烷烃在ZSM-5分子筛上吸附扩散的气相色谱研究

Study on Adsorption and Diffusion of Alkanes on ZSM-5 Molecular Sieve by Gas Chromatography

利用气相色谱法测定了不同色谱柱温度和不同载气流速下,C1~12烷烃在ZSM-5分子筛上的保留时间,并利用相关公式对测试结果进行了线性回归分析,测得了吸附热力学参数和扩散系数;考察了色谱柱温度、烷烃碳链长度和载气流速对烷烃在ZSM-5分子筛上吸附扩散的影响。实验结果表明,回归分析的线性相关性良好,色谱柱温度越高,孔道对吸附质的吸附能力越弱;在不同载气流速下,轴向扩散系数不同;随烷烃碳链长度的增加,吸附焓变呈先增大后减小的趋势,轴向扩散系数呈线性增长;C1~12烷烃在ZSM-5分子筛上的吸附焓变在-1.264^-42.975 k J/mol之间;当载气流速为2.654~4.246 cm/s时,C1~4烷烃的轴向扩散系数在0.328 8~0.551 7 cm2/s之间;当载气流速为5.308~13.270 cm/s时,C1~4烷烃的轴向扩散系数在0.430 2~1.456 4 cm2/s之间。

The retention times of C1-12 alkanes on the ZSM-5 molecular sieve chromatographic column were determined by gas chromatography under different column temperature and fl ow rate of carrier gas. The linear regression analysis of the test results was carried out by a correlation formula. The adsorption thermodynamic parameters and axial diffusion coefficients were measured. The effects of the column temperature,carbon chain length and fl ow rate of carrier gas on the adsorption and diffusion were investigated. The results showed that the correlation was good. The adsorption capacity of the pores to the alkanes decreased with increasing the column temperature and the axial diffusion coefficients were different at different fl ow rate of carrier gas. The adsorption heat change first increased and then decreased in the range of-1.264--42.975 k J/mol with increasing the carbon chain length. The axial diffusion coefficients increased with increasing the carbon chain length,and when the fl ow rate of carrier gas was in the range of 2.654- 4.246 cm/s and 5.308- 13.270 cm/s,the axial diffusion coefficients were in the range of 0.328 8- 0.551 7 cm^2/s and 0.430 2- 1.456 4 cm^2/s,respectively.