A TGA/DTA-MS investigation to the influence of process conditions on the pyrolysis of Jimsar oil shale

• TGA/DTA-MS was used to analyze the pyrolysis process and decomposition mechanism of Jimsar oil shale.
• Compounds of up to 258 amu in the products were identified and the evolution rates of the compounds were measured.
• The compositions of pyrolysis products at varied heating rates were analyzed.
• The reaction orders and activation energies of the decomposition of kerogen and carbonates were changed with heating rate.

The influence of heating rate and pyrolysis temperature on the pyrolysis of Jimsar oil shale was studied. Oil shale samples were pyrolyzed in a TG analyzer (thermogravimetric analyzer) at eight different heating rates (0.5–30 °C/min) up to a temperature of 1000 °C. The decomposition mechanism of oil shale was confirmed through online MS (mass spectrometric) combined with the TGA. Compounds of about 258 atomic mass units in the products were identified and the evolution rates of the compounds were measured. Increasing the heating rate increased the lighter alkanes/heavier alkanes ratio, unsaturated hydrocarbons/respective alkane ratio and benzene/alkyl aromatics ratio. The atomic H/C ratio of derived oil (C5–C18) decreased as the heating rate was increased from 0.5 to 15 °C/min. Then the ratio increased as the heating rate was increased to 30 °C/min. Lighter hydrocarbons evolved at lower temperature and their formation rates were higher. The H/C ratio of derived oil (C5–C18) increased firstly and then decreased with the increase of pyrolysis temperature (<620 °C). The pyrolysis kinetics of oil shale was calculated using Friedman-Carroll method. The reaction order and activation energy were changed with heating rate. And the reliability of the calculated activation energies was verified through DTA (differential thermal analysis).