Synthesis of value added fatty alcohols and FAMEs by non-catalytic supercritical methanol transesterification of jojoba (Simmondsia chinensis) wax

Abstract

Nowadays jojoba (Simmondsia chinensis) wax production with an industrial or energetic objective can be focused on a bio-refinery processing perspective where the fatty alcohols are the main products and fatty acid methyl esters (FAMEs) the by-products. To date, jojoba wax methanolysis has been performed using catalytic processes where long reaction times and downstream separation and purification steps are required. However, jojoba wax transesterification using a non-catalytic process such as the supercritical methanolysis has not been reported yet. The yield of jojoba fatty alcohols and FAMEs was determined in the temperature and reaction time ranges of 250–350 °C (12–42 MPa) and 15–90 min, respectively, at a methanol-to-wax molar ratio of 15:1. The maximum experimental yield of fatty alcohols and FAMEs (95.3 and 95.4 mol%, respectively) was reached at 350 °C after 90 min of reaction. Therefore, no thermal decomposition of jojoba alcohols and FAMEs was observed under the most severe experimental reaction conditions studied, which can be explained by the highly monounsaturated nature of the products obtained and the protective antioxidant effect of β-sitosterol present in jojoba wax. The rate constants obtained for this process were: 1 × 10−5, 3 × 10−5, 1.1 × 10−4, 4.1 × 10−4 and 6.5 × 10−4 s−1, at 250, 275, 300, 325 and 350 °C, respectively, with an activation energy of 115.5 kJ/mol. In addition, response surface methodology was used to determine the optimal reaction conditions that maximize the yield of fatty alcohols and FAMEs: 338.9 °C and 90 min to obtain yields of 96.8 mol% and 97.0 mol%, respectively. Thus, it can be concluded that jojoba wax methanolysis under non-catalytic supercritical conditions is an alternative way to obtain high-added value compounds and biodiesel.