| Description |
Research of recovery and processing technology applicable to Utah tar sands is currently in progress. Development of this hydrocarbon resource has not yet occurred, principally because of high costs associated with present recovery methods. The processing of bitumens is also expected to be relatively more expensive than conventional petroleum processing because of the heavy nature and high heteroatom content of the bitumen. In processing of bitumen the primary conversion appears to be the most important step because of the possible high cost of hydrogen processing or loss in yields attendant with reducing the high molecular weight bitumen to synthetic crude. Methods and conditions of primary processing have a major effect on the composition of the products subsequently used as feedstocks for secondary processing. Secondary processing for production of fuels and other hydrocarbon products will probably utilize adaptation of processes developed for conventional petroleum. The primary process most commonly used for upgrading of heavy oils, petroleum residuum or bitumen is some form of coking such as delayed or fluid coking. For these processes the range of operating variables which can be employed is rather limited and the product distribution and quality (composition) generated is primarily a function of the feedstock composition. Because the coking process is relatively inexpensive, industrial processes are often content with optimizing coking yields and then subsequently optimizing some secondary process more specifically aimed at altering the composition to produce a desired product. Such an approach is presently used with the Athabasca deposit where 15 to 20 weight percent of the feed is converted to a high sulfur coke and the liquid products are subjected to an expensive hydrotreating to obtain a synthetic crude oil amenable to conventional refining. Recent work on the structure of Utah and Athabasca bitumens (1,2) has shown that Uinta Basin (Utah) bitumens possess a significantly different hydrocarbon and nonhydrocarbon structure than Athabasca bitumen. The higher molecular weight, higher viscosity, and lower volatility points toward a heavier material for the Uinta Basin bitumen, but the higher hydrogen content and API gravity, and the lower asphaltene content and carbon residue points toward a less aromatic bitumen. Interpretation of the structural analysis indicates that the Uinta Basin bitumen is comprised of relatively high molecular weight naphthenic hydrocarbons. The Athabasca bitumen is of lower molecular weight, but higher in aromatics. A comparison of compound type analysis suggests that Athabasca bitumen contains roughly twice the amount of aromatic carbon that Uinta Basin bitumen contains. The differences apparent in the two groups of bitumens suggested that direct adaptation of process conditions used with Athabasca bitumen may not be the most desirable route for development of processes for Utah bitumens. Therefore, several alternatives for the primary conversion of bitumen have been examined, in addition to coking. Examination of alternate processing steps served two useful purposes. First, results of such a study helped identify processes particularly amenable to this unusual feedstock. Second, by paying particular attention to the structure of the feedstock and products more will be learned about conversion mechanisms and pathways influencing residual material processing. In this paper results from coking, catalytic cracking, and hydropyrolysis of virgin Asphalt Ridge bitumen are compared. This study includes the effect of variables on yields and product composition. Product distribution and composition are compared as a function of process variables and the conversion process employed. Detailed structural analysis is used in the evaluation of the respective processes. Implications of the product structure to thermal and catalytic conversion pathways are discussed. |
