(680c) Structure-Function Relationship of Type I CO2 Adsorbents Via Coupled Calorimetric and Volumetric Measurements

In this study, a series of linear and branched molecular and polymeric amines including triethylenetetramine (TETA), tris(2-aminoethyl)amine (branched TETA), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), linear polyethylenimine (PEI, M_n=423), and branched polyethylenimine (PEI, M_n=600) on silica material were used to synthesize amine-impregnated silica (Type I sorbents). The number of secondary amines in the amine structure increased in the order of b-TETA, TETA, TEPA, PEHA, and PEI amine materials. The experiments were performed in the equilibrium and isothermal conditions at various CO₂ concentrations for different temperatures and amine weight loadings. A variety of information from VA/DSC combination that includes differential and integral heat of adsorption, CO₂ adsorption capacity, distribution of adsorption site energies, energetic heterogeneity and lateral interaction, and thermodynamic parameters for the aminosilica materials have been investigated as a function of secondary amine. By combining an automated volumetric adsorption (VA) instrument and a commercial differential scanning calorimetry (DSC), we simultaneously evaluated the differential and integral heats of adsorption and adsorption isotherms of CO₂ adsorption on solid aminosilica materials. The volumetric adsorption instrument is used to measure CO₂ adsorption capacity at various CO₂ partial pressures while heat of adsorption at each equilibrium partial pressure is directly measured in DSC concurrently. The results demonstrated that heat of adsorption demonstrated non monotonic behavior with experimental variables, such as temperature and weight loading. At constant weight loading with increases in the ratio of secondary to primary amines, the heat of adsorption decreased. In general, branched amine molecules and PEI demonstrated larger heats of adsorption and lower capacities than linear versions.