Athabasca oilsands samples were obtained from the Syncrude Facility,. Fort McMurray, Alberta, Canada. 2.2 Catalytic Reactions. Catalytic cracking reactions ...
CHARACTERIZATION OF NATURAL ZEOLITECRACKED OILSANDS BITUMEN BY VAPOR PRESSURE OSMOMETRY AND ELEMENTAL ANALYSIS M.M. Rahman*, A.S.M. Junaid, C. Street, W. Wang, W.C. McCaffrey and S.M. Kuznicki Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2V4 1. Introduction The Athabasca field is one of the world’s largest reserves of heavy crude oil and bitumen. Extraction of this resource is complicated by the high density and viscosity of the oil, and by its contamination with high levels of heavy metals and heteroatoms. Significant research effort has been dedicated to the development of alternatives to hot water extraction for heavy crude oil processing. One promising technique is the catalytic cracking of heavy oil using natural zeolite minerals1-2, an approach which addresses both the deficit of medium distillate fractions and the decreasing demand for heating oil. Small amounts of the cost effective, naturally abundant and readily accessible catalyst are used in the single-pass process. A number of methods can be used to determine the average molecular weight (AMW) of heavy oil and its fractions, such as NMR3, UV-fluorescence technique4 and laser desorption-mass spectrometry.5-7 Vapor pressure osmometry (VPO) has been used extensively to determine the average molecular weights of heavy oil fractions.8-19 The VPO method is cost effective and simple, and although it requires a calibration curve, it’s faster than the absolute methods. In addition, VPO analysis gives relatively accurate AMW values compared to the other methods. In this study, Wiehe’s VPO method19 was used to characterize the products of bitumen samples cracked using natural zeolites catalysts at different reaction temperatures. Also, possible mechanistic pathways are proposed to explain the existing moderately inverse relationship between the aromaticity of the products with the atomic H/C ratio. 2. Experimental Section 2.1 Materials. Clinoptilolite (SC) and sedimentary Ca-chabazite (CC) were obtained from the Saint Clouds deposit in New Mexico and the Bowie deposit in Arizona, respectively, and ground to 1400 kPa, leak tested and heated for 1 h at the specified temperature (300 or 350 °C). After 1 h the reaction was quenched by submersing the reactor in cold water. The system was allowed to reach thermal equilibrium, degasified, and then stripped of light oil fractions by re-heating at 150 °C. The condensate was collected using an ice-water bath cold trap. 2.3 Extraction of Bitumen by Organic Solvents. 80 g of each reacted mixture was placed in a double thickness, porous extraction thimble. The liquid hydrocarbon products were extracted with toluene (150 mL) by refluxing at moderate temperature in a Soxhlet apparatus for 6-8 h. The extracted products were collected by evaporating the toluene under vacuum in a rotary evaporator. The remaining bitumen samples were dried in an oven at 110 °C until constant weights were observed prior to the addition of the condensate fractions in to the products.
2.4 Average Molecular Weight Measurement by VPO AMW of bitumen samples were measured by KNAUER vapor pressure osmometer (ASTM standard D2503-92). Calibration constant (KCalib) was determined by calibrating the instrument using sucrose octacetate (679 g/mole) as an internal standard and 1,2-dichlorobenzene as a solvent at 130 ºC in order to minimize the molecular associations. 3. Results and Discussion The AMW of the liquids generated from bitumen samples reacting at 300 and 350 ºC are shown in Figure 1. All cracked samples had lower AMW compared to the bitumen extracted from raw oilsands (1409 g/mole), a decrease which is more significant at high temperature reactions. More importantly, the decrease in AMW is more dramatic in products from the catalyzed reactions, especially at 350 ºC. The results show that with 5% CC the AMW decreases to one-third (300 ºC) and one-fourth (350 ºC) of that of the raw bitumen sample. Average molecular formula of these catalytically cracked products consist of C30 and C23 carbon containing skeletons respectively (Tables 1 and 2). Compared to the raw sample the skeletal carbon numbers decreased by 68 (C98 to C30) and 75 (C98 to C23) for 5% CC catalyzed reactions at 300 and 350 ºC respectively. This significant reduction in skeletal size indicates substantial cracking by SC and CC catalysts, which lowered the AMW of the liquid products.
Fig. 1: AMW of liquid products from 300 and 350 ºC reactions Table 1: Elemental Analysis of Liquid Products from 300 ºC Reactions
Table 2: Elemental Analysis of Liquid Products from 350 ºC Reactions
Prep. Pap.-Am. Chem. Soc., Div. Fuel Chem. 2012, 57 (1), 203
Proceedings Published 2012 by the American Chemical Society
Elemental analysis results demonstrated a significant decrease in S and N concentrations in the liquid products from the catalyzed reactions regardless of the temperature, compared to the raw bitumen sample (Tables 1 and 2). This is very significant as it indicates desulfurization and denitrogenation activities for these catalysts, suggesting new routes for bitumen upgrading to cleaner low heteroatoms-containing fuels. Results in Table 1 and 2 shows that H/C atomic ratios decrease slightly by catalytic cracking reactions as compared to that of the raw oilsands bitumen sample. Corresponding incremental increase in aromaticity (determined by 13C NMR) correlates the atomic H/C decrease. A slight aromaticity increase in the liquid product samples with H/C atomic ratio around 1.3-1.4 can be best explained by assuming production of low amounts of polynuclear aromatic hydrocarbons samples compared to the high quantity of light hydrocarbons.20-22 A reasonable mechanistic pathway that can explain the increase in the aromaticity by natural zeolite catalyzed cracking is presented below (Scheme 1). This involves carbonium ion generation by the catalysts for chemical transformations of the organic compounds present in the bitumen sample. A Lewis acid site of the catalyst23, abstracts a hydride ion from a paraffin hydrocarbon to produce carbonium ion (I), or from a naphthanilic hydrocarbon to produce carbonium ion (II). Typically, carbonium ions participate in catalytic cracking of hydrocarbons. Further deprotonation and hydride transfer sequences convert the cyclic hydrocarbons to aromatic hydrocarbon derivatives (Scheme 1), increasing the overall aromaticity of the liquid products. O Si
O
O Al *
Si
+
Si
RH
O Si
Al H
+
R
Carbonium ion (I) Cat.
R = Aliphatic or aromatic hydrocarbon
* Lewis acid site H H
R O Si
O
O Al *
Si
O
Si
Si
Al
H
+
H
R
Hydride abstraction
H H Carbonium ion (II)
Cat.
-H
H
H H
H
R
H
H R
R
+H
+H Cat.
-H H
H
H
-H
H
H
H
+H R
R
H
Cat.
H H
H
H
H
Scheme 1: Conversion of cyclic aliphatic hydrocarbons to aromatic hydrocarbons. Intra molecular cyclization of the long chain carbonium ion (III) can also takes place by the donation of electrons from carboncarbon double bond to the carbonium ion and regeneration of the cyclic carbonium ion. Further abstraction of hydride ion by the catalyst regenerates the carbonium ion. Continuing these sequences may also generate the aromatic hydrocarbon derivatives (Scheme 2).
H
H
R
R
R
R
R
H H
H H
+
+H
H
H H H
H
H
H
H
-H H
Carbonium ion (III)
H
H +
Cat.
H
H
H
+
Cat.
Cat.:H R
R
H H
H
+ H+
5. Conclusion Natural zeolites act as active cracking agents even at very moderate thermal conditions (as low as 300 ºC). The average molecular weights and skeletal chain length of the liquids produced by cracking reactions were significantly lower than that of the raw bitumen, or the liquids produced by thermal cracking reactions. Additionally, substantial S and N removal capacity of these catalysts are observed, suggesting an alternative desulfurization and denitrogenation process for oilsands bitumen. Acknowledgement We would like to acknowledge our funding authority, the Centre for Oil Sands Innovation (COSI) at the University of Alberta for their financial support. References (1) Kuznicki, S.M., McCaffrey, W.C., Bian J., Wangen E., Koenig A., Lin C.H. Micropor. Mesopor. Mat., 2007, 105, 268–272. (2) Junaid, A.S.M.; Yin, H.; Koenig, A.; Swenson, P.; Chowdhury, J.; Burland, G.; McCaffrey, W.C.; Kuznicki, S.M. Appl. Catal. A: Gen. (2009), 354(1-2), 44-49. (3) Strausz, O.P.; Mojelsky, T.W.; Lown, E.M. Fuel, 1992, 71, 1355-1363. (4) Greonzin, H. and Mullins O.C. Energy Fuels, 2000, 14, 677684. (5) Tanaka, R.; Sato, S.; Takanohashi, T.; Hunt, J. E.; Winans, R. Energy Fuels, 2004, 18, 1405-1413. (6) Yang, M.G. and Eser, S. ACS Reprints, ACS New Orleans Meeting, 1999, 768. (7) Fujii, M.; Yoneda, T.; Sato, M; Sanada, Y. J. Jpn. Pet. Inst., 2000, 43, 149-156. (8) Acevedo, S.; Gutierrez, L. B.; Negrin, G. and Pereira, J.C. Energy Fuels, 2005, 19, 1548-1560. (9) Dettman, H.; Inman, A.; Salmon, S. Energy Fuels, 2005, 19, 1399-1404. (10) Fuhr, B.; Scott, K.; Dettman, H., and Salmon, S. Prepr. Pap. Am. Chem. Soc., Div. Pet. Chem., 2005, 50 (2), 264-265. (11) Yarranton, H.W. and Masliyah, J.H. AIChE J., 1996, 42 (12), 3533-3543. (12) Nali, M. and Manclossi, A. Fuel Sci. Technol. Int., 1995, 13(10), 1251-1264. (13) Rakotondradany, F.; Fenniri, H.; Rahimi, P.; Gawrys, K. L.; Kilparrick, P.K.; and Gray, M.R. Energy Fuels, 2006, 20, 2439-2447. (14) Yufeng, Y.; Shuyuan, L.; Fuchen, D.; Hang, Y. Pet. Sci., 2000, 6, 194-200. (15) Castro, L.V. and Vazquez F. Energy Fuels, 2009, 23, 16031609. (16) Guzman, A.; Bueno, A.; Carbognani, L.; Pet. Sci. Technol., 2009, 27, 801-816. (17) Kapadia, M.; Patel, M.; Joshi, J.; J. Polym. Res., 2009, 16, 499-512. (18) Amemiya, R.; Saito, N.; Yamaguchi, M. J. Org. Chem., 2008, 73, 7137-7144. (19) Wiehe, I.A. Ind. Eng. Chem. Res., 1992, 31, 530-536. (20) Ohshima S. Nenryo Kyokaishi,1985, 64, 9, 735-739. (21) Yoshida R. Nenryo Kyokaishi,1975, 54, 5, 332-338. (22) Retcofsky H.L. and Friedel R.A. Anal. Chem., 1971, 43, 3, 485-487. (23) Hatch L. F., Hydrocarbon Process, 1969, 77-88.
- H+ H
Aromatic hydrocarbon
H
Scheme 2: Generation of aromatic hydrocarbons from cyclization of long chain carbonium ions. Prep. Pap.-Am. Chem. Soc., Div. Fuel Chem. 2012, 57 (1), 204
Proceedings Published 2012 by the American Chemical Society
