Field of the invention
The present invention provides a process for the preparation of tetrachloromethane using trichloromethane. Tetrachloromethane is a valuable precursor in the synthesis of refrigerant and other commercial products.
Background of the invention
Hydrofluoroolefins products are emerged as more acceptable alternatives to fluorocarbon products. Tetrachloromethane is used in the preparation of chlorinated propanes, which are valuable precursor in the preparation of hydrofluoroolefins.
U.S. Patent Number 4,661,648 discloses a process for preparation of tetrachloromethane by chlorinating trichloromethane in presence of radical initiator.
U.S. Patent Number 9,160,177 discloses a process for preparation of tetra chloromethane by chlorinating the partially chlorinated methanes in presence of free radical catalysts in a solvent selected from tetrachloromethane.
PCT Publication Number 2018/009459 discloses a process for preparation of tetrachloromethane by photochlorinating a mixture of tetrachloromethane and trichloromethane.
The above prior art process either results in the formation of considerable amount of hexachloroethane as a byproduct or necessitate the use of tetrachloromethane as a solvent. The prior art does not disclose an efficient method of separating tetrachloromethane from the product stream.
It is been observed by the present inventors that the distillation of product stream containing hydrochloric acid, trichloromethane and tetrachloromethane at high temperature cause charring of the product, thereby increasing the amount of heavies and reducing the yield of tetrachloromethane. Charring also leads to choking re-boilers and column that increases the acidity and affects the performance and efficiency of the reactor.
There is a need in the art to provide an efficient, selective and industrially applicable process for the preparation of tetrachloromethane with low acid content, to meet its high demand as a valuable raw material for hydrofluoroolefins.
The present invention provides an efficient method for separating tetrachloromethane from the product stream comprising hydrochloric acid, tetrachloromethane and trichloromethane.

Objects of the invention
The present invention provides a process for the preparation of tetrachloromethane from trichloromethane by photochlorination, wherein the tetrachloromethane have low acid content.
Summary of the invention
The first aspect of the present invention provides tetrachloromethane with low acid content.
The second aspect of the present invention provides process for preparation of tetrachloromethane
comprising the steps of:
a) chlorination of trichloromethane in presence of radical initiator to obtain a product stream;
b) adding an entrainer 1 to the product stream and removing hydrochloric acid by distillation to obtain a mixture 1;
c) adding an entrainer 2 to the mixture 1 and removing entrainer 1 to obtain a mixture 2;
d) washing and neutralizing the mixture 2;
e) distilling mixture 2 to remove entrainer 2 to obtain a mixture 3;
f) distilling mixture 3 to remove trichloromethane and to obtain mixture 4;
g) distilling tetrachloromethane from mixture 4.
The third aspect of the present invention provides a process for purification of reaction product from chlorination of trichloromethane using an entrainer.

BRIEF DESCRIPTION OF DRAWING
Figure 1 describes the flow of the process.
DETAILED DESCRIPTION OF INVENTION:
As used herein, the term “heavies” refers to the byproducts formed by the decomposition of product stream at high temperature. The heavies contains trichloroethylene, bromodichloromethane, hexachloroethane, pentachloroethane or the like.
As used herein, the term “product stream” comprises of chlorine, hydrochloric acid, trichloromethane and tetrachloromethane.
As used herein, the term “continuous mode” refers to a process where the materials are continuously in motion undergoing chemical reaction and simultaneously producing product.
As used herein, the term “radical initiator” includes Ultra Violet (UV) light, azobisisobutyronitrile, 1,1'-azobis(cyclohexanecarbonitrile), di-tert-butyl peroxide, benzoyl peroxide, methyl ethyl ketone peroxide, acetone peroxide decachlorobutane or an octachlorobutene or combinations of any number of these.
As used herein, the term “ultraviolet light” refers to light emitted by the source selected from UV lamp, sodium light and electromagnetic radiation.
As used herein, the term “entrainer 1” includes the compounds which enables the separation of hydrochloric acid by distillation without raising the temperature of the distillation column beyond 70-1000C, thereby preventing the decomposition of the reaction mixture. Examples of entrainer 1 include monochloromethane, dichloromethane, trichloromethane and tetrachloromethane.
Entrainer 1 reduces the temperature at the bottom of the distillation column that is used for separation of hydrochloric acid and thereby decreasing the amount of heavies.
As used herein, the term “entrainer 2” includes the compounds which enables the separation of entrainer 1 from the reaction mixture. Examples of entrainer 2 includes monochloromethane, dichloromethane, trichloromethane and tetrachloromethane
Entrainer 2 reduces the temperature at the bottom of the distillation column that is used for separation of entrainer 1 and thereby decreasing the amount of decomposition by-products.
As used herein, the term chlorination refers to the reaction of chlorine with trichloromethane in presence of ultraviolet light or in presence of a radical initiator or both. The chlorination reaction is carried out at a temperature ranging from 30°C to 60°C at a pressure range of 10-15 bars.
The chlorination is carried out with a molar ratio of trichloromethane slightly higher than chlorine. The molar ratio of chlorine to trichloromethane ranges from 1:1.1 to 1:2.
Chlorine is the limiting reactant and fed in such proportion that only slight chlorine is left after the reaction. The free chlorine is hazardous and needs to be removed through scrubbing. It is established that most preferable molar ratio of chlorine to trichloromethane is 1:1.1 to 1:1.5.
As used herein, the term “product stream” refers to the mixture obtained by the chlorination of trichloromethane and comprises of trichloromethane, hydrochloric acid, tetrachloromethane and chlorine.
As used herein, the term “mixture 1” refers to the mixture obtained by the addition of entrainer 1 and comprises of entrainer 1, monochloromethane, dichloromethane, trichloromethane, tetrachloromethane, hydrochloric acid, chlorine, and heavies wherein hydrochloric acid and chlorine are in the range of less than 300 ppm.
As used herein, the term “mixture 2” refers to the mixture obtained by removing entrainer 1 by distillation and adding entrainer 2 to the distillation column and comprises mainly of monochloromethane, dichloromethane, trichloromethane, tetrachloromethane, hydrochloric acid, chlorine, entrainer 2 and heavies, wherein hydrochloric acid and chlorine are in the range of less than 100 ppm.
As used herein, the term “mixture 3” refers to the mixture obtained by removing entrainer 2 and comprise mainly of trichloromethane, tetrachloromethane and heavies.
As used herein, the term “mixture 4” refers to the mixture obtained by removing trichloromethane and comprise mainly of tetrachloromethane and heavies.
As used herein, the term “washing” refers to the treatment of the mixture with water.
As used herein, the term “neutralizing” refers to the treatment of the reaction mixture with alkali such as sodium hydroxide or potassium hydroxide.
As used herein, the term “isolating” refers to the known methods of isolating the product from the reaction mixture such as distillation.
In an embodiment of the first aspect of the present invention, tetrachloromethane produced by the process of the present invention has low content of acid of less than 5ppm.
In another embodiment of the first aspect of the present invention, the tetrachloromethane produced by the process of the present invention has low content of hexachloroethane less than 150ppm.
In an embodiment of the second aspect of the present invention, the chlorination is carried out at a temperature of 30°C to 60°C at a pressure range of 10-15 bars.
In another embodiment of the second aspect of the present invention, the process is carried out in a continuous mode.
In another embodiment of the second aspect of the present invention, the entrainer 1 is monochloromethane or dichloromethane.
In another embodiment of the second aspect of the present invention, the hydrochloric acid is removed from the distillation column maintaining a top temperature of -15 to -29°C and the bottom temperature of ….85°C to 115°C at a pressure range of 10-15 bars.
In another embodiment of the second aspect of the present invention, the entrainer 1 is removed by distillation.
In another embodiment of the second aspect of the present invention, the entrainer 2 is added to efficiently remove entrainer 1.
In another embodiment of the second aspect of the present invention, the entrainer 2 is monochloromethane or dichloromethane.
In another aspect of the embodiment of the second aspect of the present invention, the entrainer 1 and entrainer 2 can be same. If entrainer 1 and 2 are same then the steps 5 and 6 becomes optional.
In another embodiment of the second aspect of the present invention, washing and neutralization is carried out using a basic solution.
In another embodiment of the second aspect of the present invention, tetrachloromethane is isolated sequential distillation of entrainer 2 followed by distillation of trichloromethane and finally tetrachloromethane.
In another embodiment of the second aspect of the present invention, entrainer 1, entrainer 2, trichloromethane are recycled back to either the reactor or the distillation column after requisite washing and compressing.
In an embodiment of the present invention, the process is as illustrated in figure 1. As referred in figure 1, trichloromethane ‘1’ and chlorine ‘2’ are fed to the reactor A to get the product stream ‘3’. The product stream ‘3’ and entrainer 1 ‘14’ are fed to the distillation column ‘B’ to remove hydrochloric acid ‘4’and to obtain mixture 1 ‘5’ at the bottom. The mixture 1 ‘5’ and entrainer 2 ‘15’ are fed to the distillation column C to remove entrainer 1 and chlorine ‘6’ and to obtain mixture 2. The mixture 2 is fed to the distillation column D to remove entrainer 2 ‘8’ and obtain mixture 3 ‘9’. The mixture 3 is fed to distillation column ‘E’ to remove trichloromethane and obtain mixture 4 ‘11’. The mixture 4 ‘11’ is fed to the distillation column to remove heavies ’13 and obtain tetrachloromethane ‘12’. Trichloromethane is recycled back to the reactor.

EXAMPLES
Example 1: Preparation of tetrachloromethane
Liquid trichloromethane (1500-1800 kg/hr) was reacted with chlorine (800-1050 kg/hr) using UV light at temperature (30-60) °C to obtain a product stream. The product stream and dichloromethane (1200-1800 kg/hr) was passed through the distillation column and heated to a temperature of 100-106°C to remove hydrochloric acid and to obtain mixture 1. The mixture 1 and monochloromethane (1500-2000) was passed through another distillation column and heated at a temperature of 110-115°C to remove monochloromethane and obtain mixture 2. The mixture 2 is subsequently washed with water and caustic solution. The mixture 2 is then passed through another distillation column and heated at a temperature of 105-110°C to remove Dichloromethane and to obtain mixture 3. The mixture 3 is distilled to remove trichloromethane to obtain mixture 4. The mixture 4 is distilled to obtain tetrachloromethane and remove heavies.
Purity of tetrachloromethane: 99%
Acid content: Less than 10 ppm
Amount of heavies: less than 20 ppm

Example 2: Preparation of tetrachloromethane
Liquid trichloromethane (1500-1800 kg/hr) was reacted with chlorine (800-1050 kg/hr) using UV light at temperature (30-60) °C to obtain a product stream. The product stream and monochloromethane (600-800 kg/hr) was passed through the distillation column and heated to a temperature of 80-90°C to remove hydrochloric acid and to obtain mixture 1. The mixture 1 and Dichloromethane (1500-2000 kg/hr) was passed through another distillation column and heated at a temperature of 105-120°C to remove monochloromethane and obtain mixture 2. The mixture 2 is subsequently washed with water and caustic solution. The mixture 2 is then passed through another distillation column and heated at a temperature of 105-120°C to remove Dichloromethane and to obtain mixture 3. The mixture 3 is distilled to remove trichloromethane to obtain mixture 4. The mixture 4 is distilled to obtain tetrachloromethane and remove heavies.
Purity of tetrachloromethane: 99%
Acid content: less than 10 ppm
Amount of heavies: Less than 20 ppm

Example 3: Preparation of tetrachloromethane
Liquid trichloromethane (1500-1800 kg/hr) was reacted with chlorine (800-1050 kg/hr) using UV light at temperature (30-60) °C to obtain a product stream. The product stream and monochloromethane (600-800 kg/hr) was passed through the distillation column and heated to a temperature of 80-90°C to remove hydrochloric acid and to obtain mixture 1. The mixture 1,monochloromethane (200-300 kg/hr) and Dichloromethane (1000-1200 kg/hr) was passed through another distillation column and heated at a temperature of 100-110°C to remove monochloromethane and obtain mixture 2. The mixture 2 is subsequently washed with water and caustic solution. The mixture 2 is then passed through another distillation column and heated at a temperature of 100-110°C to remove Dichloromethane and to obtain mixture 3. The mixture 3 is distilled to remove trichloromethane to obtain mixture 4. The mixture 4 is distilled to obtain tetrachloromethane and remove heavies.
Purity of tetrachloromethane: 99%
Acid content: less than 10 ppm
Amount of heavies: Less than 20 ppm

Example 4: Preparation of tetrachloromethane
Liquid trichloromethane (1500-1800 kg/hr) was reacted with chlorine (800-1050 kg/hr) using UV light at temperature (30-60) °C to obtain a product stream. The product stream, monochloromethane (300-500 kg/hr) and dichloromethane (400-600 kg/hr) was passed through the distillation column and heated to a temperature of 70-95°C to remove hydrochloric acid and to obtain mixture 1. The mixture 1 and Dichloromethane (1200-1500 kg/hr) was passed through another distillation column and heated at a temperature of 105-110°C to remove monochloromethane and obtain mixture 2. The mixture 2 is subsequently washed with water and caustic solution. The mixture 2 is then passed through another distillation column and heated at a temperature of 105-120°C to remove Dichloromethane and to obtain mixture 3. The mixture 3 is distilled to remove trichloromethane to obtain mixture 4. The mixture 4 is distilled to obtain tetrachloromethane and remove heavies.
Purity of tetrachloromethane: 99%
Acid content: less than 10 ppm
Amount of heavies: Less than 20 ppm

WE CLAIM:
1. A process for preparation of tetrachloromethane with low acid content,
comprising the steps of:
a) chlorination of trichloromethane in presence of radical initiator to obtain a product stream;
b) adding an entrainer 1 to the product stream and removing hydrochloric acid by distillation to obtain a mixture 1;
c) adding an entrainer 2 to the mixture 1 and removing entrainer 1 to obtain a mixture 2;
d) washing and neutralizing the mixture 2;
e) distilling mixture 2 to remove entrainer 2 to obtain a mixture 3;
f) distilling mixture 3 to remove trichloromethane and to obtain mixture 4;
g) distilling tetrachloromethane from mixture 4.
wherein, the product stream” comprises of chlorine, hydrochloric acid, trichloromethane and tetrachloromethane.
2. The process as claimed in claim 1, wherein the radical initiator used in step a) is selected from ultra violet light, azobisisobutyronitrile, 1,1'-azobis(cyclohexanecarbonitrile), di-tert-butyl peroxide, benzoyl peroxide, methyl ethyl ketone peroxide, acetone peroxide decachlorobutane or an octachlorobutene or a mixture thereof.

3. The process as claimed in claim 1, wherein the entrainer 1 and 2 used in step b) and c) are selected from monochloromethane, dichloromethane, trichloromethane and tetrachloromethane.

4. The process as claimed in claim 1, wherein the chlorination reaction is carried out at a temperature ranging from 30°C to 60°C at a pressure range of 10-15 bars.

5. The process as claimed in claim 1, wherein the chlorination reaction is carried out with a molar ratio of trichloromethane slightly higher than chlorine.

6. The process as claimed in claim 5, wherein the molar ratio of chlorine to trichloromethane ranges from 1:1.1 to 1:2.

7. A tetrachloromethane has low content of acid of less than 5ppm.