Oxygen enrichment from air through multilayer thin low-density polyethylene films

Several multilayer thin low-density polyethylene (LDPE) films were fabricated by blown thin film having a thickness of 7 mum and an area of 130 cm(2). They were characterized for their oxygen-enrichment performance from air by a constant pressure-variable 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 31degreesC. 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 23degreesC. The results demonstrate a possibility to prepare an oxygen-enriching membrane directly from air, based on the easily obtained thin LDPE films. (C) 2002 John Wiley Sons, Inc.