Optimal process design of biogas upgrading membrane systems: Polymeric vs high performance inorganic membrane materials

Membrane separation is a key technology for biogas purification. Multistaged processes based on either cellulose acetate (CA) or polyimide (PI) materials are classically used for this application. In this study, a systematic process synthesis optimization is performed in order to identify the most cost effective solution for three different membrane materials (CA, PI and zeolite) and three different outlet pressure levels (5, 10 and 15 Bar). It is shown that a costly (i.e. 2000 EUR per square meter vs 50 for CA and PI) but high performance membrane material such a zeolite offers the best cost effective solution compared to commercially available polymeric membranes. Increasing the outlet pressure increases the purification cost. Two stages processes with recycling loops offer the best balance between purity, recovery, complexity and cost, whatever the outlet pressure level. The use of vacuum pumping is shown to improve the process economy, while expander and extra feed compression do not show an interest.