Avaliação da atividade catalítica de compostos a base de estanho (IV) em reações de alcoólise de ácidos graxos (AG), triacilglicerois (TAG), misturas AG:TAG e na hidrólise de TAG

Abstract

The objective of this work is to develop catalysts that are active in simultaneous conversion of triacylglycerides and fatty acids into fatty acid methyl esters. Three Sn(IV) complexes, named butyl stannoic acid (BTA), di-n-butyl-oxo-stannane (DBTO) and dibutyltin dilaurate (DBTDL), were initially tested as catalysts for esterification reaction of fatty acids in the presence of methanol as alcoholysis agent. Parameters like reaction time, temperature, and catalyst amount were systematically evaluated in this work. All complexes were active at relative high reaction temperatures, but BTA displayed the highest activity. Former studies have already demonstrated that these same complexes display good catalytic activity in methanolysis of triacylglycerides (TAGs). These results prompted us to test BTA catalyst also in simultaneous esterification/transesterification reactions from a mixture of free fatty acids (FFAs) and TAGs in the presence of methanol. The BTA was able to convert mixtures of fatty acid methyl esters (FAMEs) with excellent yields of up to 96% during 4 hours with simple isolation procedures. The BTA was also tested in the hydrolysis of TAG and conversions were quite satisfactory, reaching approximately 98% at 160 ° C. From the results obtained it was possible to determine that, in comparison to hydroesterification reactions, the simultaneous esterification/transesterification is the best route to obtain FAMEs using this type of catalyst. The complexes exhibiting general formula R4-xSn(C11H20O2)x, wherein R = C4H9 or CH3 and x= 1 ou 2, were tested in order to evaluate the influence of the nature of different ligands bearing the metal center, on the esterification conversion. The results obtained in this study may suggest the following catalytic activity order: dimetildiundecenoate tin > dibutildiundec-10-enoate tin > tributilundecenoate tin, supporting a significant influence of the stereo effect in esterification reaction.