Field of invention
The present invention provides a process to prepare hexafluoropropene (HFP).
Background of the invention
The HFP is finding increase use as a co-monomer for the industrial preparation of polymers based on tetrafluoroethylene (TFE). HFP is commercially prepared by pyrolyzing TFE.
The U.S Patent No. 3,306,940 describes a process to prepare TFE and HFP simultaneously by pyrolyzing chlorodifluoromethane to a mixture of TFE and HFP.
The U.S Patent No. 3,459,818 describes a process to prepare TFE and HFP by pyrolyzing a mixture of chlorodifluoromethane and TFE formed by partial pyrolysis of chlorodifluoromethane to TFE, followed by removal of hydrochloric acid.
The U.S Patent No. 5,334,783 describes a process to prepare HFP by thermal cleavage of a mixture consisting of chlorotetrafluoroethane and perfluorocyclobutane and TFE. The process describes specific mole(s) of each components at specific temperature and pressure.
Problem
The present inventors observed that the prior art results in lower selectivity of HFP, that is, less than almost 10% conversion of reactants to HFP. Also, TFE is highly reactive and explosive raw material thus, leading safety concerns. Further, reaction conditions like involvement of high temperature (>1000oC) makes the reaction industrially non-feasible and difficult to handle.
Solution to problem
The present inventors found that upon changing the reactant feed to chlorodifluoromethane (R22) and mixture of chlorotetrafluoroethane (R124) with octafluoro cyclobutane (OFCB) led to the high conversion of reactants to HFP and much higher selectivity of 30% of HFP is obtained. Additionally, the present invention avoids the use of explosive reactants like TFE and high temperature. 2
Summary of the invention
The present invention provides a process to prepare hexafluoropropene comprising;
a) supplying chlorodifluoromethane and mixture of chlorotetrafluoroethane with octafluoro cyclobutane, as preliminary mixed or separately, to a reaction vessel,
b) supplying heat to the reaction vessel to obtain a first mixture containing hydrogen chloride,
c) removing hydrogen chloride from the first mixture to obtain a second mixture, and
d) subjecting the second mixture to compression and distillation to obtain hexafluoropropene.
Detailed Description of the Invention
The present invention provides a process to prepare hexafluoropropene comprising;
a) supplying chlorodifluoromethane and mixture of chlorotetrafluoroethane with octafluoro cyclobutane, as preliminary mixed or separately, to a reaction vessel,
b) supplying heat to the reaction vessel to obtain a first mixture containing hydrogen chloride,
c) removing hydrogen chloride from the first mixture to obtain a second mixture, and
d) subjecting the second mixture to compression and distillation to obtain hexafluoropropene.
The process of the present invention may be continuous system process or a batch system process. In the continuous process, the supply of chlorodifluoromethane and mixture of chlorotetrafluoroethane with octafluoro cyclobutane to the reactor and the withdrawal of the reaction mixture containing hexafluoropropene from the reactor are continuously conducted, respectively. In the batch system production, either one of the supply of chlorodifluoromethane and mixture of chlorotetrafluoroethane with octafluoro cyclobutane in step a) may precede the other, or they may be conducted simultaneously. 3
From the viewpoint of the production efficiency, the process of the present invention is preferably a continuous system process.
It is considered that raw materials, chlorodifluoromethane and mixture of chlorotetrafluoroethane with octafluoro cyclobutane undergo a thermal decomposition to form hexafluoropropene.
The supply amount of chlorodifluoromethane and mixture of chlorotetrafluoroethane with octafluoro cyclobutane to be supplied to the reactor is chlorodifluoromethane (0.005 to 50 wt%), chlorotetrafluoroethane (20 to 30 wt%) and octafluoro cyclobutane (25 to 50 wt%).
In the process of the present invention, the reaction mixture withdrawn from the outlet of the reactor contains unreacted raw material from an outlet of the reactor contains unreacted raw materials components, the reaction product, byproducts, etc. Thus, byproduct such as hydrogen chloride is removed and the desired product hexafluoropropene is separated from outlet. The rest of the outlet materials such as unreacted raw material along with fresh chlorodifluoromethane and mixture of chlorotetrafluoroethane with octafluoro cyclobutane are supplied to the reactor.
The temperature of chlorodifluoromethane and mixture of chlorotetrafluoroethane with octafluoro cyclobutane to be supplied to the reactor are preferably made to be from 700oC to 880oC.
While the present invention has been described in terms of its specific embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention.
The terms “furnace”, “reaction vessel” and “reactor” are interchangeable.
The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention.
Example
Process for the Preparation of Hexafluoropropene.
4
In the experiment one reaction furnace was employed which consists of high nickel alloy tube of length 470mm and 1/2 inch in diameter and having wall thickness of 2.9 mm. The electrical resistance furnace of 1500 watt rated capacity was employed to heat this tube. The effective heating zone of this tube was 175 mm. The feed gases (chlorotetrafluoroethane with octafluorocyclobutane and chlorodifluoromethane were fed with flow 12.5 LPH (liters per hour) and 2.5 LPH respectively from the cylinders. These gases were entered into this tube which was at temperature 820oC. The tubing outlet was immersed in water bath. The product gases were cooled and passed through caustic trap (300 ml 20% caustic) followed by sulphuric acid trap (100 ml sulphuric acid). After the sulphuric acid trap the sample of the gases were taken in gas sampling tube and checked in the Gas chromatographic weight percentage analysis. Feed Composition:
R22:(124+OFCB)= 25:75
OFCB (%)
R124mix (%)
Heavies (%)
R22 %
38.777984
22.614464
10.63104
27.68 Results are follows:
Temperature (°C)
RT (sec)
TFE (%)
HFP (%)
CTFE (%)
R226 (%)
Heavies (%)
PFiB%
R22%
OFCB%
R124mix%
R12%
820
1.47
18.3
31.68
2.37
0.57
16.45
4.51
3.95
8.99
6.82
0.82 Conversion: 80% Yield: 75%
TFE (tetrafluoroethylene)
HFP (hexafluoropropene)
CTFE (chloro trifluoro ethylene)
R226 (Monochlorohexafluoropropane)
R12 (Dichlorodifluoromethane)

We claim:
1. A process to prepare hexafluoropropene comprising;
a) supplying chlorodifluoromethane and a mixture of chlorotetrafluoroethane with octafluoro cyclobutane, as preliminary mixed or separately, to a reaction vessel;
b) supplying heat to the reaction vessel to obtain a first mixture containing hydrogen chloride;
c) removing hydrogen chloride from the first mixture to obtain a second mixture; and
d) subjecting the second mixture to compression and distillation to obtain hexafluoropropene.
2. The process as claimed in claim 1, wherein chlorodifluoromethane and mixture of chlorotetrafluoroethane with octafluoro cyclobutane are supplied to the reaction vessel in the range of chlorodifluoromethane (0.005 to 50 wt%), chlorotetrafluoroethane (20 to 30 wt%) and octafluoro cyclobutane (25 to 50 wt%).
3. The process as claimed in claim 1, wherein chlorodifluoromethane and mixture of chlorotetrafluoroethane with octafluoro cyclobutane are supplied to the reaction vessel at a temperature in the range of from 700oC to 880oC.
4. The process as claimed in claim 1, wherein the process is continuous system process or a batch system process.
5. The process as claimed in claim 1 or 4, wherein the process is continuous.
6. The process as claimed in claim 5, further comprising supplying unreacted raw material along with fresh chlorodifluoromethane and mixture of chlorotetrafluoroethane with octafluoro cyclobutane to the reaction vessel.