Solvent-free enzymatic esterification of free fatty acids with glycerol for biodiesel application: Optimized using the Taguchi experimental method

Presence of free fatty acids along with glycerides poses a technical difficulty for biodiesel production. This work used a Taguchi L9 design to optimize the solvent-free enzymatic process to result in the esterification of oleic acid with glycerol. Under optimal conditions the esterification reaction temperature of 60 degrees C, enzyme dose of 5 wt%, glycerol: oleic acid molar ratio of 5:1, and reaction time of 3 h, a 75.235 +/- 2.19% conversion of oleic acid to esters was achieved. With the addition of molecular sieves, the conversion increased to 86.73% +/- 1.09%. However, using the parameters predicted by Taguchi design (60 degrees C, 5 wt%, 5:1, and 4.5 h), 88.5% +/- 1.11% of oleic acid could be converted to esters derivative. Diglycerides were the major product, and the reaction equilibrium was attained after 4 h. The immobilized enzyme could be used up to seven times with only a 10% reduction in the conversion. Thus, the process can efficiently reduce the free fatty acid content of oil to make it suitable for biodiesel production.

Automated summary

This study optimized the solvent-free enzymatic process for esterification of oleic acid with glycerol using Taguchi L9 design, achieving high conversion rates. The addition of molecular sieves further increased the conversion rate. The immobilized enzyme could be reused multiple times with minimal reduction in conversion. This method effectively reduces the free fatty acid content of oil, making it suitable for biodiesel production.