Title of Invention

"AN IMPROVED PROCESS FOR THE PREPARATION OF 2H-HEPTAFLUOROPROPENE (FM-200)"

Abstract

An improved process for production of 2H-heptafluoropropene (FM-200) comprising in the step of converting hexafluoropropene (HFP) to FM-200 in a combo-system by reacting 0.026 to 0.100 mol hexafluoropropene with 0.032 to 0.127 mol tetrabutylammonium fluoride trihydrate using DMF, DMSO, the reaction temperature being maintained at 120°-170°C, the water present in tetrabutylammonium fluoride is removed by distillation, the gas mixture obtained contains FM-200 and un-reacted HFP and by product dimmer and 1-butene, the said un-reacted hexafluoropropene (HFP) is separated by converting it into a dimmer using anhydrous HF or by reacting with triethylamine or tetrabutly amine at 20-100°C and the said by-product dimmer and 1-butene is separated from the mixture by passing through bromine in Carbon tetrachloride at 0 to 150°C.

Full Text

FIELD OF INVENTION The present invention relates to an efficient and improved process for the preparation of 2H-heptafluoropropane (HFC-227ea), a potent fire-extinguishing agent. More particularly, the present invention relates to a process for producing HFC-227 ea which is an industrially viable one pot process. PRIOR ART Three commonly known halogenated fire suppression agents viz. bromotrifluoromethane (CF2Br, Halon 1301) , bromochlorodifluoromethane (CFiBrCI, Halon 1211) and 1,2-dibromotetrafluoroethane (BrCFiCFiBr, Halon 2402) have been successfully employed - and even today billions of dollar worth of assets are protected by these agents. They find application in total flooding fire suppression systems, with tens of thousand of systems installed worldwide. The value of these agents lies in their clean and electrically nonconductive nature. Unlike water or foaming agents, which can cause secondary damage to assets such as paper based materials, which is often worse than the fire damage itself; the Halon agents leave no corrosive or damaging residues following extinguishments. The agents are elctrically non conductive and hence are applicable for use on sensitive electronic equipment such as that found in electronic data processing (EDP) or telecommunication facilities. But the major problem with this type of compounds is that they are responsible of the depletion of stratospheric ozone layer. Due to their implication in the destruction of stratospheric ozone, the production and use of these agents is being severely restricted under the Montreal Protocol (CFCs and Halons are to be phased out over the period 1996-2030) [R.E.Banks, J. Fluorine Chemistry, vol.67, 193 (1994); A. Mcclloch, J. Fluorine Chemistry, vol.100, 163 (1999)]. As a result of ban on production and use of Halons and other CFCs, intensive efforts have been undertaken in the industrial, academic and governmental sectors to develop substitutes for these ozone layer depleting agents. A large number of alternatives have been proposed [M.L. Robin, "Halogenated Fire Suppression Agents" in Halon Replacements: Technology and Science, ACS Symposium Series 611, A.W. Miziolek and W. Tsang, eds., American Chemical Society, Washington, DC, 1995]. One of the widely investigated Halon 1301 replacements is HFC-227ea, which is a zero ozone depletion potential (ODP) Halon replacement developed by Great Lakes Chemical Corporation [U.S. Patent 5,124,053 (6/23/92); M.L. Robin, "Properties and Performance of FM-200," Proceedings of the 1994 Halon Options, Technical Working Conference, May 3-5,1994, Albuquerque, NM]. FM-200 has been proven to be the preferred replacement for Halon 1301 in numerous applications. It is an active fire suppressant, extinguishing flames through a combination of physical and chemical mechanisms. The physical contribution to flame suppression stems mainly from the heat absorbing ability of the agent, which results in a lowering of the flame temperature and a slowing of the radical chain reactions occurring in the flame. HFC-227ea also acts chemically by removing key chemical species involved in the flame chain reactions responsible for flame propagation. Looking into the increasing demand of Halon 1301 replacements and in particular FM-200, a process for the production of the said compound is required. A few processes are reported in the literature for preparation of Ou f'"*6 e*'>rg ' ^ agerrt. 1. The conventional method involves the addition of anhydrous hydrofluoric acid to hexafluoropropene (HFP) to produce the HFC-227ea [British Patent 902,590 (8/1/62)]. But, the major disadvantages of the process are: i) It uses highly corrosive reagents (anhydrous HF) and it poses problem of material handling and requires more capital investment for the manufacturing unit. ii) Another disadvantage of the process is that it poses disposal problem of the harzardous liquid waste, iii) Another disadvantage of the process is that it gives poor yeild. 2. Another reported method involves high temperature vapour phase addition of corrosive HF on hexafluoropropene (HFP) in presence of fluorination catalyst (a chromium salt) [Allen Cap-on, chem Abs. Vol.135, p.!8382n (2001) Mario Joseph Nappa, V.N.M. Rao and A.C.Stevert]. The major disadvantages of the process are : i) It uses highly corrosive reagents (anhydrous HF) and it poses problem of material handling and requires more capital investment for the manufacturing unit. ii) Another disadvantage of the process is that it poses disposal problem of the hazardous liquid waste. iii) Another disadvantage of the process is that it gives poor yield. iv) There is also the problem of disposal of chromium and other hazardous wastes. v) Another disadvantage of the process is that perfluoroisobutylene, which is a highly toxic compound, is produced as a by product and comes as an impurity in order of 10 ppm. 3. A fire extinguishing agent is also prepared by the reaction of elemental fluorine gas with 2-trifluoromethyl-3,3,3-trifluoropropionic acid [U.S. Patent 6, 191,326 (Feb 20, 2001); Otsuka, Tatsuya/Aoyama and Hirokazu (Diakin Industries)]. The major disadvantages of the process are : i) It is very difficult to control the reaction of elemental fluorine and special materials are required for handling and high safety precautions are needed, ii) The process is also not cost effective. 4. Recently P.S. Bhadury, S. Singh, M. Sharma, R.C. Malhotra, K.Sekhar (Canadian Journal of Chemistry, vol. 82, Number 9, p. 1381-1385, September 2004) have reported three different methods for synthesis of FM-200. According to this literature FM-200 can be synthesized by: a) Wittig type reaction (Ylide method) b) Salt method and c) Tetrabutylammonium fluoride (TBAF) method. a. Ylide method : This method involves reaction between Wittig reagent (triphenyl phosphine, dibromodifluoromethane and zinc) with 2-iodoheptafluoropropane. This method despite being facile has the following drawbacks : i) The process is cost inefficient and the yield is low (64% by weight). ii) Another drawback is that bromodifluoromethane (CF2BrH) is formed as a byproduct along with the desired product of a fire extinguishing agent. Removal of this compund, which is an ozone layer depleting agent itself, is both difficult and cost intensive, iii) Another major disadvantage of this method is that one of the precursors (CF2Br2) is an ozone depleting agent itself, therefore supply or availability of precursor will pose a problem in the future. iv) Further disadvantage of this process is that the atom economy of the process is very low and it produces lot of waste, removal/disposal of which is very difficult. v) This process is not eco-friendly. b. Salt method : The salt method involves the reaction of sodium chlorodifluoroacetate with HFP in presence of solvent DMF at 150°C This method suffers from the following drawbacks : i) Very low yield (29% by weight). ii) Another drawback of the process is that chlorodifluoromethane{CF2CIH)is formed as a byproduct, which is another ozone deleting agent, undermines all the efforts for manufacturing HFC-227ea. iii) Also the separation/purification of the desired product (FM-200) is difficult. c. Tetrabutylammonium fluoride (TBAF) method: In TBAF method anhydrous tetrabutylammonium fluoride trihydrate is used as a source of hydrogen fluoride (HF) and hexafluoropropene (HFP) is used as a reagent for the synthesis of FM-200. The major disadvantages of this process are: f i) It gives low purity product (only 10%) and the conversion is very low. ii) Another disadvantage of this process is that the product contains un-reacted HFP, a toxic compound, (about 90%), which is detrimental for the use of FM-200 as a fire extinguisher. The product obtained by this method when analyzed by GC-MS, was found to contain about 90% hexafluoropropene, 7-8% FM-200, 1-butene and another byproduct. Probably, when the author analyzed the product, the separation was not sufficient in GC and the peak of hexafluoropropene and FM-200 merges together and it was assumed as pure FM-200. iii) Another disadvantage of the process is that it requires completely anhydrous TBAF, which needs drying of laboratory grade TBAF.3H2O under stringent condition (0.1 mm Hg vacuum, over a boiling water bath for 6 hrs). Complete drying of TBAF is extremely difficult. iv) Another disadvantage of the process is that it needs transfer of highly viscous liquid, obtained after drying of TBAF.3H2O, into another round bottom flask for carrying out the reaction. v) Further disadvantage of the process is that it is a multi steps process and it needs more cycle time for preparation. vi) Still further disadvantage of this process is that it need larger quantity of TBAF Yet another object of the present invention is to propose an improved process for preparation of FM-200 where the product can be separated from the reaction mixture easily. A further object of the present invention is to propose process in which a combo-system is used where the reaction and separation by distillatior is carried out in a single equipment (combo-system) so as to increase the yield and as well as to reduce the batch time, energy requirement and cost of production. DESCRIPTION OF THE PROCESS According to this invention there is provided an improved process for production of 2H-heptafluoropropene (FM-200) comprising in the step of converting hexafluoropropene (HFP) to FM-200 by reacting hexafluoropropene with tetrabutylammonium fluoride trihydrate using DMF, DMSO, the reaction temperature being maintained at 120°-170°C, the gas mixture obtained contains FM-200 and small amount of un-reacted HFP and by product dimer and 1-butene. According to the present invention, the process for preparation of FM-200 involves one step reaction between HFP and HF, which is generated in situ by heating a TBAF. 3H2O in DMF. The process involves the following steps: The present invention proposes use of optimum amount of tetrabutylammonium fluoride trihydrate. The present invention proposes that the gas liquid reaction was carried out in reactor made of measuring cylinder. By utilizing the reactor system the residence time has been increased and the conversion is increased greatly. OBJECTS OF THE INVENTION An object of the present invention is to propose an improved eco-friendly process for the preparation of FM-200, a fire extinguishing agent. Another object of the present invention is to propose an improved process for production of FM-200 which provdes higher yield. Still another object of the present invention is to propose an improved process for preparation of FM-200, which is cost effective. Yet another object of the present invention is to propose an improved process for preparation of FM-200, in which less number of working steps are involved. A further object of the present invention is to propose an improved process for preparation of FM-200, in which mild operating conditions are used. A still further object of the present invention is to propose an improved process for production of FM-200, which provides higher conversion of precursor towards the desired product. Still a further object of the present invention is to propose an improved process for production of FM-200 in which no side products or by products are formed. Yet another embodiment of the present invention proposes tha the gas liquid reaction was carried out in reactor made of measuring cylinder where the moisture present in the tetrabutylammonium fluoride trihydrate is removed by distillation in the initial stage during the heating of the reaction mixture. Therefore no extra energy is required for the removal of water/moisture form the mixture. Yet another embodiment of the present invention proposes use of carbon tetrachloride/other suitable solvent for separation of 1-butene from the product mixture. A. CONVERSION OF HFP TO HFC-227ea i) Tetrabutylammonium fluoride trihydrate (TBAF. 3HzO) is suspended in laboratory grade DMF and heated gently to about 40°C with constant stirring, till a clear solution is obtained. ii) The above solution is charged into a in reactor made of measuring cylinder connected to a double walled glass condenser. Dry nitrogen is purged through the solution slowly. iii) The solution of the reactor is heated till it boils, with continuous purging of nitrogen. The temperature is maintained in the range of 130 to 170°C for a period of 30-45 minutes. The HFP is bubbled through the solution of the reactor at 145-150°C. The product gas mixture is collected from the outlet of the condenser. The evolved gases contain FM-200 (>90%) small amount of un-reacted HFP and some other byproducts. B. PURIFICATION BY SEPARATION The gas mixture obtained from the above step is allowed to bubble through the solution of bromine in carbon tetrachloride taken in a bubble column reactor, kept at subzero temperature by ice-salt mixture. The bubble column reactor is connected with a condenser. In this step all the by-products (alkenes/substituted alkenes) are converted to their bromo derivative, which are retained in the liquid phase. The outlet gas, which is pure FM-200, is collected in a tedlar bag. WORKING EXAMPLES Exampie-1 Commercial tetrabutylammonium fluoride trihydrate (TBAF.SFfeO) [10 g, 0.032 mol] was suspended in 4 ml of laboratory grade DMF and heated gently to about 40 °C with constant stirring. Volume of the solution was found to be 20 ml at 30 °C and the solution was charged in a reactor, made of measuring cylinder, connected with a double walled glass condenser. Dry nitrogen gas was purged through the solution slowly. The content was heated until boiling set in. The liquid solution was maintained in the range of 145 to 150 °C for a period of 30 minutes. Then hexafluoropropene [4 g, 0.026 mol] was bubbled from tedlar bag through the content of the reactor maintained at 145-150 °C. The product gases were collected in tedlar bag. Content of the tedlar bag was re-bubbled through a solution of bromine in carbon tetrachloride cooled to subzero temperatures, with an ice bath. The product gas was again collected in fresh tedlar bag [3.2 g, 0.018 mol) pure HFC-227ea was obtained. The product was characterized by GC-MS and NMR and the purity was checked using GC-MS. Example-2 Commercial tetrabutylammonium fluoride trihydrate (TBAF.3H20) [40 g, 0.127 mol] was suspended in 32 ml of laboratory grade DMF and heated gently to about 40 °C with constant stirring. Volume of the solution was found to be 75 ml at 30 °C and the solution was charged in a reactor, made of measuring cylinder, connected with a double walled glass condenser. Dry nitrogen gas was purged through the solution slowly. The content was heated until boiling set in. The liquid solution was maintained in the range of 145 to 150 °C for a period of 30-45 minutes. Then hexafluoropropene [15 g. 0.100 mol] was bubbled from tedlar bag through the contents of the reactor maintained at 145-150 °C. The product gases were collected in tedlar bag. Content of the tedlar bag was re-bubbled through a solution of bromine in carbon tetrachloride cooled to subzero temperatures, with an ice bath. The product gas was again collected in fresh tedlar bag. [12.75 g, 0.075 mol) pure HFC-227ea was obtained. The product was characterized by GC-MS and NMR and the purity was checked using GC-MS. Exam pie-3 Commercial tetrabutylammonium fluoride trihydrate (TBAFJFbO) [15 g, 0.047 mol] was suspended in 12 ml of laboratory grade DMF and heated gently to about 40 °C with constant stirring. Volume of the solution was found to be 35 ml at 30 °C and the solution was charged in a reactor, made of measuring cylinder, connected with a double walled glass condenser. Dry nitrogen gas was purged through the solution slowly. The content was heated until boiling set in. The liquid solution was maintained in the range of 145 to 150 °C for a period of 30-45 minutes. Then hexafluoropropene [5 g, 0.033 mol] was bubbled from tedlar bag through the contents of the reactor maintained at 145-150 °C. The product gases were collected in tedlar bag. Contents of the tedlar bag were re-bubbled through a solution of bromine in carbon tetrachloride cooled to subzero temperatures, with an ice bath. The product gas was again collected in fresh tedlar bag. [4.5 g, 0.026 mol) pure HFC-227ea was obtained. The product was characterized by GC-MS and NMR and the purity was checked using GC-MS. CLAIM: 1. An improved process for production of 2H-heptafluoropropene (FM-200) comprising in the step of converting hexafluoropropene (HFP) to FM-200 in a combo-system by reacting 0.026 to 0.100 mol hexafluoropropene with 0.032 to 0.127 mol tetrabutylammonium fluoride trihydrate using DMF, DMSO, the reaction temperature being maintained at 120°-170°C, the water present in tetrabutylammonium fluoride is removed by distillation, the gas mixture obtained contains FM-200 and un-reacted HFP and by product dimmer and 1-butene, the said un-reacted hexafluoropropene (HFP) is separated by converting it into a dimmer using anhydrous HF or by reacting with triethylamine or tetrabutly amine at 20-100°C and the said by-product dimmer and 1-butene is separated from the mixture by passing through bromine in Carbon tetrachloride at 0 to 150°C. 2. An improved process for production of 2H-heptafluoropropene (FM-200) as claimed in claim 1, wherein mechanical and magnetic stirring in glass or glass lined assemblies are used. 3. An improved process for production of 2H-heptafluoropropene (FM-200) substantially as herein described.

Documents:

1471-DEL-2005-Abstract-(28-01-2009).pdf

1471-del-2005-abstract.pdf

1471-DEL-2005-Claims-(28-01-2009).pdf

1471-del-2005-claims.pdf

1471-DEL-2005-Correspondence-Others-(28-01-2009).pdf

1471-del-2005-correspondence-others.pdf

1471-del-2005-correspondence-po.pdf

1471-del-2005-description (complete).pdf

1471-del-2005-form-1.pdf

1471-DEL-2005-Form-2-(28-01-2009).pdf

1471-del-2005-form-2.pdf

1471-del-2005-form-26.pdf

1471-del-2005-form-3.pdf