Acidic/amphiphilic silica nanoparticles: new eco-friendly Pickering interfacial catalysis for biodiesel production

Silica nanoparticles have been designed by surface modification to stabilize solventless catalytic Pickering emulsions for effective biodiesel production. With respect to this, and based on full physicochemical characterization of both nanoparticles and emulsions, an optimum balance between inert (i.e., alkyl chains) and active (i.e., sulfonic acids) surface functional groups to obtain amphiphilic and catalytic properties was achieved with C-18-SiO2-SO3H (C-18 : SO3H molar ratio = 54 : 46 with a degree of grafting of 48%). Under optimal conditions, biphasic transesterification of several vegetable oils with methanol in the presence of these modified silica catalysts proceeds at competitive rates: the conversion of triglycerides is higher than 92% at 90 degrees C after 12 h. In addition, the catalytic system was not deactivated by the presence of free fatty acids in the crude feedstock and the nanoparticles could be repeatedly used at least 5 times without any loss of activity.