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BACKGROUND Polybenzoxazine ( PBZ) membranes have received increasing attention for serving as a high performance membrane for pervaporation processes owing to their good mechanical properties, high chemical resistance, high thermal stability, and low synthesis cost. This study aims to develop PBZ membrane and NaA-PBZ mixed matrix membrane ( MMM) for purification of ethanol/water mixtures using a pervaporation process and to investigate the effects of preparation parameters on the membrane performance, including precursor concentrations, number of dippings, amount of NaA zeolite loading, temperature, and ethanol concentration. RESULTS It was found that PBZ membrane and NaA-PBZ MMM exhibited excellent stability in all feed ethanol concentrations tested, with a low degree of swelling. The highest separation factor of the pure PBZ membrane was more than 10 000 while the NaA-PBZ MMM was even higher, up to and, in some cases, higher than 100 000 with the highest permeation flux of 1071 g m−2 h−1 when using 25 wt% PBZ precursor with 15 wt% NaA zeolite loading. The permeation flux of MMM increased with increase in temperature or a decrease in the feed ethanol concentration. Swelling increased when the ethanol concentration was increased, revealing the hydrophobic behavior of NaA-PBZ MMM. CONCLUSION The membranes are capable of purifying ethanol over a wide feed ethanol concentration range with excellent performance and properties that promise great potential for use in bioethanol purifying applications. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

A novel silver ion-exchange treatment of zeolite was introduced in this work to change the physical and chemical adsorption properties of penetrants in the zeolite. EDX data confirm the complete replacement of sodium ion in zeolite NaA by silver ion, whereas XRD patterns and BET results show no changes in some physical properties of zeolite after the silver ion-exchange treatment. Polyethersulfone (PES)-zeolite NaA mixed matrix membranes (MMMs) and PES-zeolite AgA MMMs were fabricated at high processing temperatures with different zeolite loadings. Cross-sectional SEM images of these two types of MMMs indicate the interface between polymer and zeolite phases is comparable before and after the silver ion-exchange treatment. The effects of silver ion-exchange treatment of zeolite and zeolite loadings on the gas separation performance of these MMMs were investigated. CO2 permeability of PES-zeolite AgA MMMs is higher than that of PES-zeolite NaA MMMs, whereas their CH4 permeability is lower than that of PES-zeolite NaA MMMs. This trend is the result of the reversible reaction between silver ion and CO2 molecule. CO2 and CH4 permeability of PES-zeolite AgA MMMs decreases with increasing zeolite content arising from the effects of partial pore blockage of zeolite and polymer chain rigidification, whereas their CO2/CH4 selectivity increases with an increase in zeolite loadings and the highest value reaches 59.6 at 50 wt % zeolite loading because of a combined effect of the facilitated transport mechanism of silver ion and the molecular sieving mechanism of zeolite. Both CO2-induced plasticization test and CO2/CH4 mixed gas measurement were performed to examine the applicability of these developed PES-zeolite AgA MMMs in industry. Results prove that this type of composite membrane material is a superior candidate for the practical separation of natural gas. [ABSTRACT FROM AUTHOR]

It has been demonstrated that a novel p-xylenediamine/methanol soaking method could efficiently remove the polymer--zeolite interface defects of the mixed-matrix structure. In this work, the mixed-matrix structure is in the form of an ultrathin (1.5-3 µm) polysulfone/ zeolite beta mixed-matrix layer that is supported by a neat Matrimid® layer in dual-layer composite hollow fibers. The particle's loading in this thin layer has reached 30 wt %. The ideal selectivities of the mixed-matrix hollow fibers (30 wt % of zeolite)for O2/N2 and CO2/CH4 separation were roughly 30 and 50% superior to that of the neat PSF/Matrimid® hollow fibers, respectively. Investigation of the morphology of the mixed-matrix selective layer and its relation with gas separation performance indicated that without p-xylenediamine/methanol solution treatment, the outer layer showed various polymer--zeolite interface structures in different fibers with the same heat treatment procedures; this situation might lead to the different selectivities after coating. However, by applying p-xylenediamine/methanol processing on the fibers before thermal treatment, the fibers obtained a more uniform structure and improved attachment between polymer matrix and zeolite surface. Hydrogen bonding was proposed as the possible mechanism for the tighter attachment between the two phases. The improvement of separation efficiency was presumably related to the polymer chain rigidification, partial pore blockage, and/or favorable interaction between the gas penetrants and zeolite framework. [ABSTRACT FROM AUTHOR]