Measurements of vapor pressures of alkanes by thermogravimetry.

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.