硅胶自环己烷溶液中吸附苯甲酸和苯的计量置换吸附模型

在293~313 K温度范围, 研究了硅胶在环己烷溶液中对苯甲酸和苯的吸附. 发现苯甲酸能非常好地服从计量置换吸附模型(SDM-A). 在用SDM-A处理苯的吸附时, 出现折线形的吸附等温线, 折线的转折点正好是单分子层吸附与多分子层吸附的分界点. 基于SDM-A, 研究了吸附热力学, 建立了吸附热力学的计算公式. 发现在环己烷溶液中苯甲酸被硅胶吸附是自发的、放热的熵增大过程, 而苯被吸附是自发的放热的熵减少过程, 苯甲酸的吸附自由能大于苯, 而吸附焓小于苯, 这是因为苯甲酸有更大的亲吸附剂作用和疏溶剂作用的结果.

A Model of Stoichiometric Displacement for the Adsorption of Benzoic Acid and Benzene by Silica Gel from Cyclohexane Solution

Adsorption of benzoic acid and benzene from cyclohexane solution by silica gel was studied under 293~313 K. It was indicated that adsorption of benzoic acid by silica gel well fit the stoichiometric displacement mode for adsorption(SDM-A). But for benzene, when treated with SDM-A there was a turning point in its adsorption isotherm, which corresponding to the dividing point between monomolecular and multimolecular layer adsorption. Thermodynamics formulae of adsorption were also set up based on SDM-A. It was demonstrated that benzoic acid was spontaneously adsorbed by silica gel accompanied with an entropy increase process, but for benzene it was accompanied with an entropy decrease process. The free energy change for adsorption of benzoic acid was larger than that of benzene and the adsorption enthalpy change was reversed because of the stronger affinity to silica gel and the stronger solvophobic ability for benzoic acid than that for benzene.