Hybrid membrane for better carbon capture

A HYBRID membrane made from a polymer and a metal-organic framework (MOF) is the most efficient yet for capturing CO₂ from flue gas, according to researchers at Lawrence Berkeley National Laboratory, US.

The membrane is more than eight times more permeable to CO₂ than membranes made from polymer alone. Permeability is key to the effectiveness of carbon capture membranes, and a problem with most current CCS membranes, which have relatively low permeability. Chemical engineer and researcher Norman Su led the research to develop the membrane with Jeff Urban, facility director of the Inorganic Nanostructures Facility at the National Laboratory’s Molecular Foundry, a nanoscale research centre. They believe the research will lead to the commercial production of much higher performing and cost-effective membranes for CCS.

The material is a porous 3D crystal with a very large internal surface area. It is made from polysulfone polymer and the MOF UiO-66-NH₂. The membrane contains about 50% MOF, which creates continuous channels throughout the material for the CO₂ to flow into. The researchers call these “carbon dioxide highways”. However, this is not the only way in which the material absorbs CO₂. The gas molecules can also diffuse through the polymer in the conventional manner, giving the material dual transport pathways.

Previous hybrid membranes created have only contained up to 30% MOF. Exceeding this threshold  weakens the membrane and breaks the continuity of the channels in the material. Su and Urban overcame the problems by using the amine derivative of the UiO-66 MOF. The amine group interacts with polar backbone groups in the polysulfone polymer, increasing the strength of the membrane.

“This is the first hybrid polymer-MOF membrane to have these dual transport pathways, and it could be a big step toward more competitive carbon capture processes,” said Su.

Energy & Environmental Science DOI: 10.1039/C5EE02660A