Tar formation characteristic of integrated process of coal pyrolysis with dry reforming of low carbon alkane over Ni/La₂O₃-ZrO₂

Coal pyrolysis integrated with dry reforming of low-carbon alkane (CP-DRA) is an effective way to improve tar yield. Ni/La₂O₃-ZrO₂ with a La/Zr ratio of 4 was a good catalyst for DRA to inhibit carbon deposition and obtain high tar yield in CP-DRA. In this study, the fraction distribution and component of tars from CP-DRA and coal pyrolysis in N₂ atmosphere (CP-N₂) were characterized by using several methods to understand the effect of DRA on coal pyrolysis. The isotope trace method was also used to discuss the role of low-carbon alkane in CP-DRA. The results showed that the tar from CP-N₂ is mainly composed of aliphatic compounds with more C_al, H_al and CH+CH₂, and the tar from CP-DRA contains more C_ar, H_ar, and CH₃, and has lower weight-average molecular weight and more light tar content than CP-N₂. A small amount of C₂H₆ addition in CP-DRA will raise the ratio of H_β and CH+CH₂. Electron paramagnetic resonance (EPR) analysis shows that the tar from CP-DRA has a higher radical concentration while the corresponding char has a lower radical concentration. The isotope trace experiment showed that alkanes provide ·H, ·CH₃, etc. to stabilize the radicals from coal pyrolysis and result in more alkyl aromatic compounds during CP-DRA.