Enzyme‐assisted deacidification of Jatropha crude oil by statistical design of experiments

Abstract

Jatropha curcas L. crude oil has variable and often high free fatty acid content. As free fatty acids are corrosive, the crude oil has to be refined prior to its utilization in technical applications. Conventional refining processes have several environmental and energetic shortcomings, and there is a clear need for more sustainable pathways. In this study, an enzymatic method was studied for the neutralization of Jatropha oil. Detailed insight into the process was achieved by means of a statistical design of experiments utilizing an immobilized lipase from Rhizomucor miehei. The free fatty acids were esterified with glycerol. The most important impact factors and interactions between factors were identified with regard to acid number reduction and the MAG, DAG, and glycerol content. Validation experiments showed that the models obtained for acid number and, mono‐ and DAG development were valid and adequate for optimizing the esterification reaction for the desired application. The results generated in this study open the possibility of modifying – within limits – the vegetable oil composition depending on the target application requirements. The acid number of the crude Jatropha oil could be decreased to 0.4 mg KOH per g oil by means of enzymatic esterification. The MAG content can be adjusted between 1.5 and 5.0% (w/w) and DAG content between 15.6 and 27.1% (w/w). The enzyme regeneration procedure that was developed allows multiple use of the enzyme at practically constant activity.Practical applications: Due to the advantages of an enzyme‐assisted neutralization procedure, future industrial application of this technology is of great interest. Higher oil yields, no generation of waste water, and the avoidance of aggressive chemicals mean this process has greater sustainability than the conventional approach requiring the addition of strong bases to the oil in order to saponify the free fatty acids. Currently, enzymatic processes tend not to be economically viable due the relatively high cost of the enzymes. However, the costs are likely to decrease in the future as demand for them increases. Additionally, enzyme regeneration, which was carried out successfully in this work, offers the opportunity to further lower the process costs.Jatropha curcas L. crude oil exhibits variable and often high free fatty acid content. Free fatty acids were esterified with glycerol utilizing an immobilized lipase from Rhizomucor miehei. Detailed insight into the process was achieved by means of statistical design of experiments yielding significant and valid mathematical models enabling the optimization of several process parameters.