Heterogeneous Catalyzed Esterification of Caproic Acid and Lauric Acid with Isoamyl Alcohol from Fusel Oil

The industry of bioethanol produces a by-product known as fusel oil, which represents around 0,5 vol% of the production of bioethanol and which contains mainly amyl alcohol isomers [1]. These alcohols represent 41-85 vol% of fusel, depending on the raw materials and operating conditions of the fermentation step [2]. One of those isomers, isoamyl alcohol, is a raw material in the production of value added esters largely used as flavors, fragrances, plasticizers and bio solvents in food, cosmetic and pharmaceutical industry. There are some esters that also exist in the heaviest fraction of fusel oil, such as isoamyl caproate and isoamyl laurate; isoamyl caproate is used in green apple and pineapple-like flavor formulations and on the other hand, isoamyl laurate smells like peach and wine.

The aim of this project is to carry out a kinetics study of the production of isoamyl caproate and isoamyl laurate using Amberlyst 35WET cationic exchange resin as catalyst and stirring speeds of 600 rpm and 700 rpm. The experimental design used is Box-Behnken for three factors: temperature, reactants molar ratio and catalyst loading. All the samples from the reacting system were analyzed by acid value determination. Reaction temperature was varied between 90°C and 110°C, and the catalyst loading was studied in the range between 0,5% and 3% m/m of the reacting mixture.

In the two cases one of the reactants is put in excess. For isoamyl laurate reaction isoamyl alcohol is the excess reactant and, on the contrary, for isoamyl caproate reaction this is used as limiting reactant in order to prevent two liquid phases in the reactor. Molar ratios of 2:1, 3:1 and 4:1 are planned in the experiment design, however until now only the molar ratio 2:1 has been analyzed.

In both cases, the reactions achieve conversions higher than 90% for temperatures above 100°C but reaction time is larger for isoamyl caproate production (8-9 hours) than isoamyl laurate production (6-7 hours). Reactions are strongly temperature dependent rather than the catalyst loading. Changes of temperature from 90°C to 100°C represent changes of 40% in conversion while changes of catalyst loading between 0,5% to 3% represent changes only of 4% in conversion. It can be concluded that it is not necessary to use large amounts of resin to improve the process yield.

References

[1] Z. KÜCÜK y K. CEYLAN, «Potential Utilization of Fusel Oil: A Kinetic Approach for Production of Fusel Oil Esters Through Chemical Reaction,» Turkish Journal of Chemistry, nº 22, pp. 289-300, 1998.

[2] F. Leyva, Á. Orjuela, A. Kolah, C. Lira, D. Miller y G. Rodríguez, «Isoamyl propionate production by reactive distillation,» Separation and Purification Technology, nº 146, pp. 199-212, 2015.