Study On Synthesis Of Ethyl Butyrate By Butyric Acid Fermentation Broth Extraction Coupling With Esterification

Ethyl butyrate is one of the short chain ester, which is widely used in food, flavor,chemical, and energy industry. It is mainly produced by chemical synthesis at present. Inrecent years, biofuel is becoming more and more attractive because of the decrease andunrenewable of petroleum resources and the increasing environment pollution caused bychemical engineering process. Given that ethyl butyrate is expected to be a new biofuel andthe need for inartificial spice is growing, ethyl butyrate production from microbialfermentation has broad application prospects. Since there have a lot of studies on ethanol andbutyric acid production from microbial fermentation by using cheap biomass, ethyl butyratecan be synthesized by the reaction of these ethanol and butyric acid using lipase as catalyst. Inview of this, extraction coupling with esterification of butyric acid fermentation broth for theproduction of ethyl butyrate have been researched in this study, as to lay the foundation forthe integrated fermentation-extraction-esterification process for the production of ethylbutyrate.In order to integrated extraction-esterification process of butyric acid fermentation broth,tri-n-octylamine (TOA)-cyclohexane was adopted as extractive agent and esterificationreaction medium. In order to separate butyric acid from fermentation broth efficiently, effectsof extraction equilibration time, pH of butyric acid fermentation broth, TOA concentration,phase ratio on butyric acid extraction were studied. The optimal conditions were as follows:the pH of butyric acid fermentation broth was2-3; molar ratio of TOA to butyric acid was2:3-1:1; when multi-step extraction was used, phase ratio was0.3; when one stage extraction,phase ratio was1.0.Esterification reaction conditions catalyzed by Novozym435in extractive agent wereevaluated. Effects of TOA concentration, reaction temperature, amount of Novozym435,substrates concentration, substrate molar ratio (ethanol: butyric acid) on initial reaction rateand esterification yield in extractive agent were studied. The optimal conditions were asfollows: molar ratio of TOA to butyric acid in fermentation broth was2:3, reaction temperature was40oC, amount of Novozym435was8g/L, substrates concentration was0.4-0.6mol/L, and substrate molar ratio was2:1.On the basis of the above, the synthesis of ethyl butyrate catalyzed by Novozym435inthe extractive phase after extracting butyric acid from fermentation broth was researched.Effect of3molecular sieve dosage on initial reaction rate and esterification yield in theextractive phase was studied, and the optimal dosage was40g/L. In all of above optimalconditions, the esterification reaction had approached equilibrium in5h, and the esterificationyield was81.42%. Good operational stability of Novozym435in this reaction system wasobserved. Finally, effect of TOA concentration on synthesis of ethyl butyrate by butyric acidfermentation broth extraction coupling with esterification was investigated. The resultsindicated that the maximum ethyl butyrate yield relative to butyric acid in fermentation broth(0.65mol/mol) was obtained when molar ratio of TOA to butyric acid in fermentation brothwas2:3.