Abstract
An automated vibrating-tube densimeter was developed for solvent mixtures at elevated temperatures and pressures, and was employed to measure the density of ethanol-water mixture at 250 °C and 15, 20, 30, and 40 MPa as a continuous function of the composition over the entire range. Oscillation of the vibrating tube was excited with a piezoelectric actuator, and was monitored with a laser-Doppler vibrometer, enabling the density measurements without electromagnetic attachments. High-resolution and high-throughput measurements were attained by the three improvements: (i) miniaturization of the vibrating tube, (ii) accurate determination of the natural frequency of the vibrating tube from the free damped oscillation waveform after the excitation, and (iii) automated continuous composition change by a flow-mixing system using four syringe pumps. The continuous density data allowed calculations of the excess and partial molar volumes without the ambiguity arising from interpolation of discrete data. The volumetric information will facilitate not only the design of novel chemical processes under solvothermal conditions but also the understanding of microscopic solution structure in sub- and supercritical solvent mixtures.