Breakthrough curves and adsorption isotherms of terpene mixtures in supercritical carbon dioxide

The adsorption of a mixture of thirteen terpenes from supercritical carbon dioxide on silanized silica was studied with the aim of simulating essential-oil fractionation. Adsorption isotherms were obtained at temperatures of 310 and 320 K for isochoric conditions of a carbon dioxide density of 750 kg m(-3). The equilibrium loadings, measured at individual solute concentration from 0.9 to 8 mg of solute per g of solvent were of the same order of magnitude for hydrocarbon and oxygenated terpenes. Temperature had only a minor influence. The adsorbed quantities were low, in the range of 10 mg of solute per g of sorbent. An explanation is offered by considering the adsorption of the supercritical solvent. Measurements of carbon dioxide adsorptive capacities for several mixtures showed that the solvent did indeed compete for adsorption. Due to their complex behaviour, the capacity data of the solutes were regressed according to an empirical Langmuir-like equation instead of a Langmuir model. The influence of temperature and density on the equilibrium loadings and on the breakthrough volumes are also discussed. (C) 1998 Elsevier Science B.V.