Potassium leaching during triglyceride transesterification using K/γ-Al2O3 catalysts

A K/γ-Al2O3 catalyst was prepared using the wet impregnation method with K2CO3 as a precursor salt. During the activation process, a clear interaction between potassium carbonate-derived species and the support took place resulting in the formation of K aluminate-like species, as observed by evolved gas analysis by mass spectrometry (EGA-MS) and infrared spectroscopy (FTIR). This catalyst was tested in the transesterification of sunflower oil with methanol, achieving a methyl ester yield close to 100% after 1 h. However, when it was used in successive runs the catalyst showed a strong decrease in its catalytic performance. It is established experimentally that the performance in the first run was mainly due to a homogeneous contribution from active basic species dissolved in methanol. The leaching of potassium species in the reaction media was not avoided although a clear interaction between active phase and support was observed. The present work stresses the obligation of the reutilization and of the verification of the leaching of active species in analogous catalytic systems based on alkaline and alkaline-earth metal oxides when used in the transesterification reaction with methanol.