US2364416A - Separation of thiophenols from hydrophobic liquid mixtures - Google Patents

Description

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Patented Dec. 5, 1944 SEPARATION OF THIOPHENOLS FROM HYDROPHOBIC- LIQUID. MIXTURES George W. Ayers, J12, and Meyer's. Agruss, Chicago; and Richmond T. BelltDeerfield, 111., assign'ors to The Purev Oil Company; Chicago, Ill-.,.

a corporation of Ohio No'Drawing. "Application June2'1, 1941,

' Serial No. 399,228

6; Claims.

This invention relates to a method for separate ing thiophenols from hydrophobic liquidurnixr tures containing-thesame and is more particularly concernedwith a. method for separating thiophenols from acid oils.

Mixtures of thiophenols, phenols and other oil-soluble weakly acidic organic compounds bta ined from hydrocarbon. oils by extraction with caustic alkali, are generally called acid oils. Acid oils may contain substantial.quantities-of thiophenols, as well as 'alk-yl phenols and other organic acidic compounds such. as naphthenic acids and in some cases varyingamounts of polycyclic aromatic ring. phenolic compounds The amount of thiophenols present in .a specific acid oil is dependent upon the. composition of the original hydrocarbon oil and the treatmentv to which the oil. has been subjected. The acid oils are usually obtained by extracting. cracked mineral oil distillates with strong. aqueous alkali metal hydroxide solutions andthe acid oils. separated from the resulting extract by springing with su tabl acidic material. springing may be effected. by adding sufficient acidic material to the aqueous alkali solution to neutralize the Acid oils as thus preparedordinarily con'- tain undesirable alkyl mercaptans. Acid oils substantially free of alkyl mercaptans -may be readily obtained. by steam stripping or' boiling the aqueous alkali solutions'prior to the springing operationi Thiophenols in acid oils havebeen: separated from alkyl phenols in the'past' byextracting the acidoils with an organic'water insoluble solvent for alkyl phenols in the presence of aqueous solution of an alkali metal hydroxide i'nan amount approximately equivalentto the thiophenol content of the acid oil. Under such conditions alkyl phenols preferentially dissolve in the solvent. This method, however, does. not producesubstam tially pure thiophenols It. has now beendiscoveredthat substantially pure thiophenolfractions and. substantially pure thiophenol compounds may be separatedirom acid oils which are substantially free of alkyl mercaptans by precipitation with heavy metal salts.

It is an object of this invention to recover thiophenols from acid oils in a substantially pure form.

It is another object of this invention to recover thiophenols substantially free of other weakly acidic organic compounds" and free of v relatively high proportions of thiophenols.

each other from acid oils which are substantially free-of alkyl mercaptans.

It'is still a further object of this invention to efllciently separate thiophenols from acid oils.-

Other objects and advantages will'be apparent from th following' more detailed description.

As previously indicated, it has been found that thiophenols may be separated from acid oils that are substantially free of alkyl mercaptans in a relatively pure state by precipitation with heavy metal salts" such as salts of the heavy metalsof Groups 1, 2 and 4 of the periodic table. In order to avoid contamination with alkyl mercaptans, such materials ar removed from the aqueous alkaline solutions which have been employed to extract the acid oils from hydrocarbon oils; preferably by steaming and/or boiling; Those alkaline solutionswhich have been used a plurality of times for the extraction of petroleum oil's'and: regenerated by steam stripping are preferred since these solutions ordinarily contain When heavy metal salts are added to acid oils obtained from such alkali solutions, heavy metal'salts of thiophenols are formed and these salts, precipitatein a relatively pure form. This may be effected by simply agitating the acid oils with aqueoussolutions or suspensions of appropriate heavy metal salts, preferably aqueous solutions of salts of those heavy metals that are precipitated fromacidicsolutions with hydrogen sulfide. Heavy metal salts which have been found suitable for this purpose include water soluble salts of mercury, silver. and lead. Particularly good results have. been. obtained with water soluble salts of mercury. Suitable salts include mercuric cyanide, mercuric acetate, silver acetate, sllvernitrate and, lead. acetate.

After precipitation of the heavy metal salts of the thiophenols from the acid oil, the salts are separatedtherefromby filtration or other ap propriate. means. These salts. may be further purified. by' fractionalcrystallization from an appropriate solvent such as. aqueous alcoholis olution. Thiophenols are then recovered from the heavy metal salts thereof by dispersing, i. e., suspending or dissolving the heavy metal. thiophenolic salts: in. a suitablelliquid such as a low boilingshydrocarbon liquid and acidifying the liquid as for example, by passing hydrogen sulfide therethrough, which frees the thiophenols. Other acidifying agents can be used but best results areobtalned by the use of an acid reagent which precipitates the heavy metal in the form subsequently separated from the petroleum hy-.

drocarbon solvent by distillation. Individual thiophenols may be separated from each other in the same or a subsequent distillation by carethat the precipitates formed are of uniform composition and are simple salts of individual thiophenols which are readily purified as contrasted to precipitates obtained with other heavy metals which are complex mixtures of various thiophenol salts. It is exceedingly difficult to obtain substantially pure thiophenols from the latter precipitates.

The substantially pure thiophenols maybe employed as solubility promoters in aqueous alkali metal hydroxide solutions for enhancing the ability of such solutions to extract mercaptans from petroleum oils. Pure thiophenols are also in] fractionation by virtue of difference in boiling point. It is, of course, apparent that the original acid oils may be fractionated prior to the precipitation therefrom of the heavy metal salts of thiophenols. In this way the phenolic heavy metal salts may be directly precipitated as substantially pure individual thiophenol compounds.

In a specific example, acid oil obtained by aqueous alkali extraction of a mixture of cracked and straight run Van Zandt and Schuler gasolines was separated from the alkali extracting solution by acidification and decantation. A portion of the acid oil was contacted with an equal volume of 10% aqueous mercuric cyanide solution and the White precipitate of mercuric aromatic mercaptide separated by decantation and washed with water. The washed precipitate was crystallized repeatedly from hot 80% aqueous ethyl alcohol solution by simply cooling the solution. The resulting material was identified as substantially pure mercuric o-tolyl mercaptide. This material constituted more than half of the origina1 mercaptide precipitated. The purified white mercuric o-tolyl mercaptide was suspended in heptane and hydrogen sulfide gas passed through the suspension until precipitation of black mercuric sulfide was complete. This acidifies the thiophenol salts and frees the aromatic mercaptan which dissolves in the heptane. After washing with water, the aromatic mercaptan-heptane solution layer was distilled and o-thiocresol recovered as a residue.

In another example, a separate portion of the same acid oil was fractionally distilled and a fraction obtained, the boiling range of which was close to theboiling point of o-thiocresol. O-thiocresol boils at 194 C. and the boiling range of this fraction was 174 C. to 214 C. This narrow boiling fraction of the acid oil was treated with an aqueous solution of mercuric cyanide to precipitate mercuric aromatic mercaptide in a manner similar to that described in connection with the treatment of the first portion of acid oil. The precipitate was suspended in heptane, hydrogen sulfide passed through the suspension to precipitate mercuric sulfide and to free the aromatic mercaptan. The heptane solution of aromatic mercaptide was then distilled to remove heptane. The residue from the distillation of the heptane layer was fractionally distilled, yielding substantailly pure o-thiocresol.

The fractional crystallization steps which were carried out in the aforementioned procedures may be reduced in number or eliminated by employing sufiiciently sharp fractionation of the acid oil prior to the precipitation of the heavy metal salt.

While salts of thiophenols may be precipitated by the use of salts of metals other than those specified herein, it has been found that it is only by the use of salts of the metals herein disclosed useful as additives for enhancing the lubricating properties of mineral lubricating oil and may also be employed as odorizing agents for natural gas. In general, the purified thiophenols may be employed instead of the corresponding hydroxy benzenes in many organic syntheses for the preparation of sulfur containing compounds whereby sulfur from the sulfhydryl group, instead of oxygen from the hydroxy group, is present in the final product.

The foregoing general description of the invention and the specific example described are sufficient to enable one skilled in the art to appreciate its value. The invention is not limited to the specific examples disclosed but is to be interpreted as broadly as the prior art permits in view of the following claims.

What is claimed is:

1. The process of separating substantially pure thiophenols from acid oils containing the same which are substantially free of alkyl mercaptans comprising contacting the acid oils with watersoluble salts of metals selected from the group consisting of mercury, lead and silver whereby to precipitate metal salts of thiophenols, separating said precipitated salts, dispersing the separated salts in a hydrocarbon liquid boiling below the boiling point of thiophenol, treating the dispersed salts with sufiicient hydrogen sulfide to convert dispersed salts to an oily layer of substantially pure thiophenols dissolved in the hydrocarbon liquid and to precipitate metal sulfide and separating substantially pure thiophenols from the hydrocarbon liquid by fractionation.

2. Process in accordance with claim 1 in which the acid oils are fractionated prior to contacting with the water-soluble salt to separate a narrow boiling fraction approximating the boiling point of the pure thiophenol to be obtained.

3. The process of preparing a substantially pure thiophenol from acid oils containing the same which are substantially free of alky1 mercaptans comprising fractionating the acid oils to obtain a narrow boiling fraction which boils somewhat above and somewhat below the boiling point of the pure thiophenol, contacting the narrow boiling fraction with water soluble salt of mercury whereby to precipitate mercury-thiophenol compound, separating said precipitated compound, dispersing the separated compound in a hydrocarbon liquid boiling below the boiling point of the thiophenol, acidifying the dispersion with hydrogen sulfide to precipitate mercury-sulfide and to free thiophenol as a solution in said hydrocarbon liquid and separating the thiophenol from the hydrocarbon liquid.

4. Process in accordance with claim 3 in which the substantially pur thiophenol is o-thiocresol and the narrow boiling fraction boils from about 174 C. to 214 C.

5. Process in accordance with claim 1 in which the precipitated salts are purified by functional aqueous alcohol solution and crystailizing the dissolved salts therefrom by cooling the solution, suspending the crystallized salts in a low boiling hydrocarbon liquid from which thiophenols can be readily separated, contacting the suspension with hydrogen sulfide until precipitation of mercury as sulfide is complete and separating the liberated thiophenols from the dispersing liquid.

GEORGE W. AYERS, JR. MEYER S. AGRUSS. RICHMOND T. BELL.