Renewable hydrogen-rich syngas from CO2 reforming of CH4 with steam over Ni/MgAl2O4 and its process optimization

Abstract

In this study, carbon dioxide reforming of methane with steam was carried out over Ni/MgAl2O4 catalyst in a fixed bed reactor. Various characterization methods were employed, such as X-ray diffraction, nitrogen adsorption–desorption isotherm, transmission electron microscopy, and field emission scanning electron microscopy to validate the synthesis of freshly annealed catalyst. The effects of process variables, such as reaction temperature, catalyst weight, steam-to-carbon ratio, and methane-to-carbon dioxide feed ratio, were evaluated using response surface methodology through a four-factor, three-level central composite design. Quadratic regression models were chosen in this investigation to analyse the interactions between process variables towards CH4 and CO2 conversions, as well as hydrogen yield. The optimum values for the process variables were set by maximizing the H2 yield and CH4 and CO2 conversions in the process model. In this study, the results indicated that catalyst weight was the most significant factor that determined the yield of hydrogen and the conversion of CH4 and CO2. The process optimization suggested the optimum process for reasonably high CH4 conversion (96.13%), CO2 conversion (53.77%), and high H2 yield (53.14%) can be obtained at 697.65 °C, S/C of 2.42, CH4/CO2 of 1.92, and catalyst weight of 2.30 g, which was then demonstrated by reproducing the experimental results. The spent catalyst was sent for characterization to determine the graphitic carbon formation on catalyst surface.