Investigation of the Thermal Behavior and Interaction of Venezuelan Heavy Oil Fractions Obtained by Ion-Exchange Chromatography Parviz Rahimi* and Thomas Gentzis National Centre for Upgrading Technology, 1 Oil Patch Drive, Suite A202, Devon, Alberta T9G 1A8, Canada Edgar Cotte ´ PDVSA, Intevep, Caracas 1070A, Venezuela Received October 11, 1998. Revised Manuscript Received January 2, 1999 The coking propensity of Hamaca heavy oil (+510 °C) and its fractions separated by ion-exchange chromatography was investigated using hot-stage microscopy. The initial time of mesophase formation and its growth rate were measured for each fraction. The results showed that the amphoteric fraction was the most prone to coke formation, followed by the basic and acidic fractions. Mesophase formation for the neutral and aromatic fractions was delayed, and its growth rate was considerably slower. The relative order of coking propensity of the fractions is amphoteres > bases > Hamaca resid > acids > neutrals > aromatics. Although the Hamaca resid contained high concentrations of aromatic and neutral components with a relatively lower coking propensity, its coking propensity was much more similar to that of the acidic and basic fractions, which were less abundant in the resid. This propensity shows that the interactions among the individual components were not proportional to their concentrations in the feed and that the amphoteric fraction may have had a larger influence on coke formation relative to the other components. It was further observed that under the reaction conditions employed, the amphoteric fraction had high viscosity, did not develop a distinct mesophase stage, and formed fine-grained mosaic coke over a very short period of time. The results of this work may be used to assess the feasibility of selective removal of problematic components in the feedstocks prior to processing. Introduction Predicting the product yields and quality during the hydrocracking of heavy oils is challenging because of the complexity of the cracking reactions and the vari- ability in the chemical composition of the feedstocks. The use of analytical techniques that provide not only consistent and meaningful results, but also sufficient quantities of resid fractions for further evaluation and analyses is crucial. Petroleum fractions can be obtained using techniques such as distillation, SARA, liquid chromatography (LC), supercritical fluid extraction (SCFE), and ion-exchange chromatography (IEC). Fur- thermore, the relationships between the chemical com- position of the feedstocks and the products are well established. For instance, the yields of gas, gasoline, light gas oil (LGO), and heavy gas oil (HGO) and amount of coke that result from fluid catalytic cracking (FCC) of the Californian Wilmington resid were shown to depend on feedstock composition. 1 There is evidence that the majority of the light products, such as gas and gasoline, are derived primarily from the neutral com- ponents of the feed. Large amounts of coke and small quantities of methane and C 2+ hydrocarbons that form during the processing of petroleum heavy ends are attributed to the acidic and basic components in the feed. It has also been shown that the polar compounds present in acidic and basic fractions not only influence the storage stability and utilization of distillates but also play a key role in sediment formation in diesel fuels. 2,3 Ovalles et al. 4 studied the thermal stability and interfacial activity of acid, basic, and neutral fractions in the Cerro Negro Crude Oil from Venezuela, obtained by the IEC method. Following characterization of the fractions via spectroscopic techniques (FTIR, H and 13 C NMR), they concluded that acid fractions behaved as natural surfactants in stabilizing oil/water emulsions and that it was the hydrophilic portion of the surfac- tants that showed higher acidity and high concentration of polar constituents. Acid fractions are known to be responsible for coke formation, 5 to deactivate heteroge- neous catalysts in day-to-day operations of refineries, * To whom correspondence should be addressed. (1) Green, J. B.; Zagula, E. J.; Reynolds, J. W.; Wandke, H. H.; Young, L. L.; Chew, H. Energy Fuels 1994, 8, 856-867. (2) Pedley, J. F.; Hiley, R. W.; Hancock, R. A. Fuel 1988, 67, 1124- 1130. (3) Pedley, J. F.; Hiley, R. W.; Hancock, R. A. Fuel 1989, 68, 27- 31. (4) Ovalles, C.; del Carmen Garcia, M.; Lujano, E.; Aular, W.; Bermudez, R.; Cotte ´, E. Fuel 1998, 77, 121-126. 694 Energy & Fuels 1999, 13, 694-701 10.1021/ef980220m CCC: $18.00 © 1999 American Chemical Society Published on Web 03/04/1999