Investigation into the yields and characteristics of products from lignite low-temperature pyrolysis under CO2 and N2 atmospheres

Abstract

A slow pyrolysis experiment was performed in a fixed-bed reactor to investigate the effects of a CO2 atmosphere on lignite pyrolysis behavior. Four different reaction temperatures of 450, 500, 550, and 600 °C with 30 min pyrolysis were considered. Results indicate that lignite pyrolysis in a CO2 atmosphere gives higher gas and water yields compared with those in a N2 atmosphere. Meanwhile, CO2 creates higher yields of small molecule gases such as CO, CH4, C2H6, and C3H6; however, the yield of H2 in a CO2 atmosphere is lower than that in a N2 atmosphere at 600 °C. There are higher yields of benzene, toluene, ethylbenzene, xylene (BTEX), polycyclic aromatic hydrocarbons (PAHs), and phenols in the CO2 atmosphere at 450 °C. All of the results clarify that the CO2 atmosphere promotes cleavage of the 3–5 ring structure in char and of the aliphatic side chain in the volatiles at 450 °C. Also, the CO2 atmosphere enhances thermal cracking of the 3–5 ring structure in char and volatile matter evolved from the thermal degradation of lignite and also reacts with volatile matter at 600 °C.