On the Study of Thermal Transitions in Selected n-Paraffins Using Differential Scanning Calorimetry

Abstract

The results obtained from a study of the thermal transformations of polymorphic long-chain normal paraffins (n-C32H66 and n-C36H74) are presented here. The research was performed using a power-compensated Differential Scanning Calorimeter (DSC). Both heating and cooling experiments were performed in dynamic nitrogen atmosphere. Thermodynamic data for both polymorphic transitions, as well as the fusion endotherms, were determined from the DSC thermal curves. Using the heats of transition (∆H), in Joules/gram, obtained from the data in the DSC thermal curves, molar heats of transition (∆H), in kJ/mol, were calculated and compared to previously published values. The molar entropy of transition (∆S) was then calculated for each of the observed thermal events. Additional information is given by the author on obtaining the best results from the use of DSC for the thermal behavior of n-paraffins. This manuscript opens with a review of most of the early work and the results it provided dealing with polymorphism of n-paraffin solids. Some of this referenced work was performed prior to the advent of computerized analytical instrumentation.

Keywords

• differential scanning calorimetry (DSC)
• entropy of transition (∆S)
• heat of transition (∆H)
• n-paraffins
• polymorphism