(63b) Evaluation of Process Variables Interaction by Biodiesel Production from Castor Oil Ethanolise

Biodiesel is an alternative biodegradable and nontoxic fuel, which is essentially free of sulfur and aromatics. It is usually produced by a transesterification and esterification reaction of vegetable or waste oil respectively with a low molecular weight alcohol, such as ethanol and methanol. This work presents the transesterification process of refined and pharmaceutical castor oil with ethanol in the presence of sodium ethoxide as catalyst, because it presents better conversion and smaller reaction time. Chemically, this oil contains approximately 90% of ricinoleic acid, what gives to the oil some important characteristics, such as its ethanol solubility at 30°C, allowing reaction at low temperature. Different variables affect the castor oil transesterification such as reaction temperature, ethanol : castor oil molar ratio, catalyst concentration, level of agitation and reaction time. The agitation was kept constant. The reaction is very fast, and conversions larger than 90% are reached within 15 min. However, the time was considered 90 min, since the reaction was stable. The proposed process of biodiesel production was evaluated and optimal operating conditions range was identified by application of the factorial design and response surface methodology. Response-surface methodology (RSM) was used, to have a systematic procedure to simultaneous take into consideration many variables at different levels and the interactions between those variables, using a smaller number of observations than conventional procedures. The studied variables were reaction temperature, catalyst concentration and ethanol : castor oil molar ratio. The experiments were carried out according to a 23 complete factorial design plus three central points and six axial points, called star points. High-performance size-exclusion chromatography, also called gel-permeation chromatography, was used to evaluate the influence of different variables affecting the transesterification. A second-order model was obtained to predict conversion as a function of temperature, catalyst concentration and ethanol castor oil molar ratio. The model had been found to describe the experimental range studied adequately. Good phase separation was obtained with the methodology developed. The best results for laboratory-scale reactions were obtained at 30°C and 1% of sodium ethoxide by weight of castor oil. A small scale up was realized with a batch reaction, mechanical agitation and sodium hydroxide as catalyst. The effect of the scale up was interpreted by variations of ethyl ester conversions.