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

PEREDA, S.; FORTUNATTI MONTOYA, M.; HEGEL, P.

Coimbra

Congreso; First Iberian Meeting on Supercritical Fluids; 2020

CIEPQPF

Glycerol acetates are high-added value biosurfactants that find applications in differentindustrial sectors. Previous studies show the supercritical CO2 technology has a greatpotential for the fractionation of these highly viscous, amphiphilic, and non-volatileproducts (mono, di, and triacetyl glycerol) according to the quality standards of the foodand cosmetic industry [1-3]. A proper design of fractionation columns and their furtherscale-up to commercial scale requires a robust thermodynamic model for phaseequilibrium and PVT predictions [4], as well as proper correlations for physical propertieslike viscosity to assess the mass transfer and estimate the height of theoretical stages [5].Physiochemical properties of these multicomponent mixtures are difficult to predict dueto the complex nature of this system [6]. Thus, in this work, we determine experimentallythe 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 % to70 mol %). Operating conditions were selected based on phase equilibrium predictionswith the GCA-EOS of a high-pressure fractionation column [2]. First, a variable volumeequilibrium cell is used to measure bubble points and saturated liquid molar volumes ofglycerol acetates + CO2 mixtures. Thereafter, a high-pressure falling ball type viscometeris used to determine the dynamic viscosity of saturated liquid mixtures in the same rangeof pressure, temperature and CO2 concentrations. As it is well known, temperature and CO2 concentration has a significant effect on bothdensity and viscosity measurements (Figure 1 and 2). The measured molar volumes arebetween 70 cm3/mol and 130 cm3/mol, while the viscosities are between 5 mPa.s and 20MmPa.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 ofCO2 in the liquid mixture reduces the viscosity and this effect is more evident attemperatures lower than CO2 critical temperature. Viscosity of the saturated glycerolacetates + CO2 liquid mixtures follows the relationship proposed by Litovitz et al [7], itdecays exponentially with temperature wherever the CO2 concentration in the system.