Field of the invention
The present invention provides a process for preparation of monofluoroethane.
Background of the invention
Monofluoroethane is a colorless, odorless and flammable gas. Owing to their low global warming potential, they do not harm the ozone layer as much as chlorofluorocarbons and thus are being explored as potential refrigerants.
Journal of organic chemistry, 3, 26-32, 1938 discloses a process for addition of hydrogen fluoride to the olefin double bond. The reaction is carried out at different temperature in the absence of catalyst. The product recovered is in the form oil and need purification steps. Further, purification process aren’t described in the said reference.
US Patent No. 3988385 discloses a process for preparation of alkyl halide comprising the step of reacting a stream of an olefin and isoparaffin with hydrogen fluoride to produce a mixture of ethylene and monofluoroethane that require cumbersome separation. Thus the process is not viable for producing monofluoroethane at commercial scale.
GB Patent No. 406284 provides a process for preparation of alkyl halides by reacting olefins and hydrogen fluoride in presence of zinc fluoride at a temperature 100°C and a pressure of 50 atmospheres. It is difficult to maintain high pressure of 50 atmospheres at industrial scale.
There is a need in the art to provide a safe, selective and industrially applicable process for the preparation of monofluoroethane.
The inventors of present invention performed multiple reactions at varying temperature and pressure conditions, with and without catalyst to optimize the process for preparation of monofluoroethane.
Objects of the invention
The present invention provides a process for the preparation of monofluoroethane with better conversion and selectivity at lower temperature and pressure.
Summary of the invention
One aspect of the present invention provides a process for preparation of monofluoroethane
comprising the steps of:
a) reacting ethylene and hydrogen fluoride in a reactor filled with catalyst under pressure to obtain reaction mixture;
b) isolating monofluoroethane from step-a) reaction mass.

DETAILED DESCRIPTION OF INVENTION:
As used herein, Hydro fluorination refers to reaction of hydrocarbon with hydrogen fluoride.
Catalyst refers to a substance, which increases the rate of a chemical reaction without itself undergoing any permanent change.
Continuous process refers a process where the materials are continuously in motion undergoing chemical reaction and simultaneously isolating product.
One aspect of the present invention provides a process for preparation of monofluoroethane
comprising the steps of:
a) reacting ethylene and hydrogen fluoride in a reactor filled with catalyst under pressure to obtain reaction mixture;
b) isolating monofluoroethane from step-a) reaction mass.
In preferred embodiment, a process for preparation of monofluoroethane wherein the process is continuous.
In preferred embodiment, the monofluoroethane is isolated wherein the purity is greater than 95%.
In an embodiment, the pressure is less than 50Kg/cm2 and preferably less than 30Kg/cm2.
In most preferred embodiment, the pressure used for the preparation of monofluoroethane is less than 10Kg/cm2.
In a preferred embodiment, the reactor used for the preparation of monofluoroethane is Inconel.
In an embodiment, the reaction for preparation of monofluoroethane is carried out at a temperature between 323K to 573K. In preferred embodiment, the reaction is carried out at a temperature between 363K to 425K.
In a preferred embodiment, hydrogen fluoride in the process for preparation of monofluoroethane is anhydrous.
In preferred embodiment, the reaction for preparation of monofluoroethane is in vapor phase.
The catalyst may be selected from chromia, activated carbon, chromium fluoride, nickel fluoride, aluminum fluoride, alumina, copper fluoride, chromia-alumina and mixture thereof. The preferred catalyst for the present invention is aluminum fluoride with activated carbon.
In an embodiment, the catalyst used for preparation of monofluoroethane is aluminium fluoride. In a preferred embodiment, the catalyst is fluorinated alumina having surface area in the range of 10 -30 m2/gm. The fluorinated alumina is prepared by passing anhydrous hydrogen fluoride through alumina catalyst.
In an embodiment, the catalyst used for preparation of monofluoroethane is activated carbon having surface area in the range of 700-1200 m2/gm.
In an embodiment, the catalyst used for preparation of monofluoroethane is chromia. In a preferred embodiment, the chromia catalyst is activated by passing anhydrous hydrogen fluoride through it. Fluorinated chromia may include chromia with impregnations of zinc or manganese oxide and having surface area in the range of 20 to 50 m2/gm. Fluorinated chromia-alumina having surface area in the range of 10-40 m2/gm may also be used as a catalyst.
In an embodiment, the catalyst used for preparation of monofluoroethane is recycled for future batches.
In an embodiment, unconverted ethylene from the process for preparation of monofluoroethane is recovered and recycled back to Inconel reactor.
In an embodiment, the reaction mixture obtained from reactor in step-a) is scrubbed into water reactor to isolate monofluoroethane.
In another embodiment, the molar ratio of hydrogen fluoride to ethylene is 3:1 for the preparation of monofluoroethane.
In an embodiment, the selectivity for monofluoroethane is greater than 90%.
The addition of hydrogen fluoride to double bond is exothermic in nature, assuming this fact step-a) reaction is carried out under moderately low-pressure condition and lower temperature.
In an embodiment, step-a reaction is carried at a temperature between 323-573 K. The preferred temperature of this step is 363K-425K giving high conversion and selectivity. Exothermicity in hydro fluorination is very little, or negligible for present invention. The Step-a) reaction is carried out under a pressure of less than 50 Kg/Cm2 gauge, preferably less than 30 Kg/cm2 gauge and most preferably less than 10 Kg/Cm2 gauge to obtain best result.
The reaction of step-a) is carried out in vapor phase. The molar ratio of hydrogen fluoride to ethylene is 3:1 for present invention. The hydro fluorination is carried out with and without catalyst to find out the optimum conditions. The Hydro fluorination of ethylene has given better selectivity and higher conversion with catalyst.
A calculated amount of catalyst is used for present invention for better selectivity and conversion.
The residence time of reactant can range from 1 – 100 seconds, preferably from 10 – 50 seconds, more preferably from 20 – 40 seconds.
The reaction mixture obtained from outlet of Inconel reactor was scrubbed into water reactor to remove unreacted hydrogen fluoride. Monofluoroethane, free of hydrogen fluoride, was isolated from the outlet of water scrubber.
The catalyst used in the preparation of monofluoroethane is recycled for the future batches. The process of activation of catalyst can be used for preparation of monofluoroethane.
The conversion for preparation of monofluoroethane is greater than 40%. The unconverted ethylene was recycled back to reactor for hydrofluorination.
Unless stated to the contrary, any of the words “comprising”, “comprises” and includes mean “including without limitation” and shall not be construed to limit any general statement that it follows to the specific or similar items or matters immediately following it.
Embodiments of the invention are not mutually exclusive, but may be implemented in various combinations. The described embodiments of the invention and the disclosed examples are given for the purpose of illustration rather than limitation of the invention as set forth in the appended claims.
The following example is given by way of illustration and therefore should not be construed to limit the scope of the present invention.

EXAMPLE
Example 1: Preparation of monofluoroethane
Activated carbon (210gms) was filled in Inconel reactor. The ethylene and hydrogen fluoride, both in vapor phase were charged in Inconel reactor in continuous mode at 423K at 6Kg/cm2. The outlet of the reactor was charged in water scrubber. Water outlet was collected to isolate monofluoroethane and analyzed.
Selectivity= 95.69%
Conversion= 83.29%
Example 2: Preparation of monofluoroethane
Chromia CP 200A (210gms) was filled in Inconel reactor. The ethylene and hydrogen fluoride, both in vapor phase were charged in Inconel reactor in continuous mode at 363K at 6Kg/cm2. The outlet of the reactor was charged in water scrubber. Water outlet was collected to isolate monofluoroethane and analyzed.
Selectivity= 97.02%
Conversion= 97.21%
Example 3: Preparation of monofluoroethane
Aluminum fluoride (396gms) was filled in Inconel reactor. The ethylene and hydrogen fluoride, both in vapor phase were charged in Inconel reactor in continuous mode at 363K at 6Kg/cm2. The outlet of the reactor was charged in water scrubber. Water outlet was collected to isolate monofluoroethane and analyzed.
Selectivity= 97.50%
Conversion= 96.19%
Example 4: Preparation of monofluoroethane
Chromia CP 200A (210gms) was filled in Inconel reactor. The ethylene and hydrogen fluoride, both in vapor phase were charged in Inconel reactor in continuous mode at 398K at 6Kg/cm2. The outlet of the reactor was charged in water scrubber. Water outlet was collected to isolate monofluoroethane and analyzed.
Selectivity= 94.67%
Conversion= 72.25%

Example 5: Preparation of monofluoroethane
Aluminum fluoride (260gm) was filled in Inconel reactor. The ethylene and hydrogen fluoride, both in vapor phase were charged in Inconel reactor in continuous mode at 363K at 7Kg/cm2. The outlet of the reactor was charged in water scrubber. Water outlet was collected to isolate monofluoroethane and analyzed.
Selectivity= 97.75%
Conversion= 98.5%
Example 6: Preparation of monofluoroethane
Chromia CP 200A (260gm) was filled in Inconel reactor. The ethylene and hydrogen fluoride, both in vapor phase were charged in Inconel reactor in continuous mode at 363K at 7Kg/cm2. The outlet of the reactor was charged in water scrubber. Water outlet was collected to isolate monofluoroethane and analyzed.
Selectivity= 96.32%
Conversion= 96.21%
Example 7: Preparation of monofluoroethane
Chromia CP 200A (260gm) was filled in Inconel reactor. The ethylene and hydrogen fluoride, both in vapor phase were charged in Inconel reactor in continuous mode at 363K at 5Kg/cm2. The outlet of the reactor was charged in water scrubber. Water outlet was collected to isolate monofluoroethane and analyzed.
Selectivity= 97.70%
Conversion= 97.20%
Example 8: Preparation of monofluoroethane
Aluminum fluoride (260gm) was filled in Inconel reactor. The ethylene and hydrogen fluoride, both in vapor phase were charged in Inconel reactor in continuous mode at 363K at 5Kg/cm2. The outlet of the reactor was charged in water scrubber. Water outlet was collected to isolate monofluoroethane and analyzed.
Selectivity= 98.48%
Conversion= 88.8%

Example 9: Preparation of monofluoroethane
Aluminum fluoride (260gm) was filled in Inconel reactor. The ethylene and hydrogen fluoride, both in vapor phase were charged in Inconel reactor in continuous mode at 363K at 4Kg/cm2. The outlet of the reactor was charged in water scrubber. Water outlet was collected to isolate monofluoroethane and analyzed.
Selectivity= 98.36%
Conversion= 62.1%
Example 10: Preparation of monofluoroethane
Aluminum fluoride (260gm) was filled in Inconel reactor. The ethylene and hydrogen fluoride, both in vapor phase were charged in Inconel reactor in continuous mode at 373K at atmospheric pressure. The outlet of the reactor was charged in water scrubber. Water outlet was collected to isolate monofluoroethane and analyzed.
Selectivity= 74.49%
Conversion= 12.36%
Example 11: Preparation of monofluoroethane
Aluminum fluoride (260gm) was filled in Inconel reactor. The ethylene and hydrogen fluoride, both in vapor phase were charged in Inconel reactor in continuous mode at 473K at atmospheric pressure. The outlet of the reactor was charged in water scrubber. Water outlet was collected to isolate monofluoroethane and analyzed.
Selectivity= 73.59%
Conversion= 16.58%
Example 12: Preparation of monofluoroethane
Aluminum fluoride (260gm) was filled in Inconel reactor. The ethylene and hydrogen fluoride, both in vapor phase were charged in Inconel reactor in continuous mode at 573K at atmospheric pressure. The outlet of the reactor was charged in water scrubber. Water outlet was collected to isolate monofluoroethane and analyzed.
Selectivity= 37.49%
Conversion= 8.14%
Example 13: Preparation of monofluoroethane
The ethylene and hydrogen fluoride, both in vapor phase were charged in Inconel reactor without catalyst in continuous mode at 373K at 7Kg/cm2. The outlet of the reactor was charged in water scrubber. Water outlet was collected to isolate monofluoroethane and analyzed.
Selectivity= 88.74%
Conversion= 74.54%
Example 14: Preparation of monofluoroethane
The ethylene and hydrogen fluoride, both in vapor phase were charged in Inconel reactor without catalyst in continuous mode at 398K at 7Kg/cm2. The outlet of the reactor was charged in water scrubber. Water outlet was collected to isolate monofluoroethane and analyzed.
Selectivity= 84.66%
Conversion= 11.7%
Example 15: Preparation of monofluoroethane
The ethylene and hydrogen fluoride, both in vapor phase were charged in Inconel reactor without catalyst in continuous mode at 423K at 0.5Kg/cm2. The outlet of the reactor was charged in water scrubber. Water outlet was collected to isolate monofluoroethane and analyzed.
Selectivity= 79.5%
Conversion= 0.26%
Example 16: Preparation of monofluoroethane
The ethylene and hydrogen fluoride, both in vapor phase were charged in Inconel reactor without catalyst in continuous mode at 423K at 0.25Kg/cm2. The outlet of the reactor was charged in water scrubber. Water outlet was collected to isolate monofluoroethane and analyzed.
Selectivity= 0.0%
Conversion= 0.46%

We Claim:
1. A process for preparation of monofluoroethane, comprising the steps of:
a) reacting ethylene and hydrogen fluoride in a reactor filled with catalyst under pressure to obtain reaction mixture;
b) isolating monofluoroethane from step-a) reaction mass.

2. The process as claimed in claim 1, wherein process is carried out at a temperature between 323K to 573K.

3. The process as claimed in claim 1, wherein ethylene and hydrogen fluoride are charged in vapour phase to the reactor.

4. The process as claimed in claim 1, wherein catalyst may be selected from chromia, activated carbon, chromium fluoride, nickel fluoride, aluminium fluoride, alumina, chromia-alumina, copper fluoride or mixture thereof.

5. The process as claimed in claim 4, wherein catalyst is activated in presence of hydrogen fluoride.

6. The process as claimed in claim 1, wherein process for preparation of monofluoroethane is continuous.

7. The process as claimed in claim 1, wherein the molar ratio of hydrogen fluoride to ethylene is 3:1.

8. The process as claimed in claim 1, wherein residence time of reactant can range from 1 – 100 seconds.