US2470336A - Halogenation of aromatic hydrocarbons - Google Patents

Description

May 17,1949. A. s. BRUNJES ETAL HALOGENATION OF AROMATIC HYDROCARBQNS Original Filed June 22, 1942 Z Y m/ m mmw w M5 fwa w j 4 w w m w w w 5. m M 5 a \w m 3 mm 1 6 w [M lly-Di I w a Patented May 17, 1949 HALOGENATION OF AROMATIC HYDROCARBONS Austin S. Brunjes, Plandome, N. Y., and Marcel J. P. Bogart, Teaneck, N. J., assignors to The Lummus Company, New York, N. Y., a corporation of Delaware Original application June 22, 1942, Serial No. 447,983. Divided and this application July 20, 1945, Serial No. 606,250

2 Claims.

This invention relates to an improved method for carrying out the halogenation of an aromatic hydrocarbon and specifically relates to the chlorination of benzene.

As is well known, chlorinated benzenes are commonly used as a base material in the production of many chemicals. More particularly, phenol and other products are obtained by the suitable conversion of monochlorbenzene. The chlorination of benzene to produce substantial yields of monochlorbenzene cannot be readily carried out, however, except by the most careful control of the conditions of the reaction, particularly the temperature, in order to prevent undue side reactions from taking place.

An important object of our invention is to provide an improved process for specifically controlling the reaction between chlorine and benzene whereby the maximum yield of monochlorbenzene and the minimum yield of polychlorbenzones are obtained, or alternatively, the production of a maximum yield of polychlorbenzenes.

A further object of our invention is to provide an improved continuous process for halogenating aromatic hydrocarbons such as benzene to produce desired halogenated hydrocarbons such as chlorbenzene useful in the production of industrial materials, which process is particularly adapted for large-scale, economical operation and simplified control. 7

Further objects and advantages of our invention will appear from the following description of a preferred form of embodiment thereof taken in connection with the attached drawing, in which the figure is a vertical sectional view of a reaction chamber devised for performing our improved process, related apparatus being shown in schematic flow diagram.

This application is a division of our copending patent application, Serial No. 447,983, filed June 22, 1942, which has matured into Patent No. 2,395,777.

The reaction vessel I comprises a vertical series of sections. The lowest section H is a feed chamber and may have a neutralizing chamber. This section also acts as the foundation for the entire vessel. It is surmounted by several shelland-tube heat exchange and reaction sections, of which three, l2, l3 and I, are shown. The uppermost section l may be termed the vapor chamber section.

With a reaction such as halogenation of aromatic hydrocarbons, it is highly desirable to provide optimum temperature control at the zone of reaction, and it is also found desirable to pro- 2 vide for individual unit replacement of apparatus. For these reasons the sections l2, l3 and I4 are independent, having tube sheets l6 and I8, I8a and I9, and 19a and Il, respectively, to which the reaction tubes 20, 2| and 22 are secured. These tubes are in alignment and provide for the desired fiow of reactants as hereinafter described. Each tube is filled with a suitable packing 23, which may consist of any suitable material such as ceramic or iron rings. We prefer to use Raschig rings or the like, and these may be treated with ferric chloride if desired.

A controlled inlet of the reactants (benzene and chlorine) to these tubes can be accomplished most successfully according to our invention by injecting the benzene through a chamber of chlorine. This may be accomplished by introducing the chlorine as a gas into chamber llb through inlets 26 and forcing the benzene as a liquid into chamber Ila through inlet 25 and thence through distributor plate 28.

This plate 28 contains a plurality of nozzles 29 in alignment with the lower ends of the reaction tubes 20, which are desirably V-notched as at 20a. This assures the distribution of the mixture of benzene and chlorine into these tubes aided by the jet action of the nozzles 29. It is to be noted that the chlorine inlets 26 are positioned above the lower end of the tubes 20 so that the chlorine enters each of the reaction tubes.

The reaction sections l2, l3 and H are preferably so arranged within the reaction vessel I0 that a suitable cooling medium can be independ. ently circulated about them in indirect heat exchange therewith. This is most important when the reaction is exothermic and it is necessary to regulate the temperature of the reaction to prevent side reactions from taking place. This is the case in the formation of chlorbenzenes, the formation of monochlorbenzene being best accomplished at temperatures of 40 to 45 C., whereas formation of polychlorbenzenes is best accomplished at around to C. For this reason, it is necessary precisely to control the cooling effect in the respective sections.

We have found that water is a satisfactory cooling medium. Cooling water inlet nozzles 30, 30a, and 30b, respectively, may beinterconnected with inlet manifold 32 and cooling water. discharge nozzles 3|, Ma, and 3lb,-respectively, may be interconnected to the discharge manifold 33. If desired. the cooling water may pass through the upper two sections [3 and [4 in series if so desired and cross-connection 34 may be used for 3 this purpose. Suitable valves will be provided for regulating the flow of cooling water.

It will generally be necessary to remove the largest amount of heat in the lowermost heat exchange-reaction section II, and a close temperature control in this section is necessary. For this purpose valve 35 can be interconnected with a suitable temperature controller generally indicated at 36 so that the flow of cooling water through inlet nozzle 30 may be automatically controlled by the exit temperature of reaction section II. It is to be noted that the several heat exchange-reaction sections are desirably provided with baiiies 38 for the suitable distribution of the cooling water about the reaction tubes.

Benzene and chlorine reactants as previously indicated pass upwardly through the reaction tubes and come into contact with the packing therein. This packing provides for a substantially complete mixing of these reactants and also insures that the reactants come into intimate contact with each other. The reaction takes place for the most part in the lower portion of the reacting tubes, although the reacting tubes are sufllciently long so that the reaction is substantially complete by the time that the reactants havetraversed the length of these tubes. The ends of these tubes are also V-notched at the top, which facilitates the separation of the gases from the liquid products at the upper part of the reaction zone.

Apparatus may be used for counterfiow chlorination by introducing benzene at top and chlorine at bottom when it is desirable to do so.

The mixture of reaction products discharged from the reaction tubes is partially in the liquid and partially in the vapor state. This reaction mixture consists of chlorbenzenes, unreacted benzene, and hydrogen chloride. The liquid portion of the reaction mixture is removed through nozzle 39. The vapor portion of the reaction mixture is removed from reaction vessel I through nozzle 40 and is passed through line 4| to condenser 42 wherein the vaporized benzene and chlorbenzene are condensed. A suitable cooling medium may be circulated through condenser 42 by means of lines 43. The condensed material is separated from the uncondensed hydrogen chloride in separator 44, from which the condensate is returned through line 45 to the vapor chamber section I 5. The uncondensed hydrogen chloride will be removed in its gaseous state through line 47 to a suitable recovery system or the like. It is to be noted that the condensate is reintroduced into section through nozzle 48, which is so designed that its discharge is below the upper end of the reacting tubes 22. Thus nozzle 48 discharges the condensate below the level of liquid in section l5,-which aids in the recovery of the liquid product.

The liquid portion of the reaction mixture removed through nozzle 39 is passed through line 50 into heater 5| wherein a portion of this liquid is heated to the boiling point to remove as much hydrogen chloride as possible. A suitable heating material such as steam may be circulated through heater 5| as by means of lines 52 and 52a for this purpose. The partially vaporized liquid is passed through line 84 into the flash chamber 55 wherein the vaporized portion of the liquid is separated from the unvaporized portion. This vaporized portion comprises the hydrogen chloride dissolved in the liquid together with some benzene and chlorbenzene va- 4 pore. The vapors are passed through line 56 for admixture with the vapors in line 4|. Any liquid contained therein will drop back to the chamber IS with the vapor portion continuing to the condenser 42.

The liquid in flash chamber 55 is removed therefrom through line 58 and may be withdrawn as product at 58a or be introduced through nozzle 59 into the neutralizing chamber 60 formed by the dished head 6! and the bottom of the section II. This liquid comprises benzene and chlorbenzene containing a very small percentage of dissolved hydrogen chloride and, if a neutral product is desired, it may b neutralized by adding a neutralizing agent such as caustic soda. This is suitably introduced into the neutralizing chamber through nozzle 62. An agitator 63 driven by motor 64 is provided to effect a mixing of caustic with the benzene and chlorbenzene. The neutralized product is discharged from chamber 60 through nozzle 66 and may be passed to a suitable settler (not shown) in which the sludge of caustic and sodium chloride is settled out and separated from the benzene and chlorbenzene.

We have found it preferable to fabricate reaction vessel ID as an integrated unit as shown. In this manner not only is a compact vessel provided, but the amount of space necessary for the equipment is materially reduced. As indicated,

the bottom of the feed chamber section II may be provided with a suitable drain 68. The neutralizing chamber may also be provided with a suitable drain 69 as well as a vent 10 for the removal of any uncondensable material. Ordinarily we find it desirable to operate the reaction section under a slight superatmospheric pressure.

The method is particularly adapted for the maximum production of monochlorbenzene and in such case appropriate temperatures are obtained by the use of controlled flow of the cooling liquid. However, if it is desired to produce a maximum yield of polychlorbenzenes, higher temperatures are desirable, and it may be found desirable to introduce steam in the heat exchange sections rather than water.

The method is also adapted to further chlorinate partially chlorinated aromatic hydrocarbons or other organic liquids by changin the type of feed. It may also be found desirable to introduce additional amounts of either chlorine or benzene or both at intermediate points along the length of the reaction tubes'by introducing either or both materials into the compartments between the respective tube sheets i8 and We and I9 and l9a. Such operation may be found desirable to better control the reaction.

Although we have shown and'described a preferred form of embodiment of our invention, it will be understood that modifications may be made thereto; therefore, only such limitations as appear in the calims appended hereinafter should be made.

We claim:

1. A continuous method of chlorinating benzene to produce maximum amounts of monochlorbenzene and minimum amounts of polychlorbenzene with high conversion of benzene, which comprises providing a spaced group of long, catalyst packed reaction tubes extending vertically; continuously introducing gaseous chlorine into a confined space surrounding the lower ends of said tubes; continuously feeding liquid benzene into said confined space by means of a plurality of nozzles, each of which is directed into the lower end of one of the reaction tubes; removing the heat of reaction separately from vertically spaced sections of said group of tubes in accordance with the amount of heat generated therein to maintain an approximately uniform temperature of 40 to 50 C. throughout the long reaction tubes; providing a confiined collecting space around the upper ends of the reaction tubes; separately removing the vapor and liquid portions of the mixture of reaction products issuing from said reaction tubes; cooling the vapor portion thus removed to condense the benzene and chlorbenzene contained therein; venting the uncondensed hydrogen chloride; and returning the condensate to the collecting space.

2. A continuous method of chlorinating benzene to produce maximum amounts of monochlorbenzene and minimum amounts oi polychlorbenzene with high conversion of benzene, which comprises providing a spaced group of long, catalyst packed reaction tubes extending vertically; continuously introducing gaseous chlorine into a confined space surrounding the lower ends of said tubes; continuously feeding liquid benzene into said confined space by means of a plurality of nozzles, each of which is directed into the lower end of one of the reaction tubes; removing the heat of reaction separately from vertically spaced sections of said group of tubes in accordance with the amount of heat generated therein to maintain approximately uniform temperature conditions throughout the long reaction tubes; providing a confined collecting space around the upper ends of the reaction tubes; separately removin the flashing operation jointly with the vapor portion of the issuing mixture.

AUSTIN S. BRUNJES. MARCEL J. P. BOGART.

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

UNITED STATES PATENTS Number Name Date 914,223 Alysworth Mar. 2, 1909 1,180,964 Auger Apr. 25, 1916 1,380,067 Koch et a1 May 31, 1921 1,432,761 Koch Oct. 24, 1922 1,892,397 Jenkins Dec. 27, 1932 2,016,658 Tramm Oct. 8, 1935 2,395,777 Brunjes et a1. Feb. 26, 1946 FOREIGN PATENTS Number Country Date 513,947 Great Britain Oct. 26, 1939 OTHER REFERENCES Grogglns: Unit Processes in Organic Syntheses (1935), pages 154-5.

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