Macauba oil as an alternative feedstock for biodiesel: Characterization and ester conversion by the supercritical method

Abstract

In this work different samples of Brazilian macauba oil obtained from mechanical pressing were characterized and production of esters of fatty acids using a catalyst-free continuous process under supercritical alcohols was assessed. Analysis of oil samples showed that the major fatty acid on pulp oil was oleic acid (mean value 62.8%), the amount of free fatty acid (FFA) was very high (37.4–65.4%), samples contained glycerides (7.4–16.5% TAG, 14.2–16.8% DAG and 1.0–3.4% MAG) and moisture was around 1.0%. Oil was processed in a continuous reactor using supercritical methanol or ethanol and the effects of temperature (573, 598, 623 and 648K), pressure (10, 15 and 20MPa), oil to alcohol molar ratio (1:20, 1:30 and 1:40), water concentration (0, 5 and 10wt% added) and the flow rate of reaction mixture (1.0, 1.5, 2.0, 2.5 and 3.0mL/min) on process efficiency were evaluated. The highest ester content achieved in reactions with supercritical methanol was 78.5% (648K, 15MPa, 1:30 oil:methanol molar ratio, 5wt% water and 2.5mL/min flow rate), while with supercritical ethanol was 69.6% (598K, 15MPa, 1:30 oil:ethanol molar ratio, 5wt% water and 2.0mL/min flow rate). The extent of the reaction was explored using a novel parameter, convertibility, which corresponds to the maximum ester content attainable from the feedstock. According to the convertibility of macauba pulp oil, the highest ester content corresponded to efficiencies of 98.0% and 86.9%, respectively. Results demonstrate that macauba oil might be a potential alternative for biodiesel production, though purification steps should be taken into account to achieve biodiesel specifications.