Process for oxidizing fluorinated olefins and catalysts useful for the purpose

A process for oxidizing fluorinated olefins to the corresponding epoxides by reacting a fluoroolefin with oxygen in a concentration, in the reaction mixture, ranging from 1 to 60% by volume, at a temperature up to 250.degree. C. and in the presence of a catalyst consisting of porous silicon dioxide in a crystalline form, with a high purity degree and carrying metal oxides of the first transition series, or copper oxides or lanthanide oxides or mixtures thereof.

BACKGROUND OF THE INVENTION 1. Field of the invention 
This invention relates to a process for oxidizing fluorinated olefins to 
the corresponding epoxides and to the catalyst useful for the purpose. 
More in particular, the present invention relates to a process for 
oxidizing tetrafluoroethylene and hexafluoropropene, and to the relevant 
catalyst. 
2. The prior art 
Processes for oxidizing fluorinated olefins, for example 
tetrafluoroethylene and hexafluoropropene to the corresponding epoxides, 
such as the processes described in U.S. Pat. Nos. 3,775,438, 3,775,439 and 
3,775,440, are known in the art. 
According to what is described in this literature, hexafluoropropene and 
tetrafluoroethylene are oxidized with oxygen, either pure or mixed with 
inert gases, in the presence of a catalyst essentially consisting of 
silica. 
The catalyst, which has a SiO.sub.2 content ranging from 60 to 95% by 
weight, is used in different forms, particularly as a gel, as ground 
glass, as macroporous beads or also as sand. 
These processes, although they permit to obtaining sufficiently high yields 
and conversions to epoxides, have very evident limits, which render them 
little suited to be utilized on a commercial scale. One of these limits is 
due to the catalyst life: in fact the catalyst becomes disactivated unless 
it is continuously treated with water or steam. 
Another limit is due to the fact that the oxidation reaction, under certain 
conditions, requires a higher pressure than the atmospheric pressure or 
the use of high temperatures and in both cases the drawbacks are not 
negligible: in the former case, the hazard, in the latter case, the risk 
of using a temperature close to the epoxide decomposition temperature and, 
by consequence, of reducing the yield of finished product. 
Subsequently, other processes for preparing in particular hexafluoropropene 
oxide have been proposed and are described in the published Japanese 
patent application Nos. 77/53804, 77/53805 and 77/53806. 
Like in the other cases, oxidation occurs by direct contact between 
fluoroolefin and catalyst, but the catalyst is composed of a product based 
on silica, which carries promoters selected from transition metals, such 
as copper, chrome, manganese, iron, zinc, palladium and cerium. 
Also in such cases, however, the shortcomings which highly limit the 
described processes, mainly as regards conversions and reaction yields, 
are still existing. The corresponding values are very low also owing to 
the too high reaction temperatures generally ranging from 250.degree. to 
300.degree. C. 
THE PRESENT INVENTION 
Thus, it is an object of the present invention to provide a process for 
oxidizing fluorinated olefins which is not affected by the abovesaid 
drawbacks. 
More in particular, it is an object of the present invention to provide a 
process for oxidizing fluorinated olefins C.sub.2 -C.sub.6 and in 
particular tetrafluoroethylene and hexafluoropropene with high reagent 
conversions and yields and under reaction conditions which are consistent 
with the stability of the product. 
Another object of the present invention is the catalyst suitable for the 
oxidation of fluoroolefins to epoxides. 
The Applicant has now surprisingly found--and this is the object of this 
invention--that these and still other objects can be achieved by 
conducting the direct reaction between fluorinated olefin and oxygen in 
the presence of an oxidizing catalyst consisting of a crystalline form of 
porous silicon dioxide having a high purity degree and carrying oxides of 
metals of the first transition series or of lanthanides or mixtures 
thereof. 
The term metals of the first transition series means the ones comprised, in 
the Periodic Table, between scandium and zinc. Preferred metals are 
copper, cobalt, cerium and chrome. 
The process according to the present invention can be conducted either 
continuously or discontinuously. 
According to a preferred embodiment, the oxidation reaction is conducted 
continuously by conveying the fluorinated olefin and the oxygen over a 
fixed or fluid catalytic bed and by keeping the reagents in contact for a 
time ranging from 100 to 1000 seconds. 
Oxygen can be fed in the form of air or of another gas mixture containing 
at least 20% by volume of oxygen; the diluting gas is inert and can be, 
for example, helium or carbon dioxide. 
Generally it is preferred to use pure oxygen, at a concentration, in the 
reaction mixture, ranging from 1 to 60% by volume. 
Prior to the oxidation reaction, the catalyst is subjected to an activation 
step which can be accomplished by causing to flow on it either the 
reagents themselves or fluoroderivatives selected from 
dichlorodifluoromethane, tetrafluoromethane, hexafluoroethane, 
tetrafluoroethylene, hexafluoropropene, gaseous hydrofluoric acid or acid 
fluorides such as trifluoroacetylfluoride or carbonyl difluoride, either 
pure or diluted in inert gases, such as nitrogen, at temperatures from 
0.degree. to 300.degree. C. depending on the activator type. 
The oxidation reaction is conducted at atmospheric pressure or slightly 
above it, to overcome the pressure drops due to the catalytic bed, and at 
a temperature up to 250.degree. C. In particular, if the produced epoxide 
is that of tetrafluoroethylene, the reaction temperature is lower, 
preferably below 50.degree. C.; conversely, if the produced epoxide is 
that of a fluoroolefin having a number of carbon atoms from 3 to 6, the 
temperature preferably ranges from 50.degree. to 250.degree. C. 
The epoxide so obtained can be recovered from the reaction mixture 
according to any known methods, such as distillation or washing. 
A further object of the present invention is the catalyst used in this 
process. 
Said catalyst is a material consisting of a carrier additioned with metal 
oxides, which exhibits excellent catalytic properties in the oxidation 
reactions, in particular in the oxidation reactions of fluoroolefins to 
epoxides. 
The carrier is a crystalline form of porous silicon dioxide at a high 
purity degree, in particular with an aluminum content in a concentration 
below 0.1% by weight, and characterized by a X-ray diffraction pattern (Cu 
K .alpha.) with the following main reflection angles: 
Z.theta.=7.94.degree.; 8.85.degree.; 23.08.degree.; 23.94.degree.. 
The structure of the pure crystalline phase is porous with regular pores; 
such characteristic is evidenced by the specific surface values determined 
by absorption of nitrogen, such surface being attributable for over 50% to 
pores with an average diameter below 1 nm. 
The total surface area ranges from 300 to 600 m.sup.2 /g 
The morphology of the crystallites is variable: the individuals appear in 
the octahedral or prismatic form with geminate prisms having an average 
size above 300 nm, and in any case easy to be distinguished from any other 
amorphous materials by means of electronic scanning microscopy. 
Said carrier can be prepared according to known methods, as is described in 
Nature vol. 271 page 512 (1978), or is commercially available under the 
trademark SILICALITE.RTM.. 
The promoters, which consist of oxides of metals of the first transition 
series, i.e. those comprised, in the Periodic Table of elements, between 
scandium and zinc, or of lanthanides or of mixtures thereof, are 
additioned to the carrier by impregnating same either with the oxide or 
with any salt provided it is capable of decomposing by calcination in 
order to give rise to the corresponding oxide. 
The promoters can be carried in amounts even higher than 40% by weight and, 
according to a preferred formulation of the catalyst object of the present 
invention, amounts in the range of from 1 to 30% by weight are utilized. 
Any metal oxide of the above-cited group is capable of promoting the 
oxidation reaction of fluorinated olefins, however, preferred metal oxides 
are those of copper, cobalt, cerium and chrome. 
The carrier impregnated with the transition metal salt is calcined in oven 
at temperatures ranging from 300.degree. to 800.degree. C., and is then 
subjected to an activating treatment as described hereinbefore.

A few illustrative but not limitative examples are given hereinafter in 
order to facilitate the comprehension of the present invention and the 
practising of same. 
EXAMPLE 1 
90 g of commercial SILICALITER.RTM. (S-115 Union Carbide) were impregnated 
with 39 ml of an aqueous solution containing 18.6 g of 
Cu(NO.sub.3).sub.2.3H.sub.2 O. 
After impregnation, the impregnated catalyst was permitted to digest during 
4 hours at room temperature, whereafter it was dried at 120.degree. C. for 
16 hours. 
It was calcined at 500.degree. C. for 4 hours in air, whereupon 4.5 g of an 
inert binder (Bentonite) were added and the whole was kneaded with 45 ml 
of distilled water. 
It was dried at 120.degree. C. for 16 hours and calcined at 540.degree. C. 
for 2 hours in air. At least, the catalyst was ground and subjected to 
screening: the 32-80 mesh fraction was collected and definitively 
activated at 100.degree. C. in a nitrogen stream containing 0.1% of 
hydrofluoric acid, during 5 hours. 
On the spectrophotometric analysis (X-ray) the catalyst exhibited the 
following reflexes attributable to copper oxide: 
EQU 2.theta.(Cu K .alpha.)=38.75.degree.; 36.60.degree.; 48.97.degree. 
besides the following, much more intense reflexes of the crystalline silica 
used as carrier: 
EQU 2.theta.=7.94.degree.; 8.85.degree.; 23.08.degree.; 23.94.degree.. 
30 g of the catalyst so prepared were introduced into a cylindrical 50-cc 
reactor made of Incoloy and externally heated. 
The reactor was heated to 170.degree. C. and a gaseous mixture of 
hexafluoropropene and oxygen in the ratio 90:70, namely 90 cc/h of 
hexafluoropropene and 70 cc/h of oxygen, was fed. 
After about 1 hour the temperature was adjusted at 160.degree. C. (maximum 
temperature along the catalytic bed). The outflowing gases were subjected 
to gas chromatographic analysis and their composition resulted to be the 
following: O.sub.2 =14.1%; CO.sub.2 +COF.sub.2 =21.8%; C.sub.3 F.sub.6 
O=21.1%; C.sub.3 F.sub.6 =30.6%. 
The resulting balance was corresponding to a conversion of 41.3% of the 
perfluoropropene with 75.6% of selectivity in epoxide. 
After a 27-hour run, the gas composition was slightly varied as follows : 
O.sub.2 =17%; CO.sub.2 +COF.sub.2 =23.7%; C.sub.3 F.sub.6 O=21.8%; C.sub.3 
F.sub.6 =35.2%, which was corresponding to a conversion of 45.5% of the 
hexafluoropropene with a selectivity of 74.5% in epoxide. 
EXAMPLE 2 
A flow consisting of 180 cm.sup.3 /h of C.sub.3 F.sub.6 and 140 cm.sup.3 /h 
of O.sub.2 was made to pass over 30 g of catalyst prepared according to 
the procedure of example 1 but in sizes of a mean diameter of 2 mm and 
activated for 3 hours with a nitrogen flow containing 0.5% of hydrofluoric 
acid, while the temperature was maintained on the average at 140.degree. 
C. and not exceeding 147.degree. C. 
After 4 hours, the conversion and the selectivity were stabilized on 
practically constant values, i.e. a conversion of about 30% and a 
selectivity in C.sub.3 F.sub.6 O higher than 77% from the 5th to the 50th 
hour of run. 
A typical analysis of the outflowing gases after 43 h and 30 minutes was 
the following: O.sub.2 =20.4%; CO.sub.2 +COF.sub.2 =11.7%; C.sub.3 F.sub.6 
O=17.5%; C.sub.3 F=50.1%, corresponding to a conversion of 29.7% and to a 
selectivity of 82.6%. 
After an eighty-hour run the catalyst was cooled and discharged. The 
sample, subjected to X-ray analysis, still revealed the reflexes of the 
starting SILICALITE with an intensity comparable to that of the starting 
sample. 
EXAMPLE 3 
3.5 g of a catalyst prepared as in example 1 (size: 32-80 mesh) were 
introduced into a 10-cc microreactor made of Incoloy. 
The reactor was heated to 200.degree. C. and a mixture consisting of 90 
cc/h of hexafluoropropene and 70 cc/h of oxygen was made to flow on the 
catalytic bed so prepared. 
After 1 hour the heating was adjusted in such manner that in the warmest 
point of the catalytic bed the temperature was of 200.degree. C. 
A practically constant conversion of the gas was observed and after a 
14-hour run the analysis was as follows: O.sub.2 =25.16%; CO.sub.2 
+COF.sub.2 =9.8% C.sub.3 F.sub.6 O=9.7%; C.sub.3 F.sub.6 =53.7%, what was 
corresponding to a conversion of 19.15% and to a selectivity of 75.9%. 
EXAMPLE 4 
A catalyst was prepared under the same conditions described in example 1, 
except for the employed amount of Cu(NO.sub.3).sub.2.3H.sub.2 O, that in 
the present case was of 3.7 g. 
The final activation was carried out at 100.degree. C. in a nitrogen stream 
containing 0.5% of hydrofluoric acid, during 1 hour. 
3.5 g of the catalyst so prepared were introduced, in a size of 32-80 mesh, 
into a 10-cc microreactor made of Incoloy. 
The reactor was heated to 200.degree. C. and a mixture of 90 cc/h of 
hexafluoropropene and 70 cc/h of O.sub.2 was conveyed thereinto. 
The composition of the outflowing gases stabilized, after 2 hours, at a 
stable value and after 7 hours was as follows: 
O.sub.2 =8%; CO.sub.2 +COF.sub.2 =16.5%; C.sub.3 F.sub.6 O=13.5%; C.sub.3 
F.sub.6 =52.0%, what was corresponding to a conversion of 27% and to a 
selectivity of 69%. 
EXAMPLE 5 
10 g of a catalyst, in a size of 32-80 mesh, consisting of cobalt oxide on 
silicalite, prepared as in example 1 but using, however, cobalt nitrate 
instead of copper nitrate with the same amount of metal in gram atoms, 
were introduced into a 20-cc microreactor. It was heated to 230.degree. C. 
and a mixture consisting of 90 cc/h of C.sub.3 F.sub.6, 70 cc/h of O.sub.2 
and 30 cc/h of N.sub.2 was sent thereinto. 
The regular operating conditions were reached after a few hours, and the 
temperature was stabilized at 180.degree. C. with a conversion of about 
30%. 
After a 6-hour run the conversion was stable and the outflowing mixture 
exhibited the following composition: 
EQU O.sub.2 +N.sub.2 =48.3%; CO.sub.2 +COF.sub.2 =4.2%; C.sub.3 F.sub.6 
O=12.4%; C.sub.3 F.sub.6 35.5%. 
what was corresponding to a conversion of 31% and to a selectivity of 74.7% 
to epoxide. 
EXAMPLE 6 
3.5 g of a catalyst in a size of 32-80 mesh, consisting of cerium oxide on 
silicalite, prepared as in example 1, but using cerium nitrate in the 
place of copper nitrate, with the same amount of metal in gram atoms, were 
introduced into a 10-cc microreactor. 
It was heated to 230.degree. C. and a mixture of 90 cc/h of C.sub.3 F.sub.6 
70 cc/h of O.sub.2 +30 cc/h of N.sub.2 was made to flow thereinto during 
half an hour, whereafter the temperature was gradually lowered. 
Regular operating conditions were reached at 195.degree. C. and at this 
temperature a quite stable conversion was observed. 
After 4 hours, an analysis of the outflowing gases revealed the following 
compositions: 
EQU O.sub.2 +N.sub.2 =38%; CO.sub.2 +COF.sub.2 =14.8%; C.sub.3 F.sub.6 O=8.6%; 
C.sub.3 F.sub.6 =36.6%. 
The conversion was of 27.9% and the selectivity of 61.2%. 
EXAMPLE 7 (comparative test) 
90 g of a commercial activated carbon designated as KAS/S HYDRO-LINE were 
ground and screened and the 32-80 mesh fraction was collected. 
It was impregnated with an aqueous solution containing 9 g of Cu(CH.sub.3 
COO).sub.2.H.sub.2 O by means of the double-impregnation technique. It was 
dried at 100.degree. C. for 16 hours in air and it was calcined at 
300.degree. C. during 4 hours in nitrogen, then at 200.degree. C. during 4 
hours in air. 
3 g of the catalyst so prepared were introduced into a 10-cc microreactor. 
It was heated to 100.degree. C. and a mixture of 90 cc/h of 
hexafluoropropene and 70 cc/h of oxygen was made to flow thereinto. 
During the test, the temperature was brought from 100.degree. to 
200.degree. C. The conversion of hexafluoropropene was in any case 
practically complete; the outflowing gases revealed no traces of 
hexafluoropropene epoxide but of other oxidation and pyrolysis products 
such as COF.sub.2, CO.sub.2, CF.sub.4, CF.sub.3 COF, C.sub.2 F.sub.4, 
cyclic C.sub.3 F.sub.6 and other high-boiling products. 
EXAMPLE 8 (comparative test) 
50 g of commercial SiO.sub.2 sol designated as Ketjensol were additioned 
with 50 ml of distilled water. 
It was acidified with dilute HNO.sub.3 up to a pH =6, and 4 g of 
Cu(NO3).sub.2.3H.sub.2 O were added to such solution. 
Precipitation was carried out with an aqueous solution of KOH at 10%. It 
was filtered, repeatedly washed and dried at 120.degree. C./16 h in air. 
It was calcined at 500.degree. C. during 4 hours in air, whereafter the 
catalyst was subjected to grinding and to screening, and the 32-80 mesh 
fraction was collected. 
3.5 g of the catalyst so prepared were introduced into a 10-cc 
microreactor. A flow of 90 cc/h of hexafluoropropene and 70 cc/h of oxygen 
was made to pass over this catalytic bed, while the reactor was heated up 
to 300.degree. C. At 300.degree. C. the conversion begun and after 1 hour 
the temperature was decreased to 160.degree. C., whereafter it was 
maintained constant. 
The outflowing gases were almost exclusively composed of the unaltered 
reagents. Now it was heated to 210.degree. C.; in such way it was possible 
to observe the following composition of the reacted mixture: CO.sub.2 
+COF.sub.2 =10.2%; O.sub.2 =36.5%; C.sub.3 F.sub.6 =51.8%, with traces of 
epoxide. The conversion was of 15%, but the selectivity for epoxide was 
lower than 1%. 
EXAMPLE 9 (comparative test) 
A catalyst consisting of copper carried on a zeolite containing aluminium 
was prepared by ionic exchange with copper nitrate on synthetic Fujasite 
(LZY-52 available from Union Carbide). The resulting product was calcined 
at 540.degree. C. and subjected during 1 hour to a nitrogen stream at 
100.degree. C. which contained 0.1% of hydrofluoric acid. 
On 2.4 g of said catalyst (32-80 mesh) there were made to pass 180 cm.sup.3 
/h of C.sub.3 F.sub.6 and 40 cm.sup.3 h of O.sub.2 at an initial 
temperature of 200.degree. C. 
After 3 hours at 200.degree. C., the outflowing gas had the following 
composition: 
EQU O.sub.2 =23.6%; CO.sub.2 =14.1%; C.sub.3 F.sub.6 O=nihil; C.sub.3 F.sub.6 
=62.0%. 
The temperature was then lowered to 150.degree. C. with the same gas flow, 
and the following composition of the outflowing gas was observed: 
EQU O.sub.2 =26.0%; CO.sub.2 =1.15%; C.sub.3 F.sub.6 O=0.15%; C.sub.3 F.sub.6 
=71.2%. 
After further 3 hours of run under these conditions, it was cooled down and 
the catalyst was discharged: the weight thereof resulted to be increased 
by 17% in consequence of the absorbed bed fluorine, while the X-ray 
analysis revealed that the crystalline structure of the starting Fujasite 
was for the most part no longer present, thus giving rise to an amorphous 
material. 
Although the invention has been described in conjunction with specific 
embodiments, it is evident that many alternatives and variations will be 
apparent to those skilled in the art in light of the foregoing 
description. Accordingly, the invention is intended to embrace all of the 
alternatives and variations that fall within the spirit and scope of the 
appended claims.