Study on the relevant parameters for the single maceral compositions in thermal maturation

The centrifugally separated samples of lignite from the Yunnan province of mainland China (maceral materials of specific gravity <1.25) were used in a thermal simulation experiment to evaluate changes in maceral composition at different stages of thermal evolution. Separated samples consisted mainly of desmocollinite, which was found difficult to correctly categorize in the maceral composition analysis and may require further specific attention. When simulation temperature reached supermaturation at >500 °C (Ro% = 3.25), the pyrolysis parameter S ₁ exceeded S ₂ due to the desorption effect after high temperature maturing of hydrocarbons. Pr/Ph ratios increased with maturity, reaching a maximum (7.000) in the oil window range (300 °C; 0.85 Ro%) and subsequently decreasing. Largest oil yields were found at 350 °C (Ro% = 1.35), which may be considered the optimum maturation temperature for these separated samples. Our thermal simulation experiment suggests that the critical temperature for these separated lignite samples is in the vicinity of 300–350 °C, with a corresponding Ro% of 0.85–1.35.