Carbon Dioxide Capture by Tertiary Amidine Functional Adsorbents

In the recent past carbon dioxide capture from gas streams has been done using multiple methods. These methods include cryogenic, membrane, O2/CO2 recycle combustion systems, physical absorption, and chemical absorption. The most common of these methods is chemical absorption, which typically uses primary and secondary amines. MEA and DEA are the most common amines used for carbon dioxide capture. These amines bind carbon dioxide at a 2:1 molar ratio. These systems are liquid systems that require large amounts of energy for regeneration and recirculation. Liquid amine systems typically bind 2.5 to 4 mol CO2/kg absorbent at the 2:1 molar ratio. Liquid tertiary amines and amidines have been shown to bind carbon dioxide at a 1:1 molar ratio, thereby reducing the volume of amine, but the binding is much slower. Amine blends have been used to compensate for this difference. In order to reduce regeneration and recirculation costs and increase CO2 binding capacity solid adsorbents are being considered. Solid adsorbents using amidines allow for low regeneration costs and twice the carbon dioxide capacity per mol of adsorbent. This research focuses on the creation of amidine functionalized solid adsorbents to bind carbon dioxide in the presence of water. Amidine and guanidine functional groups increase capacity for carbon dioxide binding. Several amidine compounds and a guanidine containing compound have been synthesized and show increased binding capacity of carbon dioxide compared to conventional liquid systems. By reducing molecular weight of the nonbinding portion of the polymer, an amidine polymer can bind almost two times that of the other adsorbents created. The polyamidine bound 9.30 mol CO2/kg polymer while the polyguanidine bound over 6 mol CO2/kg polymer. These experiments were done in a 10 mL batch reactor at 45 psi at room temperature. Water (liquid) was added prior to the experiment at a 1:1 molar ratio with the binding sites in the polymer. There is still much work to be done to understand amidine polymer binding completely, including kinetic tests, but there is much promise in amidine polymer adsorbent technology