ADSORPTION OF METHANOL AND SUPPORTING ELECTROLYTE ON SILICA AND ALUMINA IN MIXED-SOLVENT SYSTEMS

Methanol adsorption on silica (388 m2/g) is independent of the ionic strength and decreases with increase of pH. Maximum adsorption of ≈0.5 mmol/g is observed at initial methanol concentration of ≈2.5 mol dm-3 at sufficiently low pH, and it is low when compared with the concentration of ionizable hydroxyl groups on the surface of silica. Methanol adsorption on alumina is zero within experimental error. The negative surface charge of silica is almost entirely compensated by cation adsorption. Both charge and cation adsorption decrease when water is replaced with a mixed solvent. With alumina, the compensation is much lower and both charge and adsorption are independent of the solvent composition up to 30% w/w of methanol and ethanol. ζ potentials calculated from adsorption data are compared with the measured values. It follows from this comparison that the slipping plane distance increases with the ionic strength in aqueous systems. This trend is even more pronounced with mixed solvents. © 1993 Academic Press, Inc.