Kinetic and equilibrium study on formic acid decomposition in relation to the water-gas-shift reaction.
Kinetic and equilibrium study on formic acid decomposition in relation to the water-gas-shift reaction.
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DOI：
10.1021/jp0626768
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发表时间：
2006-09
期刊：
影响因子：
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通讯作者：
Y. Yasaka;Ken Yoshida;Chihiro Wakai;N. Matubayasi;M. Nakahara
中科院分区：
文献类型：
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作者：
Y. Yasaka;Ken Yoshida;Chihiro Wakai;N. Matubayasi;M. Nakahara
研究了水煤气变换反应中间体甲酸在170-330 ℃热水中的水热脱羰反应动力学和平衡，以了解和控制水热WGS反应。(1)H和（13）C NMR光谱法用于分析液相和气相中的猝灭反应混合物作为时间的函数。只有脱羰反应是由HCl催化的，并且该反应对于[H（+）]和[HCOOH]都是一级反应。因此，由于甲酸的未抑制电离，无HCl的反应为一级半（1.5）反应。因此，HCl加速的脱羰反应路径可以及时与脱羧反应分开。通过使用热水中一氧化碳的亨利常数（气体溶解度数据）分别确定脱羰反应的速率和平衡常数。在170、200、240和280 ℃下，饱和曲线的液体分支上的脱羰反应速率常数分别为1.5 × 10（-5）、2.0 × 10（-4）、3.7 × 10（-3）和6.3 × 10（-2）mol（-1）kg s（-1）。脱羰反应的Arrhenius图呈线性，活化能为146 +/- 3 kJ mol（-1）。在170、200、240和280 ℃下，平衡常数K（CO）= [CO]/[HCOOH]分别为0.15、0.33、0.80和4.2。范特霍夫图得出焓变Δ H = 58 +/- 6 kJ mol（-1）。脱羧速率也在酸性和碱性条件下在240-330 ° C下测量。该速率对溶液pH值的依赖性很弱，在330 ℃时约为10（-4）mol kg（-1）s（-1）。此外，在330 ℃下，平衡常数K（CO2）= [CO（2）][H（2）]/[HCOOH]估计为1.0 × 10（2）mol kg（-1）。
Kinetics and equilibrium are studied on the hydrothermal decarbonylation and decarboxylation of formic acid, the intermediate of the water-gas-shift (WGS) reaction, in hot water at temperatures of 170-330 degrees C, to understand and control the hydrothermal WGS reaction. (1)H and (13)C NMR spectroscopy is applied to analyze as a function of time the quenched reaction mixtures in both the liquid and gas phases. Only the decarbonylation is catalyzed by HCl, and the reaction is first-order with respect to both [H(+)] and [HCOOH]. Consequently, the reaction without HCl is first and a half (1.5) order due to the unsuppressed ionization of formic acid. The HCl-accelerated decarbonylation path can thus be separated in time from the decarboxylation. The rate and equilibrium constants for the decarbonylation are determined separately by using the Henry constant (gas solubility data) for carbon monoxide in hot water. The rate constant for the decarbonylation is 1.5 x 10(-5), 2.0 x 10(-4), 3.7 x 10(-3), and 6.3 x 10(-2) mol(-1) kg s(-1), respectively, at 170, 200, 240, and 280 degrees C on the liquid branch of the saturation curve. The Arrhenius plot of the decarbonylation is linear and gives the activation energy as 146 +/- 3 kJ mol(-1). The equilibrium constant K(CO) = [CO]/[HCOOH] is 0.15, 0.33, 0.80, and 4.2, respectively, at 170, 200, 240, and 280 degrees C. The van't Hoff plot results in the enthalpy change of DeltaH = 58 +/- 6 kJ mol(-1). The decarboxylation rate is also measured at 240-330 degrees C in both acidic and basic conditions. The rate is weakly dependent on the solution pH and is of the order of 10(-4) mol kg(-1) s(-1) at 330 degrees C. Furthermore, the equilibrium constant K(CO2) = [CO(2)][H(2)]/[HCOOH] is estimated to be 1.0 x10(2) mol kg(-1) at 330 degrees C.