Yields and composition of oil obtained by isothermal pyrolysis of the Moroccan (Tarfaya) oil shales with steam or nitrogen as carrier gas

Pyrolysis of the Tarfaya oil shales has been studied in the temperature range 400-600 degrees C using a modified Fisher-assay type pyrolysis set-up with nitrogen or steam as a carrier gas. The analysis of the experimental results provided a comparison of temperature effects on the pyrolysis products in the presence of two different carrier gases. The experimental results show that the temperature has an important influence on the oil yield, which increases with increase in temperature (T) for the two carrier gases, and reaches a maximum at T = 525 degrees C. At temperatures greater than 550 degrees C the yields are lower than those obtained by the Fisher assay method. This loss of oil yield is more pronounced in the case of water vapor, and can be attributed to cracking reactions of oil, steam gasification of the kerogen, bitumen and oil vapor, which may be catalyzed by the mineral matrix at high temperatures. The temperature has also an influence on the composition and the chemical characteristics of the produced oil. (C) 2000 Elsevier Science B.V. All rights reserved.