Enzymatic synthesis of biodiesel from fatty acids. Kinetics of the reaction measured by fluorescent response of Nile Red

Production of biodiesel (B) from free fatty acids (F) was investigated. Different amounts of F dissolved in B were esterified by methanol or ethanol with help of lipase Novozym 435. The kinetic model included (i) steady-state scheme; (ii) reversible inhibition of the enzyme by alcohols; and (iii) aggregation of water W + W ↔ WW. The aggregated form WW imitated large water droplets with low chemical activity. Forward and backward reactions were recorded using the calibrated fluorescent signal from Nile Red. The relevant rate constants were calculated and used in computer simulations. The model demonstrated that content of F could be decreased below the specification level of 0.25% by means of the enzymatic conversion exclusively. It was found that the reaction could be accomplished in one step starting from content of F ≤ 1%, water = 100 ppm and MeOH = 6% or EtOH = 13%. The higher levels of F (≥4%) would require three cycles where MeOH (≥4%) or EtOH (≥7%) are added at the beginning of each step, and water is dried to 100 ppm between the steps. The designed kinetic scheme is a part of the general biodiesel reaction model, which is currently under construction.

• Enzymatic conversion of fatty acids to biodiesel was characterized.
• The rate constants were used to model behavior of the system.
• It is possible to reduce fatty acids in biodiesel below the specification level.
• Different amounts of fatty acids require 1–3 steps of conversion.
• The scheme is a part of a general model for enzymatic production of biodiesel.