PREPARATION AND AIR-SEPARATION PROPERTIES OF MEMBRANE BLENDS OF LOW-MOLECULAR-WEIGHT LIQUID-CRYSTALS WITH CELLULOSE DERIVATIVES

Four kinds of low-molecular-weight liquid crystals (LCs) (cholesteryl oleyl carbonate (COC), the benzoate-containing mixture LC DYC, p-heptyl-p'-cyanobiphenyl (7CB), p-phentylphenol-p'-methoxybenzoate (5PMB) and four cellulose derivatives (ethyl cellulose (EC), cellulose diacetate, cellulose triacetate, cellulose nitrate) were used to prepare blend membranes of thickness 13-45 mum by a solution casting technique. The oxygen permeability, the oxygen/nitrogen separation factor, the permeation flux Q(OEA) and the oxygen concentration Y(o2) of the oxygen-enriched air (OEA) through the cellulose derivative membranes with different LCs were studied by a constant pressure-variable volume method. The experimental results show that the membrane-forming ability, uniformity, toughness and air-separation properties of the cellulose derivatives have been improved by adding no more than 12 wt% LC. The air-separation properties of the resulting membranes vary significantly with membrane composition, temperature and pressure difference. Of all the membranes, the COC/EC (4/96) membrane of thickness 18 mum exhibits the highest Q(OEA) value of 1.8 x 10(-4) cm3 (STP) s-1 cm-2 and maintains the Y(o2) value of 38.8% in a single operation.