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

Hydrogen (H) separation and purification is challenging because of the high purity and recovery requirements in particular applications, as well as the critical properties of H and its associated components. Unlike pressure swing adsorption, cryogenic- and membrane-based technologies are currently employed for H separation. Membrane-assisted (case-I) and cryogenic-assisted (case-II) separation and purification of H were evaluated in this study in terms of the energy, exergy, and economic aspects of the processes. In case-I and case-II, H 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 H purity and recovery rates are the main limitations of case-I. In terms of exergy, the H 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 H separation and purification technologies for improving the overall H economy.