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Ultrasound-assisted transesterification of refined palm oil (RPO) and crude palm oil (CPO) to produce biodiesel using a palm oil mill fly ash supported calcium oxide (CaO) catalyst is studied in this work. The reaction time is significantly reduced from a maximum of 360 min under conventional mixing to just 30 min with the use of ultrasound. Under ultrasonic cavitation, the required catalyst loading and methanol to oil molar ratio to produce comparable yields and fatty acid methyl esters (FAME) conversions as conventional mixing are lower. For RPO, the ultrasound-assisted transesterification conditions of 60% ultrasonic amplitude, 30 min reaction time, 4 wt.% catalyst loading, and 9:1 methanol to oil molar ratio result in maximum biodiesel yield and FAME conversion of 85.23% and 97.02%, respectively. As for CPO, maximum biodiesel yield of 73.23% and FAME conversion of 97.04% are obtained under the same conditions with the exception of a methanol to oil molar ratio of 12:1. Key physicochemical properties of the produced biodiesels are found to be within the limits set by EN 14214 and ASTM D 6751. Catalyst reusability tests indicate that the catalyst can be used up to three consecutive cycles after regeneration using methanol washing followed by recalcination at 850°C for 2 h.

Heterogeneous catalyzed transesterification has been proposed as a promising technology to mitigate the limitations of homogeneous transesterification such as wastewater generation, low free fatty acids, low water tolerance, and inability to recycle the catalyst. This work aims to evaluate a refined palm biodiesel synthesis process through heterogeneous catalyzed transesterification. Three major process variables were studied over a reaction duration of 3–6 h, including the reaction temperature (45–65 °C), percentage of catalyst loading (4–6 wt.%), and methanol to oil molar ratio (6:1–12:1). The highest biodiesel yield of 88.58% was recorded under the conditions of temperature 55 °C, catalyst loading 4 wt.% and methanol to oil molar ratio 9:1 at 5 h. A pseudo-first order reaction mechanism was applied in the kinetic analysis of the fatty acid methyl esters (FAME) concentrations. In addition, the activation energy and pre-exponential factors, as determined through the kinetic analysis, were 31.2 kJ/mol and 680.21 min−1, respectively. The key fuel properties of the produced palm biodiesel were determined to be acceptable according to the ASTM D 6751 and EN 14214 standards. The developed catalyst could feasibly be reused for the palm biodiesel synthesis up to the third cycle with lower reaction performance in the fourth cycle.