Response Surface Optimization of Biodiesel Production via Catalytic Transesterification of Fatty Acids Oil from Jatropha seeds was extracted by supercritical CO 2 . A catalytic transesteri- fication reactor was employed for biodiesel production from extracted oil in which fatty acids like palmitic, stearic, oleic, and linoleic acid were converted to fatty acid methyl esters (FAMEs) with sodium methoxide as the catalyst. Gas chromatogra- phy-flame ionization detector (GC-FID) analysis identified and quantitatively de- termined the amount of FAMEs. Response surface methodology (RSM) was ap- plied to find the optimal operating conditions in order to maximize the biodiesel yield. Under the RSM-predicted optimum conditions, the maximum yields of four individual FAMEs and their combination as biodiesel were determined. The RSM model demonstrated that the linear and square terms of four variables and the in- teraction of flow rate and dynamic time significantly influence the biodiesel yield. Keywords: Biodiesel, Catalytic transesterification, Jatropha oil, Response surface methodology, Supercritical fluid extraction Received: May 16, 2013; revised: November 09, 2014; accepted: January 15, 2015 DOI: 10.1002/ceat.201300328 1 Introduction The limitation in resources, nonuniform distribution, and envi- ronmental pollution of petroleum products, and also increasing demands for fuel are important driving forces to search for an alternative source of energy which can be verified by vegetable oils, animal fats, or waste cooking oil. Biodiesel, an alternative diesel fuel, is biodegradable and nontoxic, has a higher flash point and improved cetane number with lower production of pollutants and emission compositions [1]. Moreover, biodiesel is formed from oils containing oxygen, which improves burn- ing in contrast to diesel fuel [2]. Jatropha curcas (JC) as a potential natural source of biodiesel has been considered due to its high seed oil content and com- patibility to tropical and subtropical climates. JC is a drought- resistant shrub or tree up to 5–7 m high, adaptable to poor soil, and producing seeds for 50 years [1, 3, 4]. Biodiesel from Jatro- pha oil has similar properties to that of diesel produced from petroleum. The presence of toxic components in oil and seed cake makes it a nonedible source that can be used for nutrition- al purposes only with detoxification [5–10]. Besides, nonedible oil has attracted attention because of the high cost of raw mate- rial in the case of edible oils without the problem of fuel versus food crisis [1]. In addition to the potential as fuel substitute, the oil is used in soap manufacturing and as lubricant in the wood industry [4, 7, 11]. The seeds oil is composed of 88.2–97.3 kg kg –1 triglycerides with high content of fatty acids which is employed for biodiesel production. Most fatty acids in Jatropha oil are unsaturated (78.9 %) which leads to suitable combustion [4, 12]. Diesel is a hydrocarbon with 8–10 carbon atoms per molecule, whereas Jatropha oil has 16–18. This high molecular weight and chemical structure causes high viscosity (37–54.8 cSt at 30 °C) for the JC oil. The use of pure vegetable oils in diesel engines causes major problems such as gum formation and lower fuel atomization due to high viscosity and low volatility [7, 12]. Consequently, methods have to be applied to reduce the oil viscosity and modify the properties of vegetable oils, e.g., blending, microemulsification, pyrolysis, and transesterification [14]. Among these procedures, transesterification is preferen- tially used for acceptable efficiency and lower production cost of catalyst [15]. Transesterification is a chemical three-step reaction between triglyceride and alcohol in the presence of an alkali, acidic, or enzymatic catalyst to produce fatty acid meth- yl esters (FAMEs; biodiesel) [12]. FAMEs were obtained via transesterification from different vegetable oils such as soybeans [16], peanuts [17], pumpkin [18], castor [19], Pongamia pinnata [20], rapeseed [21], and waste vegetable oil [22] as well as via sub- critical hydrolysis and supercritical methylation [23–25]. Recently, transesterification of simulated Jatropha oil made from sesame seed oil with similar composition was investigated using five different solid acid catalysts (zeolites). The final con- version reached 61 % after 3 h under atmospheric pressure and 115 °C [26]. Catalytic hydrocoversion of Jatropha oil was car- ried out via transformation of triglycerides to linear chain al- kanes via hydrodeoxygenation reaction and conventional hy- drocracking reaction. Maximum conversions of 61 % and 65 % Chem. Eng. Technol. 2015, 38, No. 00, 1–10 ª 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.cet-journal.com Maliheh Mir Seyyed M. Ghoreishi Isfahan University of Technology, Department of Chemical Engineering, Isfahan, Iran. – Correspondence: Prof. Seyyed M. Ghoreishi (ghoreshi@cc.iut.ac.ir), Isfahan University of Technology, Department of Chemical Engineer- ing, Isfahan 84156-83111, Iran. Research Article 1 These are not the final page numbers! ((