Effect of process conditions on equilibrium, reaction kinetics and mass transfer for triglyceride transesterification to biodiesel: Experimental and modeling based on fatty acid composition

Abstract

Detailed reaction kinetics of oil transesterification were studied based on mechanism and reaction scheme of individual triglyceride, diglyceride, monoglyceride, glycerol and fatty acid methyl ester containing different combinations of gadoleic, linoleic, linolenic, oleic, palmitic and stearic acids determined by high-performance liquid chromatography. Pre-exponential factors and activation energies were correlated with molecular structure in terms of chain lengths and double bonds by response surface models. The activation energies of forward reactions were 47–61kJmol−1 with backward ones being 31–49kJmol−1, depending on component structure. Mass transfer during initial emulsion phase was acknowledged by determining diffusivities, distribution coefficients, molar volumes, boiling points and viscosities of individual components. Model was validated for a wide range of temperatures, hydrodynamic conditions, dispersed and continuous phase ratios, and methanolysis catalyst concentrations. Rotational speed had the most profound influence on the duration of transport phenomena-limited region spanning the latter to 27min upon use of 100rpm. Economics of the process were finally evaluated in terms of alcoholysis cost and price breakdown. Proposed methodology may be usefully applied to transesterification syntheses employing heterogeneous catalysis and enzymes, as well as various renewable resources such as microalgae lipids, waste oils, bioethanol and biobutanol.