Transesterification of triglycerides applying zeolitic heterogeneous catalysts

The transesterification of triglycerides is a well-established process due to its relevance in the production of fatty acid methyl esters (biodiesel). Commonly, homogeneous catalysts, e. g. sodium hydroxide and sodium methanolate, are used. The main drawback is that these catalysts necessitate several washing and purification steps. An appropriate solid catalyst would, therefore, reduce the product separation and purification steps. Thus, basic zeolites with faujasite structure and Si/Al = 1 (low silica X zeolites, LSX) have been tested in the transesterification of glycerol trioctanoate with methanol and ethanol, respectively, in a batch set up at ambient pressure and boiling temperature of the corresponding alcohol as well as in an autoclave at elevated temperatures between 100 and 150 °C and 50 bar pressure.
Among these catalysts, the potassium exchanged low silica X zeolite (K-LSX) revealed the highest catalytic activity resulting in the total conversion of glycerol trioctanoate with methanol to octanoic acid methyl ester and glycerol after 1 h reaction time, while in case of ethanol 2 h reaction time were required. Total conversion of glycerol trioctanoate in the autoclave at 100 °C was accomplished after 46 min. Furthermore, catalyst extrudates based on K-LSX were applied as catalysts in the transesterification of glycerol trioctanoate with methanol in a semi-continuously operated trickle bed reactor and exhibited a constant high performance resulting in methyl ester yields over 70 mol% and glycerol yields up to 25 mol%. Beside application of these zeolites as industrial catalysts for biodiesel production, use as catalyst in the production of fine chemicals could benefit to new ecological benign and sustainable processes.