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KOÇ UNIVERSITY

GRADUATE SCHOOL OF SCIENCES & ENGINEERING

CHEMICAL AND BIOLOGICAL ENGINEERING

MS THESIS DEFENSE BY ÖZGE KADIOĞLU

 

Title: Separation Performance of MOF Adsorbents and Membranes: Effect of Charge Equilibration Methods

 

Speaker: Özge KADIOĞLU

 

Time: 08.08.2018, 09:00

 

Place: ENG B29

Koç University

Rumeli Feneri Yolu

Sariyer, Istanbul

Thesis Committee Members:

Assoc. Prof. Seda KESKİN AVCI (Advisor, Koç University)

Assoc. Prof. Alper UZUN (Koç University)

Asst. Prof. İlknur ERUÇAR FINDIKÇI (Özyeğin University)

Abstract:

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 were conducted. 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 performing molecular simulations both for single-component gases and the 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, the 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 through 2244 experimental structures. Our results show that, CO2 is more sensitive to the charge assignment methods due to its quadrupolar nature. IQEq method tends to overestimate the adsorption selectivities and APSs of MOFs compared to the QEq method. The calculated correlation factors (SRCC) quantifying the similarity on the adsorption evaluation metrics predicted from two different sets of simulations using the IQEq and QEq were found to be in the range of 0.73-0.84. We also compared the CO2 uptake and the CO2 adsorption selectivities computed using the IQEq method with the ones computed by using DDEC. The high correlation coefficients indicate that 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.

 

 

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