Incorporation of multiwalled carbon nanotubes (MWNT) on the gas permeation properties of H2, CO2, O2, and N2 gases in poly(ether-block-amide) (Pebax-1657) membrane has been investigated. Pebax-1657 was dissolved in the ethanol−water mixture and cast on an ultraporous polyethersulfone substrate followed by complete solvent evaporation. Nanocomposite membranes were prepared by dispersion of MWNT in concentrations of 0−5% of polymer weight in the Pebax solutions with sonication for 2 h to ensure uniformity. Cross-linking was carried out in hexane medium using 2,4-toluylene diisocyanate (TDI). The permeabilities of pure gases were measured at room temperature, and the ideal selectivities were determined at pressures varying from 1−3 MPa using an indigenously built high-pressure gas separation manifold. For neat Pebax membrane, high permeabilities of 55.8 and 32.1 barrers were observed for CO2 and H2 gases, respectively, whereas that of N2 was as low as 1.4 barrers. The selectivity of cross-linked 2% MWNT Pebax membrane was enhanced from 83.2 to 162 with increasing feed pressure (1−3 MPa) for the CO2/N2 gas pair, whereas the corresponding values for H2/N2 and O2/N2 systems were found to be in the range 82.5−90 and 7.1−6.8, respectively. The membranes were characterized by scanning electron microscopy (SEM) to study surface and cross-sectional morphologies. Fourier transform infrared (FT-IR), wide-angle X-ray diffraction (WAXD), and ion exchange capacity (IEC) studies were carried out to determine the effect of MWNT incorporation on intermolecular interactions, degree of crystallinity, and extent of cross-linking, respectively. Fractional free volume (FFV) calculations based on density measurements were conducted along with water sorption studies to explain permeation behavior. The use of modified block copolymer membranes provides a means for separation of CO2 from N2 in power plants, H2 recycle from ammonia purge gas, O2 enrichment from air for medical applications, and CO2 removal from water-gas shift reaction to improve H2 yield.

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In this study, a thin-film composite membrane based on hydrophilized polyamide was synthesized for the concentration of an aqueous fructose solution using a forward-osmosis (FO) technique. The membrane was prepared by the addition of excess mphenylenediamine along with a small quantity of dipolar aprotic dimethyl sulfoxide solvent in the aqueous reaction bath followed by excess trimesoyl chloride in an organic bath with a longer time provided for interfacial polymerization to minimize fructose losses. The effect of operating parameters such as draw NaCl concentration, cross-flow velocity, and temperature on FO performance was evaluated. Membrane characterization was performed using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction to study the physicochemical properties. A coupled model based on molecular modeling and computational fluid dynamics was developed to study the diffusion behavior and concentration profiles of the two solutions within the process. A detailed economic estimation for the production of crystalline fructose sugar is presented. The study reveals the significant potential of FO as an economical process for concentration of sugar solutions using brine as the draw solution. V C 2016 Wiley Periodicals, Inc. J.Appl. Polym. Sci. 2017, 134, 44649.

2-Hydroxypropionic acid, commonly known as lactic acid (LA), is a valuable chemical widely used for the manufacture of green solvents such as ethyl lactate and biodegradable polymers such as poly­(lactic acid) (PLA). LA is manufactured by fermentation molasses and whey. Isolation of LA from aqueous broths by conventional methods is energy intensive. Reactive extraction through membranes using specific reagents could prove to be a cost-effective alternative for LA recovery. This study focuses on reactive separation of LA using a novel indigenously developed hydrophobic H-beta zeolite/polyvinylidene fluoride (PVDF) mixed matrix membrane. Experiments were conducted using a stirred cell assembly consisting of two bell shaped glass pipe reducers containing aqueous LA separated by the membrane from an organic solution of tri-n-octylamine (TOA) carrier in alcoholic medium. Effects of experimental parameters such as the concentration of TOA in organic phase and zeolite loading on the rate of acid extraction were evaluated by increasing the TOA concentration from 206 to 620 mol/m3 and the extent of zeolite loading from 1 to 25% (w/w) of (PVDF) polymer. SEM analysis was carried out to oversee zeolite distribution on the PVDF surface, whereas TGA was used to determine the maximum operating temperature. XRD study was done to investigate the influence of zeolite loading on intersegmental spacing in the polymer, while FT-IR helped in the identification of interactions between the inorganic filler and organic polymer. A mass transfer correlation was deduced by taking into account all possible reactions involved in formation of the complexes. An optimum extraction of nearly 34% was obtained using 25% zeolite loading, 206 mol/m3 TOA in 1-octanol, and 100 mol/m3 acid concentration, at a stirring rate of 400 rpm over a processing time of 1 h. Continuous separation of LA by a membrane contactor could help improve the fermentation yield of the acid by preventing the inhibition of lactate dehydrogenase enzyme, which is affected by the product itself. Such reactive extractions by membrane contactors could be successfully scaled up using a hollow fiber modular configuration.

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and available online hereCet article fait partie du dossier thématique ci-dessous publié dans la revue OGST, Vol. 70, n°2, et téléchargeable ici

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