Kinetic Treatment of Evaporation via Thermogravimetric Analysis: The Case of d‑Limonene

Evaporation from a surface under atmospheric conditions can be difficult to characterize because the process involves both thermodynamics and kinetics. Thermogravimetric analysis was used to study the evaporation of d-limonene under several nitrogen flow rates above the surface. Instead of the common thermodynamic analysis, a kinetic treatment resulted in an activation energy of evaporation that is mostly composed of the enthalpy of vaporization with a smaller, additional energy due to the diffusion of molecules through the laminar boundary layer above the evaporating surface. As the flow rate over the sample increased from 60 to 200 mL/min, the activation energy decreased from 57.3 to 49.7 kJ mol–1 and approached reported enthalpy of vaporization values. Thus thermogravimetric analysis can be used to quantitatively characterize both the kinetic and thermodynamic aspects of nonequilibrium evaporation processes.