VOL. 11, NO. 6, MARCH 2016 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences ©2006-2016 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 4045 TWO-STEP TRANSESTERIFICATION OF CALOPHYLLUM INOPHYLLUM OIL: OPTIMIZATION AND REACTION KINETICS Nunung Prabaningrum, Mondjo, Galeh Dharmawan Pratama, Yuasti Hasna Fauziyah and Ghoziah Putri Hardini Department of Engineering Physics, Faculty of Engineering, Universitas Gadjah Mada Jalan Grafika Yogyakarta, Indonesia E-Mail: nunung.prabaningrum@ugm.ac.id ABSTRACT Calophyllum inophyllum oil is a non-edible oil, which the plant is widely available in Indonesia, with a very high free fatty acid content of around 30% or acid value of 60 mg KOH·g -1 . Two-step transesterification comprised hydrochloric acid-catalyzed esterification and sodium hydroxide-catalyzed transesterifications was conducted in batch processes. The first step esterification was carried out with molar ratio of methanol to oil of 35:1, hydrochloric acid concentration of 15 wt.%, and stirring speed of 500 rpm for 3 h reaction time at 60 °C. This esterification reduced the acid value of Calophyllum inophyllum oil from (59.97  2.71) mg KOH·g -1 to (5.33  0.71) mg KOH·g -1 . In second step transesterification, response surface methodology, a central composite design, was utilized to optimize reaction conditions which maximized biodiesel yield and minimized acid value. The optimum conditions included molar ratio of methanol to oil of 11.95, sodium hydroxide concentration of 1.26 wt.% for 1.52 h reaction time at 50 C were established. At these optimum conditions, the maximum biodiesel yield of (84.90  0.31) % and minimum acid value of (0.303  0.015) mg KOH·g -1 were achieved which were comparable with predicted values. The second step of transesterification was the second-order reaction with reaction rate constant of 0.047 to 0.180 (M -1 ·min -1 ) at 30 to 50 C. The activation energy of 54.53 kJ·mol -1 was obtained. Keywords: Two-step transesterification, calophyllum inophyllum oil, biodiesel, free fatty acid content, central composite design. INTRODUCTION Recently, the world oil reserves are running low. Until the end of 2013, world oil reserves were recorded in the value of 1687.9 billion barrels. If there are no sources of new oil reserves, the oil will be consumed in just 53.3 years [1]. Nevertheless, until the end of 2014, petroleum was still the most dominant fuel used. Based on data collected by the International Energy Agency (IEA), 40.7% of world fuel consumption derived from petroleum [2]. This consumption is predicted increasing continuously in line with population growth and increasing the world income per capita [3]. In Indonesia, diesel fuel is the second most consumed petroleum fuel. In 2012, 37% petroleum consumption came from diesel fuel [4]. As other derived petroleum products, diesel fuel is a non-renewable fuel with the limited reserves. Hence, the alternative fuel source is required to substitute diesel fuel or to be mixed with it. Biodiesel is one of this alternative fuels. Biodiesel is composed some fatty acid alkyl esters derived from vegetable oils or animal fats. Biodiesel has some advantages than petro-diesel, which are renewable fuel, biodegradable, non-toxic, lower green- house gas emissions, and higher flash point. The most selected method to produce biodiesel is transesterification, which is the reaction between triglyceride contained in vegetable oils or animal fats and short-chained alcohol in the presence of catalyst [5]. Nowadays, biodiesel is produced from edible oils which led higher cost in its production and vied as consumed food. Usage of non-edible oils could be the problem-solving to reduce the cost of biodiesel fuel and they are not consumed as foods. One of non-edible oils with large abundance in Indonesia is Calophyllum inophyllum oil. This oil could be obtained by extracting oil from its seeds. Calophyllum inophyllum seeds have high oil content of 40 to 70% [6]. This oil content is higher than oil content in soybean, sunflower, and canola seeds. However, Calophyllum inophyllum oil has very high free fatty acid content which is able to disrupt transesterification with alkaline (base) catalyst, since saponification could take place to produce soap instead of biodiesel [5, 6]. To overcome high free fatty acid content, transesterification catalyzed with acid catalyst could be applied [7]. Another method to produce biodiesel from high free fatty acid content is two step transesterification which comprised of acid-catalyzed esterification as the first step and followed by alkaline-catalyzed transesterification as the second step [8, 9]. Some research works had been investigated to produce biodiesel from Calophyllum inophyllum oil with different free fatty acid contents and various catalyst types. The heterogeneous-catalyzed transesterification of Calophyllum inophyllum oil were reported by Arumugam and Ponnusami [10]. The maximum oil conversion of 96.82% was obtained with 16:1 molar ratio of methanol to oil, 3 wt.% catalyst concentration for 3 h at 80°C. Ong, et al. [11] used phosphate acid to remove gum in Calophyllum inophyllum oil with 29.65% free fatty acid content. This pre-treatment oil was esterified with sulfuric acid catalyst followed by transesterification with sodium hydroxide. These processes could reduce the free fatty acid content to be lower than 2% with high oil conversion of 98.92%. One step transterification of 15% free fatty acid content Calophyllum inophyllum oil with heterogeneous sulphonated carbon catalyst during 5 h reaction time could convert oil to biodiesel with 99% purity [12]. Two step transesterifications of this oil has