Measurement and modeling of the phase behavior of the (carbon dioxide plus water) mixture at temperatures from 298.15 K to 448.15 K

An analytical apparatus has been designed to study the phase behavior of fluid mixtures of relevance to CO2-enhanced oil recovery and carbon dioxide storage in deep aquifers or depleted oil fields. The fluid phases are circulated by means of a dual-channel magnetically-coupled pump and aliquots may be withdrawn from the re-circulation loops, by means of high-pressure sampling valves, for analysis by gas chromatography. The high-pressure cell is fitted with a special probe that may be rotated in order to draw liquid into the re-circulation loop from different heights within the cell, thereby permitting the study of three-phase vapor-liquid-liquid equilibria. The working temperature range of the apparatus is from (298 to 448) K and the maximum working pressure is 50 MPa. In this work, measurements have been made on the binary system (CO2 + H2O) at temperatures from (298.15 to 448.15) K and pressure from (1.5 to 18.0) MPa, and the results are compared with the available literature data. Vapor-liquid-liquid and liquid-liquid equilibrium points were also measured at T = 298.15 K. Standard uncertainties were 0.04 K for temperature, 0.04% of reading for pressure, and typically 3 x 10(-4) and 8 x 10(-4) for the mole fractions in liquid and vapor phases respectively. The results have been correlated by means of an asymmetric approach based on the Peng-Robinson equation of state, for the vapor phase, and an extended form of Henry's law incorporating the NRTL solution model, for the aqueous liquid-phase. The ability of the Krichevsky-Kasarnovsky (KK) approach to correlate the data has also been evaluated. (C) 2012 Elsevier B.V. All rights reserved.