Biogas dry reforming using nickel supported on regenerated spent bleaching earth

Abstract

Currently, spent bleaching earth (SBE) is an abundant solid waste generated from crude palm oil refining that is discharged into landfills in Malaysia. It comprises a high percentage of silicon oxide (55-80 wt.%) and aluminium oxide (5-20 wt.%) with the potential to be reused as catalyst support. This study aims to evaluate the potential of nickel supported on regenerated spent bleaching earth (RSBE) for dry reforming of biogas into syngas. The RSBE was treated with different concentrations of nitric acid (x = 0.25M, 0.5M, 0.75M, and 1.0M), and then doped with 10 wt.% nickel using the wet-impregnation method. Subsequently, the synthesized catalysts were characterized to determine their reducibility, acidity, crystallinity, and the total surface area. The increase in acid concentration during RSBE treatment reduced the total surface area, acidity, and strength of the metal-support interaction of the Ni-RSBE catalysts. However, the high surface area, acidity and strong metal-support interaction of catalysts are beneficial to dry methane reforming in terms of anti-deactivation and catalytic activity. The performance of the catalysts was evaluated using a micro fixed bed reactor at 800 °C, 0.2 g of catalyst, and CH4/CO2 ratio of 1.2 at atmospheric pressure. The 10 wt.% Ni-RSBE catalyst with 0.25M and 0.5 M of acid treatment had almost similar catalytic performance to that without acid treatment. The conversion of CH4 and CO2 achieved was 55 to 57%, and 40 to 44%, respectively. Therefore, the Ni- RSBE catalyst without acid treatment was selected to further study the effect of nickel loading, reaction temperature, and CH4/CO2 ratio on the dry reforming of methane. Results showed that the presence of nickel promotes the dry reforming of methane as evident from the methane conversion, which increased from 15 to 56% with nickel loading from 0 to 15%. Besides, CH4 and CO2 conversion and syngas yield increased reaction temperature between 700 °C to 850 °C. In the aspect of the biogas feed ratio, the CH4 conversion and H2 yield decreased with the increase in the biogas feed ratio (0.7 - 1.5).