High Pressure Equilibrium And Critical Curves Of Binary Systems Containing Supercritical CO₂

CO2 is not only an abundant natural carbon resource, but also green gas. Its effective utilization is an important object for environmental protection and material resource. The excellent properties of supercritical CO₂ are suitable for supercritical fluid extraction and supercritical fluid reaction. The study on high-pressure phase behavior of binary systems containing SCCO₂ is necessary for its applications. So a series of systems containing CO₂ have been experimentally investigated and calculated. A set of variable-volume autoclave with a quartz window has been made domestically for the first time. The accurate volume of a sample can be measured with a hall-effect probe, and the precise adjustment within wide range of temperatures and pressures can be actualized. At high pressure, the samples can be taken directly from the autoclave with a small steel vessel. So the accurate vapor-liquid equilibrium data can be obtained. The experiment equipment is proved to be reliable and accurate comparing with literature data. A simple equipment was also built up for the analysis the composition of the vapor and liquid samples. The vapor-liquid equilibrium data (including ingredient, density and volume) of the four binary systems (SCCO₂+ dimethyl carbonate, SCCO₂+diethyl carbonate, SCCO₂+ ethyl acetate and SCCO₂+ ethyl propionate) have been measured at different temperatures and pressures with isothermal static analytical method. The vapor-liquid equilibrium data show that the solubilities of SCCO₂ are higher in the four esters. The solubilities in the carbonates are higher than that in fatty acid esters, which reveals the principle that the similar structure makes the high solubility. And the higher the molecular weight is, the longer the carbon line is, the lower the solubility of SCCO₂ is. However the contents of the four esters in SCCO₂ are all low, and the differences among the contents are very little. The high-pressure GLE data are also calculated with eight methods for above four systems. The PR and PRSV EOS and four different mixing rules are used. The Suitability of those EOSs and calculated precision are discussed systemically. Three methods showed excellent calculation effects which each other were made up of (PR EOS with activity coefficient and associated theory) and (PR EOS with var der waals mixing rules). The critical curves are estimated. The results show the critical curves of the investigated systems belong to the second sub-kind of the first kind. In a word, the high pressure GLE data of the binary systems containing SCCO2 could provide abundant fundamental data for the study of the solution theory containing SCCO2 and the calculation of GLE, and advanced the development of the phase equilibrium theory and the calculation methods. At the same time, it could provide the necessary data for the design of SCCO2 extraction and reaction and put forward the relating methods.