Alcohol-acetone-cellulose acetate phase diagrams incorporated with methanol, ethanol, and isopropanol as nonsolvents are calculated according to a new form of the Flory-Huggins equation. Nonsolvent-cellulose acetate interaction parameters are measured by swelling experiments. Concentration-dependent nonsolvent-solvent interaction parameters are obtained by vapor-liquid equilibrium and the Wilson equation. It is shown that alcohol is a week coagulant compared with water, and water Ͼ methanol Ͼ ethanol Ͼ isopropanol for cellulose acetate. The phase diagrams characteristic of acetone-cellulose acetate combined with water, methanol, ethanol, and isopropanol as nonsolvents is different, which leads to the different morphological structure of a cellulose acetate membrane. The structure of a water coagulated membrane has large macrovoids from liquid-liquid phase separation. A methanol coagulated membrane has a honeycomb-like structure from spinodal microphase separation. An ethanol or isopropanol coagulated membrane has a thicker, dense top layer from the delay time phase separation.
ABSTRACT:The bipolar membranes were prepared by charged material of polysulfone as a base. The bipolar membranes were composed of a solvent-resistant anion exchange layer with a crosslinking matrix prepared by the reaction of chloromethylated polysulfone in DMF with diamine, an interfacial layer made from chloromethylated polysulfone solution in DMF containing cation exchange resin and amine, and a cation exchange layer made from sulfonated polysulfone dispersing cation resin powder. The prepared bipolar membrane can exhibit lower voltage drop over 100 mA/cm 2 . The critical requirement for producing bipolar membranes of low potential drop is the creation of a thin interfacial region with a low electrical resistance and a suitable chemical structure, which act to catalyze water splitting.
ABSTRACT:Integrally skinned asymmetric cellulose acetate membranes made by the wet phase inversion for removal of CO 2 from natural gas were investigated. The membrane was cast with the membrane-forming systems of cellulose acetate-acetone and quench media, such as methanol, ethanol and isopropanol, respectively, without heattreating and multistage exchange process. By means of evaluation on separating characteristics of the membrane for CO 2 /CH 4 , observation of morphologies by scanning electron photomicrographs and analysis of the phase diagrams on the membrane-forming systems, it has shown that the membrane-forming system of cellulose acetateacetone-methanol is quite suitable to prepare integrally skinned asymmetric cellulose acetate membranes for gas separation with good selectivity CO 2 /CH 4 Å 30 and flux coefficient Å 2.4 1 10 05 cm 3 /cm 2 0 s 0 cm Hg.
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