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Pb(II) solution has been treated by a column packed with 5 mm-diameter spheroids of poly(m-phenylenediamine) powder that has been entrapped in polyvinylalcohol, via dynamic adsorption. The effect of operation conditions on the adsorbability and desorbability has been investigated and optimized systematically. The results show that a lower flow rate gives a higher adsorptivity at a fixed Pb(II) concentration because of longer contact time, and higher Pb(II) concentration gives higher adsorptivity at a fixed flow rate. The highest adsorptivity reaches up to 75.9% for Pb(II) concentration of 500 mg·L–1 at the flow rate of 1 mL·min–1. The release of Pb(II) from the Pb(II)-adsorbing column has been revealed using 0.1 M HNO3 as an eluant, with an elution efficiency of 98.1%, effectively regenerating the column. The regenerated column could be circularly used several times. The Adams-Bohart and Wolborska sorption models have been used to describe the dynamic sorption of Pb(II) through the packed column. It is ve...

Fourier-transform infrared (FTIR) and proton nuclear magnetic resonance (NMR) spectroscopies and wide-angle x-ray diffraction were used to analyze the molecular chain structures of thermotropic liquid-crystalline terpolymers from p-acetoxybenzoic acid, polyethylene terephthalate, and p-acetoxyvanillic acid, or 1,4-diacetoxybenzene/terephthalic acid. The general features of FTIR spectra of the oriented terpolymer films and NMR spectra for the terpolymers in solution with the variation of terpolymer composition are discussed. The assignments of the resonance peaks in FTIR and proton NMR spectra are given. The number-average degree of polymerization of the terpolymers is estimated to be up to 34 by end-group analysis based on the NMR spectra. The meridional scans of x-ray diffraction of the as-drawn terpolymer ribbons are being used to characterize the aperiodic characteristics and persistence length of the terpolymer chain. The persistence length of the terpolymers seems to increase with an increase in the ...

Thermotropic liquid crystalline terpolymers consisting of three units of p-oxybenzoate (B), ethylene terephthalate (E), and vanillate (V), were studied through a high-resolution thermogravimetry to ascertain their thermostability and kinetics parameters of thermal decomposition in nitrogen and air. Overall activation energy data of the major decomposition have been calculated through four calculating techniques. The thermal degradation occurs in three steps in nitrogen, but in four steps in air due to an additional thermo-oxidative step. The thermal degradation temperatures are higher than 436°C in nitrogen and 424°C in air and increase with increasing B-unit content at a fixed V-unit content of 5 mol%. The temperatures at the first maximum weight-loss rate are higher than 444°C in nitrogen and 431°C in air and increase slightly with an increase in B-unit content. The first, second, and third maximum weight-loss rates almost maintain at 10–11, 10–11, and 3.6–5.3%/min regardless of copolymer composition an...

The water-casting method is one of the most important techniques for the preparation of pinhole-free ultrathin film for air separation. Strong interest exists in the optimizations of preparing routes of the ultrathin film and of the fabrication of the ultrathin-film composite membranes with a variety of polymers. A number of water-casting solvents with high spreadability over water are offered in the present review. Progress made in the inconsecutive and continuous preparations of ultra-thin films is reviewed in detail. The oxygen perms electivity, air separation performance, and the stability of ultrathin-film composite membranes are discussed with a detailed citation of references. This review also compares the performances through ultrathin-film composite membranes fabricated by the water-casting method with other methods.

Air separation properties and stabilities of four blend membranes, 1–30-μ.m thick, prepared from ethyl cellulose (EC) with a small amount of nematic and cholesteric liquid crystals, such as p-heptyl-p'-cyanobiphenyl (7CB), p-pentylphenol-p'-methoxybenzoate (5PMB), benzoate-containing liquid crystal mixture (DYC), and cholesteryl oleyl carbonate (COC), were investigated by the variable volume method. To provide more significant information guiding membrane-based air separation, air was directly used as the test gas. The membranes showed both higher oxygen permeability, P O2 , and oxygen over nitrogen separation factor, P O2 /P N2 , in the temperature range of the liquid crystalline phase. Oxygen-enriched air (OEA) flux, Q OEA, and oxygen concentration. Y O2 increased simultaneously with increasing transmembrane pressure difference. Stability studies revealed that the efficiencies of concentrating oxygen using 1–7-μm thick DYC/EC (9/91) membranes laminated to porous polyethersulfone membranes were ...

Composite membranes for air separation were prepared from a liquid crystal DYC-modified ethyl cellulose (EC) thin film ranging in thickness from 1 to 7 μm and a porous polyethersulfone support with a thickness of 120 μm. The effects of DYC/EC (9/91) solution concentration, water, and operating parameters such as temperature, pressure, and time on the air-separation properties of the composite membranes were examined by a constant pressure—variable volume method. The permeate flux and oxygen concentration of the oxygen-enriched air (OEA) through the membranes increase significantly with increasing operating pressure difference. With decreasing casting solution concentration, or with increasing humidity around the membranes or operating temperature, the OEA flux increases greatly while the oxygen concentration sometimes decrease slightly. An increase in the operating time leads to an OEA flux decline, but the oxygen concentration rose when the operating time was varied for 70 hours. However, a furt...

Air separation of a cholesteric liquid crystalline triheptyl cellulose/ethyl cellulose (3/97) binary composite membrane prepared from tetrahydrofuran, chloroform, and dichloromethane solutions was studied at different pressure differences across the membrane by the variable volume method. With an increasing pressure difference in the range from 0.06 to 0.42 MPa, the flux and the oxygen concentration of the oxygen-enriched air through the membrane both increase. The air separation capability depends on the boiling point of the membrane-forming solvent and the membrane thickness.