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 (H-2)-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 H-2 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 degrees C) and gasification temperatures (600-800 degrees C) on the H-2 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 H-2 yield (16.8 mmol/g(biomass)) and H-2 concentration (75.0%). The wet-mixed sorbent gave superior results, affording a higher H-2 yield (21.2 mmol/g(biomass)) and H-2 concentration (79.8%) with the same CaO:MgO molar ratio of 2:1. The CO2 yield was also reduced to 1.14 mmol/g(biomass) compared to that with the dry mixed sorbent (1.72 g mmol/g(biomass)). The oxygenated compounds mainly derived at the devolatilization temperature of 600 degrees C were conceivably preferable to the sorption-enhanced hydrogen production in the gasification, leading to the highest yield and concentration of H-2. Increasing the gasification temperature above 600 degrees C provided a higher H-2 yield but caused a lower H-2 concentration. A comprehensive discussion on these aspects related to volatile components released from different temperatures and reactivity of sorbents is provided. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.