Formation and inhibition of polycyclic aromatic hydrocarbons from the gasification of cyanobacterial biomass in supercritical water.

ABSTRACT

Polycyclic aromatic hydrocarbons (PAHs) formation and inhibition from supercritical water gasification (SCWG) of cyanobacterial biomass were investigated. High reaction temperature, long residence time, and low feedstock concentration favoured higher molecular weight (HMW) PAH formation. The total PAH yield reached 34.80 µg g-1 at 500 °C, 22.5 MPa, and 10 min. The main PAHs formed in the liquid phase and the solid residue were 3-ring and 4-ring PAHs, which were generated from the cycloaddition reaction of lower molecular weight (LMW) PAHs. In addition, 2-ring PAHs were produced from the Diels-Alder reaction of phenols and unsaturated hydrocarbons. The possible control methods for PAH formation during the SCWG of cyanobacterial biomass were proposed. H2O2 addition effectively inhibited the reaction pathways underlying PAH formation, and the addition at more than 1.0% concentration suppressed H2 production. The work revealed that the inhibition of PAHs was achieved in terms of improving the oxidisation condition during the SCWG process for converting wet biomass or organic wastes to energy sources.