Co-pyrolysis of lignite and Shendong coal direct liquefaction residue

•An interactive effect was testified to exist in the co-pyrolysis of lignite and DLR.•Interactive effect was caused by the organic components and poor fluidity of DLR.•Optimal conditions for enhancing the yield and upgrading of tar were acquired.

To utilize the coal direct liquefaction residue (DLR) and improve the tar yield and quality, experimental studies on co-pyrolysis of lignite and DLR were conducted with a fixed-bed reactor under atmospheric pressure in high purity nitrogen. In-situ micro-Raman experiments, Soxhlet extraction, scanning electron microscope, and X-ray energy spectra analysis were also performed to explore the interaction mechanisms during the co-pyrolysis process. The results indicated that there was an interactive effect between lignite and DLR, which increased the tar yield. This interaction was attributed to the hydrogenation of organic components in the DLR and mass transfer process in pyrolysis of DLR. Also, the co-pyrolysis of DLR and lignite with ratio of 0.15, pyrolysis temperature of 550 °C and particle size range of 0.425–0.85 mm resulted in the most pronounced interactive effect on the high tar yield. Under optimal operational conditions, the tar yield of co-pyrolysis reached 8.8 wt.% and the yield of n-hexane soluble was 61.4 wt.%.