高温高压下草酸脱羧反应中的拉曼光谱研究

Research on Raman Spectra of Oxalic Acid During Decarboxylation under High Temperature and High Pressure

应用水热金刚石压腔结合拉曼光谱技术研究了高温高压下草酸溶液的热稳定,使用拉曼光谱对其脱羧反应及产物进行监测。结果表明低温升温过程中,草酸的拉曼谱图中各个特征振动峰没有发生变化,随着温度的继续升高,其特征振动峰逐渐变弱。达到一定温度后,羧基的拉曼特征峰消失,草酸发生脱羧反应:C2H2O4—2CO2+H2生成CO2和H2。高温高压下草酸发生热分解的温度压力之间呈线性关系,其线性回归方程为P(MPa)=12.839 T(K)-5 953.7,R2=0.99。草酸脱羧反应的摩尔体积变化与温度压力的关系为ΔV(cm-3.mol-1)=16.69-0.002P(MPa)+0.005 2T(K),R2=0.99。

The present research studied the thermal stability of oxalic acid under high temperature and pressure and its in-situ transformation by Raman spectroscopy using a hydrothermal diamond anvil cell.Raman spectra allow the detection of ionic and covalent atomic aggregates through the acquisition of vibrational spectra that are characteristic of their structures and molecular bond types.The result showed that there was no change in characteristic vibrational Raman peaks of oxalic acid in the low-temperature stage.With the increase in temperature and pressure,the characteristic vibrational Raman peaks of oxalic acid became weaker and the peaks disappeared at a certain high temperature,and decarboxylation happened.Oxalic acid decomposes to produce CO2 and H2,according to the reaction： C2H2O4—2CO2＋H2.It was found that the decarboxylation was highly related with pressure and that the decarboxylation would be hindered at high pressure.Decarboxylation of oxalic acid under high temperature and pressure showed a linear relationship between temperature and pressure.The data fitting generated the formula： P（MPa）=12.839T（K）-5 953.7,R2=0.99.The molar volume change of decarboxylation of oxalic acid can be described by ΔV（cm-3·mol-1）=16.69-0.002P（MPa）＋0.005 2T（K）,R2=0.99.