Dimerization and Viscosity of Acetic Acid Vapor

Abstract

Abstract Results of new relative measurements on the vapor of acetic acid are reported. The measurements were based on a single calibration at room temperature with a theoretically calculated viscosity value of argon. Nineteen isochoric series, differing in density, were performed in an all-quartz oscillating-disk viscometer from 298 to 598 K and for densities between 0.5 and 61 mol m-3. The uncertainty of the experimental data is ±0.5% at low densities and ±(0.3−0.4)% at high densities increasing with temperature. This is inferior compared with measurements on simple gases due to adsorption effects on quartz at low temperatures and to thermal decomposition at high temperatures. Isotherms recalculated from the original isochoric data show with decreasing density a strong curvature with negative slope, particularly at low temperatures. The further evaluation accounts for the fact that a strong dimerization depending on temperature occurs in acetic acid vapor. The isotherms, resulting from an association model which considers additional interactions between monomers and dimers, show a smaller curvature in terms of the mole fraction of monomers. Viscosity values for monomers and dimers were deduced using a simplified equation for the viscosity of a gas mixture. These values are restricted to 570 K due to thermal decomposition and low mole fractions of the dimers at high temperature. Furthermore, viscosity values for the saturated vapor could be determined at low temperatures.