The gasification of wet biomass using Ca(OH)2 as CO2 absorbent: The microstructure of char and absorbent

Aimed at the hydrogen production by gasification of wet biomass coupled CO2 absorption, the microstructures of chars produced from gasification of wet/pre-dried biomass and several possible stages of absorbent were studied with N2 adsorption, XRD and SEM. The results show that all the chars examined have essentially microporous structures of pore size less than 2 nm, and the char obtained from gasification of wet biomass at 923 K exhibits larger surface area (ABET) of 430.87 m2 g−1 and total pore volume (Vpore) of 0.188 m3 g−1 than those (368.15 m2 g−1 and 0.157 m3 g−1) from pre-dried biomass at the same temperature. The great change of microstructures in the absorbents was observed in the gasification process. The CaO generated from the dehydration of Ca(OH)2 has larger ABET and Vpore, than its former Ca(OH)2, and the increase of pore mainly belongs to mesopores ranges (pore size between 2 nm and 50 nm). However, the generated CaO suffers from a jam of mesopores with the formation of CaCO3 which will cause incomplete utilization. Although the burning of SR sample can realize CaO generation, the regenerated CaO with a totally deteriorated pore networks suggests poor reactivity. With the increase of temperature the CO2 absorption by CaO is weakened gradually except in low temperature range of less than 973 K, meaning that the maximum temperature of the process should not exceed the decomposition temperature of CaCO3.