Influence of residence time and catalyst regeneration on the pyrolysis-zeolite catalysis of oil shale

Oil shale from the Kark region of Pakistan has been pyrolysed in a fixed be d batch reactor and the properties of the derived shale oil determined. The reactor system was then modified to incorporate a second reactor where the derived vapours from oil shale pyrolysis were passed directly to the secon d reactor containing zeolite ZSM-5 catalyst. The influence of the process p arameters of vapour residence time (VRT) over the catalyst and the regenera tion of the catalyst were examined. The yield and composition of the derive d gases before and after catalysis were determined. In addition, the yield and composition of the derived oil in terms of total nitrogen and sulphur c ontent and the content of aromatic hydrocarbons in the oils was investigate d. The results showed that the yield of oil after catalysis was reduced wit h a consequent higher yield of gases and formation of coke on the catalyst. The main gases from the pyrolysis of oil shales were CO2, CO, H-2, CH4, C2 H4, C2H6 and C3H6, C3H8 and minor concentrations of other hydrocarbon gases . The main role of catalysis was to convert the long chain alkanes and alke nes in the oil to lower molecular weight, short chain, alkyl substituted an d iso species and high concentrations of aromatic hydrocarbons. Total nitro gen and sulphur contents in the oils were markedly reduced after catalysis. This reduction was reflected in the reduced concentration of nitrogen and sulphur containing aromatic hydrocarbons. The influence of longer VRTs was to increase the formation of aromatic hydrocarbons, reduce the nitrogen, an d sulphur compounds in the oils. The influence of catalyst regeneration, in volving five regenerations was not significant on the yield and composition of the derived catalytically upgraded oils. (C) 2001 Elsevier Science B.V. All rights reserved.