Abstract
In this work, the transesterification of methyl estolides (ME) extracted from the lipid component present in the sewage scum was investigated. Methyl 10-(R)-hydroxystearate (Me-10-HSA) and Fatty Acid Methyl Esters (FAMEs) were obtained in a single step. A three-level and four factorial Box–Behnken experimental design were used to study the effects of methanol amounts, catalyst, temperature, and reaction time on the transesterification reaction using aluminum chloride hexahydrate (AlCl3·6H2O) or hydrochloric acid (HCl) as catalysts. AlCl3·6H2O was found quite active as well as conventional homogeneous acid catalysts as HCl. In both cases, a complete conversion of ME into Me-10-HSA and FAMEs was observed. The products were isolated, quantified, and fully characterized. At the end of the process, Me-10-HSA (32.3%wt) was purified through a chromatographic separation and analyzed by NMR. The high enantiomeric excess (ee > 92%) of the R-enantiomer isomer opens a new scenario for the valorization of sewage scum.
Highlights
Hydroxy Fatty Acids (HFAs) are valuable raw materials widely used for several industrial applications, including resins, polymers, cosmetics, biofuels, biolubricants, and additives in coatings and paintings [1,2]
Many of these natural sources are found as part of estolides, oligomeric fatty acid esters formed by hydroxy acyl groups bonded together with ester bonds [7]
For the first time, an efficient method was proposed for the synthesis of Me-10-(R)-Hydroxystearic acid (10-HSA) and Fatty Acid Methyl Esters (FAMEs) by direct conversion of methyl estolides isolated from sewage scum
Summary
Hydroxy Fatty Acids (HFAs) are valuable raw materials widely used for several industrial applications, including resins, polymers, cosmetics, biofuels, biolubricants, and additives in coatings and paintings [1,2]. The use of AlCl3·6H2O favored a convenient separation of products between the two phases: the catalyst was recovered entirely, with the upper methanol phase along with the water produced during the reaction, whereas the methyl esters were present in the lower oily phase [45] This resultant oily phase was recovered and pure FAMEs (75–80%wt) were collected by vacuum distillation (Figure 2). ME already have a potential market value as biolubricants [8,9,10]; to obtain a complete valorization of the lipid component, a further improvement of the reaction by-products could help to improve the economy of the overall process For these reasons, the transesterification reaction of ME with methanol for the synthesis of Me-10-HSA and FAMEs was investigated, by optimizing the process parameters. It was already demonstrated that the partial substitution of water coordinated to the aluminum center in AlCl3·6H2O produces a mixed-aquo-alcohol complex, which acts as a Brønsted acid
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