Two stage pyrolysis of oil shale using a zeolite catalyst

Oil shales were pyrolysed in a fixed bed reactor and the chemical compositi on of the oils and gases from the pyrolysis of the oil shales were characte rised. The reactor system was then modified to incorporate a second reactor where the derived vapours from oil shale pyrolysis were upgraded on-line u sing zeolite ZSM-5 catalyst at low pressure. The influence of catalyst temp erature from 400 to 550 degrees C, on the yield and composition of the deri ved oils and gases was determined. In particular, the aromatic and polycycl ic aromatic composition of the oils was determined. Gases were analysed bef ore and after catalysis by off-line packed column gas chromatography. The o ils were analysed by liquid chromatography fractionation followed by gas ch romatography/mass spectrometry. The results showed that the main gases from the pyrolysis of oil shales were, CO2, CO, H-2, CH4, C2H4, C2H6, C3H6, C3H 8 and minor concentrations of other hydrocarbon gases. After catalysis the concentration of all the hydrocarbon gases were increased. The yield of oil after catalysis was reduced with a consequent higher yield of gases and fo rmation of coke on the catalyst. The influence of catalyst temperature was to further increase the gas yield and decrease the yield of oil. Total nitr ogen and sulphur contents in the oils were markedly reduced such that at th e catalyst temperature of 550 degrees C a 67% reduction in nitrogen and a 5 6% reduction in sulphur was achieved. The pyrolysis oil contained mainly al kanes and alkenes however, after catalysis almost all of the long chain alk anes and alkenes were converted to lower molecular weight material, of the short chain, alkyl substituted and iso forms. In addition, the pyrolysis oi l contained significant concentrations of single ring aromatic compounds an d polycyclic aromatic hydrocarbons, consisting of mainly, benzene, naphthal ene, biphenyl and phenanthrene and their alkylated derivatives. After catal ysis the concentrations of these species were increased in the derived cata lysed oils. The aromatic and polycyclic aromatic compounds in the oils show ed a marked increase in concentration as the catalyst temperature was incre ased to 550 degrees C. Nitrogn and sulphur containing aromatic and polycycl ic aromatic compounds were reduced in concentration after catalysis, reflec ting the overall decreases in nitrogen and sulphur contents in the oils. (C ) 2000 Elsevier Science B.V. All rights reserved.