Mechanism of pressurised pyrolysis of Australian brown coal for hydrogen-rich syngas formation

Conversion of fossil fuels to hydrogen-rich syngas is a promising approach for efficient utilisation of these fuels. This study aims to investigate the mechanism of pyrolysis of Australian brown coal into high-value-added products, such as hydrogen-rich syngas. A custom-designed reactor was developed, and the pyrolysis temperature and pressure ranged from 500 to 800 °C and from 0.1-1.6 MPa, respectively. Detailed analysis of reaction products showed that temperature and pressure dramatically affected the yield and composition of pyrolysis products, the secondary reaction pathways, and elemental transformation modes during pyrolysis. The results showed that the concentration of H 2 and CO in the gas fraction increased dramatically with pyrolysis temperature, due to enhanced transfer of hydrogen and carbon from char and tar into a light gaseous phase. Elevated pressures reinforced the cracking of tar molecules due to prolonged residence time, leading to higher gas and CH 4 yields. The promotion of secondary reactions at high pressures contributed to the removal of oxygen in the tar via polycondensation and deoxygenation into gases or/and char, depending on the temperature. The gas composition was affected by the interaction between gases under high pressures, especially through methanation. The highest concentration and yield of syngas (i.e., 57.03 % and 11.47 mmol Gas/g Coal (daf)) were observed at 800 ℃ and under 1 bar. Based on the findings of the study, a reaction pathway was proposed for chemical transformations of brown coal during pyrolysis.