Valorization of Low Quality Waste Cooking Oil (LQWCO) Via Catalytic Transesterification

Abstract

The large volume of waste cooking oil (WCO) produced globally (~ 5.0 to 10.0 billion gallons/yr) and the associated market size of $11.6 to $12.8 billion USD inferred that the development of more valorization strategies is essential. One of the feasible upgrading options currently considered is the transesterification into biodiesel. However, developing catalyst that is resistant to FFAs and other impurities in the waste cooking oil (WCO) is still being investigated. We have herein demonstrated the successful development of a red mud (RM) material with good potential to catalyze very low quality waste cooking oil (LQWCO) upgrading. The LQWCO feed contains 37.50% of free fatty acids (FFAs) in addition to 4.5% of other impurities. Interestingly, for the transesterification reaction performed at 60^oC using 0.3g of RM catalyst and 1:5 (oil: methanol) volume ratio for 1.0h, the RM catalyst produced 95.05% yield of biodiesel that was stable for five (5) repeated cycles of reaction. Additionally, the final biodiesel product contains negligible concentrations of FFAs, showing the ability of the RM material to catalyze combined in-situ esterification-transesterification process. The overall activity of this catalyst was much higher than that observed with each of the acid-modified charcoal systems (i.e. HSMC and HPMC). The RM catalyst was characterized to exhibit the oxides: Fe₂O₃ (42.0%), Al₂O₃ (22.5%), SiO₂ (15.5%), Na₂O (12.0%) and CaO (8.0%). Thus, the overall activity could be associated to the synergic effects of the various active sites in these oxide systems. The RM catalyst has strong industrial potentials for upgrading of WCO of low quality.