Improved performance of PDMS/silicalite-1 pervaporation membranes via designing new silicalite-1 particles

Incorporating Mixed-Ligand Zeolitic Imidazolate Framework into Polydimethyldiethoxysilane (PDMDES) Membrane for Enhancing Alcohol Pervaporation Recovery

In the present study, a zeolitic imidazolate framework with mixed ligands, ZIF-8-90, was synthesized and embedded into an ultrathin polydimethyldiethoxysilane (PDMDES) matrix to prepare a ZIF-8-90/PDMDES mixed matrix membrane (MMM) for the enhanced recovery of alcohols from dilute aqueous solutions via pervaporation, using a facile solution coating method. The synthesized ZIF-8-90 particles demonstrated superior hydrophobicity and thermal stability compared to those of both ZIF-8 and ZIF-90 particles. Furthermore, the hydrophobicity, thermal stability, and sorption ability for alcohols of the ZIF-8-90/PDMDES MMM were significantly improved, attributed to the incorporation of mixed-ligand ZIF-8-90. Notably, the MMMs displayed two distinct cross-sectional morphologies: (1) ZIF-8-90 particles enveloped by PDMDES polymer forming filler bulges and (2) an accumulation of ZIF-8-90 particles resembling a brick-wall-like structure. The MMM incorporating 2.5 wt % ZIF-8-90 exhibited the optimal performance among the fabricated MMMs with various ZIF-8-90 loadings, spanning from 0 to 3.2 wt %. The effects of feed concentrations and operation temperatures were systematically investigated. The best pervaporation performance was achieved using the 2.5 wt % ZIF-8-90-filled MMM, effectively separating a 5.0 wt % ethanol/water mixture at 60 °C, yielding a distinguished total flux of 7.70 kg·m-2·h-1, an improved separation factor of 9.96, and an extraordinarily high PSI of 68.99 kg·m-2·h-1. Comparative analyses highlighted the superior pervaporation performance of the ZIF-8-90/PDMDES MMM over ZIF-8/PDMDES MMM, ZIF-90/PDMDES MMM, and other MMMs, underscoring its potential for practical applications in alcohol recovery.

Preparation of modified MFI-type/PDMS composite membranes for the separation of dichlorobenzene isomers via pervaporation

Zeolite-polymer composite membranes have become promising and effective materials for the pervaporative separation of liquids, especially for isomeric mixtures. In this paper, silicalite-1/PDMS composite membranes have been used to investigate the separation of dichlorobenzene (DCB) isomers via pervaporation for the first time. Silicalite-1 zeolites modified by the silane coupling agent, NH3-C3H6-Si(OC2H5)3, have been incorporated into polydimethylsiloxane (PDMS). Then, the silicalite-1/PDMS composite membranes have been successfully prepared on porous polyvinylidene fluoride (PVDF) supports. The morphology and structure of the silicalite-1 zeolites and silicalite-1/PDMS composite membranes have been characterized by XRD, FTIR, SEM and BET techniques. The results show that the modified silicalite-1 zeolite particles have smaller pore sizes dispersed more uniformly in the active layers of the silicalite-1/PDMS composite membranes and present fewer aggregation and pinholes formed by the accumulation of zeolite particles. The silicalite-1/PDMS composite membranes are all dense and continuous with good homogeneity. To evaluate the pervaporative separation performance of the DCB isomers, the unmodified and modified silicalite-1/PDMS composite membranes have been further tested in single-isomer and binary-isomer systems at 60 °C. The modified silicalite-1/PDMS composite membranes present higher DCB isomer separation factors. The separation factors of the modified silicalite-1/PDMS composite membranes in the binary-isomer systems for p-/o-DCB and p-/m-DCB are 3.53 and 5.63, respectively. The permeate flux of p-DCB through the modified silicalite-1/PDMS composite membranes in the p-/o-DCB binary-isomer system is 116.7 g m-2 h-1 and in the p-/m-DCB binary-isomer system, it is 93.5 g m-2 h-1. The result provides a new approach towards the pervaporative separation of DCB isomers from their mixture for future industrialization applications.

Silicalite-1/PDMS Hybrid Membranes on Porous PVDF Supports: Preparation, Structure and Pervaporation Separation of Dichlorobenzene Isomers

Separation of dichlorobenzene (DCB) isomers with high purity by time− and energy−saving methods from their mixtures is still a great challenge in the fine chemical industry. Herein, silicalite-1 zeolites/polydimethylsiloxane (PDMS) hybrid membranes (silicalite-1/PDMS) have been successfully fabricated on the porous polyvinylidene fluoride (PVDF) supports to first investigate the pervaporation separation properties of DCB isomers. The morphology and structure of the silicalite-1 zeolites and the silicalite-1/PDMS/PVDF hybrid membranes were characterized by XRD, FTIR, SEM and BET. The results showed that the active silicalite-1/PDMS layers were dense and continuous without any longitudinal cracks and other defects with the silicalite-1 zeolites content no more than 10%. When the silicalite-1 zeolites content exceeded 10%, the surfaces of the active silicalite-1/PDMS layers became rougher, and silicalite-1 zeolites aggregated to form pile pores. The pervaporation experiments both in single-isomer and binary−isomer systems for the separation of DCB isomers was further carried out at 60 °C. The results showed that the silicalite-1/PDMS/PVDF hybrid membranes with 10% silicalite-1 zeolites content had better DCB selective separation performance than the silicalite-1/α−Al2O3 membranes prepared by template method. The permeate fluxes of the DCB isomers increased in the order of m−DCB < o−DCB < p−DCB both in single-isomer and binary-isomers solutions for the silicalite-1/PDMS/PVDF hybrid membranes. The separation factor of the silicalite-1/PDMS/PVDF hybrid membranes for p/o−DCB was 2.9 and for p/m−DCB was 4.6 in binary system. The permeate fluxes of the silicalite-1/PDMS/PVDF hybrid membranes for p−DCB in p/o−DCB and p/m−DCB binary−isomers solutions were 126.2 g∙m−2∙h−1 and 104.3 g∙m−2∙h−1, respectively. The thickness−normalized pervaporation separation index in p/o−DCB binary−isomers solutions was 4.20 μm∙kg∙m−2∙h−1 and in p/m−DCB binary−isomers solutions was 6.57 μm∙kg∙m−2∙h−1. The results demonstrated that the silicalite-1/PDMS/PVDF hybrid membranes had great potential for pervaporation separation of DCB from their mixtures.

Improving the Gas-Separation Properties of PVAc-Zeolite 4A Mixed-Matrix Membranes through Nano-Sizing and Silanation of the Zeolite

Mixed-matrix membranes containing synthesised nano-sized zeolite 4A and PVAc were fabricated to investigate the effect of zeolite loading on membrane morphology, polymer-filler interaction, thermal stability and gas separation properties. SEM studies revealed that, although the membranes with 40 wt % nano-sized zeolite particles were distributed uniformly through the polymer matrix without voids, the membranes with 15 wt % zeolite loading showed agglomeration. With increasing zeolite content, the thermal stability improved, the permeability decreased and the selectivity increased. The effect of silanation on dispersion of 15 wt % zeolite 4A nanoparticles through PVAc was investigated by post-synthesis modification of the zeolite with 3-Aminopropyl(diethoxy)methylsilane. Modification of the nanoparticles improved their dispersion in PVAc, resulting in higher thermal stability than the corresponding unmodified zeolite membrane. Modification also decreased the rigidity of the membrane. Partial pore blockage of the modified zeolite nanoparticles after silanation caused a further decrease in permeability, compared to the 15 wt % unmodified zeolite membrane.

Application of polyurethane membrane with surface modified ZSM-5 for pervaporation of phenol/water mixture

In the present work, β-cyclodextrin was grafted to the surface of ZSM-5 via 2,3-epoxypropyl trimethylammonium chloride (ETMAC) and epichlorohydrin (EPI) as the bridging agent by ion exchange and sequential grafting. The mixed matrix membranes were prepared using polyurethane (PU) and ZSM-5 before and after modification. Modified ZSM-5 and corresponding MMM were characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and scanning electron microscope (SEM). These membranes were applied for the removal of phenol from aqueous solution in pervaporation process. The results showed that modified ZSM-5 dispersed homogeneously in polymer. The flux and pervaporation separation index of PU increased greatly with a limited decrease in selectivity by the addition of modified ZSM-5. The increased feed temperature enhanced both the flux and separation factor of PU and modified PU membranes.