Fractionation of glycerol acetates by supercritical technology

M. FORTUNATTI-MONTOYA; F. SANCHEZ; P. HEGEL; S. PEREDA

Córdoba

Congreso; XI Iberoamerican Conference on Phase Equilibria and Fluid Properties for Process Design; 2018

Universidad Nacional de Córdoba

The glycerolysis of acetic acid is an interesting industrial alternative to promote valorization of excess glycerol from biodiesel production, as well as that of acetic acid, both renewable products whose prices are going down due to market saturation. The reaction between glycerol and acetic acid is reversible and produces a mixture of glycerol acetates: monoacetin (MA), diacetin (DA), and triacetin (TA), which are high value-added products with applications in different industrial sectors. For instance, glycerol acetates can be used as fuel additives because of its anti-knock properties, as sweeteners or emulsifiers in the manufacture of food products [1] and also find a broad range of applications in the elaboration of cosmeceuticals [2]. The mixture of glycerol acetates, as it is produced in the conventional synthesis, have a low value in comparison with purified MA and DA [3]. Thus, the fractionation and purification of the glycerol acetates is key for the elaboration of value added products.In this work we study the fractionation of a commercial mixture of glycerol acetates using supercritical CO2. This technology has reached industrial scale in food applications [4] and it is being widely used for the production of valuable natural extracts for pharmaceuticals [5]. The use of CO2 as solvent shows several advantages, highlighting for this study three important aspects: 1) the products (extracts and raffinates) are not contaminated during the separation process because CO2 is an innocuous solvent and, in any case, it is completely released after depressurization, 2) the technology operates at moderate temperatures, in general below 60 ºC, avoiding thermal degradation, and 3) it enables the processing of viscous liquids since the dissolution of supercritical CO2 in the liquid substrates substantially decreases its viscosity and surface tension, fact that enhances fluid-dynamic and mass-transfer properties[6]. Previous studies carried out with the GCA equation of state show that the supercritical CO2 show good selectivity to fractionate glycerol acetates[7]. Moreover, the phase equilibrium engineering points out that the separation process would be feasible in a pressure and temperature range of 90 to 130 bar and 293 to 333 K, respectively. The aim of this work is to evaluate experimentally the fractionation of a commercial mixture of glycerol acetates using CO2 technology. Also, the effect of minor concentrations of glycerol (excess reactant that should be recycled) was assessed. Supercritical CO2 fractionations of a mixture comprising 18.6 wt% of TA, 45.1 wt% of DA, 31.3 wt% of MA and 5 wt% of glycerol were carried out in the operating window identified by means of the GCA equation of state.