Catalytic gasification of biomass (Miscanthus) enhanced by CO sorption.

The main objective of this work concerns the coupling of biomass gasification reaction and CO sorption. The study shows the feasibility to promote biomass steam gasification in a dense fluidized bed reactor with CO sorption to enhance tar removal and hydrogen production. It also proves the efficiency of CaO-CaAlO/olivine bi-functional materials to reduce heavy tar production. Experiments have been carried out in a fluidized bed gasifier using steam as the fluidizing medium to improve hydrogen production. Bed materials consisting of CaO-based oxide for CO sorption (CaO-CaAlO) deposited on olivine for tar reduction were synthesized, their structural and textural properties were characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), and temperature-programmed reduction (TPR) methods, and the determination of their sorption capacity and stability analyzed by thermogravimetric analysis (TGA). It appears that this CaO-CaAlO/olivine sorbent/catalyst presents a good CO sorption stability (for seven cycles of carbonation/decarbonation). Compared to olivine and Fe/olivine in a fixed bed reactor for steam reforming of toluene chosen as tar model compound, it shows a better hydrogen production rate and a lower CO selectivity due to its sorption on the CaO phase. In the biomass steam gasification, the use of CaO-CaAlO/olivine as bed material at 700 °C leads to a higher H production than olivine at 800 °C thanks to CO sorption. Similar tar concentration and lighter tar production (analyzed by HPLC/UV) are observed. At 700 °C, sorbent addition allows to halve tar content and to eliminate the heaviest tars.