Thermal probe of vapor–liquid thermodynamic equilibrium

Vapor pressure data and evaporation/sublimation rate of liquid and solid samples are key parameters for designing new process units in terms of design, operability, and safety. In addition, for the case of hazardous materials, health and environmental aspects become essential. Conventional methods for obtaining these data mostly require significant material, time, and energy. Thermal analysis methods including differential scanning calorimetry (DSC) and thermogravimetry (TG) can both offer a platform for studying transition behavior of liquids/solids to the vapor phase. Yet, there are limitations, operational considerations, and analysis precautions to be accounted for in order to obtain highly valuable data. In particular, specific cautions should be taken for the case of liquid mixtures. Therefore, it is essential that the fundamentals and underlying principles of using DSC and TG methods for vapor pressure data generation are comprehensively understood so that one can effectively tune the methods according to the specific nature of the study. The dynamic nature of these methods develops a quasi-equilibrium state, where one should attempt to optimize the conditions as such that the temperature program effect becomes negligible on the initial condition of the sample. In this work, an integrative approach is followed to discuss the fundamentals and operational aspects of using DSC and TG for generating accurate vaporization and vapor pressure data of liquid samples. Specific attention is dedicated to elaborate on optimizing not only the experimental conditions to achieve isothermal boiling, but also data analysis step. Therefore, different considerations regarding post-run analysis are discussed. Moreover, due to the high importance of hydrocarbons, specific attention is also given to the application of these two methods to obtain vapor pressure data of hydrocarbons. The constructive discussions in this work develop an overview of the fundamentals of the method, provide the most significant contributions to the topic in a unifying manner, and suggest inputs and highlight the limitations of the techniques for future studies.