Thermodynamic Properties of Inclusion Complexes between 尾-Cyclodextrin and Naphthenic Acid Fraction Components

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• 作者：Mohamed H. Mohamed ; Lee D. Wilson ; John V. Headley ; Kerry M. Peru
• 刊名：Energy & Fuels
• 出版年：2015
• 出版时间：June 18, 2015
• 年：2015
• 卷：29
• 期：6
• 页码：3591-3600
• 全文大小：534K
• ISSN：1520-5029

文摘

The spectral displacement technique was used to determine the 1:1 equilibrium binding constants (K₂) of the complexes formed between 尾-cyclodextrin and carboxylate anion guests, including either single components or mixtures in aqueous solution at variable temperatures (25鈥?5 掳C). A van鈥檛 Hoff analysis of the results afforded thermodyamic parameters (螖H掳, 螖S掳, and 螖G掳) of the single-component carboxylate anions and complex mixtures of carboxylic acid species, referred to as naphthenic acids (NAs). Three types of single-component examples of NAs with variable hydrogen deficiency (z) values were studied: n-octanoic (z = 0; S1), trans-4-pentylcyclohexanecarboxylic acid (z = 鈭?; S2), and dicyclohexylacetic acid (z = 鈭?; S3). The carboxylate anion mixtures were obtained from commercial suppliers and an industrial source obtained from oil sands process water. The estimated K₂ values decrease with increasing temperature, and the standard Gibbs energy change (螖G掳) for complex formation is generally favorable (from 鈭?6 to 鈭?8 kJ/mol) and largely enthalpy-driven (from 鈭?2 to 鈭?0 kJ/mol). The change in entropy of complex formation (螖S掳) for S1, S2, and S3 varies (鈭?3 and 44 J mol^鈥? K^鈥?) depending on the guest size and relative lipophilicity. The positive correlation between complex stability, host鈥揼uest size-fit complementarity, and lipophilicity of the carboxylate anion reveals the importance of the hydrophobic effect, as evidenced by compensation phenomena for such host鈥揼uest complexes.