Synthesis of biodiesel using potassium fluoride (KF) supported by hydrotalcite and process optimization by Box–Behnken design

Abstract

Biodiesel has been developed using a heterogeneous catalyst potassium fluoride (KF) supported on hydrotalcite (HT) and waste frying oil (WFO) as feedstock. Hydrotalcite was synthesized by co-precipitation method using mixture of Mg(NO 3 ) 2 ·6H 2 O and Al(NO 3 ) 2 ·9H 2 O slowly added to a solution containing NaOH and Na 2 CO 3 and calcined at 500°C. KF was impregnated on hydrotalcite at KF/HT load ratio of 80:100 by addition of a small amount of water. Biodiesel was developed using KF/HT as heterogeneous catalyst by transesterification. Box-Behnken Design using Minitab 15.1 Statistical Software and DesignExpert (Demo version 8.0.6.1) software were used as statistical tool for design of experiments and optimization of fatty acid methyl ester yield. A high yield and conversion of biodiesel was obtained by optimization of variables affecting the reaction. The variables affected the reaction in the priority order of: catalyst amount>>molar ratio (methanol to oil)>reaction time. A 12:1 methanol to WFO molar ratio, 2.5 wt.% of catalyst at 60°C in 1 h reaction time gave a high fatty acid methyl ester yield of >98 %. The quantitative analysis of the product (i.e., biodiesel) was done on a Fourier-transform-nuclear magnetic resonance spectrometer.