In situ transesterification of Cynara cardunculus L. seed oil via direct ultrasonication for the production of biodiesel

Alkaline transesterification of Cynara cardunculus L. seed oil with methanol for biodiesel production is investigated. Both in situ transesterification and conventional transesterification were studied using ultrasonication (24 kHz, without external heating) and mechanical stirring (600 rpm, 60 °C). For in situ transesterification, the use of ultrasonication and mechanical stirring led to similar high % FAME content (96.0 and 93.0% respectively) after 20 min. However the % yield of the extracted methylesters using mechanical stirring was lower compared to ultrasonication (50.4 and 85.1% respectively). For in situ transesterification via ultrasonication the optimum conditions were: 9.5% NaOH w/w of oil and a 550:1 methanol to oil molar ratio. In conventional transesterification, using ultrasonication, a high % FAME content of methylesters (97.0%) was obtained after 20 min. Respective % FAME content for mechanical stirring was 95.8% after 1 h. In both cases of conventional transesterification 1% w/w of oil NaOH as catalyst and a 7:1 methanol to oil ratio were used. The kinetics used for methanolysis reaction using sonication or mechanical stirring involved the irreversible second order reaction followed by the reversible second order reaction close to equilibrium. Cynara biodiesel properties determined, comply with the specifications of the European Standard EN 14214.