US2589689A - Photochemical chlorination process - Google Patents

Description

March 18, 1952 J. GOVERNALE ETAL 2,589,689

PHOTOCHEMICAL CHLORINATION PROCESS Filed Nov. 12, 1949 2 SHEETSSHEET 1 INVENTORS LUKE J. GOVERNALE JAMES H. HUGUET BY CLARENCE M. NEHER M1ilrch 1952 L. J. GOVERNALE ETAL 2,589,689

PHOTOCHEMICAL CHLORINATION PROCESS Filed NOV. 12. 1949 2 SHEETSSHEET 2 HQ 2 INVENTORS LUKE J. GOVERNALE 7 JAMES H. HUGUET BY CLARENCE M. NEHER Patented Mar. 18, 1952 PHOTOCHEMICAL CHLORINATION PROCESS Luke J. Governale, James H. Huguet, and Glarence M. Neher, Baton Rouge, La., assignors to .Ethyl Corporation, New York, N. Y., a. corporation of Delaware Application November 12, 1949, Serial N 0. 126,902

3 Claims.

This invention relates to the photochemical chlorination of hydrocarbons. More particularly, the invention relates to the manufacture of alkyl chlorides, especially ethyl chloride, by the photochemical chlorination of alkane hydrocarbons.

The direct substitution chlorination of alkane hydrocarbons has been recognized as a possible method of economically producing compounds such as isopropyl chloride and ethyl chloride. However, the substitution chlorination reaction has not found extensive use in commercial operations because of various practical difficulties. For example, in carrying out a substitution chlorination by the action of heat, frequent trouble is encountered because of the tendency of the reactants to carbonize or burn, yielding only carbon and hydrogen chloride. The use of actinic light to initiate and maintain a substitution chlorination has been frequently suggested. However, in previous methods of conducting a photochemical chlorination, unpredictable operating diificulties are frequently encountered. An outstanding dimculty has been the tendency of commercial reactions to foul the light transmitting surfaces of either the actinic light source or of the reacting vessels. This fouling results in the reduction of the light actually introduced to the reaction zone, so that frequent shut-downs for cleansing are required. The impurities responsibe for these dimculties are, for example, ferric chloride in the chlorine stream and hydrocarbons of relatively high molecular weight in the gaseous hydrocarbon feed stream. It is thought that the higher molecular weight hydrocarbon impurities are themselves chlorinated to give a tarry material which deposits on the light transmissive surfaces. Ferric chloride impurity, combined with tarry film, results in a dark coating which is responsible for the difficulty and interruptions to operation already described. A further disadvantage and limitation of prior attempts to utilize a photochemically initiated chlorination of gaseous hydrocarbons has been the usual necessity of removing through the reactor walls the large amount of heat generated by the reaction. Since reactor walls have frequently been constructed of light transmissive material of low thermal conductivity, the usual consequence of the heat removal requirement has been that small tubes of relatively limited capacity have been employed.

Theobject of our invention is to provide a new continuous process for the photochemical chlorination of ethane. A further object is to provide a reaction method capable of adoption to practically any quantity of feed materials without a multiplicity of reaction units. Another object is to provide greatly increased utilization of actinic light. A still further object is to provide a process which is not limited by the necessity of removing the heat generated by the reaction.

These objects are attained by our process which comprises premixing chlorine and ethane in the dark and thereafter photochemically reacting in the presence of hydrochloric acid fully dispersed throughout the reacting gases. By hydrochloric acid we mean the aqueous solution of hydrogen chloride. The term fully dispersed means that the hydrochloric acid is dispersed as discrete particles or droplets uniformly distributed across the transverse area of a reaction zone, but the term does not include a mist or a fog. The reacting gases are maintained entirely within a zone of effective radiation from the actinic light sources.

Our process can be continuously operated without interruption which would otherwise be encountered owing to the fouling reaction already described which normally arises because of impurities in the feed materials. The process is capable of embodiment in unitary form according to the quantities to be processed. The eifectiveness of the actinic light utilized is increased by our process by a factor as great as 25 fold. A further result of our process is that the operation of any specific embodiment is not limited by heat transfer requirements as in some previous methods.

The process is more easily understood by reference to the accompanying figures. Figure 1 illustrates a simple embodiment characterized by dispersion of the hydrochloric acid by means solely of the kinetic energy of a jet of the mixed feed gases. Figure 2 is a sectional view of apparatus for an additional embodiment characterized by a multiplicity of light sources and by a dual dispersion of hydrochloric acid. Figure 3 is a transverse sectional view of the apparatus of Figures 2 on plane 33.

Referring to Figure 1, a reaction chamber I I consists of a tube of heat resistant borosilicate glass. Chlorine is supplied by line 13 and line I2 denotes the ethane feed line. The two feed streams are combined and mixed in line I i leading directly into the reactor II. The actual introduction of the premixed feeds is through jet I5. A supply of aqueous hydrochloric acid l6is maintained in the reactor at a depth sufficient 'tinic light, predominating chlorination reaction, as well as some entrained hydrochloric acid. Liquid hydrochloric acid is returned by line 26 to the supply 15 at the bottom of the reactor. Non-condensed products of the reaction are discharged by line 22 from the water-cooled condenser I9 and flow to subsequent condensers for liquificaticn and recovery. Ac-

in light of 3600 Angstrom units wave length, is supplied to the reacting gases by a fluorescent tubular light 2 I.

In an operation of the embodiment illustrated by Figure 1, gaseous chlorine was fed through line 13 at the rate of 12.1 grams per minute. Ethane gas was fed at the rate of 5.87, grams per minute through line l2. The mole or volume proportions of'the mixed feed in line 14 was then 0.8? part of chlorine by volume per one of ethane. Sufficient hydrochloric acid i6 was added, before start of operation to form a liquid level of one-eighth to one-fourth inch above the outlet of the feed jet 15. During operation, of course, the liquidwas continuously blown upwardly by the-jet action of the feed gases and no precise liquid level was observable.

The superficial velocity of the mixed feed gases in'the reactor was approximately 0.2 foot per'secnd, the .gases being exposed to the action of the actinic light 2! for a total period of approximately '20 seconds. The chlorine was completely reacted and converted to chloroethanes and hydro-,

gen chloride. In one hour of operation, approxi- 'mately 548 grams of chloroethanes were recovered, containing 7 percent by weight ethyl chloride and percent by weight of dichloroethanes. Approximately 55 percent of the ethane fed was recovered as ethyl chloride. 'servable fouling of the walls of the reactor during the reaction. The chlorine fed was completely reacted at the start and throughout the operation.

The use of the dispersed hydrochloric acid accordingto our invention has been found particularly beneficial in insuring that the best yields obtainable are obtained. The benefits of the dispersed liquid hydrochloric acid were amply demonstrated in an attempt to carry out the chlorination reaction in the same reactor as used in the above embodiment, but without the dispersed hydrochloric acid phase present. Chlorine and ethane were premixed and fed at the same rate and proportions as in the foregoing example. It was found, however, that only percent of the ethane fed was converted to ethyl chloride. In contrast, it will be noted in the example already given that by our process, percent of the'ethane was converted to ethyl chloride. In other words, carrying out the photochemical chlorination by our process results in 25 percent more ethyl chlo ride being produced from the same amount of feeds.

The foregoing example should be considered as merely illustrative of a typical embodiment wherein the hydrochloric acid liquid is dispersed solely by the kinetic energy of the feed gases. This mode of operation is entirely satisfactory,

providing that the hydrochloric acid is uniform- There was no obly and fully dispersed throughout the reaction zone. The acid must, of course, be maintained in suificient quantity to always supply liquid available for dispersion by the jet of feed gases. If the quantity of acid is inadvertently diminished below this required level, the reaction temperature will greatly increase with possible damage to the reaction tube and with pyrolysis of the chloroethane products. This contingency can be safeguarded against by provision of dual and independent sources of dispersed hydrochloric acid. This mode of operation is illustrated with reference to Figures 2 and 3. A specific advantage of the process is also illustrated in connection with Figures 2 and 3, that is, that the process is not limited to operation in specific apparatus because of the heat transfer duty. In prior photochemical gas-phase reactions, the apparatus was limited in size owing to the necessity of transferring, primarily through the reactor walls, the heat released by the reaction. The present process is not subject to this limitation.

Referring to Figure 2, the reactor body 3| is a steel shell lined with suitable acid resistant material. Chlorine and ethane containing gases are fed through lines 32 and 33 respectively. These feed gases are mixed in pipe 34 and are disjets. The liquid level can be observed by means of sight glass 44. The premixed gases are discharged at a velocity sufficient to create a strong upward spray 45 of the hydrochloric acid. The level of acid and the velocity of inlet gases can be varied as necessary to provide a fully dispersed, fine spray. As an example of suitable conditions, a liquid level of from 2 to 6 inches above the jets and a gas velocity of 200 to 400 feet per second is highly eflicient in forming a uniformly distributed spray. The gases pass upwardly through the reaction zone and are fully irradiated by light emanating from fluorescent lights 46, 41, 48 and 49. The lights are suspended in wells 58, 5|, 52, 53 formed of a suitable actinic light transmissive heat resistant glass.

In addition to the upward spray 45 induced by the jet action of the feed gas streams, a downward shower or spray 54 of hydrochloric acid is supplied through spray nozzles 55, 55, 51, 58. This second spray insures that a dispersed liquid phase will be present throughout the reaction zone. Various methods can be used to form the spray 54. The preferred method is to use spray nozzles as shown. These spray nozzles necessarily are the type which produce a solid cone, that is, where the spray is substantially uniform throughout the sprayed volume. If a reactor of square or rectangular cross section is used, nozzles of the type shown in U. S. Patent 2,305,210 are particularly suitable. It is not essential, however, that spray nozzles be used. If desired, the downward spray 54 can be formed by utilizing a perforated distributor plate. In this case, the holes or perforations should be e to 3% inch in diameter. Whichever method of forming the spray 54 is utilized, the primary requirement is that it be substantially uniformly distributed throughout the reaction volume, and that the spray should not be so fine as to resemble a for; or mist.

The reacting gases flow upwardly and are continually in contact with the dispersed liquid hydrochloric acid. The reacted products are discharged from the reactor through nozzle 59 and flow through line 66 to an absorber 67, wherein hydrogen chloride is absorbed by awter, introduced through line 69. The hydrochloric acid solution thus formed is discharged from the absorber 61 by line 10. The rest of the product gases then pass through line 68 to a condenser H wherein the chlorinated hydrocarbons are liquified. The partially liquid mixture leaving the condenser H is passed to a separatory drum 72 through line 13. The liquified products are discharged from the separator 12 through line M to storage or use. Noncondensed gases, comprising unused ethane and inert diluent gases, are discharged through line 15 for disposal.

The heat produced by the reaction is absorbed practically instantaneously by the dispersed hydrochloric acid. The heat results in an increase in the sensible heat of the hydrochloric acid and some vaporization of the acid. Sensible heat is removed by circulation of the acid from the reactor through line 60 and by pump 6| to a cooler 62. The cooled acid is recycled by the supply line 63 to the spray heads for the downward spray 54, or to the main supply 43.

The heat removed by vaporization of hydrochloric acid is removed in the absorption of acid in absorber 51. The reduction in the amount of acid circulating is compensated by make-up water introduced through line 64.

Figure 3 is a transverse sectional view at 3-3 of the reactor shown by Figure 2. This sectional view shows a typical disposition of light sources within a reactor of circular cross section, to provide full irradiation throughout the reaction volume. The light sources 46, 4?, 48, 49 are positioned radially on the same circle as the feed gas jets 35, 36, 31, 38. The sprays of hydrochloric acid, both upward 45 and downward 54, are angularly positioned between the light sources. It will be noted that the position of the light sources and the dimensions of the reactor are such that the full cross section of the reaction space is included or covered by the zones of effective radiation from the light sources, as indicated by lines 65, 61, 68, 69 denoting the zone boundaries.

By zone of effective radiation, we mean the space adjacent to a source of actinic light wherein the chlorination occurs as rapidly in the presence of the dispersed hydrochloric acid phase as in the purely gas phase. We have found that the dispersed hydrochloric acid used in the process has surprisingly little adverse effect on the effectiveness of actinic light. Even when the maximum amount of hydrochloric acid is used. sufiicient to absorb most of the reaction heat by sensible heat increase alone, the zone of effective radiation is much greater than in prior methods. For example, in a, prior method wherein the reacting gases are dispersed within a continuous phase of liquid, we have found that the zone of effective radiation did not extend more than three inches from the actinic light source. In contrast, with the same actinic light source, our process provides an effective zone extending approximately 12 inches from the light source. The efficiency of the actinic light was thus increased 16 fold, corresponding to the increase in volume of the reaction zone.

In a specific embodiment, as illustrated by Fi ures 2 and 3, chlorine was fed to the reactor 3| through line 32 at the rate of 1760 pounds per hour. A commercial ethane stream, containing 82 volume percent ethane, was fed to the reactor through line 33 at a rate supplying 709 pounds of ethane per hour. The feed streams, mixing in line 34, were then forced into the reaction space through jets 35, 36, 31, 38 and 39 at a velocity of approximately 300 feet per second. The velocity of the reacting gases in the reactor was substantially lower, being only about 0.9 foot per second.

The reacting gases reacted smoothly and completely in their passage up the reactor, prior to discharge through line 66. The chlorinated ethane product stream removed from the process by line 14 mounted to 1353 pounds per hour, including 760 pounds of ethyl chloride. Substantially all the chlorine fed was reacted, 96 percent of the chlorine feed being recovered as hydrogen chloride or chloroethanes. No observable fouling was noted during an extended period of operation. The reaction temperature was uniformly maintained at 150 F. throughout the reactor owing to the efficient heat removal by the dual sprays of hydrochloric acid.

- The preferred source of actinic light for the process are fluorescent lights which emit light predominating in light of 3600 angstrom units wave length. A particular light source available utilizes approximately 10 watts per foot of length. Other light sources can be utilized, although it will be found that the zone of effective radiation is diminished. Suitable alternative light sources are the common tungsten filament lights and infra-red lamps. We have found, however, that a greater power input is required for the latter sources to be reasonably effective.

The process is not restricted to a specific volumetric ratio of the chlorine and ethane fed. If the volumetric ratio of chlorine: ethane is too large, it has been found that a smaller percentage of the chlorine will be reacted, if the chlorine feed rate is unchanged. Thus, if the chlorine fed is completely reacted at a volume ratio of 0.5:1.0 part chlorine ethane, the chlorine conversion will decrease to about percent at a ratio of 3.0110. A high conversion can be obtained even in such instances by reducing the total feed rate while maintaining the feed ratio constant. When ethyl chloride is the desired product, the highest conversion will be obtained in the chlorine ethane volume ratio of 0.8:l.0 to 1.2:1.0.

The chlorination reaction proceeds at a surprisingly rapid rate, the actual rate being affected by the concentration of the chlorine. It has been found that, at the feed ratios preferred for ethyl chloride production (0.8:1.0-to 1.2:l.0) percent or more of the chlorine is reacted within one second. Further reaction of the residual chlorine requires appreciably longer. A reaction time of six seconds or more is required for conversion of 98 percent or more of the chlorine.

A further significant advantage of the process is that it is capable of continuous operation without shutdowns due to fouling of the light transmitting surfaces. For example, we have operated an embodiment of the process for a period of about 30 hours. At the termination of operation, the reactor was carefully inspected and there was no detectable fouling of the light transmittal surface. In contrast, in a gas phase chlorination, in the absence of a liquid phase, numerous instances have been noted in which fouling occurred within a period of one hour or less. Our process is capable of operation almost indefinitely because of the cleaning action of the hydrochloric acid spray.

It should be noted that the process achieves a separation of the heat dissipating and the light transmitting elements of the reactor. On the other hand, in former tubular reactors, the re actor Wall is in the main heat transmitting surface available for dissipation of heat generated by the reaction. As a result, high reactant temperatures were developed except at points immediately adjacent the reactor walls. Such processes were therefore limited in application by the limitation on reactor size. In the present process, the heat is uniformly removed throughout the body of reacting gases by the uniformly dispersed hydrochloric acid droplets. A uniform temperature distribution across the reaction volume is achieved, so that the process is not limited to a specific size embodiment. Our process can be carried out on virtually any scale required. It is necessary only that provision be made for uniform dispersion of the hydrochloric acid in the reactant gases and for location of light sources so that the reacting gases are all within the zone of effective radiation.

As an illustration of the benefits of this separation of the light and heat transmitting functions, in one reactor (as illustrated in Figures 2 and 3), we have reacted as much chlorine and ethane as formerly required 52 individual reaction tubes.

The absolute quantity of hydrochloric acid used is not critical. In general, in embodiments utilizing an external acid cooler (as in Figure 2), it will be found preferable to circulate suflicient hydrochloric acid to allow removal of approximately '70 or 80 percent of the reaction heat by sensible heat increase. A preferred circulation rate is l to 5 gallons of hydrochloric acid ,per pound of chlorine fed.

In general, it has been found that variation in temperature and pressure do not have a great effect on the completeness or efficiency of reaction. These variables will have an effect principally on the specific reactor volume required for a given capacity, and upon the concentration of the hydrochloric acid.

The operating temperature will be controlled by the quantity of hydrochloric acid circulated. At high circulation rates, for example, the temperature will be lowered and the concentration of the hydrochloric acid will be increased. The usual operating temperature is from 200 F. to 150 F. These temperatures correspond to hydrochloric acid concentrations of about 20 to 30 percent by weight, respectively.

An increase in pressure of operation results in an increase in the strength acid circulated. It is preferred to operate at pressures slightly above atmospheric sufficient to overcome normal flow resistances in subsequent lines and equipment. The usual range of operating pressure is from 5 to pounds per square inch Numerous modifications are, of course, possible of the hydrochloric in the process to adapt it to specific situations. For example, it is possible to produce hydrochloric acid solution within the reactor, instead of by subsequent absorption from the reactor products. If this is desired, hydrochloric acid is continuously withdrawn and suflicient make-up water is added. Another variation which is desirable in some instances is based upon complete removal of reaction heat by vaporization, without any cooling of the hydrochloric acid. If this method is employed, a heat exchanger is not required for cooling circulating liquid acid. A disadvantage of removing all the heat by vaporization of the liquid phase is that the capacity of the reactor is diminished, owing to the dilution of the reacting gases.

Other modifications and embodiments of the invention are possible, within the scope of the process, which is limited only by the following claims.

We claim:

1. A process for chlorinating ethane comprising reacting chlorine and ethane in the gaseous phase under the influence of actinic light, discrete droplets of hydrochloric acid being distributed through the reaction zone in a sufficient amount to remove the heat of reaction but insufiicient to substantially shield the gaseous chlorine and ethane from the actinic light radiations.

2. A process for the gas phase chlorination of ethane comprising reacting from about 0.8 to about 1.2 parts of chlorine by volume premixed with one part of ethane under the influence of actinic light, discrete droplets of hydrochloric acid being distributed through the reaction zone in sufficient quantity to remove the heat of reaction. but insufficient to substantially shield the gaseous chlorine and ethane from the actinic light radiations, said droplets of hydrochloric acid being at least in part formed and distributed by feeding the chlorine and ethane through a body of hydrochloric acid.

3. A process for producing ethyl chloride comprising reacting chlorine and ethane in the gaseous phase under the influence of light predominantly of about 3600 angstrom units wave length, discrete droplets of hydrochloric acid being distributed through the reaction zone in a sufiicient amount to remove the heat of reaction but insufiicient to substantially shield the gaseous chlorine and ethane from the light radiations.

LUKE J. GOV ERNALE.

JAMES H. HUGUET.

CLARENCE M. NEHER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,393,509 Archibald et al. Jan. 22, 1946 2,499,129 Calfee et a1. Feb. 28, 1950

Claims (1)

1. A PROCESS FOR CHLORINATING ETHANE COMPRISING REACTING CHLORINE AND ETHANE IN THE GASEOUS PHASE UNDER THE INFLUENCE OF ACTINIC LIGHT, DISCRETE DROPLETS OF HYDROCHLORIC ACID BEING DISTRIBUTED THROUGH THE REACTION ZONE IN A SUFFICIENT AMOUNT TO REMOVE THE HEAT OF REACTION BUT IN SUFFICIENT TO SUBSTANTIALLY SHIELD THE GASEOUS CHLORINE AND EHTANE FROM THE ACTINIC LIGHT RADIATIONS.

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