Investigation of the interaction between intermediates from gasification of biomass in supercritical water: Formaldehyde/formic acid mixtures

Abstract

Supercritical water gasification (SCWG) is a promising technology for converting wet biomass and waste into renewable energy. While the fundamental mechanism involved in SCWG of biomass is not completely understood, especially hydrogen (H2) production produced from the interaction among key intermediates. In the present study, formaldehyde mixed with formic acid as model intermediates were tested in a batch reactor at 400 °C and 25 MPa for 30 min. The gas and liquid phases were collected and analyzed to determine a possible mechanism for H2 production. Results clearly showed that both gasification efficiency (GE) and hydrogen efficiency (HE) increased with addition of formic acid, and the maximum H2 yield reached 17.92 mol/kg with a relative formic acid content of 66.67% in the mixtures. The total organic carbon removal rate and formaldehyde conversion rate also increased to 67.33% and 89.81% respectively. The reaction pathways for H2 formation form mixtures was proposed and evaluated, formic acid promoted self-decomposition of formaldehyde to generate H2, and induced a radical reaction of generated methanol to produce more H2.