Transesterification of Castor Oil Catalyzed by Liquid Enzymes: Optimization of Reaction Conditions

Enzymes as catalysts for biodiesel production are emerging as a sustainable alternative to chemical catalysts. Enzymatic transesterification has the benefit of a low sensitivity to the water and free fatty acids content in the feed. The choice of feedstock represents a crucial point to the process economy. Based on this, and considering its low influence with food production, castor oil was investigated as a potential feedstock. Compared to other vegetable oils, it has a higher polarity resulting in better system homogeneity during reaction. The enzyme tested as catalyst was Eversa Transform. Four main reaction parameters were investigated for the optimization of the reaction route: the temperature was varied from 35 to 45 °C, the water content between 0-10 wt%, the enzyme content in the range of 2-10 wt%, and the alcohol-to-oil molar ratio from 4.5 to 7.5. The Response Surface Methodology was used to determine the optimal reaction conditions to get a high biodiesel yield and a low free fatty acids concentration. The results obtained showed that at 35 °C, 5 wt% of enzymes, 5 wt% of water, and a 6.0 alcohol-to-oil molar ratio, the yield in biodiesel was about 94% with a content of free fatty acids of about 6%. This condition was used to develop a reaction equilibrium model using Aspen Plus V8.8. For the main components the difference between the simulated and the experimental data was less than 6%.