Investigation of the surface layer of dimethyl ether/triethylene glycol solutions

Abstract

Method for calculating density and concentrations profiles of dimethyl ether (DME) solutions in triethylene glycol (TEG) was proposed in the paper. The thickness values of the surface layer of solutions were determined, and its structure was studied. The method for determining the effective surface concentration of the solution was proposed. The studies were performed in the framework of the gradient theory using the Peng-Robinson equation of state in single-fluid approximation with a modified procedure for determining the SE coefficients. The studies were conducted in order to determine the effective composition of the surface layer of the solution. It is this solution composition rather than of the bulk liquid phase composition that must be taken into account when interpreting the experimental data on the saturated vapor pressure and surface tension of solutions. As a result, it was found that the effective thickness of the surface layer of the solution increases with a decrease in the DME amount in solution, and as approaching the critical temperature tends to infinity. Herewith, surface layer of the studied solutions is composed of two sublayers. DME partial molar density profiles have a maximum. This means that the surface layer of the solution is enriched with this component. Analysis of the results has shown that the difference between the component concentrations in the surface layer and in the bulk liquid phase of the solution increases with temperature. The results are of fundamental importance in both the experimental investigation of the solution properties, and thermodynamic modeling of phase equilibria of solutions and forecasting their surface tension.