Catalytic pyrolysis of lignin with red mud derived hierarchical porous catalyst for alkyl-phenols and hydrocarbons production

Abstract

Red mud (RM) was activated by a feasible digestion-precipitation method followed by calcination at 600 °C (denoted as ACRM), which was used as a novel catalyst during the thermal degradation of the lignin. The prepared catalyst was then applied to the lignin derived from agricultural waste using a vertical fixed-bed microreactor between 350–650 °C. The texture characteristics of the activated RM were characterized by XRF, FTIR, XRD, TEM, SEM-EDS, NH3-TPD, and the N2 isothermal absorption method. The analysis results indicated that the ACRM catalyst possessed a high specific surface area, hierarchical porosity, acidity and active metal oxides (Fe2O3, Al2O3, and TiO2). Maximum bio-oil yield (25 wt.%) was observed at 550 °C, however, the bio-oil yield exhibited an overall declined trend in comparison to the non-catalytic pyrolysis at the corresponding pyrolysis temperatures. The relative contents of alkyl-phenols and the hydrocarbons significantly increased using the ACRM catalyst at 550 °C, which was attributed to the strengthening of dehydroxylation, demethylation, demethoxylation, and alkylation reactions. The study demonstrated the ACRM could be used as a promising catalyst for upgrading the pyrolysis vapours of lignin with considerable economic and ecological benefits.