Metrological analysis on measuring techniques used to determine solubility of solids in supercritical carbon dioxide

Abstract

Supercritical carbon dioxide is commonly used as a green solvent in extraction processes. Precise data on the phase equilibrium of the mixture are vital to optimize process efficiency. The solutes extracted with scCO2 can exist in either a solid or liquid phase. The techniques developed to measure equilibrium, though similar, differ depending on the solute’s state. This work selects the most commonly used measuring techniques to determine the solubility of solids in scCO2 and analyzes the main sources of uncertainty. Six techniques are presented, studied, and compared: semi-flow, static analytic, static synthetic, chromatographic, capacitance cell, and nuclear magnetic resonance. The static synthetic method exhibits the lowest uncertainty, Ur(s) = 0.40 %, followed closely by the semi-flow method, Ur(s) = 0.50 %. Nuclear magnetic resonance is reported to have the highest uncertainty according to the literature, Ur(s) = 6 %. Other aspects, such as pricing or experimentation time, are also considered in the comparison, but no real analysis was performed since these characteristics are more volatile.