Vapor-liquid equilibrium (VLE) data (T,p,x,y) are vital for the development of mixture thermodynamic models. Herein, we demonstrate the use of nuclear magnetic resonance (NMR) spectroscopy as an in- situ method for the measurement of VLE. The experiment is carried out entirely inside a high- pressure NMR sample tube. The simultaneous measurement of liquid- and vapor-phase composition was achieved by the addition of a sealed glass capillary to the NMR sample tube; in this way, a small amount of the liquid phase wicks into the wedge-shaped gap between the capillary and the inner wall of the NMR tube. The presence of a suspended liquid phase was confirmed by X-ray computed tomography (XCT), and its behavior was examined by computational fluid dynamics (CFD). The components of the two phases are observed as distinct signals in the NMR spectra. The temperature-dependent spectrum of methanol, which is contained in the sealed capillary, provides an in-situ measurement of temperature. Vapor density was measured instead of pressure. This was accomplished by calibration with gas-phase ethane at known densities. With this approach, we provide proof-of-concept results at 291.2 K on binary mixtures of (R125 + R143a), (R125 + R32), (neopentane + ethane), and (benzene + ethane).
Journal of Chemical and Engineering Data
nuclear magnetic resonance (NMR) spectroscopy, vapor-liquid equilibrium (VLE), refrigerant mixtures, x-ray computed tomography (XCT), computational fluid dynamics (CFD), methanol thermometer