Correlation Method for Conversion Determination of Biodiesel Obtained from Different Alcohols by ¹H NMR Spectroscopy

Abstract

This work presents a correlation method that uses 1H NMR spectra for determining the conversion during transesterification of vegetable oil with 10 alcohols: methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, 1-pentanol, isopentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-decanol, 1-dodecanol, and benzyl alcohol. Conversions ranging from 70 to 99%, depending on primary alcohol used, are obtained using organic catalyst N,N′,N″-tris­(3-(dimethylamino)­propyl)­guanidine. Catalysts, alcohols, and intermediate products can cause signal overlapping, debilitating the use of the conventional 1H NMR method. Thus, our method uses the correlation between the triplet signal of α-carbonylmethylene and two signals of unsaturated parts of the fatty acid chain, where signal overlapping does not occur, hence, adding robustness and flexibility to the method. The method is applicable for unsaturated oils and is not affected by the amounts of residual alcohol, catalyst, or intermediate products, making it ideal for conversion determination and in situ monitoring of complex mixtures. In addition, we present a systematic analysis of the 1H NMR spectra of biodiesels produced with the mentioned alcohols.

Biodiesel Synthesis From Cucumis melo Var. agrestis Seed Oil: Toward Non-food Biomass Biorefineries

“…A distinctive peak that appeared at 3.6 shows the presence of hydrogen adjacent to the electronegative atom in the biodiesel spectrum corresponding to methoxy (-OCH 3 ) (Figure 7 upper). Previous studies are evidence of the presence of methoxy at this position (Joseph et al, 2010;Faraguna et al, 2017;Dawood et al, 2018;Munir et al, 2020;Ullah et al, 2020). Other conspicuous peaks include 0.876-0.884 ppm showing terminal methyl protons (-CH 3 ), 2.033-2.786 ppm α-methylene protons (-CH 2 ), 1.252-1.636 ppm for β-methylene protons (-CH 2 ), 5.322-5.350 ppm depicts Olefinic protons (-HC=CH), respectively.…”

“…On transesterification, triglyceride is converted into respective alkyl ester depending on the alcohol used, and glycerol part on substitution with alcohol results in the appearance of an NMR signal ranging between 5.3-3.3 ppm. Faraguna et al (2017) observed peaks of H 1 NMR spectra ranging from 4.3 to 3.5 ppm with assigned biodiesel and protons of different alcohols used to produce biodiesel. A distinctive peak that appeared at 3.6 shows the presence of hydrogen adjacent to the electronegative atom in the biodiesel spectrum corresponding to methoxy (-OCH 3 ) (Figure 7 upper).…”

Biodiesel Produced from Propanol and Longer Chain Alcohols—Synthesis and Properties

“…They investigated the effects of various physical and chemical parameters (the influence of water on hydrolysis, molar ratio of reactants, catalyst amount, temperature, stirrer speed (rpm), and desiccant on esterification) to achieve optimum conditions and the maximum yield of the biolubricant (fatty acid octyl esters) in the shortest possible time. Additionally, Faraguna et al [77] synthesized hexyl, heptyl, octyl, decyl, and dodecyl esters with a guanidine catalyst obtaining conversions 67.6-95.4% [78] and developed a correlation method for conversion determination by 1 H NMR spectroscopy and a method for determining the amount of FAAE added into diesel with FTIR for FAAE obtained from C 1 -C 12 .…”

Cocatalytic Activity of the Furfuryl and Oxanorbornane-Substituted Guanidines in the Aldol Reaction Catalyzed by (S)-Proline

“…Our ongoing interest in guanidine chemistry is primarily oriented toward the role of intramolecular hydrogen bonding on the basicity and application of novel derivatives as the homogenous catalysts in the conversion of waste cooking oil to biodiesel [32][33][34]. In 2022, we described a simple synthesis of a series of polycyclic oxanorbornanes containing a guanidine moiety by the cycloaddition/hydrogenation approach [35].…”