Experimental measurement and modeling of quinizarin solubility in pressurized hot water

Abstract

In the field of natural products, anthraquinones are an important category of secondary metabolites present in various vegetable species. They are highly bioactive compounds, potentially useful for therapeutic applications, as antiviral, anti-bacterial and anti-cancer agents. Extraction processes using pressurized hot water offer an environmentally friendly alternative to traditional extraction and purification methods applied to anthraquinone-containing plants. Knowledge on high-pressure phase equilibria of anthraquinone + solvent mixtures is required to evaluate the potentiality of these processes. The need is for both, experimental data and thermodynamic models that are able to predict phase boundaries at different process conditions. In this work, the solubility of 1,4-dihydroxy-9,10-anthraquinone (quinizarin) in pressurized hot water has been measured, using a simple and reliable dynamic method. For the binary quinizarin + H2O, the measurements were performed at (333, 353, 373, 393, 413, 443, 463) K and pressures of (30, 60 and 90) bar. The group-contribution with association equation of state (GCA-EOS), with the definition of a cyclic ketone functional group (CyC[dbnd]O) was used to calculate solid-liquid equilibria of binary mixtures of anthraquinones with pressurized hot water. This model was able to give a good representation of the solubility behaviour of quinizarin in water.