Valorization of red mud industrial waste: Methylation of a mixture of fatty acids from waste cooking oil with dimethyl sulfate in the production of biodiesel

Bayer process is the majority method in global alumina production, generating a significant volume of waste alkaline red mud (WARM) solution. The lack of an economical route of disposal or application leads to the accumulation of a large quantity of WARM, which poses a serious threat to the ecosystem. This study introduces a new method of synthesis of FAME from three fatty acids (FAs) (oleic, linoleic and stearic acids) or a mixture of FAs obtained from waste cooking oil (WCO). Methylation of FAs and a mixture FAs was achieved in the liquid phase over a 2h period at 60°C using dimethyl sulfate (DMS) in the presence of NaOH or WARM solution. Both bases yielded excellent yields (97.80 to 98.34% using NaOH and 96.88 to 99.00% with WARM solution) in all the esterification processes. This process is inexpensive, efficient, and environmentally friendly. Although DMS is a highly toxic, carcinogenic, and environmentally hazardous, the excess DMS was transformed to Na2SO4, which can be used as a dessicant. The DMS was manipulated in a ventilated hood by a masked operator using a syringe. The WARM solution reagent could be recovered and reused up to 10 times with conversions of 98.54 to 94.79%.