264454 Kinetics of Mixed Alcohol Ethanol/Butanol Esterification of Butyric Acid

Thursday, November 1, 2012: 4:30 PM
334 (Convention Center )
Arati Santhanakrishnan1, Dennis Miller1, Lars Peereboom1, Carl T. Lira1 and Abigail Shannon2, (1)Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI, (2)MichiganState University, East Lansing, MI

 

The growing need to reduce our dependence on fossil sources for fuels and chemicals has led to the exploration of alternate pathways for the use of greener chemicals and their manufacture from bio based sources. Esters of higher alcohols (alcohols with more than two carbons) are an industrially important class of compounds and economically viable processes for making them need to be designed. Blends of esters are being studied as fuel additives to biofuels for their high energy density and favorable fuel properties(1).  One route for producing esters that is currently being extensively studied is the esterification of carboxylic acids with alcohols using acid catalysts(2). The catalyst used may be homogeneous such as sulfuric acid, or para-toluene sulfonic acid (pTSA). Heterogeneous catalysts used include cationic exchange resins.

Mixed alcohols are obtained from the condensation of alcohols to higher alcohols(3), the Fischer-Tropsch synthesis of alcohols from syn gas(4) and fusel alcohols produced from ethanol fermentation. The simultaneous esterification of these alcohol mixtures would be a good use of these mixed alcohol streams and improve the profitability of these processes. Since these reactions are equilibrium limited, one option for driving them forward is reactive distillation where the products are separated from the reaction mixture as and when formed. The design of a reactive distillation process requires a good understanding of the kinetics of the reaction system.

It is not known whether the presence of one alcohol would accelerate or inhibit the rate of reaction of another, or if the formation of these mixed esters over complicates the recovery process. In this study, the kinetic behavior of butyric acid undergoing esterification by ethanol and butanol has been investigated under homogeneous (pTSA) and heterogeneous catalysis (Amberlyst 70). The fermentation of butyric acid from biomass has sparked interest in the production of many chemicals using butyric acid as a building block. Apart from their potential as biofuel components, ethyl butyrate and butyl butyrate serve as food flavoring agents and green solvents(5).

The kinetics were first studied separately, and then in alcohol mixtures of varying relative compositions of ethanol and n-butanol. Reaction equilibrium constants were first determined experimentally from samples taken after reactions had reached equilibrium. UNIFAC (UNIversal Functional Activity Coefficient) was used to calculate the activity coefficient values. Concentration profiles of activity-based fits and experimental data of mixed alcohol esterification runs show that the models fit experimental data reasonably well. Activity and mole fraction based fits were found to be indistinguishable.  An additive combination of individual models was found to predict the mixed alcohol esterification system reasonably well. The kinetic model fitted to experimental data is useful for simulating reactive distillation columns to drive the equilibrium limited simultaneous esterification reactions forward.

References

1.         I. K. Mbaraka, D. R. Radu, V. S. Y. Lin, B. H. Shanks, Journal of Catalysis 219, 329 (2003).

2.         A. Chakrabarti, M. M. Sharma, Reactive Polymers 20, 1 (1993).

3.         W. Ueda, T. Ohshida, T. Kuwabara, Y. Morikawa, Catalysis Letters 12, 97 (1992).

4.         T. J. Mazanec, Journal of Catalysis 98, 115 (1986).

5.         D. W. Armstrong, H. Yamazaki, Trends in Biotechnology 4, 264 (1986).


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