US3598876A - Selective halogenation of hydrocarbons - Google Patents

Abstract

THE SELECTIVE MONO-HALOGENATION OF SATURATED HYDROCARBONS IS EFFECTED BY CHARGING A SATURATED HYDROCARBON AND A HALOGENATING AGENT TO A THERMAL DIFFUSION ZONE IN WHICH OPPOSING WALLS OF THE ZONE ARE MAINTAINED AT A TEMPERATURE DIFFERENTIAL FROM ABOUT 100* TO ABOUT 200*C. THE HYDROCARBON AND HALOGENATING AGENT WILL REACT THEREIN TO FORM MONO- AND POLY-HALOGENATED HYDROCARBONS. THE MONO-HALOGENATED HYDROCARBON WILL BE REMOVED FROM AN INTERMEDIATE POINT IN THE ZONE WHILE THE POLY-HALOGENATED HYDROCARBON WILL BE REMOVED FROM A LOWER PORTION OF THE ZONE.

Description

g- 10, 1971 H. s. BLOCH SELECTIVE HALOGENATION OF HYDROCARBONS Filed NOV. 13, 1967 United States Patent @flice 3,598,876 Patented Aug. 10, 1971 3,598,876 SELECTIVE HALOGENATION F HYDROCARBONS Herman S. Bloch, Skokie, 111., assignor to Universal Oil Products Company, Des Plaines, Ill. Continuation-impart of application Ser. No. 411,071, Nov. 13, 1964. This application Nov. 13, 1967, Ser. No. 684,595

Int. Cl. C07c 17/10 US. Cl. 260-660 Claims ABSTRACT OF THE DISCLOSURE The selective mono-halogenation of saturated hydrocarbons is effected by charging a saturated hydrocarbon and a halogenating agent to a thermal diffusion zone in which opposing walls of the zone are maintained at a temperature differential from about 100 to about 200 C. The hydrocarbon and halogenating agent will react therein to form monoand poly-halogenated hydrocarbons. The mono-halogenated hydrocarbon will be removed from an intermediate point in the zone while the poly-halogenated hydrocarbon will be removed from a lower portion of the zone.

This application is a continuation-in-part of my co-pending application Ser. No. 411,071, filed Nov. 13, 1964, now abandoned.

This invention relates to a process for the halogenation of hydrocarbons, and particularly to a process for the halogenation of parafiinic hydrocarbons. More specifically, the invention is concerned with a process for the selective mono-halogenation of paraffinic hydrocarbons.

In many chemical processes or reactions a particularly desirable starting material comprises a mono-halogenated hydrocarbon. A specific example of one of these processes is the preparation of detergents. Heretofore, detergents comprising long-chain alkylaromatic sulfonates have been prepared and used as such. However, many of these longchain alkyl substituents were highly branched in configuration. The increasing use of detergents of this type has resulted in contamination or pollution of many streams, rivers, lakes, etc., inasmuch as it has now been discovered that detergents of this type are non-biodegradable. In this respect the sight of streams, rivers, etc., containing large amounts of foam has become increasingly prevalent. This may result in a contamination of the water supply for many cities or towns which depend upon these rivers or streams as a source of water supply.

In order to combat this disadvantage, detergents which are prepared now and in the future must, of necessity, be biodegradable in nature. These biodegradable detergents must contain long-chain alkyl substituents which are straight-chain in configuration or which may contain a minimum amount of branching, said branching preferably comprising no more than methyl radicals. This straightchain configuration of the alkyl chain will permit the organisms which destroy the detergents to, in effect, eat their way up the chain thereby destroying the molecule and allowing the detergent to be assimilated in the water without the concurrent production of undesired and lasting foam or suds.

A particular source of relatively straight-chain alkyl radicals which may be utilized as a starting material for the preparation of biodegradable detergents comprises the normal aliphatic paraflinic hydrocarbons which are separated from isomeric mixtures of normal and branched chain paraffius by any means well known in the art, one particular means of separation being the use of molecular sieves. These long-chain aliphatic paraflinic hydrocarbons,

preferably ranging from about 9 to about 15 carbon atoms in length, will, after treatment thereof, be utilized as alkylating agents for benzene or toluene to prepare biodegradable detergents. This pretreatment of the aliphatic paraffinic hydrocarbon may, if so desired, be effected by halogenating the paraflins whereby an alkyl halide of desired configuration is produced. Another type of treatment is to partially oxidize the aliphatic paraflinic hydrocarbon to produce an alcohol, either the alcohol or halide then being utilized as the alkylating agent. It is preferable that the alkyl halide which is to be used as an alkylating agent contain only one halogen substituent so that the resulting alkylaromatic compound contain the aliphatic substituent in a straight chain. The position of the halogen radical in the chain is relatively immaterial, said halogen substituent being on either the 1-, 2- or 3-carbon atom or other carbon atoms in the chain. While the foregoing discussion is concerned mainly with the halogenation of a relatively longchain aliphatic paraflinic hydrocarbon, other types of hydrocarbons such as cycloparaffinic hydrocarbons and aromatic hydrocarbons which also may contain an alkyl sidechain are also subject to mono-halogenation according to the process of this invention.

Heretofore, the prior art has shown the chlorination of gaseous hydrocarbon such as methane while passing the reactants between walls which may be maintained at different temperatures. The gaseous hydrocarbon and chlorine are passed through the reactor upwardly from the bottom thereof and the entire reaction products are removed from the top portion of said reactor. However, merely maintaining the walls of the reactor at different temperatures is not sufficient in and of itself to provide a thermal diffusion separation zone. In contradistinction to this prior art, the present invention is concerned with a process for halogenating paraflinic hydrocarbons in a liquid phase and thereafter separating the mono-halogenated paraffins from the poly-halogenated hydrocarbon within the thermal diffusion zone, said halogenation and separation of the different products being effected in a single stage operation. One advantage of effecting the halogenation according to the process of the present invention includes a high selectivity toward the mono-halogenated product, as against the less desired poly-halogenated product, as well as the direct drawoff of the relatively pure product. When utilizing the process of the present invention it is preferred to charge the saturated hydrocarbon, and particularly a paraffinic hydrocarbon of the type hereinafter set forth in greater detail, and the halogenating :agent to the top of the thermal diffusion zone, and flow the reacting mixture downwardly therethrough while withdrawing the mono-halogenated product from an intermediate point and the undesired poly-halogenated product from a lower portion of the zone.

It is therefore an object of this invention to provide a process for the selective halogenation of saturated hydrocarbons.

A further object of this invention is to provide a process for the selective mono-halogenation of paraffinic hydrocarbons utilizing a thermal diffusion apparatus.

In a broad aspect, one embodiment of this invention resides in a process for halogenating a paraffiuic hydrocarbon containing from about 4 to about 20 carbon atoms which comprises introducing said hydrocarbon and a halogenating agent comprising chlorine or bromine into the upper portion of a thermal diffusion zone having opposing walls maintained at different temperatures, the hotter wall being at a temperature in the range of from about 50 C. to about 200 C. and the cooler wall being at a lower temperature in the range of from about 0 to about 50 C., the temperature differential between said hotter wall and said cooler wall being from about 50 C. to about 200 C., reacting said hydrocarbon and said halogenating agent while passing downwardly between said walls, thereby forming monoand poly-halogenated hydrocarbons, separating mono-halogenated hydrocar bons from poly-halogenated hydrocarbon within said thermal diffusion zone and withdrawing the former from an intermediate point in the height of said zone and withdrawing separated poly-halogenated hydrocarbons from the lower portion of said zone.

A specific embodiment of this invention is found in a process for the selective mono-bromination of dodecane which comprises introducing dodecane and bromine to the upper portion of a thermal diffusion zone having opposing walls maintained at different temperatures, the hotter wall being at a temperature in the range of from about 50 C. to about 200 C. and the cooler wall being at a temperature in the range of from about C. to about 30 C., reacting said dodecane and bromine while passing the mixture downwardly between said walls, thereby forming mono-bromododecane and poly-bromododecane, separating mono-bromododecane from polybromododecane within the thermal diffusion zone, withdrawing the mono-bromododecane from an intermediate point in the height of said zone, and thereafter withdrawing separated poly-bromododecane from the lower portion of said zone.

Other objects and embodiments will be found in the following further detailed description of the present invention.

As hereinbefore set forth the present invention is concerned with a process for the selective mono-halogenation of saturated hydrocarbons and particularly paraffinic hydrocarbons.

In the halogenation of hydrocarbons, and particularly in the preparation of sec-alkyl bromides from n-paraffins, some difficulty has been experienced in obtaining the selective mono-halogenation or mono-bromination and subsequently separating mono-brominated product from diand poly-brominated product, the difficulty being attributed to the thermal instability of the bromo compounds. The process of the present invention will overcome the difficulty by permitting high selectivity as well as a relatively easy separation of the various halogenated, and especially brominated, species without the decomposition of the halogenated products. In addition, the process of this invention will permit a ready separation of the various species even if the hydrocarbon feed consists of several homologs of such a boiling range that the highest boiling hydrocarbons overlap in boiling point the lowest boiling mono-halogenated products. As hereinbefore set forth, I now propose to halogenate, and specifically brominate, hydrocarbons such as n-parafiins of relatively long-chained configuration in a thermal diffusion apparatus. This apparatus, in one embodiment thereof, consists of a relatively narrow, annular space between two walls which are heat-conductive in nature and which are provided with means for maintaining heat differential or gradient between said walls. The annular space or slit widths between the closely spaced parallel walls are extremely narrow. The space or slit width may range in size from about 0.01 inch to about 0.25 inch, the opposed faces of the vertical, liquid-impervious walls being smooth and spaced substantially equidistantly from one another to form the aforementioned slit. The temperature controlling means whereby a heat differential may be maintained between the walls will comprise means for heating one wall, which will hereinafter be designated by the term hot wall and means for cooling the opposite wall, hereinafter referred to as the cool wall. The aforementioned heating and cooling means which are utilized in the apparatus required to effect the process of the present invention will comprise those which are well known in the art and may consist of electrical wires, tubes for hot gases, water pipes for either hot or cold water, or any other known heat transfer means. The thermal diffusion apparatus, which will hereinafter be described in greater detail, will also contain means such as ports, inlets, outlets, etc. communicating with the slit or annular space whereby the hydrocarbon feed and the halogenation agent may be charged to the apparatus as well as means for withdrawing the various halogenated products including the mono-halogenated hydrocarbon and the polyhalogenated hydrocarbon.

Due to the difference in boiling points and molecular weights, if a mixture of paraffinic hydrocarbons, monohaloparafl'ins and poly-haloparaffins is fed to a thermal diffusion unit, the mixture is readily separated into three layered products. The paraffins will be found in the upper portion of the unit, the mono-haloparaffins at an intermediate level, while the poly-haloparafiins are at the bottom thereof. Therefore, it is readily apparent that the halogenation, and particularly bromination, of hydrocarbons can be effected by feeding paraffinic hydrocarbons to the upper portion of a thermal diffusion unit, also feeding the halogenating agent to the upper portion, and subsequently withdrawing mono-halogenated paraffins from an intermediate level and the poly-haloparaffins from a lower level. By utilizing halogenating agents such as bromine and chlorine and controlling the rate of feed of the halogenating agent so that essentially all of it reacts in the top portion of the unit, while the halogenated paraffins travel downward, there results a minimum of poly-halogenation and a greater percentage of mono-halo products will be achieved thereby. This high selectivity of mono-halohydrocarbon formation will be especially advantageous when preparing long-chain alkyl monohalides for use as alkylating agents in the preparation of biodegradable detergents.

The present invention will be further illustrated with reference to the accompanying drawing which illustrates a simplified thermal diffusion unit which may be utilized to effect mono-halogenation of parafiinic hydrocarbons according to the process of the present invention. Various valves, condensers, pumps, controllers, etc. have been eliminated as not being essential to the complete understanding of the present invention. The utilization of these, as well as other similar appurtenances, will become obvious as the drawing is described.

Referring now to the drawing, a hydrocarbon, either ahphatic paraffinic, cycloaliphatic paraffinic or aromatic 1n nature, the preferred charge comprising an aliphatic parafiinic hydrocarbon containing from about 4 to about 20 carbon atoms, is charged to a thermal diffusion unit 1 through line 2 into the upper portion of said unit. A halogenating agent comprising elemental bromine, elemental chlorine, etc. is also charged to the upper portion of thermal diffusion unit 1 through line 3. The thermal diffusion unit in one embodiment thereof comprises a cell which contains at least two liquid-impervious walls made of heat-conducting material, said walls being closely spaced so as to form a relatively narrow space between said walls. As has been previously discussed the narrow space between said walls, in one embodiment hereof, will comprise a vertical slit having a thickness of from about 0.01 inch to about 0.25 inch. These walls comprise a hot wall 4 and a cold wall 5. Each wall is provided with heat transfer means of the type hereinbefore set forth, said means being capable of maintaining a temperature differential or gradient between the faces of said walls. As hereinbefore set forth, the hydrocarbon and the halogenating agent along with diluent gas for the halogenating agent, if one is desired, are continuously charged to the upper portion of unit 1. Unit 1 is also provided with line 6 wherein hydrogen bromide or hydrogen chloride which is formed during the halogenation may be withdrawn along with any diluent gas which has been employed. The mono-halohydrocarbon is continuously withdrawn from an intermediate portion of unit 1 through line 7. While only one line has been illustrated, it is contemplated within the scope of this invention that several lines for withdrawal of the mono-haloparaflin may be employed at rvarious positions adjacent to the intermediate portion of the unit. If dior poly-halohydrocarbons are formed, they will flow in a downward manner to the bottom portion of unit 1 where they will be withdrawn from the unit through line 8. Likewise, in the drawing only one poly-halohydrocarbon withdrawal line has been illustrated, although more than one line may be utilized. It is to be understood that the drawing illustrates only one form of a thermal diffusion apparatus which may be used and that it is contemplated within the scope of this invention that other types of apparatus may be used and said apparatuses which are tubular in shape or which consist of a multiple tube type of thermal diffusion apparatus may also be used. In particular, all

halogenated products may be withdrawn from a bottom drawoff point 8 (7 being not used) and the effluent passed to a second thermal diffusion unit whence mono-brominated products are withdrawn from the bottom, this series of units therefore being equivalent to the single unit with multiple withdrawal points illustrated herein.

The heat-conductive walls which make up a portion of this apparatus may be of any suitable material, the only limitation being that the material be inert to the reactants and capable of being heated or cooled by external means. Suitable metals which may be used include stainless steel, copper, brass, or other alloys which are heat conductive, as well as non-metallic materials such as glass, porcelain, and the like.

As hereinbefore set forth, in the preferred embodiment of this invention both walls are provided with heat transfer means which are capable of maintaining a temperature gradient between the inner faces of the walls. It is contemplated within the scope of this invention that the temperature of the hot wall should not be above the boiling or decomposition point of the hydrocarbons which are introduced into the unit at the pressure used, and, likewise, the temperature of the cold wall should not be below the freezing point or crystallization point of the hydrocarbons as well as the mono-halogenated and polyhalogenated hydrocarbons. For example, the temperature of the hot wall may be maintained in a range of from about 50 up to about 200 C., depending upon the particular hydrocarbon which is to undergo halogenation. At the same time, the temperature of the cold wall is maintained at a relatively low temperature in the range of from about 0 up to about 50 C., the preferred range being from about 0 to about 30 C., the temperature gradient preferably being as much as about 50 C., to about 200 C. Although it is preferred to operate the process under atmospheric pressure it is also contemplated within the scope of this invention that the selective halogenation of the parafiinic hydrocarbon be effected under superatmospheric conditions ranging from 2 up to 50 atmospheres or more, the pressure being that which is sufficient to maintain a major portion of the reactions in a liquid phase, in order that the paraffinic hydrocarbon be selectively halogenated and separated to recover the desired mono-halogenated hydrocarbon from the polyhalogenated hydrocarbon.

Examples of saturated hydrocarbons, and particularly parafiinic hydrocarbons, which may be subjected to the selective halogenation process of the present invention comprise those which preferably contain from about 4 to about carbon atoms in length and may be either straight-chain or branched-chain in configuration, the straight-chain parafiins being preferred. Specific examples of these compounds will include n-butane, n-pentane, nhexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pent-adecane, n-hexadecane, n-heptadecane, n-octadecane, n-nonadecane, n-eicosane, and branched-chain isomers thereof.

By utilizing a continuous method of operation it is possible to achieve a high selectivity of mono-halogenation, and particularly mono-bromination, and, in addition,

it is easy to separate the different products in relatively pureform. This ease of separation and selectivity will offer a distinct advantage over the former methods which have been used in order to obtain mono-halogenated hydrocarbons. This continuous process is simple in form inasmuch as the parafiins and the halogenating agent can be set into the upper portion of the cell while withdrawing the mono-halogenated product from an intermediate level and the diand poly-halides from a lower level. Inasmuch as the halogenating agent, preferably an elemental halogen, will normally travel upwardly as it reacts in the paraffinic zone and the halogenated parafiins will travel downwardly, a minimum of halogenation of the haloparaffins will be achieved in such a process and therefore, as hereinbefore set forth, a high selectivity of mono-halogenation will be achieved. Another advantage which will be found by utilizing the process of the present invention is that it is possible to use a fairly wide boiling range of feed stocks as starting materials with the concurrent ease of separation of halogenated products thus adding another advantage over the methods now in use to obtain the desired products.

The following examples are given to illustrate the process of the present invention which, however, are not intended to limit the generally broad scope of the present invention in strict accordance therewith.

EXAMPLE I A thermal diffusion apparatus comprising two liquidimpervious stationary walls of heat-conductive material spaced about 0.05 inch apart is utilized in this experiment. One wall is provided with heating means while the other wall is provided with cooling means. The heating means comprise conduits through which hot gases are fed, while the cooling means comprise conduits through which cold water flows. The hot wall is maintained at a temperature of about 170 C., while the cold wall is maintained at a temperature of about 20 C. The apparatus is also provided with outlet means at an intermediate portion and a lower portion thereof. A hydrocarbon cut comprising ndodecane derived from a hydrocarbon mixture which was subjected to separation utilizing molecular sieves is charged to the thermal diffusion apparatus through one inlet means in the upper portion of the apparatus, at a rate equal to the rate of liquid withdrawal from the reactor. Elemental bromine is also charged to the apparatus through another inlet means in the upper portion thereof. The dodecane is present in the thermal diifusion apparatus in a mole ratio of about 15 moles of dodecane per mole of bromine fed per hour. The mono-bromododecane is continuously withdrawn from the outlet means in the intermediate portion of the apparatus, while any diand poly-bromododecanes which are formed are withdrawn from the lower portion of the apparatus. The hydrogen bromide which is formed in the upper portion of the apparatus is withdrawn from the top of said apparatus and recovered.

EXAMPLE II In this example a thermal diffusion apparatus is utilized similar to that described in Example I above, but the walls of the zone are maintained at a distance apart of about 0.15 inch. To this apparatus is charged a stream of undecane which is purified before admission into said apparatus by admixture with sulfuric acid followed by heating and cooling. The two layers are separated, the undecane is washed with water, 10% sodium hydroxide solution and again with water. Following this, the hydrocarbon is dried by passage over sodium sulfate and thereafter charged to the apparatus. The bromine is also purified by distillation to remove any metals which may be present and is then charged to the apparatus. The hot wall of the apparatus is maintained at a temperature of about 160 C., while the cold wall is maintained at a temperature of about 15 C., thereby maintaining a temperature gra dient of about C., throughout the length of the ap- 7 paratus. The monobromoundecane is continuously withdrawn from the intermediate portion of the apparatus and purified by conventional means, while any polybromoundecanes which may have'formed are withdrawn from the bottom portion of the apparatus.

EXAMPLE III In this example a thermal diffusion apparatus compris ing two liquid-impervious stationary walls are spaced at a distance of about 0.15 inch apart. The hot wall of the thermal diffusion apparatus is maintained at a temperature of about 150 C. while the cooled wall of the apparatus is maintained at a temperature of about C. The charge stock in this experiment comprises decane which is previously passed through a silica gel column, collected in a flask, purged of air by a steady stream of nitrogen and stored under a nitrogen blanket until used. Bromine along with nitrogen which acts as a diluent gas is charged through the apparatus through inlet means at the upper portion thereof in such an amount that the mole ratio of decane to bromine is about moles of decane per mole of bromine fed per hour. The monobromodecane is continuously withdrawn through outlet means at an intermediate portion of the apparatus, while poly-boromdecanes, to the extent formed, are withdrawn through outlet means at a lower portion of the apparatus. In addition, hydrogen bromide which is formed during the bromination of the decane and diluent gas comprising nitrogen are continuously withdrawn from the top of the apparatus.

I claim as my invention:

1. A process for halogenating a paraffinic hydrocarbon containing from 4 to 20 carbon atoms which comprises introducing said hydrocarbon and a halogenating agent comprising chlorine or bromine into the upper portion of a thermal diffusion zone having opposing closely spaced vertical parallel walls maintained at different temperatures, the hotter wall being at a temperature in the range of from about 50 C. to about 200 C. and the cooler wall being at a lower temperature in the range of from about 0 to about 50 C., the temperature differential between said hotter wall and said cooler wall being from about 50 C. to about 200 C., reacting said hydrocarbon and said halogenating agent while passing downwardly between said walls, thereby forming mono and poly-halogenated hydrocarbons and hydrogen halide, removing said hydrogen halide from the upper portion of said thermal diffusion zone, separating by thermal diifusion mono-h alo genated hydrocarbon from poly-halogenated hydrocarbon within said thermaldiffusion zone and withdrawing said mono-halogenated hydrocarbon from an intermediate point in the height of said zone and withdrawing separated poly-halogenated hydrocarbons from the lower portion of said zone. i

2. The process as set forth in claim 1, further characterized in that said halogenating agent is bromine. 3. The process as set forth in claim 1, further characterized in that said halogenating agent is chlorine.

4. The process as set forth in claim 1, further characterized in that said hotter wall is at a temperaturein the range of from about C. to about 200 C. and said cooler wall is at a, temperature in the range of from about 0 C. to about 30 C. i 5. The process as set forth in claim 1, further char acterized in that said hydrocarbon is a straight-chain paraffin containing from 10 to 20 carbon atoms. 6. The process as set forth in claim 5, furthercharacterized in that said hydrocarbon is decane. 7. The process as set forth in claim 5, further characterized in that said hydrocarbon is undecane. 8. The process as set forth in claim 5, further char acterized in that said hydrocarbon is dodecane. 9. The process as set forth in claim 5, further char acterized in that said hydrocarbon is pentadecane.

10. The process of claim 1 wherein the opposing walls of said thermal diffusion zone are spaced apart a distance of about 0.01 inch to about 0.25 inch.

References Cited UNITED STATES PATENTS 2,168,260 8/1939 Heisel et al. 260660X 2,898,384 8/1959 Viriot 260658 3,316,294 4/1967 Feighner 260-662X FOREIGN PATENTS 378,873 8/1932 Great Britain 260-660 BERNARD HELFIN, Primary Examiner M. W. GLYNN, Assistant Examiner US. Cl. X.R.

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