A Novel Equipment for VLE Studies: Ethanol and Water System at Moderate Pressures and Data Verification with a Direct Point-to-Point Test.

A new multipurpose rectification tower was tested. Made of stainless steel, this two-section piece of equipment is filled with Raschig rings. It can be used to study vapor-liquid equilibrium (VLE) and determine and verify azeotropes in mixtures, as well as the vapor pressures of pure substances. The tower was designed to enable both external recirculation of the phases and internal countercurrent circulation, generating intimate contact between nonmiscible phases. Due to the material it is made of, it can be operated at pressures other than atmospheric pressure. The degradation of the fluids' quality can also be prevented. Experimental data obtained at 101, 300, 500, and 700 kPa using ethanol and water mixtures were verified by consulting bibliographic sources and applying the point-to-point test of Fredenslund et al. The reorganized errors observed when applying the point-to-point test suggested developing a new verification routine using the differential form of the Gibbs-Duhem equation. This new VLE validation procedure was tested using bibliographic data and was found to be more restrictive than the point-to-point test.