Energy & Fuels 2007, 21, 2831-2839
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High Temperature Simulated Distillation of Athabasca Vacuum Residue Fractions. Bimodal Distributions and Evidence for Secondary “On-Column” Cracking of Heavy Hydrocarbons Lante Carbognani,† Joaquin Lubkowitz,‡ Manuel F. Gonzalez,† and Pedro Pereira-Almao*,† AICISE, Chemical and Petroleum Engineering Department, UniVersity of Calgary, 2500 UniVersity DriVe N.W., Calgary, Alberta, T2N 1N4, Canada, and Separation Systems Inc., 100 Nightingale Lane, Gulf Breeze, Florida 325621 ReceiVed February 27, 2007. ReVised Manuscript ReceiVed July 5, 2007
Decreasing conventional oil reserves and existence of large heavy oil and bitumen reservoirs demand novel and cost-effective production and upgrading schemes. One three sequential steps “visbreaking-adsorptioncatalytic steam gasification” upgrading process was recently introduced by the group. Thermal cracked heavy molecules were shown to be key components for improved adsorption over solid sorbents. Characterization of the feedstock and the visbroken products is an important part of the study. In this paper, high temperature simulated distillation (HTSD) characterization is covered. Bimodal and monomodal HTSD chromatographic distributions were observed depending on sample relative abundance of heavy resins and asphaltenes. These polar compounds are responsible for the high temperature chromatographic mode. Secondary “on-column” cracking of heavy petroleum components was observed, however not contributing dramatically to the relative abundance of the chromatographic modes. Changes brought by thermal cracking reactions were observed to change detector responses for asphaltene compounds. It seems that this aspect is related to heteroatomic species affecting the burning properties of asphaltene samples. The abundance of the high temperature chromatographic mode was proposed as a feasible crackability (“visbreakability”) index for bimodal petroleum samples. Also, preliminary findings suggest that the HTSD FID response within the second chromatographic mode can be a general indicator of sample thermal maturity, either induced or geothermal.
Introduction Dependence on heavy hydrocarbon feedstocks for fulfilling global energy demand is forecasted for the near-midterm future.1 Heavy hydrocarbons (HC) like bitumen and heavy oil (HO) typically comprise more than 50% (w/w) of distillation residua (500 °C+).2 One combined “visbreaking-adsorptioncatalytic steam gasification” upgrading process has been recently studied and proposed as a feasible alternative for vacuum residua, illustrated with one Athabasca bottom.3-5 Thermal cracked (TC) heavy hydrocarbons were generated by a mild visbreaking technique (VB). Compounds within the most severely cracked visbroken products proved to be key components having increased adsorptivity over solids acting as both * Corresponding author. Telephone: (403) 220-4799. Fax: (403) 2103973. E-mail:
[email protected]. † University of Calgary. ‡ Separation Systems Inc. (1) Roberts, P. The End of Oil: On the Edge of a Perilous New World; Mariner Books: 2005. (2) Altgelt, K. H.; Boduszynski, M. M. Composition and Analysis of HeaVy Petroleum Fractions; Marcel Dekker: New York, 1994. (3) Sosa, C.; Gonzalez, M. F.; Carbognani, L.; Perez-Zurita, M. J.; LopezLinares, F.; Pereira-Almao, P.; Moore, R. G.; Hussein, M. Visbreaking Based Integrated Process for Bitumen Upgrading and Hydrogen Production. Presented at The 2006 Canada International Petroleum Conference, Calgary, AB, June 2006; Paper No. CICP 2006-074. (4) Gonzalez, M. F.; Carbognani, L.; Pereira-Almao, P. Selective adsorption of thermal cracked heavy molecules. Submitted for publication in Catal. Today 2007; special issue for papers presented within the Symposium “Catalysis and Processes for Heavy Oil Upgrading”, 19th CSC, May 2006, Saskatoon, SA, Canada. (5) Carbognani, L.; Gonzalez, M. F.; Pereira-Almao, P. Energy Fuels 2007, 31 (3), 1631.
adsorbents and catalysts for steam gasification.4,5 Characterization studies carried out showed that VB produced higher proportions of intrinsically unstable asphaltenes plus decreasing amounts of resins, facts that correlate with stability properties of the visbroken products as a function of process severity.5 Further characterization for the feedstock and VB products contemplated the determination of distillation properties, since cuts yield is probably the single most important property for a hydrocarbon feedstock.6 Distillation aspects investigated by means of gas chromatography simulated distillation (GCSD) will be the main focus for this work. Gas chromatography simulated distillation, i.e., distillation equivalent to true boiling range determination carried out by gas chromatography, is a technique pioneered by Eggertsen, Green, and co-workers in the 1960s.7-8 Packed column GCSD enabled analyses requiring milligram sample sizes instead of kilograms and time responses of hours instead of days compared with accepted physical standard distillation methods.9 GCSD with packed columns was a well-established methodology for oil products testing during the 1980s.10 Generalized use of capillaries, in particular wide bore metal wall thin film coated columns, allowed the development of GCSD methodologies for (6) Yergin, D. The Prize; Simon & Schuster: New York, 1991. (7) Eggersten, F. T.; Groennings, S.; Holst, J. J. Anal. Chem. 1964, 32, 904. (8) Green, L. E.; Schmauch, L. J.; Worman, J. C. Anal. Chem. 1964, 36, 1512. (9) ASTM-D-2892. Standard Test Method for Distillation of Crude Petroleum (15-theoretical plates columns). (10) ASTM-D-2887. Standard test method for Boiling Range Distribution of Petroleum Fractions by Gas Chromatography.
10.1021/ef070106g CCC: $37.00 © 2007 American Chemical Society Published on Web 08/18/2007
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high boiling vacuum residua.11,12 Calculated equivalent boiling points for very large alkane compounds were proposed and adopted for calibration of high temperature simulated distillation (HTSD) methodologies.13 By following the former developments, elution of compounds up to 720 °C and molecules up to C116 were described at the end of the 1980s and the beginning of the 1990s.14,15 HTSD is nowadays routine in petroleum laboratories,16 being already standardized under ASTM protocols.17 A good correlation between physical distillation and HTSD results (less than 2% deviation) has been published for a large set of oils spanning different API gravities.18 Reviews on simulated distillation (SimDist) are available in the open literature.19,20 However, agreement within the oil community concerning the equivalence of SimDist to physical distillation has not been reached so far. From a recent article, it appears that SimDist results are in between volume and weight percent physical results.21 Recent articles show that mild approaches for SimDist such as supercritical fluid chromatography22,23 are under study for avoidance of deleterious effects caused by the high temperature set points employed in HTSD.24 High-speed GCSD is another field of research showing recent interest, with elution of large hydrocarbons such as nC44 having been described in about 70 s, suggesting a dramatic decrease in analysis time for near foreseeable methodologies.25 One aspect that caught the attention of several authors was the possibility that HTSD operating temperatures can induce hydrocarbon cracking inside the column.18-20,22-24,26 The feasibility for this was demonstrated by thermogravimetry under flow and vacuum conditions.24 However, cracking within chromatography HTSD separations to the best of our knowledge has only been reported by very fast heating rates (180 °C/min) of long alkane compounds. This fast heat flow was set up only within the cold on-column injector.27 Definitive proof for cracking of petroleum hydrocarbons inside HTSD columns has not been published. One virgin Athabasca vacuum resid and its thermal cracked residua were studied within this work by means of HTSD. Sample crackability and secondary “on-column” HTSD cracking are topics addressed in the paper. Monomodal and bimodal (11) Trestianu, S.; Zilioli, G.; Sironi, A.; Saravalli, C.; Munari, F.; Galli, M.; Gaspar, G.; Colin, J. M.; Lovelin, J. L. J. High Resolut. Chromatogr. Chromatogr. Commun. 1995, 8, 771. (12) Lipsky, S. R.; Duffy, M. L. J. High Resolut. Chromatogr. Chromatogr. Commun. 1988, 9, 376. (13) Glinzer, O. Erdoel Kohle, Erdgas, Petrochem. 1985, 38, 213. (14) Curvers, J.; van den Engel, P. J. High Resolut. Chromatogr. Cromatogr. Commun. 1989, 12, 16. (15) Thomson, J. S.; Rynaski, A. F. J. High Resolut. Chromatogr. Chromatogr. Commun. 1992, 15, 227. (16) Dettman, H.; Inman, A.; Salmon, S. Energy Fuels 2005, 19, 1399. (17) ASTM D-7169-05. Standard Test Method for Boiling Point Distribution of Samples with Resid such as Crude Oils and Atmospheric Resids by High Temperature Gas Chromatography. (18) Villalanti, D. C.; Maynard, J. B.; Raia, J. C.; Arias, A. A. Yield Correlations Between Crude Assay Distillation and High Temperature Simulated Distillation (HTSD) (web released, www.distillationgroup.com). (19) Peaden, P. A. J. High. Resolut. Chromatogr. 1994, 17 (4), 203. (20) Villalanti, D. C.; Raia, J. C.; Maynard, J. B. J. Chromatogr. Sci. 1996, 34, 20. (21) Ceballo, C. D. Vision Tecnol. 1998, 6 (1), 69. (22) Thiebaut, D. R. P.; Robert, E. C. Analusis 1999, 27 (8), 681. (23) Dularent, A.; Dahan, L.; Thiebaut, D.; Bertoncini, F.; Espinat, D. Oil Gas Sci. Technol.sReV. IFP 2007, 62 (1), 33. (24) Schwartz, H. E.; Brownlee, R. G.; Boduszynski, M. M.; Su, F. Energy Fuels 1987, 13, 93. (25) Lubkowitz, J. A.; Meneghini, R. J. Chromatogr. Sci. 2002, 40 (5), 269. (26) Barman, B. N.; Cebolla, V. L.; Membrado, L. Crit. ReV. Anal. Chem. 2000, 30 (2/3), 75. (27) Johansen, N. G.; Hutte, R. S. Prepr.sAm. Chem. Soc., DiV. Pet. Chem. 1991, 36, 212.
Carbognani et al.
Figure 1. High temperature simulated distillation for the Athabasca vacuum resid and the heavy fraction from its visbroken products. Products are identified according to their “operational” visbreaking yields (% w/w).3-5 Dividing lines for AGO/VGO (nC20), and for the end of distillation according to ASTM-D 7169 (nC100)17 are included.
HTSD distributions were studied for crude oils of varying properties and correlated with the distributions of isolated SARA group types (saturates, aromatics, resins, and asphaltenes). Natural (geochemical) and induced (visbreaking) maturity influences on asphaltene bimodality was explored with a set of samples isolated from light, medium, and heavy oils. Experimental Section Vacuum Residua and Crude Oil Samples. Athabasca vacuum resid (VR) and its visbroken products (VB) were studied. The VR from an upgrader was provided by Suncor. Details on VB products generation and stability aspects have been reported elsewhere.4,5 Athabasca VR visbroken products from preparative scale runs (400 g) were studied in detail during this work.4,5 Several crudes from a data bank existing in the Schulich School of Engineering, University of Calgary, were selected for elution pattern comparison under HTSD conditions. These samples will be described directly under Results and Discussion. One heavy crude oil sample from the Venezuela Orinoco basin was included in the comparison. Standard Hydrocarbons. The response of the flame ionization detector was investigated for commercially available hydrocarbons. These were acquired from Sigma-Aldrich and were used as received. SolVent and Sample Preparation. Carbon disulfide (CS2), ACS reagent (>99.9%) from Sigma-Aldrich, was used for sample solution preparation. Solutions for GC analysis were prepared by weighing about 200 mg of sample and 12.5 g of solvent (10 mL of pipetted CS2) with 0.1 mg accuracy. Samples and solvent were weighed inside 20 mL glass scintillation vials provided with metal caps. Homogenized sample solutions were transferred to 2 mL Agilent autosampler vials. HTSD Details and Operating Conditions. An Agilent 6890N gas chromatograph provided with an autosampler and automatic injector was used for HTSD analysis. A 5 m × 0.53 µm, 0.1 µm film column provided by Separation Systems was selected for SimDist analysis (P/N SS 112-102-01).28 The injected sample solution amount was 0.2 µL. “Near column injection” was carried out with the Separation Systems designed cold injector.28 The flame ionization detector (FID) was maintained at 430 °C, provided with 450 mL/min air, 40 mL/min H2, and 25 mL/min N2 (makeup gas). The column was eluted with helium at a flow rate of 20 mL/min. Temperature programming for the column was 15 °C/min from 40 (28) Separation Systems, Inc. (www.SeparationSystems.com).
HTSD of Athabasca Vacuum Residue Fractions
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Table 1. Estimation of % w/w Distributions for Distillation Fractions of Athabasca Feed and Its Visbroken Products samplea
light distillatesb
distillates in heavy productc (
