(516b) New Highly CO2-Selective Amine-Based Membranes for Carbon Capture

CO₂ capture from flue gas in coal- and/or natural gas-fired power plants and from <1% CO₂ concentration sources, e.g., the residual flue gas after the primary CO₂ capture system and coal-mine gas streams, requires a high CO₂/N₂ selectivity of 140 along with a very high CO₂ permeance of about 700 GPU (1 GPU = 10^-6 cm³ (STP)/(cm² · s · cmHg)) or higher in order to use a stand-alone membrane process. For the CO₂ capture, we have synthesized new amine-containing membranes, showing a high CO₂/N₂ selectivity of >140 and a high CO₂ permeance of >1000 GPU. The membrane was scaled up to 14 inches in width using continuous roll-to-roll fabrication. Aided by a material balance equation, three variables, namely the coating-knife gap setting, web speed, and coating solution concentration, were identified as the critical factors to control the membrane selective layer thickness. This resulted in the membrane with a selective layer of <200 nm. The scale-up membrane was fabricated into spiral-wound membrane modules for testing with simulated flue gas containing about 20% CO₂, 77% N₂, 3% O₂ and 1 – 3 ppm. Both the scale-up membrane and the membrane modules exhibited similar results as the flat-sheet membrane tested in the lab. The membrane module has been scaled up to a size of more than 10,000 cm² membrane area. The module showed stable CO₂ permeance and CO₂/N₂ selectivity results for 1,700 hours. Techno-economic analysis has shown that the post-combustion capture process using the membrane is promising for meeting DOE’s capture cost target set for 2025. For carbon capture from <1% CO₂ concentration sources, we have elucidated the carrier saturation phenomenon. With reducing the CO₂ concentration in the feed gas, both CO₂ permeance and CO₂/N₂ selectivity increased. These were mainly due to more available free amine carriers for CO₂ molecular transport at lower CO₂ concentration conditions.