正构烷烃在介孔5A沸石中的吸附

Adsorption of n-paraffins on mesoporous 5A zeolites

分别选取具有不同碳原子数的正庚烷、正辛烷和正癸烷为吸附质,微孔及具有不同晶内介孔孔隙度的介孔5A沸石为吸附剂,通过重量吸附法测定了3种正构烷烃在293、308和318 K 3个温度下在微孔和介孔5A沸石上的吸附等温线,并从热力学的角度对其进行了分析。Langmuir、Langmuir-Freundlich和Toth 3种吸附模型对从实验获得的吸附数据的拟合结果表明,不同于烷烃分子在微孔5A沸石内的吸附,3种烷烃在介孔5A沸石上的吸附可用Langmuir-Freundlich和Toth两种吸附模型得到较好的拟合,在同一温度下,3种正构烷烃在介孔5A沸石内的最大吸附量均大于各自在微孔5A内的最大吸附量,但吸附质与吸附剂相互作用力随中孔的引入而减小,并由于微介孔吸附的共存,使得表面吸附多相性增加;另外,基于吸附数据计算获得的烷烃分子在沸石表面的吸附亨利常数和初始吸附热数据表明,沸石晶内介孔的存在,使其亨利常数和初始吸附热均减小;另外,由Clausius-Clapeyron方程计算得到的等量吸附热随表面吸附量变化的趋势表明,3种正构烷烃在介孔5A沸石内吸附热均随吸附量的增加而减小,其中以癸烷的变化最为明显。

Adsorption equilibrium isotherms of n-hetpane, n-octane and n-decane on 5A zeolites with intracrystalline mesopores were studied by gravimetric technique at 293, 308 and 318 K, and were compared with that on microporous 5A zeolite. The adsorption data from the three n-paraffins on mesoporous 5A zeolites are well correlated by the Langmuir-Freundlich and Toth models. Due to the coexistence of micropores and mesopores on mesoporous 5A zeolites, the maximum adsorption capacity is higher and the energetic heterogeneity is more obvious, while the affinity to the adsorbent evaluated by Henry＇s constant and the heat of adsorption at zero coverage decrease in the presence of mesopores in zeolite crystals. The isosteric heat of adsorption calculated by Clausius-Clapeyron equation decreases with the increase of surface coverage of n-paraffins. The change of decane is most obviously.