Co-pyrolysis characteristics and synergistic mechanism of low-rank coal and direct liquefaction residue

In this study, the co-pyrolysis of low-rank pulverized coal (SJC) and direct liquefaction residue (DCLR) was comparatively examined. The structure and composition of tar and the evolution characteristics of gas during pyrolysis were analyzed through GC-MS, TG-FTIR, and other analytic techniques. Results showed that SJC+DCLR co-pyrolysis exhibited a significant synergistic effect. SJC and DCLR served as hydrogen donors to facilitate the hydrogenation of small molecular free radical fragments through pyrolysis, which increased the tar yield by 5.55%. Aromatic hydrocarbon and phenol contents in tar decreased by 11.88% and 7.94%, respectively, and alkane content increased by 12.25%. H-2 content in gas decreased by 19.05%, and CH4 content increased by 19.60%. Co-pyrolysis could be divided into three stages. In the first stage, adsorbed water and CO2 were removed at room temperature to 344.91 degrees C, and the weak chemical bond between SJC and DCLR began to break. In the second stage, SJC and DCLR became pyrolyzed, small molecular free radical fragments were hydrogenated, large amounts of tar and small-molecule gases were produced at 344.91-643.35 degrees C, and synergistic effect was primarily observed. In the third stage, condensation reaction occurred between small molecular free radical fragments at 643.35-845.75 degrees C, thereby producing solid coke and a small amount of gas.