Hydrogen production via sorption enhanced biogas steam reforming using nickel-based catalysts

Abstract

Hydrogen production via sorption enhanced biogas steam reforming is a process that combines CO₂ adsorption and hydrogen production in one unit operation. CaO is selected as an adsorbent because it has the highest stoichiometric adsorption capacity (78.6%) when compared with Li₂ZrO₃, K-Li₂ZrO₃, Na₂ZrO₃ and Li4SiO₄. CO₂ adsorption tests of CaO were carried out at different temperatures (450, 500, 550 and 600°C). The CO₂ sorption results showed the highest adsorption capacity at 600°C (0.2849 gCO₂/gCaO). In addition, the effect of steam in the feed of the CO₂ sorption process was considered. The results indicated that CO₂ sorption with the presence of steam (0.6724 gCO₂/gCaO) was higher than that without steam effect because steam can increase adsorption capacity by increasing CaO porosity. Four types of bed arrangement for sorption enhanced biogas steam reforming at S/C of 3, CH4/CO₂ of 1.5, reaction temperature of 600 °C and atmospheric pressure were performed. The results exhibited that bed arrangement type II (12.5 wt.% Ni/Al₂O₃ mixed with CaO) offered the highest improvement of CH₄ conversion (93% with CO₂ sorption effect and 80% without CO₂ sorption effect) and of purity of hydrogen product (97.3% with CO₂ sorption effect and 60% without CO₂ sorption effect). It was clear that when a lower reaction temperature of 500 °C was tested, the higher improvement of CH₄ conversion was increased (91.2% with CO₂ sorption effect and 27% without CO₂ sorption effect). Furthermore, when the catalyst was loaded on adsorbent as support (12.5 wt.% Ni/CaO and 5.4 wt.% Ni/CaO), the deactivation was observed.