Ex-situ and in-situ catalytic pyrolysis of Naomaohu coal with red mud-modified char and red mud leaching solution

Abstract

Pyrolysis is an enabling technology to extend the value chain of coal while reducing its emissions. To improve the product distribution of coal pyrolysis at a reasonable cost, this work explored the utilization of industrial waste-derived red mud modified char (RMMC) and red mud leaching solution (RMLS) for ex-situ and in-situ catalytic coal pyrolysis, respectively. The structural and compositional features of RMMC catalyst and RMLS-loaded coals were revealed by XRD, physisorption, FT-IR, XPS, and Raman spectroscopy. The pyrolysis experiments with RMMC and RMLS were conducted in a two-stage fixed bed reactor and a one-stage fixed bed reactor, respectively. As compared to non-catalytic pyrolysis, RMMC increased the light tar fraction by 28.3 %, dropped the heavy tar yield from 4.4 wt% to 2.0 wt%, and reduced the contents of heteroatoms (O/N/S) in tar significantly at 500 °C. With 0.25 wt% RMLS, the light tar fraction was increased by 21.7 %, and the heavy tar yield was lowered to 2.8 wt%. This work demonstrated the feasibility and potential of RMMC and RMLS-catalyzed coal pyrolysis to empower both coal and aluminum industries.