The role of carbon nanotube (CNT) as filler in a membrane matrix became popular recently. CNT is believed to solve the trade-off issue between permeability and selectivity, and also fouling problems in membrane filtration applications. Their fullerene form is a key point to provide a higher pore size on membrane surface as well as empty space called porosity in membrane structures. However, the hydrophobicity characteristic of CNT has made it difficult to distribute and it tends to agglomerate with each other which leads to a decrease in the dispersion ability in a solvent and, in the same way, a decline in the compatibility of a membrane structure. Functionalization of CNT is expected to solve those problems. Moreover, membrane hydrophilicity, which is provided by the existence of hydrophilic functionalized CNT, is aimed to achieve the anti trade-off between permeability and selectivity based on a electrostatic repulsion concept. By an electrostatic repulsion process, a pollutant will be repelled from attaching to a membrane surface while water will be strongly attracted and be transported through the membrane. Therefore, various approaches have been investigated to functionalize CNT for achieving a high dispersion of CNT as well as high compatibility between CNT and a polymer matrix which lead to improvement of modified membrane properties and performances. This paper reviews the progress of CNT functionalization applied in membrane filtration during the years 2006 up to 2016. The influence of functionalized CNT in improving membrane properties as well as membrane performances is specifically highlighted.

/pdf/functionalized-carbon-nanotube-cnt-membrane-progress-and-51t2l52ihg.pdf

Functionalized carbon nanotube (CNT) membrane: progress and challenges

A critical review of waste resources, synthesis, and applications for Zeolite LTA

Atomic layer deposition (ALD) is a technology offering the possibility to prepare thin films of high quality materials on high aspect ratio substrates with precise thickness control, high uniformit...

/pdf/atomic-layer-deposition-for-membranes-basics-challenges-and-2a1lw3iy45.pdf

Atomic Layer Deposition for Membranes: Basics, Challenges, and Opportunities

Pervaporation membrane materials: Recent trends and perspectives

Organic solvents are widely used in a variety of industrial sectors. Reclaiming and reusing the solvents may be the most economically and environmentally beneficial option for managing spent solvents. Purifying the solvents to meet reuse specifications can be challenging. For hydrophilic solvents, water must be removed prior to reuse, yet many hydrophilic solvents form hard-to-separate azeotropic mixtures with water. Such mixtures make separation processes energy intensive and cause economic challenges. The membrane processes pervaporation (PV) and vapor permeation (VP) can be less energy intensive than distillation-based processes and have proven to be very effective in removing water from azeotropic mixtures. In PV/VP, separation is based on the solution-diffusion interaction between the dense permselective layer of the membrane and the solvent/water mixture. This review provides a state-of-the-science analysis of materials used as the selective layer(s) of PV/VP membranes in removing water from organic solvents. A variety of membrane materials, such as polymeric, inorganic, mixed matrix, and hybrid, have been reported in the literature. A small subset of these are commercially available and highlighted here: poly(vinyl alcohol), polyimides, amorphous perfluoro polymers, NaA zeolites, chabazite zeolites, T-type zeolites, and hybrid silicas. The typical performance characteristics and operating limits of these membranes are discussed. Solvents targeted by the U.S. Environmental Protection Agency for reclamation are emphasized and ten common solvents are chosen for analysis: acetonitrile, 1-butanol, N,N-dimethyl formamide, ethanol, methanol, methyl isobutyl ketone, methyl tert-butyl ether, tetrahydrofuran, acetone, and 2-propanol.

Review: Membrane Materials for the Removal of Water from Industrial Solvents by Pervaporation and Vapor Permeation.

Linde Type A (LTA) zeolite-based membranes have demonstrated excellent selectivity in pervaporation due to their unique structural framework and interaction with water. The development of LTA zeolite membranes for commercial application is limited by some parameters, particularly the complexity of the membrane preparation required to produce reproducible defect-free membranes and the high costs required for the membrane materials. In addition, the high content of Al in the zeolite framework makes the LTA zeolite membrane unsuitable for acidic conditions. A number of modification techniques have been proposed to produce a thin, defect-free, and high permselectivity LTA zeolite membrane with high reproducibility. Two major approaches are generally used to produce defect-free zeolite membranes, i.e. modifying either the seeding step or the synthesis process. Since the self-supported zeolite membrane has low mechanical stability, the LTA zeolite membrane is usually synthesized on an inorganic support to give better properties. Zeolite membrane costs can be reduced by several methods such as replacing the support, manufacturing a higher flux zeolite membrane, and fabricating a polymer–zeolite membrane. One should consider, however, that changing the support can dramatically influence and even reverse the obtained separation behavior. Despite various techniques used to prepare dense LTA zeolite membranes, a facile mass production technique with a highly reproducible result remains a significant challenge. To present a clear background for LTA zeolite and its performances in pervaporation, this paper includes a brief discussion on the recent trends related to LTA zeolite membranes. Some topics are discussed, including the features inherent to LTA zeolite, the transport phenomena in zeolite structures, preparation methods of LTA zeolite membranes, and the challenges associated with preparation. Furthermore, critical issues related to LTA zeolite membranes in pervaporation will be discussed to develop the topic further.

/pdf/lta-zeolite-membranes-current-progress-and-challenges-in-1rbkl26p8h.pdf

P. T. Dharmawijaya

Papers

LTA zeolite membranes: current progress and challenges in pervaporation