A model that describes the pure evaporation kinetics is introduced. This model takes into account gas diffusion and convective gas transport; it describes the evaporation kinetics under the general conditions of thermogravimetric measurements. The model is used to determine the equilibrium vapour pressure in a relatively wide temperature range. The validity of the model is checked against experimental data of triethanolamine (TEA) and water evaporation. The applicability of isoconversional methods to the evaporation kinetics is also studied. Besides, it is shown that the degree of TEA decomposition depends on the surrounding atmosphere and on the conditions for gas evaporation; the easiest the gas evaporation, the smallest the degree of decomposition. In view of the volatiles formed, a reaction pathway is proposed for the thermal decomposition of TEA