Recovery, Purification, Analysis and Chemical Modification of a Waste Cooking Oil

Disposing of residual cooking oil is a major environmental concern, so its conversion into commercial products is a desirable goal. To design the chemical modification of a domestic waste oil into valuable biochemicals other than biodiesel, we analyzed a series of its samples, collected over a period of three years, using quantitative 1 H-NMR. This analysis, allowing a quick determination of its main chemical characteristics, has rendered the image of a vegetable oil with an almost constant composition over time and with a relative low content of saturated fatty acids. To make this collection protocol more economical, we projected its chemical transformation into esters and epoxidized esters of long chain and branched alcohols, which could find employment as biolubricants and/or bioplasticizers. The one-pot transesterification of the waste cooking oil into esters of commercially available and biodegradable Guerbet alcohols was obtained under environmentally friendly conditions by employing commercial CaO as a catalyst. Additionally, microwave irradiation of this reaction allowed to optimize the energy expenditure by significantly reducing the reaction time as compared with reactions run under conventional heating. To improve their oxidation stabilities, the resulting esters were epoxidized under conditions useful to minimize side-reactions. An investigation of their main rheological properties shows that some of the resulting products display characteristics that make their use as biolubricants or bioplasticizers predictable. The entire process represents a virtuous example of circular economy. Graphical Abstract