Green hydrogen enrichment with carbon membrane processes: Techno-economic feasibility and sensitivity analysis

Biohydrogen production from biomass through dark fermentation provides a great potential to achieve a green hydrogen economy for sustainable energy development. However, the purification of fermentative biohydrogen usually contains 30-40 vol% CO2 at small-scale plants requires advanced separation technologies. Carbon molecular sieving membranes are considered as an alternative solution in this application. This work focuses on the techno-economic feasibility analysis of H2-selective carbon membrane systems for biohydrogen enrichment by investigation of process design, optimization of operating parameters, and the selection of membrane materials. High vacuum operation on the permeate is favorable to reduce the specific cost as the membrane-related capital cost is dominating the total cost. While the operation with feed gas compression provides better separation performance, and the minimum specific cost of $ 0.026/Nm3 at 6 bar was identified to achieve the hydrogen recovery of 90%. A two-stage carbon membrane system is technically feasible to reach the biohydrogen purity of >99.5 vol% with the specific cost of $ 0.06/Nm3, which is lower than pressure swing adsorption. The sensitivity analysis indicates that the carbon membrane system is scalable and flexible in responding to the variation of plant capacity with the feed flow ranges from 500 to 2500 Nm3/h without significant changes in production cost. Compared to the enhancement of membrane selectivity, improving hydrogen permeance by developing submicrometer asymmetric carbon membranes is urgently needed to increase its competitiveness for biohydrogen purification.