| Separation is the most intensive process of investment and energy consumption in the chemical industry,and the efficient separation of molecules with extremely similar structure is a challenging target in the chemical process.Adsorptive separation of these molecules based on porous solid materials is a more competitive technology compared with the energy-and cost-intensive cryogenic distillation.Metal-organic frameworks(MOFs)have drawn lots of interests for the adsorption and separation due to their highly designable and diverse structures,precisely controllable and uniform pore size.However,factors such as the highly cost of preparation,poor water and/or thermal stability have greatly restricted their applications in industry.In this thesis,the cheap and rigid four-and six-membered ring enol cycloketone ligands are introduced to construct chemical stable MOFs,which can be scale-up and molding easily,for adsorptive separation of the noble gases,C2-C8 molecules with highly similar structures.Besides,the adsorption performances and mechanism for these guest molecules are systematically evaluated,hoping some contribution of theoretical and technical support can be provided for the industrial application of MOF materials.The four-membered ring enol cycloketone based Ca(squarate)was successfully synthesized using hydrothermal and diffusion methods,and the crystal structure was obtained by the single-crystal X-ray diffraction,and the ethylene and propylene purification performances of Ca(squarate)were systematically evaluated.The pore size(6.94 A)of Ca(squarate)is large enough to accommodate all the C2 hydrocarbons,thus lead to moderate separation selectivity for ethane/ethylene and acetylene/ethylene,5.9 and 8.1,respectively.However,the pore size within Ca(squarate)matches well with the diameter of C3 hydrocarbon molecules which could lead to excellent ability to simultaneously capture trace propyne and propadiene molecules,obtaining high purity of propylene in only one-step.The volumetric uptake capacities of propyne(105.92 cm3/cm3)and propadiene(114.61 cm3/cm3)on Ca(squarate)are the highest among all reported porous materials at relatively low pressure as to 5 mbar and 298 K.The adsorption mechanism of C2 and C3 molecules within Ca(squarate)was studied through DFT simulation combined with single crystal X-ray diffraction,demonstrating that the strong ?-? stacking and C-H…O supermolecules interaction were the dominant adsorption interaction between the ?-electron from the unsaturated guest molecules and aromatic ligands within Ca(squarate)framework.Similarly,the four-membered ring enol cycloketone ligand,squaraic acid,was chose to construct a rigid Co(squarate)and its crystal parameters were solved through single-crystal X-ray diffraction.Besides,its separation performance of Xe/Kr at extremely dilute concentrations was fully measured.Co(squarate),featuring a perfect pore size(4.1 A×4.3 A)comparable with the kinetic diameter of Xe(4.047 A)as well as pore surface decorated with polar hydroxyl groups,is able to effectively discriminate Xe atoms,leading to strong adsorption binding sites for Xe molecules due to the combination of microporous confinement and polarization.The adsorptive separation and Henry selectivity of Xe/Kr were estimated to be 69.7 and 51.4,respectively,which was superior to the benchmark CROFOUR-1-Ni(22 and 24.3),ranking the first place among all reported materials.The feasibility of Xe capture and Xe/Kr separation performances were further measured through the dynamic breakthrough experiments.DFT calculations revealed that the strong interaction between Xe and the framework is a result of the synergy between optimal pore size and polar porosity.Encouraged by the above work,a similar six-membered ring enol cycloketone ligand,2,5-dihydroxy-1,4-benzoquinone,was introduced to form a series of isostructural M(?)-dhbq(M=Mg,Zn,Co,Mn)materials,of which pore size can be precisely controlled at 5.4-5.6 A.Mn-dhbq exhibited the highest adsorption amount for Xe among these isostructural materials and the separation selectivity of Xe/Kr was about 11.3,which was comparable to that of the famous SBMOF-1(16)and CO3(HCOO)6(12)MOFs.All the M(?)-dhbq materials exhibited good performances for Xe/Kr separation as confirmed by the direct fix-bed dynamic breakthrough experiments.Additionally,the dominant adsorption mechanism was demonstrated by DFT calculations,and the polarization of noble gases induced by the open metal sites played an important role in adsorption binding sites.Due to the pore size of the series of M(?)-dhbq materials was slight larger than the dynamic diameter of n-hexane(4.3 A),comparable to 3-methylpentane(5.0-5.5 A),and smaller than that of 2,3-dimethylbutane(5.8 A),the adsorptive separation of hexane isomers on these materials was systematically explored.The single-component vapor adsorption isotherms measured at 303-393 K revealed that Mn-dhbq material showed an exceptionally separation performance for selective adsorption of di-,mono-branched and straight hexane isomers by rationally controlled the adsorptive temperature.The other M(?)-dhbq(M=Mg,Zn,Co)materials,having a smaller pore size compared with that of Mn-dhbq,could only capture the smallest n-hexane molecules.The separation performances on the series of molded-shape and scale-up synthesis of M(?)-dhbq materials were fully characterized and investigated.The multi-component of hexane isomers fix-bed breakthrough experiments were conducted on the M(?)-dhbq samples,confirming their dynamic adsorptive separation of hexane isomers.The adsorptive separation of xylene isomers was further evaluated on Mn-dhbq material and it exhibited an excellent performance for separation of xylene isomers with the selectivity of 37.87 and 34.78 for PX/OX and PX/MX,respectively,at 363 K,which set a new benchmark for xylene isomers separation among reported MOFs materials.The affinity to xylene isomers was further confirmed through the TG analysis of Mn-dhbq@gylene samples.The dipole-dipole(Mn?+…C?-)and hydrogen bonds(H…O)as well as the ?-? stacking interactions between xylene isomer and aromatic ligands within the framework were the dominant adsorption interactions which was fully investigated by the DFT simulations.Fix-bed breakthrough experiments further conducted to confirm the dynamic xylene separation performance of the 1-2 mm shape-molded Mn-dhbq particles. |
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