Biodiesel fuels from vegetable oils:: Transesterification of Cynara cardunculus L. oils with ethanol

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 degreesC), catalyst type (sodium hydroxide and potassium hydroxide), catalyst concentration (0.25-1.5 wt %), and ethanol/oil molar ratio (3:115:1). 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 degreesC temperature. This biodiesel has very similar properties to those of no. 2 diesel fuel.