Articles FT-Raman Spectroscopy Quantification of Biodiesel in a Progressive Soybean Oil Transesterification Reaction and Its Correlation with 1 H NMR Spectroscopy Methods Grace Ferreira Ghesti,* Julio Lemos de Macedo, Ine ˆs Sabioni Resck, Jose ´ Alves Dias, and Sı ´lvia Cla ´udia Loureiro Dias* Laborato ´ rio de Cata ´ lise, Instituto de Quı ´mica, UniVersidade de Brası ´lia, caixa postal 4478, Brası ´lia-DF, 70904-970, Brazil ReceiVed December 29, 2006. ReVised Manuscript ReceiVed May 29, 2007 Biodiesel fuel (fatty acid esters) has become more and more attractive due to its environmental benefits. Transesterification is the most common and important method for making biodiesel from vegetable oils or animal fats. Several studies have focused on the development and improvement of analytical methods for monitoring biodiesel production and determining the fuel quality. Analytical procedures reported in the literature include chromatographic methods (e.g., gas chromatography, high-performance liquid chromatography, gel permeation chromatography, etc.) and spectroscopic methods [e.g., 1 H and 13 C NMR, near infrared, Fourier transform infrared spectroscopy, and recently, Fourier transform (FT)-Raman]. The study presented in this paper expands our previous research, in which FT-Raman spectroscopy combined with partial least squares (PLS) multivariate analysis was successfully applied to the quantification of soybean oil/ethyl ester mixtures. The FT-Raman/PLS methods developed by our group were used to monitor and quantify a transesterification reaction process involving soybean oil and ethanol to produce fatty acid ethyl esters (biodiesel) over 22 h catalyzed by a heterogeneous Lewis acid catalyst. The results were successfully correlated with two 1 H NMR spectroscopic methods reported in the literature and a new 1 H NMR method proposed in this work that can be easily extended to other vegetable oils. The correlation coefficients (R 2 ) obtained from the linear fit between FT-Raman measurements and the above 1 H NMR methods were 0.9974, 0.9847, and 0.9972, respectively. 1. Introduction Biodiesel is defined by the American Society for Testing and Materials (ASTM) as a fuel comprised of monoalkyl esters of long-chain fatty acids derived from vegetable oils or animal fats meeting the requirements of ASTM D 6751. 1,2 Biodiesel has distinct advantages when compared to petroleum-derived diesel fuel (petrodiesel). It is derived from renewable resources; is biodegradable; is nontoxic; has low emission profiles, a higher flash point, and excellent lubricity; and can be used either pure or blended with petrodiesel fuel. 1,3,4 The use of vegetable oils as fuel has been known since the Paris Exposition in 1900. 4 However, due to its higher molecular mass and kinematic viscosity, its direct use in diesel engines resulted in several operational problems (e.g., poor atomization, carbon deposits due to incomplete combustion, oil ring sticking, lubricating problems, etc.). 1,4,5 To solve these problems, four possible solutions were investigated in literature: transesteri- * Corresponding authors. Phone: 55-(61)-3307-2162. Fax: 55-(61)-3368- 6901. E-mail: scdias@unb.br (S.C.L.D.) and grace@unb.br (G.F.G.). (1) Ma, F.; Hanna, M. A. Bioresour. Technol. 1999, 70,1-15. (2) ASTM D 6751-03a. Annu. Book ASTM Stand. 2005, 05.04, 609- 614. (3) Knothe, G. J. Am. Oil Chem. Soc. 1999, 76, 795-800. (4) The Biodiesel Handbook; Knothe, G., Gerpen, J. V., Krahl, J., Eds.; American Oil Chemists’ Society Press: Champaign, IL, 2005. (5) Meher, L. C.; Sagar, D. V.; Naik, S. N. Renew. Sustain. Energy ReV. 2006, 10, 248-268. VOLUME 21, NUMBER 5 SEPTEMBER/OCTOBER 2007 © Copyright 2007 American Chemical Society 10.1021/ef060657r CCC: $37.00 © 2007 American Chemical Society Published on Web 07/17/2007