Separation of value-added chemical groups from bio-oil of olive mill waste

Abstract

The sector of olive oil (Olea europaea) produces a large quantity of waste per year which is usually dried and deoiled resulting in a by-product known as Olive Mill Wastes (OMW). This waste can be used as a source of energy; however, its composition also indicates a potential use as a source of chemicals. Intermediate pyrolysis of OMW resulted in a bio-oil composed of value-added products divided in two phases: an aqueous phase (AP) containing acetic acid, monosaccharides and phenolic derivatives, and a non-aqueous phase (NAP) composed of phenolic derivatives and fatty acids and their methyl esters. The main purpose of the study was to separate these compounds in interest chemical groups to increase the value of the residue inside biorefinery concept. Two liquid-liquid extraction methods, an extraction at original pH and an acid-base extraction, were studied. The results showed that acid-base extraction method, performed with hexane at pH 12 followed by an ethyl acetate extraction at pH 6, was the best method to extract value-added chemical groups in both AP and NAP bio-oil phases. Acetic acid used as chemical platform was found together with monosaccharides, that could be used to study its viability in biogas/bioethanol production, in AP aqueous phase. Phenolic derivatives, potentially useful in food, pharmaceutical and/or cosmetic industry, were found in both AP hexane and NAP ethyl acetate phases. Finally, methyl esters of fatty acids which could be directed to produce biodiesel were found in NAP hexane phase. As a result, this study allows the revaluation of OMW as a first step towards circular economy and bioeconomy.