STUDY OF EVAPORATION OF ORGANIC POLLUTANTS BY THERMOGRAVIMETRIC ANALYSIS - EXPERIMENTS AND MODELING

Evaporation of four pure organic compounds of interest as environmenta l contaminants, i.e., naphthalene, hexachlorobenzene (HCB), 4-chlorobi phenyl (4-CBP), and n-decane, was studied at constant heating rates of 5, 10, and 25 degrees C/min by thermogravimetric analysis (TGA). The three aromatic solids began to evaporate at or below their melting poi nt and were completely vaporised well below their boiling points. The extent of evaporation at a fixed temperature increased with decreasing heating rate and when pressure was decreased from 10(5) to 10(4) Pa. Evaporation during heat-up was modelled as one-dimensional mass transf er to the ambient gas, of vapor in equilibrium with liquid in the TGA crucible. The surface area of evaporating liquid and the thickness of the concentration boundary layer was respectively estimated from appar atus geometry, and by best fitting model predictions to isothermal eva poration data. CFD analysis of the boundary layer supported use of a 1 -D, stationary boundary layer approximation. At 10 degrees C/min the m odel predictions are in good agreement with experiment for evaporation of HCB and 4-CBP, but do not satisfactorily represent n-decane evapor ation, apparently because of inadequate knowledge of the liquid surfac e area. The model captured well the observed effects of total pressure and the broad trends with changing heating rate. (C) 1997 Elsevier Sc ience B.V.