The present invention provides a process for co-production of hydrofluoropropene and hydrofluorocarbon from a solution of trichlorodifluoropropanes.

BACKGROUND OF THE INVENTION
Fluoropropenes and hydrofluorocarbon are important compounds and possess several applications as refrigerants, blowing agent and solvents.
Fluoropropenes are known to have zero ozone depletion potential (ODP) and low global warming potential (GWP) therefore show promise as refrigerants, blowing agents, solvents, heat transfer agents etc.
Hydrofluorocarbons, particularly difluoromethane, are widely used in commercial and residential air conditioner as a substitute for R-410A. Difluoromethane exhibits heat transfer coefficients higher than those of R-410A under the same operating conditions.
The mixtures containing fluoropropenes and hydrofluorocarbons find plenty of application in refrigeration, air conditioning and heat pump systems.
U.S. Pat. No. 2996555 provides a process for preparation of 2,3,3,3-tetrafluoropropene using trichlorodifluoropropane and hydrogen fluoride in presence of chromium oxyfluoride catalyst in vapour phase. The trichlorodifluoropropane, particularly 1,1,1-trichloro-2,2-difluoropropane is solid in nature (boiling point of 102°C) and requires continuous heating at above 100°C in order to pass it through the catalyst. The continuous heating at high temperature may degrade starting material and impact purity of the final tetrafluoropropene.
Therefore, there is a need in the art to develop a process for preparation of tetrafluoropropene in vapour phase that is economic and industrially viable.

OBJECT OF THE INVENTION
The main object of present invention is to provide a process for co-production of fluoropropene and hydrofluorocarbon from a solution of chlorofluoropropanes in a chlorinated solvent. The present invention provides an economic process for co-production of tetrafluoropropene and hydrofluorocarbon.

SUMMARY OF THE INVENTION
The present invention provides a process for co-production of fluoropropene and difluoromethane comprising a step of hydrofluorination of chlorofluoropropane using hydrogen fluoride in dichloromethane in presence of chromia catalyst.

DETAILED DESCRIPTION OF THE INVENTION
As used herein, the inert gas is selected from nitrogen, xenon, argon or like.
As used herein, the material of the reactor employed in carrying out the present invention is selected from group consisting of Hastelloy, Inconel, Monel and/or fluoropolymers linings. The fluoropolymer refers to fluorinated ethylene-propylene (FEP), polytetrafluoroethylene (PTFE), polychlorotrifluoro-ethylene (PCTFE) and polyvinylidene fluoride (PVDF) or like. Preferably the reactor is Inconel.
As used herein, the fluoropropene is selected from a group consisting of 2,3,3,3-tetrafluoropropene (1234yf), 1,3,3,3-tetrafluoropropene (1234ze), 3-chloro-1,1,1-trifluoropropene (1233zd) or the like.
As used herein the product stream of a fluoropropene such as 2,3,3,3-tetrafluoropropene may further comprise of compound selected from hydrogen fluoride, hydrogen chloride, 2-chloro-3,3,3-trifluoropropene, 1,1,1,2,2-pentafluoropropane, 1-chloro-1,1,2,2-tetrafluoropropane, 1,1-dichloro-1,2,2-trifluoropropane, 1,1,1-trichloro-2,2-difluoropropane.
As used herein, the chlorofluoropropane is selected from a group consisting of 1,1,1-trichloro-2,2-difluoropropane (HCFC-242bb), 1,1,1,2,2-pentafluoropropane (HFC-245cb), 2-chloro-1,1,1,2-tetrafluoropropane (HFC-244bb), 1,1,1,2- tetrachloro-2-fluoropropane (HCFC-241bb) and 1,1,1,2,2-pentachloropropane (HFC-245cb), 1,1,1-trichloro-2,3-difluoropropane (HCFC-242cb) or the like.
As used herein, the process of hydrofluorination in the presence of a catalyst involves fluorination as well as dehydrohalogenation to obtain fluoropropene. The hydrofluorination is carried out using an anhydrous hydrogen fluoride. The molar ratio of hydrogen fluoride w.r.t chlorofluoropropane and dichloromethane is selected in a range from 2-10 moles and more preferably 3-8 moles.
As used herein the anhydrous refers to moisture content of less than 1000ppm and more preferably between 100-500ppm.
As used herein, the catalyst for hydrofluorination is a chromia catalyst.
As used herein, the chromia catalyst of the present invention is either crystalline, amorphous or a mixture thereof and is in the form of granules, pellets or sticks. The chromia catalyst of the present invention may be supported on carbon, alumina, silica or mixture thereof or unsupported. The chromia catalyst may additionally contain metal selected from a group consisting of zinc, tin, iron, chromium, copper, nickel or like in the range of 0.1 % to 1 % mass percentage. The chromia catalyst of the present invention may contain 0.01 to 25% by weight zinc.
The chromia catalyst of the present invention has surface area from 90-150m2/g and pore volume of greater than 0.2cc/g.
In an embodiment, chromia catalyst of the present invention is supported on carbon. The chromia catalyst of the present invention is amorphous in nature and used in the pellet form.
In another embodiment, chromia catalyst is dehydrated in a vapour phase reactor with inert gas at 100-200°C.
In a specific embodiment, the chromia catalyst of the present invention is chromium oxyfluoride of formula CrOxFy, wherein x and y is 1 or 2, provided x+y is 3. The chromia oxyfluoride of the present invention is heated with hydrogen fluoride to form activated catalyst. The concentration of hydrogen fluoride may vary from 1-100 % and more preferably 50-90 % in a mixture of nitrogen and hydrogen fluoride. The chromia catalyst is activated before fluorination and dehydrohalogenation.
In an embodiment of present invention, activated catalyst is prepared in-situ and is used without isolation.
In an embodiment, a solution of chlorofluoropropane in dichloromethane is prepared and passed through chromia catalyst to produce fluoropropene.
The contact time of hydrogen fluoride and chlorofluoropropane in a reactor is 5-50 sec.
In a specific embodiment, the present invention provides a process for co-production of 1234yf and difluoromethane by hydrofluorinating a solution of 1,1,1-trichloro-2,2-difluoropropane in dichloromethane with hydrogen fluoride in vapour phase in presence of chromium oxyfluoride catalyst.
A solution of 1,1,1-trichloro-2,2-difluoropropane which can be easily vaporised charged into reactor.
In another specific embodiment, present invention provides a process for preparation of 1234yf, comprising the steps of:
a) activating chromia catalyst using hydrogen fluoride in presence of an inert gas;
b) simultaneous fluorination and dehydrohalogenation of a solution 1,1,1-trichloro-2,2-difluoropropane in dichloromethane with hydrogen fluoride in presence of activated catalyst to obtain a reaction mixture comprising 2,3,3,3-tetrafluoropropene and difluoromethane; and
c) separating reaction mixture to obtain 2,3,3,3-tetrafluoropropene and difluoromethane.
In another specific embodiment, the present invention provides a process for co-production for tetrafluoropropene and difluoromethane, comprising the steps of:
a) activating chromia catalyst using hydrogen fluoride, optionally in presence of an inert gas;
b) simultaneous fluorination and dehydrohalogenation of a solution of 1,1,1-trichloro-2,2-difluoropropane in dichloromethane with hydrogen fluoride in presence of an active catalyst to obtain a composition comprising 2,3,3,3-tetrafluoropropene and difluoromethane.
In an embodiment, simultaneous fluorination and dehydrohalogenation is carried out using anhydrous hydrogen fluoride at a temperature selected in the range of 150 to 600°C and more preferably in the range from 300-400°C. The temperature of reactor is increased slowly or 20-50°C per hour. The simultaneous fluorination and dehydrohalogenation in vapour phase are a continuous process.
A solution of 1,1,1-trichloro-2,2-difluoropropane in dichloromethane is charged in vaporisation zone using a dosing pump.
In another embodiment, vapours of hydrogen fluoride and 1,1,1-trichloro-2,2-difluoropropane in dichloromethane are mixed in static mixer before passing through active catalyst.
In another embodiment, vapours of hydrogen fluoride and 1,1,1-trichloro-2,2-difluoropropane in dichloromethane are separately charged on active catalyst.
In a specific embodiment, solution of 1,1,1-trichloro-2,2-difluoropropane in dichloromethane is charged in a vaporisation zone, vaporised, and mixed with hydrogen fluoride vapours in a static mixer at a temperature in the range 150-300°C before passing through active catalyst.
The concentration of dichloromethane in a solution of trichlorodifluoropropane in dichloromethane is between 5% to 95%, preferably 5% to 50% and more preferably 5% to 30%.
The selectivity of formation of 2,3,3,3-tetrafluoropropane and difluoromethane depends upon the concentration of 1,1,1-trichloro-2,2-difluoromethane and dichloromethane in solution.
In an embodiment, where the concentration of dichloromethane is 10% and 1,1,1-trichloro-2,2-difluoropropane is 90%, the selectivity of formation of 2,3,3,3-tetrafluoropropene is between 70-95% and selectivity of difluoromethane is between 8% to 10%.
In an embodiment, where the concentration of dichloromethane is 5% and 1,1,1-trichloro-2,2-difluoropropane is greater than 90%, the selectivity of formation of 2,3,3,3-tetrafluoropropene is greater than 75-95% and selectivity of difluoromethane is between 3-5%.
In an embodiment, reactor outlet stream is washed with water and isolated to obtain a composition comprising 2,3,3,3-tetrafluoropropene and difluoromethane.
In an embodiment, present invention provides a composition comprising 2,3,3,3-tetrafluoropropene and difluoromethane.
In an embodiment, reactor outlet stream is washed with water and separated by distillation to obtain a stream comprising majority of 2,3,3,3-tetrafluoropropene and another stream comprising majority of difluoromethane.
In another embodiment, the 2,3,3,3-tetrafluoropropene and difluoromethane are separated by pressure swing distillation.
In another embodiment, reactor outlet stream is washed with water and isolated a composition comprising 2,3,3,3-tetrafluoropropene and difluoromethane.
In an embodiment, catalyst, and excess hydrogen fluoride is recovered, regenerated and recycled.
In specific embodiment, a solution of 1,1,1-trichloro-2,2-difluoropropane in dichloromethane and hydrogen fluoride are vaporised and passed through active catalyst at a temperature 400°C.
In a specific embodiment, a solution of dichloromethane and 1,1,1-trichloro-2,2-difluoropropane is vaporised at 150-200°C and mixed with vaporised hydrogen fluoride and passed through active catalyst at a temperature 350°C.
In an embodiment, a solution of 1,1,1-trichloro-2,2-difluoropropane in dichloromethane and hydrogen fluoride are vaporised and passed through catalyst from separate inlets at 300°C.
In another specific embodiment, the present invention provides a process for preparation of 2,3,3,3-tetrafluoropropene, comprising the steps of:
a) activating chromia catalyst using hydrogen fluoride in presence of an inert gas;
b) charging a solution of 1,1,1-trichloro-2,2-difluoropropane in dichloromethane (10%) and hydrogen fluoride in vaporising zone and mixed in static mixer;
c) charging mixed vapours of a solution of 1,1,1-trichloro-2,2-difluoropropane in dichloromethane and hydrogen fluoride in reaction zone over active catalyst to carry out simultaneous fluorination and dehydrohalogenation at 300-400°C to obtain a reaction mixture containing 2,3,3,3-tetrafluoropropene and difluoromethane;
d) separating a stream comprising 2,3,3,3-tetrafluoropropene and another stream comprising difluoromethane from step-c reaction mixture.
The concentration of 1,1,1-trichloro-2,2-difluoropropane in dichloromethane ranges from 5-10%.
In a specific embodiment, a composition may comprise 2,3,3,3-tetrafluoropropene in 75-90% and difluoromethane in 3-10%, wherein a solution of trifluorodichloropropane in dichloromethane (10%) is used.
Tetrafluoropropene and difluoromethane are isolated by any method known in the art, for example, chemical separation, extraction, acid-base neutralization, distillation, evaporation, and filtration or a mixture thereof.
1,1,1-trichloro-2,2-difluoropropane used for present invention is having purity greater than 80 % and more preferably 90 % and most preferably between 95-99 %.
In an embodiment, 1,1,1-trichloro-2,2-difluoropropane is prepared from 1-chloro-2,2-difluoropropane in presence of catalyst in a reactor selected from Hastelloy, Inconel, Monel and/or fluoropolymers linings.
In an embodiment, 1-chloro-2,2-difluoropropane may be prepared from fluorination of 2,3-dichloropropene or fluorination of 1,2,2-trichloropropane.
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.

EXAMPLES
Example 1: Preparation of 2,3,3,3-tetrafluoropropene and difluoromethane.
Chromia catalyst was charged in an Inconel reactor and reactor temperature was heated to 180°C. Nitrogen was passed through the reactor at 180°C for 15 hours. Then, reactor temperature was reduced to 100°C and hydrogen fluoride was passed at a constant flow rate. The reactor temperature was slowly heated to 350°C along with hydrogen fluoride flow. A solution of 1,1,1-trichloro-2,2-difluoropropane in dichloromethane (5%) and hydrogen fluoride (0.5 moles) were vaporised separately and mixed in a static mixer. The mixed stream was passed through the active catalyst bed at 300°C. The reactor outlet stream was scrubbed in water and washed gas was collected at -60°C.
Reaction mixture analysis: 2,3,3,3-tetrafluoropropene: 76.11%; Difluoromethane: 3.77% and small amount of 1,1,1,2,2-pentafluoropropane and 2-chloro-3,3,3-trifluoropropene, which was removed through distillation.
Example 2: Preparation of 2,3,3,3-tetrafluoropropene and difluoromethane.
Chromia catalyst was charged in an Inconel reactor and reactor temperature was heated to 180°C. Nitrogen was passed through the reactor at 180°C for 15 hours. Then, reactor temperature was reduced to 100°C and hydrogen fluoride was passed at a constant flow rate. The reactor temperature was slowly heated to 350°C along with hydrogen fluoride flow. A solution of 1,1,1-trichloro-2,2-difluoropropane in dichloromethane (10%) and hydrogen fluoride (0.5 moles) were vaporised separately and mixed in a static mixer. The mixed stream was passed through the active catalyst bed at 300°C. The reactor outlet stream was scrubbed in water and washed gas was collected at -60°C.
Reaction mixture analysis: 2,3,3,3-tetrafluoropropene: 75.5%; Difluoromethane: 8.5% and small amount of 1,1,1,2,2-pentafluoropropane and 2-chloro-3,3,3-trifluoropropene, which was removed through distillation.

WE CLAIM:

1. A process for co-production of 2,3,3,3-tetrafluoropropene and difluoromethane comprising the step of hydrofluorination of 1,1,1-trichloro-2,2-difluoropropane in dichloromethane in presence of a chromia catalyst.
2. The process as claimed in claim 1, wherein the chromia catalyst is activated using hydrogen fluoride in presence of an inert gas.
3. The process as claimed in claim 1, wherein the hydrofluorination is carried out using hydrogen fluoride in a molar ratio 2-10 moles with respect to 1,1,1-trichloro-2,2-difluoropropane.
4. The process as claimed in claim 1, wherein the hydrofluorination is carried out at a temperature of 150 to 600°C.
5. The process as claimed in claim 1, wherein hydrofluorination involves passing a solution of 1,1,1-trichloro-2,2-difluoropropane in dichloromethane through a chromia catalyst.
6. The process as claimed in claim 1, wherein a solution of 1,1,1-trichloro-2,2-difluoropropane in dichloromethane is charged in a vaporisation zone, vaporised, and mixed with hydrogen fluoride vapours in a static mixer at a temperature in the range 150-300°C before passing through the catalyst.
7. The process as claimed in claim 1, wherein the chromia catalyst is crystalline, amorphous or a mixture thereof and is in the form of granules, pellets or sticks.