Solid pure component property effects on modeling upper crossover pressure for supercritical fluid process synthesis: a case study for the separation of Annatto pigments using SC-CO2

Abstract

In this work a new method to predict upper crossover pressure based on equations of state is developed and applied to systems containing supercritical CO2 and Annatto (Bixa orellana) pigments. The calculation of the solubility of bixin in supercritical carbon dioxide is done using the Peng–Robinson–LCVM–UNIFAC equation of state and the effect of any uncertainty of some solid pure component properties on the upper crossover pressure is also investigated. The calculation of the solubility of norbixin in supercritical CO2 is also done but in a completely predictive way using only solubility parameter data and group contribution since no experimental data of solubility is available. For both systems pure component parameters are initially estimated by group contribution and subsequently tuned by the model. It is also shown that the slope of sublimation pressure curve plays a major role in the accuracy of the upper crossover pressure determination. Furthermore, the present method can be used for upper crossover pressure analysis regardless of the equation of state and mixing rules adopted to calculate the fugacity coefficient of solid solute in the fluid phase. The results for solubility and crossover pressure calculated with this method are in good agreement with experimental data for CO2–bixin available in literature. The method described here can be useful to any solid–fluid system of interest in supercritical fluid extraction process synthesis.