Effect of supercritical carbon dioxide over the esterification of levulinic acid with ethanol using montmorillonite K10 as catalyst

Abstract Alkyl levulinates are green chemicals that have the ability to modify physical properties of both gasoline and diesel, which makes their use as fuel additives of great importance. An interesting route for their production is the ethyl esterification using solid catalysts, which still needs improvement. The use of supercritical CO2 (scCO2) as solvent may enhance the reaction yield, in such a way that the objective of this work was to combine the use of a solid catalyst (montmorillonite K10) and scCO2 to achieve the esterification of levulinic acid to obtain ethyl levulinate. Moreover, understanding the relationship between the amount of CO2, reactants and the catalyst can be a key to determine how scCO2 works in this type of reaction. The results obtained after a systematic study have shown that the combined effect of scCO2 and montmorillonite K10 allow the obtainment of 90.9 % of conversion after 126 min of reaction at 180 °C, with a molar ratio of 6:1 and 10 wt% of catalyst, while reactions performed using the same conditions and without scCO2 provided 82.9 % of conversion after 138 min. Furthermore, the presence of scCO2 also helped montmorillonite K10 to retain its catalytic activity after 4 reuse cycles, while under the absence of scCO2, a decrease in the levulinic acid conversion was already observed in the first reuse cycle. The results presented in this work are a step further for the use of montmorillonite K10 along with scCO2 in industrial scale.