Nuclear Magnetic Resonance (1.40 T) and Mid Infrared (FTIR-ATR) Associated with Chemometrics as Analytical Methods for the Analysis of Methyl Ester Yield Obtained by Esterification Reaction

Abstract

In this work, we compared 1.40 T nuclear magnetic resonance (NMR) to 7.05 T (60 and 300 MHz for proton, respectively), and mid-infrared with attenuated total reflectance (FTIR-ATR), associated with chemometrics methods, for the quantification of the reaction yield during esterification of fatty acids with methanol. The results showed that the integrated intensities of the ester C=O stretching region, relative to the total C=O stretching region, is useful to quantify the fatty acid methyl ester (FAME) concentration. Comparing the results obtained by the different final models: NMR (1.40 T and 7.05 T), FTIR-ATR using multivariate partial last squares regression (PLS) with orthogonal signal correction (OSC), and univariate ordinary least squares (OLS), the NMR of 1.40 T (60 MHz for proton) showed more advantages when compared to a high field spectrometer, due to the non-use of cryogenic and solvents and less laborious work for obtaining results. Keywords: biodiesel, esterification, mid-infrared, q-NMR, chemometrics IntroductionThe interest for using alternative fuels has grown in the last decade. 1 The increasing demand for energy and environmental awareness are leading researchers to look for new environmentally acceptable renewable resources. In this context, the interest for biodiesel has increased a lot since it is produced using renewable resources (oils and fats from both vegetable and animal sources), it is biodegradable, and it can be directly placed on diesel engines without any mechanical modifications, due to their similar physical chemical properties. Also it does not contain sulfur compounds, it releases less particulate matter and it is less toxic. 2,3The most common method used to produce biodiesel is the transesterification of fats and oils, using a strong base as catalyst (like NaOH, KOH or KOCH 3 ). It consists in the reaction between triacylglycerides and short chain alcohols to produce esters and glycerol. It is a reversible process and excess of alcohol is used for moving the equilibrium towards the products. However, this process needs feedstocks containing low concentrations of free fatty acids and water because they react with the basic catalysts forming soaps which hinders the purification of the biodiesel, increasing the cost of the production. 4 An alternative way is the esterification of fatty acids. 5,6 This reaction normally uses homogeneous acid catalysis with strong Brønsted acids such as H 2 SO 4 and HCl that are corrosive and should be neutralized when the process is finished. To overcome this problem, solid Lewis acids can be used allowing easy separation and continuous operation in reactors. 2The most common method used to monitor the reaction yield during the esterification is the determination of the amount of fatty acids, usually performed using chromatographic methods or titration with alcoholic solution of KOH (method described by AOCS Cd 3a-63). 7,8 Despite being very effective methods for this kind of analysis, they have the disadvantage of consuming large amounts of organ...

Analysis of the Content of Fatty Acid Methyl Esters in Biodiesel by Fourier‐Transform Infrared Spectroscopy: Method and Comparison with Gas Chromatography

“…This analytical method requires previous sample treatment, tedious calibrations, long analysis times, and it is an expensive technique, among other disadvantages (Soares et al, ). Recently, less complicated analytical methods, such as nuclear magnetic resonance (NMR) or infrared spectroscopy (IR), have been developed for the characterization of oils and biodiesel samples (Adewale et al, ; Alonso et al, ; Aziziana and Kramer, ; Beltrán Sanahuja et al, ; Cruz et al, ; Dubé et al, ; Forfang et al, ; Guillén et al, ; Gelbard et al, ; Jin et al, ; Kachel et al, ; Kachel‐Jakubowska et al, ; Kollar et al, ; Matwijczuk et al, ; Mei Han and Chee Liang, ; Monteiro et al, ; Morgenstern et al, ; Oliveira et al, ; Siatis et al, ; Vrtiška and Šimáček, ), although some of them require costly equipment and analysis.…”

“…Some researchers used FTIR spectroscopy to monitor biodiesel production using enzymatic hydroesterification from low‐cost feedstocks (olive pomace oil and acid oil from soapstock of vegetable oil) (Cruz et al, ) and to quantify the yield of esterification reaction of fatty acid and methanol (Kollar et al, ), but they do not analyze the biodiesel obtained by the transesterification reaction. In contrast, Dubé et al () monitored the intermediates and products of the transesterification of TAG to FAME from waste frying oil, but they could only give quantitative data for the sum of the reaction intermediates (TAG + diacylglycerols + monoacylglycerols).…”

Use of Co/Fe-Mixed Oxides as Heterogeneous Catalysts in Obtaining Biodiesel

“…Once it was confirmed that the viscosity had been reduced to values close to the norm, we proceeded to the quantification and confirmation of the conversion by diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) and 1 H-Nuclear magnetic resonance (NMR) spectroscopy [46], as well as the verification of the international parameters of density, corrosion of the copper foil and turbidity. These parameters can be used to verify the feasibility of the products' application as biofuels in internal combustion engines.…”