Effect of ion exchange rate of Y–type zeolite on selective adsorption of 2,6– and 2,7–dimethylnaphthalene isomers in supercritical carbon dioxide

Abstract

The selective adsorption amounts of 2,6– and 2,7–dimethylnaphtalene (DMN) isomers dissolved in supercritical carbon dioxide (SC-CO2) on barium (Ba) ion-exchanged Y-type zeolite were measured by a constant volume method at 308.2 K. The total concentrations of 2,6– and 2,7–DMN in SC-CO2 were measured with an ultraviolet detector. The concentration ratio of 2,6– and 2,7–DMN in SC-CO2 was analyzed by gas chromatography. The separation coefficients of 2,6–DMN (2) and 2,7–DMN (3) are defined by K32 =; (Q3/C3)/(Q2/C2), where Q2 and Q3 (mol/g–zeolite) are the amounts of 2,6– and 2,7–DMN adsorbed on Y–type zeolite and C2 and C3 (mol/cm3) are the concentrations of 2,6– and 2,7–DMN in SC-CO2, respectively. The separation coefficients in SC-CO2 on Ba ion-exchanged Y–type zeolite are much higher than those in liquid octane. The separation coefficients in SC-CO2 using Ba ion-exchanged Y–type zeolite depend on ion exchange rate and amount of chloride remained on the zeolite. The separation coefficients at high pressure using Ba ion-exchanged Y–type zeolite which is higher ion exchange rate and contains lower chloride in SC-CO2 system are much higher than those using NaY–type zeolite. Therefore, the use of ion-exchanged zeolite will be useful in applications such as the design of pressure swing adsorption and supercritical chromatography processes.