Coordinatively unsaturated metal organic frameworks for olefin separations
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The research presented in this thesis aims to assess the capacity of metal organic frameworks with open metal sites for the separation of olefin mixtures. Chapter 1 provides a background to the field, including industrial separation techniques, metal organic frameworks and their applications and the current state-of-the- art for olefin separation. Chapter 3 describes the experimental techniques used in this research. Ethylene and propylene adsorption and desorption isotherms on Ni-CPO-27 and HKUST-1 at a range of temperatures are presented and compared in Chapter 4, and used to calculate isosteric heats of adsorption at varying coverages using the virial method. These pure component isotherms are used in Chapter 5 to predict selectivities for the separation of binary mixtures using ideal adsorbed solution theory. Temperature programmed desorption is used in Chapter 5 to calculate the enthalpy of desorption using Redhead’s method and the heating rate variation method, and the two results are compared. The results presented in Chapters 4 and 5 conclude that propylene/ethylene separation is possible using adsorption onto metal organic frameworks with open metal sites. A new in situ environmental gas cell for single crystal X-ray diffraction is developed in Chapter 6, and the challenges encountered during this development process are discussed. The dehydration of one framework, Co-CPO-27, is studied in detail using the environmental gas cell. A dehydrated structure of HKUST-1, obtained using the gas cell, is presented for the first time. Crystal structures for the complete dehydration-adsorption-delivery cycle for biologically active NO on Co-CPO-27 are presented in Chapter 7, showing the utility of the in situ gas cell for prolonged experiments in multiple different gaseous environments. The crystal structure of NO-loaded Co-CPO-27 improves upon the models suggested in the literature, and the treatment of the dual occupancy of the open metal sites by water and NO is discussed in depth. A crystal structure of CO-loaded Co-CPO-27 is obtained for the first time, and crystal structures of Co-CPO-27 in ethylene and propylene environments are presented.
Thesis, PhD Doctor of Philosophy