Cyclic Sulfides in a Petroleum Distillate RUSSELL H. BROWN AND SEYMOUR MEYERSON Research Department, Standard Oil Co. (Indiana), Whiting, Ind. Certain high-sulfur petroleum distillates have a distinctive, unpleasant odor even when freed of mercaptans. Although this odor can readily be removed by treatment with sulfuric acid, it was of interest to determine the nature of the compounds responsible. The offensive components, about 0.1 o/a of the untreated distillate, were concentrated by mercuric chloride treatment of the oil obtained by dilution of the spent sulfuric acid. Qualitative analytical tests, physical properties, and elementary analysis-coupled with molecular weight and the absence
T
HE increased production of high-sulfur petroleum emphasizes the need for greater knowledge of the sulfur compounds present in these “sour” crude oils. Distillates derived from certain sour crudes, even when freed of mercaptans (thiols), have a pronounced and offensive odor which is eliminated by treatment with sulfuric acid. The small volume of oil obtained by dilution of t h e sulfuric acid extract with water is a concentrate of t h e malodorous components and has a high sulfur content. These facts suggest that sulfur compounds present in small amounts are responsible for the offensive odor. The sulfur compounds in low-boiling distillates have been extensively studied, and individual sulfur compounds of four classes have been identified. ,Mercaptans and t h e disulfides to which they oxidize are familiar constituents of virgin naphthas, but they are not responsible for the characteristic odor of high-sulfur petroleum because the odor persists after removal of these components. Dialkyl sulfides and their cyclic analogs, the thiacycloalkanes, have also been identified in naphthas from sour crude oils. The dialkyl sulfides of higher molecular weight have odors described as similar to that of ether, whereas the odors of the corresponding thiacycloalkanes are offensive (14). Thiophenes do not appear to be present in virgin distillates (8). These observations suggest that cyclic sulfides are responsible for the persistent odor of mercaptan-free distillates from high-sulfur crude oil. Little has been added t o the information on the nature of the sulfur compounds in higher-boiling virgin distillates since the pioneering work of Mabery (6) 45 years ago. From a Canadian petroleum he obtained a series of sulfides, “hexylthiophane” through “octadecylthiophane,” which he considered cyclic in structure. Similar compounds have recently been reported (8) in a Russian petroleum. The structures of these compounds can only be surmised from analogy to the simpler cyclic sulfides of proved structure isolated from naphthas. Thiacyclopentane and thiacyclohexane were found in an Iranian petroleum ( I S ) ; thiacyclopentane and its 2-methyl and 3-methyl derivatives were found in fractions of petroleum from Mexico (1,2, 12) and in a virgin gasoline from California ( I O ) . In the present work, mass-spectrometric analysis and Raney nickel desulfurization facilitated the study of the sulfur compounds in a high-sulfur distillate. Mass-spectrometric examination of the sulfur compounds made possible the determination of precise molecular weights and reduced the number of possible structures, Similar examination of the hydrocarbons produced by Raney nickel desulfurization ( 7 ) of the mixture provided additional information on the structures of the original sulfur compounds. 2620
of double bonds-indicate that the concentrate is a mixture of saturated cyclic sulfides with five- and six-membered rings. Mass-spectrometric analysis of narrow fractions obtained by distillation showed clearly the presence of mono-, di-, and tricyclic sulfides. A hydrocarbon mixture obtained by desulfurization consisted of the three classes of saturated hydrocarbons expected from the proposed three types of thiacycloalkanes. These findings add to our rather limited knowledge of the nature of the sulfur compounds present in certain distillate fuels.
INVESTIGATIONS The mataria1 selected for stud3 was the 165” to 280” C. fraction of a high-sulfur virgin distillate of West Texas origin. The compounds responsible for the characteristic odor of the high-sulfur virgin distillate were isolated from the sulfuric acid with which the distillate had been treated and directlv from untreated distillate. Selected cuts obtained by fractional distillation of the concentrate and the hydrocarbon mixture obtained by desulfurization were analyzed by the mass spectrometer. Isolation of Malodorous Components. The acid sludge formed in commercial treatment with sulfuric acid provided a convenient source of the compounds responsible for the odor of the untreated distillate. Upon dilution with an equal volume of water, three layers were formed. The dark, viscous lower layer and the aqueous middle layer were discarded. The oil layer was washed with aqueous sodium hydroxide solution and was separated into two parts by treatment with concentrated aqueous mercuric chloride solution. About 40y0 of the oil obtained by dilution of the spent acid formed a pastelike complex with the mercury salt. The portion of the oil that failed to react with mercuric chloride had a bland, inoffensive odor; most of the sulfur in this oil was present as disulfides. The malodorous compounds were recovered from the mercuric chloride complex by suspending the paste in methanol and saturating the suspension with hydrogen sulfide. llIercuric sulfide was removed by filtration, the methanol solution was diluted with water, and the oil that separated was taken up in petroleum ether. The resulting solution was washed with aqueous sodium hydroxide. The solvent was removed by evaporation, and the odorous portion of the high-sulfur distillate was obtained in a concentrated form. Further concentration resulted from retreatment of this product with mercuric chloride and recovery from the complex formed. When the product isolated from the mercuric chloride complex was added back to the acid-treated distillate, the original, distinctive odor of the untreated oil was restored. The physical properties and elemental analysis of the concentrate obtained are given in Table I. The odorous components were also isolated by mercuric chloride treatment of the distillate. A 1-liter sample of the mercaptan-free oil was stirred for 2 hours a t 20’ C. with 500 ml. of saturated aqueous mercuric chloride solution. An oil- and waterinsoluble mercuric chloride complex separated, and the characteristic odor of the distillate was removed. The concentrate recovered from the mercuric chloride complex weighed 0.97 gram, equivalent to about 0.1% of the virgin distillate. The physical
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 44, No. 11
-PETROLEUM-COMPOSITION Table I.
Physical Properties and Elemental Analysis of Odor Concentrates From Spent Acid
From Distillate
0.927 1.4886 170
0,927 1.4890 174
Specific gravity, 2O0 C . Refractive index, ngo Molecular weight I3
Oxygen Hydrogen-to-carbon ratio
.... 1.87
0.1 1.96
sample was ermitted t o vaporize at room temperature into the expansion clamber until the pressure was no longer increasing. The maw spectrum was then obtained in the conventional manner. I n Table I V are listed the peak heights obtained a t specific masses above 90 in the spectra of the four fractions of t h e extract. Table V lists the peak heights obtained at specific masses above 90 in the mass spectrum of the desulfurized material. Minor peaks, including those due to isotopic effects, have been omitted. Qualitative conclusions only can be drawn from the mass spectra of liquid samples handled in this manner.
Table IV. properties and elemental analysis of the concentrate are included in Table I. The concentrate obtained directly from the distillate had the same odor a s that obtained from the spent sulfuric acid. Refractive index, specific gravity, and elemental analysis, as well as infrared and mass-spectrometric analysis, demonstrate the similarity of the two concentrates, All subsequent work was carried Q U t on t h a t obtained from spent acid. To gain additional information about the chemical nature of the concentrate, a number of simple qualitative analytical tests were made. The results of these tests are summarized in Table 11. Table 11.
Summary of Chemical Properties of Concentrate Insoluble in dilute acids and bases Soluble without structural change in sulfuric acid Strongly adsorbed by silica gel ( 4 ) Forms oil- and water-insoluble complex with mercuric chloride Forms water-soluble sulfonium salts Highly refractory toward desulfurization by sodium Reacts vigorously with bromine with evolution of hydrogen bromide Mercaptan-free; no lead sulfide formation on treatment with sodium plumbite and sulfur
d e 186 184 182 172 170 168 158 157 156 155 144 143 142 141 130 129 128 127 115 113 101 95 93 91
Partial Mass Spectra of Fractions of Concentrate
Fraction 4
Peak Height Fraction Fraction 7
11
.. ..
.. ..
.. .. ..
0.9
3.9 2.0
5.5
19.1 17.3 3.8 1.7 14.1 21.0 15.2 3.5 7.2 57.8 1.2 3.5 69.0 8.0 50.0 21.6 4.1 3.0
11.1 3.9 2.9 1.2 3.0 11.5 1.0 2.6 3.2 24.4 5.1 4.8 35.2 4.5
..
..
..
.. .. ..
27.7 12.9
..
..
8.7 29.7
.. ..
63.8 1.5 23.7 11.0 0.6 1.8
.. .. ..
.. ..
18.2 10.5 2.1 1.3
Fraction 20 2.0 6,O 3 5 4.0 7.8 3.0 2.0 4.7 3.0 6.0 2.6 12.2 3.2 9.0 3.5 16.4 5.0 8.3 24.4 12.3 21.5 16.0 10.9
Ion Species CiiHzzS CiiHzaS +a CiiHisS CioHzoS +a CioHuS+a CioHiaS +a CgHiaS +a COHi?S+ C9HiaSCa CsHinS CsHiaS CaHiaS CsHi4S +a CsHiaS+ C7HirS +a CiHiaS CiHizS +a CiHiiS CnHiiS++ CsHsS CsHoSI C7H11' +
+
+
+
a Probable molecule ion.
DISCUSSION Mass-Spectrometric Examination. A 100-gram sample of the concentrate was separated by distillation at reduced pressure into 30 fractions of equal volume in an all-glass concentric-tube column (9) at 50 to 1 reflux ratio. Boiling point and refractive index data indicated t h a t the concentrate contained the large number of homologs expected from a petroleum product boiling from 165' to 280" C . Four fractions were chosen for massspectrometric analysis; selected properties are given in Table 111.
Table 111.
Properties and Analysis of Fractions of Concentrate
Fraction
Boiling Point, OC., Mm.
4 7 11 20
77(20) 87(20) 100 (20) 105(10)
Elemental Analysis, Weight % Specific Refractive Gravity, Index, Hydro20° C. naDo Carbon gen Sulfur 0.910
0 911
0.922 0.951
1.4801 1.4831 1.4896 1.5011
68 10 69.15 70.58 70.10
11.40 11.70 12.15 11.14
20.3 19.2 17.9 17.4
A 10-gram sample of the concentrate was desulfurized with Raney nickel. The sample was added to 50 ml. of absolute ethyl alcohol and refluxed for 6 hours with 30 grams of Raney nickel catalyst prepared at 50' C. in such a way t h a t it contained large amounts of hydrogen (7). The reaction mixture was cooled t o 0" C. and diluted with 50 ml. of water. The hydrocarbon layer, after separation and washing with cold water t o remove traces of alcohol, weighed 6.5 grams and contained 1.2% sulfur. Mass-spectrometric examination of the four fractions and of the desulfurized concentrate was made with a Consolidated Model 21-102 instrument. Several circuit modifications ( 3 ) were incorporated t o facilitate work with high-molecular-weight compounds. The sample was placed in a test tube equipped with a standard taper connected t o the metal inlet system. After noncondensables had been pumped out of the space above the liquid, the
November 1952
The sulfur content and the low nitrogen and oxygen contents, coupled with an average molecular weight of about 170, indicate that the concentrate is composed largely of compounds having one atom of sulfur per molecule. The absence of mercaptans is indicated by the lack of lead sulfide separation when the oil is treated with sodium plumbite solution and sulfur. Unlike the concentrate, dialkyl sulfides of high molecular weight have bland odors and, at 0" C., undergo a mild reaction with bromine in which no hydrogen bromide is produced. The specific gravity of typical dialkyl sulfides in the boiling range of the odor concentrate is about 0.84, while t h a t of the concentrate is about 0.93. The hydrogen-to-carbon atomic ratio of dialkyl sulfides is always above 2.0-at a molecular weight of 174 i t is 2.2-whereas t h a t for the concentrate is less than 2.0. The presence of alkylalkenyl sulfides could explain this low hydrogen-to-carbon ratio and could also account for an unpleasant odor. However, infrared analysis fails to indicate the required double bonds; furthermore, olefinic double bonds are not likely to survive treatment with sulfuric acid. Thus, neither dialkyl nor alkylalkenyl sulfides offer a satisfactory explanation of the properties of the odor concentrate. A cyclic sulfide structure can readily account for the properties summarized in Tables I and 11. T h e presence in virgin petroleum products of sulfides having three- or four-membered rings has never been shown. T h e occurrence in petroleum of cyclic sulfides having rings of more than six members is also unlikely. A saturated five- or six-membered cyclic structure is in complete accord with all of the properties of the concentrate, and compounds of this type have been identified in light distillates from several crude oils. T h e basic procedures followed in interpreting the massspectrometric data presented in Tables I V and V have bern de-
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Table V.
Partial Mass Spectrum of Desulfurized Concentrate
d e
Peak Height
168 166 156 154 152 142 140 139 138 137 128 127 126 125 124 123 114 113 112 111 110 109 100 99 98 97 96
0 01 7 0 2 4 3 1 7 1.4 4.8 4.3 1.7 3.3 3.8 3.6 7.6 19.7 4.4 10.8 4.7 13.3 16.7 47.8 12.8 19.2 3.5 2.8 40.3 76.5 24.3 29.8
Q5 a
Ion Species C12H24+a CnHzz +5
CIlH24+'
CiiHzz +4
CiiH20 +'
Probable molecule ion.
scribed by Rock (11). The procedure t h a t proved most fruitful was the inspection of mass numbers and mass intervals to identify ion species. A knowledge of the chemical history and behavior of the samples narrowed the field of possible components. Thus, the indicated absence of olefinic bonds and of rings containing fewer than five and more than six atoms proved helpful. When hydrocarbons and hydrocarbon derivatives are subjected t o electron bombardment under the conditions that prevail in the ion source, heavier components may contribute to the observed peak heights a t the molecular weights of possible lighter components. Among the most probable ionization processes are those that involve the loss of integral alkyl radicals; thus, the mass spectrum of a compound of molecular weight X will generally show prominent peaks a t m/e values 15, 29, 43, etc., units less than X , as well as a t X and X minus 1. I n addition, the spectra of cyclic compounds frequently exhibit prominent peaks a t m/e values 28, 42, etc., units less than X , although not a t X minus 14. Heavier cyclic components in a wide-boiling mixture may therefore contribute to peaks at the molecular weights of lighter members of the same homologous series, so that lighter components cannot always be identified as certainly as heavier ones. No such effects complicate the detection of members of two different homologous series whose empirical formulas differ by two or more hydrogen atoms. Those ion species in Tables I V and V t h a t are probable molecule ions, rather than ionized molecular fragments, are indicated. The data presented in Table IV reveal t h a t the four fractions of the concentrate contain three series of sulfur compounds. The molecule ions resulting from the two heaviest members of each series in any one sample can be identified with confidence. The members of t h e first series constitute all of fraction 4 and part of fractions 7, 11, and 20. These compounds have molecular weights of 186, 172, 158, 144, and 130, and t h e empirical formula C,H2,S. All but t h e compound of molecular weight 130 are present beyond doubt. Inasmuch as olefinic bonds are absent these compounds must contain one saturated ring and be either alkylcycloalkyl sulfides or thiacycloalkanes. Members of t h e second series constitute the remainder of fractions 7 and 11 and part of fraction 20. These compounds have molecular weights of 184, 170, 156, 142, and 128, and t h e empirical formula C,H2,-2S. They must contain two rings. T h e presence of the four highest molecular weight members of t h e
2622
series is certain. B cycloalkylthiacycloalkane structure could explain the Cn, Cl0, and CScompounds but not the CSor C? compounds. A condensed-ring structure accounts for all five molecular lveights. Evidence for t h e presence in a Middle East gas oil of sulfur compounds a ith tlyo homoc>clic rings has been obtained by Hoog ( 5 ) . Possible structures of the C8 members of this seriep are :
Two members of a third series appear in fraction 20 and have niolecular weights of 182 and 168, which correspond to the empirical formula C,Hz,-qS n-ith n equal to 11 and 10. These compounds must contain three rings. Such a compound with only ten or eleven carbon atoms must have a condensed-ring structure in which the sulfur atom is incorporated in one of the rings. The CIOcompound can be made up only of three condensed five-membered rings The Cn compound may be a methyl O sulfide or have a skeleton containing derivative of the C ~ cyclic one six-membered ring and t n o five-membered rings. Possible structures for the C ~member O of this seiies are:
;\lass-spectrometric data on the desulfurized concentrate pio.vide further information on the nature of the first sene? of sulfur compounds and confirm the structures proposed for the second and third series. The data in Table V reveal the presence of three series of hydrocarbons: acyclic alkanes of molecular weights 156, 142, etc.; monocyclic alkanes of molecular neights 168, 154, 140, etc.; and dicjclic alkanes of molecular aeights 166, 152, 138, etc. The alkanes of t h e first seiies are the normally expected products of Raney nickel desulfurization of alkylthiacycloalkanes containing the same number of carbon atoms. If the first series of sulfur compounds were alk) Icycloalkyl sulfides, alkanes containing up to 11 carbon atoms viould have to represent side-chain fragments of sulfides containing a t least 16 carbon atoms, the presence of which is ruled out by the boiling range of the original distillate. Analogy 11 ith the thiacycloalkane structures of t h e second and third series of sulfur compounds supports the assignment of thiacyclopentane and thiacyclohexane structures to the members of t h e first seiies. Possible structures of the CSmembers of this series are:
The monocycloalkanes and dicycloalkanes comprising the second and third series of hj-drocarbons are the normally expected products of Raney nickel desulfurization of saturated dicyclic and tricyclic sulfides, respectively, each containing a nuclear sulfur atom. The presence of condensed-ring compounds in the higherboiling fractions is in keeping with the observed marked increase in specific gravity with increasing boiling point The lack of evidence of the presence of tricyclic sulfides containing fewer than ten carbon atoms tends to confirm t h e validity of t h e assumption t h a t three- and four-membered ring structures are absent and need not be considered. Although dialkyl sulfides may have been present in small quantities, no indication of their presence was found in the four
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 44, No. 11
PETROLEUM-COMPOSITION fractions examined in t h e mass spectrometer. This fact is in keeping with t h e work of Haresnape, Fidler, and Lowry (4), who found t h a t t h e sulfides of a 118’ C. petroleum fraction were 85% dialkyl and 15% cyclic, while those of a 137”C. fraction from t h e same source were 16% dialkyl and 85% cyclic. LITERATURE CITED (1) Friedman, W., and Canesco, C., PetroEeum Refiner, 22, 1 (1934). (2) Friedman, W., and Rodriguez, C., Ibid., 25, 53 (1946). (3) Grubb, H. M., and Meyerson, S.,“Electrical Alterations to the CEC Type 21-102 Mass Spectrometer,” Consolidated Engineering Corp., Mass Spectrometer Group Report No. 76 (1950). (4) Haresnape, D., Fidler, F. A., and Lowry, R. A., IND. ENG. CHEM.,41,2691 (1949). (5) Hoop, H., Rec. trav. chim. Pays-Bas, 69, 1289 (1950).
(6) Mabery, C. F., and Quayle, W. O., Am. Chem. J., 35,404 (1906). (7) Mozingo, R . , Wolf, D. E., Harris, S.A., and Folkers, K., J. Am. Chem. SOC.,65,1013 (1943). (8) Nametkin, S.S., and Sosnina, A. S., J . Inst. Petroleum, 36, 74A
(1950). ENG.CHEM.,ANAL.ED., (9) Naragon, E. A., and Lewis, C. J., IND. 18,448 (1946). (10) Polly, 0. L., Byrnes, A. C., and Bradley, W. E., IND.ENQ. CHEM.,34,755 (1942). (11) Rock, S. M., Anal. Chem., 23, 261 (1951). (12) Teutsch, I., Petroleum Z., 30, No. 20, 1 (1934). (13) Thierry, E. H., J . Chem. SOC.1925,2756. (14) Von Braun, J., and Trumpler, A., Ber., 43, 545 (1910).
RECEIVED for review April 14, 19.52. ACCEPTEDAugust 7, 1952 Presented before the Division of Petroleum Chemistry, Symposium on Nonhydrocarbon Constituents of Petroleum, at the 121st Meeting of the AMERICAN CHEMICAL SOCIETY, Milwaukee, Wis.
of Molecular Structure and Properties Lubricating Oil Components JAMES C. LILLARD, WILLIAM C. JONES, JR., AND JAMES A. ANDERSON, JR. Humble Oil & Refining Co., Baytown, Tex. RESENT methods of re-
structed of stainless steel tubT h e effects of lube oil refining methods on quality are ing inch in inside diameter fining lubricating oils based primarily on empirical correlations of data from from petroleum have and 52 feet in length. T h e various routine physical properties measurements. A column as constructed is been established t o a large exfundamental approach to the refining problems requires a similar to those which have tent upon empirical relationknowledge of molecular structure of the lube oils, but such ships, because knowledge of been employed by the Nainformation has been largely lacking in the past. In the the composition of the oils is tional Bureau of Standards. present work, which is part of a long-range program of relimited and the influence of search along these lines, several wax-free lube oil samples I n a typical run on this molecular structure upon covering a wide boiling range and derived from different equipment a 600- t o 625-1111. lubricant quality characteriscrudes have been separated into concentrates of various lube sample was mixed with tics, such as viscosity index, compound types by silica gel percolation. Narrow fracan equal volume of n-heptane is not completely defined. Intions of the percolates were characterized by measurements and placed in one of the blowformation of this type would, cases used for feed and solutilizing refractive index, carbon-hydrogen ratio, vishowever, be of considerable cosity, and ultraviolet and infrared spectra. These data vent introduction. This mixuse in the development or indicate the lubes to be composed primarily of five chart u r e was.charged, u n d e r modification of lube refining acteristic classes, paraffin-naphthenes, condensed naphabout 25 pounds per square processes and in adjusting thenes, aromatic naphthenes, naphthalenes, and higher inch nitrogen pressure, t o the operations for optimum utiliaromatics. The techniques developed will be useful for top of the %-foot column, zation of refinery stocks The which was packed with about characterizing any lube stocks and have been shown by present work is part of a 3500 grams of 28- t o 200example to be useful for following the solvent action of long-range program of rephenol extraction. mesh Davison silica gel. s e a r c h a l o n g t h e s e lines Sample return lines were prowhich has been encouraged vided whereby the charge by recent developments in separation techniques, such as silica lines could be displaced up t o the head of the column and a readgel percolation, and b y the introduction of spectrometric methods ing takenon the blowcase before actually introducing charge to the for typing compound structures. The portion of the investigasilica gel bed. The rate of flow of the charge down the column tion reported here includes detailed composition studies of a raw was maintained a t about 4 feet per hour by adjustment of nitrogen and a solvent refined medium motor oil cut and presents prepressure. As the oil moved down the column, i t was necessary t o liminary data illustrating the application of developed characteriincrease the pressure gradually to a range of 135 t o 500 pounds, zation techniques to study the changes in composition of lubridepending on the viscosity of the charge stock and the amount cants upon solvent refining. of adsorption taking place. The lube charge was discontinued when the desired amount of oil-n-heptane mixture had entered the SILICA GEL PERCOLATION column. The addition of n-heptane as a developer was started The study of the molecular structure and properties of lubriand continued until the issuing percolate had a refractive index cating oil components had a s its first prerequisite the segregation not differing from the refractive index of pure n-heptane by more of the components into groups of common category. There were than about 5 units in the fourth decimal place. Time requirenumerous indications in the literature a t the start of the work ments prohibited further elutriation. From 6 to 10 liters of n(8-10) t h a t silica gel percolation might be a n effective tool for heptane were usually required to reach this condition. Percolate separation, and, accordingly, a column for this purpose was conwas segregated into small samples or fractions; since the first November 1952
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