Alkylation of Fatty Acids in Supercritical Alcohols

Abstract

Higher alcohol esters of fatty acids have various applications such as flavors, fuels, and lubricants. In this study, nbutyl and isoamyl esters of lauric acid and stearic acid have been synthesized at subcritical and supercritical conditions. Isoamyl alcohol, n-butanol, lauric acid, and stearic acid were chosen as reaction precursors as they can be derived from renewable feedstock. The effects of molar ratio of alcohol to fatty acid, temperature, and time on the esterification reactions were investigated. Maximum conversions up to 90% were obtained for the reactions of butanol with lauric acid and stearic acid, respectively. Similarly, maximum conversions of 80% were obtained for the reactions of isoamyl alcohol with lauric acid and stearic acid, respectively. The reactions were modeled by assuming pseudo-first-order kinetics, and the activation energies were determined.

Esterification of Sebacic Acid in Near-Critical and Supercritical Methanol

“…Although carboxylic acids are not as acidic as mineral acids, at higher loading (at lower molar ratios) they could contribute substantially to acid catalysis. Being a dibasic acid, the effect is much more pronounced than those observed for reaction of fatty acids with different alcohols . Thus, sebacic acid and methoxide ion (from methanol) contribute toward esterification at different molar ratios.…”

“…The effect of pressure on yield is usually minimal at operating pressures that are greater than twice the critical pressure of the alcohol (as there is no significant change in the density with pressure). ,, However, to confirm the same for sebacic acid–methanol system, the effect of pressure was studied at 623 K at molar ratios 5 and 40 over the pressure range (50–300 bar) and represented in Figure . At constant temperature, in order to achieve different reactor pressures, the reactor loading was suitably manipulated, i.e., lower loading for lower pressures.…”

“…This phenomenon of increased conversion at lower molar ratios was observed for reactions between fatty acids and alcohols. 15,21 This can be explained on the basis of increase in acid catalytic activity, due to increased sebacic acid loading. Although carboxylic acids are not as acidic as mineral acids, at higher loading (at lower molar ratios) they could contribute substantially to acid catalysis.…”

“…Being a dibasic acid, the effect is much more pronounced than those observed for reaction of fatty acids with different alcohols. 15 Thus, sebacic acid and methoxide ion (from methanol) contribute toward esterification at different molar ratios.…”

“…The reaction procedure is that of isochoric reaction systems, where a predetermined amount of reactants is sealed into the batch reactor and heated to the required temperature (consequently reaching the desired pressure). This procedure is reported by many authors and has also been used in our previous studies. − The reactant loading was calculated using a PR-EOS (Peng–Robinson equation of state) (with Lorentz–Berthelot (LB) mixing rules). The pure component critical properties for methanol were taken from NIST fluid property database.…”