Esterification of oleic acid using subcritical isoamyl alcohol

SANTOS, M.; RODRÍGUEZ-RUIZ, A.C.; MILANESIO, J. M.; MAGARIO, I.; VELEZ, A.R.

Los Cocos, Córdoba

Conferencia; VI Iberoamerican Conference on Supercritical Fluids (PROSCIBA 2023); 2023

IPQA/PLAPIQUI

In the current environmental context, two objectives are of particular importance. Firstly, the quest for bioproducts to replace non-biodegradable and/or non-renewable source-derived products. Secondly, the valorization of by-products to maximize resource yields, results in improved profits, making such processes more attractive for investment and the replacement of unsustainable methods.Fusel oil, a by-product of the bioethanol fermentation process, could be utilized to produce emulsifier substances. Fusel oil is a mixture of water and various alcohols, including ethanol, butanol, and isoamyl alcohol, being the last in the major proportion of the blend. Currently, this by-product is primarily used for energy production in bioethanol plants. However, the components of fusel oil can also be transformed into more valuable compounds. The esterification with carboxylic acids is one of the possibilities. Long-chain carboxylic acids such as oleic acid can be obtained from vegetable oils on a large scale. The resulting products can be used as bio-emulsifiers or bio-lubricants in the cosmetics, pharmaceutical, and food industries, among others. Furthermore, oleochemical esters have very low or negligible toxicity and are generally biodegradable.The production of esters using sub or supercritical alcohols has gained relevance in recent years. Firstly, it does not require a catalyst, which eliminates the need for neutralization and separation steps typically found in conventional esterification processes catalyzed by strong acids or bases. Secondly, the high temperatures involved in the process often significantly enhance the conversion of reactants and the reaction rate, resulting in the products being obtained in a shorter time. In the case of reactions involving biphasic mixtures at moderate temperatures, the use of elevated temperatures promotes the mutual solubility of the reagents and reduces limitations due to mass transfer phenomena.In the present study, the esterification of technical-grade oleic acid (77% purity) with isoamyl alcohol was carried out under subcritical conditions. The experiments were conducted in a continuous tubular reactor of 16,4 mL at a fixed pressure of 100 bar. The effect of temperature on the reaction rate and the final conversion of the acid was investigated over the range of 220°C to 300°C, using a fixed molar ratio of isoamyl alcohol to oleic acid of 3:1. Similarly, the influence of the molar ratio of isoamyl alcohol to oleic acid on the same responses was analyzed within the range of 1:3 to 3:1. Mass flow rates used in the experiments ranged from 0.4 to 5.6 g/min. Acid conversion over the mass flow rates was monitored through the acidity index of the collected product samples. The presence of esters was confirmed through gas chromatography with a Flame Ionization Detector (FID).The results showed that temperature had a positive effect on the conversion of oleic acid, with higher temperatures resulting in higher conversion rates. The conversion values of oleic acid achieved ranged from 70% to 85% for the lowest mass flow rates. In the experiments conducted at temperatures of 300°C and 260°C, the final conversion rates were nearly identical.With regard to the initial molar ratio of isoamyl alcohol to oleic acid, an excess of either of the two reagents resulted in an increase in the conversion rate. At the lowest tested mass flow rate, a 1:1 molar ratio achieved a 64% conversion. Meanwhile, for ratios of 3:1 and 1:3, the conversion values of the limiting reagent were similar, at 85% and 82%, respectively. The obtained results were promising and serve as the starting point for future studies that will delve into aspects such as reaction kinetics and the utilization of fusel oil as a reactant. The presence of water in fusel oil will potentially modify the expected conversion percentages, as water is a product of the reversible esterification reaction studied in this work.