Evaluation of the Sublimation Process of Some Purine Derivatives: Sublimation Rate, Activation Energy, Mass Transfer Coefficients and Phenomenological Models

Caffeine and theophylline are compounds with important applications in the pharmaceutical industry and other fields of the chemical industry. These purine derivatives have simple chemical structures, therefore, the evaluation of their sublimation process contributes to the development of mass transfer analysis methods that can later be applied to other compounds with more complex structures. With the help of thermogravimetric analysis in isothermal conditions, the kinetic study of the sublimation of caffeine and theophylline, along with the evaluation of kinetic parameters (activation energy and the pre-exponential factor), was carried out. Global mass transfer coefficients were determined, which vary for caffeine between 53 x 10(-8) and 631 x 10(-8) mol/s.m(2).Pa, and for theophylline between 68 x 10(-8) and 441 x 10(-8) mol/s.m(2).Pa. The dimensionless equations of the form: Sh = a + b.Re-c.Sc-d have been proposed, which allow the determination of individual mass transfer coefficients at temperatures between 130 and 160 degrees C for caffeine and between 170 and 200 degrees C for theophylline.

Automated summary

This study investigates the kinetics of sublimation of caffeine and theophylline using thermogravimetric analysis, and proposes dimensionless equations to calculate mass transfer coefficients within specific temperature ranges.