US2755235A - Process for benzene hexachloride purification - Google Patents

Description

States atent' Patented July 17,. 1956 PROCESS FOR BENZENE HEXACHLORIDE PURIFICATIUN Luke J. Governale, Baton Rouge, La., assignor to Ethyl Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application October 26, 1951, Serial No. 253,456

4 Claims. (Cl. 202-57) This invention relates to improvements in the production of benzene hexachloride, and more specifically to a method for minimizing discoloration thereof during its manufacture and recovery.

Benzene hexachloride is generally prepared commercially by the photochemical chlorination of benzene. A substantial excess of benzene is employed, with the result that the product mixture is obtained in the form of a solution of the benzene hexachloride therein. This solution is treated, preferably by the evaporation of the benzene solvent at a relatively high temperature so that the henzene hexachloride thereby isolated is concurrently melted or fused. Such a recovery process is described in U. S. Patent 2,564,406. The molten benzene hexachloride so isolated is then cooled and solidified and comminuted to provide a saleable product.

It has heretofore been known that maintaining the henzene hexachloride recovered in a molten condition for an extended time results in certain decomposition and discoloration thereof. The recovery process described in the aforementioned patent avoids such decomposition by restricting the residence time of the benzene hexachloride within a limited period. While this technique has core tributed materially to producing a higher grade product, it has not fully solved the difliculties in the production of this material. It has since been found that even when the adverse effects of extended high temperature treatment are avoided, nevertheless the product frequently does not meet desirable color standards. It is now believed that thisadditionaldeteriorating factor is a result of presence of ferriferous materials of construction, in the equipment, and also in part to the presence of impurities which are sporadically but frequently encountered in the feed streams to the initial chlorination operation. In particular, it is believed that soluble iron compounds, e. g., ferric chloride are present in the reactor solution which is fed to the recovery equipment. Such soluble iron salts may be a result of the corrosion encountered from the reaction of even trace amounts of free chlorine with ferrous equipment sometimes used, and also may be attributed in part to the presence of such impurities in the original feed chlorine or benzene stream. The latter streams become contaminated by ferrous equipment conventionally used for shipping and handling these materials. In any event, it has been established that the deteriorating effect of fusion temperatures on benzene hexachloride is not the sole factor contributing to product deterioration.

Heretofore, attempts have been made to circumvent this difficulty by an aqueous caustic scrubbing operation on the reactor solution prior to the time that it is fed to the recovery unit. Such a procedure is relatively effective, but unfortunately introduces ancillary disadvantages. In particular, it appears to be virtually impossible to completely remove minute traces of aqueous solution from the treated reactor solution so that an aqueous material is continually being introduced into the recovery operation wherein the benzene is vaporized from the solution at a relatively high temperature. It is well known that the presence of aqueous material when chlorinated materials are treated at a high temperature promotes or at least facilitates the decomposition of portions of such material and the concurrent release of hydrogen chloride which in turn contributes to rapid corrosion of the equipment and also to product deterioration.

An object of the invention is to provide an improved process wherein the product deteriorating factors, other than solely the elevated temperatures employed, are substantially negated. A further object is to eliminate the necessity of treatment of the reactor solution, fed to a recovery unit, with an aqueous treating medium. An additional object is to provide a process for recovery of a high quality product without affecting the isomeric distribution therein. Other objects will appear hereafter.

Broadly speaking, my process comprises adding an amine to the benzene solution of benzene hexachloride prior to recovery and thereafter vaporizing the benzene solvent. In a preferred form of the process the amine is dissolved in the reactor solution prior to the recovery operation, and in certain proportions relative to deteriorating impurities in the said reactor solution. It has been found that the presence of dissolved iron is one of the most significant impurities resulting in product deterioration for other than thermal decomposition cans Further, when such is the case, it has been found that the preferred proportions in which the amine is to be adds-d is in the ratio of from about 1 to about 6 moles of the amine to 1 atom of the iron in the dissolved iron cornpound.

Many known amines may be operable in the present process. .Of course, one should be chosen which is appreciably soluble in benzene. The reason for the efficacy of these compounds is not presently understood, but apparently they exert a deactivatinginiluence on the factors, especially iron, whicn results in product degradation during the high temperature recovery step. By reason of availability, general efiiciency and usually relative cheapness, the aliphatic type of amine is preferred. Of these the simple tertiary monoamines, generally containing between about 3 and 18 carbon atoms, are especially satisfactory. That is to say, most useful are he aliphatic tertiary amines wherein each substituent of the nitrogen atoms is an aliphatic chain containing between 1 and 6 carbon atoms. Particular examples of such compounds are triamylamine, tributylamine, trimethylamine and trihexylamine. One peculiar fact is noteworthy in connection with these decomposition inhibitors: their efliciency is generally closely related to and governed by the particular iron content of the solution under treatment. Thus, in the case of triamylamine, additions thereof are effective when in the range of between about 5 and 25 parts by weight per part by weight of the iron. in the use of other amines for the process, a CCYI'CSPQILJZEL' range is preferred, that is, in the proportions of about 1 to 6 moles of amino nitrogen to 1 atom of iron. Exact figures will obviously vary, depending upon the reactivity of the particular amine, the number and character of the nitrogen substituents, and similar considerations. However, for the simple aliphatic tertiary amines containing a total of between 3 and 18 carbon atoms the aforesaid range will be found normally particularly effective.

In the production of benzene hexachloride by chlorination and subsequent evaporation at high temperatures of the excess benzene solvent, it is normally preferred that the amine compounds of my process be added immediately prior to recovery operations. When more convenient from an operating standpoint, however, the amine can be added, for example, to the fresh benzene feed to the chlorination reactor. Surprisingly, an amine has virtually no effect on the progress of the chlorination reaction or the desired distribution of isomers in the benzene hexachloride produced.

As already described, the essence of the process is the presence of the amine in the high temperature recovery operation, usually carried out at a temperature of 150 C. or above. Accordingly, in all instances, the amine is added so as to be in the solution fed to the recovery unit. Dependent on the particular amine employed and its vapor pressure, a small portion thereof may be vaporized with the benzene. In general, however, the volatility of the preferred amines is such that it will be retained with the benzene hexachloride product as it is isolated, thus assuring protection of the product when it is exposed to drastic conditions in its most concentrated form. For this reason, it is preferred to use an amine having an elevated boiling point, say, for example, above 150 C., as is found with tripropylamine, tributylamine and others of similar or higher molecular weight.

Surprisingly under certain circumstances the amine additive employed may itself be a contributing factor to product deterioration, thus illustrating that their beneficial etfect is derived from a deactivating coordination with other minute contaminants which normally would be responsible for deterioration entirely dissimilar from that encountered by thermal decomposition. Thus, it has been found that when triamylamine is added to a benzene hexachloride solution, which has previously been treated with caustic solution, that it itself can cause an undesirable discoloration thereof.

The following examples illustrate the manner of carrying out the process and its effectiveness in providing a desired product.

Example I A supply of commercial benzene hexachloride of desir able white color was dissolved in benzene contaminated with dissolved ferric chloride, the contaminant being present in concentrations providing 0.0033 weight percent iron based on the benzene hexachloride. To samples of this solution were added tri-normal-amylamine in such amounts that the weight ratio of amine to dissolved iron varied from to 192. Each sample was then heated to a temperature of 150 C., the benzene being evaporated and the benzene hcxachloride being fused. The benzene hexachloride samples were cooled in a short time, such that thermal decomposition could not adversely aifcct its prop erties, and then were visually inspected for color. It was found that the product was desirably white and not ottcolor when the amine content of the original solution had been between and 26 times the iron content. Less triamylamine gave a gray or black-colored product, while more caused the product to be tan.

Example II A series of chlorinations of commercial benzene, in an iron free reactor, was carried out. A product solution of about to weight percent benzene hexachloride in benzene was obtained. When this solution contained soluble iron in concentrations of 0.00002 weight percent,

or above, based on the benzene hexachloride, the prod not recovered by the method of the foregoing example was off-color, varying from gray to black. However, when triamylamine was added in proportions of from about 1 to 6 moles per atom of iron in solution, the product was acceptable and white in appearance. In some instances, the amine was added in the benzene feed to the chlorination, and no adverse effects were noted on the gamma isomer content of the benzene hexachloride produced, the resultant product containing 13 to 15 percent gamma isomer.

The chlorination was also carried out with pro-purified feed and with special precautions to prevent the intro duction of iron compounds to the system. The use of triamylamine or tributylamine (in proportions of 0.084 weight percent of the benzene hexachloride), resulted in a product having a green or greenishblue appearance of variable intensity.

From the foregoing examples the benefits of the process with respect to the desired high grade product is evident, as well as the maintenance of a high proportion of gamma isomer in the benzene hexachloride in those instances wherein the amine is added to the feed streams. It will be understood that the process is susceptible of wide variation, being limited only as defined by the following claims.

I claim:

1. The process for recovering crude benzene hexachloride which comprises adding an amine to a mixture consisting essentially of benzene, crude benzene hcxachloridc and a contaminating amount of ferric chloride, and thereafter vaporizing the benzene from said mixture, said amine being appreciably soluble in said benzene and having a boiling point above about 150 C., the quantity of amine added being sutlicicnt to minimize discoloration of the benzene hexachloride and to result in the recovery of substantially white benzene hexachloride.

2. The process of claim 1 wherein the amine is triamylamine and the triamylamine is employed in the proportion of about 1 to 6 moles per atom of ferric chloride.

3. The process of claim 1 further defined in that the amine is present in the proportion of about 1 to 6 moles per atom of iron ferric chloride.

4. The process of claim 1 further defined in that the amine is triamylamine.

References Cited in the file of this patent UNITED STATES PATENTS 1,996,730 Thomas et al Apr. 2, 1935 2,227,804 Britton et al Jan. 7, 1941 2,380,254 McCulloch July 10, 1945 2,559,569 Orloff July 3, 1951 2,567,034 Scovic Sept. 4, ll 2,692,900 Bissinger Oct. 26 1954 OTHER REFERENCES Gunther: Journal of Economic Entomology, volume 40 (1947).

Gunther et al.: Science," volume 104 (1946).

Claims (1)

1. THE PROCESS FOR RECOVERING CRUDE BENZENE HEXACHLORIDE WHICH COMPRISES ADDING AN AMINE TO A MIXTURE CONSISTING ESSENTIALLY OF BENZENE CRUDE BENZENE HEXACHLORIDE AND A CONTAMINATING AMOUNT OF FERRIC CHLORIDE, AND THEREAFTER VAPORIZING THE BENZENE FROM SAID MIXTURE, SAID AMINE BEING APPRECIABLY SOLUBLE IN SAID BENZENE AND HAVING A BOILING POINT ABOVE ABOUT 150* C., THE QUANTITY OF AMINE ADDED BEING SUFFICIENT TO MINIMIZE DISCOLOFATION OF THE BENZENE HEXACHLORIDE AND TO RESULT IN THE RECOVERY OF SUBSTANTIALLY WHITE BENZENE HEXACHLORIDE.