(720e) Continuous Density Measurements In High Pressure Fluid Mixtures and Polymer Solutions

It this paper we will describe a novel approach to continuous density measurements in fluid mixtures or solutions under pressure. The experimental system involves a variable-volume view-cell, a motorized pressure generator, a sensor that continuously monitors the position of a piston moving in the variable-volume part of the view cell, and a computer interface and dedicated software that allows real time recording of the pressure, temperature, piston position, and transmitted light intensity. At a given temperature, pressure scans are conducted first in increasing and then decreasing directions. Scan rates are easily altered by changing the settings of the motorized pressure generator. From the data generated, Pressure vs Time, Piston position vs Time plots are immediately generated. From an initial calibration of the internal volume of the cell, and the mass loading of the fluid or fluid mixture in the cell, Pressure vs Volume or Pressure vs Density plots are easily generated. Depending upon the pressure scan rate and the sampling rate employed, 5 to 9,000 data points are generated which leads to essentially continuous pressure-density curves which permit distinct identification of entrance or demarcations from one-phase regions. The data are easily correlated with smooth functions to generate Density = f(Pressure) correlations. These are then used to generate other thermodynamics properties such as the isothermal compressibility, isobaric expansivity, pressure coefficient, and excess volume. The capabilities of the system will be described with data generated for CO₂, propane, n-octane and their mixtures, as well as a polymer solution.