Postcombustion Carbon Capture Using Thin-Film Composite Membranes

Climate change due to anthropogenic carbon dioxide emissions (e.g., combustion of fossil fuels) represents one of the most profound environmental disasters of this century. Equipping power plants with carbon capture and storage (CCS) technology has the potential to reduce current worldwide CO₂ emissions. However, existing CCS schemes (i.e., amine scrubbing) are highly energy-intensive. The urgent abatement of CO₂ emissions relies on the development of new, efficient technologies to capture CO₂ from existing power plants. Membrane-based CO₂ separation is an attractive technology that meets many of the requirements for energy-efficient industrial carbon capture. Within this domain, thin-film composite (TFC) membranes are particularly attractive, providing high gas permeance in comparison with conventional thicker (∼50 μm) dense membranes. TFC membranes are usually composed of three layers: (1) a bottom porous support layer; (2) a highly permeable intermediate gutter layer; and (3) a thin (<1 μm) species-selective top layer. A key challenge in the development of TFC membranes has been to simultaneously maximize the transmembrane gas permeance of the assembled membrane (by minimizing the gas resistance of each layer) while maintaining high gas-specific selectivity. In this Account, we provide an overview of our recent development of high-performance TFC membrane materials as well as insights into the unique fabrication strategies employed for the selective layer and gutter layer. Optimization of each layer of the membrane assembly individually results in significant improvements in overall membrane performance. First, incorporating nanosized fillers into the selective layer (poly(ethylene glycol)-based polymers) and reducing its thickness (to ca. 50 nm) through continuous assembly of polymers technology yields major improvements in CO₂ permeance without loss of selectivity. Second, we focus on optimization of the middle gutter layer of TFC membranes. The development of enhanced gutter layers employing two- and three-dimensional metal-organic framework materials leads to considerable improvements in both CO₂ permeance and selectivity compared with traditional poly(dimethylsiloxane) materials. Third, incorporation of a porous, flexible support layer culminates in a mechanically robust high-performance TFC membrane design that exhibits unprecedented CO₂ separation performance and holds significant potential for industrial CO₂ capture. Alternative strategies are also emerging, whereby the selective layer and gutter layer may be combined for enhanced membrane efficiency. This Account highlights the CO₂ capture performance, current challenges, and future research directions in designing high-performance TFC membranes.