Optimization of the ethanolysis of Raphanus sativus (L. Var.) crude oil applying the response surface methodology Anderson Kurunczi Domingos a , Emir Bolzani Saad a , Helena Maria Wilhelm b,1 , Luiz Pereira Ramos a, * a Centro de Pesquisa em Quı ´mica Aplicada (CEPESQ), Department of Chemistry, Federal University of Parana ´ – UFPR – P.O. Box 19081, Curitiba 81531-990, PR, Brazil b Institute of Technology for the Development (LACTEC) – Curitiba, 81531-990, PR, Brazil Received 19 June 2006; received in revised form 20 March 2007; accepted 20 March 2007 Available online 12 June 2007 Abstract Raphanus sativus (L. Var) is a perennial plant of the Brassicaceae (or Cruciferae) family whose oil has not been investigated in detail for biodiesel production, particularly when ethanol is used as the alcoholysis agent. In this work, response surface methodology (RSM) was used to determine the optimum condition for the ethanolysis of R. sativus crude oil. Three process variables were evaluated at two levels (2 3 experimental design): the ethanol:oil molar ratio (6:1 and 12:1), the catalyst concentration in relation to oil mass (0.4 and 0.8 wt% NaOH) and the alcoholysis temperature (45 and 65 °C). When the experimental results were tentatively adjusted by linear regres- sion, only 58.15% of its total variance was explained. Therefore, a quadratic model was investigated to improve the poor predictability of the linear model. To apply the quadratic model, the 2 3 experimental design had to be expanded to a circumscribed central composite design. This allowed the development of a response surface that was able to predict 97.75% of the total variance of the system. Validation was obtained by performing one ethanolysis experiment at the conditions predicted by the model (38 °C, ethanol:oil molar ratio of 11.7:1 and 0.6 wt% NaOH). The resulting ester yield (104.10 wt% or 99.10% of the theoretical yield of 105.04 wt%) was shown to be the highest among all conditions tested in this study. The second ethanolysis stage of the best RSM product required 50% less ethanol and 90% less catalyst consumption. The amount of ethyl esters obtained after this procedure reached 94.5% of the theoretical yield. The resulting ethyl esters were shown to comply with most of the Brazilian biodiesel specification parameters except for oxidation stability. Addition of 500 ppm of BHT to the esters, however, complied with the specification target of 6 h. The application of 2 wt% Magnesol Ò after the second ethanolysis stage eliminated the need for water washing and helped generate a final product with less unreacted glycerides. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Raphanus sativus; Crude oil; Ethanolysis; Ethyl esters; Response surface methodology 1. Introduction Biodiesel is an ecologically friendly fuel because it has a lower emission profile than petrodiesel and decreases the greenhouse gas emissions from combustion ignition engines (McCormick and Alleman, 2005). In addition, bio- diesel is safer to handle (flash point above 110 °C), contains little or no sulfur or carcinogenic polyaromatic compo- nents, and decreases soot emission considerably, which is very advantageous in environmentally sensitive areas (Schuchardt et al., 1998; Ramos et al., 2003; Knothe, 2005). Furthermore, biodiesel is a suitable outlet for the vegetable oil industry requiring little or no changes in cur- rent diesel engines when used in blends and also increases engine life due to its superior lubricity over petrodiesel (Knothe, 2005; Ramos and Wilhelm, 2005). Biodiesel is chemically defined as the simple alkyl mono- esters of long chain fatty acids derived from renewable feedstocks such as vegetable oils, animal fats and recycled 0960-8524/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2007.03.063 * Corresponding author. Tel.: +55 41 3361 3175. E-mail addresses: helenaw@lactec.org.br (H.M. Wilhelm), lramos@ quimica.ufpr.br (L.P. Ramos). 1 Tel.: +55 41 3361 6191. Available online at www.sciencedirect.com Bioresource Technology 99 (2008) 1837–1845