Mild upgrading of biomass pyrolysis vapors via ex-situ catalytic pyrolysis using reduced red mud catalyst

Abstract

The co-processing of bio-oil with petroleum feedstocks is an effective strategy for enhancing commercial utilization of bio-oil, potentially facilitating the large-scale production of biofuel or oxygenated chemicals. However, the co-processing efficiency is limited by the high acid and oxygen concentrations present in bio-oil. The performance of bio-oil can be enhanced by reducing acidity and facilitating the growth of ketones and carbon chain. In this study, the influence of the reduction properties of red mud (RM) on pyrolysis products of corn stover (CS) using online catalysis was investigated. The enriching mechanism of ketones and phenols in bio-oil was also elucidated. The results showed that Fe₂O₃ transformed to Fe₃O₄ in reduced RM (RRM), increasing oxygen vacancy in the surface and larger specific surface area, acid and base sites were observed in the RRM, which not only enhanced the ketonization reactions of acids, aldehydes, esters and sugars, but also the alkylation of phenols. RM reduced at 500°C is more effective than other reduction temperatures, significantly reducing carboxylic acid content from 20.49 % to 10.51 % before catalysis. Concurrently, phenol and ketone contents increased from 20.47 % and 16.61-30.51 % and 22.72 %, respectively. The production of ketones was enhanced within moderate reaction temperatures of 400-500°C, whereas the formation of phenols was optimal at higher temperatures (550°C). This study presents a novel approach to mild deoxygenation of biomass and the cost-effective production of ketone- and phenol-enriched bio-oil.