Biogas Upgrading by Pressure Swing Adsorption Using Zeolite 4A. Effect of Purge on Process Performance

The use of bio-methane as a fuel is an important alternative to reduce the emission of greenhouse gases. Pressure swing adsorption (PSA) processes using carbon molecular sieve adsorbents are industrial state-of-the-art technologies for biogas upgrading. Replacing the CMS adsorbent with a cheaper alternative can be a way to reduce costs for downscaling the technology to make it available to farms operating at low flows and avoiding large methane emissions to atmosphere. We have evaluated the use of zeolite 4A as a selective material that partially excludes (or strongly delays) CH4 adsorption. Adsorption equilibrium and kinetics (at zero-coverage) of pure gases (283, 303 and 323K) was measured. Adsorption equilibrium was fitted with the multi-site Langmuir model and there is a difference of 3 orders of magnitude in diffusion constants. Binary breakthrough and a two-column PSA experiment were performed to validate a mathematical model. The model was used to determine good operating conditions with this adsorbent material. Bio-methane purity over 98% was obtained at a recovery biome-thane of ∼90%. These performance indicators were obtained in similar pressure conditions as commercial adsorbents used in industrial PSA units indicating that zeolite 4A is a viable alternative for biogas upgrading processes.