DEVELOPMENT OF A GENERALIZED MULTIPROPERTY APPARATUS TO MEASURE PHASE EQUILIBRIUM, DENSITY, INTERFACIAL TENSION, AND VISCOSITY OF FLUIDS AND ITS APPLICATION TO STUDY PHASE AND VOLUMETRIC BEHAVIOR IN SUPERCRITICAL CARBON DIOXIDE - HEAVY HYDROCARBON MIXTURES (NORMAL-HEXADECANE)

[摘要] A generalized apparatus was designed and developed to measure high pressure, moderate temperature, vapor-liquid-equilibria composition (VLE), densities (PVT), viscosities, and interfacial tensions, and applied to study the first two of these properties in the carbon dioxide and n-Hexadecane binary system. Two high pressure, positive displacement pumps were utilized as the variable volume equilibrium cell. The volume of the system could be adjusted by moving the pump pistons driven by synchronous motors at different speeds. Phase equilibrium was established by circulating the vapor phase through the liquid phase by means of a magnetic pump. The vapor and liquid phase compositions and densities were analysed by means of a gravitational method developed for this experiment. The viscometer is of the Rankine type. A visual cell for the measurement of interfacial tension by the pendant drop method is an integral part of the apparatus. The temperature of the system was controlled in the range of (+OR-)0.005(DEGREES)C inside an air bath for several hours. Even for more sustained operations, the temperature never varied more than (+OR-)0.02(DEGREES)C. Five isotherms were studied at 70(DEGREES)C, 60(DEGREES)C, 50(DEGREES)C, 40(DEGREES)C, and 35(DEGREES)C at pressures ranging from several atmospheres up to the critical pressure of each isotherm. The 70(DEGREES)C, 60(DEGREES)C, 50(DEGREES)C, and 40(DEGREES)C isotherms were above the critical end point (three-phase critical) of the CO(,2)-n-Hexadecane system while the 35(DEGREES)C isotherm fell below it. The critical pressures were reported to be 25.873, 21.863, 17.049, and 12.289 megaPascals, respectively. For the 35(DEGREES)C isotherm, four equilibrium regions were identified. At low pressure up to 7.970 MPa., vapor and liquid phases were in equilibrium. At 7.970 MPa., the three phases: Liquid(,1) (CO(,2)-rich phase), Liquid(,2) (n-Hexadecane-rich phase), and vapor phases, coexisted. At pressures above 7.970 MPa., Liquid(,1)-Liquid(,2) and Liquid(,2)-vapor equilibria appeared. Only liquid(,1)-Liquid(,2) equilibrium was reported since the latter region is diminishingly small. The critical pressure for the Liquid(,1)-Liquid(,2) equilibrium was reported to be 14.431 MPa. All the data were treated to determine the constants for the isothermal coexistence curve using a non-linear Statistical Analysis System (SAS) program. The shape of the coexistence curve is characterized quantitatively over the entire pressure range of each isotherm by an expansion of the reduced proximity to the critical pressure involving the critical exponents (beta) and (DELTA). An hypothesis regarding the relation between liquid-liquid equilibria at some lower temperatures and vapor-liquid equilibria at higher temperatures, more recently known as a form of supercritical extraction, is critically examined and discussed for CO(,2)-hydrocarbon systems.

[发布机构] Rice University