US2451821A - Chlorination of paraffinic hydrocarbons - Google Patents

Description

Patented Oct. 19, 1948 'CHLORINATION OF PARAFFINIC HYDROCARBONS Everett Gorin, Dallas, Tex., assignor, by mesne assignments, to Socony-Vacuum Oil Company, Incorporated, New York, N. Y'., a corporation oi New'York Application January 26, 1946, Serial'No. 643,800

Claims. (Cl. 260-659) This invention relates to a process for the -chlorination of normally gaseous hydrocarbons, The invention is concerned particularly with the production of chlorides of methane from methane and dry natural gas, 1. e., a natural gas from which most of the ethane and substantially all of the propane and higher molecular weight hydrocarbons have been removed.

Vast quantities of methane are available in the form of natural gas, the chief use of which has been its utilization as a fuel. A considerable amount of the supply is used to produce carbon black. More recently attempts have been made to increase the production of fuels for internal combustion engines by converting methane to normally liquid hydrocarbons in such synthetic processes as th Fischer process and modifications of this process and new processes have been proposed for using methane as a starting material for the production of chemical intermediates by'oxidation and chlorination processes.

,Various methods have been proposed for the chlorination of normally gaseous hydrocarbons, such as methane, to form therefrom the corresponding alkyl and alkylene chlorides. The conventlona1 method of direct chlorination with free chlorine has been used for many years. However, this method has several disadvantages which have not been entirely overcome. The reaction of free chlorine with methane is highly exothermic and hence the reaction is very dimcult to control at moderate temperatures and explosive mixtures of the reactant gases are difficult to avoid, Also large volumes of hydrogen chloride are formed in the direct chlorination process and since the reutilization of the hydrogen chloride in the chlorination process is of primary importance to make any hydrocarbon chlorination process economically feasible, it becomes necessary to incorporate with th process a coordinating chlorine recovery process such as the Deacon process.

The primary object of this invention is to produce chlorides of methane. Another object of the invention is to provide a continuous process for the chlorination of methane and natural gas wherein the chlorination reaction is readily controlled. Another object of the invention is to provide a continuous process for the chlorination of methane and natural gas wherein the hydrogen chloride produced by such chlorination is utilized in producing chlorinating agent for the process. A further object of the invention is to provide a continuous vapor Phase process for the chlorination of methane and natural gas wherein explosive mixtures of free chlorine and the hydrocarbons undergoing chlorination are avoided. -Other objects of the invention will appear hereinafter.

I have found that mercuric chloride may be reacted in the vapor phase with methane and natural gas to produce monochlorides and higher chlorinated derivatives of these gaseous hydrocarbons. The reaction of mercuric chloride with methane may be represented by the equation The above reaction takes place at temperatures ene are formed instead of the corresponding hydrocarbon chlorides. The natural gas used in my process must therefore contain only a limited amount of higher hydrocarbon, that is, preferably less than 15 mole percent of ethane and not more than 2 or 3 mole percent of propane. The conversion of normally gaseous hydrocarbonsto aromatics at temperatures above 600 C. in the presence of volatile metallic chlorides, such as mercuric chloride, is taught and claimed in my copending application entitled Conversion of normally gaseous hydrocarbons, Serial Number 400,- 296,'flled June 28, 1941, now U. S. Patent 2,396,- 697. In converting mixtures oi. mercuric chloride and normally gaseous hydrocarbons to aromatics, the mercuric chloride is completely reduced to mercury in the chlorination-dehydrochlorinationprocess. I

I prefer to operate the herein described process of converting methane to chlorinated methane at temperatures within the range oi! from about 525 C. to about 575 C. under conditions of contact time described hereinbelow such that no more than per-cent of the mercuric chloride is reduced to mercury and only minor amounts of the chlorinated hydrocarbon is reconverted to hydrocarbons. I have found that it contact times substantially greater than those required to reduce about 90 percent of the mercuric chloride are employed the ultimate product consists primarily of hydrocarbons and not chlorinated methane.- Ii. contact times below those required to obtain about 35 percent reduction of the mercuric chloride are employed the concentration of chloromethanes in the product gas is too low to permit their economical recovery. I have observed that when contact times within the range seconds are employed, 35 percent to 90 percent of the mercuric chloride is reduced. In the above expression T is the degrees Kelvin maintained in the reaction zone. Thus, for operation at a temperature of 525 C. the proper range of contact time is from about 32 seconds to about 322 seconds and for operation at 575 C. the range of contact time is from about seconds to about 50 seconds, that is, an overall range of contact time of from about 5 seconds to 322 seconds for my preferred operating temperatures. The term contact time as used in this specification and in the claims is defined as the reciprocal space velocity and is equal to the total volume of the reaction zone free space divided by the volume of reactant gases, reduced to standard conditions of temperature and pressure, passed therethrough per second. Contact time of the reactant gases in the chlorination zone as defined herelnabove is greatly reduced when operating at elevated pressures. The chlorination reaction may be carried out at pressures from atmospheric to about 200 pounds gage, preferably about 150 pounds gage. However, the pressures are in all cases maintained sufflciently low so that the reaction is carried out under vapor phase conditions.

The endothermic reaction of mercuric chloride with methane to form methyl chloride is of particular utility since the by-product mercury and hydrogen chloride can be reacted in the presence of oxygen or oxygen containing gases to reform mercuric chloride chlorinatin agent. This reaction is exothermic and furnishes an excess of heat over that required to chlorinate methane with the mercuric chloride agent. The reaction of mercury with hydrogen chloride and atmospheric oxygen to form mercurous chloride takes place at temperatures from about 50 C. to about 250 C. accordin to the equation The mercurous chloride dissociates to produce free mercury and mercuric chloride at a temperature of about 250 C. or above. The reaction between mercury, hydrogen chloride and oxygen may be carried out at temperatures above 250 C. to form mercuric chloride directly according to the equation In my process I prefer to regenerate mercuric chloride under conditions of temperature and pressure approximating temperature and pressure conditions in the chlorination zone.

The process of chlorinating methane by means of mercuric chloride may be carried out either batchwise or as a'continuous process. Thus, by the use of a multiplicity of towers packed with material having a high specific heat, that is, high heat capacity, the heat produced in the regeneration of mercuric chloride may be stored in the packing and by successively alternating the chlorination andregeneration reactions in these towers a part of the heat of regeneration may be most efflciently utilized in the chlorination process. 'Such a continuous regeneration method which is coordinated with a process for chlorinating methane or hydrocarbon mixtures consisting essentially of methane with only a minor amount of ethane is described hereinbelow. These mixtures which may be chlorinated by my process are obtained from a dry natural gas'from which substantially all of the hydrocarbons having more than two carbon atoms per molecule have been removed.

Referring to the drawing, towers I and 2 are used alternately as methane chlorination zones 'and regeneration zones. These towers are packed ily to the reactant gases in the chlorination cycle.

Suitable materials are quartz and relatively nonporous carborundum. The packing may be disposed in a series of beds as indicated or the packing may be continuous in the towers. Towers 3 and 4 which are used to recover residual mercuric chloride vapors and mercury from the gaseous eilluent of the chlorination cycle are also packed with inert packing having the above properties.

The packing in these towers should be relatively porous in order to adsorb the mercuric chloride and hence I prefer to use porous packing such as porous carborundum or crushed fire brick in towers 3 and 4.

Methane in lin It) is passed by means of compressor ll through coil I2 in furnace ii! at a pressure of about 150 pounds per square inch. Molten mercuric chloride in line I6 is passed by means of pump IT to coil 3 in furnace 13. In furnace I3 the streams of methane and mercuric chloride are raised to a temperature within the range of from about 525 C. to about 575 C. vaporized mercuric chloride in line passes to methane line 2| and the mixed vapors pass to manifold line 22 which leads to reactor i. Valves 23 and 24 in line 22 are maintained in the open position to permit free passage of the gas to reactor I while valve 25 in line 26 and valve 21 in line 28 are closed as is also valve 29 in line 22. 1

The mole ratio of methane to mercuric chloride introduced to reactor 1 should be within the range of from about three to one to about ten to one. An excess of methane is preferable in order to obtain maximum conversion of mercuric chloride to methyl chloride product and minimum formation of the higher chlorinated derivatives of methane. A high ratio of methane to mercuric chloride also prevents the condensation of the mercuric chloride and mercury product vapors. As the mixed vapors pass upward in tower l' they contact the hot packing material which has been heated in a previous regeneration cycle and the reaction indicated by 1) produces a gaseous mixture consisting of chlorinated methane, unreacted methane, hydrogen chloride, vaporized metallic mercury and unreacted mercuric chloride vapor. With valves 36 and 36 in line 31 in the open position and valves 38, 39, and 40 in lines 4!, 42, and 43 respectively closed, the vapor product passes overhead through line 44 to condenser 45. In condenser 45 the mercury and unreacted mercuric chloride vapors are condensed and the mixed product of non-condensed product gases and liquid mercury and mercuric chloride passes through line 40 to hot settler II. Settler 4'7 is operated at a temperature of from about 2'75 C. to 300 C. and at a pressure substantially the same as reactor I, that is, about 150pounds gage, and the metallic mercury and liquid mercuric chloride settle therein to form two liquid layers, the liquid mercuric chloride being supported by the liquid mercury. The liquid mercuric chloride is recycled to furnace l3 through line 48. Liquid mercury is withdrawn from settler 41 through line 40 and transferred to heater 60 by means of pump 5|. The liquid mercury is vaporized in heater 60 and the vaporized mercur passes therefrom through line 62 to line 53 through which reactant gases for the regeneration of mercuric chloride pass to tower 2 described hereinbelow.

The gaseous effluent from settler consisting of unreacted methane, chlorinated hydrogen chloride, and small amounts of mercuric chloride and mercury vapor pass overhead through valved line 80 to cooler 6| where the temperature of the gaseous mixture is lowered to the range of about 60 C. to 100 C. to condense out anyresidual mercuric chloride and mercury. The mixture is passed through line 62 to manifold line 63 and thence by line 64 to packed tower 3. valve 85 in line 84 being in the open position. Valve 61 in line 69 and valve II in line 12 are closed In order to isolate tower 3 from gaseous stream passing to tower 4. In tower 3 suspended solid mercuric chloride is deposited on the packing. With valves I5 and 11 in lines I8 and 80 respectively closed, and valve 8I in line 82 open the mixture of product gases and a small amount of mercury pass through line 84 which leads to liquid mercury sump 05 from the bottom of which any residual mercury is passed throu h line to line 49. The gaseous product passes overhead from sump 85 through valved line 81 to absorber 90.

In absorber 90 the gaseous product mixture is contacted countercurrently with a stream of hydrogen chloride-water azeotrope containing from 20 to 25 percent hydrogen chloride introduced to absorber 90 through line 9| by means of pump 92. The absorber is operated at pressures inexcess of 100 pounds gage and the azeotrope removes hydro-gen chloride from the gaseous mixture. The solubility of methyl chloride and other chlorinated methanes in the azeotrope is slight compared with that of hydrogen chloride and the azeotrope rapidly becomes saturated with the hydrocarbon chlorides after which further absorption of the hydrocarbon chloride product practically ceases. The hydrogen chloride enriched azeotrope passes from the bottom of absorber 90 through valve 93 in line 94 to fractionating tower 95 which is equipped with heating means 95 and top cooling means 91. Hydrogen chloride passes overhead from fractionator 95 to the regeneration zone 2 through line 98 which leads to line 50. If desired, the hydrogen chloride may be scrubbed with sulfuric acid to remove any water vapor before recycle to tower 2. Hydrogen chloride from an external source is introduced to line 53 through line 99. Lean azeotrope passes from the bottom of fractionator 95 through line I00 to cooler IOI and thence through line I02 to line 9I for reuse in absorbing hydrogen chloride from the product gas.

The gaseous product from absorber 90 consisting essentially of unreacted methane and chlorinated methane passes overhead through line I to absorber -I08 wherein the gas is contacted countercurrently with a suitable solvent for the aetresi chlorinated hydrocarbon such as a petroleum.

naphtha fraction. A relatively high boiling, narrow cut kerosene fraction or mineral seal oil may be used or a, chlorinated hydrocarbon such as car- 5 bon tetrachloride may be used as the absorbent liquid introduced to absorber I06"through, line I0! by means of pump I08. Absorber I00 is operated at pressures in excess of 100 pounds per square inch gage and as the absorbent descends 10 in the tower the chlorinated methane is absorbed from the product gas stream. If desired, towers I06 and 90 may be packed with suitable inert packing in order to obtain more efficient contact of the gas with the liquid absorbent. Unabsorbed methane passes overhead from absorber I06 through recycle line I09 which joins methane feed line Ill. The chlorinated methane enriched absorbent is withdrawn from absorber I06 through line III] and passes through valve III 2" to fractionator II2 which is equipped with bottom heating means H3 and top cooling means II4. Lean absorbent is Withdrawn from fractionator II2 through bottom drawoif line H5 and passes via coolerIIB and line II! to absorbent feed line I01. Chlorinated methane passes overhead from fractionator II2 through line II8. If desired, the chlorinated product may be withdrawn as a side stream from fractionator II2 (not shown) reserving top drawoff line I I0 for the elimination from the product of any trace of methane picked up by the absorbent in absorber I06 when operating the same at high pressure.

The regeneration of mercuric chloride reagent :5 by means of mercury, oxygen, and hydrogen chloride according to Equation 3 above is accomplished in tower 2 while tower I is in operation on the chlorination cycle as described hereinabove. Reaction tower 2 after being withdrawn 1:) from the chlorination cycle must be purged of hydrocarbon gases before inauguration of the regeneration cycle. With valve I 20 in line 28 and valve I2I in line 42 open and valves I22 and I23 in lines 22 and 43 respectively closed, reactor 2 i5 is purged by means of hot flue gas introduced to the reactor through lines I24, 20, and 22, and the purge gas passes from reactor 2 through lines 43, 42, and I26. Following the purging of tower 2 valves I20 and I2I are closed, valves I22 and I29 are opened and Valves I26 and l2l in lines 26 and 4| respectively are set in the open position, thus preparing the inlet and outlet manifold lines to reactor 2 forthe regeneration cycle which is described below.

Following the deposition of solid mercuric chloride on the packing in tower 4 the recovery of the solid mercuric chloride isaccomplished in the following manner. Valve I32 in line I2 and valve I33 in line 18 are opened. Valve I34 in line I35 0 which connects with hot methane feed line 2I is now opened and part of the hot methane from furnace I3 is passed through lines I35, I2, and 68 and thence through tower 4 and lines 80, I8, and I36 back to furnace fed line I0. The hot methane vaporizes the mercuric chloride and carries the vapors back to the chlorination cycle. The extent to which the packing is raised in temperature by the hot methane purge will depend on the length of time necessary to remove the deposited mercuric chloride. Since the amount \of mercuric chloride deposited is usually small, the duration .of the hot methane purge will be relatively short. When it becomes necessary to continue the hot methane purge for sufllcient time to heat the packing in tower 4 to a relatively I high temperature in order to vaporize substantially all oi the mercuric chloride the heat stored in the packing in the heating step may be recovered and the temperature oi the packing may be lowered to mercuric chloride adsorption temperatures by preheating cold methane passing to furnace ii. In order to lower the temperature oi the packing, valve I34 in line I35 is closed eration cycle, a free oxygen containing gas such as air is introduced to the process through valved 'line I50 which connects with line 53. As indicated hereinabove, hydrogen chloride is introduced to line .53 through lines 98 and 09 and mercury is introduced to line 53 from line 49. Makeup evaporated and the recovered mercuric chloride is returned to the chlorination cycle. The mercury recovered from the cooled gas is returned to the regeneration cycle.

The iollowing example illustrates the chlorination step oi my process. L

A gaseous mixture consisting oi methane and vaporized mercuric chloride in the mole ratio oi about five moles oi methane per mole oi mercuric chloride was passed through a Pyrex glass tube at X a temperature oi 530 C. ior a contact time oi mercury is introduced to line 48 through line I5I.

If desired, the mixture oi air, hydrogen chloride, and mercury vapor in line 53 may be raised in temperature by passing themixture in heat exchange with the overhead product from reactor I in line 44. The amount oi preheat given to this mixture will depend on heat losses from regeneration reactor 2. In any case the temperature oi the mixture as it enters reactor 2 is sufiiciently high to avoid {condensation oi mercury vapors from the mixture. The proportion of oxygen and mercury in the mixture should be such that at least one mole of oxygen and two atoms oi mercury are furnished respectively for each four moles of hydrogen chloride. I prefer to use at least 10 percent excess of mercury over that required by stoichiometrlc proportions as indicated by Equation 3 above in order that the hydrogen chloride may be substantially completely oxidized.

The gaseous mixture from line 53 is passed by compressor I52 through lines I53, 4|, and 43 to reactor 2 at a pressure within the range oi from atmospheric to about 200 pounds per square inch, preferably about 150 pounds per square inch. The temperature, which increases in reactor 2 due to the exothermic nature of the reaction, is maintained within the range of irom about 500 C. to about 650 C.

The reaction product from regeneration reactor 2 passes through valve I22 in line 22 and through valve I28 in line 20 to line I54 leading to condenser I55 where the temperature is lowered to the range of from about 275 C. to 290 C. or 300 0., and the mixture of liquid mercuric chloride, water vapor, oxygen depleted air, and unreacted mercury passes through line I56 to the mercuric chloride recovery zone. In the mercuric chloride recovery zone the mixture is introduced to a settler similar in operation to settler 41 from which liquid mercuric chloride is passed by line I60 to line 48 and thence to mercuric chloride feed line I6 leading to iurnace I3.

Liquid mercury is recycled from the settler in the mercuric chloride recovery zone through line IBI to line 06 which leads to mercury recycle line 49. Mercuric chloride, hydrogen chloride, and mercury in the oil gas from the settler may be recovered by cooling the gas to about 100 C. and passing the cooled gases through a packed tower such as tower 3 described above or the gas may be cooled to a lower temperature and scrubbed with water to absonb the mercuric chloride. The water solution may then be concentrated and 55 seconds. Under these conditions 47.0% oi the mercuric chloridewas reduced to metallic mercury and about 9.0 percent oi the methane was chlorinated. The yield oi chloromethanes based on the quantity oi methane and mercuric chloride reacted was quantitative. 'The chlorinated product consisted of 87.3 percent methyl chloride and 12.7 percent methylene chloride.

My invention makes possible a method ior chlorinating methane or natural gas rich in methane wherein temperature conditions are easily controlled and the processmakes possible chlorination oi these gases without danger .oi creating an 1 explosive mixture oi hydrocarbon and chlorine. The process also makes possible the reutilization oi hydrogen chloride formed in the chlorination process.

1. The process ior the manufacture of at least one chloride of methane irom methane which comprises maintaining said methane in contact with a chlorinating agent consisting oi mercuric chloride vapor in a reaction zone at a temperature within the range oi from about 500 C. to about 650 C. and fora contact time such that not more than percent of said mercuric chloride is converted to metallic mercury and recovering said chloride oi methane irom the gaseous eiiluent of said reaction zone.

2. The process for the manufacture oi achlorinated hydrocarbon which comprises passing a hydrocarbon gas stream consisting essentially oi parafllnic hydrocarbons of not more than two carbon atoms and comprising not more than 15 mole percent of ethane in contact with mercuric chloride vapor in a reaction zone at a temperature within the range of from 500 C. to 650 C. for sufficient time to convert at least 35 percent and not more than 90 percent oi said mercuric 'chlochloride is formed and recovering said chlorinated hydrocarbon irom the gaseous eilluent oi said reaction zone. I.

3. 'Ilhe process ior the manufacture oi a chlorinated hydrocarbon which comprises passing a hydrocarbon gas stream consisting essentially of parailinic hydrocarbons oi not more than two carbon atoms and comprising not more than 15 mole percent oi ethane in contact with mercuric chloride vapor in a reaction zone at a temperature within the range oi from about 500 C. to about 650 0., adjusting the contact time oi said gas with the mercuric chloride vapor in said reaction zone to a number oi seconds greater than represented ,by the expression Contact time=oI5 1o y-11.91) t and less than that represented by the expression Contact timc=5.o 10 2- 1 1.91)

where T is the temperature in degrees Kelvin in said reaction zone, and recovering said chlorinated hydrocarbon from the gaseous effluent of said reaction zone.

4. The process for the manufacture of chloromethanes which comprises passing a gaseous mixture of methane and mercuric chloride through a reaction zone at a temperature within the range of from about 500 C. to about 650 C. at a rate such that the contact time is sufficient to reduce at least 35 percent. and not more than 90 percent of said mercuric chloride to free mercury, cooling the gaseous effluent from the reaction zone to a temperature below 500 C. and sumcient to condense mercuric chloride and metallic mercury therefrom, and recovering the chloromethane product.

5. The process for the manufacture of methyl chloride from methane and mercuric chloride which comprises the steps of (1) introducing a gaseous mixture consisting essentially of methane and mercuric chloride to a chlorination zone at a temperature within the range of from about ,cury and hydrogen chloride of step 2 and hydrogen chloride introduced from an external source in contact with a free oxygen containing gas in a separate reaction zone to regenerate mercuric chloride, (4) separating mercuric chloride from the reaction product of step 3, (5) recycling the unreacted methane and unreacted mercuric chloride of step 2 and the mercuric chloride of step 4 to the chlorination zone of 10 where T is the temperature in degrees Kelvin maintained in said reaction zone to form a vapor mixture consisting essentially of unreacted methane, unreacted mercuric chloride, chlorinated .1 methane, hydrogen chloride, and free mercury;

(2) continuously fractionating the vapor mixture of step 1 to obtain separate streams consisting essentially of unreacted methane, unreacted mercuric chloride, chlorinated methane, hydrogen chloride, and free mercury, (3) continuously passing the hydrogen chloride and free mercury of step 2 in contact with a free oxygen containing gas in a separate regeneration zone whereby mercuric chloride is regenerated and water vapor is formed, (4) continuously separating the mercuric chloride from the water vapor of step 3, (5) recycling the unreacted methane and mercuric chloride of step 2 and the regenerated mercuric chloride of step 4 to step 1, and (6) recoveringchlorinated methane from step 2 of the process.

9. The process for the manufacture of at least one chloride of methane from methane and mercuric chloride which comprises the steps of (1) passing a, gaseous mixture consisting essentially of methane and mercuric chloride through a reaction zone packed with a refractory solid at a temperature withinvthe range of from about 500 C. to about 650 C. whereby said methane is chlorinated and hydrogen chloride is formed and at least percent of said mercuric chloride and not more than 90 percent of said mercuric chloride is reduced to free mercury, (2) fractionating the reaction product or step 1 to obtain separate streams of unreacted methane, at least one chloride of methane, hydrogen chloride, unreacted mercuric chloride, and free mercury, (3) passing the free mercury and hydrogen chloride of step 2 and hydrogen chloride introduced from an external source in contact with a free oxygen containing gas in a separate reaction zone packed step 1 of the process, and (8) recovering said with a refractory solid at a temperature within the range of from about 500 C. toabout 650 C. to regenerate mercuric chloride whereby at least a part of the exothermic heat of the reaction is stored in the packing of said separate reaction zone, (4) separating mercuric chloride from the reaction product of step 3, (5) recycling the unreacted methane and unreacted mercuric chloride of step 2'and the mercuric chloride of step 4 to the reaction zone of step 1, and (6) recovering said of at least one chloromethane from methane which comprises the steps of (1) continuously passing a gaseous mixture of said methane and mercuric chloride th ough a reaction zone at a temperature within the range of from about 525 C. to about 575 C. at a contact time in seconds corresponding to the expression chloride of methane from step 2 of the process.

10. The process as described in claim 9 wherein the processes of steps 1 and 3 are carried out alternately in the same reaction zone whereby at least a part of the heat stored in the reaction zone of step 3 is utilized in step 1 of the process. EVERETT GORIN.

REFERENCES CITED Country Date Great Britain Apr. 14, 1924 Number

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