US2911446A - Process for the separation of gamma benzene hexachloride - Google Patents

Description

Nov. 3, 1959 B. H. NICOLAISEN ETAL 2,911,446

PROCESS F OR THE SEPARATION OF GAMMA BENZENE HEXOCHLORIDE Filed July 7, 1953 2 Sheets-Sheet 1 CRUDE 514C? h REG a6 l0 fxrfiAcr/A/swwr/o/v E RACTOR FRESH W451; 50L VEN T? 5EPARATOR 8 WASH/ED ALPHA, CRYSTALUZER //3 BETA 01x5 //l/ I E S/JWASH SEPARArOR SOLVE/VT) 1 /2 WASHED GAMMA W45 Saws/v1 C'A/(E ST/LL F/LTRATE ZRES/DUE ma a v ATTORNEYS Nov. 3, 1959 A B. H. NICOLAIISEN ETAL 2,911,446

PROCESS FOR THE SEPARATION OF GAMMA BENZENE HEXOCHLORIDE Filed July '7, 1953 2 Sheets-Sheet 2' Etta a5 l0 fXTR/lCT/NG -50LUT/0N? EXTRAU'OH {FRESH 1 1445 50L VEN r 5EPAPA 70R &

W4 SHE'D ALPHA, 30A? 6 E BETA CA K5 TANK 2/3 O-PKSTA LL/Z ER FRESH WASH 5594 RA TOR & 5 SOLVE/VT J 1' WASHED GAMMA SURGE WASH SOLVE/VT C A K E TANK .5 TILL /L TRATE 1 R55 mug INVENTORS BERNARD H. M00; A/SEN Juoso/v A- l ,l OOD ATTORNEYS large scale.

United States Patent O F PROCESS FOR THE SEPARATION or GAMMA BENZENE HEXACHLORIDE Bernard Nicolaisen, Kenmore, and Judson A. Wood,

Niagara Falls, N .Y., assignors to Olin Mathieson Chemical Corporation, a corporationof Virginia Application July 7, 1953, Serial No. 366,602

4 Claims. (Cl. 260- 648) This invention relates to the production of gamma benzene hexachloride by separation of concentrates containing 95% or more of the 'gamma isomer of benzene hexachloride or 1,2,3,4,5,6-hexachlorocyclohexane from crude benzene hexachloride by means of solvent extraction.

Benzene hexachloride as usually manufactured by the addition chlorination of benzene contains about 10-15% of the gamma isomer, 60-80% alpha isomer, 10% beta isomer and small percentages of other benzene hexachloride isomers together with a few percent of heptachlorocyclohexane and other byproducts. The gamma isomer of benzene hexachloride is the only one of these products having significant insecticidal activity. Although the crude mixture may be used for insecticidal purposes, it is advantageous to separate concentrates of the gamma isomer which contain larger proportions of the insecticidally active isomer. I

The various isomers of benzene hexachloride may be separated by various combinations of extraction, crystallization, distillation and other processes. Many of the processes that have been proposed are not economically feasible or are ineffective. In order to obtain gamma concentrates at the lowest possible cost, the. number of steps, especially distillations and mechanical losses, must bekept to a minimum. Furthermore to be economically advantageous, a process must separate substantially all of the gamma isomer from the crude benzene hexachloride. Processes in which partially separated materials tend to accumulate cannot be used economically on a large or a continuous scale. The present invention provides a process for treating crude benzene hexachloride to recover substantially all of the gamma isomer contained therein as concentrates containing 95% or more of the gamma isomer.

Many of the known processes require long periods of extraction or crystallization approximating 48 hours. This necessitates large equipment when operated on a The present invention provides a process in which no holding times greater than about 4 hours are required and is thus amenable to continuous operation.

Although the separation of the alpha and beta isomers from the gamma isomer of benzene hexachloride is rela are obtained: an essentially gamma-free cake and a washed gamma cake. All of the isomers except. gamma and all of the by-product heptachlorocyclohexane are rejected in the first cake. The process requires only one extraction step and one crystallization step, each followed by a suitable step of separation of products. A solvent recovery still is also provided. Only one distillation of wash solvent is necessary per cycle and make-up solvent requirements are very low. No unseparated, gammacontaining residues are produced except the small amount of residue from distillation of the wash liquor. This is recycled and represents but a small proportion of the crude charged.

The invention utilizes the fact that a solution saturated with respect to any of the isomers at a given temperature will not extract further quantities of that isomer from a crude solid containing it in crystalline form. It further utilizes the fact that gamma benzene hexachloride crystallizes more readily than any of the other isomers from a solution of mixed isomers in any of the various suitable solvents. The other isomers have a greater tendency to remain in supersaturated solution than gamma.

The process of this invention is characterized by cyclic operation in which solution is circulated in a closed cycle between an extraction stage and a crystallization stage. Thus the crude solid is extracted with a solution saturated with respect to all of the isomers except gamma. Only gamma is extracted from the solid and goes. into solution. On cooling slightly, due to the higher crystallization tendency of gamma and the higher supersaturation tendency of the coproducts, the extract deposits crystals of pure gamma isomer, leaving the co-products in supersaturated solution. On warming the filtrate to the extraction temperature, the solution is saturated with respect to all isomers except gammaiand is againcapable of extracting that isomer only from the crude benzene hexachloride. v It is recycled as the extracting solvent for treatment of additional crude benzene hexachloride. An organic solvent, e.g. perchlorethylene, for benzene hexae chloride, having differential aflinity for the isomers of benzene hexachloride at least with respect to'solutiom rates is employed as the extraction and crystallization medium. Fresh solvent is used only to wash the undissolved solids remaining after the extraction step and to wash the pure gamma cake. These washings are combined and distilled to recover solvent. The minor proportions of benzene hexachloride dissolved in the washing operation remain as a residue which may be recycled to the extractor.

It is advantageous to Waslr'the cakes with water containing a small amount of a wetting agent to displace any liquor from the crystals. For this purpose, about 0.1% to about 5% of wetting agent may be used. The latter may be of the cationic type, for example, long chain quaternary ammonium salts such as lauryl pyridinium chloride, of the anionic type, for example, sulfonates or sulfates such as sodium kerylbenzenesulfonate or sodium lauryl sulfate, or agents of the non-ionic type, for example the phenoxypolyoxyethylene ethariols. These washings may be discarded. The liquor may be separated and returned to the process.

Figures 1 and 2 of the accompanying drawings illustrate in the form of diagrammatic flow plans two methods for applying the invention. In Figure 1, crude benzene hexachloride is charged to an extractor 10 which may comprise a closed, stirred vessel maintained at a suitable temperature. Recycle solution or filtrate from the separation of gamma isomer is also charged to the extractor and the mixture is thus treated for about four hours. The extraction mixture is charged to a separator prises largely alpha and beta benzene hexachloride together with minor proportions of delta benzene hexachloride and heptachlorocyclohexane which were not dissolved in the extraction step. The cake after washing with fresh solvent is substantially free from gamma isomer. The washings are segregated from the original filtrate and separated in a wash solvent still 12 into recovered wash solvent and residual benzene hexachloride both of which are recycled. The original filtrate is charged to a crystallizer 13 which is maintained at a slightly lower temperature than extractor The crystallizer may comprise a closed, stirred vessel provided with suitable means for temperature control, for example, a jacket in which a liquid may be circulated. The contents of the crystallizer are thus cooled to a temperature slightly below that of the extraction step. Under these conditions, gamma isomer crystallizes and the solution remains supersaturated in alpha, beta and delta isomers of benzene hexachloride as well as heptachlorocyclohexane and any other co-products. The mixture is charged to separator 14, suitably a centrifuge or filter, and separation is conducted at the crystallization temperature. The cake is washed with fresh solvent to obtain a pure gamma cake. The washings are collected separately from the original filtrate and sent to wash solvent still 12. The filtrate, saturated at the lower temperature with gamma isomer but supersaturated with respect to other isomers and co-products, is returned to extractor 10. At the higher temperature maintained in the extractor the solution is saturated with co-products but not saturated with respect to gamma isomer. Extraction of fresh crude benzene hexachloride therefore results in the removal of gamma isomer from the charge but no further quantities of coproducts are removed from the solid.

As illustrated in Figure 2, the liquor separated from the alpha, beta cake before washing is collected in a surge tank having a four-hour capacity, for example, and which is maintained at the extraction temperature. A. batch crystallizer 13 of, say, two hours capacity is charged from the surge tank 15 and the gamma benzene hexachloride is crystallized by cooling. The liquor from the second separator 14 before washing the gamma cake is collected in a second surge tank .16 also of four hours capacity. The liquor is maintained therein at crystallization temperature. Recycle solution is removed continuously from surge tank 16, warmed and charged to the continuous extractor. An advantage of processing according to Figure 2 is that any tendency of delta benzene hexachloride to crystallize is avoided by maintaining it in surge tank 15 at extraction temperature or slightly higher for a substantial holding period, e.g. one-half hour to 12 hours or more depending upon the capacity of the processing system. Any remaining crystal nuclei passing through separator 11 are thus disintegrated. Delta isomer is less likely to separate at the lower temperature in crystallizer 13 and contaminate the more readily crystallized gamma. The delta isomer is more likely to be present in crystalline form in the surge tank 16, which is held at crystallization temperatures or slightly lower and in the liquor recycled to the extractor where crystalline delta is desirable to prevent extraction of delta from the charge.

Several critical conditions are to be observed in the operation of the process. It is important that a condition essentially of equilibrium is obtained between crystalline and dissolved phases of the components of the charge other than the gamma isomer. This is advantageously accomplished by charging crude benzene hexachloride containing the isomers especially delta benzene hexachloride and heptachlorocyclohexane at least partially in crystalline form. Crystallized deltabenzene hexachloride and heptachlorocyclohexane in crude benzene hexachloride do not dissolve in the extraction liquor. When such isomers are present wholly in liquid form in the crude, they may dissolve and build up disadvantageously in the circulating solution. If the isomers are present in the crude charge at least partially in crystalline form, seeds or nuclei are provided on which the remainder or non-crystalline portion can crystallize to form an equilibrium solution. For this reason, it is advantageous to use a charge of crude benzene hexachloride which is somewhat aged after its recovery from the process of preparation. Commonly only a fraction of the benzene charged to the chlorination process reacts and the crude product is obtained by distilling off the excess benzene. The crude residue contains the delta and hepta compounds in liquid form for some time. In order to use the material in the present process it may advantageously be aged until at least part of these isomers have crystallized, which may require a period of several hours to several days but can be determined by microscopic analysis or by solubility determinations. Alternatively, nuclei and growing crystals may be maintained in the extraction vessel (which in effect functions as an equilibrium crystallizer) in a manner insuring that the solution leaving the vessel is essentially at equilibrium, i.e. just saturated with all components in the feed. Under this condition, the charge need not be in the crystalline state but may be in liquid form.

It is essential that the solution leaving the extraction vessel is in equilibrium at the extracting temperature with crystalline delta benzene hexachloride and heptachlorocyclohexane. On cooling to a lower temperature to crystallize the gamma benzene hexachloride, the delta and hepta components then remain completely in supersaturated solution. In addition, the gamma isomer must not supersaturate in the solution under the conditions of crystallization to an extent interfering with its separation as a solid. To accelerate crystallization, the liquor may be inoculated with a small portion of pure gamma crystals. The filtrate from the crystallization is saturated with respect to gamma at the crystallization temperature but unsaturated with respect to gamma at the higher extraction temperature. Holding time is provided in each stage to permit the desired conditions for practical operation to be attained, i.e. essentially complete equilibrium in the first stage and incomplete or non-equilibrium conditions in the second stage. Usually a period of an hour or more is necessary dependent upon temperature and contact conditions so that it is advantageous for continuous processing to provide special holding stages in conjunction with the extraction, crystallization and separation equipment. Thus unit capacity is increased and flexibility is provided in the event of operating upsets or variations.

In order that delta and hepta may not crystallize in the crystallization step but remain in supersaturated solution, it is necessary that the temperature differential between the two principal steps be small, e.g. about 5 2() C. For example, an extraction temperature of about 35 C. and a crystallization temperature of about 25 C. have been found particularly advantageous. Temperatures up to about 55 C. may be used in the extraction step but at higher temperatures the delta isomer may not be present to a suflicient degree in crystalline form and will tend to dissolve and accumulate in the circulating liquor. For this reason temperatures of about 25 50 C. are preferred for the extraction step. In order to insure the non-crystallization of delta and hepta in the crystallization step, the temperature of the latter operation should not be more than about 15 below the temperature of extraction step; For example, if the extraction is carried out'at 40 C.,'the temperature of the crystallization step preferably should not be below 25 C.

The chlorinated solvents, particularly perchloroethylene are preferred since the solubility of delta benzene hexachloride therein is lower than the solubility of gamma. This reduces the bulk of delta in the circulating liquor and reduces the possibility of crystallization of delta with the gamma isomer. Solvents in which the delta isomer is more soluble than gamma are slightly less advantageous, but are satisfactory for use as long as they are capable of maintaining delta in supersaturated solution at the lower temperature of crystallization. Other solvents which may be used include benzene, trichlorobenzcne, beta, beta- Example I A crude benzene hexachloride containing delta benzene hexachloride and heptachlorocyclohexane partially in crystalline condition and having a composition of 73.6% of alpha and beta benzene hexachlorides, 13.7% of gamma and 12.7% of delta benzene hexachloride and heptachlorocyclohexane was stirred with an equal weight of perchloroethy-lene at 35 C. for four hours. The mixture was filtered at 35 C. and the cake was washed with a small amount of fresh solvent. The washings were collected separately from the original filtrate. The latter was subsequently cooled to 25 C. and stirred for two hours. The mixture was filtered at 25 C. and the cake was washed with a small quantity of fresh solvent. The washings were kept separate from the first filtrate which was warmed to 35 C. and used for the extraction of additional crude benzene hexachloride.

After six cycles of operation as described in the preced' ing paragraph, a solution was obtained which comprised 6.1% of alpha and beta isomers, 14.4% of gamma, 19.2% of delta benzene hexachloride and heptachlorocyclohexane and 60.3% of perchloroethylene. A crude benzene hexachloride containing 75% of alpha and beta isomers, 11.5% of gamma and 13.5% of delta benzene hexachloride and heptachlorocyclohexane was stirred for 4 hours at 35 C. with about times its weight ofthe solution resulting from the above described cyclic,

operation. The mixture was then filtered at 35 C. to obtain a filtrate which was saturated at 35 C. with respect to all of the isomers. The undissolved solid contained 84.2% of alpha and beta isomers, 0.9%- of gamma, 14.9% of delta benzene hexachloride and heptachlorocyclohexane. Adhering mother liquor amounted to 12.2% of the weight of undissolved solid. The filtrate Was cooled to 25 C. and maintained at that temperature with agitation for two hours. The crystals of gamma isomer were removed by filtration and amounted to 89.3% of gamma isomer charged in the crude benzene hexachloride. The product was 98% gamma isomer.

On a larger scale and particularly using a higher ratio of recycle solution to crude charge, the gamma content of the undissolved cake is substantially all extracted. Gamma in the mother liquor is eventually completely recovered as the solution is recycled between the extraction and crystallization steps.

Example I] The crude benzene hexachloride used in this example amounted to 124 parts by weight containing 75.5% of alpha and beta isomers, 14% of gamma and 10.5% of delta benzene hexachloride and heptachlorocyclohexane. In this material the delta benzene hexachloride and heptachlorocyclohexane were present as crystalline materials. The finely divided solid was stirred for eight hours at 35 C. with 478 parts by weight of a solution containing 8% of alpha and beta isomers, 18.2% of gamma isomer, 30.1% of delta and hepta and 43.7% of carbon tetrachloride. The undissolved residue was separated by filtration and washed to remove adhering mother liquor. It then had a composition of 86.3% alpha and beta isomers, 1.8% of gamma and 11.9% of delta benzene hexachloride and heptachlorocyclohexane. The filtrate from this cake was stirred-at 25 C. for two hours and the resulting gamma benzene hexachloride crystals were removed by filtration. The filtrate was recycled to extract fresh crude benzene hexachloride. The filter cakes were washed with fresh solvent,'the washings were distilled to recover the solvent and the residual material was recycled for use in further extraction. The recovery of the gamma isomer amounted to 88.2% of 94.5% purity.

Example 111 The procedure of the preceding example was repeated using benzene as solvent with substantially the same results.

Example IV Mixed isomeric trichlorobenzenes were utilized as solvent according to the procedure described in the preceding examples with equally satisfactory results.

We claim:

1. A continuous process for the separation of gamma benzene hexachloride from a charge of crude benzene hexachloride consisting essentially of the alapha, beta, gamma and delta isomers and heptachlorocyclohexane by means of solvent extraction with a solvent capable of maintaining the delta isomer and heptachlorocyclohexane in supersaturated solution and which is characterized by cyclic operation in which solution is circulated in a closed cycle between a warm extraction stage and a cool crystallization stage, the improvement which consists in aging a charge of crude benzene hexachloride until at least part of the delta isomer and atleast part of the heptachlorocyclohexane are in crystalline form, contacting the aged crude benzene hexachloride charge in the extraction stage with solution recirculated from the crystallization stage and warmed to about 25-50 C. until the solution is saturated in gamma benzene hexachloride, the solution leaving the extraction stage characterized by being substantially in equilibrium with the non-gamma components of the charge in the extraction stage, separating the undissolved material from the extracting solution, charging the solution to the crystallization stage, crystallizing the gamma benzene hexachloride from the solution by cooling the solution to within the range of about 15 C. below the temperature in the extraction stage, separating crystals of gamma benzene hexachloride from the cooled solution, warming the solution to the extraction temperature and recirculating the resulting warmed solution saturated with the non-gamma components to the extraction stage for extraction of a fresh charge of aged crude benzene hexachloride in which the delta isomer and the heptachlorocyclohexane are at least partially in crystalline form.

2. The process of claim 1 in which a chlorinated hydrocarbon solvent is employed as the extracting and crystallizing medium. 1

3. The process of claim 2 where the chlorinated hydrocarbon solvent is perchlorethylene and the temperature employed in the extraction stage is about 35 C. and the temperature employed in the crystallization stage is about 25 C.

4. The process of claim 1 where the solution from the extraction stage is passed to a holding zone maintained at the extraction temperature before being charged to the crystallization stage and the cooled solution from the crystallization stage is passed to another holding zone Where it is continuously withdrawn, warmed to the extraction temperature and recirculated to the extraction stage.

References Cited in the file of this patent UNITED STATES PATENTS 2,438,900 Cooke et a1 Apr. 6, 1948 2,574,165 Bender etal Nov. 6, 1951 2,708,681 Vossen May 17, 1955 2,760,995 Cragg et al. Aug. 28, 1956 FOREIGN PATENTS 491,132 Belgium Mar. 16, 1950 680,955 Great Britain Oct. 15, 1952 1,024,402 France Jan. 10, 1953

Claims (1)

1.A CONTINOUS PROCESS FOR THE SEPARATION OF GAMMA BENZENE HEXACHLORIDE FROM A CHARGE OF CRUDE BENZENE HEXCHLORIDE CONSISTING ESSENTIALLY OF THE ALPHA, BETA GAMMA AND DELTA ISOMERS AND HEPTACHLOROCYCLOHEXANE BY MEANS OF SOLVENT EXTRACTION WITH A SOLVENT CAPABLE OF MAINTAINIGN THE DELTA ISOMER AND HEPTCHLOROCYCLOHEXANE IN SUPERSATURATEDF SOLUTION AND WHICH IS CHARACTERIZED BY CYCLIC OPERATION IN WHICH SOLUTION IS CIRCULATED IN A CLOSED CYCLE BETWEEN A WARM EXTRACTION STAGE AND A COOL CRYSTALLIZATION STAGE, THE IMPROVEMENT WHICH CONSISTS IN AGING A CHARGE OF CRUDE BENZENE HEXACHLORIDE UNTIL AT LEAST PART OF THE DELTA ISOMER AND AT LEAST PART UNTIL AT LEAST PART OF THE DELTA ISOMER AND AT LEAST PART CONTACTING THE AGED CRUDE BENZENE HEXACHLORIDE CHARGE IN THE EXTRACTION STAGE WITH SOLUTION RECIRCULATED FROM THE CRYSTALLIZATION STAGE AND WARM TO ABOUT 25-50*C. UNTIL THE SOLUTION IS SATURATED IN GAMMA BENZENE HEXACHLORIDE, THE SOLUTION LEAVING THE EXTRACTION STAGE CHARACTERIZED BY BEING SUBSTANTIALLY IN EQUILIBRIUM WITH THE NON-GAMMA COMPONENTS OF THE CHARGE IN THE EXTRACTION STAGE, SEPARATING THE UNDISSOLVED MATERIAL FROM THE EXTRACTING SOLUTION, CHARGING THE SOLUTION TO THE CRYSTALLIZATION STAGE, CRYSTALLIZING THE GAMMA BENZENE HEXACHORIDE FROM THER SOLUTION BY COOLING THE SOLUTION TO WITHIN THE RANGE OF ABOUT 15* C. BELOW THE TEMPERATURE IN THE EXTRACTION STAGE, SEPARATING CRYSTALS OF GAMMA BENZENE HEXACHLORIDE FROM THE COOLED SOLUTION, WARMING THE SOLUTION TO THE EXTRACTION TEMPERATURE AND RECIRCULATING THE RESULTING WARMED SOLUTION SATURATED WITH THE NON-GAMMA COMPONENTS TO THE EXTRACTION STAGE FOR EXTRACTION OF A FRESH CHARGE OF AGED CRUDE BENZENE HEXACHLORIDE IN WHICH THE DELTA ISOMER AND THE HEPTACHLOROCYCLOHEXANE ARE AT LEAST PARTIALLY IN CRYSTALLINE FORM.

Images