MOF adsorban ve membranlarının ayırma performansları: Yük dengeleme metodlarının etkileri

Metal organic frameworks (MOFs) have emerged as strong alternatives to traditional membrane and adsorbent materials due to their wide range of pore sizes, permanent porosities, and high surface areas. Considering the potential deficit of He, it is very important to develop efficient technologies for He recovery from the natural resources. In this thesis study, the first large-scale computational study to predict He/CH4 separation performances of various MOF membranes was conducted. Predictions of the molecular simulations were compared with the experimental data for He permeability of several MOF membranes. Motivated from the good agreement between experiments and simulations, 139 different MOF membranes were examined for He/CH4 separation. These 139 MOF membranes were compared with the traditional polymer and zeolite membranes. A significant number of MOF membranes was identified to exceed the Robeson's upper bound due to their high gas selectivities and permeabilities. Ideal and mixture selectivities of MOF membranes were also compared by performing molecular simulations both for single-component gases and binary gas mixtures. Results showed that selectivities and permeabilities calculated using the single-component gas data can significantly overestimate the ones calculated using the mixture data. Results of this study will be useful to guide the experiments for selecting the most promising MOF membranes for efficient He/CH4 separations. In the second part of this thesis, effects of using different charge equilibration methods, IQEq and QEq, on the ranking of MOF adsorbents for CO2/N2 and CO2/CH4 separations were investigated using 2244 MOF structures. Results show that, CO2 uptake is more sensitive to the charge assignment methods due to its quadrupolar nature. IQEq method was found to overestimate the adsorption selectivities and adsorption performance scores (APSs) of MOFs compared to the QEq method. The Spearman's rank correlation coefficients (SRCC), quantifying the similarity on the adsorption evaluation metrics predicted from two different sets of simulations using the IQEq and QEq methods, were found to be in the range of 0.73-0.84, indicating that there is a good similarity between the MOF rankings performed by using two different charge equilibration methods. Thus, it might be a good strategy to start a high-throughput computational screening study with the IQEq and narrow down the list of MOFs before implementing the DDEC method. Results of this work will be a guide for future computational studies to screen larger numbers of MOFs as adsorbents for the separation of quadrupolar molecules.