Kinetic study on disproportionations of C1 aldehydes in supercritical water: Methanol from formaldehyde and formic acid
Kinetic study on disproportionations of C1 aldehydes in supercritical water: Methanol from formaldehyde and formic acid
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DOI：
10.1021/jp066785y
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发表时间：
2007-04-12
影响因子：
2.9
通讯作者：
Nakahara, Masaru
中科院分区：
文献类型：
--
作者：
Morooka, Saiko;Matubayasi, Nobuyuki;Nakahara, Masaru
研究了C1醛类、甲醛（HCHO）和甲酸（HCOOHHOCHO）在400 ℃纯态和超临界水中在宽水密度范围（0.1-0.6 g/cm（3））内的反应途径和动力学。甲醛表现出四种反应：（i）甲醛的自缩合生成甲醇和甲酸，（ii）甲醛和甲酸之间的交叉缩合生成甲醇和二氧化碳，（iii）甲醛的非水依赖性自缩合生成甲醇和一氧化碳，以及（iv）甲醛的脱羰基生成氢气和一氧化碳。自交联反应和交叉交联反应的影响大于不依赖水的自交联反应和甲醛脱羰反应。在0.1-0.6 g/cm（3）的水密度范围内测定了自交联和交叉交联的速率常数。交叉反硝化反应的速率常数比自反硝化反应的速率常数大2-3个数量级，表明甲酸是比甲醛更强的还原剂。结合动力学结果和我们以前对自反和交叉反的平衡常数的计算研究，在过渡态理论的框架内讨论了这些反的反应机理。甲醇生产的反应路径可以通过调节水密度和反应物浓度来控制。在水密度为0.4 g/cm（3）的条件下，将甲醛与甲酸以1：2的比例混合，甲醇产率接近80%。
The reaction pathways and kinetics of C1 aldehydes, formaldehyde (HCHO) and formic acid (HCOOHHOCHO), are studied at 400 degrees C in neat condition and in supercritical water over a wide range of water density, 0.1-0.6 g/cm(3). Formaldehyde exhibits four reactions: (i) the self-disproportionation of formaldehyde generating methanol and formic acid, (ii) the cross-disproportionation between formaldehyde and formic acid generating methanol and carbon dioxide, (iii) the water-independent self-disproportionation of formaldehyde generating methanol and carbon monoxide, and (iv) the decarbonylation of formaldehyde generating hydrogen and carbon monoxide. The self- and cross-disproportionations overwhelm the water-independent self-disproportionation and the formaldehyde decarbonylation. The rate constants of the self- and cross-disproportionations are determined in the water density range of 0.1-0.6 g/cm(3). The rate constant of the cross-disproportionation is 2-3 orders of magnitude larger than that of the self-disproportionation, which indicates that formic acid is a stronger reductant than formaldehyde. Combining the kinetic results with our former computational study on the equilibrium constants of the self- and cross-disproportionations, the reaction mechanisms of these disproportionations are discussed within the framework of transition-state theory. The reaction path for methanol production can be controlled by tuning the water density and reactant concentrations. The methanol yield of similar to 80% is achieved by mixing formaldehyde with formic acid in the ratio of 1:2 at the water density of 0.4 g/cm(3).