Modeling and Techno-Economic Optimization of a Tetraamine-Appended Metal-Organic Framework for NGCC-Based CO₂ Capture Using Fixed Bed Contactors

Amine-appended metal-organic frameworks (MOFs) of the class Mg-2(dobpdc) have garnered attention recently as promising sorbents for CO2 capture but present difficult modeling challenges, in part due to their unique step-shaped adsorption isotherms. In this work, modeling and optimization of Mg-2(dobpdc)(3-4-3) (dobpdc(4-) = 4,4 '-dioxidobiphenyl-3,3 ' dicarboxylate; 3-4-3 = N,N ' bis(3-aminopropyl)-1,4-diaminobutane) is undertaken for CO2 capture from a natural gas combined cycle (NGCC) flue gas source. A new isotherm model is developed using a weighted Langmuir isotherm model that is extended to predict multistep isotherm shapes and is fit to experimental data of Mg-2(dobpdc)(3-4-3). The isotherm model is used to develop a dynamic, nonisothermal fixed bed contactor model that is validated with experimental breakthrough data. A temperature swing adsorption process using fixed bed contactors is developed to capture CO2 from an similar to 600 gross megawatt NGCC power plant. Using a cost model that closely follows the quality guidelines set forth by the National Energy Technology Laboratory, techno-economic optimization is performed using the Framework for Optimization, Quantification of Uncertainty, and Surrogates to minimize the cost of the capture system and subsequently compare it with state-of-the-art amine-based solvent systems. An uncertainty analysis of how the price of the MOF will affect the overall process economics is performed along with possible improvements due to heat recovery and high-temperature regeneration. The results show that the cost of capture is only similar to 30% higher than that of solvent capture systems under realistic heat recovery assumptions. This work also leads to an investigation of other fixed bed cycle types and contactor technologies as areas of future work.