Page - 199 - in Advanced Chemical Kinetics

Withinthischapter,wewilldisclose therecentoutcomesofaresearch inwhichultrasoundhas beenusedasawayofmonitoring theprogressof the reactionof transesterificationof soybean oilwithmethanol in thepresenceofKOHasbasiccatalyst.Thepulse/echotechniquewasused to monitor acoustic velocity throughout the reaction, composed as an in-line scheme. The resultswere related to the referencemethod based on gas chromatography (EN 14103 stan- dard)and to the 1HNMRtechnique [13–18]. 2.Fundamentalof the transesterificationreaction Let us consider the reaction TAG + 6MeOH! 3 FAME + G, where TAG (triglyceride) is soybeanoil,MeOHismethanol, FAME is the estermixture andG isglycerol. To simplify the study, there are some considerations before starting theprocess ofmonitoring the transester- ification reactionbyultrasound.As there is excess alcohol,wecanconsiderTAGasa limiting reagent, i.e.,when it is totally consumed the reactionwill finish.With the excessofmethanol, the reaction becomes irreversible,whichmeans that thewhole equilibriumof the reaction is displaced toproducebiodiesel.Another important consideration is toadmitabatch reactor in which reagents aremixedat thebeginningof the reaction,without any inlet or outlet flowof reagents further than thosemixedat time0. Thus,wedetermine theamountofTAGconsumed ðNTAGcÞ, quantified inmol, throughEq. (1), inwhichNTAG0 represents theamountofTAGinsertedinthereactorat time0(inmol),andX is therelationshipbetweentheTAGthat reactedwith theTAGinserted into thereactorat time0. NTAGc ¼NTAG0 �X (1) TheTAGinagiventime(NTAGt) isobtainedbythedifferenceof theTAGinsertedinthereactor andtheTAGconsumed,according toEq. (2) (allvaluesexpressed inmol). NTAGt¼NTAG0�NTAG0 �X (2) Thus,Eqs. (1)and (2) lead toEq. (3), asdepictedelsewhere [6, 9]. NTAGt¼NTAG0 1�Xð Þ (3) Fromstoichiometry,onecanderive toCTAG¼NTAGV , andfor liquidsV=V0 (volume isconstant), evolving toEq. (4). CTAG¼CTAG0 1�Xð Þ (4) Thedisappearance of theTAGmust be accompanied by the appearance of the FAME.How- ever, aquestionarises: howtheactual concentrationofFAMEthroughout the reaction canbe assessed?Complementary,onecouldaskhowtoknowthat in fact the reactionhasendedand ithasalreadyreachedthemaximumconversion?Thereareseveral techniquesproposed in the literature, but few canmake this determination in an in-line schemewith an accurate way Ultrasound as a Metrological Tool for Monitoring Transesterification Kinetics http://dx.doi.org/10.5772/intechopen.70501 199