Aspects of stability of K/Al2O3 catalysts for the transesterification of rapeseed oil in batch and fixed-bed reactors

Catalytically active, stable, and mechanically durable solid K/Al2O3 catalysts for the transesterification of rapeseed oil with methanol was studied. In a batch reactor, high catalytic activity was accompanied by leaching of K species, caused by glycerol, and mechanical destruction of the solid catalyst as a result of contact with the stirrer. In a fixed-bed reactor, some leaching of K species into the liquid phases was also observed, but approached 0 during 30 h of time-on-stream; the activity of the K/Al2O3 catalyst (∼83% ester yield) was stable for 100 h of time-on-stream and no mechanical destruction of the catalyst was observed. The populations of K2O and K-O-Al species for fresh and used K/Al2O3 catalysts were compared using Fourier transform infrared spectroscopy. It was found that some K2O species leached into the liquid phases at the beginning of the reaction.

Graphical AbstractIn a batch reactor, potassium leaching is caused by glycerol and mechanical damage. Use of a fixed-bed reactor minimizes mechanical damage to K/Al2O3 catalysts and provides high and stable activity, even if some potassium leaching occurs.Figure optionsDownload full-size imageDownload as PowerPoint slide