Air Separation Properties and Stabilities of Blend Membranes of Liquid Crystals with Ethyl Cellulose

Abstract

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 almost constant for a 120–510-hour operating time. The membrane possessed a Q _OEA of 9.0 × 10^?4 cm³(STP)/s.cm² and Y_O2 of 40% at 30°C and 0.41 MPa for a single-stage process. The results suggest that the membranes could be used effectively in enriching oxygen from air.     

Adsorption of Radioactive Ions 137Cs+, 85Sr2+, and 60Co2+ on Natural Magnetite and Hematite

Abstract

Natural magnetite and hematite have been used as granular sorbents for ¹³⁷Cs⁺, ⁸⁵Sr²⁺, and ⁶⁰Co²⁺ at tracer concentration levels in aqueous solutions of constant pH (range 2–10) at 25°C. The kinetics of adsorption, up to the first 60 to 90 min, followed a first-order equation. At pH 6–8 about 50% Cs, 30% Co, and 18% Sr is removed from the solution with magnetite and 78% Co with hematite. The difference in the sorption capabilities of magnetite and hematite is discussed in terms of crystal structures of these oxides.     

Fabrication of Palladium Membranes Supported on a Silicalite‐1 Zeolite‐Modified Alumina Tube for Hydrogen Separation

Thin palladium membranes were fabricated on macroporous α‐Al₂O₃ tubes by electroless plating. The silicalite‐1 (Sil‐1) zeolite serving as intermediate and diffusion barrier layer was introduced to modify the surface roughness and pore size of the porous substrate and prevent the atomic interdiffusions of the metal elements between Pd layer and the support. The Pd composite membranes were studied by scanning electron microscopy (SEM), X‐ray diffraction (XRD), and electron probe microanalysis (EPMA), revealing that morphology and structure of the Sil‐1 layer significantly influence the Pd membrane preparation. Single‐gas permeation tests were carried out with gas H₂ and N₂ to determine the permeation performance of the membranes. The resulting membrane exhibited long‐term stability under hydrogen permeation.