Monday, April 30, 2007

Basic oxides as catalysts for biodiesel production in heterogeneous media

Cristiane A. Henriques, Wallace M. Antunes, Paula M. Veiga, Karen S. Augusto, and Claudia O. Veloso. Programa de Pós-graduação em Engenharia Quimica, Universidade do Estado do Rio de Janeiro - Instituto de Quimica, Rua São Francisco Xavier, 524 - PHLC - sala 310, Rio de Janeiro, 20559900, Brazil

The fatty acid methyl esters prepared by transesterification of vegetable oils with methanol are products of commercial interest due to their use as raw materials for chemical, pharmaceutical and food industries and also as biodiesel. Biodiesel is a no-polluting alternative fuel produced from renewable resources whose chemical and physical properties closely resemble those of the petroleum diesel fuel. This work studied the transesterification of soybean oil with methanol over solid catalysts such as: MgO, ZnO, Al2O3 and Mg/Al or Zn/Mg/Al mixed oxides derived from hydrotalcites. The influence of the catalyst basicity on their catalytic performance was also evaluated as well as the effect of reaction temperature and of methanol/oil molar ratio. The results indicated that both MgO and mixed oxides were efficient to catalyze the reaction under study with a fatty acid methyl esters yield higher than 70% at 130°C. The influence of chemical composition on catalytic performance was affected by both by the association strength/density of basic sites and mesoporous volume of the samples. The fatty acid methyl esters yield was favored by the increase on reaction temperature and on methanol/oil ratio. Our results show that over basic solid catalysts high biodiesel yields are associated to more severe experimental conditions than those employed with homogeneous catalysts. However, the reduction of the processing costs due to the process simplifications along with the minimization of the environmental problems justifies the use of basic heterogeneous catalysts.