基于热重分析测定物质的蒸气压  

Measurements of vapor pressures of alkanes by thermogravimetry.

作　　者：郑青[1] 雷群芳[1] 方文军[1] 

机构地区：[1]浙江大学化学系,浙江杭州310027

出　　处：《浙江大学学报（理学版）》2008年第1期59-62,67,共5页Journal of Zhejiang University（Science Edition）

基　　金：国家自然科学基金资助项目(20573096);浙江省自然科学基金资助项目(Y404329)

摘　　要：根据自由蒸发过程的Langmuir关系,将热重分析(TGA)用于正十六烷、正十七烷和正十八烷等3个正构烷烃的蒸气压测定,分别采用常数法和比较法计算蒸气压,其结果与文献数据符合较好.结果表明,只要选择合适的参考物质,TGA可以成功地应用于未知液体物质蒸气压的测定.同时,根据从TGA实验得到的蒸发速率和蒸气压数据,计算了蒸发过程的表观活化能和平均蒸发焓,发现活化能数值仅稍大于蒸发焓,证实TGA实验中的蒸发过程接近非活化自由蒸发过程.TGA是一种快速实用的蒸气压测量新方法,尤其适用于较低压力范围的蒸气压测定,是传统实验方法的很好补充.Thermogravimetric analysis （TGA） was extended to the measurements on vapor pressures of three n-alkanes, hexadecane, heptadecane and octadecane, on the basis of the Langmuir equation for zero order vaporization process. The vapor pressures were calculated by two different methods, a constant parameter one and a comparative one, from the TGA data. These results are in good agreement with the reference data calculated from the Antoine equation. It follows that TGA can be successfully extended to the vapor pressure measurements of some liquids provided an appropriate reference sample is used. Furthermore, the apparent energies of activation for the vaporization process and the average enthalpies of vaporization are obtained through the vaporization rates and the vapor pressure data. It was found that the values of the energy of activation are only slightly larger than those of the enthalpies of vaporization and it indicated that the vaporization process during the TGA is nearly a non-activated one. The experimental results showed that the TGA method is a rapid and practical one for constructing vapor pressure curves especially at low pressure range. TGA can serve as a new remedy for the traditional methods of vapor pressure measurements.

关 键 词：热重分析 正构烷烃 蒸气压 活化能 蒸发焓 

分 类 号：O642.4[理学—物理化学]