Separation and purification of syngas-derived hydrogen: A comparative evaluation of membrane- and cryogenic-assisted approaches

Abstract

Hydrogen (H2) separation and purification is challenging because of the high purity and recovery requirements in particular applications, as well as the critical properties of H2 and its associated components. Unlike pressure swing adsorption, cryogenic- and membrane-based technologies are currently employed for H2 separation. Membrane-assisted (case-I) and cryogenic-assisted (case-II) separation and purification of H2 were evaluated in this study in terms of the energy, exergy, and economic aspects of the processes. In case-I and case-II, H2 was first produced from synthesis gas via the water-gas shift reaction and was then separated from other components using membrane and cryogenic systems, respectively. Additionally, an organic Rankine cycle was integrated with the water-gas shift reactors to recover the waste heat. A well-known commercial process simulation software, Aspen Hysys® v11, was employed to simulate both processes. Energy analysis revealed that case-I has a lower energy consumption (0.50 kWh/kg) than case-II (2.01 kWh/kg). However, low H2 purity and recovery rates are the main limitations of case-I. In terms of exergy, the H2 separation section in case-I exhibited a higher efficiency (28.4%) than case-II (14.7%). Furthermore, the economic evaluation showed that case-I was more expensive ($17.7 M) than case-II ($10.2 M) because of the high cost of the compressors required. In conclusion, this study could assist industry practitioners and academic researchers in selecting optimal H2 separation and purification technologies for improving the overall H2 economy.