Thermodynamic analysis of calcium oxide assisted hydrogen production from biogas

This paper investigates calcium oxide assisted hydrogen production from biogas. Preliminary experiments were performed to compare the catalytic performance of combined carbon dioxide reforming and partial oxidation of biogas among four different adsorbent (CaO)/catalyst (Ni/SiO2·MgO) arrangements; i.e. (i) Ni/SiO2·MgO before CaO, (ii) CaO before Ni/SiO2·MgO, (iii) Ni/SiO2·MgO mixed with CaO, and (iv) Ni/SiO2·MgO without CaO. The mixture of CaO and Ni/SiO2·MgO was found to be the best arrangement, offering the highest hydrogen yield. Thermodynamic investigation of the integrated sorption-reaction systems for hydrogen production from biogas was performed. The system can be operated under thermal neutral condition when appropriate operating parameters are adjusted. Finally based on the thermal neutral operation, the effects of H2O/CH4 and CaO/CH4 ratios on the required O2/CH4 ratio, hydrogen yield, hydrogen concentration and CO/H2 ratio in product were determined. Obviously the use of CaO adsorbent can improve hydrogen production and there is an optimum H2O/CH4 ratio which offers the highest hydrogen production at each CaO/CH4 ratio. Increasing H2O/CH4 ratio generally increases H2/CO ratio but decreases hydrogen concentration in the product.