Page - 204 - in Advanced Chemical Kinetics

Figure 5 shows that the 1H NMRmethod is very similar to the reference method (GC). After this straightforwardvalidation, comparingboth technics,weused1HNMRtoassess the conversionofanalytical curvesasdescribed inEq. (6) for the fourreactions (seeFigure6). Asdisclosed inFigure6, one cannote that each reaction reaches themaximumconversionat a givenmoment.Buthowtoknowduringthereaction that themaximumconversionhasalready beenreachedandthere isnolongeranyneedtocontinuetheprocess?NMRanalyses,aswellas GC,require thesampletobepure,whichmeansfreeofothersubstances thatmayinterferewith theanalysis. Inthisway,ultrasonicmonitoringstandsout,beingabletodeterminethemaximum point of the reaction even in thepresence of excess reagents andby-products.Figures 7 and 8 depictasetofresults forall chemical routesemployedinthepresentstudy. Figure7 showsthateachreactionhasapropagationvelocityconfiguration.Theyall startwith avalue close to thepure soybeanoil velocity.However,during the reaction time, the speedof Figure5. Variationofbiodiesel conversionduringthehomogeneous transesterificationofsoybeanoilwithmethanoland 200rpmofmechanical stirring. Figure 6. Conversion rate calculatedby 1HNMR for four transesterification reactions of soybean oil usingKOHas the basic catalyst. Advanced Chemical Kinetics204