DESC:FORM 2
THE PATENT ACT 1970
(39 of 1970)
&
THE PATENT RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)

A PROCESS FOR PREPARATION OF 2,3,3,3-TETRAFLUOROPROPENE AND INTERMEDIATE THEREOF

SRF LIMITED, AN INDIAN COMPANY,
SECTOR 45, BLOCK-C, UNICREST BUILDING,
GURGAON – 122003,
HARYANA (INDIA)

The following specification particularly describes the invention and the manner in which it is to be performed.
FIELD OF THE INVENTION
The present invention provides a process for preparation of tetrafluoropropene from chloro substituted trifluoropropanes.
BACKGROUND OF THE INVENTION
Hydrofluoroolefins, particularly, tetrafluoropropenes are important compounds and possess several applications as refrigerants, blowing agent, solvents etc.
There are several methods known in the literature for the preparation of hydrofluoroolefins.
U.S. Patent No. 2,996,555 discloses a process for preparation of 2,3,3,3-tetrafluoropropene using trichlorodifluoropropane and hydrogen fluoride. The process is carried out in presence of chromium oxyfluoride as catalyst.
U.S. Patent No. 8,633,340 discloses a process for preparing 2,3,3,3-tetrafluoropropene comprising a step of preparing 1,1,1-trifluoro-2,3-dichloropropane (243db), by contacting 3,3,3-trifluoropropene (1243zf) with chlorine in the presence of activated carbon, alumina and/or an oxide of a transition metal.
U.S. Patent No. 8,546,623 discloses a process for preparation 2,3,3,3-tetrafluoropropene comprising a step of dehydrohalogenation using zinc/chromia catalyst that contains from 0.01 to about 25% by weight zinc.
U.S. Patent No. 9,567,275 discloses a process for preparation of 2,3,3,3-tetrafluoropropene comprising steps of fluorinating 3,3,3-trifluoro-2-chloropropene (CF3CCl-CH2) with HF in the vapour phase in the presence of a chromia-containing catalyst to produce an intermediate composition comprising 1,1,1,2-tetrafluoro-2-chloropropane (CF3CFClCH3) and 1,1,1,2,2-pentafluoropropane (CF3CF2CH3), followed by de-hydrochlorinating the intermediate to produce 2,3,3,3-tetrafluoropropene.
U.S. Patent No. 8,207,384 discloses a process for preparing 2,3,3,3-tetrafluoropropene (1234yf), comprising a step of contacting 2,3-dichloro-1,1,1-trifluoropropane (243db) with hydrogen fluoride in the gas phase in the presence of a fluorination catalyst under conditions sufficient to produce 2-chloro-3,3,3-trifluoro-1-propene (1233xf).
However, there still exists a need in the art to develop a process for preparing tetrafluoropropene and intermediates, which is economical and industrially satisfactory.
OBJECT OF THE INVENTION
The main object of present invention is to provide an economical and improved process for preparation of tetrafluoropropene and intermediate thereof.
SUMMARY OF THE INVENTION
In an aspect, the present invention provides a process for preparation of 2,3,3,3-tetrafluoropropene, comprising the steps of:
(i) contacting 2,3-dichloro-1,1,1-trifluoropropane (243db) with a catalyst in absence of HF to produce a reaction mixture comprising 2-chloro-3,3,3-trifluoropropene (1233xf);
(ii) contacting 2-chloro-3,3,3-trifluoropropene (1233xf) with HF in presence of a catalyst to produce 2,3,3,3-tetrafluoropropene.
DETAILED DESCRIPTION OF THE INVENTION
In an embodiment of the present invention, the step of contacting 2,3-dichloro-1,1,1-trifluoropropane (243db) with a catalyst is carried out at a temperature of 300-370?.
In an embodiment of the present invention, the step of contacting 2,3-dichloro-1,1,1-trifluoropropane (243db) with a catalyst selected from a group consisting of chromia, chromia-alumina, fluorinated alumina, fluorinated chromia, activated carbon, phase transfer catalyst such as trioctylmethylammonium chloride or like.
In another embodiment of the present invention, the step of contacting 2,3-dichloro-1,1,1-trifluoropropane (243db) with a catalyst produces 2-chloro-3,3,3-trifluoropropene (1233xf) along with unreacted 2,3-dichloro-1,1,1-trifluoropropane (243db), hydrochloric acid. These compounds can be easily separated by using physical separation techniques.
In another embodiment of the present invention, the step of contacting 2,3-dichloro-1,1,1-trifluoropropane (243db) with a catalyst to produce 2-chloro-3,3,3-trifluoropropene is followed by a step of physical separation techniques to separate 2-chloro-3,3,3-trifluoropropene (1233xf) from a reaction mixture containing 2-chloro-3,3,3-trifluoropropene (1233xf), unreacted 2,3-dichloro-1,1,1-trifluoropropane (243db), and hydrochloric acid.
In another embodiment of the present invention, the step of contacting 2,3-dichloro-1,1,1-trifluoropropane (243db) with a catalyst produces 2-chloro-3,3,3-trifluoropropene (1233xf) along with unreacted 2,3-dichloro-1,1,1-trifluoropropane (243db), hydrochloric acid, wherein no hydrofluoric acid (HF) is present.
In another embodiment of the present invention, the step of contacting 2-chloro-3,3,3-trifluoropropene (1233xf) with HF is carried out at a temperature of 330-350?.
In another embodiment of the present invention, the step of contacting 2-chloro-3,3,3-trifluoropropene (1233xf) with HF is carried out in presence of a catalyst selected from a group consisting of chromia, chromia-Alumina.
In another embodiment of the present invention, the step of contacting 2-chloro-3,3,3-trifluoropropene (1233xf) with HF is carried out in presence of a catalyst selected from a group consisting of chromia, chromia-alumina, wherein the catalyst has been fluorinated using HF.
The reactor for present invention may be comprised of materials, which are resistant to corrosion such as hastelloy, inconel, monel and/or fluoropolymers linings.
As used herein, fluoropolymer refers to fluorinated ethylene-propylene (FEP), polytetrafluoroethylene (PTFE), polychlorotrifluoro-ethylene (PCTFE) and polyvinylidene fluoride (PVDF) or like.
The glass reactor is not compatible during reaction of fluorinated compounds. The reaction of fluorinated or chlorinated compounds produces hydrogen fluoride in the reaction mixture due to small decomposition. The hydrogen fluoride has very high reactivity with glass or silica and corrodes the reactor. This side reaction will reduce life cycle of reactor and increase equipment cost.
SiO2 + 6HF ? H2SiF6 + 2H2O [1]
In another embodiment of the present invention, the chromia catalyst is activated using hydrogen fluoride prior to its use in fluorination step.
In another embodiment of the present invention, the activation of the catalyst is carried out in-situ.
As used herein, in-situ refers to a process of preparing an intermediate in reaction and using it, without isolation.
In an embodiment, the reaction of chromia and hydrogen fluoride gives active catalyst, wherein it is used in-situ.
As used herein, “active catalyst” refers to a catalyst formed by reaction of chromia catalyst and hydrogen fluoride. The active catalyst for present invention is chromium oxyfluoride. It is observed that chromium oxyfluoride catalyst is not stable at room temperature.
In an embodiment of the present invention, the step of contacting 2-chloro-3,3,3-trifluoropropene (1233xf) with HF comprises fluorination and dehydrohalogenation.
In an embodiment, the step of contacting 2-chloro-3,3,3-trifluoropropene (1233xf) with HF, wherein the molar ratio hydrogen fluoride (HF) to 2-chloro-3,3,3-trifluoropropene (1233xf) is in the range from 2-20 equivalents.
In an embodiment, the chromia catalyst is activated in a reactor before fluorination and dehydrohalogenation. The chromia catalyst used for present invention has surface area from 90-150m2/g and pore volume of greater than 0.2cc/g.
In preferred embodiment, chromia catalyst is amorphous in nature and used in the pellet form.
In an embodiment, chromia catalyst used for present invention is supported on carbon. The chromia catalyst is present as a fixed bed catalyst.
In an embodiment, chromium oxyfluoride is prepared in-situ for preparation of tetrafluoropropene.
In specific embodiment, activation, and simultaneous fluorination and dehydrohalogenation is carried out in an Inconel reactor.
In an embodiment, fluorination and dehydrohalogenation is carried out in presence of active catalyst.
In an embodiment of present invention, active catalyst is prepared in-situ in fluorination and dehydrohalogenation reaction.
In an embodiment present invention, the step of contacting 2-chloro-3,3,3-trifluoropropene with hydrogen fluoride in reactor is 5-50 seconds.
In an embodiment, the catalyst is dehydrated before activation of catalyst using hydrogen fluoride.
In an embodiment, after dehydration, chromia catalyst is fluorinated using hydrogen fluoride or a mixture of nitrogen and hydrogen fluoride to form chromium oxyfluoride in-situ, which is the active catalyst for present invention. The concentration of hydrogen fluoride may vary from 1-100 % and more preferably 50-90 % in a mixture of nitrogen and hydrogen fluoride.
The selectivity of formation of 2,3,3,3-tetrafluoropropene is greater than 75% and more preferably greater than 85% and most preferably between 85-95%.
In an embodiment, reactor outlet stream after fluorination and dehydrohalogenation is quenched in a base solution or an aqueous scrubber. The base for present invention is selected from a group consisting of sodium carbonate, potassium carbonate, potassium hydroxide, sodium hydroxide or like. For present invention, quenching refers to neutralising acid content from a stream. The acid content may be due to presence of hydrogen fluoride, hydrogen chloride or mixture thereof.
In an embodiment, reaction outlet stream is quenched and distilled to obtain tetrafluoropropene.
In an embodiment, 2,3,3,3-tetrafluoropropene is isolated by distillation.
The catalyst and excess hydrogen fluoride is regenerated and recycled.
Tetrafluoropropene is isolated by any method known in the art, for example, chemical separation, extraction, acid-base neutralization, distillation, evaporation, and filtration or a mixture thereof.
The raw materials 2,3-dichloro-1,1,1-trifluoropropane (243db) can be commercially procured or prepared by any method known in the art.
The raw material 2,3-dichloro-1,1,1-trifluoropropane (243db) used in the process may be prepared by preparing 1,1,1,3-Tetrachloropropane (250fb) using the process disclosed in EP0131560B1, followed by fluorination of 1,1,1,3-Tetrachloropropane (250fb) using the process disclosed in US2889379/US4465786 or references therein to produce 3,3,3-trifluoropropene (1243zf), which upon chlorination (per the Chem. Eur. J., 4(9), 1807, (1998)) gives 2,3-dichloro-1,1,1-trifluoropropane (243db).
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 1,1,1,3-tetrachloropropane (250fb)
In a 5L autoclave, carbon tetrachloride (5500 g), Triethyl phosphate (81.5 g), Fe Powder (11 g) and iron chloride (21 g) were charged. The reaction mass was heated to 120? and started adding ethylene (900 g). The ethylene addition was continued for 7 hours, and the reactor pressure was maintained at 10 kg/cm2. After reaction, the reaction mass was analysed and sent to a series of distillation column where unreacted carbon tetrachloride was removed and recycled. The next column operated under vacuum, wherein pure R-250fb was removed as top cut. The bottom mass of the second distillation containing some pentachloropropane and catalyst which is again recycled back into reactor.
Purity: 99 %; Yield: 95 %.
Example 2: Preparation of 3,3,3-trifluoropropene (1243zf)
In a 1” Inconel tubular reactor, chromium fluoride (500 g) was charged. The catalyst bed temperature was raised to 220? and started addition of anhydrous hydrogen fluoride (91 g/hour) into the reactor along with 1,1,1,3-Tetrachloropropane (70 g/hour). The reactor outlet stream was passed through a water scrubber for removing acids and analysed. The pure 3,3,3-Trifluoropropene was recovered through distillation.
Conversion: >99 %; R-1243zf Selectivity: 95 %.
The example 2 process was repeated out using catalyst chromium fluoride, aluminium fluoride, chromium oxyfluoride or mixture thereof.
Example 3: Preparation of 1,2-dichloro-3,3,3-trifluoropropene (243db)
The photochemical reactor was step up for chlorination reaction and used light of wavelength, in the range of 300 to 600 nm. Chlorine (31 g/hour) and 3,3,3-Trifluoropropene (48 g/hour) were passed through the photochemical reactor which was maintained at 50? and 10 kg/cm2g. The reactor outlet sample was passed through caustic scrubber and analysed.
Conversion: 60-70 %; R-243db Selectivity: 95 %
Example 4: Preparation of 1,2-dichloro-3,3,3-trifluoropropene (243db)
Chlorine (35 g) and 3,3,3-Trifluoropropene (48 g) were charged in reactor and heated from room temp. to 100?. The chorine and 3,3,3-trifluoropropene were preheated to 100? before charging to reactor. The reactor was heated to 200? and maintained for 2-3hours at 1-10 Kg/cm2. The reactor outlet sample was passed through caustic scrubber and analysed.
Conversion > 60-70 %; R-243db Selectivity: >90 %
Example 5: Preparation of 2-chloro-3,3,3-trifluoropropene
In a 1” Inconel tubular reactor, fluorinated chromia (500 g) was charged and heated to 350?. 1,2-dichloro-3,3,3-trifluoropropene (243db, flow: 200 g/hour) was added in the reactor 350?. After reaction, the reactor outlet stream was passed through water to remove all the acids and organic sample was analysed.
Conversion: >50 %; R-1233xf selectivity: 95 %
The example 5 was repeated using catalyst chromia, chromia-alumina, fluorinated alumina, fluorinated chromia, activated carbon.
Example 6: Preparation of 2,3,3,3-tetrafluoropropene
In an Inconel reactor, chromia catalyst was filled and heated to 200°C. The nitrogen gas was passed through the reactor at 200°C for 10-15 hrs. Then, temperature was reduced to 100°C and hydrogen fluoride was passed at a constant flow rate to activate the chromia catalyst. Along with hydrogen fluoride flow, the reactor heating was started and slowly increased to 350°C. 2-chloro-3,3,3-trifluoropropene (183 g) and hydrogen fluoride (200g) were charged into vaporiser at the rate of 1.5 and 1.65 g/min respectively. The pre-vaporised hydrogen fluoride and 2-chloro-3,3,3-trifluoropropene were mixed and passed through active catalyst bed at 350°C in the reactor. The reactor outlet was purged in water scrubber and condensed at -50°C. The condensed mixture was distilled to isolate 2,3,3,3-tetrafluoropropene.
Purity: 96%; Yield: 90 %.

,CLAIMS:

WE CLAIMS:
1. A process for preparation of 2,3,3,3-tetrafluoropropene, comprising the steps of:
(i) contacting 2,3-dichloro-1,1,1-trifluoropropane (243db) with a catalyst in absence of HF to produce a reaction mixture comprising 2-chloro-3,3,3-trifluoropropene (1233xf);
(ii) contacting 2-chloro-3,3,3-trifluoropropene (1233xf) with HF in presence of a catalyst to produce 2,3,3,3-tetrafluoropropene.
2. The process as claimed in claim 1, wherein the step of contacting 2,3-dichloro-1,1,1-trifluoropropane (243db) with a catalyst, wherein the catalyst is selected from a group consisting of chromia, chromia-alumina, fluorinated alumina, fluorinated chromia, activated carbon, and trioctylmethylammonium chloride.
3. The process as claimed in claim 1, the step of contacting 2-chloro-3,3,3-trifluoropropene (1233xf) with HF is carried out at a temperature of 330-350?.
4. The process as claimed in claim 1, the step of contacting 2-chloro-3,3,3-trifluoropropene (1233xf) with HF is carried out in presence of a catalyst, wherein the catalyst is selected from a group consisting of chromia and chromia-alumina.
5. The process as claimed in claim 1, the step of contacting 2-chloro-3,3,3-trifluoropropene (1233xf) with HF is carried out in presence of a catalyst, wherein the catalyst is active catalyst.
6. The process as claimed in claim 5, wherein the active catalyst is chromium oxyfluoride.
7. The process as claimed in claim 5, wherein the active catalyst is prepared and used in-situ.
8. The process as claimed in claim 5, wherein the active catalyst is prepared by contacting catalyst with hydrogen fluoride (HF) prior to contacting with 2-chloro-3,3,3-trifluoropropene (1233xf).
9. The process as claimed in claim 1, the step of contacting 2-chloro-3,3,3-trifluoropropene (1233xf) with HF comprises fluorination and dehydrohalogenation.
10. The process as claimed in claim 1, wherein the catalyst is dehydrated before activation of catalyst using hydrogen fluoride.
Dated this 18th day of December 2024.