Effect of subcritical water on homogeneous catalysis of used cooking oil hydrolysis

Abstract

The effect of temperature and pressure on the batch hydrolysis of used cooking oil in fatty acids- (autocatalytic system), dilute acid- (pH 5.0), and dilute Cu-catalyzed systems (500 mg CuSO₄ per kg solution) was studied. The reaction was carried out using a fixed water/acylglycerides molar ratio of 30 : 1 under various temperatures (200–250 °C) and initial pressures (1.96–4.90 MPa) for 2 h. Experimental data were processed statistically using ANOVA and the Spearman correlation method aside of conventional data interpretation. The Cu-catalyzed system was superior to the other systems. Temperature had greater effect on oil hydrolysis than initial pressure. The use of CO₂ as the pressurizing gas altered fatty acid production and Cu soap formation particularly by oil dilution that also accompanied by a slight acidification of the aqueous phase. The water ionization constant was the most influencing property for fatty acid production and Cu soap formation.