Environmental Assessment of Liquid Hydrogen Production Routes

Abstract

Recently, hydrogen has been explored as an aviation energy carrier to support various critical energy challenges for the upcoming decades. Thus, conventional and non-conventional hydrogen production methods have been developed worldwide. This paper investigates Steam Methane Reforming (SMR) and Alkaline Electrolysis (AWE) hydrogen production as primary processes from an energy requirement and life cycle perspective. Besides, It also considers hydrogen liquefaction for aviation use. In this context, an attributional, Cradle-to-Gate life cycle assessment was carried out to compare the environmental impact of SMR and AWE hydrogen production processes under four German energy mix scenarios. The assessment method selected was ReCiPe 2016, and the main impact categories were climate change and acidification potential. The results show that greenhouse gas emissions from each production method highly depend on energy sources. The CO2 emissions from SMR and AWE processes in a base case scenario are 12 and 51 kgCO2eq/kgH2, respectively, and these values decrease to 7 (SMR) and 22 kgCO2eq./kgH2 (AWE) in a 2050 renewable energy scenario. Concerning the energy requirements, each process requires different energy amounts to produce 1 kgH2 (functional unit). SMR requires 11.3 kWh, AWE 61.8 kWh, and hydrogen liquefaction 5.1 kWh. In brief, hydrogen is widely promoted as an alternative energy carrier in Germany; however, depending on the production process and technical considerations, further studies are required to support and explore its applications.