Supercritical production and fractionation of fatty esters and monoglycerides

HEGEL, P.; SOTO, G.; PEREDA, S.; MABE G. ; BRIGNOLE, E.

Postdam, Berlín

Simposio; 26th European Symposium on Applied Thermodynamics; 2012

Dechema

The production of biodiesel or fatty esters from lipids with supercritical methanol (scMeOH) has gained interest in the last decade because it allows processing crude oils and fats, with high concentration of fatty acids and water without the use of catalysts. The reaction should be carried out above 580 K in order to achieve complete conversion. When milder conditions are set, also monoglycerides (MG) and diglycerides (DG), together with the glycerol, are  obtained as by-products of the transesterification process. Acylglycerols constitute common food emulsifiers and surface active agents in many industrial cleaning products.  On the other hand, carbon dioxide (CO2) presents complete solubility with fatty esters (FE) in a wide range of temperature and pressure and exhibits partial miscibility with acylglycerols (both in liquid and supercritical state); therefore, this solvent should be selective for fractionating the reaction products. Moreover, as it is well known, CO2 is a generally recognized as safe (GRAS) solvent.  The main goal of this work was to study the fractionation of FE and acylglycerols by using CO2 as a green solvent. Mixtures of FE, MG and DG were produced from the partial transesterification of high oleic sunflower oil with scMeOH in a temperature range of 556 K to 605 K and using different initial methanol to oil molar ratios  (20/1 to 40/1 methanol/oil).  Experimental data on phase equilibria of reaction products + CO2 were measured in a windowed variable volume cell. Different phase behaviors were determined at 298 K and 313 K under liquid-liquid-vapor, liquid-liquid  and liquid-vapor equilibrium conditions. These data were used to evaluate the performance of the Group Contribution with Association Equation of State (GCA-EOS) to model the ternary system in order to design a feasible separation process.  From the study carried out in this work, it was determined that with four countercurrent theoretical stages is possible to obtain acylglycerols with a concentrations higher than 98 wt.%  in the raffinate phase while the concentration of FE  is above 97 wt.% in the extract phase.