FT-Raman Spectroscopy Quantification of Biodiesel in a Progressive Soybean Oil Transesterification Reaction and Its Correlation with ¹H NMR Spectroscopy Methods

Abstract

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., 1H and 13C 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 1H NMR spectroscopic methods reported in the literature and a new 1H 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 1H NMR methods were 0.9974, 0.9847, and 0.9972, respectively.

Avaliação de metodologia eletroquímica no monitoramento da conversão de óleo de girassol em biodiesel

“…Já no espectro do produto final não há sinal referente a triglicerídeo, que corresponde assim a um éster metílico, e conclui-se que houve a conversão total do óleo em biodiesel. 17 No entanto, para a confirmação desta hipótese, foram realizados experimentos para monitorar a variação da corrente de pico em função do tempo com o potencial de redução constante de -1160 mV. A Figura 7 apresenta os resultados da variação da corrente de pico em função do tempo para três diferentes óleos -girassol, soja e canola -assim descrevendo melhor o comportamento do catalisador na reação de transesterificação.…”

Biomass ash-based heterogeneous catalysts to produce fatty acid methyl esters from waste cooking oil.

“…In recent years, various studies have focused on using 'H-NMR to monitor the transesterification reaction progress, kinetics and FAME yield among other parameters (Gelbard et al 1995;Gerhard Knothe 2000;Suppes et al 2001;Neto et al 2004;Morgenstem et al 2006;F. Jin et al 2007;Ghesti et al 2007;Cabefa et al 2011;Anderson and Franz 2012). High-resolution NMR is fast compared to conventional analytical techniques for assessing FAME yields, such as chromatographic (GC), or gel permeation methods.…”

“…Also, it is easily adapted in routine process analysis, and allows non destructive measurements o f the samples (G. Knothe 2001). High-resolution 'H NMR spectroscopy has been used to monitor the transesterification reaction (Cabega et al 2011), based on the areas of the methoxy signal at 3.7 ppm, the a-carbonyl methylene signal at 2.3 ppm (Morgenstem et al 2006), and the areas o f the glycerides signal from 4.04 to 4.25 ppm (Ghesti et al 2007). …”

“…Previously, high-resolution 'H NMR has been used to monitor reaction progress for transesterification o f biodiesel among other parameters like degree o f unsaturation, and reaction intermediates (Gelbard et al 1995;Gerhard Knothe 2000;Suppes et al 2001;Neto et al 2004;Morgenstem et al 2006;Ghesti et al 2007; F. Jin et al 2007;Cabe^a et al 2011;Anderson and Franz 2012). 'H-NMR is a fast and reliable tool that can be easily adapted for routine non-destructive analysis o f samples (Knothe 2001).…”

“…'H-NMR is a fast and reliable tool that can be easily adapted for routine non-destructive analysis o f samples (Knothe 2001). Previous studies have monitored the yields by comparing the methoxy signal at 3.7 ppm (Cabe?a et al 2011), the a-carbonyl methylene signal at 2.3 ppm (Morgenstem et al 2006) and the glyceride signal ranging from 4.04 to 4.25 ppm (Ghesti et al 2007). As the reaction progresses, the relative intensity of the methoxy signal increases and therefore can be compared with the a-carbonyl methylene signal or the glyceride signal to confirm the conversion o f FFA to biodiesel.…”