(11g) Novel Membranes for CO2 concentration and Carbon Capture

The capture of CO₂ from power plants and industrial exhaust gases could significantly reduce man-made CO₂ emissions. Widespread adoption of this technology would go a long way to solve the global climate change issue. Flue gas streams from power plants typically contain 4–20% CO₂ in mostly N₂ and are at atmospheric pressure. The objective of the separation process is to produce >99% pure liquid CO₂, at a pressure of 100–150 bars at a cost in the range of $40 – 60/ton of CO₂captured. This is a tough cost target for any process to meet. One of the best approaches seems to be to use a membrane system to perform a bulk separation that produces a CO₂ concentrate stream containing 40–80% CO₂. A membrane – assisted condensation process is then used to produce liquid CO₂. Because of prohibitive cost of compressing the flue gas feed stream to generate a driving force across the membrane, vacuum operation with a pressure of 0.2–0.3 bar on the permeate is the approach generally used. The pressure difference across the membrane is then no more than 1 bar, so very high permeance membranes must be used. Today’s best membranes made from rubbery polar polymers have a CO₂permeance of about 2000 GPU and a mixture CO₂/N₂ selectivity of 20–30 at application conditions (30°C, water saturated). Increased selectivity is not particularly helpful because of pressure ratio limitations, but 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 roughly cut the required membrane area in half, significantly reducing cost and increasing the competitiveness of the membrane process.

Compact Membrane Systems (CMS) has developed custom amorphous fluoropolymer (CAF) membranes for selective concentration of CO₂ from power plant flue gas and other industrial gases. Initial attempts to develop CMS CAF membranes for concentrating CO₂ are very encouraging (CO₂ permeance 4,500 GPU, CO₂/N₂ selectivity 20-30). The CAF membranes are also expected to have high chemical resistance and high anti-fouling capability due to their highly fluorinated nature. This presentation will discuss our promising membrane results plus downstream engineering evaluation.