Post-combustion Capture of Carbon Dioxide Emission Using Membrane Separation    

The rapidly increasing concentration of greenhouse gas carbon dioxide in the atmosphere has been related to global warming and subsequent problems. The US Energy Information Administration (EIA) predicts that total carbon dioxide emission in China will surpass 8 000 million tons per year by 2030. It is urgent to develop a solid process with high capacity, selectivity, regenerability and energy efficiency to separate carbon dioxide from flue gas. One promising approach is to capture carbon dioxide in large point sources such as power plants, which account for more than half of the carbon dioxide emitted in China. Broadly in this regard, three different types of technology exist: post-combustion capture (carbon dioxide is removed after combustion of the fossil fuel), pre-combustion capture (carbon dioxide is removed from the fuel before the combustion), and oxy-combustion (the fuel is burned in oxygen instead of air). Among the three, post-combustion capture is the best established one and also used in other industrial applications, such as soft drink production. It is well understood and can be typically built into existing power stations (known as retro-fitting) without significant modifications.
    Several approaches can be utilized in post-combustion carbon dioxide capture. These include adsorption, absorption, stripping, cryogenics, and membrane processing.
    Membrane plants using carbon dioxide-selective cellulose acetate membranes were installed in the 1980s. However, usage of cellulose acetate based membranes decreased substantially in recent years due to its potential of plasticization during the carbon dioxide capture process. Meanwhile, despite the well-known fundamental trade-off of throughput and selectivity, polymer membrane technology remains an active research area. Membrane Technology and Research (MTR) focuses on robust polymer materials which provide improved permeability or selectivity compared with conventional materials. These investigations aim at developing a new polyether-polyamide copolymer membrane that allows maximum throughput though the membrane. Carbozyme uses an enzyme catalyzed bicarbonate solution to facilitate membrane-based carbon dioxide removal from flue gas. Dr. Haibin Chen showed that the selectivity factor of carbon dioxide over oxygen or nitrogen could reach 200-300 in laboratory scale and a 90% carbon dioxide removal could be achieved. This is a substantial technical improvement over the conventional amine temperature swing technology.    
   Dr. Sebastien Reyes' group from Exxonmobil has been investigating a series of silicalite zeolites as potential membrane separation materials. Their primary goal is to separate carbon dioxide from other light gaseous hydrocarbon components in natural gas, as carbon dioxide not only reduces energy content but also corrodes transportation and storage systems in the presence of water.
     Compared with the conventional amine scrubbing procedure in post combustion carbon dioxide capture, membrane separation holds the unique advantages of low energy costs, low operating costs, and being environmental friendly. As the worldwide demand for carbon dioxide capture rapidly increases, the membrane separation technology will receive more and more attention.