Understanding the relationship between catalytic pyrolysis conditions and hydrogen production by aqueous phase reforming of the water-soluble fractions of bio-oils

Abstract

The valorization to H₂ of real aqueous fractions of bio-oil (AFBs) from catalytic pyrolysis of woodchips was carried out by aqueous phase reforming (APR). Notable gas yield (23 mmol/gTOC_o) and H₂ concentration (46 mol%) were achieved, with values among the best published for the APR of real biorefinery streams. The reforming of AFBs was favoured by a high concentration of levoglucosan and low proportion of acids and ketones, with acetone and acetic acid being the most refractory compounds to APR. Relationships between the pyrolysis conditions and the H₂ production obtained by APR were assessed, with more favourable results when the pyrolysis was carried out under the most severe conditions of those studied, i.e. 0.30 catalyst/biomass ratio and 500 °C in the catalytic step. H₂ production increased to 32 mmol/gTOC_o when 0.04 wt% formic acid was added to the reaction medium, showing that this strategy can overcome the low reforming ability of some AFB components. The Pt catalyst showed good stability after 3 consecutive reaction cycles, displaying only a slight decrease in TOC conversion and CCgas, but a moderate decrease in H₂ production and gas concentration. The loss of activity was ascribed to cumulative adsorption of high molecular weight compounds and oligomers on the catalyst surface.