The present invention relates to heat quenching systems for pyrolytic synthesis of fluorinated olefins.

BACKGROUND OF THE INVENTION
Fluorinated olefins are known for their numerous application as refrigerants, heat transfer media, propellants, foaming agents, blowing agents, gaseous dielectrics, sterilants carriers, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents, displacement drying agents and power cycle working fluids, chemical intermediates, monomers and the like.
Fluorinated olefins have been prepared using pyrolytic reactions performed by heating a feedstock comprising of methane or chlorinated methane and fluorinated ethylenes at a very high temperature.
JP Application No. 40-2132 describes a process for the preparation of olefins containing fluorine by heating a mixture of methyl chloride and chlorodifluoromethane in a molar ratio of 5: 1 at a temperature range of 600°C to 1000°C in the presence of steam.
U.S Patent No. 2,931,840 describes a process for the preparation of 2,3,3,3-tetrafluoropropene (1234yf) by heating and decomposing a mixture of methyl chloride and chlorodifluoromethane or tetrafluoroethylene at a temperature range of 700 to 950°C using a common heating means such as an electric heater in a reactor.
U.S Patent No. 7,951,982 describes a process for preparation of C3 fluoroolefins by heating halogenated methanes and halogenated ethanes at high temperatures.
PCT Pub. No 008002499 discloses a process of preparation of C3 fluoroolefins by pyrolysis of 1,1,1,2,3-pentafluoropropane.
U.S Patent No. 7,906,693 discloses a process for preparation of 1-chloro-2,3,3,3-pentafluoropropane by pyrolytic reaction of chlorofluoromethane and tetrafluoroethylene.
U.S Pub. No. 20090253946 discloses a process for preparation of 1234yf by reacting chlorotrifluoroethylene with a methyl halide at an elevated temperature.
U.S Patent No. 8,258,353 discloses a process for preparation of chlorinated or fluorinated propenes by reacted chloroethylene or chlorofluoroethylene with methane, chloromethane, fluoromethane or chlorofluoromethane at elevated temperatures and pressures.
U.S Patent No. 8,581,012 discloses a continuous, gas phase, free radical process for the production of chlorinated and/or fluorinated propene and higher alkenes from chlorinated and/or fluorinated alkanes and/or chlorinated and/or fluorinated alkenes.
U.S Patent No. 9,206,096 discloses a process for preparation of 1234yf by heating chlorodifluoromethane and chloromethane at elevated temperatures.
U.S Patent No. 9,315,432 discloses a process for preparation of 1234yf by heating chlorodifluoromethane, tetrafluoroethylene and chloromethane at elevated temperatures.
JP Patent. No. 05975096 discloses a process for preparation of a mixture of 1234yf and 1,1-difluoroethylene by reacting octafluorocyclobutane and chloromethane at an elevated temperature.
JP Pub. No. 2013227245A discloses a process for preparation of a mixture of 2,3,3,3-tetrafluoropropene and 1,1-difluoroethylene by reacting hexafluoropropene and chloromethane at elevated temperature.
All the processes are carried out at elevated temperatures and are highly exothermic in nature that results in the formation of side products that are detrimental to the yield and the purity of the final fluorinated olefins. It is highly desirable to evolve a method for efficient quenching of the heat generated in these reactions to control the impurities and enhance efficiency of the process at commercial scale.
The inventors of the present invention have developed different heat quenching systems for controlling and utilizing heat of these pyrolytic reactions.

SUMMARY OF THE INVENTION
In first aspect, the present invention provides a heat quenching system for pyrolytic synthesis of fluorinated olefins.
In second aspect, the present invention provides a process for preparation of fluorinated olefins comprising the steps of:
a) providing a feed to the reactor;
b) heating the reactor at a temperature of 400°C to 900°C;
c) passing the product stream though a heat quencher;
d) isolating the fluorinated olefin from the cooled product stream.

BRIEF DESCRIPTION OF THE FIGURE
Figure 1 depicts a design A of a heat quenching system wherein, a quencher is placed in immediate proximity to the product outlet. Reaction mass from outlet of reactor is quenched immediately in a steam generator. Steam generator is a shell and tube type exchanger preferably kettle type where reactor outlet is cooled giving its heat to demineralized water and steam is generated.
Figure 2 depicts a design B of a heat quenching system wherein, a quencher is placed in immediate proximity to the outlet of the reactor and has provision for circulation of the feed in order to pre-heat the feed.
Figure 3 depicts a design C of heat quenching system wherein, a system is equipped with a tank filled water, a pump to recirculate heat and a heat exchanger. This tank, heat exchanger and a pump acts as quencher system.
Figure 4 depicts a design D of a heat quenching system wherein, a sprinkler or more are placed in immediate proximity to the outlet of the reactor and a quencher system equipped with a graphite column, a perforated tank for spraying water, a pump for circulation and a heat exchanger.
Figure 5 depicts a design E of a heat quenching system wherein, a quencher is in the form of a U-tube, helical tube, spiral tube dipped in a water tank, fitted with a pump and a heat exchanger.

DETAILED DESCRIPTION OF THE INVENTION
As used herein, “Reactor” can be horizontal or vertical and can be heated electrically or by fuel fired furnace.
As used herein, “fluorinated olefins” refers to 1234yf, 1234ze, 1233xf, 1233zd, 1225ye, 1336mzz or the like.
As used herein, “feed” refers to the organic compounds such as halogenated methanes, halogenated alkanes, or halogenated alkenes, used for preparing fluorinated olefins. The examples of the organic compounds used as feed includes methane, chlorofluoromethane, chlorodifluoromethane, chloroform, fluoroform, dichlorofluoromethane, fluoromethane, chloromethane, tetrachloromethane, tetrafluoroethylene, octafluorocyclobutane, hexafluoropropene, chlorotrifluoroethylene, dichlorodifluoroethylene, chlorotrifluoroethylene, 1,1,1,2,3-pentafluoropropane or the like and mixtures thereof.
As used herein, the elevated temperature refers to a temperature ranging from 400°C to 900°C, preferably 550°C to 800°C.
As used herein, “design A” of a heat quenching system consists of a quencher placed in immediate proximity to the product outlet. Reaction mass from outlet of reactor is quenched immediately in a steam generator. Steam generator is a shell and tube type exchanger preferably kettle type where reactor outlet is cooled by giving its heat to water thereby generating steam to be used in the reactor.
In an embodiment of the present invention, the product mass from the reactor is quenched using a quencher of design ‘A’ as depicted in Figure 1.
This heat quenching system of design ‘A’ enables substantial heat recovery and fast quenching.
As used herein, “design B” of a heat quenching system consists of a quencher placed in immediate proximity to the outlet of the reactor and has provision for circulation of the feed in order to pre-heat the feed.
In another embodiment of the present invention, the product mass from the reactor is quenched using a quencher of design ‘B’ as depicted in Figure 2.
In another embodiment of the present invention, the design B quenching system involves cooling of product mass and pre-heating of reactor feed through a shell and tube heat exchanger.
The design B enables product mass to be cooled and simultaneously reactor feed be pre-heated. The design B enables considerable reduction in size of the reactor.
As used herein, “design C” of heat quenching system consists of a tank filled with water, a pump to recirculate heat and a heat exchanger. This tank, heat exchanger and a pump acts as quencher system.
In this embodiment the product from the reactor (vertical furnace) outlet is poured through a nozzle, into a water tank fitted with an outlet for exit of product, a pump and a heat exchanger. The water recirculated by pump and passes through heat exchanger to remove heat.
The nozzle, through which the product stream enters the water tank is made up of exotic metal alloy such as Hastelloy, Inconel, Monel or the like.
The water tank is preferably made of fluoropolymers, rubber or graphite.
The heat exchanger is made of graphite or exotic metal alloy such as Alloy 20, Hastelloy, Inconel, Monel or the like.
In another embodiment of the present invention, the product mass from the reactor is quenched using a quencher of design ‘C’ as depicted in Figure 3.
The quenching system with Design C enables immediate quenching of product stream thus is one of the most preferred option for quenching. The water tank get acidified over the period of time that can be recovered and made proper use of.
As used herein, “design D” consists of a sprinkler or more placed in immediate proximity to the outlet of the reactor and a quencher system equipped with a graphite column, a perforated tank for spraying water, a pump for circulation and a heat exchanger.
In this embodiment, the product from the reactor outlet is immediately cooled while passing through the sprinkler(s), placed in immediate proximity to the outlet of the reactor. Thus cooled product mass passes through a quencher system equipped with a graphite column, perforated tank, a pump and a heat exchanger, where gases are cooled to room temperature.
The nozzle, through which the product stream enters the tank is made up of exotic metal alloy such as Hastelloy, Inconel, Monel or the like.
The water tank is preferably made of fluoropolymers, rubber or graphite.
The heat exchanger is made of graphite or exotic metal alloy such as Alloy 20, Hastelloy, Inconel, Monel or the like.
In another embodiment of the present invention, the product mass from the reactor is quenched using a quencher of design ‘D’ as depicted in Figure 4.
The design D enables fast cooling and prevent decomposition hence formation of any side product.
As used herein, “design E” of a heat quenching system consists of a quencher in the form of a U-tube, a helical tube, or a spiral tube, dipped in a water tank, fitted with a pump and a heat exchanger.
In this invention, reactor outlet mass from vertical furnace passes through tube exchanger where it is immediately cooled and quenched. This exchanger is located just below the reactor. This exchanger is kept in water bath having continuous circulation of water. This quencher system enables rapid quenching thereby preventing decomposition and formation of side products.
The decomposition of the product gives polymerized impurities along with carbon that have not been analysed and are being termed as heavies. The heavies stick to the walls of the outlet and lead to the choking.
In another embodiment of the present invention, the product mass from the reactor is quenched using a quencher of design ‘E’ as depicted in Figure 5.
The quenching systems of the present invention enable efficient quenching of heat generated during the course of the reaction and prevent decomposition of organic thus improving operational efficiency of the process.
Thus, it is contemplated that the present reaction may be performed using a wide variety of process parameters and process conditions in view of the overall teachings contained herein. However, it is preferred in certain embodiments that this reaction step comprises a gas phase reaction, preferably in the presence of catalyst.

Example 1:
Production of 2,3,3,3 tetrafluoropropene
Tetrafluoroethylene is made to react with methyl chloride in the presence/absence of an initiator at a temperature in the range of 400 to 800oC to give 2,3,3,3 tetrafluoropropene. The reaction is highly exothermic. Temperature and residence time control are most important parameter for such reaction.
This is an exothermic reaction and the products formed are many like R-1234yf, vinyl difluoride (VdF), R-32, OFCB, HFP etc. The product leaving the furnace may decompose leading to coking if temperature at the reactor outlet is not controlled. The solution to this problem is the introduction of quencher at the furnace outlet.
In one of the experiment, the process was carried out without any cooling arrangement at the reactor outlet, the temperature at the reactor outlet increased from 550oC to 711oC in a matter of seconds. During this time the feed was cut down and nitrogen purging started, but there was pressure increase in the reactor indicating reactor choking. The reactor was cooled and the outlet section opened for inspection and found heavy carbon deposits at the point where temperature had increased to 711oC. The runaway decomposition happened after 1 hour of run. Before choking of the reactor, one sample was analysed and its complete operating condition and analysis report is given below.
The next experiments were carried out after installing quenching systems of Design A, Design B, Design C, Design D, and Design E, at the furnace outlet, so that the temperature at the furnace outlet is controlled. The furnace was able to run continuously for more than 3 days. The TFE conversion was same, but the formation of the desired product increased (R-1234yf).The results of this experiment is given below in table 1:
Table 1
Sample No. No Quenching Design A Design B Design C Design D Design E
Temp. 650 650 650 650 650 650
Press. 1.3 1.3 1.3 1.3 1.3 1.3
M.R (C1:TFE) 1.46 1.46 1.46 1.46 1.46 1.46
Initiator % w.r.t C-1 2.2% 2.2% 2.2% 2.2% 2.2% 2.2%
OFCB 12.1606% 7.1618% 3.3638% 5.6418% 5.0368% 2.6522%
R1234yf 5.0777% 10.009% 12.1227% 9.7979% 9.3893% 11.4527%
R22 2.9341% 1.8845% 1.7582% 2.2258% 1.6637% 1.8139%
Heavies 15% 5% 4.5% 5% 4% 4.2%

The results shown in table 1 show considerable reduction in the amount of heavies upon quenching using these designs thereby clearly explains the need for immediate quenching of the reaction mass to stop runaway time decomposition and to increase the yield.

CLAIMS:WE CLAIM:
1. A heat quenching system for pyrolytic synthesis of fluorinated olefins, wherein the design of heat quenching system is selected from ‘A’, ‘B’, ‘C’, ‘D’ and ‘E’, depicted in Figures 1 to 5 respectively.
2. A process for preparation of fluorinated olefins, comprising the steps of:
a) providing a feed to the reactor;
b) heating the reactor at a temperature of 400°C to 900°C;
c) passing the product stream though a heat quencher to obtain cooled product stream; and
d) isolating the fluorinated olefin from the cooled product stream.
3. The fluorinated olefins as used in claims 1 and 2 are selected from a group consisting of 1234yf, 1234ze, 1233xf, 1233zd, 1225ye and 1336mzz or a mixture thereof.
4. The process as claimed in claim 2, wherein the feed is selected from methane, halogenated methanes, halogenated alkanes, or halogenated alkenes or a mixture thereof.
5. The process as claimed in claim 2, wherein the heat quenching system is designed as ‘A’, ‘B’, ‘C’, ‘D’ and ‘E’, depicted in Figures 1 to 5 respectively.
6. The “design A” of the heat quenching system as claimed in claims 1 and 5, wherein a quencher is placed in immediate proximity to the product outlet and the reaction mass from outlet of reactor is quenched in a steam generator.
7. The “design B” of the heat quenching system as claimed in claims 1 and 5, wherein a quencher is placed in immediate proximity to the outlet of the reactor and enables simultaneous cooling of product mass and pre-heating of feed.
8. The “design C” of the heat quenching system as claimed in claims 1 and 5, wherein the quencher consists of a tank filled with water, a pump to recirculate heat and a heat exchanger and enables immediate quenching of the product stream.
9. The “design D” of the heat quenching system as claimed in claims 1 and 5, wherein the quencher consists of a sprinkler, a quencher system equipped with a graphite column, a perforated tank for spraying water, a pump for circulation and a heat exchanger and enables fast cooling and prevent decomposition.
10. The “design E” of the heat quenching system as claimed in claims 1 and 5, wherein the quencher consists of a quencher in the form of a U-tube, a helical tube, or a spiral tube, dipped in a water tank, fitted with a pump and a heat exchanger and enables rapid quenching which prevents decomposition and formation of side products.