Effect of carbon chain length on esterification of carboxylic acids with methanol using acid catalysis
Effect of carbon chain length on esterification of carboxylic acids with methanol using acid catalysis
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DOI：
10.1016/j.jcat.2006.07.013
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发表时间：
2006-10-25
影响因子：
7.3
通讯作者：
Goodwin, James G., Jr.
中科院分区：
文献类型：
--
作者：
Liu, Yijun;Lotero, Edgar;Goodwin, James G., Jr.
本文研究了羧酸链长对液相酸催化酯化反应动力学的影响。使用硫酸和商业Nafion/二氧化硅复合固体酸催化剂（SAC-13），在60 ℃下测量了一系列直链羧酸（乙酸、丙酸、丁酸、己酸和辛酸）与甲醇的反应的初始动力学。结果发现，对于H2SO 4和SAC-13，反应速率随着直链烷基链中碳数的增加而降低。这种趋势进行了讨论的极性和空间效应的α-取代基的羧基和评价的塔夫脱型相关性。采用基于机理的动力学模型，测定了SAC-13催化剂对不同羧酸的反应动力学参数，并进行了比较。此外，重要的参数，如水失活，催化剂的可重复使用性，和再生，也受到所使用的羧酸的大小。随着羧酸上烷基尾部尺寸的增加，SAC-13在随后的反应循环中经历显著更多的活性损失。反应后的催化剂的表征表明，SAC-13的失活可能是由于大体积的反应中间体截留在Nafion聚合物纳米结构域中或其上阻塞催化酸位点引起的。(c)2006年爱思唯尔公司All rights reserved.
This paper reports on an investigation into the impact of carboxylic acid chain length on the kinetics of liquid-phase acid-catalyzed esterification. Using sulfuric acid and a commercial Nafion/silica composite solid acid catalyst (SAC-13), initial kinetics were measured for the reactions of a series of linear chain carboxylic acids (acetic, propionic, butyric, hexanoic, and caprylic acid) with methanol at 60 degrees C. It was found that reaction rate decreased as the number of carbons in the linear alkyl chain increased for both H2SO4 and SAC-13. This trend is discussed in terms of the polar and steric effects of the alpha-substituent to the carboxylic group and evaluated by a Taft-type correlation. Using a mechanistically based kinetic model, the reaction kinetic parameters of SAC-13 catalysis were determined and compared for different carboxylic acids. Moreover, important parameters, such as water deactivation, catalyst reusability, and regeneration, were also affected by the size of the carboxylic acid used. SAC-13 underwent significantly more activity loss with subsequent reaction cycles as the size of the alkyl tail on the carboxylic acid increased. Characterization of the catalyst after reaction suggested that the deactivation of SAC-13 is likely caused by the entrapment of bulky reaction intermediates in or on Nafion polymeric nanodomains blocking catalytic acid sites. (c) 2006 Elsevier Inc. All rights reserved.