578
Energy & Fuels 1988,2,578-581
Reactions of Benzo[ b ]thiophene with Aqueous Metal Species: Their Influence on the Production and Processing of Heavy Oils Peter D. Clark,* Kevin L. Lesage, Gerald T. Tsang, and James B. Hyne Department of Chemistry, University of Calgary, 2500 University Drive N . W., Calgary, Alberta, Canada T2N 1N4 Received December 14, 1987. Revised Manuscript Received March 18, 1988 Steam-stimulated recovery of heavy oils containing bound sulfur (3-6 wt %) results in the formation of H2S among other gases. The reaction of benzothiophene ( l ) , a typical model for organosulfur compounds found in heavy oils, with aqueous metal cations at 240 O C was studied to understand the influence of metallic ion species found in the host reservoir minerals on H2S production. It was found that AP+, Fe3+,and V02+among others caused chemical reaction of the benzothiophene. H2Swas observed as a product, but the formation of more complex organosulfur species was the major reaction pathway. Sim 'ar reactions with aqueous platinum-group species caused considerable desulfurization indicating thLlb it may be possible to develop a new upgrading pathway for heavy oils.
Introduction Heavy oils (API 5-20) occur widely throughout the world,1~2 and in some countries, particularly Canada and Venezuela, they contribute significantly to daily oil production. For example, approximately 200 000 bbl/day of synthetic crude oil are produced from the oil sands of Alberta by a combination of surface mining, oil-minerals separation, and upgrading technologie~.~In addition, steam-stimulated recovery of the more deeply buried heavy-oil deposits in Alberta yields up to 50 000 bbl/day of heavy oil, which is used primarily in asphalt prod~ction.~ Heavy oils contain significant quantities of chemically bound sulfur' (2-6 wt %), and steam stimulation of a reservoir containing these oils is known to cause chemical breakdown of some of the organosulfur compounds, resulting in H2S and other compound^.^ The extreme conditions resulting from steam stimulation (T = 200-350 "C, P = 3.5-10.5 MPa) are partially responsible for these reactions, but the influence of aqueous metal species generated by action of steam on the reservoir minerals is considerable.5s In particular, soluble metal species of aluminum, vanadium, and nickel, all common species in a heavy oil reservoir, promote both desulfurization and polymerization of simple organosulfur compounds such as thiophene and tetrahydrothiophene.' Benzo[b]thiophene (1) and its derivatives are very common constituents of heavy oiL9 In this study we have examined the reaction of benzothiophene with aqueous metal ions typically found in a heavy-oil reservoir at conditions experienced during steam-stimulated recoveries. The data give useful insights on the behavior of aromatic (1)Berkowitz, N.;Speight, J. G. Fuel 1975,54, 138. (2)Abstracts, 3rd International Conference on Heavy Crude and Tar Sands, Long Beach CA, July 22-31,1985;Volume 111, Agenda Item no. 12 and articles therein. (3)Bowman, C. W.; du Plessis, M. P. Proceedings of the 5th World Hydrogen Energy Conference; Pergamon: New York, 1984. (4)Clark, P. D.; Hyne, J. B. AOSTRA J.Res. 1984, I , 15. (5)Clark, P. D.;Hyne, J. B.; Tyrer, J. D. Fuel 1983,62, 959. (6)Clark, P. D.;Hyne, J. B.; Tyrer, J. D. Fuel 1984,63, 125. (7)Clark, P.D.; Hyne, J. B. Fuel 1984,63, 1649. (8)Clark, P. D.; Dowling, N. I.; Lesage, K. L.; Hyne, J. B. Fuel 1987, 66, 1353. (9)Clugston, D. M.;George, A. E.; Montgomery, D. S.; Smiley, G. T.; Sawatzky,H. In Shale Oil, Tar Sands, and Related Fuel Sources; Yen, T. F., Ed.; Aduances in Chemistry 151; American Chemical Society: Washington, DC, 1976.
0887-0624/88/2502-0578$01.50/0
organosulfur compounds and indicate how these chemical reactions could affect important parameters such as oil mobility. In addition, studies were conducted with aqueous metal species derived from the catalytically active platinum metals in an attempt to probe alternative heavy-oil upgrading pathways.
Experimental Section Materials. Technical benzo[b]thiophene (97%) was distilled to remove colored impurities, and the distillate purity was checked by gas and high-performance liquid chromatography (HPLC). The sulfates of A13+,Sc3+,V02+,C$+, Mn2+,Fe2+,Co2+,Ni2+,Cu2+, and Zn2+ were obtained in 99+% purity from Alfa-Ventron (Danvers, MA) and were used without further purification. The chlorides of Ti3+,Ru3+,Os3+,Rh3+,Ir3+,Pd2+,Pt2+,and Pt4+were obtained from the Aldrich Chemical Co. (Milwaukee, WI) and also were used without further purification. Water was distilled and deionized. Procedures. Benzo[b]thiophene (0.005 mol) was placed in a quartz tube (General Electric Type 214 clear fused-quartz tubing) along with the desired metal salt (0.0005 mol) and water (0.05 mol). The tube was cooled to -196 "C and was connected to a vacuum line, and its contents were degassed by using the standard "freeze, pump, thaw" procedure. The tube was then flame sealed and was heated in a n Inconel pressure vessel containing water at 240 OC for 28 days. The water in the pressure vessel minimizes the steam pressure differential across the tube walls at the reaction temperature and drastically reduces tube failures. Following completion of the reaction and cooling to room temperature, the tubes were removed and scratched and placed in a flexible plastic tube (Cole Parmer Scientific) connected to a calibrated gas sampling loop. The system was flushed with nitrogen and evacuated, and the reaction gases were admitted to the loop by breaking the quartz tube. The volume of the reaction gases was recorded, and nitrogen was admitted to the sampling loop to bring the system to atmospheric pressure. The gases were sampled and analyzed on a Carle 311 analytical gas chromatograph equipped to analyze hydrocarbons (Cl-C5), H2S, C02, CO, Nz, and 02.H2 was measured on a Hewlett Packard 5700A gas chromatograph using a Poropak Q column. The remaining contents of the tube were extracted with dichloromethane. Black solids, insoluble in dichloromethane and water, were observed in most experiments, and these were collected, dried, and submitted for elemental analysis. These data are shown in Table I. The dried dichloromethane extracts were evaporated, and the residues were quantified and were analyzed for benzothiophene by using gas chromatography and for new organic products by gas chromatography-mass spectrometry (GC-MS). The GC-MS studies employed a H P 5890 gas chro-
0 1988 American Chemical Society
Benzo[b]thiophene-Metal
metal S
V02+ 44.7 53.2
Cation Reactions
Energy & Fuels, Vol. 2, No. 4,1988 579
Table I. Elemental Analysis (wt % of Insoluble Solids" metal speciesb Cr3+c Fe3+ Cu2+ Ru3+ Osa+ Rh3+ Ir3+ 61.7 61.2 66.2 63.4 79.4 62.8 79.1 32.3 36.1 31.3 33.9 18.2 33.7 18.7
a Determined by Microanalytical Laboratories, Vancouver, B.C., Canada. (Cr2O3-nHZ0)was present in this solid.
~
Pt4+ 87.9 11.9
pt2+ 84.7 14.7
Pd2+ 75.5 23.4
~~~
Species not listed did not produce solids. Some green oxide
Table 11. Product Distribution (wt % of Initial Benzothiophene) from the Reaction of Aqueous Metal Species with Benzothiophene at 240 OC over 28 days product distribution mass balance" metal hydrocarbon soluble organic insoluble unreacted ( % of init species gases COZ HZS products material benzothiophene benzothiophene) 0 98 100 0 0 0 0 none (H20) Al3+ 0 1.4 0.2 52.9 0 43.3 98 0 95 97 0 0 0 0 sc3+ 0 0 0 1 0 95 96 Ti3+ 0.5 25.9 4.6 61.9 94 vo2+ 0 0.9 Cr3+ 0 1.1 0.6 30.5 0.2 66.8 99 0 98 98 0 0 0 0 Mn2+ 0.1 32.6 2.1 63.3 99 Fe3+ 0 1.0 co2+ 0 0 0 1.0 0 94.0 96 0 0 0 0 0 95.0 96 Ni2+ 0.4 58.6 2.4 37.2 101 cu2+ 0.4 1.8 0 1.9 0 95 97 Zn2+ 0 0.1 3.1 80.6 5.1 5.0 96 Ru3+ 0.2 1.8 5.1 80.8 4.6 9.8 103 oS3+ 0.3 2.2 97 1.4 80.1 4.4 9.0 Rh3+ 0.4 1.7 3.8 78.8 4.1 4.9 1~3+ 0.3 1.8 ?4 2.7 33.3 101 0.4 2.0 0.1 62.1 Pd2+ 0.3 63.9 1.9 29.4 97 Pt2+ 0.3 0.7 96 4.6 78.4 5.7 5.1 Pt4+ 0.5 1.4 a Calculated on total material recovered; differences between mass balances and sum of individual components represent experimental errors.
matograph equipped with a 0.20 mm X 30 m DB-5 column and coupled to a HP 5970 mass detector. Helium carrier gas at 25 cm3 s-' was used and the temperature was ramped from 80 to 350 "C a t 5 OC min-'. The following compounds were identified in the organic extracts from reactions with A13+,V02+,C$+, Fe3+, and Cu2+,and they are listed in order of retention times obtained in the GC-MS studies: 2,3-dihydrobenzothiophene(9) (minor component), m/z 136,135; benzothienylbenzothiophenes(6-8) (major components), three separate compounds all showing m / z 266 and 133. The bold-faced numbers identify the species in Schemes I and 11. The identities of these compounds were established by reference to authentic materials;1° 8 was shown to be the 2,2'-isomer, 7 the 2,3'-isomer, and 6 the 3,3'-is0mer.~l Two further compounds, each showing m / z 296, were observed but could not be positively identified. In addition to compounds 6-9, organic extracts from reactions with Pd2+,Pt2+,Pt4+,Ru3+, Os3+,Rh3+,and Ir3+also contained the following compounds: 142- or -3-benzothienyl)-2-phenylethane (10);m/z 238, 147 (-CH2C6H,); 142- and -3-benzothienyl)-lphenylethanes (ll),two compounds at separate retention times with m/z 238,223 (-CHd; 1,4,1,3-,or 2,3-diphenylbutane (12-14), three compounds a t separate retention times with m/z 210,105 (-CH~CBH&. Trace amounts of 2,3-dihydro-(2- or -3-benzothienyl)-2- or -3-benzothiophenes (4 and 5) were also observed in all reactions. These compounds were identified by reference to authentic materids.12
Results Data for the reaction of benzo[b]thiophene (1) with a selection of aqueous metal species at 240 "C over 28 days are shown in Table 11. These data are averages of two to four experiments, and variations in quantities such as (10) Bordwell, F. G.; McKellin, W. H. J. Am. Chem. SOC.1951, 73, 2251.
(11)Clark, P. D. PhD Thesis,University of Hull,England, 1976.
Scheme I. Simplified Reaction Mechanism for Formation of Major Products [M(HZO)~]"~
[M(H~O)x~lI(n-l)+(OH)I
+
Ht
A1
KA 1.12 x
Fe
6.3 x 10-2
unreacted benzothiophene or soluble organic products were found to be f3%. Experimental variations for gaseous products were *0.05%. A temperature of 240 "C was chosen to mimic conditions found in a heavy-oil reservoir undergoing steam stimula-
Clark et al.
580 Energy & Fuels, Vol. 2, No. 4, 1988
Table 111. Percent Desulfurizationa of Benzothiophene on Reaction with Aqueous Metal Ions at 240 O C for 28 days % desulfurization Ai3+ V02+ Cr3+ Fe3+ Cu2+ Ru3+ Os3+ Rh3+ Ir3+ Pd2+ pt2+ pt4+ 0.8 13.5 11.4 10.0 11.6 27.8 36.0 20.8 31.3 10.0 11.2 38.1 Calculated on a molar basis, including sulfur found in H2S and combined as inorganic sulfides. Scheme 11. Reaction Pathways for Formation of Minor Products
CH1
CH3
I
I
(13)
+ (141
tion. The reaction time of 28 days used for this study is short in comparison to field practices, which involve steam injection over several months, but nonetheless, significant reaction was observed over this time frame. Quartz reaction vessels were chosen to avoid complications that may arise due to effects of the walls of metal autoclaves. Treatment of benzothiophene with water alone gave no appreciable reaction. Besides illustrating the general inertness of benzothiophene to these conditions, this result also showed that the quartz surface had no significant effect on the reactions. Other experiments, not recorded in Table 11, using sodium sulfate or sodium chloride, also gave no reaction of the benzothiophene, indicating that the reactions described below can be attributed to the metal species and not the counteranion. Of the first-row transition-metal species studied, only V02+, Cr3+, Fe3+, and Cu2+ gave appreciable reaction (33-63% conversion). Interestingly, A13+ also gave significant (57%)conversion of benzothiophene. All of these metal species resulted in soluble organic products as the major product type and in each case benzothienylbenzothiophenes (6-8; Scheme I) were major. components. Lesser amounts of 2,3-dihydrobenzothienylbenzothiophenes (4 and 5) and 2,3-dihydrobenzothiophene(9) were also detected. Small amounts of C02 and HzSwere observed, and for experiments with V02+,Fe3+,and Cu2+ further H2S was trapped in the form of metal sulfides (see Table I). Metal species derived from the platinum group of metals were much more reactive towards benzothiophene such that Ru3+,Os3+, Rh3+,I s + ,and Pt4+gave greater than 90%
conversion and Pt2+and Pd2+gave approximately 70% conversion. As with A13+and the reactive first-row transition-metal species, soluble organic products were the major product type. Desulfurized products (10-14) were found in addition to the dimeric products. This evidence for desulfurization with the platinum metals was supported by the observation of significant amounts of H2S in the gas phase and sulfur combined as metal sulfides. The percentage desulfurizations obtained with various metal species, calculated from the amounts of sulfur found in HzS and in insoluble residues (Table 111), show that the platinum-group-metal species are most active in terms of desulfurization. For Os3+, 36 mol % of the sulfur originally present in the benzothiophene was removed either as HzS or metal sulfide. C02was observed in many of the reactions, although in all cases it represented less than 10% of the total reaction (assuming 1mol of benzothiophene under these conditions leads to 1mol of COJ. Nevertheless, it implies that water reacts with benzothiophene since this is the only source of oxygen in the system. I t is unlikely that oxygen from sulfate would be involved in COz production since this would require reduction of sulfate to present the oxygen in a more reactive form. Moreover, earlier experiments showed sodium sulfate was inactive. The presence of COz in the products will increase the acidity of the system and gives rise to the possibility that reactions may be acid assisted. Since aqueous metal species produce acidic solutions by a solvolysis mechanism, it was decided to carry out experiments with aqueous mineral acids (HzS04,HCl). However, no measurable reaction was observed with either acid in the absence of metal ions; these observations are discussed later.
Discussion Reactions of benzothiophene with A13+,V02+,Cr3+,Fe3+, and Cu2+under high-temperature aqueous conditions yield benzothienylbenzothiophenes (6-8) as major products. In addition, GC-MS studies (see Experimental Section) showed that still higher molecular products were produced in minor amounts. This general tendancy for increasingly complex products could have considerable impact on the properties of heavy oils undergoing steam stimulation since dimerization and other polymerization type reactions between organosulfur components of the oil would lead to higher molecular weight species and increases in oil viscosity. Some evidence for viscosity increases during steam stimulation of heavy oils under certain conditions has been presented,13 and since A13+,V02+,and Fe3+are common species in heavy-oil reservoirs, then the reactions described here may offer an explanation for these increases. Moreover, similar reactions may play a role in the maturation of hydrocarbon reservoirs leading to the formation of resins, asphaltenes, and other complex species typically found in heavy oils. How do these complex products arise? Previously,12it has been shown that carbocations 2 and 3 (Scheme I) can (12) Clark, P. D.; Clarke, K.; Ewing, D. F.; Scrowston,R. W. J.Chem. SOC.,Perkin Trans. 1 1980, 677. (13) Hyne, J. B. Aquathermolysis Synopsis Report No. 50; Alberta Oil Sands Research Authority: Edmonton, Alberta, Canada, 1986.
Benzo[b]thiophene-Metal Cation Reactions
be formed by the action of moist aluminum chloride (H+A1C130H-)on benzothiophene and that these intermediates undergo self-addition reactions. Similarly, in this work protonation of benzothiophene could occur because it is known14that aqua metal ions [M(H20),]”+generate acidic solutions by dissociation (see Scheme I). However, it appears that the metal ion does more than supply protons, as mineral acids (HC1, H2SO4) gave very little reaction. Since metal ions are known to form a variety of complexes with aliphatic organosulfur compounds,16then it seems probable that they are complexed with the carbocations (2,3) through the sulfur atom. Once formed, the carbocations can react with neutral benzothiophene in an electrophilic substitution (Scheme I) to produce the dihydroproducts (4 and 5), which may aromatize to produce the benzothienylbenzothiophenes (6-8). Interestingly, one aromatization mechanism (see Scheme I) could lead to 2,3-dihydrobenzothiophene(9), and this compound was in fact observed as a minor product in many of the reactions. It is interesting that Fe3+promotes considerable reaction whereas Co2+and Ni2+are unreactive. Ferrous iron (Fez+) gave no reaction, showing that the oxidation state of the metal is important in determining the extent of reaction. Coupling this observation with the data in Table I1 leads to the suggestion that the most reactive first-row transition-metal species are ones that can be reduced to lower oxidation states. No direct evidence was obtained to support a redox mechanism since as metal sulfides are the products of the metal ions, it is difficult to determine if any reduction of the metal species has occurred. Most of the sulfides recovered (Table I) had compositions close to those expected for sulfides of metals in the same oxidation state as the starting metal species. The deviations that do occur could be explained either on the basis that most metal sulfides are nonstoichiometric compounds or on the known properties of the particular sulfide.14 For instance, the reaction with Fe3+gave iron(I1) sulfide (FeS) as opposed to iron(II1) sulfide although this is undoubtedly a reflection of the instability of iron(II1) sulfide rather than evidence for a redox mechanism. Also, experiments with C P lead to a mixture of chromium oxide and chromium sulfides because of the susceptibility of the sulfide to hydrolysis. Overall, a mechanism based on coordination of the metal species to benzothiophene via the sulfur atom and/or x-system in conjunction with proton addition to the 2,3bond seems plausible. The extent to which each metal ion promoted reaction would thus depend on its ability to coordinate to the benzothiophene or its protonated derivative. The platinum-metal species gave considerable amounts of desulfurized products (10-14) in addition to the undesulfurized products (4-9). Presumably, these compounds are derived from the dihydro derivatives (4 and 5) (Scheme 11), but the exact mechanism of their formation is not known. However, a likely pathway could involve coordination of a metal species to the “aliphatic sulfur” atom of a dihydro derivative (4 or 5) and subsequent removal of the sulfur. Such coordination would occur preferentially at the “aliphatic sulfur” and weaken the C-S bonds. The (14) Cotton, F.A.; Wilkinson, G. Advanced Inorganic Chemistry, 4th ed.; W h y : New York, 1980. (15) Murray, S. G.; Hartley, F. R. Chem. Rev. 1981, 81, 365.
Energy & Fuels, Vol. 2, No. 4, 1988 581
fact that two isomers of 10 and 11 were observed indicates that all possible isomers of the dihydro derivatives involving linkage between the 2- and 3-positions were produced from reaction of the carbocations with benzothiophene. COz was observed as a minor product, mostly from reactions with the platinum-metal species. Since C-O bond formation is occurring, we assume that the carbocations (2 and 3) are reacting with water. Organic intermediates containing oxygen were not detected, but it is probable that the COz arises by decarbonylation of an intermediate intermediate aldehyde and subsequent water shift of the CO as was the case for thiophene and tetrahydrothiophene.“’ All experiments were conducted with a 1O:l ratio of benzothiophene to metal ion and yet in many experiments, particularly ones with platinum-metal species, much more than 10% of the benzothiophene was converted. This apparent catalytic role of the metal species could be explained in a number of ways. First, the metal species may coordinate with more than one molecule of benzothiophene and thus increase total reaction over the stoichiometric amount. In addition, the metal sulfides formed may act as heterogeneous catalysts in a fashion similar to that described for catalytic hydrogenations and desulfurizations. Also, it is possible that the metal sulfides, although very insoluble in water at ambient conditions, solubilize enough at 240 “C to provide a constant supply of aquated metal ions. At present, it is not known which mechanism accounts for the reaction in excess of a stoichiometric amount of metal present. Some further work is planned, but it maybe difficult to devise experiments that determine the role of the formed metal sulfides. Previous studies with tetrahydrothiophene’~~ showed that increasing the amount of aqueous metal species in an experiment increases the rate reaction, and although equivalent experiments were not conducted with benzothiophene, similar behavior would be expected.
Conclusions It has been shown that AP+, V02+,Cr3+,Fe3+,and Cu2+ aqueous cations cause reactions of benzothiophene under conditions similar to heavy-oil steam stimulation, and dimerization type reactions can occur. In a heavy-oil reservoir this could result in linkage of molecular units containing thiophenic sulfur and adversely affect oil properties. Similar reactions occur with platinum-metal species, but processes involving desulfurization also take place, suggesting that it may be possible to develop upgrading procedures based on aqueous metal species. Acknowledgment. We gratefully acknowledge T. Holst for technical assistance, B. King for preparation of the manuscript, and the Natural Sciences and Engineering Research Council of Canada and Alberta Sulphur Research Ltd. for financial assistance. Registry No. 1, 95-15-8; 4, 114838-48-1; 5, 114838-49-2; 6, 40306-93-2; 7, 65689-54-5; 8, 66689-53-4; 9, 4565-32-6; 10 (2’benzothienyl), 28540-48-9; 10 (3’-benzothienyl), 114838-46-9; 11 (2’-benzothienyl), 99159-22-5; 11 (3’-benzothienyl),114838-47-0; 12,1083-56-3;13,1520-44-1; 14,5789-35-5; Al~(S0~)3,10043-01-3; S C ~ ( S O 13465-61-7; ~)~, VO(S04),27774-13-6;Cr2(S04),,10101-53-8; MnS04, 7785-87-7; FeSO,, 7720-78-7; C0S04, 10124-43-3; NiS04, 7786-81-4; &SO4, 7758-98-7;ZnSO,, 7733-02-0; TiCl,, 7705-07-9; RuCl,, 10049-08-8;OsCl,, 13444-93-4; RhCl,, 10049-07-7;IrC13, 10025-83-9;PdC12,7647-10-1;PtC12,10025-65-7;PtC14,13454-96-1.
