MEASUREMENT OF SOLUBILITIES OF METAL CHELATES IN SUPERCRITICAL CARBON DIOXIDE USING A QUARTZ CRYSTAL MICROBALANCE

摘要

The solubility measurement technique used in this work relies on a piezoelectric quartz crystal or a quartz crystal microbalance. This technique is an in-situ gravimetric technique, where a small amount of solute is loaded onto a piezoelectric quartz crystal. The crystal is then placed in a high-pressure cell and pressurized with supercritical carbon dioxide (SC CO_2). The solubility is quantified by the crystal's frequency change as the solute dissolves into the supercritical fluid, In this work, the solubility of copper (II) bisthenoyltrifluoroacetonate (Cu(tta)_2) in SC CO_2 was measured at different pressures (10.2 MPa to 15.7 MPa) and at a temperature of 40℃. The solubilities were 0.99x10~(-6), 2.45x10~(-6), 3.32x10~(-6) and 3.66x10~(-6) mol/mol at SC CO_2 densities of 0.643, 0.741, 0.775 and 0.790 g/cm~3, respectively. In order to verify this technique, caffeine solubilities were also measured. Caffeine solubility was determined to be 7.75x10~(-6) mol/mol at 60℃ and a SC CO_2 density of 0.322 g/cm~3. This caffeine solubility is comparable to existing literature values.