Hybrid Membrane Absorption Process for Post Combustion CO2 Capture

Gas Technology Institute (GTI) and PoroGen Corporation are jointly developing an advanced, second-generation, hollow fiber contactor (HFC) technology for post-combustion CO₂ capture.  This novel HFC process uses hollow fiber membranes as the mass contacting device that combines advantageous features of both absorption and membrane processes to generate cost-effective separation and capture of CO₂ from various emission sources.  

CO₂-containing gas flows in the tube side of the small-diameter hollow fibers with porous walls, while a CO₂ selective solvent (typically an amine solution) flows in the shell side of the hollow fibers.  CO₂ passes through the nano-porous hollow fiber walls and is absorbed in the selective solvent. The CO₂ rich solvent can be regenerated in a second HFC module operated in a reverse process. In the regeneration case, the CO₂- loaded solvent is fed to either the shell-side or the tube-side of the HFC module depending on the modes of operation and on the hydrophilic/hydrophobic properties of the membrane. CO₂ is stripped out of the solvent by heating the solvent to regeneration temperatures upstream of the HFC or by steam stripping in the HFC. 

HFC is made from a chemically and thermally stable commercial engineered polymer poly(ether ether ketone) (PEEK).  It is because of the unique characteristics of PEEK (maximum service temperature as high as 271°C), the PEEK membrane contactor has been successfully used for both absorption and solvent regeneration. The PEEK membrane contactor can provide a platform for solvent-based systems beyond conventional amines. For post combustion CO₂ capture, the measured volumetric mass transfer coefficient of the hybrid membrane absorption process is as high as 1.8 (sec)^-1 at 90% CO₂ removal, which is more than 20 time greater than the maximum mass transfer coefficient of a packed column. The large mass transfer coefficient translates to much reduced equipment size. The reduced size requirements, in turn, translate to lower solvent inventories, and smaller footprint (lower visual impact) for siting at congested power plants. Since the gas and liquid phases are not directly in contact, tests show that the solvent purity levels remain high and solvent losses, from foaming and carryover, remain low. 

The advanced HFC technology provides a step change reduction in the cost of carbon capture and offers a transformational platform for mass transfer between gas and liquid. Successful development of this technology from laboratory to commercial deployment requires collaboration between R&D and various engineering disciplines.