US2200255A - Chlorination - Google Patents

Description

H.BENDER ay M, 1940.

GHLORINATION Filed NOV. 21, 1938 2 Sheets-Sheet 1.

Caobhy a/x'r INVENTOR. Harry fle/mer ATTORNEY Condenser R E D N E B H CHLORINAT'EON Filed Nov. 21. 1938 2 Sheets-Sheet 2 FIE E FlE a INVENTOR; I Harry fiefloer ATTORNEY Ill Patented May 14, 1940 U NlTED STATES CHLORINATION Harry Bender, Antioch, Callf., assignor, by mesne assignments, to The Dow Chemical Company, Midland, Mich, a. corporationrot Michigan Application November 21, 1938, Serial No. 241,664

29 Claims.

This application is .a continuation in part of my application Ser. No. 116,598 and application Ser. No. 145,734, flied December 18, 1936, and June 1, 1937, respectively.

This invention relates to the chlorination of saturated aliphatic hydrocarbons by substitution, and more particularly to a process enabling the continuous chlorination of such hydrocarbons. This invention is particularly applicable to the chlorination of methane, ethane, propane, normal butane, isobutane, normal pentane, isopentans, 2,2-dimethylpropane, normal hexane, dimethylpropylmethane, methyldiethylmethane, dimethylisopropylmethane, and trimethylethylmethane.

It is in general the broad object of the present invention to provide a chlorination operation which can be conducted in a continuous manner and under such conditions that it lends itself readily to automatic regulation.

While the invention is applicable to the chlorination of any one of the foregoing hydrocarbons; or any one of the partially chlorinated aforementioned hydrocarbons, it will be particularly described with reference to the chlorination of methane. This is only by way of example and not by way of limitation.

The photochemical chlorination of saturated aliphatic hydrocarbons, such as those hereinbefore mentioned, is not broadly new. Various investigators have shown that such hydrocarbons react with chlorine under the influence of light. However, as far as I am aware, I am the first to enable these operations to be carried on continuously and on a large scale.

Photochemically influenced chlorination substitution reactions have been characterized by various of the previous investigators as proceed ing with'extreme violence. Apparently it has been this hazard which has kept such processes from more extensive use and application.

I have found that if, for example, the vapor phase reaction zone in which the substitution chlorination occursincludes as a component, in

addition to the hydrocarbon and chlorine, a material inert to the reaction or which at best reacts only slowly, then the reaction proceeds smoothly, without hydrocarbon carbonization, and without any explosive violence. The presence of therelatively inert material bufiers the substitution chlorination, so to.speak, and ensures that it does not proceed too violently at the temperature of operation. Thus, one can visualize the reaction space as containing three types of molecules, A, B and C, of which, A and B re- (Cl. 260661) F act. Now, the more molecules reacting, the more violent becomes the reaction. However, the C molecules, the inert ones, get in the way and stop the reaction between the reacting molecules A and B whereby the reaction is slowed down so that it only continues at what we consider a normal rate, one which is not so violent as to be classified as explosive. Thus the present invention makes possible the successful, continuous chlorination of hydrocarbons with such chlorinehydrocarbon ratios that dichlorand higher chlorinated products areproduced.

For example, I have employed successfully chlorine methane ratios of one to one, two to one and as high as four to one. This is made possible by the use of the inert material present as a buffer or reaction suppressor. With chlorine present in such high volume ratios one would ordinarily expect the hydrocarbon to decompose to carbon, frequently with explosive violence. Prior investigators have recommended the use of low chlorine methane ratios, one to six being a typical example. However, such low ratios give low yields, particularly of the components higher than the monochlorinated products. The present invention enables high yields of dichlorinated hydrocarbons and higher and this safely and continuously.

Another advantage of the present invention is that it does not require pure hydrocarbons. For example, in thermally chlorinating methane such a high temperature is required that any higher hydrocarbons chlorinate and decompose to form carbon. This causes clogging of the apparatus, aifects adversely heat transfer and otherwise interferes with the continuous operation of the process. The present process is not affected by the presence of other hydrocarbons; as a matter of fact, the present process operates, if anything, more satisfactorily on a mixture of hydrocarbons as will appear hereinafter.

In the attached drawings, Figure 1 is a diagrammatic showing of an apparatus set up for conducting the present invention, particularly as related to the partial chlorination of methane, while Figures 2 and B are schematic apparatus showings of modified reaction vessels.

Referring to the drawings, and particularly to Figure 1, a vessel 9 is provided wherein the reaction is to be conducted. This vessel is suitably constructed of any suitable material of construction, such as a steel outer vessel with a lead lining, or a nickel vessel. The vessel has a suitable top, and from this depends a light well M containing a light source IS. A header 62 is placed adjacent to the light well, and particularly at a point of strong irradiation from the light, so that the point of release of chlorine and methane is strongly irradiated. The header is supplied with chlorine-methane mix conveniently formed in the dark. Thus, line a is connected to the header and is supplied with chlorine from line b and methane from line i- The chlorine and methane released through jets ii in header 32 rise past the light source and react. I prefer that the point of release of the chlorine and methane mix be below the surface of a maintained liquid body which, under the temperature existing in the vessel, has an appreciable partial pressure. This liquid is preferably inert to .the chlorine, to the methane, and to the products of the chlorination reaction.

' Such a liquid is conveniently carbon tetrachloride, which is produced during the reaction. Also, the liquid is preferably transparent so that it becomes strongly irradiated. I have shown the liquid level as only extending part way up in the vessel. This is to the end that a vapor phase be provided in which the unreacted chlorine and methane or the partially chlorinated methane and the chlorine can react further. Ordinarily the vapor space is so adjusted relative to the length of the bubble path through the inert liquid that the retention time in the vapor space is several hundred times as long as that time required for a bubble of chlorine and methane to traverse the bubble path. Thus, in one successful apparatus, approximately half a second was required for the chlorine and methane bubbles to rise past the light through the liquid. -The retention time in the vapor space was regulated so that the vapor volume was replaced every 15 or 20 minutes. The unreacted materials in the vapor space thus have, theoretically at least, 1800 times as long to react in the vapor space as they have while present as bubbles in the liquid.

The body of carbon tetrachloride in the vessel 9 can be maintained at a high temperature, and I have successfully used temperatures varying between 30 C. and C. and a vapor temperature of 150 C. and up to 175 C. at atmospheric pressure. The temperature does not appear to have a great affect as such upon the reaction. However, I prefer operation at a relatively elevated temperature, one approaching the boiling mint of the carbon tetrachloride, because this ensures that the partial pressure of the carbon tetrachloride in the vapor space is relatively great, and that the other constituents, chloroform, dichlormethane, and methyl chloride mainly boil on while carbon tetrachloride condenses so that the partial pressure of the carbon tetrachloride in the vapor space is relatively high.

By increasing the pressure, the liquid body temperature can be increased until the operating temperature approaches that at which thermal chlorination occurs. I

I have found that the partial pressure of the third component present should preferably be at lence that carbon decomposition occurred and one of the sight glasses in the vessel was blown out. When the temperature was raised to 30 C. the reaction proceeded smoothly and continuously.

, The products vaporized from the vessel 9. pass oii through line i8 into the condenser ID. This condenser is maintained at such a temperature that it liquiiles substantially all of the vaporized products except hydrochloric acid which is permitted to pass ofi through line 2!. The liquified products are separated in liquid-gas separator 62, the liquid being run through line 82 into rectifier t3. Gaseous chlorine and partially chlorinated methanes are taken on? by line 68 for fractionation while carbon tetrachloride is removed through line 86 to be returned to the tank 9 or run to storage. The liquified products in tank a are drawn off through line 23 into a still 2 to be refined and fractionated.

The liquid in vessel a is preferably carbon tetrachloride. Since carbon tetrachloride accumulates in the vessel, it is the most convenient liquid to use as the liquid body in which to release the methane and chlorine. Any other inert material can be employed, as will presently appear.

It is to be noted that the header ti is placed very close to the light well, in fact as close as possible. In have found that if the material to be chlorinated is released in a zone where the light is of relatively low intensity it should pass through a zone where the light is intense. I have discovered that the products to be chIorinated are best initially exposed and released in a region where the intensity of the light is relatively high, and preferably at a maximum. In using, for example, lamps of the 400 watt G. E. H#1 lamps of high intensity having Pyrex glass bulbs, I have found that the header ring is best not over 2 inches below the lowest point of the pencil of light of the lamp. If the gas mixture is released below the intense irradiation region, it should pass through such a region.

It is preferred that the temperature in tank 9 be kept relatively high, because it has been my observation that the chlorination which is going on in the tank can be considered as occurring in three difierent ways. First, the gas phase reaction evidenced by chlorination of the methane in the bubbles released from the header ring. Sec- 0nd, a liquid phase chlorination reaction of partially chlorinated material which occurs throughout the liquid. Chlorine dissolves in carbon tetrachloride to a considerable extent, in fact, to

anextent sumcient to provide a very high concentration thereof compared to its concentration in the entering gas stream. This high concentration ensures that the dissolved chlorine more readily reacts with dissolved methane or partially chlorinated products.

Partially chlorinated materials are contained in and constitute largely the reflux return through line 22. Third, the chlorination of the methane which has become dissolved in the inert liquid in the vessel 9. Once chlorination of the methane has commenced, it is thereafter relatively easy to chlorinate. The liquid body temperature is kept relatively high, of the order of 50 C. or higher. As aforesaid, cooling means can be provided if under specific operating conditions this is found necessary.

In Figure 2 I have shown another piece of equipment in which the header 2 is provided with jets ll, downwardly directed. These jets are so arranged that gas released impinges directly upon the surface of the liquid body 52 maintained in the vessel and becomes substantially thoroughly saturated with carbon tetrachloride. By having the gas impinge directly upon the surface of the liquid with force," adequate mixing of the gas and the liquid is secured whereby each gas bubble, as it rises past the light, is intimately saturated with carbon tetrachloride vapor so that the chlorination reaction is buflered.

It is possible to operate the apparatus by mixing the incoming gases with vaporized inert material as carbon tetrachloride, and in Figure 3 I have shown the line H as including a supplementary carbon tetrachloride feed line 12. The vaporized carbon tetrachloride is fed in with the chlorine and methane to ensure that this mixtill ture is diluted suitably. In place of carbon tetrachloride, hexachlorethane, octachlorpropane, the vapor of other chlorinated hydrocarbons substantially inert to the chlorine and other reactants present, can be employed, and even though the hydrocarbons are not completely chlorinated. Hydrogen chloride can also provide part of the inert material partial pressure. The limiting factor is the ratio of the chlorine present to other reactive materials and to the inert or suppressing material.

If instead of feeding methane alone as the hydrocarbon one employs a natural gas or a hydrocarbon mixture containing the hydrocarbons up to those with nine carbon atoms, the process operates even more smoothly if anything. This is because under the conditions required for chlorination of the lower members of the series the higher number carbon atom hydrocarbons chlorinate readily. For example, employing a natural gas containing methane and ethane, the latter only to the extent of 3%, hexachiorethane is produced. This material has a lower vapor pressure, for a given temperature, than carbon tetrachloride. Consequently for a given partial pressure of the inert components in the vapor phase, the temperature of operation can be increased, until it closely approximates, in both the liquid and in the vapor space, that temperature at which, unde the pressure of operation, methanes chlorinate thermally. This simplifies heat extraction from the operation. Further, hexachlorethane, being a larger molecule, apparently is more effective as a suppressor for the too active methane chlorination reaction. The effect of propane, butane,'pen- 'tane, hexane, heptane and octane is similar, their l. A chlorination process comprising reacting gaseous chlorine and a hydrocarbon mixture containing at least two difierent hydrocarbons each having less than seven carbon atoms under the influence of light effectively promoting the reaction while bubbling said chlorine and said mixture up through an irradiated liquid body of liquified products of said reaction.

2. A chlorination process comprising bubbling gaseous chlorine, methane and ethane through a clear body of a substantially inert liquid while irradiating said body with light effectively promoting substitution chlorination of said methane and said ethane to form chlorinated methanes and hexachlorethanes while maintaining a temperature below the boiling point of at least one of the chlorinated methanes and hexachlorwith said liquid and into said vapor space to the promoting effect of light to effect substitution chlorination of each of said hydrocarbons, and produce chlorinated hydrocarbons, and maintaining a temperature below the boiling point of at least some of said chlorinated hydrocarbons V to condense at least some of said chlorinated hydrocarbons and provide said liquid body.

4. A chlorination process comprising releasing gaseous chlorine and a hydrocarbon mixture containing at least methane and ethane, to pass into contact first with a liquid'body substantially inert to the chlorine and second into a vapor space, subjecting that gaseous chlorine and hydrocarbon mixture released into contact with said liquid and into said vapor space to the promoting effect of light to effect substitution chlorination of each of said hydrocarbons and produce chlorinated hydrocarbons, and maintaining a temperature below the boiling point of at'least some of said chlorinated hydrocarbons to condense at least some of said chlorinated hydrocarbons and provide said liquid body.

5. A chlorination process comprising bubbling gaseous chlorine and a hydrocarbon mixture containing atleast two different hydrocarbons, each hydrocarbon having less than seven carbon atoms, through a liquid body acting as a substantial solvent for the chlorine while substantially inert to the chlorine and then into a vapor space, subjecting that gaseous chlorine and hydrocarbon mixture released into contact with said liquid and into said' vapor space to the promoting effect of light to effect substitution chlorination of each of said hydrocarbons and produce chlorinated hydrocarbons, and maintaining a temperature below the boiling point of at least some of said chlorinated hydrocarbons to condense at least some of said chlorinated hydrocarbons and provide said liquid body.

6. A chlorination process comprising bubbling gaseous chlorine and a hydrocarbon mixture containing at least methane and ethane through a liquid body acting as a substantial solvent for the chlorine while substantially inert to the chlorine and then into a vapor space, subjecting that gaseous chlorine and hydrocarbon mixture released into contact with said liquid and into said vapor space to the promoting effect of light to effect substitution chlorination of each of said hydrocarbons and produce chlorinated hydrocarbons, and maintaining a temperature below the boiling point of at least some of said chlorinated hydrocarbons to condense at least some of said chlorinated hydrocarbons and provide said liquid body.

7. A chlorination process comprising releasing gaseous chlorine and a hydrocarbon mixture containing at least methane and ethane and in which the methane-chlorine ratio is at least in the volume ratio of one to one, to pass into contact first with a liquid body substantially inert to the chlorine and second into a vapor space, subjecting that gaseous chlorine and hydrocarbon mixture released into contact with said liquid and into said vapor space to the promoting effect of light to effect substitution chlorination of each some of said chlorinated hydrocarbons and of said hydrocarbons and produce chlorinated hydrocarbons, and maintaining a temperature below the boiling point of at least some of said chlorinated hydrocarbons to condense at least provide said liquid body.

8. A chlorination process comprising bubbling gaseous chlorine and a hydrocarbon mixture containing at least methane and ethane and in which the methane-chlorine ratio is at least in the volume ratio of one to one, through a liquid body acting as a substantial solvent for the chlorine while substantially inert to the chlorine and then into a vapor space, subjecting that gaseous chlorine and hydrocarbon mixture released into contact with said liquid and into said vapor space to the promoting eilect of light to efiect substitution chlorination of each of said hydrocarbons and produce chlorinated hydrocarbons, and maintaining a temperature below the boiling point of at least some of said chlorinated hydrocarbons to condense at least some of said chlorinated hydrocarbons and provide said liquid body.,

9. A chlorination process comprising reacting chlorine and a hydrocarbon with less than seven carbon atoms in the gas phase in which the chlorine to hydrocarbon ratio is at least one to one by volume, while subjecting the chlorine and hydrocarbon to the promoting activity of light, and maintaining in said vapor phase components providing a partial pressure at least equal to one fourth of the'total pressure on said vapor phase at the temperature of operation, said components being products of the reaction substantially inert to the chlorine, to the hydrocarbon, and to any substitution product of the hydrocarbon.

10. A chlorination process comprising reacting chlorine and the hydrocarbon methane in the-gas phase in which the chlorine to hydrocarbon ratio is .at least one to one by volume, while subjecting the chlorine and hydrocarbon to the promoting activity of light, and maintaining in said vapor phase carbon tetrachloride suilicient to provide a partial pressure at least equal to one fourth of the total pressure on said vapor phase at the temperature of operation.

11. A chlorination process comprising reacting chlorine and a mixture of hydrocarbons with less than four carbon atoms in the gas phase in which the chlorine to hydrocarbon ratio is at least one to one by volume, while subjecting the chlorine and hydrocarbon to the promoting activity of light, and maintaining in said vapor phase suflicient products of the reaction substantially inert to chlorine'in said vapor phase to provide a partial pressure at least equal to one fourth of the total pressure on said vapor phase at the temperature of operation.

12. A chlorination process comprising reacting chlorine in the gas phase with a hydrocarbon of less than seven carbon atoms while promoting the reaction with light to produce some partially chlorinated hydrocarbon and some totally chlorinated hydrocarbon, the chlorine to reactive hydrocarbon ratio being such that at the temperature in said gas phase said hydrocarbon has a tendency to decompose rapidly to carbon, and

maintaining in said gas phase suilicient of said partially chlorinated hydrocarbon to suppress 'said'hydrocarbon decomposition substantially entirely. V

13. A chlorination process comprising reacting tained substantially free of any chlorine in the gas phase with a mixture of hydrocarbons of less than three carbon atoms while promoting the reaction with light to produce some partially chlorinated hydrocarbon and some totally chlorinated hydrocarbon, thechlorine to reactive hydrocarbon ratio being such that at the temperature in said gas phase said hydrocarbon has a tendency to decompose at a rapid rate to carbon, and maintaining in said gas phase suflicient of said partially chlorinated hydrocarbon to suppress said hydrocarbon decomposition substantially entirely.

14.. A chlorination process comprising reacting chlorine in the gas phase with a mixture of hydrocarbons of less than three carbonatoms while promoting the reaction with light, the chlorine to reactive hydrocarbon ratio being such that at the temperaure in said gas phase said hydrocarbon decomposes to carbon, and maintaining in said gas phase suflicient carbon tetrachloride and hexachlorethane to suppress said hydrocarbon decomposition.

15. A chlorination process for a" mixture of hydrocarbons of three and less carbon atoms comprising releasing a gaseous mixture of chlorine and said hydrocarbons into contact with a body of chlorinated hydrocarbons derived from said process while subjecting said body and a vapor phase above it to light to promote said reaction, said mixture passing from contact with said body into said vapor phase, which phase is substantially in equilibrium with said body.

16. A process for chlorinating methane comprising bubbling chlorine and methane in intimate contact through a maintained body of an irradiated liquid substantially inert to chlorine, said body being at a temperature of about 60 0.

1'7. A process for production of chlorinated methanes from methane and chlorine comprising releasing a premixed stream of chlorine and methane under the surface of a body of liquid carbon tetrachloride, said stream being mainirradiation prior to said release, and irradiating said liquid body intensely at the point of release.

18. A process for production of chlorinated methanes from methane and chlorine comprising releasing a premixed stream of chlorine and methane under the surface of a substantially clear inert body of a liquid having an appreciable partial vapor pressure at the temperature exist ing in the body, said stream being maintained substantially free of any irradiation prior to said ly at the point of release.

19. A process for production of chlorinated methanes from methane and chlorine comprising releasing chlorine and methane into a substantially clear inert body of a liquid having an .appreciable partial vapor pressure at the temperature existing in the body, irradiating intensely the point of release of said methane and chlorine, bubbling the chlorine-methane through said body while irradiating the entire liquid body, and further irradiating said chlorine-methane upon release into a vapor space above said body wherein the retention time is several hundred times the time chlorine-methane bubbles spend in rising through the liquid body.

20. A process for production of chlorinated methanes from methane and chlorine comprising preforming in the dark a chlorine-methane mix, releasing said chlorine-methane mix into a substantially clear inert body of a liquid'hav ing an appreciable partial vapor pressure at the aaoaass temperature existing inthe body, irradiating intensely the point of release of said methane and chlorine, bubbling the chlorine-methane through said body while irradiating the entire liquid body, and further irradiating said chlorine-methane upon release into a vapor space above said body wherein the retention time is several hundred times the time chlorine-methane bubbles spend in rising through the liquid body.

21. A process for production of chlorinated hydrocarbons from saturated aliphatic hydrocarbons having less than seven carbon atoms, said process comprising releasing chlorine and said hydrocarbon into a substantially clear and inert liquid body, irradiating intensely the point of release of said hydrocarbon and chlorine, bubbling the chlorine-hydrocarbon through said body while irradiating the entire liquid body, and further irradiating said chlorine-hydrocarbon upon release into a vapor space above said body wherein the retention time is several hundred times the time chlorine-hydrocarbon bubbles spend in rising through the liquid body.

22. A process for chlorinating methane comprising photochemically catalyzing a chlorinemethane mixture to induce and effect vapor phase reaction in said mixture under substantially anhydrous conditions and in the presence of liquid and gaseous carbon tetrachloride at a temperature of about 60 C.

23. 'Chlorinating in the vapor phase at a temperature of about C. a saturated aliphatic hydrocarbon of less than seven carbon atoms with chlorine while strongly irradiating said hydrocarbon and chlorine to catalyze reaction thereof while maintaining in said vapor phase such a partial pressure of a material inert to chlorine, to said hydrocarbon and to products of the chlorination, that destructive chlorination of said hydrocarbon to form carbon does not occur.

24. A process for the production of a chlorinated aliphatic hydrocarbon from a saturated aliphatic hydrocarbon having less than seven carbon atoms comprising releasing'chlorine and said hydrocarbon in gaseous form into intimate contact to form a gaseous mixture thereof, passing the gaseous mixture into contact with a maintained body containing products of the chlorination of said hydrocarbon to saturate substantially said gaseous mixture with vapor from said body and bring said gaseous mixture sub 5 stantially into equilibrium with said body. and subjecting the substantially saturated gaseous mixture to light adapted to promote reaction of said hydrocarbon and the chlorine.

25. A process for methane chlorination comprising releasing a methane chlorine mixture into contact with a maintained liquid body composed mainly of carbon tetrachloride to saturate substantially said mixture, and subjecting the substantially saturated mixture to light adapted to promote the reaction of said methane and chlorine to eflect reaction thereof.

26. A process for methane chlorination comprising ejecting a methane chlorine mixture into contact with a surface of a maintained liquid go body composedmainly of carbon tetrachloride to saturate substantially said mixture, and subjecting the substantially saturated mixture to light adapted to promote the reaction of said methane and chlorine to efi'ect reaction thereof.

2'7. A process for effecting methane chlorination comprising substantially saturating a mixture of chlorine and methane with carbon tetrachloride and subjecting the substantially saturated mixture to light adapted to promote o reaction of the methane and the chlorine.

28. A process for eflecting methane chlorination comprising substantially saturating a mixture of chlorine and methane with gaseous carbon tetrachloride and subjecting the substantially saturated gaseous mixture to light adapted to promote reaction of the methane and the chlorine.

29. A process for methane chlorination comprising passing a methane chlorine mixture into contact with a maintained liquid body composed mainly of carbon tetrachloride and subjecting the liquid body and said mixture to light promoting the reaction of said methane and chlorine to eflect reaction thereof.

HARRY BENDEB.

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