Kinetic study of isothermal oil shale pyrolysis: 2. Evaluation of the organic pyroproducts distribution

Abstract

An isothermal fluidized bed reactor was used to pyrolyze small samples of 0.2–3 mm oil shale particles under an inert gas flow (nitrogen). A cooled Tenax trap was used for collecting the liquid organic products eluted from the reactor at different temperatures and time intervals (during the isothermal reaction). The trapped products were concentrated, and injected by means of a CDS 320 apparatus into a gas chromatograph. The gas chromatographic (GC) profile was utilized as an indication for the distillation curve rather than for the characterization of single compounds, the overall GC profile was used for kinetic interpretation. The analyses of gaseous and liquid samples, which were taken at different time intervals during the isothermal reaction, indicate only a slight change in the product distribution, e.g. an increase in the light-end products with the progress of the reaction. A decrease in sulphur-containing products was found to correlate with reaction progress. These observations indicate that diffusion or volatilization are probably not the rate-determining steps. Light-end (< C 10) products were more abundant at high temperatures than at lower temperatures; with larger particle size the reverse trend was observed. Moreover, the branched and the alicyclic fractions were observed less as the bed temperature increased, indicating an enhanced cracking, mainly of the branched and the alicyclic fractions, at these higher temperatures. The effect of particle size is explained on the basis of heat transfer effects. The mechanism previously proposed for alkene/alkane production was also found to be adaptable to the fluidized bed experiments.