A study was made of the transesterification reaction of Cynara cardunculus L. oil by means of ethanol, using sodium hydroxide and potassium hydroxide as catalysts. The objective of the work was to characterize the ethyl esters for use as biodiesels in compression ignition motors. The operation variables employed were temperature (25-75 °C), catalyst type (sodium hydroxide and potassium hydroxide), catalyst concentration (0.25-1.5 wt %), and ethanol/oil molar ratio (3:1-15:1). Oil mass (200 g), reaction time (120 min), and alcohol type (ethanol) were fixed as common parameters in all the experiments. The evolution of the process was followed by gas chromatography, determining the concentration of the ethyl esters at different reaction times. The biodiesel was characterized by determining its density, viscosity, high heating value, cetane index, cloud and pour points, characteristics of distillation, and flash and combustion points according to ISO norms. The biodiesel with the best properties was obtained using an ethanol/oil molar ratio of 12:1, sodium hydroxide as catalyst (1%) and 75 °C temperature. This biodiesel has very similar properties to those of no. 2 diesel fuel.

A study was performed of the transesterification reaction of used frying oil by means of methanol, using sodium hydroxide, potassium hydroxide, sodium methoxide, and potassium methoxide as catalysts. The objective of the work was to characterize the methyl esters for use as biodiesels in compression ignition motors. The operation variables used were methanol/oil molar ratio (3:1−9:1), catalyst concentration (0.1−1.5 wt %), temperature (25−65 °C), and catalyst type. Also, experiments in two stages of reaction, with separation of the glycerol in the first stage, were carried out. The evolution of the process was followed by gas chromatography, determining the concentration of the methyl esters at different reaction times. The biodiesel was characterized by its density, viscosity, high heating value, cetane index, cloud and pour points, characteristics of distillation, flash and combustion points, saponification value, and iodine value according to ISO norms. The biodiesel with the best properties was obtained using a methanol/oil molar ratio of 6:1, potassium hydroxide as catalyst (1%), and 65 °C temperature. This biodiesel had properties very similar to those of no. 2 diesel. The two-stage transesterification was better than the one-stage process.

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