CO2 Adsorption study on pure and chemically activated chars derived from commercial biomass gasifiers

The carbonaceous by-product of biomass gasification processes is known as char. Although nowadays char is treated as a waste, it could be valorized as cheap precursor for activated carbons (ACs) due to their similarities in terms of physical-chemical properties and mechanism of formation. In particular, this study wants to assess char suitability as substitute/precursor of AC for CO2 adsorption. Five chars were taken from five different commercial biomass gasifiers installed in South-Tyrol (Italy) and characterized through elemental analysis, physisorption analysis, and scanning electron microscopy. CO2 adsorption/desorption capacity of chars were investigated through thermogravimetric analysis and their performances were compared with two commercial ACs selected as reference. The effects of adsorption temperature (T-ads = 50-75-100 degrees C), CO2 concentration (CO2: N-2 = 1:1-1:4), chemical activation (with KOH or ZnCl2), and adsorption cycles were investigated. The highest uptake (3.7%) was measured for char activated with KOH, at T-ads = 50 degrees C and CO2:N-2=1:1.