Characteristics of processed shales affecting oil yield loss to coke

Abstract

The objective of this research was to further examine coking during hot-solid recycle retorting. Specifically the relationship between process-induced macroporosity and the reactivity of the shale mineral matrix was investigated. Photomicrographs support a direct relation between coking and the development of macroporosity in oxidized substrates. As access to the mineral matrix increases, the effect of processing on its reactivity becomes more important. The coking activity of illite, the major mineral component of the shale used, increased slightly when heat-treated to 973 K, but further heat treatment to 1323 K decreased its reactivity. Coke deposited on combusted shale and illite either blocked access to and/or deactivated coking sites, significantly reducing substrate reactivity. Carbon removal from the illite by oxidation at 773 K increased reactivity threefold over untreated illite. Combusted shale had fewer active coking sites, as measured by temperature-programmed desorption analysis, than gasified shale. This was consistent with deactivation of the mineral matrix with increased temperature treatment. Results also indicated that deactivation of the mineral matrix was possible by heat and steam treatments. The data provided further evidence that the amount of oil yield loss to coke was primarily controlled by process-induced macroporosity, allowing access to a reactive mineral matrix.