Production of biodiesel from mixed waste vegetable oil using an aluminium hydrogen sulphate as a heterogeneous acid catalyst

Al(HSO₄)₃ heterogeneous acid catalyst was prepared by the sulfonation of anhydrous AlCl₃. This catalyst was employed to catalyze transesterification reaction to synthesis methyl ester when a mixed waste vegetable oil was used as feedstock. The physical and chemical properties of aluminum hydrogen sulphate catalyst were characterized by scanning electron microscopy (SEM) measurements, energy dispersive X-ray (EDAX) analysis and titration method. The maximum conversion of triglyceride was achieved as 81 wt.% with 50 min reaction time at 220 °C, 16:1 molar ratio of methanol to oil and 0.5 wt.% of catalyst. The high catalytic activity and stability of this catalyst was related to its high acid site density (-OH, Brönsted acid sites), hydrophobicity that prevented the hydration of -OH group, hydrophilic functional groups (-SO₃H) that gave improved accessibility of methanol to the triglyceride. The fuel properties of methyl ester were analyzed. The fuel properties were found to be observed within the limits of ASTM D6751.