Synergistic study between CaO and MgO sorbents for hydrogen rich gas production from the pyrolysis-gasification of sugarcane leaves

This study focused on investigating the sorption-enhanced hydrogen (H2)-rich gas production during the pyrolysis-steam gasification of biomass in a two-stage fixed-bed reactor. The mixed CaO/MgO sorbents were employed in order to enhance the H2 production through the water-gas shift reaction associated with the capturing of CO2. The CaO/MgO sorbents prepared by dry- and wet-physical mixing with different molar ratios were examined. In addition, the effect of different devolatilization temperatures (400-800 °C) and gasification temperatures (600-800 °C) on the H2 yield were explored. It was found that the dry-mixed CaO/MgO sorbent exhibited a synergistic effect in the pyrolysis-steam gasification of the biomass, where a CaO:MgO molar ratio of 2:1 gave the highest H2 yield (16.8 mmol/gbiomass) and H2 concentration (75.0%). The wet-mixed sorbent gave superior results, affording a higher H2 yield (21.2 mmol/gbiomass) and H2 concentration (79.8%) with the same CaO: MgO molar ratio of 2:1. The CO2 yield was also reduced to 1.14 mmol/gbiomass compared to that with the dry mixed sorbent (1.72 mmol/gbiomass). The oxygenated compounds mainly derived at the devolatilization temperature of 600 °C were conceivably preferable to the sorption-enhanced hydrogen production in the gasification, leading to the highest yield and concentration of H2. Increasing the gasification temperature above 600 °C provided a higher H2 yield but caused a lower H2 concentration. A comprehensive discussion on these aspects related to volatile components released from different temperatures and reactivity of sorbents is provided.