Water gas shift membrane reactors

Water gas shift is a well-known reaction in which carbon monoxide reacts with steam to give carbon dioxide and hydrogen, representing an important step in the industrial production of hydrogen. The main role of this reaction is to increase the hydrogen content in the feed for the production of bulk chemicals such as methanol, ammonia, and hydrocarbons. It is today a crucial step in all of the thermochemical and catalytic technologies involved in the "biomass to liquid" processes. Water gas shift is an equilibrium-limited reaction moderately exothermic and favored at lower temperature, but in this condition it requires a suitable catalytic system, being limited by kinetic reasons. It is typically performed in conventional reactors via a two-stage process: a high-temperature shift (typically 643-673K, 10-60bar) and a low-temperature shift (~473K, 10-40bar). The first step is catalyzed by an iron oxide/chromium catalyst whereas in the second stage it is promoted by using a catalyst based on Cu/ZnO(Al<inf>2</inf>O<inf>3</inf>). In the Fischer-Tropsch reactors catalyzed by iron catalyst, water gas shift is a parallel reaction and two different chemical regimes can be observed depending on the operative conditions. An alternative device for generating high-grade hydrogen from the water gas shift reaction is the membrane reactor. This chapter analyzes and resumes the recent advancements in the water gas shift reaction in membrane reactors, paying particular attention to hydrogen-selective membrane utilization for high-temperature applications.