Upgrading the Strategy of Multistage Torrefaction Liquid by the Selective Oxidation Reaction Route Using a Reusable MgO-Based Au/Al2O3 Catalyst

Abstract

The thermal conversion of biomass resource materials into potential bio-oil by either pyrolysis or torrefaction is an attractive process with significant economic concern. However, upgrading the multistage torrefaction liquid products into valuable compounds is the greatest challenge in the biorefinery industry due to the presence of large multiple complex molecules. The product mainly contains a significant portion of acetic acid and furfural at the low-temperature fraction. In this study, we have aimed to upgrade the furfural molecule along with acetic acid by the selective oxidation reaction route. Initially, the Au/Mg(OH)2 catalyst was employed, and the loss of catalytic activity was observed in a short period due to the instability of the materials in the acidic medium. However, using a sacrificial magnesium oxide (MgO) base with a Au/Al2O3 catalyst remarkably improved the oxidation rate and the stability of the material (both in the model compound and torrefaction stream). In every catalytic cycle, the soluble Mg2+ ion can be regenerated, and it can be successfully employed for next consecutive reactions. This understanding should help scale up the furoic acid production from the multistage torrefaction liquid.