Integrated process of coal pyrolysis with catalytic reforming of simulated coal gas for improving tar yield

Abstract

An integrated process (CP-RSCG) was proposed by coupling coal pyrolysis (CP) with catalytic reforming of simulated coal gas (RSCG) to improve tar yield, and the interaction mechanism was discussed by isotopic tracing. The results show that CP-RSCG can simultaneously improve the quantity and quality of tar. The highest tar yield (16.9 wt%) was obtained in the integrated process at 650 °C, which is 16.6% higher than that under N2 atmosphere. Compared with pyrolysis under simulated coal gas (SCG) without reforming catalyst, the CP-RSCG process can further improve tar yield, which is attributed to the catalytic activation of SCG over Ni-based catalyst to produce active H and CHx free radicals and their participation in tar formation. This enhancement is related with the gas composition in pyrolysis atmosphere. Moreover, this process can be further strengthened by optimizing the gas composition in SCG, introducing steam into SCG and using the catalyst with high catalytic performance. The gas generated by CP-RSCG can be used as SCG for circulatory pyrolysis to enhance tar yield. The analysis of tar composition showed that the light tar content increases, whereas the asphaltene content decreases. The isotopic tracing experiments with D2, CD4 and 13CH4 as tracers confirmed that the radicals generated from the reforming of SCG could combine the coal pyrolysis radicals to retard the polymerization reaction among large radicals. This work provides a simple route to improve tar yield by utilizing pyrolysis gases in coal pyrolysis process.