UPGRADING OF HEAVY CRUDES AND BITUMEN FROM DIFFERENT GEOGRAPHICAL SOURCES – COMPARISON OF ASPHALTENES ISOLATED BEFORE AND AFTER THERMAL TREATMENT
Dettman H., Salmon S., Ross A. and Patmore D.
Devon, Alberta, Canada T9G 1A8
As sources of conventional crude decline, refineries will become more dependent on heavy crudes and bitumens as feedstocks. A significant fraction of these oils consist of components that have boiling point (bp) > 524EC (975°F). Consequently, the production of high-value products like gasoline and diesel require the large molecules in this fraction, called vacuum residue (resid), to be cracked to form smaller molecules (ideally, bp < 343EC). Unlike their conventional oil counterparts, heavy crudes and bitumens from different geographical locations can have quite different thermal behaviors.
The key to understanding why thermal behaviour varies in terms of resid conversion, coking tendency, gas-make, and product quality and distribution is hidden in the molecular characteristics of the resid fractions. A standard method for characterizing resid fractions is the “saturates-aromatics-resins-asphaltenes” (SARA) analyses. However, inferences of thermal reactivity based on these fractions may be misleading. If the saturates from one oil consist of mostly paraffins, while saturates from another oil consist of mostly naphthenes, their thermal reactivities will be very different. Consequently, reactivity correlations based on either fraction will give erroneous results for the other. More information is needed.
At NCUT, heavy oils from around the world were thermally treated under visbreaking conditions in an autoclave. The feeds and total liquid products (TLP) were fractionated using distillation and SARA techniques. The asphaltenes were further fractionated using gel permeation chromatography (GPC). Analyses including carbon type analyses using NMR and FTIR were performed. Comparisons of carbon type contents with respect to thermal behaviour have been made.