A Brønsted ammonium ionic liquid-KOH two-stage catalyst for biodiesel synthesis from crude palm oil

Palm biodiesel from crude palm oil (CPO) was prepared via transesterification in a two-stage process using acidic ionic liquid as first step catalyst as opposed to using directly the alkaline-catalyzed transesterification which was found to be unsuitable. The esterification of the free fatty acids (FFA) of the CPO was carried out using triethylammonium hydrogensulfate (Et3NHSO4) as the pre-catalyst in the first stage, in which the acid value was reduced from 6.98 to 1.24 mg KOH/g of oil followed by the use of KOH-catalyzed transesterification in the second stage. The effects of molar ratio of methanol to crude palm oil feed, the amount of ionic liquid and the reaction temperature were evaluated for the percent conversion of FFA. The conversion rate of FFA attained was 82.1% when 5.2 wt.% of Et3NHSO4 was used for the reaction of methanol with CPO at a ratio of 15:1 respectively, and at reaction temperature of 170 °C for 3 h. The second alkali-catalyze step was performed under agitation with stirrer speed of 600 rpm at 60 °C using 1.0% KOH for 50 min. The final biodiesel product was analyzed using gas chromatography (GC) with a reaction yield of 96.9%. The density, kinematic viscosity, acid value, ester content and other properties of the biodiesel sample were also measured and compared to the ASTM and the European biodiesel specifications.

► Preparation of palm biodiesel via transesterification in a two-stage process using acidic ionic liquid as pre-catalyst.
► The influences of molar ratio of methanol to crude palm oil, ionic liquid amount, and reaction temperature were explored.
► The conversion rate of FFA attained 82.1% while using 5.2 wt.% of Et3NHSO4 in specific reaction condition.
► The acid value was reduced from 6.98 to 1.24 mg KOH/g oil.
► The final biodiesel product was analyzed by gas chromatography (GC) with reaction yield of 96.9%.