In the present work, high-performance mixed matrix membranes containing amines have been developed for effective CO 2 removal at high pressures (15-28 bar) and high temperatures (103-121 °C). The membrane was synthesized by compatibly embedding amino-functionalized multi-walled carbon nanotubes (AF-MWNTs) as mechanical reinforcing fillers in the crosslinked polyvinylalcohol-polysiloxane/amine blend. The surface functionalization of MWNTs allows strong coupling with the hydrophilic membrane matrix to form a nano-reinforced facilitated transport membrane, which achieved exceptional CO 2 selectivity and permeability via the facilitated transport mechanism as well as attractive membrane stability via the incorporation of MWNTs. The synthesized membranes exhibited an average CO 2 permeability of 957 Barrers coupled with high selectivities vs. H 2 (56), CH 4 (264), and N 2 (384) at 107 °C and 15 bar. The effects of AF-MWNT loading, high molecular weight species content, selective layer thickness, feed pressure, relative humidity, and temperature on membrane performance were thoroughly studied for a fundamental understanding of membrane properties. Furthermore, a mathematical model has been used to describe and explain the thickness-dependent CO 2 transport behavior in the membrane. The combination of high CO 2 permeability and good selectivities vs. CH 4 , H 2 , and N 2 , along with enhanced mechanical stability, makes the membrane a promising candidate for the gas separation applications at high pressures.
Zeolites are microporous, crystalline aluminosilicates with the framework made up of T-O-T (T = Si, Al) bonds and enclosed cages and channels of molecular dimensions. Influencing and manipulating the nucleation and growth characteristics of zeolites can lead to novel frameworks and morphologies, as well as decreased crystallization time. In this study, we show that manipulating the supersaturation during synthesis of zeolite X/Y (FAU) via dehydration led to extensive nucleation. Controlled addition of water to this nucleated state promotes the transport of nutrients, with a 4-fold increase in the rate of crystal growth, as compared to conventional hydrothermal process. Structural signature of the nucleated state was obtained by electron microscopy, NMR, and Raman spectroscopy. This extensively intermediate nucleated state was isolated and used as the starting material for zeolite membrane synthesis on porous polymer supports, with membrane formation occurring within an hour. With this time frame for growth, it becomes practical to fabricate zeolite/polymer membranes using roll-to-roll technology, thus making possible new commercial applications.
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