E. Alpay et Cn. Kenney, ADSORBENT PARTICLE-SIZE EFFECTS IN THE SEPARATION OF AIR BY RAPID PRESSURE SWING ADSORPTION, Chemical Engineering Science, 49(18), 1994, pp. 3059-3075
Experimental and theoretical investigations into air separation by rap
id pressure swing adsorption over zeolite 5A are presented. These conc
entrate on the effect of adsorbent particle size on the separation per
formance of the unit undergoing simple cycles consisting of pressurisa
tion and depressurisation steps. An optimum particle size for maximum
cyclic equilibrium product oxygen purity is shown to exist; this is ac
curately predicted by model simulation. Calculations indicate that for
beds containing very small particles, a poor separation results from
ineffective pressure swing, and for beds containing very large particl
es from intraparticle diffusional limitations. For the zeolite 5A adso
rbent used in this work, theoretical calculations indicate that the ra
te limiting intraparticle diffusion is described by a parallel combina
tion of molecular and Knudsen diffusion within the macropores of the a
dsorbent particles. Axial dispersion within the bed is also shown to h
ave a significant effect upon the cyclic equilibrium value of the cycl
e-average product oxygen purity. In addition to measurements at the cy
clic equilibrium, temporal profiles of the product oxygen purity durin
g the approach to cyclic equilibrium are shown. Under certain operatin
g conditions, an overshoot of oxygen purity is found to exist. This be
haviour can be attributed to ineffective pressure swing within the pro
duct end region of the bed, and thus to the poor utilisation of adsorb
ent in this region