A carbonate mineral, dolomite, was used as a heterogeneous catalyst to produce methyl-esters from soybean oil. The samples were analyzed by XRF, TGA, XRD, TPD-CO2, and SEM. The calcination of dolomite at 800°C/1？h resulted in a highly active mixed metal oxides. In addition, the influence of the reaction variables such as the temperature, catalyst amount, and methanol/soybean oil molar ratio in methyl-ester production was optimized by the application of a central composite design in conjunction with the response surface methodology (RSM). The XRF analysis is carried out after the reuses procedure which shows that the deactivation process is mainly due to the selective calcium leaching. Overall, the calcined dolomite exhibited high catalytic activity at moderate operating conditions for biodiesel production. 1. Introduction The increase in the number of publications addressing the topic biodiesel in recent years is noticeable [1]. This is due to the environmental benefits that the biodiesel fuel provides [2]. Conventional biodiesel production is performed through a transesterification reaction of triglycerides with mono-alkyl alcohols (i.e., methanol and ethanol) [3]. Homogeneous alkaline catalysts have been widely used since the process produces high amount of methyl-esters in a short reaction time [4, 5]. In order to solve the problem related to the purification step, solid base catalysts have been considered as an alternative to homogeneous base catalysts [6, 7]. Occasionally, the synthesis processes of heterogeneous catalysts can contribute to an additional cost of the final product. However, the use of a simple, safe, and low cost heterogeneous catalyst for the biodiesel production reaction can be effective to an industrial application [8, 9]. Dolomite is a natural carbonate mineral typically represented by a stoichiometric chemical composition of CaMg(CO3)2 [10]. During the calcinations, the carbonate groups are decomposed generating their respective basic oxides (MgO and CaO) [11, 12]. The alkaline oxides CaO and MgO are frequently used as heterogeneous catalysts for biodiesel production [13–15]. Therefore, the solid dolomite catalyst, which is an environmentally acceptable material with high basicity and low cost, is possibly an efficient and promising alternative catalyst for biodiesel production. Several studies [11, 16–20] have reported the use of calcined and/or modified dolomite as a solid catalyst for biodiesel production; however the operating conditions involved a longer reaction time with high methanol/oil ratio and catalyst weight, none
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