Synergistic effects on thermochemical behaviors of co-pyrolysis between bio-oil distillation residue and bituminous coal

•Blending bituminous coal could improve the behaviors of pyrolysis of distillation residue.•The synergistic interaction was observed during co-pyrolysis of the blends.•The synergistic effects were prone to occur at lower temperatures.•The gas products were quantitatively analyzed by infrared peak area.•Coats-Redfern and Flynn-Wall-Ozawa method were applied to obtain kinetics parameters. Co-pyrolysis characteristics of bio-oil distillation residue and bituminous coal were investigated through thermogravimetric analysis coupled with Fourier transform infrared spectrophotometer (TGA-FTIR). The addition of bituminous coal changed the behaviors and kinetics of pyrolysis reaction. With temperature increasing, synergistic effects rapidly increased at relatively low temperatures, and then kept a decreasing tendency with different rates until a relatively steady state. The results of the quantitative analysis of chemical functional group by the peak area of infrared spectroscopy indicated that the addition of bituminous coal had a positive effect on the production of CO2 and CO, and a negative effect on the functional groups containing CH, CC and CO bond. The co-pyrolysis mechanism and kinetics parameters were calculated by the Coats-Redfern and Flynn-Wall-Ozawa method, suggesting that the activation energy and the reaction order of co-pyrolysis increased with mixing ratio increasing in main step. The lowest activation energy (73.17kJ/mol by Coast-Redfern method and 71.46kJ/mol by Flynn-Wall-Ozawa method) was obtained by blending 20wt% bituminous coal.