Studying the evolution of gas during the decomposition process of oil shale provides information about the changes of its composition, as well as an understanding of the mechanism of the pyrolysis process. Earlier mainly the CO2 atmosphere was used to observe the effect of the sweep gas on the production of pyrolysis products. In the current study, the Fischer assay method was used to analyze the pyrolysis of Estonian kukersite oil shale with CO2, CO2/steam, N2 and N2/steam sweep gases. The gaseous products were collected offline using a sample bag. Gas chromatography (GC) was performed to investigate the evolution of C1–C3gases, H2, CO2 and CO. Subsequently, the results from each test were analyzed and compared. It was shown that in comparison with N2, pyrolysis in CO2increased the production of alkanes and hydrocarbon (HC) gases. Also, the generation of CH4 and CO gases was enhanced with CO2, while the concentration of H2 in the pyrolysis gas did not significantly change with either environment. The tests carried out in the presence of steam showed that unlike the N2 atmosphere, CO2/steam decreased the production of total hydrocarbons, H2, CO2 and CO.
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