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

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.