Continuous fractionation of glycerol acetates. Physicochemical properties glycerol acetates + CO2 mixtures at high pressure

FORTUNATTI MONTOYA, MARIANA; PEREDA, SELVA; HEGEL, PABLO E.

Santiago de Compostela

Encuentro; 1º Encuentro Ibérico de Fluidos Supercríticos; 2020

Universidad de Santiago de Compostela

Glycerol acetates are high-added value biosurfactants that find applications in different industrial sectors. Previous studies show the supercritical CO2 technology has a great potential for the fractionation of these highly viscous, amphiphilic, and non-volatile products (mono, di, and triacetyl glycerol) according to the quality standards of the food and cosmetic industry [1-3]. A proper design of fractionation columns and their further scale-up to commercial scale requires a robust thermodynamic model for phase equilibrium and PVT predictions [4], as well as proper correlations for physical properties like viscosity to assess the mass transfer and estimate the height of theoretical stages [5]. Physiochemical properties of these multicomponent mixtures are difficult to predict due to the complex nature of this system [6]. Thus, in this work, we determine experimentally the density and viscosity of CO2 saturated glycerol acetates mixtures at different pressures (30 bar to 150 bar), temperatures (25 °C to 50 °C) and CO2 concentrations (30 mol % to 70 mol %). Operating conditions were selected based on phase equilibrium predictions with the GCA-EOS of a high-pressure fractionation column [2]. First, a variable volume equilibrium cell is used to measure bubble points and saturated liquid molar volumes of glycerol acetates + CO2 mixtures. Thereafter, a high-pressure falling ball type viscometer is used to determine the dynamic viscosity of saturated liquid mixtures in the same range of pressure, temperature and CO2 concentrations.As it is well known, temperature and CO2 concentration has a significant effect on both density and viscosity measurements (Figure 1 and 2). The measured molar volumes are between 70 cm3/mol and 130 cm3/mol, while the viscosities are between 5 mPa.s and 20 mPa.S, according to CO2 concentration and temperature. Molar volume of saturated liquid mixtures increases slightly with temperature at a given CO2 concentration and it decays drastically with CO2 concentration at constant temperature (Figure 1). Viscosity of saturated liquid mixtures is significantly affected by both variables. The presence of CO2 in the liquid mixture reduces the viscosity and this effect is more evident at temperatures lower than CO2 critical temperature. Viscosity of the saturated glycerol acetates + CO2 liquid mixtures follows the relationship proposed by Litovitz et al [7], it decays exponentially with temperature wherever the CO2 concentration in the system.