Hydrogen from methane in a single-step process

Abstract

Addition of a calcium-based CO2 acceptor to commercial steam methane reforming catalyst permits the production of 95+% H2 in a single-step process. The combined reforming, shift, and CO2 separation reactions have been studied using a laboratory-scale fixed-bed reactor as a function of temperature, steam-to-methane ratio, acceptor-to-catalyst ratio, feed gas flow rate, and methane content of the feed gas. The combined reactions were sufficiently rapid above 550°C that equilibrium was closely approached at all reaction conditions studied. The H2 content of the product gas was relatively independent of temperature with the primary impurity at lower temperatures being CH4. Higher temperatures resulted in increased CH4 conversion but decreased carbon oxide removal leaving CO and CO2 as the primary impurities. Potential advantages of the single-step process, in addition to reducing the number of processing steps, include improved energy efficiency, elimination of the need for shift catalysts, and reduction in the temperature of the primary reactor by 150–200°C. Key unanswered problems involving the single-step process include continuous separation of catalyst and acceptor and the durability of the acceptor for multiple cycle operation.