ADSORPTION OF SHORT-CHAIN ALCOHOLS FROM DECANE SOLUTIONS ONTO KAOLINITE

Adsorption of short chain alcohols in decane solutions onto kaolinite has been investigated by Fourier transform infrared spectroscopy (FTIR ) for analysis of the alcohol content, The alcohols were methanol, eth anol, 1-propanol, 2-propanol, and 1-butanol, The isotherms have been m athematically modeled by (i) a basic Langmuir equation, and (ii) a two -term Langmuir equation, In both cases, the equations were modified to take into account the self-association of alcohol molecules in the hy drocarbon solution, The methanol isotherm exhibits two plateaus of dif fering extent, in addition to a strongly increasing isotherm near the solubility limit. It is suggested that this complex isotherm is to be interpreted in terms of monolayer adsorption and condensation in micro pores, followed by condensation at the basal surface at higher concent rations, The results further show adsorption isotherms for ethanol, pr opanol, and butanol in agreement with monolayer adsorption, The calcul ated area per molecule for the assumed monolayer increases from about 0.15 nm(2) for ethanol to 0.34 nm(2) for butanol, However, 2-propanol gives slightly lower adsorption density than 1-propanol, indicating st eric repulsion between the branched chain of the adsorbed molecules, T he lower adsorption density of the higher alcohol molecules at the ads orption plateau is possibly caused by steric interactions between the flexible alcohol chains, preventing adsorption onto neighboring sites. (C) 1995 Academic Press, Inc.