US2525153A - Process for recovering aromatic mercaptans from catalytic gasoline - Google Patents

Description

Patented Oct. 10, 1950 PROCESS FOR RECOVERING AROMATIC MERCAPTAN S FROM CATALYTIC GASO- LINE John K. McClennan, Brooklyn, N. Y., and Barney R. Strickland, Westfield, N. J., assignors to Standard Oil Development Company, a corporation of Delaware No Drawing. Application September 17, 1947,

Serial No. 774,662

4 Claims. (Cl. 260-609) The present invention is concerned with an improved process for the production of aromatic mercaptans. The invention is more particularly concerned with the segregation of aromatic mercaptans or thiophenolic compounds from cracked gasolines, particularly from catalytically cracked gasolines.

It is known in the art-to produce hydrocarbons boiling in the motor fuel boiling range by various distillation, reforming, and cracking procedures. No attempt will be made to outline or discuss these processes since they are well known. The products from such processes generally contain varying amounts of aliphatic and aromatic mercaptans. In general, thermally cracked stocks may contain minor amounts of aromatic mercaptans, such as thiocresols for example. However,

to a 50% yield of 400 F. end point gasoline, the amount of aromatic mercaptan sulfur in the gasoline is about 0.017 gram per 100 milliliters of gasoline.

As pointed out heretofore, catalytically cracked gasolines contain mercaptans, substantially all of which are aromatic in nature. We have now discovered a peculiar Phenomenon with respect to catalytically cracked gasolines containing these aromatic mercaptans. We have discovered that when oxygen is present, oxidation of oleflns and dioleflns in the gasoline is catalyzed by the presence of these aromatic mercaptans. The olefins and dioleflns are oxidized to peroxides, which in turn destroy the aromatic mercaptans and produce excessive gum in the hydrocarbon mixture.

The aromatic mercaptans which may be present are thiophenols, thiocresols, or thioxylenols.

These may all be considered as being mono. or

di-alkyl substituted thiophenols in which the alkyl group contains one to three carbon atoms. Specifically, the aromatic mercaptans which may be present are thiophenol, methyl thiophenol, dimethyl thiophenol, ethyl thiophenol, diethyl thiophenol, propyl thiophenol, and dipropyl thiophenol.

This phenomenon is fllustrated by the following table:

Table I .Efiect of mercaptans 1 and hydrocarbon composition on peromidation and air sweetening Inspections alter Air Initial Inspections Contact Stock Per. Cu Cu Dish ASTM Per. Cu ASTM No. No Gum l Gum I No. No. Gum

75 Diisobutylene. {25 Z Dimethyl butadiene} 0 0 4 1 0 0 1 i +n-Heptyl Mercaptan 0.6 29 6 0.2 0.3 26 3 +Th1ocresol 7.1 27 120 17 13. 7 0 34 neptane (base) 0 4 3 0 1 +n-Heiityl Mercaptan; 0 30 5 2 0 33 3 +p-Th ocresol.-. trace 28 7 3 trace 26 2 l Mercaptans added to theoretical copper number of 30. I Yule, J. A. C. and Wilson, 0. P. Jr. Ind. Eng. Chem. 23, 1254 (1931).

1 Francis, 0. K., Oil 6: Gas Journal 36, No. 11, 99

' Rureau of Mines, Reports of Investigations N0. 3152, November 1931. a

that is, 30 milligrams of mercaptan sulfur per 100 milliliters of gasoline. This figure corresponds to approximately 0.035% sulfur as aromatic mercaptans. Or again, when a mixed gas oil of about 0.8% sulfur is catalytically cracked noted from the table that the base stocks contained no peroxides and substantially no gum. both before and after air contact.

Stocks B and C consisted of the base stock A, plus sufiicient mercaptans to result in a theoretical copper number of 30. Similarly stocks E and F consisted of the base stock D, plus sufllcient mercaptans to produce a theoretical copper number of 30. Two mercaptans were added to each fuel base; normal heptyl mercaptan which is an aliphatic mercaptan, and parathiocresol which is an aromatic mercaptan. It will be observed from the table that addition of the aliphatic mercaptan to either fuel base did not appreciably increase the gum content of the blend. The peroxide number after contacting with air as contrasted to before contacting with air, was also not increased, indicating that no oxidation took place.

However, in noting the effect of adding the aromatic mercaptan, parathiocresol, to the oleilnic base stock A, it will be observed that this was effective in increasing the gum materially after contact with air, and alsoin increasing the peroxide number of the blend after air contact. This indicates oxidation of the dioleflns and olefins while the decrease of the copper nun. ber indicates the destruction of the aromatic mercaptan. The resulting gum formation of 34 is excessively high and would necessitate further acid treating or redistillation. In the case where ,parathiocresol was added to normal heptane, it will be noted that the addition of this aromatic mercaptan was not eifective in increasing the gum content or in changing the peroxide number of the stock.

These results, show that when an aliphatic mercaptan is added to either a paraflinic or olefinic fuel base, no oxidation of the mercaptan occurs and no gum formation results from air contact. on the other hand, when an aromatic mercaptan is added to an olefinic fuel base, oxidation of the mercaptan does occur with resulting gum formation. The fact that these results do not occur with paraflinic base fuel stock, shows 7 the importance of the hydrocarbon composition on these reactions.

These results are further substantiated by the following data secured with hydrocarbon mixtures boiling in the motor fuel boiling range derived from catalytically cracked gasolinei The table shows the results of tests on two low pressure distillates, mixtures A and B. It will be observed that after air contact the copper number of these mixtures had decreased materially while the peroxide number had increased.

These results show the oxidation of oleflns and diolefins in the fuel mixtures with the accompanying destruction of aromatic mercaptans.

The exact mechanism of the reactions involved in this phenomenon is not known. However, it is believed that olefins and diolefins in the presence of oxygen, catalyzed by the aromatic mercaptans,

form eroxides which destroy the aromatic mercaptans and form gum products. The result is a gasoline containing a relatively large amount of gum which necessitates further treatment of the product.

In accordance with our invention therefore we propose to remove these aromatic mercaptans, particularly from catalytically cracked gasolines, by treating these gasolines with caustic solution before the cracked stock is allowed to contact oxygen. We then propose to treat and handle the caustic containing the aromatic mercaptans so as to segregate the aromatic mercaptans.

Aromatic mercaptans may be readily and substantially completely removed by caustic washing, as indicated by the following table.

It will be observed from this table that washing the two samples with 10% of a 15 B. sodium hydroxide solution was effective in reducing the copper number of the samples treated to 2 or less, showing substantial removal of aromatic mercaptans. Due to the susceptibility of the mercaptans to oxidation, it is essential that this process be carried out in the complete absence of oxygen. If carried out in the absence of oxygen, the aromatic mercaptans are extracted by the caustic solution in a recoverable form; if oxygen is present, however, the mercaptans are converted to a form not recoverable with caustic.

The process of our invention may be readily understood by the following examples illustrating the same.

Example I Five gallons of a hydrocarbon mixture secured by catalytically cracking a high sulfur gas oil, of 620 F. mid-boiling point and 1.5% sulfur, at a 968 F. reactor temperature to give a 64% gasoline yield, was treated with 200 milliliters of 20 B. caustic solution in an atmosphere of nitrogen.

' The caustic extract was removed from the oil.

The extract was then acidified and extracted with ether. The ether. was evaporated and the residual oil stirred with caustic. A portion of the oil was insoluble in caustic and was extracted with ether. This material had a 13.55% sulfur content and was probably disulfide formed by air oxidation of mercaptans since some exposure to air had occurred during handling. The caustic solution was then acidified to a pH of 11. The oil which separated had a sulfur content of 1.97% and a definite cresol odor. The caustic was then acidified to 9 pH. The oil which was separated had a sulfur content of 4.38% and a definite cresol odor. The caustic was then acidified to a pH of 2 and a third fraction separated. The sulfur content of this fraction was 18.92%. This material had a disagreeableodor resembling that of pure. The following tabulation shows the fractions obtained:

layers, one layer consisting of the hydroxide solution containing the mercaptans, the other layer Table W P ta Mcercizntan ercen ge on ent Fraction 0! Crude Description urgent by On No.

Product falc. as

T iocresol) Per cent Per cent 10 Material insoluble in caustic 13.55 0 50 Material liberated at a pH ol approximately 11. 1. 97 0 Material liberated at pH of approximately 9.-.- 4'. 38 0 20 Material liberated at pH of approximately 2 i8. 92 70 Fraction 4, believed to be thiocresol, was identified as such by preparing the mercury derivative and analyzing it for carbon, hydrogen, sulfur, mercury, and molecular weight. All values obtained checked the theoretical for the mercury derivative of thiocresol as shown in the following tabulation:

Example II Another operation was run similar to that described with respect to Example I, except the sample was allowed to be in contact with air for 16 hours at room temperature. Under these conditions no yield of aromatic mercaptans was secured.

Example III Another experiment was made in which catalytic naphtha distillate was extracted with. aqueous caustic solution, being careful to exclude all oxygen. The caustic extract was acidified in stages, first to a pH of 9. The oil which separated was extracted with ether and was essentially phenolic in nature. The caustic extract was then further acidified to a pH of 2, whereupon another oily layer separated. This product was also recovered by extraction with ether and consisted principally of thiocresols. The yield of thiocresols obtained in this experiment was somewhat greater than was obtained in Example I.

The process of our invention comprises segregating aromatic mercaptans, as for example isomeric thiocresols, from cracked gasolines, particularly from catalytically cracked gasolines. The invention essentially comprises the initial step of contacting the cracked distillate boiling in the range from 100 to 400 F. with an alkali metal hydroxide solution capable of dissolving the mercaptans. Sodium hydroxide, and potassium hydroxide specifically are suitable for this purpose. It is essential that the gasoline be contacted with the hydroxide solution prior to having the gasoline come in contact with oxygen. The amount and strength of hydroxide solution used is not critical. The strength may vary from about 5 Be. to about 40 B. and the amount from about 5% to 20%. After contacting with hydroxide solution, the mixture of hydroxide solution and gasoline distillate will separate in two consisting. of the gasoline distillate. The hydroxide layer may be withdrawn and acidified to segregate the aliphatic mercaptans and phenols from the aromatic mercaptans. While hydrochloric acid was the acid used in the examples to acidify the hydroxide solution, any mineral acid is suitable. The aliphatic mercaptans and phenols are substantially completely released from the hydroxide solution on acidification to a pH of approximately 9. The aliphatic mercaptans and phenols separate as an oily layer which may be withdrawn. The remaining hydroxide solution may then be acidified to approximately 2 [pH to recover a maximum yield of aromatic mercaptans. The aromatic mercaptans also separate out as an oily layer which may be withdrawn. During the acidification of the hydroxide solution it is desirable to exclude oxygen, as some olefins may still be present in the hydroxide solution. The essence of our invention is the segregation of aromatic mercaptans from cracked gasolines in the absence of oxygen by contact with a hydroxide solution, followed by recovery of the aromatic mercaptans by suitable acidification of the hydroxide solution.

Our process may be modified somewhat. For

.example, the hydroxide solution, after removable from the oil, may be completely acidified rather than acidifying in the step-wise fashion as described. A suitable solvent may then be used to extract aliphatic mercaptans, phenols, and aromatic mercaptans from the hydroxide solution. For example, ether or a normally liquid light parafiinic hydrocarbon, such as pentane or hexane, or a liquid aromatic hydrocarbon, such as benzene, may be used as the solvent. The solvent may then be removed to produce a crude residual oil comprising the extracted constituents, that is, aliphatic mercaptans, phenols, and aromatic mercaptans. This crude residual oil may then be treated with caustic solution which will dissolve the above constituents without redissolving the small quantities of entrained oil products still present. The phenols and aliphatic mercaptans may then be separated from the aromatic mercaptans as described heretofore by partial acidification.

The process of our invention is not to be limited by any theory as to mode of operation, but only in and by the following claims in which it is desired to claim all novelty insofar as the prior art permits.

We claim:

1. The process for segregating and recovering aromatic mercaptans from gasolines containing aliphatic mercaptans, phenols, and aromatic mercaptans, which comprises treating'the gasoline in the absence of oxygen with an aqueous solution of an alkali metal hydroxide selected from the group consisting of sodium hydroxide and potassium hydroxide, withdrawing the hydroxide extract 7 from the gasoline, acidifying said.ext'.act to a pH of about 9 whereby an oily phase separates which phase comprises the aliphatic mercaptans and phenols, withdrawing said oily phase, acidifying the remaining hydroxide extract to a pH of about 2 whereby a second oily phase separates which phase comprises the aromatic mercaptans, and withdrawing said second oily phase.

2. The process according to claim 1 in which oxygen is excluded from the hydroxide solution.

3. The process according to claim 1 wherein, after acidifying the hydroxide extract respectively to a pH of about 9 and a pH of about 2, the hydroxide solution is extracted with ether.

4. The process of recovering aromatic mercaptans which comprises the steps of treating a catalytically cracked gasoline in the absence of oxygen with an aqueous solution of an alkali metal hydroxide selected from the group consisting of sodium hydroxide and potassium hydroxide, withdrawing the hydroxide extract from the gasoline, acidifying said extract to a pH of about 9 whereby an oily phase separates comprising the aliphatic mercaptans and phenols, withdrawing said oily phase, acidifying the remaining hydroxide extract to a pH of about 2 whereby a second oily phase separates comprising the aromatic mercaptans, and withdrawing said second oily phase.

JOHN K. MCCLENNAN.

BARN'EY R. STRICKLAND.

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

UNITED STATES PATENTS Number Name Date 1,704,246 Halloran Mar. 5, 1929 1,752,709 Stoll Apr. 1, 1930 2,013,203 Davis et a1 Sept. 3, 1935 2,053,752 Vobach et a1 Sept. 8, 1936 2,218,139 Benson et al. Oct. 15, 1940 2,222,170 Craig et a1 Nov. 19, 1940 2,245,317 Bannerot June 10, 1941 2,364,416 Ayers et al Dec. 5, 1944

Claims (1)

1. THE PROCESS FOR SEGREGATING AND RECOVERING AROMATIC MERCAPTANS FROM GASOLINES CONTAINING ALIPHATIC MERCAPTANS, PHENOIS, AND AROMATIC MERCAPTANS, WHICH COMPRISES TREATING THE GASOLINE IN THE ABSENCE OF OXYGEN WITH AN AQUEOUS SOLUTION OF AN ALKALI METAL HYDROXIDE SELECTED FROM THE GROUP CONSISTING OF SODIUM HYDROXIDE AND POTASSIUM HYDROXIDE, WITHDRAWING THE HYDROXIDE EXTRACT FROM THE GASOLINE, ACIDIFYING SAID EXTRACT TO A PH OF ABOUT 9 WHEREBY AN OILY PHASE SEPARATES WHICH PHASE COMPRISES THE ALIPHATIC MERCAPTANS AND PHENOIS, WITHDRAWING SAID OILY PHASE, ACIDIFYING THE REMAINING HYDROXIDE EXTRACT TO A PH OF ABOUT 2 WHEREBY A SECOND OILY PHASE SEPARATES WHICH PHASE COMPRISES THE AROMATIC MERCAPTANS, AND WITHDRAWING SAID SECOND OILY PHASE.