Lithium-based sorbent from rice husk materials for hydrogen production via sorption-enhanced steam reforming of ethanol

The sorption-enhanced steam reforming of ethanol (SE-SRE) has the potential to produce the high-purity hydrogen. It is essential to obtain suitable reforming catalysts and CO2 sorbents in the SE-SRE process. We first prepared Ni-based catalysts by using three synthesis methods involving sol-gel, impregnation, and co-precipitation. Characterizations and catalytic activity tests results revealed that sol-gel route produced the most promising catalyst with 80% selectivity to H-2 and the favorable structure of SG-Ni/Al2O3 was responsible for its superior performance. Then, different waste materials (rice husk ash, fly ash, kaolin) as silica source were employed to prepare Li4SiO4 sorbents for CO2 capture. The chemical composition of the silicon sources and the crystalline phase, specific surface area and morphology of these synthesized sorbents were characterized and results indicated that rick husk ash with large specific surface area and loose structure is the optimal silicon sources. Cyclic carbonation/calcination tests showed that RH-Li4SiO4 sorbent from rick husk material without acid treatment possesses the excellent CO2 sorption capacity up to 36.57 wt% and cyclic stability. The presence of impurity phases (MgO, Al2O3, K2O, etc.) in the RH-Li4SiO4 sorbent is beneficial to the CO2 adsorption. Moreover, the influence of steam on the CO2 capture of RH-Li4SiO4 sorbent was further investigated. We found that its CO2 adsorption performance was improved in the existence of steam. The integration of the optimized SG-Ni/Al2O3 catalyst and RH-Li4SiO4 sorbent with different packing methods was finally considered in the SE-SRE system. The four-layer interval packed catalyst and sorbent exhibited the best performance over the ten consecutive SE-SRE/regeneration cycles with a stable and high selectivity to H-2 (> 93%), confirming the potential for high-purity H-2 by adsorption enhancement.