Recent developments in membrane technologies for CO₂separation

Separation of carbon dioxide from other gases is critically important for many industrial applications, such as hydrogen production [1-3], natural gas puri-cation [4], biogas puri-cation [5], CO₂scrubbing of power plant combustion exhausts [6], and capture of CO₂from advanced power generation sources such as the integrated gasication combined cycle (IGCC) [7,8]. Carbon capture and storage (CCS) is an efcient way to reduce CO₂concentration in the atmosphere. It is a three-step process including capture of waste CO₂from other emissions before entering the atmosphere, CO₂transportation to a storage site, and its permanent storage. Among them, the CO₂capture is the most challenging key step in which new adsorbent materials need to be developed. Three main approaches have been proposed for the separation of CO₂/CH₄and CO₂/N₂mixtures: absorption with liquid solvents, membranes, and adsorption using porous solids. Conventional adsorbent materials rely on either chemisorption or physisorption to capture CO₂. Amine scrubbing has been extensively used in order to remove CO₂from gases and utilizes alkanolamines such as monoethanolamine (MEA) in aqueous solutions as the adsorbent, relying on the chemical reaction between the amine group and CO₂to generate carbamate or bicarbonate [9]. The biggest problem with amine scrubbing, however, is that large amounts of heat are needed to release absorbed CO₂during adsorbent regeneration. Moreover, the amine scrubbing solutions are corrosive and chemically unstable upon heating. Additionally, because of their liquid form, their handling is considerably more difficult than that of solid adsorbents. In amine-functionalized absorbents such as mesoporous molecular sieves in solid form although they partially overcome some of the aforementioned limitations, their parasitic energy waste is still pretty high [10]. In contrast, physisorption between solid adsorbents and CO₂molecules is a reversible process that requires much less energy for desorption. Traditional adsorbents such as zeolites and activated carbons have been extensively studied for CO₂capture [11,12].