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Studies on Adsorption and Membrane Separation Properties of Metal-Organic Frameworks

Author: WuDong
Tutor: ZhongChongLi; Guillaume Maurim
School: Beijing University of Chemical Technology
Course: Chemical Engineering and Technology
Keywords: metal-organic framework molecular simulation adsorption separation CO2capture flexible framework membrane separation
CLC: TQ028
Type: PhD thesis
Year: 2013
Downloads: 49
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Abstract


Metal-organic frameworks (MOFs), a new kind of nanoporous materials, have a wide potential application in gas storage, separation, catalysis, drug delivery and optical devices due to their various structures, multi-functional, large surface area and free volume, and adjustable pore surface. Although a large number of MOFs have been synthesized, in principle the number of MOFs to be synthesized is infinite.The application of MOFs in gas adsorption and membrane separation is one of the most promising fileds, and many MOFs show outstanding results in these applications. However, the large number of MOFs makes finding a suitable MOF for special industrial application difficult. Recently, computational chemistry, as a complement to experimental study, provides a swift and convenient approach to screen the MOF candidates and shorten the design and research period. As a result, it is important to screen best MOFs based on the combination of the two approaches. In this work, screening the best MOF candidates for specific separations were studied, in which both adsorption and membrane separations are studied. The main works are:1. Molecular simulations were performed to study a diverse collection of105MOFs for their ability to remove CH4from CH4/H2mixture involved in the process of H2purification. The information obtained based on such a large database will allow us to find out the structure-property relationship for CH4/H2adsorptive separation in MOFs, as well as to identify the key influencing factor. The new parameter,"adsorbility"(AD), was defined in this work to characterize the property of the MOFs, and the applicability was validated in this study.2. With the aid of molecular modeling combined with CBAC method, the separation performance of105MOFs with a large chemical and topological diversity for CO2capture from flue gas was examined under industrial pressure condition. A QSPR model was built from this extended series of MOFs in order to rationalize the resulting CO2/N2selectivity, and the new parameter "adsorbility" also shows good feasibility in this system. In addition, it thus leads us to tune a typical MOF UiO-66(Zr) with outstanding separation performance and a newly designed and highly selective MOF was obtained based on the QSPR strategies 3. For the newly synthesized UiO-66(Zr)-(COOH)2MOF obtained by the modification of UiO-66(Zr) using the dicarboxylic groups, a new flexible forcefield was developed for it to investigate the dynamic property of the framework. MD simulation was performed to validate the forcefiled by good description of the lattice property of the MOF and diffusion of CO2in the framework.4. In combination with the newly developed and validated flexible forcefiled for UiO-66(Zr)-(COOH)2, the dynamic separation of CO2from the CO2/CH4and CO2/N2mixture was further investigated for this MOF. As a result of the strong interaction of CO2with the framework, the functionalized UiO-66(Zr)-(COOH)2show high CO2selective performance as pure membrane. Furthermore, this MOF was used as additives to the fabrication of pure polymer membranes, and the resulted mixed matrix membranes (MMMs) also show high CO2separation ability.5. The modified chem-4Li MOF with the doping of metal Li in IRMOF-1shows strong interaction with CO2and thus exceptional CO2capture capability. A systematic study was conducted to explore the CO2separation ability for various industrial systems:CO2/H2, CO2/N2, CO2/O2, CO2/CO and CO2/C2H4. Further study was performed to reveal the underlying mechanisms for selectivity enhancement due to the adjustment of the pore structure by Li doping. The change of preferential adsorption sites and molecular-level segregation phenomena were also analyzed. It was found that metal doping is an effective way to enhance the separation performance of MOFs.

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CLC: > Industrial Technology > Chemical Industry > General issues > Chemical processes ( physical processes and physical and chemical processes ) > Separation process
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