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

Red mud (RM) was activated by a feasible digestion-precipitation method followed by calcination at 600 degrees 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 degrees C. The texture characteristics of the activated RM were characterized by XRF, FTIR, XRD, TEM, SEM-EDS, NH3-TPD, and the N-2 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 degrees 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 degrees 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.