Synthesis of methyl esters from soybean oil using ZnO loaded with alkali metal salts as catalyst

Abstract

This research studied the cuse of six alkali metal salts (Li2CO3, Na2CO3, K2CO3, KNO3, KCl and KOH) loaded on ZnO as heterogeneous catalyst for transesterification of soybean oil with methanol. The catalysts were characterized by BET, XRD, FTIR, SEM, XPS, TG-DTA and CO2-TPD to study the differences in their characteristics and properties effecting transesterification. The results showed that all of the investigated solid catalysts had potential to be used as heterogeneous catalysts for the transesterification. The order of activity of the solid catalysts is K2CO3/ZnO >KOH/ZnO >Na2CO3/ZnO >KNO3/ZnO >Li2CO3/ZnO >KCl/ZnO. The ZnO loaded with 30 wt.% of K2CO3 and calcined at 600oC for 5 h was found to exhibit the highest basicity and catalytic activity among all catalysts investigated. The maximum methyl esters content achieved was 77.48 wt.%. The optimum condition was achieved using methanol-to-oil molar ratio of 9:1, catalyst amount of 3 wt.% operated at normal boiling point of methanol for 48 h. In addition, it is noteworthy that THF can speed up the transesterification reaction as a phase-merging agent. The results also showed that the catalytic activity of the catalysts depended upon both basic properties and the surface area but basicity was more dominant effect. Reusability of the catalyst was investigated and found that activity of the reused catalyst was significantly decreased due to the leaching of alkali metal from the surface into the solution. This was confirmed by the absence of IR peak corresponding for bonding between alkali metal salt and ZnO. Catalyst prepared in this work behaves like homogenous catalyst