| Biodiesel made from waste cooking oil (WCO) frequently requires antioxidants to meet oxidation stability specifications set forth in ASTM D6751 or EN 14214. In contrast, unrefined cottonseed oil (CSO), containing tocopherols and high concentrations of gossypol, a toxic polyphenolic antioxidant, is unique for biodiesel processing because it produces biodiesel resulting in higher oxidation stability. During biodiesel production, however, only a portion of these endogenous natural antioxidants are suspected to be retained. Because the economics of biodiesel manufacturing rely upon inexpensive sources of triglycerides, emphasis was placed upon developing improved alternative commercially-viable processing strategies where WCO is the main source of methyl esters (WCOME) and CSO is used as a supplemental source of triglycerides and antioxidants in a 4:1 ratio. This study compares four commercially-viable processing methods which attempt to increase the oxidation stability of WCO:CSO biodiesel. The measurement of the many endogenous antioxidant concentrations in the finished biodiesel was not performed; instead, the induction period (IP) was used to measure the bulk oxidative stability increase of the finished biodiesel. The novel processing strategies developed for this study utilize the solvent properties of fatty acid methyl esters and glycerol and are sustainable because they avoid additional chemical inventory for the biodiesel processor. This study concludes that two new processing strategies, a "reduced glycerol process" or an "extraction process", resulted in a biodiesel product that had statistically significant improved oxidation stability when compared to common processing strategies, a "mixed oil process" or a "separate oil process". Another significant finding is that high shear homogenization during transesterification reduced reaction time from the published typical one hour to 16 minutes. |
