Effect of pressure and H2 on the pyrolysis characteristics of lignite: Thermal behavior and coal char structural properties

The aim of the present work was to investigate the effect of pressure and H2 on the pyrolysis characteristics of lignite. Thermogravimetric behavior during lignite pyrolysis was studied under different Ar or H2 pressures using a pressurized thermogravimetric analyzer (P-TGA). Structural properties of coal chars obtained from P-TGA were investigated by the application of elemental analyzer, Fourier transform infrared spectroscopy, X-ray diffraction analyzer, and gas sorption surface area and pore size analyzer. CO2 gasification reactivity of coal chars was also evaluated by TGA tests. The results demonstrated that the weight loss for lignite pyrolysis increased in the presence of H2 and it became more remarkable with rising pressure. Meanwhile, conversion of C and H during pressurized hydropyrolysis was promoted to a higher level considerably. Aromaticity as well as graphitization degree for coal chars were both intensified with addition of H2, especially under elevated pressures. As to the mesopore structure, BET specific surface area of coal chars from hydropyrolysis increased obviously in comparison with that of coal chars obtained in Ar atmosphere, especially under pressurized conditions. Moreover, coal chars from hydropyrolysis exhibited higher CO2 gasification reactivity.