H2 production by sorption enhanced steam reforming of biomass-derived bio-oil in a fluidized bed reactor: An assessment of the effect of operation variables using response surface methodology

Abstract

High-purity H2 was produced by the sorption enhanced steam reforming (SESR) of acetic acid, a model compound of bio-oil obtained from the fast pyrolysis of biomass, in a fluidized bed reactor. A Pd/Ni–Co hydrotalcite-like material (HT) and dolomite were used as reforming catalyst and CO2 sorbent, respectively. The hydrogen yield and purity were optimized by response surface methodology (RSM) and the combined effect of the reaction temperature (T), steam-to-carbon molar ratio in the feed (steam/C) and weight hourly space velocity (WHSV) upon the sorption enhanced steam reforming process was analyzed. T was studied between 475 and 675°C, steam/C ratio between 1.5 and a 4.5mol/mol and WHSV between 0.893 and 2.679h−1. H2 yield, H2 selectivity and H2 purity, as well as the CH4, CO and CO2 concentrations in the effluent gas, were assessed. The operating temperature proved to be the variable that had the greatest effect on the response variables studied, followed by the WHSV and the steam/C ratio. The results show that the H2 yield, H2 selectivity and H2 purity increased, while the CH4, CO and CO2 concentrations decreased, concurrently with the temperature up to around 575–625°C. Higher values of the steam/C ratio and lower WHSV values favored the H2 yield, H2 selectivity and H2 purity, and reduced the CH4 concentration. It was found that the SESR of acetic acid at atmospheric pressure and 560°C, with a steam/C ratio of 4.50 and a WHSV of 0.893h–1 gave the highest H2 yield of 92.00%, with H2 purity of 99.53% and H2 selectivity of 99.92%, while the CH4, CO and CO2 concentrations remained low throughout (0.04%, 0.06% and 0.4%, respectively). The results also suggested that a slow CO2 capture rate led to a poor level of hydrogen production when the SESR process was carried out at low temperatures, although this can be improved by increasing the sorbent/catalyst ratio in the fluidized bed.