Green And Carbon Nanotube-Based Solid Acids For Production Of Fatty Acid Methyl Ester Via Transesterification And Esterification

Biodiesel is a type of clean, environmentally friendly and renewable biomass energy, it is also a good alternative energy source to petrochemical diesel. Biodiesel which is usually prepared by transesterification reaction or esterification reaction of vegetable oil with methanol in the presence of catalyst. So, it is very meaningful to seek a type of high-efficiency and easy-recycling catalyst.A series of polymer-carbon nanotubes composite materials (CNT-P-SO3H) were prepared by covalent grafting of multi-walled carbon nanotubes (CNT) with sulfonic acid-functionalized polymers (P-SO3H) including poly(3-vinyl-1-sulfonic acid imidazolium chloride)-grafted multi-walled CNT (CNT-PVSAIC), poly(4-vinyl-l-sulfonic acid pyridinium chloride)-grafted multi-walled CNT (CNT-PVSAPC), and poly(4-styrenesulfonic acid)-grafted multi-walled CNT (CNT-PSSA).Such functionalization method provides a facile route to obtain various polyelectrolyte brushes on the surface of CNT in order to improve the dispersibility and modulate the acidity of CNT, to selectively introduce functional groups and densely create active sites over CNT for potential catalytic applications. Both CNT-PVSAIC and CNT-PVSAPC consist of cationic polyelectrolyte chains functionalized by sulfonic acid groups. Whereas, CNT-PSSA is composed of anionic polymer brushes grafted by sulfonic acid groups. The prepared CNT-P-SO3H materials exhibit catalytic activity as carbon-based solid acids in liquid phase transesterification of triglycerides with methanol and esterification of oleic acid with methanol, which are typical model reactions for biodiesel production.The catalytic performance of CNT-P-SO3H catalysts is attributed to the combination of mesoporous structure together with well extended P-SO3H coating over the outer surface of the CNT, providing the formation of dense but uniform surface distribution of active sites. Moreover, surface exposure of active sites can facilitate the access of reactants and promote the migration of reagents away from the catalysts.