Study On Phase Equilibrium Of Solid Solutes In Supercritical Or Subcritical Fluids

In recent decades, supercritical and subcritical fluids technology has a wide range of applications in chemical industry, medicine, material preparation, and other fields. Among them, supercritical carbon dioxide (SCCO2), as a result of its non-toxic, inexpensive, and environmental friendly, has become one of the most commonly supercritical fluids that be used. Nevertheless, the difficulty in the wide applications of SCCO2is its weak dissolving capability, especially for polar and/or high molecular weight solutes such as pharmaceuticals. This disadvantage results in the limitation of its application in reaction, separation and material preparation processes.1,1,1,2-Tetrafluoroethane (R134a), with its strong polarity and lower critical pressure that comparison with SCCO2, has become a hot pot that many researchers focused on. In this paper, the solubilities of single and mixed solid solutes in SCCO2and subcritical R134a with and without cosolvents have been done in experimental and theoretical research. The specific contents are as follows:On the aspects of experimental research, the solubility measurement of p-aminosalicylic acid in SCCO2with and without cosolvents were implemented from (11.0to21.0) MPa with temperature at (308,318,328) K by the dynamic flow method, and the kinds of cosolvents were ethanol, acetone and ethylene glycol (mole fraction is0.04); solubilities of p-aminosalicylic acid,p-hydroxybenzaldehyde, m-hydroxybenzaldehyde and the mixture of the hydroxybenzaldehyde isomers in subcritical R134a were measured at the temperature range from (308,318and328) K and pressure between (5.0and15.0) using the static method. This work provides a foundation support to the supercritical and subcritical fluids extraction.On the base of experimental data, a systematic analysis of the change of the solubilities of solid solutes in supercritical and subcritical fluids with temperature and pressure has been done; the influence of the kinds of cosolvents, the location of functional group and the interaction of solute and solvent molecules has been studied; the effect factor of cosolvent (e), solubility enhancement factor (δ), improvement effect factor (μ) in the mixed solute and solvents system, separation factor (SF) and separation efficiency (SE) were calculated and analyzed.The solubilities of the solutes in pure SCCO2and subcritical R134a were correlated with Chrastil model, Mendez-Santiago and Teja (MST) model, Kumar-Johnston (KJ) model, Sung-Shim (SS) model and Jouyban-Chan (JC) model; and Chrastil-G model, MST-Sauceau model, Sovova model and Sovova-T model were used to correlate the solubilities of solutes in SCCO2and subcritical R134a with cosolvents, and all of which obtained good agreements.The molecular interaction energy between solute and solvent molecules was calculated using Gaussian software to futher clarify the change rule of the solubilities of solutes in supercritical and subcritical fluids. For the supercritical and subcritical fluids systems, a new prediction model which combined kinds of factors that affect the solutes solubility was proposed.365solubility experimental data that been published in literatures were used to calculate the new model, and196solubility experimental data of10solutes were adopted to test the new prediction model.