Microchannel enabled reforming of glycerol to hydrogen over Ni-based catalysts

Abstract

The aim of this study is to investigate glycerol steam reforming (GSR) and oxidative glycerol steam reforming (OGSR) over Ni-based catalysts in a microchannel reactor. The parametric study to investigate effects of reaction temperature, molar steam-to-carbon ratio in the feed (S/C), total flow rate and microchannel reactor configuration (packed and coated) on glycerol conversion and product distributions in GSR are investigated in the context of a parametric plan. Moreover, OGSR reactions are performed to study the effects of temperature and molar carbon-to-oxygen ratio at the inlet (C/O) on glycerol conversion and product distributions. 5 wt.% Ni/Al2O3 and 10 wt.% Ni/Al2O3 catalysts with 3-μm particle size (used in coated microchannel configuration) and 60-80 mesh (250 – 177 μm) size of 5 wt.% Ni/Al2O3 catalyst is prepared using incipient-to-wetness impregnation method. Blank tests show that the microchannel reactor components do not remain inert during the reactions. It is observed that glycerol conversion increases with temperature. Thermal decomposition of glycerol leads to production of methane, ethane and ethylene, and coke. S/C ratio affects the products distribution via the water gas shift reaction. Higher S/C ratios result in higher H2 selectivity which is defined as the moles of H2 produce per moles of glycerol converted. However, sintering of the Ni particles has a negative impact on glycerol conversion. Decreasing the total flow rate leads to an exponential increase in glycerol conversion because of increase in residence time. Coated microchannel configuration shows higher conversions and H2 selectivities than those observed in the packed microchannel configuration. OGSR experiments are found to give glycerol conversions significantly higher than those observed in GSR. Higher O2 content in the feed improves conversions, but decrease H2 yields and selectivity. Coke formation over catalyst surface in GSR and OGSR is inevitable. SEM and EDX analysis of catalysts are carried out to provide insight into the dispersion of active metal and carbon formation over catalyst surface at different values of temperature and S/C ratio.