Membrane process design for biohydrogen purification with simultaneous CO₂ capture: Feasibility and techno-economic assessment

In this work, a membrane separation process is designed and optimized to purify dark fermentative biohydrogen by removing CO₂. A CO₂-selective PVAm-based nanocomposite membrane was selected considering its high CO₂/H₂ separation performance and unique features suitable for the process. We tested the membrane performances under the separation conditions to provide a more accurate simulation basis. Several design scenarios were investigated. A two-stage process with a recycle stream is determined as the optimal design, in which the specific cost for purifying H₂ to 99.5 vol% with H₂ loss of <10% reaches only 0.156 $/Nm3. The techno-economic feasibility study of biohydrogen purification with simultaneous CO2 capture was also performed through an alternative design by introducing a 3rd-stage using the same membrane or an H2-selective membrane. Adding a 3rd-stage membrane can capture and purify CO2 as a side product of various purities, which further decreases the H2 loss, leading to additional economic benefits.