The purification of fermentatively produced hydrogen using membrane technology: a simulation based on small-scale pilot plant results

Hydrogen is known as one of the most promising energy carriers of the future. Its production in a sustainable manner is therefore an important step towards a competitive alternative to fossil energy sources. Dark fermentation is such a sustainable pathway, as hydrogen is produced via biotechnological conversion of biomass. But, the resulting hydrogen-rich gas from fermentation still needs to be upgraded, which can be done via membrane technology. In this work, an innovative small-scale process was developed, membrane modules were assembled and tested, and the purification method was simulatively investigated. The laboratory tests with pure gases showed that the utilized commercially available H₂-selective membranes have an ideal H₂/CO₂-selectivity of 3.3, at the respective process conditions. When applying gas mixtures, the H₂/CO₂-selectivity was reduced. To further investigate the purification method, an Aspen Plus^® gas permeation simulation model was used. The single-stage model was evaluated and it reflected the results from field and laboratory tests well. Furthermore, three different multi-stage setups were developed, simulated, and analyzed. The utilization of H₂-selective material in a two-stage process resulted in a specific energy demand of 0.400 kWh/Nm³H₂, but achieved no sufficient hydrogen purity. Compared to that, the use of CO₂-selective membranes demanded only 0.296 kWh/Nm³H₂. The recycle to feed ratio, as well as the H₂-puriy of 95.5 vol% in the product was also in favor of the CO₂-selective membranes compared to the commercially available H₂-selective material.