A novel static analytical apparatus for phase equilibrium measurements

Abstract

A new static analytical apparatus that enables reliable phase equilibria measurements for vapour–liquid equilibrium (VLE), liquid–liquid equilibrium (LLE) and vapour–liquid–liquid equilibrium (VLLE) data of small volumes (maximum 18cm3) has been designed. The operating temperature of the apparatus ranges from 253 to 473K and the operating pressure ranges from 100 to 1600kPa. In this work, the sampling of each phase is accomplished with a single standard mobile Rapid-Online-Sampler-Injector (ROLSI™). To enable sampling with the ROLSI™ sampler at pressures below the carrier gas pressure, a special arrangement of the sampling circuit is necessary. Such a setup was not used in this current study and consequently limited the sampling pressure to pressures above that of the carrier gas. A novel technique that compensates for the volume change within the equilibrium cell, which would normally occur due to movement of the ROLSI™ capillary, was used. The degassing of reagents prior to measurements is carried out on a simple degassing unit using the vacuum rectification method. Phase equilibrium data for previously reported systems were first measured to test the operation of the newly developed apparatus. The test systems included VLE measurements for the 2-methoxy-2-methylpropane+ethyl acetate system at 373.17K; LLE measurements for the hexane+acetonitrile and methanol+heptane systems at 350kPa; and VLLE measurements for the hexane+acetonitrile system at 348.20K. New experimental VLE data were also measured for systems of interest to petrochemical companies, viz. the ethanol+2-methoxy-2-methylbutane system at 398.25 and 413.19K (novel higher temperatures) and the 2-methylpent-2-ene+ethanol system at 383.20K. The VLE data are regressed with thermodynamic models using the combined method. Thermodynamic consistency testing (point and direct tests) is also performed for all the newly measured experimental data.