Process for purifying 1,1,1-trifluoro-2,2-dichloroethane from isomer 1,1,2-trifluoro-1,2-dichloroethane

Abstract

The 1,1,2-trifluoro-1,2-dichloroethane content is reduced or removed from 1,1,1-trifluoro-2,2-dichloroethane by contacting a gaseous mixture comprising said compounds with chrome oxide (Cr.sub.2 O.sub.3) either as such or supported, at temperatures from 180.degree. to 400.degree. C.

Description

The present invention relates to a process for reducing or removing impurities consisting of isomer 1,1,2-trifluoro-1,2-dichloroethane (hereinafter referred to as Al23a) from 1,1,1-trifluoro-2,2-dichloroethane (hereinafter referred to as Al23 ).

The need for having available industrial processes for preparing Al23 as free as possible from Al23a has been recognized.

Such need is particularly recognized, for example, by the manufacturers of polyurethane foams, for the production of which Al23 is used as foaming agent. In such case, the Al23a contained therein decomposes and forms HCl, which corrodes the metal circuits of the plants.

The industrially most interesting processes for the preparation of Al23 are based on the hydrofluorination of tetrachloroethylene in the gas phase, in the presence of proper catalysts.

Such a process is described for example in U.S. Pat. No. 4,766,260.

Such a preparation process gives always rise to Al23a in amounts ranging from 5 to 20%, depending on the reaction conditions. Said product is difficult to be distilled-off from Al23.

In principle it is possible to carry out the reaction under such conditions as to minimize the formation of Al23a, for example by using high temperatures (about 360.degree. C.); however this is of little practical interest because under such conditions the process selectivity towards Al23 is too low, while unacceptable amounts of by-products are obtained.

It is also possible to reduce the Al23a content in the final reaction product by subjecting the Al23 and Al23a mixture to a treatment with anhydrous HF in the presence of the same catalyst as is used for its preparation, thereby obtaining the preferential fluorination of Al23a to 1,1,1,2-tetrafluoro-2-chloroethane (Al24).

However, the selectivity of such reaction is not high enough, wherefore also the fluorination of considerable amounts of Al23 occurs.

The Applicant has now surprisingly found a process --constituting the object of the present invention--which permits the reduction or removal of Al23a from its mixtures with Al23 by means of a highly selective and highly efficient reaction, said process consisting in reacting a gaseous mixture comprising said compounds with chrome oxide, either as such or supported, at temperatures ranging from 180.degree. to 400.degree. C., but preferably from 220.degree. to 320.degree. C.

Under such conditions, a dismutation of Al23a to products easily removable from Al23 takes place, and in a few cases also a conversion of Al23a into Al23, with sparing or no decomposition of the latter.

By "chrome oxide", whenever used herein, is meant Cr.sub.2 O.sub.3, generally in the form of pellets, suitable for being used in fixed beds, as well as the chrome oxyfluorides.

Said chrome oxides are utilizable as such or, preferably, supported on aluminium trifluoride, comprising the crystallographic forms .beta., .gamma. and .DELTA., the form .gamma. and/or .beta. being preferably prevailing.

The crystalline chrome oxides are preferred, although it is possible, for the purposes of the invention, to utilize also them in the amorphous form.

The carried catalyst can be prepared by impregnating the alumina with a water solution of a chrome salt, preferably the chloride, then by treating said impregnated alumina with HF at high temperature, until obtaining the desired alumina fluorination degree, which preferably, but not necessarily, corresponds to an AlF.sub.3 content of at least 90 moles per cent of the original alumina. Such a process is described in U.S. Pat. No. 4,766,260. According to a preferred method, such a catalyst is prepared by impregnating AlF.sub.3, obtained by at least partial fluorination of Al.sub.2 O.sub.3, according to known techniques, with a water solution of CrCl.sub.3, then by treating the impregnated AlF.sub.3 with nitrogen, optionally in the presence of oxygen in order to promote the formation of the chrome oxide crystalline structure, and then with anhydrous HF in hot conditions.

Such a process is described for example in European patent application Ser. No. 282,005.

The use of a carrier makes the catalyst not only more efficient, but also suited to be used in fluidized bed reactors.

The chrome content of the carried catalysts ranges from 1 to 10% by weight, calculated as metallic chrome on the catalyst total weight.

The catalyst in the form of chrome oxide pellets can be prepared according to conventional methods, for example by precipitation of Cr(OH).sub.3 from solutions of a proper chrome salt, by subsequent extrusion and drying. Calcination at a temperature from 500.degree. to 700.degree. C. can follow in order to obtain Cr.sub.2 O.sub.3 in the crystalline form.

The chrome oxide in pellets can be activated prior to reaction by heating to 300.degree.-400.degree. C. with anhydrous HF, preferably in the same reactor, in which it will be used as a catalyst.

In the reaction, the contact time of the gaseous mixture comprising Al23 and Al23a with the catalyst can vary over a wide range. Generally, said contact time ranges from 1 to 200 seconds, but preferably from 10 to 110 seconds. The pressure is not particularly critical; generally it is operated at atmospheric pressure or at a slightly higher pressure.

The catalyst activity is only very slightly affected by deactivation phenomena; in any case it can be restored by treatment with hot air.

The following examples are given to illustrate the invention but not to limit the scope thereof.

EXAMPLE 1

(A) An aluminium fluoride having a specific surface of about 26 m/g prepared by fluorination of Al.sub.2 O.sub.3 with anhydrous HF up to an AlF.sub.3 content of 94% by weight, was impregnated with a water solution of CrCl.sub.3.6H.sub.2 O in an amount of 492 g of CrCl.sub.3.6H.sub.2 O per kg of AlF.sub.3, by means of one of the methods of the art, and was dried at 120.degree.-150.degree. C., so obtaining a catalyst containing 8% by weight of chrome. The utilized aluminium fluoride had a particle size ranging from 20 to 200 microns, on the average of 80 microns, and was composed for 20% of the .DELTA. form and for 80% of the .gamma. form. 400 g of this catalyst were introduced into a tubular reactor made of Inconel 600.RTM., having an inside diameter of 5 cm and a length of 80 cm, and equipped with a porous bottom of sintered Inconel 600. (B) The catalyst introduced into the above-described reactor was heated up to 400.degree. C. in a nitrogen flow for 10 hours, then it was treated with 80 g/h of anhydrous HF for 2-3 hours at 350.degree. C. Lastly, the temperature was reduced to 240.degree. C. and the feeding of 153 g/h (1 mole/h) of a mixture containing 80 moles-% of Al23 and 20 moles-% of Al23a was started. The gases leaving the reactor were bubbled in water in order to absorb acidity traces, were condensed and then analyzed by means of gas chromatography (G.C.). By varying the temperature and the contact time, the results reported in Table 1 were obtained. TABLE 1______________________________________Operative conditions and obtained products Contact time =Contact time = 25 seconds 50 secondsComposition Temperature Temperatureobtained after (.degree.C.) (.degree.C.)reaction 240 260 240______________________________________A115 (moles-%) 0.0 0.2 0.2A125 (moles-%) 0.8 4.0 0.3A114 (moles-%) 0.3 1.0 0.2A124 (moles-%) 11.7 16.5 7.9A1112 (moles-%) 0.1 0.1 0.0A133 (moles-%) 0.2 0.8 0.1A113 (moles-%) 0.1 0.2 0.2A123a (moles-%) 4.2 1.6 6.7A123 (moles-%) 74.4 65.7 77.3A1111* (moles-%) 3.2 2.8 3.1A122* (moles-%) 0.8 0.3 0.5A1120* (moles-%) 0.2 0.7 0.0A1110* (moles-%) 3.9 6.0 3.3______________________________________ *Recyclable products A115 = CF.sub.3 CClF.sub.2 A143 = CF.sub.3 CH.sub.3 A125 = CF.sub.3 CHF.sub.2 A134a = CF.sub.3 CH.sub.2 F A114 = CClF.sub.2 CClF.sub.2 A124 = CF.sub.3 CHClF A1112 = CClF.dbd.CClF A133 = CHF.sub.2 CHClF A113 = CCl.sub.2 FCClF.sub.2 A1111 = CClF.dbd.CCl.sub.2 A122 = CHCl.sub.2 CClF.sub.2 A1120 = CHClCCl.sub.2 A1110 = CCl.sub.2 .dbd.CCl.sub.2

EXAMPLE 2

400 g of the catalyst prepared according to example 1 (A) were introduced into the reactor illustrated in said example and were fluidized for 10 hours at 400.degree. C. in an air flow.

Utilizing a mixture of Al23 and Al23a in a molar ratio of 80/20, the results reported in Table 2 were obtained.

TABLE 2__________________________________________________________________________Operative conditions and obtained productsCompositionobtained after T = 250.degree. C. T = 250.degree. C. T = 240.degree. C. T = 220.degree. C.reaction t = 18" t = 21,5" t = 23" t = 50"__________________________________________________________________________A115 (moles-%) 0.0 0.0 0.0 0.0A125 (moles-%) 0.7 1.6 1.2 0.3A114 (moles-%) 0.2 0.3 0.2 0.1A124 (moles-%) 10.6 12.6 12.2 8.8A1112 (moles-%) 0.1 0.1 0.1 0.1A133 (moles-%) 0.1 0.2 0.2 0.1A113 (moles-%) 0.2 0.1 0.1 0.1A123a (moles-%) 1.7 0.3 0.4 2.3A123 (moles-%) 80.4 76.3 79.2 83.4A1111* (moles-%) 2.6 2.1 1.9 2.1A122* (moles-%) 0.4 0.2 0.2 0.5A1120 (moles-%) 0.1 0.2 0.1 0.0A1110* (moles-%) 2.8 5.9 4.3 2.2__________________________________________________________________________ *Recyclable products

EXAMPLE 3

A water solution of CrCl.sub.3 was treated with sodium hydroxide, thereby obtaining the precipitation of chrome hydroxide in the form of gel.

This gel was washed with water, dried in air at room temperature and the resulting paste was extruded in the form of little cylinders having a diameter of about 5 mm. These were calcined in air at 550.degree. C., so obtaining Cr.sub.2 O.sub.3 in the crystalline form, which was charged into the reactor of example 1.

Table 3 shows the results obtained by causing a Al23/Al23a mixture in a 80/20 molar ratio to flow over such catalyst.

TABLE 3__________________________________________________________________________Operative conditions and obtained productsCompositionobtained after T = 260.degree. T = 300.degree. T = 320.degree. T = 260.degree. T = 240.degree. T = 220 T = 320.degree. T = 300.degree. T = 280.degree.reaction t = 24" t = 23" t = 22" t = 90" t = 82" t = 90" t = 45" t = 46" t = 47"__________________________________________________________________________A115 (moles-%) 0.1 0.1 0.1 0.1 0.0 0.0 0.1 0.0 0.0A125 (moles-%) 0.0 1.2 3.4 2.1 1.4 0.4 2.9 1.1 5.0A114 (moles-%) 0.4 1.1 1.9 2.0 1.0 0.4 1.6 1.0 4.0A124 (moles-%) 3.1 14.6 18.6 15.5 16.4 11.5 17.0 16.5 12.0A1112 (moles-%) 0.1 0.2 0.3 0.1 0.1 0.1 0.2 0.2 2.0A133 (moles-%) 0.1 0.3 0.5 0.5 0.6 0.4 0.4 0.5 0.4A113 (moles-%) 0.8 0.6 0.6 0.8 0.5 0.5 0.7 0.6 0.5A123a (moles-%) 12.0 3.7 1.4 0.5 1.8 4.7 1.0 2.1 5.4A123 (moles-%) 80.6 68.8 58.5 65.1 67.9 72.2 59.6 66.2 72.0A1111* (moles-%) 0.9 2.8 3.2 1.9 3.2 3.9 3.4 3.2 3.2A122* (moles-%) 0.4 0.5 0.3 0.2 0.5 1.4 0.3 0.5 1.1A1120 (moles-%) 0.1 0.9 2.2 1.1 0.7 0.3 2.3 1.3 0.6A1110* (moles-%) 1.0 4.8 8.4 9.8 5.6 3.7 10.2 6.4 3.4__________________________________________________________________________ *Recyclable products

EXAMPLE 4

2.0 g of the catalyst of example 1 were charged into a tubular Inconel reactor having a diameter of 8 mm, The reactor was fed with 1.5 g/h of an organic mixture containing Al23 (85.9%) and Al23a (13.8%) and with 1.0 g/h of HF. The analysis of the outflowing gases was carried out via GLC at different reaction temperatures and with contact times of about 5-7 seconds. The following results were obtained:

______________________________________Temperature A123 A123a CF.sub.3 CHFCl CF.sub.3 CHF.sub.2.degree.C. % % % %______________________________________240 88.3 11.5 0.14 0280 86.0 9.5 4.5 0.04320 60.6 2 34.3 3.08360 31.7 0.2 42.9 25.5380 20.1 0.2 23.7 56.2400 17.2 0.3 20.8 62______________________________________

EXAMPLE 5

2.35 g of a catalyst composed of Al.sub.2 O.sub.3 pellets (4-8 meshes) impregnated with CrCl.sub.3.6H.sub.2 O were treated firstly with nitrogen, then with HF at 360.degree. C. until obtaining an AlF.sub.3 content equal to 59.5% by weight, then they were charged into a tubular Inconel reactor. The catalyst contained 5.8% by weight of chrome. A mixture composed of Al23 (82.20%) and of Al23a (17.47 was fed to the reactor at a temperature of 260.degree. C., using different contact times; the outflowing gases were analyzed via GLC and the following results were obtained:

______________________________________ ContactTest time Al23 Al23a CF.sub.3 CHFCl CF.sub.3 CHF.sub.2No. sec. moles-% moles-% moles-% moles-%______________________________________1 2.5 77.5 2.2 15.7 0.682 11 79.6 0.27 15.1 0.33______________________________________

There were treated about 3.1 g of gaseous mixture in test 1 and 1.0 g in test 2, whereafter the catalyst can be regenerated and reutilized several times.

Claims

1. A process for selectively reducing or removing 1,1,2-trifluoro- 1,2-dichloroethane from its mixtures with 1,1,1-trifluoro-2,2-dichloroethane which comprises contacting a gaseous mixture comprising 1,1,2-trifluoro- 1,2-dichloroethane and 1,1,1-trifluoro-2,2-dichloroethane with a chrome oxide at temperatures ranging from 220.degree. to 320.degree. C. for a time ranging from 10 to 110 seconds under such conditions that dismutation of 1,1,2-trifluoro-l,2-dichloroethane occurs to yield a dismutation product, or products, removable from 1,1,1-tri-fluoro-2,2-dichloroethane.

2. A process for selectively reducing or removing 1,1,2-trifluoro- 1,2-dichloroethane from its mixtures with 1,1,1-trifluoro-2,2-dichloroethane which comprises contacting a gaseous mixture comprising 1,1,2-trifluoro- 1,2-dichloroethane and 1,1,1-trifluoro-2,2-dichloroethane with a chrome oxide carried on an aluminum trifluoride, at temperatures ranging from 220.degree. to 320.degree. C. for a time ranging from 10 to 110 seconds under such conditions that dismutation of 1,1,2-tri-fluoro-1,2-dichloroethane occurs to yield a dismutation product, or products, removable from 1,1,1-trifluoro-2,2-dichloroethane.

3. The process of claim 1 wherein the chrome oxide is in the crystalline form.

4. The process of claim 1, wherein the mixture of 1,1,2-trifluoro-1,2-dichloroethane and 1,1,1-trifluoro-2,2-dichloroethane is obtained in the preparation of 1,1,1-trifluoro-2,2-dichloroethane by hydrofluorination of perchloroethylene.

5. The process of claim 2, wherein the chrome oxide is in the crystalline form.

6. The process of claim 2, wherein the mixture of 1,1,2-trifluoro- 1,2-dichloroethane and 1,1,1-trifluoro-2,2-dichloroethane is obtained in the preparation of 1,1,1-trifluoro-2,2-dichloroethane by hydrofluorination of perchloroethylene.

7. The process of claim 1, further including the step of removing a dismutation product of 1,1,2-trifluoro- 1,2-dichloroethane from a mixture comprising 1,1,1-trifluoro-2,2-dichloroethane.

8. The process of claim 2, further including the step of removing a dismutation product of 1,1,2-trifluoro- 1,2-dichloroethane from the mixture comprising 1,1,1-trifluoro-2,2-dichloroethane.