Within five years, four large power plants in Europe will be outfitted — for testing at the pilot scale — with energy-efficient CO2-filtering membranes that are being developed at the Norwegian University of Science and Technology (NTNU; Trondheim; edlinks.chemengonline.com/6901-531). Professor May-Britt Hägg, head of the membrane research group (MEMFO) at NTNU’s chemical engineering department, says that the membrane is the first cost-effective means of removing CO2 from flue gas. Hägg also says that the membrane can easily retrieve 85% of the CO2 at 90% purity.
Conventionally, carbon capture from flue gas has required large absorption towers where gas is bubbled through a hazardous amine solution, which must then be transported to an energy-intensive desorption tower for CO2 removal. Among the proposed alternatives, supported liquid membranes have tended to degrade quickly, due to entrainment of CO2-carrier liquids in the gas flow. MEMFO’s membrane resolves these issues by using a comparatively immobile polyvinylamine nanoplastic as a “fixed-site–carrier,” with NH4F crosslinked in its polymer structure for improved anion exchange. When saturated with water vapor from the flue gas, the amine and fluoride ions will individually complex with CO2 as bicarbonate. Frequent regeneration of the membrane is not needed as the HCO3– anion reemerges as CO2 after it is shuttled through (diagram).
The membrane has been tested at laboratory scale for five years using a simulated flue gas of heated nitrogen, methane, carbon dioxide and water vapor. “We are about to build a small pilot for a small gas stream (about 0.15 Nm3/h) focusing much on durability of the membrane over time when exposed to real flue gas,” says Hägg. “If tests go well, we will go for a larger pilot in about three years.”
MEMFO was recently awarded €1 million for its participation in Nanostructured Membranes against Global Warming,” a €13-million consortium project with 26 European institutions and industrial partners.