Membrane gas separation technologies for biogas upgrading

Biogas is a renewable energy source like solar and wind energies and mostly produced from anaerobic digestion (AD). The production of biogas is a well-established technology, but its commercial utilization is limited because on-site purification is needed before its transport or use. Biogas composition varies with the biomass digested and contains mainly methane (CH4) and carbon dioxide (CO2), as well as traces of hydrogen sulfide (H2S), ammonia (NH3), hydrogen (H-2), nitrogen (N-2), carbon monoxide (CO), oxygen (O-2). In some cases dust particles and siloxanes are present. Several purification processes including pressurized water scrubbing, amine swing absorption, pressure swing adsorption, temperature swing adsorption, cryogenic separation and membrane technologies have been developed. Nevertheless, membrane technology is a relatively recent but very promising technology. Also, hybrid processes where membranes are combined with other processes are believed to have lower investment and operation costs compared with other processes. In this report, a discussion on the different materials used to produce membranes for gas separation is given including inorganic, organic and mixed matrix membranes, as well as polymer of intrinsic microporosity (PIM). Advantages and limitations for each type are discussed and comparisons are made in terms of permeability and diffusivity for a range of operating conditions.