Fractionation of glycerol acetates by supercritical technology

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

Córdoba, Argentina

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

IPQA CONICET-UNC

The glycerolysis of acetic acid is an interesting industrial alternative to promote valorization of excessglycerol from biodiesel production, as well as that of acetic acid, both renewable products whoseprices are going down due to market saturation. The reaction between glycerol and acetic acid isreversible 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. Forinstance, glycerol acetates can be used as fuel additives because of its anti-knock properties, assweeteners or emulsifiers in the manufacture of food products [1] and also find a broad range ofapplications in the elaboration of cosmeceuticals [2]. The mixture of glycerol acetates, as it isproduced in the conventional synthesis, has 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 valueadded products.In this work we study the fractionation of a commercial mixture of glycerol acetates using supercriticalCO2. This technology has reached industrial scale in food applications [4] and it is being widely usedfor the production of valuable natural extracts for pharmaceuticals [5]. The use of CO2 as solventshows several advantages, highlighting for this study three important aspects: 1) the products (extractsand raffinates) are not contaminated during the separation process because CO2 is an innocuoussolvent and, in any case, it is completely released after depressurization, 2) the technology operates atmoderate temperatures, in general below 60 ºC, avoiding thermal degradation, and 3) it enables theprocessing of viscous liquids since the dissolution of supercritical CO2 in the liquid substratessubstantially decreases its viscosity and surface tension, fact that enhances fluid-dynamic and masstransferproperties [6]. Previous studies carried out with the Group Contribution with Associationequation of state (GCA-EoS) show that the supercritical CO2 depicts good selectivity to fractionateglycerol acetates [7]. Moreover, the phase equilibrium engineering points out that the separationprocess 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 commercialmixture of glycerol acetates using CO2 technology. Also, the effect of minor concentrations ofglycerol (excess reactant that should be recycled) was assessed. Supercritical CO2 fractionations of amixture comprising 18.6 wt% of TA, 45.1 wt% of DA, 31.3 wt% of MA and 5 wt% of glycerol werecarried out in the operating window identified by means of the GCA equation of state.