Analyses of one-step liquid hydrogen production from methane and landfill gas

Conventional liquid hydrogen (LH₂) production consists of two basic steps: (1) gaseous hydrogen (GH₂) production via steam methane reformation followed by purification by means of pressure swing adsorption (PSA), and (2) GH₂ liquefaction. LH₂ produced by the conventional processes is not carbon neutral because of the carbon dioxide (CO₂) emission from PSA operation. A novel concept is herein presented and flowsheeted for LH₂ production with zero carbon emission using methane (CH₄) or landfill gas as feedstock. A cryogenic process is used for both H₂ separation/purification and liquefaction. This one-step process can substantially increase the efficiency and reduce costs because no PSA step is required. Furthermore, the integrated process results in no CO₂ emissions and minimal H₂ losses. Of the five flowsheets presented, one that combines low and high temperature CO/CH₄ reforming reactions in a single reactor shows the highest overall efficiency with the first and second law efficiencies of 85% and 56%, respectively. The latter figure assumes 10% overall energy loss and 30% efficiency for the cryogenic process.