酯类基础油热氧化过程中的拉曼光谱分析

摘要

In this work,based on the continuous heating measure by DXR laser microscopic Raman spectrometry,the change regulations of the Raman feature peaks of ester base oils,such as trimethylolpropane trioleate (TMPTO),tridecyl trimellitate (TDTM) and dioctyl adipate (DOA) were investigated under online heating condition.Changing characteristics of ester oil molecular structure during the thermal oxidation process were studied.The results showed that some Raman peak positions and Raman intensity of ester oil varied with the increase of heating temperature.The C—H stretching vibration peak of methyl and methylene and the shear vibration peak of methylene of ester base oil are very sensitive to temperature.With the increase of temperature,the peak intensity has different degrees of weakening but could basically recover after cooling down.There is no obvious variation on C ＝ O vibration peak with the increase of temperature.The C ＝ C stretching vibration peak position of TMPTO ester base oil gradually shifts to higher wave region with the increase of temperature and will recover after cooling.Under the isothermal condition,the Raman intensity of TDTM base oil has no obvious change,the Raman intensity of C—H stretching vibration peak of methylene of DOA ester base oil and the Raman intensity of ＝ C—H,C ＝ C and—CH2— of TMPTO ester base oil decrease with the increase of oxidation time.Therefore,in situ Raman spectroscopy could be used to monitor the continuous thermal oxidation process of unsaturated ester oils,but it has some limitations in the monitoring of high-temperature oxidation of saturated ester oil and aromatic ester oil.%将DXR激光显微拉曼光谱仪与Linkam FTIR600控温台联用,测定了连续加热、恒温氧化过程中三羟甲基丙烷油酸酯(TMPTO)、偏苯三酸三异酸酯(TDTM)、己二酸二异辛酯(DOA)等酯类基础油的拉曼特征峰的变化规律,探讨了热氧化过程中酯类油分子结构的变化特点.研究发现,随着加热温度的提高,酯类基础油的部分拉曼峰的峰位与峰强均发生了明显变化;酯类基础油的甲基与亚甲基的C—H伸缩振动峰及亚甲基的剪式振动峰对温度很敏感,随着温度的升高发生了不同程度的峰强衰减,冷却后可基本恢复;C=O振动峰随温度的升高变化不明显;TMPTO酯类基础油的C=C双键伸缩振动峰随着温度升高逐渐向高波区移动冷却后可恢复,=C—H和C=C的伸缩振动峰强冷却后不能完全恢复;恒温下随着氧化时间的延长,TDTM和DOA基础油的拉曼峰无明显变化,与TMPTO基础油的=C—H、C=C及—CH2—相关的拉曼峰呈规律性衰减.因此可运用原位拉曼光谱法对不饱和酯类基础油中连续氧化进行监测.而原位光谱法对饱和酯类油和芳香酯类油高温连续氧化过程的监测具有一定的局限性.