Four ZSM-5 zeolite catalysts with different Si/Al ratios for the catalytic cracking of C4 fractions to produce ethylene and propylene were prepared in this study.First,the adsorption isotherms of pure n-butane and butene-1 and their mixtures on these catalysts at 300K and p=0—100kPa were measured using the intelligent gra- vimetric analyzer.The experimental results indicate that the presence of Al can significantly affect the adsorption of butene-1 than that of n-butane on ZSM-5 zeolites.Then,the double Langmuir(DL)model was applied to study the pure gas adsorption on ZSM-5 zeolites for pure n-butane and butene-1.By combining the DL model with the ideal adsorbed solution theory(IAST),the IAST-DL model was applied to model the butene-1(1)/n-butane(2)binary mixture adsorption on ZSM-5 zeolites with different Si/Al ratios.The calculated results are in good agreement with the experimental data,indicating that the IAST-DL model is effective for the present systems.Finally,the adsorp- tion over a wide range of variables was predicted at low pressure and 300K by the model proposed.It is found that the selectivity of butene-1 over n-butane increases linearly with the decrease of Si/Al ratio.A correlation between the selectivity and Si/Al ratio of the sample was proposed at 300K and p=0.08MPa. Four ZSM-5 zeolite catalysts with different Si / Al ratios for the catalytic cracking of C4 fractions to produce ethylene and propylene were prepared in this study. First, the adsorption isotherms of pure n-butane and butene-1 and their mixtures on these catalysts at 300K and p = 0-100 kPa were measured using the intelligent gra- vimetric analyzer. The experimental results indicate that the presence of Al can significantly affect the adsorption of butene-1 than that of n-butane on ZSM-5 zeolites. Shin, the double Langmuir (DL) model was applied to study the pure gas adsorption on ZSM-5 zeolites for pure n-butane and butene- 1. Combining the DL model with the ideal adsorbed solution theory (IAST), the IAST-DL model was applied to model the butene-1 (1) / n-butane (2) binary mixture adsorption on ZSM-5 zeolites with different Si / Al ratios. The calculated results are in good agreement with the experimental data, indicating that the IAST- DL model is effective for the present systems. Finally, the adsorp tion over a wide range of variables was predicted at low pressure and 300K by the model proposed. It is found that the selectivity of butene-1 over n-butane increases linearly with the decrease of Si / Al ratio. A correlation between the selectivity and Si / Al ratio of the sample was proposed at 300K and p = 0.08MPa.