Extraction of Huadian oil shale with water in sub- and supercritical states

Water extraction experiments were carried out in a semi-continuous operatio n apparatus with the substrate being Huadian oil shale from Jilin Province of China. Both non-isothermal and isothermal extraction techniques were emp loyed. The effects of temperature and pressure were investigated in terms o f degree of conversion, extract as well as gas yield and formation rate, an d the compositions of extract and gas. For non-isothermal extraction, tempe rature varied from ambient value to 500 degrees C and pressure stayed eithe r at 15 or 30 MPa. Isothermal extraction experiments were carried out at fo ur levels of temperature from subcritical to supercritical conditions and t wo supercritical pressures of 25 and 30 MPa. The results indicated that the extract was obtained mainly in the temperatu re range between 300 degrees C and 500 degrees C and gas formation was only observed at temperatures higher than 350 degrees C. A maximum formation ra te exists for extract and gas at about 390 degrees C. The major extract com ponent is asphaltene and the major gas formed is CO2 for non-isothermal ext raction. The large increase in the formation rate of H-2 and CH4 at high te mperature results in a secondary increase of gas formation rate starting at 460 degrees C. The isothermal extractions show that a conversion plateau e xists when temperature is over 400 degrees C where a maximum extract yield was also found. The experimental findings were explained well in terms of t he variation of hydrocarbon solubility in water and the degree of pyrolysis of oil shale. Water extraction shows a higher conversion, slightly lower e xtract yield, more oil content than toluene extraction. The isothermal resu lts re-establish that nonisothermal extraction technique is a useful tool i n searching the optimal extraction conditions. (C) 1999 Elsevier Science Lt d, All rights reserved.