Measurement of diffusion coefficients in the cyclohexane/toluene/polystyrene system using perturbation gas chromatography

Abstract

A semi-automated vibrating tube densimeter designed for operations between 100 and 700 K and to 70 MPa is described. This densimeter features continuous flow of the sample fluid and a fluid conditioning system that rapidly brings the fluid to the operating temperature. Both of these features minimize the residence time at the measurement temperature of the sample, making the densimeter suitable for the fluids that decompose or are unstable. Two microcomputers are used for data acquisition and temperature control (~3 mK). A measurement technique (incremental pressure method) has been developed that decreases measurement time while reducing the quantity of sample required. The incremental pressure method also allows measurements at pressures that are below the saturation pressure of the calibration fluid. Densities measured using the incremental pressure method compared within 0.1% to densities measured using another technique (sequential flow method). Densities of toluene, ethylbenzene, and 2,2,4-trimethylpentane measured at temperatures between 323.15 and 600 K at pressures to 15 MPa are presented. These densities are internally consistent within 0.1% at temperatures to 500 K, and compare within 0.2% of literatures values for toluene and 2,2,4-tri,ethylpentane. At temperatures above 500 K, the densities of 2,2,4-trimethylpentane are internally consistent within 0.2% and compare to literature values within 0.2-0.3%. The densities measured at 580, 590, and 600 K for 2,2,4-trimethylpentane are at temperatures above that of any previous measurements. At temperatures above 520 K for toluene and above 400 K for ethylbenzene, the measured densities show a systematic difference of 0.4-0.5% from other reported values.