Graphene-based membranes – a new opportunity for CO2 separation

Currently, membrane separation processes play a very significant role in the separation industry. Widely used membrane processes include microfiltration, ultrafiltration, nanofiltration, reverse osmosis, electrolysis, dialysis and gas separation. In particular, membrane-based gas separation is commonly used for O2/N2, H2/N2, H2/CH4, H2 recovery from ammonia plants or in oil refinery processes, CH4 separation from biogas, CO2/ CH4, and volatile organic compound (VOC) removal. Among these, CO2/N2 separation has been a hot issue in membrane fields because of an urgent need for CO2 capture from fossil-fuelled power plants, in industrial processes and in the fuel production and transformation sectors, to prevent global warming and climate change. But what are challenges for CO2 capture? CO2 capture can be done with technologies presently available, but this will increase power generation costs, will require more fossil fuel for the same power generation capacity and will increase our reliance on fossil fuels, increasing the supply security concerns. On top of this, there is no experience with CO2 capture at the power plant scale. CO2 capture technologies can be classified into either process or technology platform/components. The process component includes post-combustion decarbonization (conventional power plants), precombustion decarbonization (new power plants) and denitrogenation (new power plants). The technology component includes membranes, absorption, adsorption, cryogenics, carbon extraction, biotechnology and energy conversion. Undoubtedly, the best technology for individual CCS applications depends on the power plant and its fuel characteristics. A current leading technology for post-combustion CO2 capture is amine absorption. Indeed, amine absorption is a proven, mature technology for separating CO2. However, the cost of CO2 capture from flue gas with amines is still high (US$40–80/t CO2), while the US Department of Energy target requires below $30/t CO2 [1]. In addition, amine energy requirements are also high (>30% of the power plant production), while the US Department of Energy target is <20% parasitic energy loss. Amines are adversely affected by oxygen and SO2, and amine adds 3 m/h/MW in water usage [2]. Amine plants cover ~5 acres; therefore, large numbers of towers are needed so that the scaling advantage of absorption processes disappears. In this regard, membrane-based gas separations offer great potential as an energy-efficient, low-cost CO2 Carbon Management (2014) 5(3), 251–253