instance 32 (CH
3
F), 125 (CHF
2
CF
3
), 134a (CF
3
CH
2
F), 227 (CF
3
—CHF—CF
3
or CF
3
—CF
2
—CHF
2
), 236 (CF
3
CH
2
CF
3
or CF
3
CFHCF
2
H) etc., up to hydrofluorinated series ends also higher than 4, 5 carbon atoms are therefore requested in their use also in mixtures, as solvents, refrigerants, foaming agents for polymeric resins, extinguishing agents, propellants for aerosol, sterilizing mixtures, etc.
The 227ea synthesis by hydrofluorination with the use of HF, Cl
2
and catalysts of the relevant chlorinated compounds is known from the prior art. However the chlorinated precursors are not easily preparable with a good purity degree and yield. Besides for compounds with 3 or more carbon atoms as for 227ea, such preparation is difficult and for the hydrofluorination in gaseous phase is still more problematic, as it requires conditions leading to not very high yields and selectivity. See for instance patent application WO 92/13817 which describes also the 227 synthesis from chlorofluorinated precurosors in gaseous phase obtaining extremely complex hydrochlorofluorinated product mixtures in various ratios by employing HF and Cl
2
and CrO
3
or Cr
2
O
3
/Al
2
O
3
catalyst.
The fluorination in homogeneous liquid phase with HF of the relevant chlorinated precursors with the use for instance of antimony-based catalysts, such as SbCl
5
and SbF
5
, etc., is also described in the prior art. However these hydrofluorinations generally show not high yields and selectivity. Besides there is a catalyst rapid deactivation, due to pitch formation, which must be moreover brought again to the initial oxidation state for instance by using chlorine.
It is to be noticed that the antimony compound use is difficult for its toxicity. See patent application WO 96/02483.
Other known processes for the 227 synthesis relate to the reduction with hydrogen on catalysts or in gaseous phase of the relevant chlorinated precursor. The yields and selectivities of these processes are not high; therefore the reactants recycle is necessary: this operation can be difficult when the separation is not easy. Besides the catalyst has a not long duration. Besides the precursors are not easy to be prepared. See EP 539,989, EP 562,509, EP 39,471.
The synthesis by summing HF to perfluoropropene is also known, by using a slightly basic tertiary amine to promote the sum reaction. However the yields and selectivities are unsatisfactory and besides there is the drawback of the aminic reactant consumption. See EP 634,384.
The synthesis by summing the HF to pentafluoroproene on Cr
2
O
3
catalyst is also known. Also in this case the yields and selectivities ar not good. Besides this process relates to the preparation of 236, which can be used as precursor of 227. See U.S. Pat. No. 5,563,304.
The 227ea synthesis starting from perfluoroisobutene in a basic aqueous alcoholic medium for the presence of triethylamine is also described. 227ea is obtained only in a very low percentage. Besides, it is to be noticed that the starting perfluoroisobutene is commonly considered a very toxic compound. See U.S. Pat. No. 5,573,654.
There are also other patents on the 227 purification from the unreacted perfluoropropene. See for instance U.S. Pat. No. 5,475,169, which uses for the 227ea purification from the unreacted PFP a reaction with NaOH, KOH and alcohols. U.S. Pat. No. 5,621,152 leads to the elimination also of very reduced amounts, 50 ppm, of perfluoropropene by passing the mixture on alumina.
The need was felt to have available an industrial process for preparing 227ea with high yields and selectivity, without leading to the contemporaneous presence of 227ca, wherein the unreacted PFP amount or, in case, of other olefin is very reduced, in the range of 3% by weight.
An object of the present invention is a perfluoropropene (PFP) hydrofluorination process in gaseous; phase to obtain CF
3
—CHF—CF
3
(227ea), characterized in that, as catalyst, fluorinated alumina containing at least 90% by weight, preferably 95W of AlF
3
, preferably in gamma form, optionally containing a compound of trivalent chromium under oxide, oxyfluoride or fluoride form, or mixtures threof, is used, the chromium amount as metal being in the range 1-15% by weight, preferably 2-10% by weight, the HF/PFP molar ratios range from about 4:1 to 20:1, preferably from 6:1 to 14:1, more preferably from 8:1 to 11:1, the hydrofluorination process temperature being in the range 320°-420° C., preferably 340-°400° C., still more prefrably 340°-370° C., the feeding gas pressure being in the range 1-30 absolute atm, preferably 2-10, still more preferably 5-10.
Preferably the PFP amount at the end of the reaction being lower than 3% by weight, preferably lower than 0.05% by weight.
The contact time ranges from 10 to 50 sec, preferably from 20 to 30 sec.
The catalyst used in the present invention is obtainable for example by the process described in previous patents in the name of the Applicant. See for isntaiice U.S. Pat. No. 5,345,014 herin incorporated by reference. Tests carried out: by the Applicant on the final catalyst of U.S. Pat. No. '014 have shown that after the activation or regeneration phase the chromium is present in the form of oxide, oxyfluoride and fluoride. The oxide and fluoride amounts, by weight, are generally of the same order.
It is to be noted that by the invention process 227 in the ea form is obtained without the presence of 227ca (CF
3
—CF
2
—CHF
2
). This represents an advantage from the industrial point of view since the two 227 isomers are difficult: to be separated with the usual separation methods, such as distillation, since they have very close boiling temperatures.
With the invention process high yields of 227ea higher than 95% by weight, preferably higher than 97% by weight, still more preferably higher than 99% are obtained., by operating in the preferred range of the above mentioned process variables.
It has been surprisingly and unexpectedly found that the invention catalyst deactivation rate is very low: the PFP reactant conversion does not lower more than 0.05 moles/h preferably 0.02 moles/h, more preferably 0.01 moles/h for running times in the range of 200 h or higher. From the industrial point of view this is an advantage since the catalyst regeneration is not frequent, obtaining substantially constant PFP conversions.
Besides it has been surprisingly and unexpectedly found that with the invention process an amount of perfluoroisobutene by-product lower than 0.1 ppb is obtained.
Besides the invention process by giving very high PFP conversions does not require the unreacted product recycle, remarkably simplifying the process from the industrial point of view.
The reaction mixture can be purified from the small PFP amounts or from other olefins formed in the process by using processes known in the art, for instance U.S. Pat. No. 5,475,169 and U.S. Pat. No. 5,621,152 herein incorporated by reference.
The catalyst used for the hydrofluorination in gaseous phase of the present invention is in a form suitable for the use in fluidized bed or fixed bed reactor. The flu

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