Pyrolysis and Evaluation of Oil shale Product Yield and Composition from Tchikatanga-Makola (Congo) Oil Shale

Abstract

In this work the pyrolysis and evaluation of the product yield from Tchikatanga-Makola (Congo-Brazzaville). The TGA and DTG were performed at different heating rates of (5, 10, 15, 30, 50 °C/min); the final temperature reached was 760°C. Fischer Assay analysis of oil shale is 8.12 wt%. The optimal pyrolysis temperature was between 480°C to 540°C, which in an average was 520°C. The results of this work revealed that increasing the pyrolysis temperature to 540°C increases the oil yield. Although the ratio of gas/oil was lower, it was found that at heating rates of 2 and 5°C/min the gas yield increased, and at heating rate of 30ºC/min, the oil yield was higher representing the optimal heating rate of pyrolysis. The gas analysis indicated that the gas pyrolysis contain H₂, CO, CO₂, N₂, H₂S and some C₁-C₄ hydrocarbon. As the temperature increased to 520°C, the oil yield decreased while the gaseous emission still increased. The amount of gaseous hydrocarbon increases due to the secondary reactions such as cracking and aromatization of oil derived from oil shale during retorting, however, the content of CO did not change much. But CO₂ decreases due to the decarboxylation of organic matter. The oil analysis shows that the shale oil is essentially composed of 60% aliphatic, 23% non-hydrocarbons, 11% aromatics and 6% asphatenes. The elementary analysis of the oil from pyrolysis is mainly composed of C, H, S, N, O and H/C ratio. Hydrogen and carbon contents in oil shales are higher and increase by increasing the heating rate. This possibly explains the presence of aromatic hydrocarbon products existing in shale oil.