Abstract EN:

Transesterification of vegetable oil attracts a lot of interest since it enables to produce biodiesel. A lot of work has been carried out recently towards the development of new more eco-friendly processes involving heterogeneous catalysts instead of the traditional homogeneous process. This work focuses on the use of solid zinc aluminates-based catalysts for vegetable oil transesterification. Those catalysts have good stability and activities. Even though they behave as basic solids, they also present Lewis and Brønsted acid sites on their surface. The aim of this work is to determine the involvement of the different sites of these catalysts in the transesterification reaction. Work was carried out on a series of ZnAl2O4 solids with increasing Zn/Al ratio. This series was characterised in term of structural and acid-base properties. The latter were assessed by adsorption of molecular probes followed by IR or microcalorimetry: CO was used as a probe for acid sites, CO2, MeOD and acetonitrile were used for basic sites. The catalytic activity of the same series of samples was studied in the transesterification reaction of rapeseed oil and methanol. A kinetic model was developed based on the experimental results in order to determine the kinetic constants of the three reaction steps of the reaction. A correlation between the characterisation and the catalytic results allowed us to suggest that the presence of Lewis acid/Lewis base pairs in which the acid site is weak is the key parameter determining the activity of the solids in the transesterification reaction of triglycerides with methanol