Flourinated Membranes for CO2 concentration and Carbon Capture

The capture of CO₂ from power plants and industrial exhaust gases could significantly reduce CO₂ emissions. Flue gas streams are at atmospheric pressure and typically contain 4–20% CO₂ in mostly N_2. The objective of the separation process is to produce >99% pure liquid CO₂, at a pressure of 100–150 bars at a cost of $40 – 60/ton of CO₂ captured. Membranes have been suggested as a cost-effective method to concentrate teh CO2 found in flue gas streams to allow condensation to liquid CO₂. Because of the prohibitive cost of compressing the flue gas feed stream to generate a driving force across the membrane, vacuum operation on the permeate is more cost-effective. However, the pressure difference across the membrane is no more than 1 bar, so very high permeance membranes must be used. Today’s best membranes made from rubbery polar polymers have a CO₂ permeance of about 2000 GPU and a mixture CO₂/N₂ selectivity of 20–30 at operating conditions. Membranes with higher permeances would help reduce cost. For example, a membrane system for a typical 500 MW_e coal power plant is likely to have ~1 million m² of membranes, which would be a significant fraction of the plant cost. A doubling of membrane CO₂ permeance without selectivity loss would reduce the required membrane area by half, significantly reducing cost and increasing the competitiveness of the membrane process.

Compact Membrane Systems (CMS) has developed high permeance custom amorphous fluoropolymer (CAF) membranes for selective concentration of CO₂ from power plant flue gas and other industrial gases. The initial CAF results for concentrating CO₂ are very encouraging with very high permeances >2500 GPU. The CAF membranes also have high chemical resistance and high anti-fouling capabilities due to their highly fluorinated nature. This presentation will discuss our promising membrane results plus downstream engineering evaluation.