Improved methods for the selective isolation of the sulfide and

Energy & Fuels 1989,3,449-454

449

Improved Methods for the Selective Isolation of the Sulfide and Thiophenic Classes of Compounds from Petroleum J. D. Payzant, T. W. Mojelsky, and 0. P. Strausz* Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2 Received November 22, 1988. Revised Manuscript Received March 6,1989

Improved methods are described for the isolation of the sulfide and thiophenic classes of compounds from petroleum. These methods are based on the ability to selectively oxidize the sulfur atom in the two different chemical environments and the large difference in polarity between the oxidized and unoxidized forms. The reagent tetrabutylammonium periodate in toluene/methanol will oxidize the sulfides to highly polar sulfoxides in high yield without affecting the thiophenic compounds. A subsequent chromatographic step permits the isolation of a polar fraction containing the sulfoxides. Reduction of this polar fraction regenerates the sulfides, which are isolated by chromatography. The sulfide content was found to vary from 2.6% to 16% of the heavy oils and bitumens of Alberta. A second oxidation of the remaining fraction, after removal of the sulfides, using m-chloroperbenzoic acid under anhydrous neutral conditions converts the thiophenes into their corresponding polar sulfones, which are isolated from the mixture by a subsequent chromatographic step. Reduction regenerates the thiophenic compounds, which are purified again by chromatography. The content of the thiophenic compounds was found to vary from 0.3% to 7.6% of the various conventional oils, heavy oils, and bitumens examined. Application of the separation scheme to a variety of petroleums reveals that the relative abundances of the isomeric monomethyldibenzothiophenesvary systematically with the thermodynamically unfavored 1-methyl isomer declining in abundance with depth of burial of the petroleum.

Introduction The production of liquid transportation fuels from petroleum usually requires the reduction of the sulfur content to low levels. In order to assist in the development of suitable catalysts for the removal of sulfur, a large number of sulfur compounds have been isolated and identified from petroleum.'-' Sulfur may occur in petroleum as mercaptans, disulfides, sulfides, and thiophenic compounds. Mercaptans and disulfides are absent from the bitumens and heavy oils of northern Alberta, and the sulfur is present as cyclic sulfides and thiophenic compounds. Thus the detailed characterization of the sulfur compounds in these petroleums requires a method for the selective isolation of the sulfide and thiophenic classes of compounds. In the past, many of the methods for isolating sulfur compounds from petroleum have been based on distillation and/or mercuric chloride adduct These procedures are tedious and applicable only to the isolation of individual compounds. We desired methods that would isolate the various classes of sulfur-containing compounds from petroleum in high yield and purity. Previously, we described a method for the isolation of sulfides from petroleum based on the selective oxidation of the sulfides to their corresponding sulfoxides using photochemically generated singlet oxygen and applied this method to a number of petroleumsa8 The procedure takes advantage of the widely differing polarity of sulfides and sulfoxides and the ease by which they may be separated by chromatography on silica gel. Reduction of the isolated sulfoxides regenerates the sulfides, which are purified by a subsequent chromatographic step. However, when the sulfur is in a five-membered ring, the photooxidation may lead to products other than ~ulfoxides.~We therefore investigated the action of other oxidizing reagents and *Author to whom all correspondence should be addressed.

0881-06 2418912503-0449$01.50/0

found that tetrabutylammonium periodate fulfilled all the necessary criteria. A number of methods have been reported for the isolation of thiophenic compounds from petroleums and other fossil fuels, including chromatography on silver nitratelo or palladium chloride" impregnated silica gel. A method for the isolation of thiophenic compounds involving the oxidation to their corresponding polar sulfones followed by chromatography, reduction back to the corresponding thiophenic compounds, and chromatographic isolation of the low-polarity thiophenic compounds has been described.12 This procedure, similar in principle to the method described above for the isolation of sulfides, employed 30% H202/aceticacid/benzene (16-h reflux) as the oxidizing conditions. Unfortunately, under these conditions further oxidation of the aromatic rings often takes place. As a consequence, the reduction of the sulfones fails to regenerate the original compounds and the recoveries of some thiophenic compounds were subsequently reported ~

~

~~

(1) Smith, H. M. Bull.-U.S. Bur. Mines 1968,642, 1-136. (2) Rall, H. T.;Thompson, C. J.; Coleman, H. J.; Hopkins, R. L. Bull.-U.S. Bur. Mines 1972, 659, 1-187. (3) Gal'pern, G. C. Int. J. Sulfur Chem. 1971, B6, 115-130. (4) Gal'pern, G. C. Russ. Chem. Rev. (Engl. Transl.) 1976,45,701-720. (5) Gal'Dern. G. C. The Chemistrv of Heterocvclic Comoounds. Thiobheneanaits Derivatives; Gonowiiz, S.,Ed.; J. Wiley & Sob: New York, 1985; pp 325-351. (6) Orr, W. L. Oil Sand and Oil Shale Chemistry; Strausz, 0. P., Lown, E. M., Eds.; Verlag Chemie: Weinheim, FRG,1978; pp 223-243. (7) Orr, W. L. Org. Geochem. 1986,10,499-516. ( 8 ) Payzant, J. D.; Montgomery, D. S.; Strausz, 0. P. Org. Geochem. 1986, 9,357-369. (9) Takata, T.;Ishibashi, K.; Ando, W. Tetrahedron Lett. 1985, 26, 4609-46 12. (10) Joyce, W. F.; Uden, P. C. Anal. Chem. 1983,55, 540-543. (11) Nishioka, M.; Campbell, R. M.; Lee, M. L.; Castle, R. N. Fuel 1986, 65, 27C-273. (12) Willey, C.; Iwao, M.; Castle, R. N.; Lee, M. L. Anal. Chem. 1981, 53, 400-407.

0 1989 American Chemical Society

Payzant et al.

450 Energy & Fuels, Vol. 3, No. 4, 1989

to be very 10w.13J4 The oxidation of thiophenic compounds to the corresponding sulfones is often complicated by side reactions resulting from the loss of aromaticity of the thiophene ring.15 Many reagents and conditions have been used for the generation of sulfones by o~idation;'~,'' however, m-chloroperbenzoicacid under anhydrous neutral conditions has been reported to be a particularly mild reagent for the oxidation of thiophenes.ls We have found that when this reagent was used, the undesired oxidation of the aromatic rings is reduced, the time required for the procedure is shortened, and the yield of thiophenic compounds is increased. Recently a number of different terpenoid sulfides possessing an isoprenoid carbon framework have been isolated and identified from the maltene fraction of Athabasca and various sulfides, thiophenes, and benzo[b]thiophenes possessing a linear carbon framework from the pyrolysis oil of Athabasca a ~ p h a l t e n e . ~ In~addition, a variety of sulfides and thiophenes possessing isoprenoid and linear carbon frameworks have been identified in various oils and sediment^.^^-^^ The terpenoid sulfides turned out to be sensitive indicators of the geological history of the deposit. The distribution by carbon number of the bicyclic terpenoid sulfides shows pronounced variations as a function of the depth of burial (temperature) of an oil and the degree of water washing of a tar sand formation, and thus this parameter often exhibits distribution patterns characteristic of bitumen from different layers within a given deposit.s The distribution by carbon number of the bicyclic terpenoid sulfides is influenced by exposure to steam under conditions designed to stimulate in situ steam recovery and thus may act as an index of the thermal stress a produced bitumen has experienced during the recovery operation. Some thiophenic compounds are also generated under these conditions. In addition the pyrolysis of Athabasca asphaltene releases an abundance of sulfur-containing compounds, principally a variety of thiophenic compounds and sulfides. Examination of the detailed structures of (13)Kong, R. C.; Lee, M. L.; Iwao, M.; Tominaga, Y.; Pratap, R.; Thompson, R. D.; Castle, R. N. Fuel 1984,63, 702-708. (14)Nishioka, M.; Lee, M. L.; Castle, R. N. Fuel 1986,65, 390-396. (15)Raasch, M. S. The Chemistry of Heterocyclic Compounds. Thiophene and its Derivatives; Gonowitz, S., Ed.; J. Wiley & Sons: New York, 1985;pp 571-627. (16)Schank, K.The Chemistry of Sulphones and Sulphoxides; Patai, S., Rappoport, Z., Stirling, C., Eds.; J. Wiley & Sons: New York, 1988; pp 165-232. (17)Block, E. Reactions of Organosulfur Compounds; Academic Press: New York, 1978;p 16. (18)Mukherjee, D.; Dunn, L. C.; Houk, K. N. J.Am. Chem. Soc. 1979, 101, 251-252. (19)Payzant, J. D.; Montgomery, D. S.; Strausz, 0. P. Tetrahedron Lett. 1983,24, 651-654. (20)Payzant, J. D.; Cyr, T. D.; Montgomery, D. S.; Strausz, 0. P. Tetrahedron Lett. 1985,26, 4175-4178. (21)Payzant, J. D.; Cyr, T. D.; Montgomery, D. S.; Strausz, 0. P. Geochemical Biomarkers; Yen, T. F., Moldowan, J. M., Eds.; Harwood Academic: New York. 1988:DD 133-147. (22)C p , T.D.; Pay&, J..D.; Montgomery, D. S.; Strausz, 0. P. Org. Geochem. 1986,9,139-143. (23)Pavzant, J. D.; Montgomery, - D. S.; Strausz, 0. P. AOSTRA J. Res. 1988,-4,117-131. (24)Brassell, S. C.; Lewis, C. A.; de Leeuw, J. W.; de Lange, F.; Sinninghe Damst6, J. S. Tetrahedron Lett. 1984,25, 1183-1186. (25)Brassell, S.C.; Lewis, C. A.; de Leeuw, J. W.; de Lange, F.; Sinninghe Damst6, J. S. Nature 1986,320, 160-162. (26)Sinninghe Damst6, J. S.; ten Haven, H. L.; de Leeuw, J. W.; Schenck, P. A. Org. Geochem. 1986,10, 791-805. (27)Sinninghe Damst6, J. S.; de Leeuw, J. W.; Kock-van Dalan, A. C.; de Zeeuw, M. A.; de Lange, F.; Rijpstza, W. I. C.; Schenck, P. A. Geochim. Cosmochim. Acta 1987,51, 2369-2391. (28)de Leeuw, J. W. Organic Marine Geochemistry;Sohn, M. L., Ed.; American Chemical Society: Washington DC, 1986;pp 33-61.

1

Maltene

1

(n-C4HghN104 Chromatography Toluene

20% Methanolitoluene

6 Unoxidized

MCPBA Chromatography

Toluene

Polars 8

Chromatography

20% Methanolltoluene

1

Aromatics

P Sulfones

LiAlHi Chromatography Toluene Thiophenic ComDounds

r-l Residue

Figure 1. Flow diagram for the separation of the sulfide and thiophenic classes of compounds from the maltene fraction of petroleum. The details of the separation are given in the Experimental Section.

these pyrolytic fragments suggests that they are derived by the thermal decomposition of a polymer possessing a linear carbon framework.23 In order to characterize the distribution by carbon number and the structures of the various sulfides and thiophenic compounds, it is necessary to isolate them from the petroleum for further study. In this paper, we describe our methodology for the isolation of these compound classes, based on the ability to selectively oxidize the sulfur atom in the sulfide or thiophenic class of compounds.

Experimental Section General Data. All solvents were reagent grade and mere distilled in an all-glass and Teflon apparatus prior to use except for ether, which was used as received. The solvents toluene, n-pentane, dioxane, and chloroform were distilled from CaH2. GC-FID Analysis. The fractions were examined by using an HP-5830A gas chromatograph (GC) employing hydrogen carrier gas, an injector with a split ratio of ca. 15:1, and a flame ionization detector (FID). The column used was J&W fused silica 30 m X 0.25 mm coated with 0.25-pm poly(5% phenylsiloxane-95% methylsiloxane) (DB-5). Samples were injected in the form of a toluene solution and the GC was temperatwe programmed from 75 to 310 OC at 4 OC/min. Oxidation of Sulfides with Tetrabutylammonium Periodate. The procedure is illustrated for Syncrude maltene. To a 100-mL round-bottom flask equipped with a reflux condenser and a magnetic stirring bar were added maltene (0.998 g), tetrabutylammonium periodate (0.15 g), methanol (5 mL), and toluene (25 mL). The mixture was stirred and refluxed for 30 min,after which it was cooled to room temperature and transferred to a separatory funnel with n-pentane (25 mL). The organic phase was extracted with water (3 X 40 mL), concentrated by using a rotary evaporator, and applied, by using a small volume of npentane, to a column of silica gel (40 g, equivalent to Merck 7734) prewashed with n-pentane. The column was eluted with n-pentane (50 mL) followed by toluene (200 mL). These fractions were

Energy & Fuels, Vol. 3, No. 4, 1989 451

Isolation of Sulfides and Thiophenes

T23

Table I. Results of Sulfide and Thiophenic Compound Determination for Heavy Oils and Bitumens of Alberta

Syncrude

620

%

%

depth, m

sample location 0 Syncrude Syncrude Pit 920 Bellshill 12-28-4112W4 Lake 670 Lloydmi- 16-3-401W3 nster 4-21-85558 Peace 18W5 River not ca. 500 Wolf Lake available

asphdtenes 17.0 e 13.6 20

thio% phenic sulfidesasb compdaSb 6.9 f 0.9e 3.1

6.4 f 0.5d

2.6

5.7

16

H o m e sulfides

5.5

7.6 T23

14

3.6

1

2.9

Wolf Lake

a As percent of the maltene. Errors are twice the standard deviation. cAverage of three determinations. dAverage of four determinations. e Not determined.

combined and concentrated with a rotary evaporator to yield the unoxidized material, which was used in the next stage for the isolation of the thiophenic compounds (Figure 1). The column was then eluted with 20% methanol/toluene (200 mL) to afford the polar sulfoxide fraction (Figure 1). Reduction of the Sulfoxides to Sulfides. The polar sulfoxide fraction above was concentrated in a 100-mL round-bottom flask equipped with a reflux condenser and a magnetic stirring bar. Lithium aluminum hydride (LiAlH4)(0.2 g) and dioxane (ca. 15 mL) were added and the mixture stirred and refluxed for 1 h. The reaction flask was cooled in ice-water and the excess LiAlH4 destroyed by the cautious addition of water (a few mL) followed by toluene(20 mL), n-pentane (30 mL), and 10% H$04 (30 mL). The resulting mixture was stirred a t room temperature for ca. 15 min, after which it was transferred to a separatory funnel. The layers were separated and the organic phase was extracted with 5% H$04 (1 X 30 mL) and water (2 X 30 mL). The organic phase was concentrated by using a rotary evaporator and applied, by using a small amount of 20% tolueneln-pentane, to a column of silica gel (20 g), prewashed with n-pentane. The column was then eluted with 20% tolueneln-pentane (100 mL) to afford, after solvent removal, the sulfides as an orange oil (0.0637 g, 6.4% of the maltene). The results of the analysis for sulfides of a variety of petroleums from Alberta are summarized in Table I, and the GC-FID traces for some sulfides are shown in Figure 2. Oxidation of the Thiophenic Compounds to Sulfones with m-Chloroperbenzoic Acid. In a dry 125-mL Erlenmeyer flask equipped with a magnetic stirring bar was placed m-chloroperbenzoic acid (1.5 g, S 8 5 % technicalgrade),powdered anhydrous sodium bicarbonate (2.5 g), and methylene chloride (40 mL). The suspension was stirred a t room temperature for 30 min to neutralize the m-chlorobenzoic acid present and to allow the mchloroperbenzoicacid to dissolve. The unoxidized fraction from the tetrabutylammoniumperiodate oxidation (Figure 1) was added with 10 mL of methylene chloride. The reaction mixture was stirred at room temperature for 30 min, after which a solution of Na2S203.5H20(3.0 g) in water (20 mL) was added in one portion, and the resulting mixture was stirred for an additional 15 min. The reaction mixture was then transferred to a separatory funnel with water (50 mL) and n-pentane (100 mL). The aqueous phase was withdrawn, and the organic phase was extracted with 5% NaOH (2 X 50 mL) and water (1 X 50 mL), concentrated by using a rotary evaporator, and applied to a column of silica gel (40 g) prewashed with n-pentane. The column was then eluted with toluene (150 mL) to give the saturate and aromatic compounds and subsequently with 20% methanol/toluene (200 mL) to give the polar fraction containing the sulfones (Figure 1). Reduction of the Sulfones to Thiophenic Compounds. The polar fraction from the m-chloroperbenzoic acid oxidation (see above and Figure 1) was placed in a 100-mLround-bottom flask equipped with a magnetic stirring bar and a reflux condenser. LiAlH4(ca. 0.3 g) was added, the reaction flask was chilled in an ice-water bath and dry ether (50 mL) was added cautiously via

i

Bellshill Lake

GC Time Direction Figure 2. GC-FID traces for several sulfide fractions from different Alberta petroleums. The peaks labeled BI3 and Bm correspond to the bicyclic terpenoid sulfides with 13 and 20 carbons, respectively. The peak labeled TB corresponds to the tetracyclic terpenoid sulfide with 23 carbons, and peaks due to the hopane sulfides are indicated a t the end of the traces. The clusters of peaks spaced one carbon apart on the Bellshill Lake trace correspond mainly to complex mixtures of isomeric monocyclic sulfides possessing a linear carbon framework. These sulfides have been removed by biodegradation from the upper two samples.

the reflux condenser. After the initial reaction had subsided, the reaction mixture was stirred and heated at reflux for 1 h, after which the reaction flask was cooled in an icewater bath and the excess LiA1H4was destroyed by the cautious addition of water (a few milliliters). The reaction mixture was allowed to come to room temperature, after which toluene (20 mL) and 5 % HzSO4 (20 mL) were added and the mixture stirred for ca. 15 min. The reaction mixture was transferred to a separatory funnel with toluene (20 mL) and water (20 mL). The aqueous layer was withdrawn and the organic phase washed with water (2 X 30 mL). The organic phase was concentrated with a rotary evaporator and applied to a column of silica gel (20 g) prewashed with n-pentane using a small amount of toluene. Elution with toluene (75 mL) and subsequent removal of the solvent using a rotary evaporator gave the thiophenic compounds (0.0615 g, 6.2% of the maltene). The results of the analysis for the thiophenic compounds in a variety of petroleums from Alberta are summarized in Table I, and some GC-FID traces are shown in Figure 3.

Results and Discussion Method for Separating the S u l f i d e s . T h e overall scheme for t h e separation of the sulfides and thiophenic compounds from the maltene is outlined in Figure 1. The method is based on the large difference in polarity between t h e high-polarity sulfoxides and the low-polarity sulfides and the ease with which they may be interconverted. Selective oxidation of t h e maltene fraction of petroleum

Payzant et al.

452 Energy & Fuels, Vol. 3, No. 4,1989 Syncrude

2 f l l

I

Peace River

.Wolf Lake

'~1,

Bellshill Lake

GC Time Direction

Figure. 3. GC-FIDtraces for thiophenic compound fractions from Alberta petroleums. The peak labels are as follows: (1) dibenzothiophene; (2) 4-methyldibenzothiophene;(3) 2- and 3methyldibenzothiophene;(4) 1-methyldibenzothiophene. Samples are arranged in order of their depth of burial. Note the shift toward lower molecular weight compounds and a reduction in the amount of the unresolved complex mixture with increasing depth

of burial.

converts the sulfides to sulfoxides, and subsequent chromatography on silica gel separates the highly polar sulfoxides and other polar compounds from the maltene. The sulfoxides may then be converted back to sulfides by reduction with LiAlH4. A subsequent chromatographic step separates the low-polarity sulfides from the other polar substances. Sulfoxides are unique in that reduction with LiA1H4 removes the oxygen atom from the sulfur. This contrasts with the corresponding carbon system, the carbonyl group, which is reduced under these conditions to an alcohol. Alcohols are polar compounds, and they are easily separated from sulfides. The selective oxidation of sulfides to sulfoxides is central to the present method. The oxidizing reagent must oxidize sulfides to sulfoxides but not oxidize the sulfur in a thiophenic ring. In addition, the oxidizing reagent must stop at the sulfoxide stage rather than continuing on to the sulfone since six-membered-ring saturated sulfones are very difficult to reduce back to sulfides.* Many oxidizing reagents will convert sulfides to sulfoxides;whowever, most of them will convert sulfoxides to sulfones when used in excess. In the isolation of sulfides from petroleum, it is

necessary to employ an excess of reagent since the quantity of sulfides is unknown, as is the amount of oxidizing reagent that may be consumed in other reactions with the petroleum. Initially, we employed photochemically generated electronically excited singlet oxygen that oxidizes sulfides to sulfoxides but not to sulfones? Unfortunately, singlet oxygen is reported to attack the carbon framework when the sulfur atom is in a five-membered ring to form complex oxidation products other than sulfoxides? although the reagent is satisfactory when the sulfur is in a six-membered ring or an acyclic structure. The reagent tetrabutylammonium periodate in refluxing chloroform has recently been reported to oxidize sulfides to sulfoxide^.^^ We found the reagent to be unsatisfactory when employed in dry (distilled from CaH,) chloroform or toluene. Generally, the yield of sulfoxide when 2-dodecylthiolane was used as substrate was low (99% converted after a 20-min reflux to the corresponding sulfoxides (98%) and sulfones (2%). After 60 min, the yield of sulfone had increased to 10%. The conditions described in the Experimental Section (30-min reflux) offer a compromise between maximum conversion to sulfoxide and minimum sulfone production. The reaction is very dependent on the exact conditions employed. Small deviations in conditions from those used here may produce unacceptable results. Sulfones of saturated sulfides are difficult to reduce,29 and thus their production should be minimized for maximum recovery of the sulfides. The thiophenes 2-dodecyl-5-methylthiophene, benzo[ b ]thiophene, 2-n-butylbenzo[b]thiophene, and dibenzothiophenewere unaffected by these reaction conditions after a 4-h reflux, and thus the reagent selectively oxidizes the sulfur in a saturate ring but not the sulfur in an aromatic thiophene ring. The solvent dioxane (bp 100 "C) is preferred to either diethyl ether or tetrahydrofuran for the LiAlH, reduction step since preferential reduction of certain sulfides in these lowerboiling solvents has been 0b~erved.l~ The results of the sulfide analyses for several petroleums from Alberta are summarized in Table I. As may be seen, there is considerable variation in the content of sulfides in the petroleums examined, ranging from 16% for Peace River, a bitumen, to 2.6% for Lloydminster, a heavy oil. The GC-FID traces of some selected sulfides are shown in Figure 2. As may be seen there is considerable variation between the samples. Bellshill Lake contains substantial quantities of monocyclic sulfides possessing a linear (nalkane) carbon framework, and these appear as partially resolved clusters of peaks on the lower trace.32 These sulfides are biodegraded by certain microorganisms,33and thus they are not present in the other samples shown in Figure 2, which are extensively biodegraded. Much of the material of these samples consists of an unresolved complex mixture of polycyclic sulfides, which manifests itself as a broad underlying hump in the GC-FID traces. Nevertheless, a number of prominent peaks appear on the upper two traces of Figure 2, and we assign these to a ~

~~

(31) Santanillo, E.; Manzocchi, A.; Farachi, C. Synthesis 1980,

(29)Weber, W. P.;Stromquist, P.; Ito, T. I. Tetrahedron Lett. 1974, 30,2595-2598. (30)Madeaclaire, M.Tetrahedron 1986, 42,5459-5495.

563-565. (32)Schmid, J. C.;Connan, J.; Albrecht, P.Nature 1987,329,54-56. (33)Fedorak, P.M.; Payzant, J. D.; Montgomery, D. S.;Westlake, D. W. S. Appl. Enuiron. Microbiol. 1988, 54,1243-1248.

Isolation of Sulfides and Thiophenes Chart I

4 13

..

Energy & Fuels, Vol. 3, No. 4, 1989 453 T a b l e 11. Rate of Oxidation of Compounds by m -Chloroperbenzoic acid" % remaining after

compd

0 min

15 min

benzo[ b]thiophene 2-n-butylbenzo[b]thiophene dibenzothiophene phenanthrene anthracene pyrene

100

16