Progressing Thin-Film Membrane Designs for Post-Combustion CO2 Capture: Performance or Practicality?

Tremendous potential is seen in membrane technology for realizing efficient post-combustion CO2 capture from power plant flue gas, the largest anthropogenic source of emission. However, an examination of existing literature revealed a substantial gap between the sheer number of lab-scale materials with extraordinary CO2/N-2 separation performance and the small fragment of large-scale commercial developments that still perform below the new competitive industrial targets. An effective material approach aiming to bridge this gap is the multilayer thin-film composite (TFC) membrane design, which allows for the transformation of thick dense membranes with excellent theoretical intrinsic performances into a practical thin (<1 & mu;m) to ultrathin-film (<100 nm) configuration with high CO2 permeance and CO2/N-2 selectivity. Unavoidably, many design constraints surfaced during this transition due to the challenges of ultrathin-film fabrication, porous substrate design, increased vulnerability and deviation of gas transport properties at the thin-film state, which all compromise the scalability of TFC membranes. Yet, these constraints are often overlooked topics in current TFC membrane studies as they are generally performance-pursuing and tend to be more zealous about the discovery or re-innovating of novel selective layer materials with less concern over practicality issues. In this perspective, key existing TFC design criteria are revisited for each TFC component/layer with a critical evaluation of their oversight for some of the practical considerations, while keen research suggestions are being made in areas that could potentially enhance the performance or scalability of current designs, such as materials recommendation, structural modification targets, mechanistic study of thin-film state transport, and knowledge development for upscaling. Besides the conventional layer-on-layer TFC design, an integrated layer concept established on a microporous gutter layer is also proposed here. Lastly, the potential for translating existing flat sheet TFC designs into the industrially favorable hollow fiber configuration has been quite rigorously assessed.