Effects of CO2 on coal rapid pyrolysis behavior and chemical structure evolution

Rapid pyrolysis of Shenfu bituminous coal was conducted with a wall temperature 1073-1473 K and residence time 0-750 ms in both CO2 and N-2 atmospheres to study the pyrolysis mechanism in CO2 atmosphere. The interest was focused on mass loss, gas yield, element content of chars and a series of chemical structure parameters (CH2/CH3, Har/H, fa and (R/C).) obtained by FT-IR analyses. The results show that varied impacts dominated on pyrolysis at different temperatures in CO2 atmosphere. Mass loss decreased at 1073 K but increased at 1273 and 1473 K. Both heterogeneous reaction of CO2 with char and homogeneous reactions of CO2 with volatile occurred during pyrolysis in CO2 atmosphere. The combined effect of enhanced polycondensation of aromatic rings and C-CO2 reaction has been found to increase the mass loss of char. More H-containing free radicals generated during polycondensation, which consequenctly increase combination possibility with other radical fragments to inhibit the cross-linking reaction.