Produção enzimática de biodiesel via hidroesterificação utilizando como matéria-prima óleo de soja residual

Abstract

Almost all of the industrial units use transesterification reactions catalyzed by alkaline to produce biodiesel. This route of production is characterized by the need to use refined oils as raw material. The oil refining in this case corresponds to 80% of the final cost of the biofuel. As an alternative, there is the possibility to use the hydro-esterification rout, which allows the use of unrefined or even residual oils in the synthesis of biodiesel. This rout represents the most in-depth alternative in the production of biodiesel. The hydro-esterification involves two steps: reaction of hydrolysis followed by esterification. The use of the lipase catalyst in both steps of the hydro-esterification should result for the process high selectivity, high specificity, mild operating conditions and high purity of the products. Therefore, the mean of this project was to produce biodiesel via hydro-esterification rout catalyzed by immobilized lipase using residual soybean oil (frying) as raw material. The lipase of Geotrichum candidum (GCL) was produced by submerged fermentation and applied in its free form in the hydrolysis reaction. The subsequent esterification step was catalyzed by the lipase of Pseudomonas fluorescens (PFL), a commercial lipase. The PFL was immobilized by styrene-divinylbenzene (Sty-DVB) using interfacial adsorption method. The residual soybean oil (waste cooking oil) used was characterized and it showed a density of 0.92 g/ml (25 ° C), peroxide indices of 9.50 ± 0.02 meq/kg, total acidity of 0.60 ± 0.01 mg/g, and others studied parameters. The hydrolysis reaction catalyzed by the GCL was optimized using a central composite rotational design (CCRD) for two variables: fraction of residual oil (% m / m) and lipase concentration (U / g system). The use of factorial design allowed obtaining a total fatty acids conversion in 60 min of reaction at 40 ° C and 1000 rpm. The system was compounded by a residual soybean oil fraction of 20% ​​(m / m), without the use of solvents or emulsifying agents. The esterification reaction was catalyzed by PFL-Sty-DVB and performed with a maximum concentration of free fatty acids of 1000 mM. The conversion to biodiesel reached was 80% in only 3 hours of reaction. The biodiesel produced was characterized according to ANP standards for the composition of esters, viscosity and the amounts of free glycerol, monoacylglycerol (MAG), diacylglycerol (DAG) and triacylglycerol (TAG) of esters.