ABSTRACT
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], CO2 scrubbing of power plant combustion exhausts [6], and capture of CO2 from advanced power generation sources such as the integrated gasi‚- cation combined cycle (IGCC) [7,8]. Carbon capture and storage (CCS) is an ef‚cient way to reduce CO2 concentration in the atmosphere. It is a three-step process including capture of waste CO2 from other emissions before entering the atmosphere, CO2 transportation to a storage site, and its permanent storage. Among them, the CO2 capture 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/ CH4 and CO2/N2 mixtures: 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 CO2 from gases and utilizes alkanolamines such as monoethanolamine (MEA) in aqueous solutions as the adsorbent, relying on the chemical reaction between the amine group and CO2 to generate carbamate or bicarbonate [9]. The biggest problem with amine scrubbing, however, is that large amounts of heat are needed to release absorbed CO2 during 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 dif‚cult 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 CO2 molecules is a reversible process that requires much less energy for desorption. Traditional adsorbents such as zeolites and activated carbons have been extensively studied for CO2 capture [11,12].
