GB1576239A - Production of chlorinated methanes - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO THE PRODUCTION OF CHLORINATED METHANES (71) We, THE LUMMUS COMPANY, a Corporation organized and existing under the Laws of the State of Delaware, United States of America, of 1515 Broad Street, Bloomfield, New Jersey 07003, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to the production of chlorinated hydrocarbons, and more particularly, to the production of chlorinated methanes.

In the production of chlorinated methanes from methane, the chlorinated methane effluent includes unreacted methane, as well as chlorinated methanes which are to be recycled through the chlorinated methane production step. In prior proposed procedures, such unreacted methane and recycled chlorinated methanes are recovered from the effluent by fractional distillation; however, such fractional distillation increases the overall cost of the process.

According to this invention there is provided a process for producing chlorinated methane production zone wherein a gaseous recycle stream comprising unreacted methane and methyl chloride is introduced into the chlorinated methane production zone, said process comprising: (a) withdrawing from the chlorinated methane production zone a gaseous effluent containing unreacted methane, methyl chloride, methylene chloride, chloroform, carbon tetrachloride, water vapour and hydrogen chloride; (b) cooling the effluent to condense a portion thereof, said condensed portion comprising an organic phase containing a major portion of the carbon tetrachloride and chloroform present in the effluent, and an aqueous phase; (c) recovering the organic and aqueous phases; (d) compressing and cooling the uncondensed portion of the gaseous effluent to condense a further portion of the effluent at a temperature of from 40"F to 1000F at a pressure of from 50 to 300 psig, and provide a remaining gaseous stream containing from 75% to 100% of the total quantity of recycled unreacted methane and from 60% to 90% of the total quantity of recycled methyl chloride to be introduced into the chlorinated methane production zone in said gaseous recycle stream, said condensed further portion containing a further organic phase and a further aqueous phase; (e) recovering the further organic and aqueous phases; (f) recovering the remaining gaseous stream without drying and fractionation for recycle to the chlorinated hydrocarbon production zone; and (g) introducing said remaining gaseous stream into the chlorinated methane production zone as a portion of said gaseous recycle stream.

In a preferred process in accordance with the present invention chlorinated methanes are produced by introduction of fresh feed methane, recycle unreacted methane and recycle chlorinated methane(s) (at least methyl chloride and generally also methylene chloride) into the chlorinated methane production zone wherein the fresh feed and recycle is converted to chlorinated methane product. A chlorinated methane effluent, containing unreacted methane, chlorinated methanes (methyl chloride, methylene chloride, chloroform and carbon tetrachloride), water vapour and hydrogen chloride is withdrawn from the chlorinated methane production zone and aqueous hydrogen chloride and a portion of the chlorinated methane product is separated therefrom. The remaining effluent, containing unreacted methane, chlorinated methanes and water vapour is then compressed and cooled to effect the condensation of a further portion thereof and provide a remaining gaseous recycle stream containing from 75% to 100%, preferably from 90% to 100%, of the required methane recycle, and from 60% to 90% of the required methyl chloride recycle. If methylene chloride is also to be recycled, the remaining gaseous recycle stream includes from 5% to 50% of the required methylene chloride recycle. In this manner, a major portion of the required recycle is recovered without a fractional distillation and without requiring drying of the effluent prior to the fractional distillation.

The amount of recycle required in the process is dependent upon the desired product distribution between the four chlorinated methane products. If the product distribution requires large amounts of the heavier product; i.e., carbon tetrachloride, then greater amounts of the lighter chlorinated methanes must be recycled. An important advantage of the present invention resides in the fact that irrespective of the amount of required recycle of each component to provide the desired product distribution, the major portion of the required recycle is obtained without fractional distillation of the effluent, and without drying of the effluent.

In order that the invention may be more readily understood and so that further features thereof may be appreciated the invention will now be described by way of example with reference to the accompanying drawing which is a simplified schematic flow diagram of one embodiment of the present invention.

Although the invention will be particularly described with respect to the production of chlorinated methanes by a method that includes the molten salt technique, it is to be understood that the chlorinated methane effluent may be produced by a method including techniques other than a molten salt technique.

Referring to the drawing, a molten salt mixture of the higher and lower valent chloride of multivalent metal and a melting point depressant; in particular, a mixture of cuprous and cupric chloride in combination with a melting point depressant, such as potassium chloride, in line 10, is introduced into an oxidation reactor, schematically indicated as 11. In the oxidation reactor, the molten salt is contacted with molecular oxygen, generally introduced as air, through line 12, to produce copper oxychloride. The oxidation is generally effected at a temperature of from 600" to 900 . Chlorine values in the form of hydrogen chloride and/or chlorine may also be introduced into the oxidation reactor, with such chlorine values reacting with the molten salt to increase the higher valent chloride content thereof.

A molten salt mixture, containing cuprous chloride, cupric chloride and copper oxychloride, withdrawn from the oxidation reactor 11, through line 13, is introduced into a chlorinated methane production zone, schematically indicated as 14. In the chlorinated methane production zone 14, the molten salt is contacted with fresh feed methane introduced through line 15, hydrogen chloride, chlorine or mixtures thereof, introduced through line 16, and a recycle stream, including unreacted methane and chlorinated methanes, introduced through line 17, to effect production of chlorinated methanes. Zone 14 is generally operated at temperatures in the order of 700" to 1,000"F, with the lower temperatures within the specified range being preferred.

Molten salt recovered from the chlorinated methane production zone 14 is recycled to the oxidation reaction zone through line 10.

A chlorinated methane production effluent, including chlorinated methanes; in particular comprising, for example, methyl chloride, methylene chloride, chloroform and carbon tetrachloride; unreacted methane, water vapour, hydrogen chloride, carbon dioxide and non-condensables, is withdrawn from chlorinated methane production zone 14 through line 21 and passed through a condenser 22 wherein the effluent is indirectly cooled to a temperature which effects condensation of an aqueous hydrogen chloride solution, and in addition, some chlorinated hydrocarbons. The effluent is cooled in condenser 22 to a temperature in the order of from 80"F to 250"F and at a pressure in the order of 10 to 100 psig in order to effect such condensation. Cooling could be effected by means other than indirect cooling.

The cooled effluent, in line 23, is introduced into a separator 24 wherein the condensed portion is separated into an organic phase comprised of heavier chlorinated methanes, and an aqueous phase of dilute hydrochloric acid. The condensed organic phase is withdrawn from separator 24 through line 25 and may be employed, if desired, as a quench liquid in the chlorinated methane production zone. Alternatively, if desired, such condensed chlorinated methanes can form a part of the reaction product.

The condensed aqueous phase is withdrawn from separator 24 through line 26 and such aqueous phase may be further treated to effect stripping of any chlorinated methanes therefrom, followed by concentration thereof to recover a more concentrated aqueous hydrogen chloride solution.

The uncondensed portion of the chlorinated methane effluent, containing substantially all of the unreacted methane, chlorinated methanes, water vapour, some hydrogen chloride, carbon dioxide and non-condensables is withdrawn from separator 24 through line 41 and introduced into a direct contact quench vessel 42 to effect further separation of chlorinated methanes. In quench vessel 42, the effluent is cooled to a temperature in the order of 50"F to 1500F, at a pressure of in the order of from 5 to 100 psig in order to effect further condensation of chlorinated methanes. Although the invention has been particularly described with respect to the use of direct contact cooling in a quench vessel, other means of effecting cooling of the effluent for condensing chlorinated methanes may also be employed.

In quench vessel 42, the chlorinated methane effluent is directly contacted with an aqueous quench liquid, introduced through line 43, to directly cool the effluent and condense additional water vapour and chlorinated methanes therefrom. The condensed portion forms an aqueous phase and an organic phase in the bottom of the quench tower 42.

The condensed organics, recovered from quench tower 42 through line 44, forms a part of the chlorinated methane product. In general, the organics recovered through line 44 contain all four of the chlorinated methanes. Moreover, the cooling in vessel 42 is generally effected in a manner such as to condense most of the chloroform and carbon tetrachloride from the effluent, whereby the remaining gaseous effluent recovered from the quench tower contains substantially all of the unreacted methane, methyl chloride, small portions of methylene chloride, and small portions of chloroform and carbon tetrachloride.

The condensed aqueous phase is withdrawn from quench tower 42 through line 45, and is preferably combined with alkali, such as sodium hydroxide, in line 46, in order to maintain alkaline conditions in the aqueous phase. A first portion of the aqueous phase is passed through line 47, including quench cooler 48, wherein the aqueous phase is cooled to a temperature suitable for providing the cooling requirements for quench tower 42. The cooled quench effluent is introduced into tower 42 through line 43. The remaining portion of the aqueous phase withdrawn from tower 42, in line 52, may then be further treated to separate any chlorinated methanes therefrom. The stripped aqueous phase is then discarded, as a waste water stream.

The uncondensed portion of the chlorinated methane production effluent, containing substantially all of the unreacted effluent, containing substantially all of the unreacted methane, chlorinated methanes (primarily methyl chloride and methylene chloride) some water vapour, carbon dioxide and non-condensables, is withdrawn from quench tower 42 through line 49. The effluent in line 49, is compressed, schematically indicated as 61, and cooled by indirect heat exchange in cooler 62 to effect condensation of further chlorinated methanes. The cooled and compressed stream in line 63 is at a temperature of from 40"F to 100"F, preferably a temperature of from 40"F to 60"F, and at a pressure of from 50 to 300 psig, preferably from 100 to 200 psig. The pressure and temperature of the stream in line 63 is coordinated within the hereinabove described conditions to effect condensation of a portion of the effluent and provide a remaining gaseous recycle stream which includes from 75 to 100%, preferably from 90 to 100% of the required methane recycle (as should be apparent the total methane recycle is designed for essentially 100% of unreacted methane even though the gaseous recycle stream may contain less than such 100% requirements) and from 60% to 90% of the required methyl chloride recycle. If methylene chloride is being recycled, the remaining gaseous recycle stream provides from 5% to 50% of the required methylene chloride recycle. The remaining gaseous recycle stream may also include small amounts of chloroform and carbon tetrachloride.

The mixed stream in line 63 is introduced into a gas-liquid separation vessel, schematically indicated as 64, wherein the gaseous recycle stream is separated from a condensed aqueous phase and a condensed organic phase.

The gaseous recycle stream is withdrawn from separation vessel 64 through line 67 for recycle through line 17 to the chlorinated methane production zone 14. A portion of the stream in line 67 may be withdrawn as a slip stream through line 68 for effecting removal of carbon dioxide and non-condensables. The chlorinated methane present in the stream in line 68 may be recovered as reaction product and/or recycled to the chlorinated methane production zone.

The aqueous phase is withdrawn from vessel 64 through line 65, and such aqueous phase may be further treated to strip chlorinated hydrocarbons therefrom, prior to discarding same. The organic phase is recovered from vessel 64 through line 66 and forms a part of the overall reaction product. The remaining portion of the required recycle (methane, if any; methyl chloride; methylene chloride, if any; and chloroform, if any) is recovered, by fractionation from stream 66. Alternatively, all or a portion of such required remaining recycle is obtained from stream 44. The remaining recycle requirements recovered (not shown) from stream 66 and/or stream 44 is added to recycle stream 67 through line 71.

The remaining portion of the uncondensed effluent is recycled to the chlorinated methane production zone through line 17.

The chlorinated methanes may be produced by other than a molten salt technique, although such a technique is preferred. For example, the chlorinated methanes may. be produced by an oxychlorination wherein methane is directly contacted with oxygen and hydrogen chloride.

As a further modification, the various cooling steps may be effected otherwise than as particularly described.

The invention will be further described with respect to the following example; Example The following is illustrative of the composition of particular streams employed in producing a final product in which the product distribution of methyl chloride: methylene chloride: methylene chloride: chloroform: carbon tetrachloride is 20/30/40/10 wt.%. The gaseous recycle stream in line 67 includes about 98% of the methane recycle; about 64% of the methyl chloride recycle and about 10% of the methylene chloride recycle. Details of the process are shown in the following table which relates data to the apparatus described above and illustrated in the accompanying drawings.

TABLE STREAM 49 67 66 65 Vapour From Vapour From Chlorohydrocarbon Vessel 42 Vessel 64 Liquid From Water From Vessel 64 Vessel 64 COMPONENT Mol/Hr Lb/Hr Mol/Hr Lb/Hr Mol/Hr Lb/Hr Mol/Hr Lb/Hr CH4 914.0 14624 906.6 14505 7.4 119 C2H4 + C2H6 1.9 55 1.8 52 0.1 3 N2 113.3 3172 113.1 3166 0.2 6 O2 20.0 640 20.0 639 - 1 CO 15.1 423 15.1 423 CO2 187.0 8228 169.3 7450 17.7 778 CH3Cl 395.2 19958 195.9 9892 199.3 10066 1 CH2Cl2 133.3 11317 13.9 1180 119.4 10137 1 CHCl3 34.0 4060 1.6 193 32.4 3867 CCl4 4.4 677 0.1 22 4.3 655 C2H2Cl2 0.1 10 - - 0.1 10 C2H4Cl2 + C2H3Cl3 0.1 10 - - 0.1 10 H2O 11.3 203 1.0 18 1.6 29 8.7 156 TOTAL 1829.7 63377 1438.4 37539 382.6 25681 8.7 158 Recycle Component Percent of Recycle Quantity Provided In Stream 67 CH4 98.3% CH3Cl 63.9% CH2Cl2 10.5% The present invention is particularly advantageous in that the major portion of the methane and chlorinated methanes required for recycle to the chlorinated hydrocarbon production zone are recovered from the chlorinated methane effluent, without the necessity of fractional distillation. In addition, such recycle is provided without effecting drying of the recycle stream.

Claims (8)

WHAT WE CLAIM IS:

1. A process for producing chlorinated methanes in a chlorinated methane production zone wherein a gaseous recycle stream comprising unreacted methane and methyl chloride is introduced into the chlorinated methane production zone, said process comprising: (a) withdrawing from the chlorinated methane production zone a gaseous effluent containing unreacted methane, methyl chloride, methylene chloride, chloroform, carbon tetrachloride, water vapour and hydrogen chloride; (b) cooling the effluent to condense a portion thereof, said condensed portion comprising an organic phase containing a major portion of the carbon tetrachloride and chloroform present in the effluent, and an aqueous phase: (c) recovering the organic and aqueous phases; (d) compressing and cooling the uncondensed portion of the gaseous effluent to condense a further portion of the effluent at a temperature of from 40"F to 100"F at a pressure of from 50 to 300 psig, and provide a remaining gaseous stream containing from.

75% to 100% of the total quantity of recycled unreacted methane and from 60% to 90% of the total quantity of recycled methyl chloride to be introduced into the chlorinated methane production zone in said gaseous recycle stream, said condensed further portion containing a further organic phase and a further aqueous phase: (e) recovering the further organic and aqueous phases; (f) recovering the remaining gaseous stream without drying and fractionation for recycle to the chlorinated hydrocarbon production zone; and (g) introducing said remaining gaseous stream into the chlorinated methane production zone as a portion of said gaseous recycle stream.

2. A process according to Claim 1 wherein said gaseous recycle stream further includes methylene chloride, said remaining gaseous stream containing from 5% to 50% of the total quantity of recycled methylene chloride to be introduced into the chlorinated methane production zone in said gaseous recycle stream.

3. A process according to Claim 1 or Claim 2 wherein the cooling of step (b) is effected to a temperature of from 50"F to 1500F at a pressure from 5 to 100 psig.

4. A process according to any of the preceding claims wherein chlorinated methanes are - produced in the chlorinated methane production zone by contacting fresh feed methane with hydrogen chloride, with or without chlorine, or chlorine or a molten mixture containing cuprous chloride, cupric chloride and copper oxychloride.

5. A process according to any one of the preceding claims wherein the compression and cooling of step (d) is to a temperature of from 40"F to 60"F at a pressure of from 100 to 200 psig.

6. A process for producing chlorinated methanes substantially as herein described with reference to the accompanying drawing.

7. A process for producing chlorinated methanes according to Claim 1 and substantially as herein described with reference to the Example.

8. A chlorinated methane product made by a method according to any one of the. preceding claims.