Several multilayer thin low-density polyethylene (LDPE) films were fabricated by blown thin film having a thickness of 7 m and an area of 130 cm 2 . They were characterized for their oxygen-enrichment performance from air by a constant pressurevariable volume method in a round permeate cell with an effective area of 73.9 cm 2 . The relationship between oxygen-enrichment properties, including oxygen-enriched air (OEA) flux, oxygen concentration, permeability coefficients of OEA, oxygen, nitrogen, as well as separation factor through the multilayer LDPE films, and operating parameters, including transfilm pressure difference, retentate/permeate flux ratio, temperature, as well as layer number, are all discussed in detail. It is found that all of the preceding oxygen-enrichment parameters increase continuously with an increase of transfilm pressure difference from 0.1 to 0.65 MPa, especially for the trilayer and tetralayer LDPE films. The oxygen concentration and separation factor appear to rapidly increase within the retentate/permeate flux ratio below 200, and then become unchangeable beyond that, whereas the OEA flux and the permeability coefficients of OEA, oxygen, and nitrogen seem to remain nearly constant within the whole retentate/permeate flux ratio investigated, especially for the monolayer and bilayer LDPE films. The selectivity becomes inferior, whereas the permeability becomes superior, as the operating temperature increases from 23 to 31°C. The highest oxygen concentration was found to be 44.8% for monolayer LDPE film in a single step with air containing oxygen of 20.9% as a feed gas and operating pressure of 0.5 MPa at a retentate/permeate flux ratio of 340 and 23°C. The results demonstrate a possibility to prepare an oxygen-enriching membrane directly from air, based on the easily obtained thin LDPE films.

Blend membranes of 2,2Ј-bipyridine (2BP) or 4,4Ј-bipyridine (4BP) with ethyl cellulose (EC) containing no more than 25 wt % BP are prepared and evaluated for their oxygen enrichment by both the constant pressure-variable volume method and the constant volumevariable pressure method. The actual air-separation ability through the 2BP/EC blend membrane containing 1.5-7 wt % 2BP are enhanced while the permeated flux is slightly increased in comparison with the virgin EC membrane. Among the 2BP/EC blend membranes examined, the 2BP/EC blend membrane containing 3 wt % 2BP offers the best oxygen/nitrogen permselectivity and yields the highest oxygen concentration of 42.7% at the transmembrane pressure difference of 0.75 MPa and 25°C.Like other homogeneous dense membranes, the BP/EC blend membrane demonstrates strong dependencies on the transmembrane pressure difference, retentate/permeate flux ratio, and operating temperature. It possesses higher activation energy of oxygen and nitrogen permeation than those of the virgin EC membrane in the tested temperature range of 9.7-60°C. The CO 2 over CH 4 permselectivity through EC membranes can be improved by introducing 4BP, and the ideal oxygen over nitrogen separation factor through the 4BP/EC (10/90) membrane increases 16% at the upstream pressure of 10 bar compared with the virgin EC membrane.

A series of copolymers between o-toluidine (OT) and vinyl acetate (VA) was synthesized by a chemically oxidative polymerization, which was carried out by three different methods: suspension solution precipitation, emulsion and inverse emulsion copolymerizations by using iron trichloride, and ammonium persulfate as oxidant. The progress in the copolymerization, polymerization yield, structure, and properties of the resulted OT/VA copolymers were systematically characterized by solution potential/ temperature monitor, laser particle size, FTIR, UV-vis, and thermogravimetry techniques. The results show that the diameter, spectral characteristics, solubility, film formability, electrical conductivity, and thermostability of the virgin polymer particles formed exhibit a nonmonotonic dependence on the OT/VA ratio, suggesting an occurrence of an oxidative copolymerization between OT and VA monomers.