Immobilization of a lipase activity from Aspergillus niger MYA 135 and its application in the biodiesel synthesis

Abstract

Lipases have been widely used in the organic synthesis of industrially important chemicals such as emulsifiers, surfactants, wax esters, biopolymers, structured lipids, flavor-associated esters, and biodiesel. Concerning the biodiesel production, in order to get an efficient biodiesel production, the proper selection of the immobilization matrix and the subsequent reaction optimization have attracted the interest of several researches in recent years. In this work, those steps were carried out by using the one factor at a time optimization method. Thus, a culture supernatant from Aspergillus niger MYA 135 showing a lipase activity was firstly immobilized by adsorption on different low-cost supports (sand, PET and PP plastic, rubber, silicone, glass beads, silica gel and bagasse) applying a vacuum drying procedure. All biocatalysts were evaluated at 40 °C, at 800 rpm, and in the presence of different combinations of oil (soybean or waste frying oils) and alcohols (ethanol or butanol). After a three-stepwise addition of the corresponding alcohol, the biodiesel synthesis was evaluated by thin layer chromatography (TLC). The most promising reaction mixture comprised a lipase activity immobilized in silica gel as biocatalyst, and soybean oil and butanol as substrates. Then, the following parameters were analyzed: a) the enzyme concentration (1, 2, 3 and 4 ml of culture supernatant), b) the molar ratio oil:alcohol (1:3, 1:4, 1:5, 1:6, 1:7), and c) the reaction time (the addition of alcohol carried out in three equal parts every 24, 12, 6 or 3 h). In addition, the crosslinking immobilization technique was also studied. Taking into account the qualitative analysis by TLC, the best conditions for biodiesel production were: 2 ml of culture supernatant immobilized in silica, 1:4 soybean oil to butanol molar ratio, and a reaction time of 18 h. Under these optimal reaction conditions, a biodiesel yield of 93.36 % (w/w) was achieved in a solvent free system. The composition of fatty acid butyl esters was 12.97 % palmitic acid, 6.57 % estearic acid, 25.15 % oleic acid, 45.24 % linoleic acid, 4.72 % linolenic acid, 0.67 % araquidic acid, 0.34 % eicosenoic acid, and 3.83 others. Finally, it is interesting to mention that the cloud point of butyl esters is around 10 °C lower than that of methyl esters, meaning that they have better performance under cold conditions.