Novel adsorbent hollow fibres for oxygen concentration
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Novel adsorbent hollow fibres for oxygen concentration J.M. Nevell · S.P. Perera
Received: 15 May 2010 / Accepted: 10 January 2011 / Published online: 27 January 2011 © Springer Science+Business Media, LLC 2011
Abstract The research examined the development of adsorbent hollow fibres as a low pressure drop structure for the production of oxygen-enriched air. The potential benefits of using a low pressure drop flexible adsorbent structure with molecular sieving properties over a bed packed with pellets include a low attrition resistance which could extend the life of the adsorbent structure. Highly macroporous, highly adsorbent loaded (up to 90 wt%) fibres were produced. By increasing adsorbent density, the separative performance and nitrogen loading were improved. The separative performance of the adsorbent fibre was found to be slightly inferior to that of the bed of smaller 0.4–0.8 mm beads, as the diffusion path length was longer in the fibres and caused increased mass transfer resistances within the macroporous structure. The pressure drop through the fibre was found to be 40 to 70 times lower than that through an equivalent packed bed of 0.4–0.8 mm beads. This experimental feasibility study has demonstrated that the novel zeolite fibre configuration shows good potential for the production of oxygen-enriched air in a low energy, short cycle time, pressure swing process. The challenges of improving the performance of the adsorbent fibres and their operating parameters are described. Keywords Low pressure drop structure · Adsorbent hollow fibre · Pressure swing adsorption · Oxygen concentration
J.M. Nevell () · S.P. Perera Department of Chemical Engineering, University of Bath, Bath, UK e-mail: [email protected] S.P. Perera e-mail: [email protected]
1 Introduction The use of pressure swing adsorption (PSA) to separate air was based on two significant breakthroughs; the development of synthetic zeolites that preferentially adsorb nitrogen over oxygen by Milton (1959a, 1959b) and the invention of efficient pressure swing cycles by both Skarstrom (1960) and Guerin de Montgareuil and Domine (1960). Historically zeolites 5A and 13X have been the most commonly used adsorbents for oxygen concentration. More recently advanced zeolites such as LiLSX have been developed with improved separation performances (Chao 1989). In a standard PSA system zeolite crystals are entrapped with clay binder to form beads used in a packed bed. Ruthven and Xu (1993) showed that within adsorbent beads sorption kinetics are dominated by macropore diffusional resistance, and that desorption rate is strongly dependent on bead size. For this reason state of the art medical oxygen concentrators such as that invented by Appel et al. (2004) now contain small zeolite beads (such as Zeochem Z12-07 LiLSX beads with a size distribution of 0.4–0.8 mm). Appropriate bead size is related to the bed size, with larger commercial fixed bed PSA devices generally having a bead size larger than 2–3 mm in equivalent diameter (Feng et al. 1998). Pressure drop is
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