Abstract
Membrane separation technology is considered to provide very promising solutions to energy and environmental challenges and has gained rapid growth in the past decades. The membranes designed with commercial polymers, crosslinked polymers, and porous coordination polymers (PCPs) or metal-organic frameworks (MOFs) exhibit outstanding performance regarding high selectivity and solvent permeability. Mixed matrix membranes (MMMs) or PCP-based mixed matrix membranes have desirable characteristics as they contain both properties of the polymer and inorganic fillers. In this study, the new MOF was synthesized and used as the filler in preparing MMMs and tested for hexane isomers adsorption selectivity. Two polymers were attempted in preparing MMMs: tertbutyl-polybenzimidazole (PBI-BuI) (synthesized) and Polyethersulfone (PES) (commercial polymer). The first part of this study was to develop a new MOF for separation of hexane isomers to improve the octane number of gasoline. MOFs are crystalline materials composed of metal precursors and organic linkers. These materials usually exhibit high thermal and chemical stability and a large surface area. The mixed ligands (carboxylic acid and pyrazole) approach was adopted for constructing MOFs using the solvothermal method. This resulted in a new MOF {[Zn(1,3-H2BDP)2(TPA)2]·DMF}n (1dmf), where 1,3-H2BDP= 1,3-benzenedipyrazole, TPA = terephthalic acid and DMF = N,N-dimethylformamide, for which the structure was established by single crystal X-ray Diffraction (SCXRD). Further characterization involved powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The activated phase (1a) was obtained when the as-synthesized sample (1dmf) heated at 250 ⁰C under a dynamic vacuum for 16 hours. The structural changes upon activation were observed by SCXRD analysis. Adsorption experiments were conducted by soaking 1a in hexane isomers as liquid binary, ternary, and quaternary mixtures. The results show the material to be selective for linear hexane (nHx) over monobranched {3-methylpentane (3MP) and 2-methylpentane (2MP)} and dibranched {2,2-dimethybutane (2,2DMB) and 2,3-dimethybutane (2,3DMB)} hexane isomers, with the uptake trend of nHx > 3MP > 2MP > 2,3DMB > 2,2DMB. The obtained adsorptive selectivity coefficients were found to be 2.48±0.01, 2.24±0.12, 3.79±0.035, 9.02±0.57, 5.75±0.48, 3.23±0.042, 3.44±0.035 for nHx/2MP, nHx/3MP, nHx/2,2DMB, nHx/2,3DMB, 2MP/2,2DMB, 3MP/2,2DMB, 3MP/2,3DMB, respectively.
M.Sc. (Chemistry)