Novel Approach to Hydrogen Production with Suppressed COx Generation from a Model Biomass Feedstock
The alkaline thermal treatment of biomass has recently been proposed as a novel method for producing high purity H2 with suppressed COx formation under moderate reaction conditions (i.e., 523 K and ambient pressure). This technology has a great potential for sustainable bioenergy production because it can handle a wide range of feedstocks including biomass and biogenic wastes with high water content. Unfortunately, due to the complexity of the reactions involved, the alkaline thermal treatment of biomass is still poorly understood. In this study, using a model biomass system of glucose, a series of noncatalytic kinetic and mechanistic studies was performed to investigate the effects of reaction temperature and reactant ratios in terms of H2 conversion, purity, and formation rates of H2 as well as gaseous products such as CH4, CO, and CO2. The CO concentration is one of the important factors for the utilization of the product gas because CO is generally poisonous to catalytic systems such as those found in proton exchange membrane (PEM) fuel cells. Thus, high CO concentration would require additional gas cleanup processes. This study found that NaOH does play an important role in suppressing CO and CO2 formation while facilitating H2 production and promoting CH4 formation. The noncatalytic alkaline thermal treatment of glucose resulted in a maximum H2 conversion of about 27% at 523 K with a stoichiometric mixture of NaOH and glucose. While the H2 conversion was limited in the absence of catalyst, the moderate reaction conditions, low COx concentration, and solid–solid reaction scheme give advantages over conventional biomass conversion technologies. The solids analysis confirmed the presence of Na2CO3 in the solid product, indicating the inherent carbon management potential of the alkaline thermal treatment process.