Hybrid Membranes Incorporating Hollow Frameworks For Ethanol Dehydration Process Intensification

Hybrid membranes,which integrate the advantages of polymers and fillers,are promising to conquer the intrinsic“trade-off”effect and achieve the simultaneous improvememt of permeability and selectivity.This study utilizes ethanol/water mixture as separation system.As the synergetic intensification of solution and diffusion processesforguidingideology,thefreevolumeproperties,hydrophobicity/hydrophilicity,molecular sieving effect and interfacial morphologies of hybrid membranes are optimized by tailoring the topology structure and chemical composition of fillers,namely,integrating the superiotities of hollow structure and frameworks.The main research works are as follows:Hollow zeolitic imidazolate framework-8?HZIF-8?nanospheres were blended with sodium alginate?SA?.The pore on HZIF-8 shell possessed a diameter of 3.4?,which held the molecular sieving effect of water molecules and ethanol molecules,thus enhancing the solubility selectivity of hybrid membranes.The hollow structure of HZIF-8 minished diffusion resistance for water molecules,which increased the permeation flux as well as separation factor.Besides,the interference effect of HZIF-8on SA chains elevated the fractional free volume and also provided desired free volume cavity size,thus enhancing the permeability and selectivity of hybrid membranes simultaneously.At the loading content of 6 wt%,the maximum performance was achieved with permeability of 2846 and separation factor of 1884.Bimetallic metal-organic frameworks nanocages Fe^?-HMOF-5 were synthesized and then doped in SA by physical blending method.The introduction of Fe³⁺ions provided hydrophilic coordinatively unsaturated sites with preferential adsorption ability towards water molecules.The hollow structure effectively shortened the diffusion distance,thus contributing to the rapid transport of molecules.The unique chemical composition and physical structure of Fe^?-HMOF-5 enhanced the solution and diffusion process of hybrid membranes.The hybrid membrane with 6 wt%Fe^?-HMOF-5 display permeability of 3463 and separation factor of 3423.To further improve the compatibility of polymer and fillers,a kind of covalent organic framework?COF?with hollow structure:H-TpBD was incorporated in SA matrix to fabricate hybrid membranes.The hydrophilic H-TpBD improved the solubility selectivity of hybrid membrane by preferentially absorbing water molecules.Its hollow structure ensured the free diffusion of water molecules,which was in favor of the simultaneous enhancement of permeability and selectivity.Besides,H-TpBD could bond with SA chains,which not only disrupted the packing manner of SA chains,but also eliminated the non-selective interfacial morphologies.The optimized separation performance was obtained in 6 wt%H-TpBD loaded hybrid membrane with permeability of 4442 and separation factor of 1651.