Rhamnolipids: Highly Compatible Surfactants for the Enzymatic Hydrolysis of Waste Frying Oils in Microemulsion Systems

Abstract

In this work we explore a novel application for rhamnolipid (RHL) biosurfactants as emulsifiers for water-in-oil microemulsions, focused on enhancing the state of the art of oil hydrolysis in emulsion systems. We show that RHL can form microemulsions with a stability comparable to that provided by the widely used synthetic surfactant bis(2-ethylhexil) sulfosuccinate (AOT). In addition, we test RHL-based microemulsions as reaction media for the enzymatic hydrolysis of waste frying oil (WFO) to produce added-value products. To this aim, we analyse the influence on the hydrolysis degree of several key parameters, such as the amount of co-surfactant, the water/surfactant molar ratio, and the oil volume fraction in the organic phase. Remarkably, under the same conditions RHL leads to a 35% higher hydrolysis degree than AOT. Furthermore, RHL also increases the average hydrolysis rate and shows an extraordinary enhancement of the enzyme stability in comparison to AOT. Our results demonstrate that RHL can be considered as a potential renewable substitute for synthetic AOT in microemulsions, and pioneer a more sustainable valorisation of WFO. In a wider perspective, they highlight new opportunities for the use of RHL in other enzyme-based processes.