Study of gas evolution during oil shale pyrolysis by TQMS

Real-time gas evolution during pyrolysis of two Green River Formation (Colorado) oil shales, one eastern U.S. Devonian shale, and two Chinese shales was monitored using a triple quadrupole mass spectrometer (TQMS). We calculated kinetic parameters for hydrocarbon generation. For water, carbon oxides, and sulfur gases, we compared evolution profiles and identified the organic/inorganic precursors of each species. We also monitored nitrogen- and sulfur-containing naphtha components. Hydrocarbon gas profiles, except for CH4, are similar for all shales, and their rates of evolution reach a maximum at around the temperatures of maximum oil evolution. The evolution profiles for H2, CH4, H2O, CO, and CO2 at high temperatures are affected by the amount of char remaining in shale, carbonate minerals, and the water-gas shift reaction. The water profile, in general, consists of waters from surface dehydration, kerogen pyrolysis, and mineral dehydration. Mineral dehydration was the dominant water source for all shales, but the temperature ranges for the major water peak varied because of widely different mineral composition. Chinese shales evolved much more water than U.S. shales. Major differences between shales were seen in the sulfur gases.