Hydrogen production

Abstract

Hydrogen (H2) is mainly used in chemical industry currently. In the near future, it will also become a significant fuel due to advantages of reductions in greenhouse gas emissions, enhanced energy security, and increased energy efficiency. To meet future demand, sufficient H2 production in an environmentally and economically benign manner is the major challenge. This chapter provides an overview of H2 production pathways from fossil hydrocarbons, renewable resources (mainly biomass), and water. And high-purity H2 production by the novel CO2 sorption-enhanced gasification is highlighted. The current research activities, recent breakthrough, and challenges of various H2 production technologies are all presented. Fossil hydrocarbons account for 96 % of total H2 production in the world. Steam methane reforming, oil reforming, and coal gasification are the most common methods, and all technologies have been commercially available. However, H2 produced from fossil fuel is nonrenewable and results in significant CO2 emissions, which will limit its utilization. H2 produced from biomass is renewable and CO2 neutral. Biomass thermochemical processes such as pyrolysis and gasification have been widely investigated and will probably be economically competitive with steam methane reforming. However, research on biomass biological processes such as photolysis, dark fermentation, photo-fermentation, etc., is in laboratory scale and the practical applications still need to be demonstrated. H2 from water splitting is also attractive because water is widely available and very convenient to use. However, water splitting technologies, including electrolysis, thermolysis, and photoelectrolysis, are more expensive than using large-scale fuel-processing technologies and large improvement in system efficiency is necessary. CO2 sorption-enhanced gasification is the core unit of zero emission systems. It has been thermodynamically and experimentally demonstrated to produce H2 with purity over 90 % from both fossil hydrocarbons and biomass. The major challenge is that the reactivity of CO2 sorbents decays through multi-calcination-carbonation cycles.