Thermodynamic analysis of calcium oxide assisted hydrogen production from biogas

Abstract

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/SiO 2·MgO) arrangements; i.e. (i) Ni/SiO 2·MgO before CaO, (ii) CaO before Ni/SiO 2·MgO, (iii) Ni/SiO 2·MgO mixed with CaO, and (iv) Ni/SiO 2·MgO without CaO. The mixture of CaO and Ni/SiO 2·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 H 2O/CH 4 and CaO/CH 4 ratios on the required O 2/CH 4 ratio, hydrogen yield, hydrogen concentration and CO/H 2 ratio in product were determined. Obviously the use of CaO adsorbent can improve hydrogen production and there is an optimum H 2O/CH 4 ratio which offers the highest hydrogen production at each CaO/CH 4 ratio. Increasing H 2O/CH 4 ratio generally increases H 2/CO ratio but decreases hydrogen concentration in the product.