Process integrated screening of metal organic frameworks for CO2 capture from natural gas fired power plants
Creators: Bharath, Yogashree
Publisher: name: University of Alberta Library
Year: 2024

<p>Separation of CO2 from dilute sources, such as natural gas flue gas or air, is challenging.Use of pressure swing adsorption may not cater to efficient separation. Hence, temperatureswing adsorption processes are proposed. However, a multitude of challenges are associatedwith the development of such processes. Most unique and important challenge is themarriage of an ideal adsorbent with an ideal process design. The main aim of this thesis isto address this grand challenge of adsorption. The thesis consists of results obtained frommodeling, simulations and experimental analysis.The primary goal of the thesis is to identify physisorbents from structural databasesusing a performance informed screening methodology. The Computationally Ready Experimental(CoRE) MOF was considered for this work. To understand the performance ofall the materials in the selected database in a 3-step TSA process, GCMC simulations wereperformed to obtain adsorption equilibrium data. The data was fit to appropriate isothermmodels. Rigorous multi-objective process optimization to evaluate the performance of aMOF under realistic process conditions was performed. In order to speed up the optimizationand without compromising on the accuracy, a machine learning framework wasdeveloped. 13 metal organic frameworks were selected and ranked based on process performance,material metrics such as selectivity and CO2 capacity, pore size and equlibriumcapacity of CO2 under humid conditions.The 13 MOFs were obtained from high throughput computational screening. An informeddecision involving economics, yield, conditions was considered for synthesis. Only 3 MOFs were synthesized and validated experimentally. Extensive experimental capaignswere carried out to characterize these MOFs. It was found that there were discrepanciesbetween simulated isotherms and experimentally obtained isotherms. The thesis developsmethodologies for computational screening, material characterization for CO2 capture. Italso identifies challenges in these workflows and how they can be overcome.The performance of novel adsorbents reported in literature was evaluated in a single 3-step temperature swing adsorption cycle. The novel material, a tetraamine appended MOF,exhibited properties highly suited for CO2 capture from dilute sources. Extensive numericalsimulations were performed to comprehend the impact of isotherm shape, heat transfercoefficient, feed temperature and heat capacity of solid on adsorption and desorption dynamicsin a fixed bed. A multi-objective optimization was performed to identify operatingconditions that achieve low steam consumption and high productivity while maintaininghigh purity (≥ 95%) and high recovery (≥ 90%). It was found that high purity and highrecovery are obtained only when the process is isothermal. Thermal fronts propagatingthrough the column impact the process performance. We show that the process cannotachieve recovery targets, i.e., ≥ 90%, unless heat is removed from the system rapidly. Thelowest achievable specific steam consumption is ≈ 45 kgsteam kg−CO12 and highest achievableproductivity is ≈ 0.1 molco2 m−ads3 s−1 in an isothermal scenario.</p>