Design and preliminary results of an NMR tube reactor to study the oxidative degradation of fatty acid methyl ester

• Published in: Biomass & bioenergy Vol. 47; pp. 188 - 194
• Main Authors: Chuck, Christopher J., Jenkins, Rhodri W., Bannister, Chris D., Han, Lu, Lowe, John P.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.12.2012; Elsevier
• Subjects: Aldehydes; Alternative fuels. Production and utilization; Applied sciences; Biodiesel; Degradation; Energy; Esters; Ethyl alcohol; Exact sciences and technology; FAME; Fuels; Microorganisms; Miscellaneous; NMR; Nuclear magnetic resonance; Oxidation; Tubes; Degradation; NMR; Oxidation; FAME; Biodiesel; Instrumentation; Biofuel; NMR spectrometry; Design; Hydrogen 1; Oxidative degradation; Reactor; Fatty acid methyl ester; Degradation product
• ISSN: 0961-9534; 1873-2909
• DOI: 10.1016/j.biombioe.2012.09.043

Biodiesel is the fatty acid alkyl esters produced by the transesterification of vegetable, animal or microbial lipids. After ethanol, it accounts for the largest proportion of global biofuel production. Yet, due to the level of polyunsaturation, biodiesel is also oxidatively unstable. When biodiesel oxidises the viscosity increases, which leads to reduced fuel performance and in extreme cases can lead to engine failure. To aid in understanding the process of this degradation a specialist NMR tube rig was designed to assess the oxidation of biodiesel. The NMR tube rig allowed the in situ1H NMR measurement of the sample while air was bubbled through at fixed intervals. The methyl esters of linolenic acid (18:3), linoleic acid (18:2) and oleic acid (18:1) were oxidised at 110 °C over a 24 h period. The decomposition of biodiesel is complex, and there is more than one mechanism involved in the degradation. Using this rig the onset of oxidation for 18:3 and 18:2 was found to be almost instantaneous. The rate of oxidation was found to be slightly less for 18:2 than 18:3 while the maximum rate was observed for 18:3 from the beginning of the oxidation, this was only observed after 280 min for 18:2. The oxidation of 18:1 started at approximately 500 min and, slowly degraded during the remaining reaction time. The formation of a number of secondary oxidation products such as aldehydes, ketones, alcohols and formates were also quantified. ► A specialist NMR rig was designed to measure the oxidation of FAME in situ. ► Oxidation of 18:1, 18:2 and 18:3 was observed over 24 h at 110 °C. ► The maximum rate was found at the start of the reaction for 18:3. ► The rate was highest for 18:2 after 300 min but never reached a maximum for 18:1.