Experimental study of retrograde adsorption in supercritical fluids

The effect of near-critical conditions on the adsorption breakthrough curves of three different solutes in supercritical carbon dioxide was studied in a fixed bed adsorber using a bonded silica stationary phase. The experimental data were taken at two different temperature conditions (308 and 323 K) at a pressure of 90 bar. In this regime, the increase in column retention time, under which we term retrograde adsorption conditions, is quire evident and leads to an increase in the efficiency of the adsorption column as a separation device when purifying the gas stream from dilute contaminants. We also evaluated a ternary separation in the naphthalene-benzoic acid-carbon dioxide system attempting to purify binary mixtures of naphthalene and benzoic acid. We show that column performance, as a solute separation device for these components, is degraded relative to what we expected from studying each individual component's adsorption data in supercritical carbon dioxide. This result would he consistent with strong synergistic effects between these two solute species, in the near-critical fluid phase, a result that has been reported in the prior literature. (C) 2000 Elsevier Science B.V. All rights reserved.