Effect of process solids on secondary reactions during oil shale retorting

Abstract

The effect of solids processing, oil vapour-solids interactions and contact time on coke formation from oils produced during Eastern US oil shale pyrolysis was investigated. Both long and short vapour contact time reactors were used to study the coking reactivity of sand, processed shales and clay minerals typically associated with Eastern US oil shales. BET nitrogen surface area and reflected light microscopy were used to correlate physical properties of the solids with carbon deposition. Combusted shales were more reactive coking substates than pyrolysed or gasified shales. Physical measurements indicated that macropores and fractures (not measured by BET) were important in coke formation. Steam treatment of oxidized shale decreased coking without changing measured physical properties. This is possible evidence for chemical alteration of the mineral matrix. Combustion temperature (773 versus 1098 K) did not affect the reactivity of oxidized shales. Therefore, high coking cannot be attributed to temperature-induced activation of the mineral matrix. Coking on clay minerals correlated to nitrogen BET surface area. Process-induced macroporosity, which allowed access to an active mineral matrix, was postulated as important in coke deposition.