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Appl. Sci. 2017, 7(4), 396; doi:10.3390/app7040396

Oxidation Products of Ester-Based Oils with and without Antioxidants Identified by Stable Isotope Labelling and Mass Spectrometry

1
AC2T Research GmbH, Viktor-Kaplan-Straße 2C, 2700 Wiener Neustadt, Austria
2
Institute of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9, 1060 Vienna, Austria
*
Author to whom correspondence should be addressed.
Academic Editor: Jun Kubota
Received: 2 March 2017 / Revised: 3 April 2017 / Accepted: 10 April 2017 / Published: 16 April 2017
(This article belongs to the Special Issue Lubricant Additives)
View Full-Text   |   Download PDF [3711 KB, uploaded 16 April 2017]   |  

Abstract

As lubricants with a high thermo-oxidative stability such as synthetic esters are gaining more importance in the lubricant market, a detailed knowledge regarding their oxidative degradation behaviour is of high importance. In order to reveal their degradation products and processes, a novel approach combining artificial alteration, isotope labelling based on oxidation with 16O2 and 18O2, and mass spectrometry (MS), was applied to a bis(2-ethylhexyl) adipate base oil. The degradation products such as 2-ethylhexanol and its monoesters with short-chain fatty acids pinpointed the C–O ester bond as the site prone to oxidative attack, allowing the collection of information about the oxidation mechanisms. Furthermore, the influence of the antioxidant (AO) 4,4′-methylene-bis(2,6-di-tert-butylphenol) as an additive on the oxidation behaviour and resulting products was studied: blends containing AO showed a remarkably higher resistance against oxidation. However, similar degradation products were obtained after AO depletion and without AO. AO cleavage occurred at the carbon atom that bridges the phenols to give 2,6-di-tert-butyl-p-benzoquinone and 3,5-di-tert-butyl-4-hydroxybenzoic acid. By applying the isotope labelling approach, sites of preferential oxidative cleavage and hence differentiation of the origin of oxygen atoms—either from the atmosphere or from base oil components—can be unambiguously related in oxygen-containing base oils, as well as in blends with additives. View Full-Text
Keywords: oxidation; synthetic lubricant; ester base oil; antioxidant; thermo-oxidative stability; isotope labelling; mass spectrometry; degradation processes; lubricant chemistry; additive oxidation; synthetic lubricant; ester base oil; antioxidant; thermo-oxidative stability; isotope labelling; mass spectrometry; degradation processes; lubricant chemistry; additive
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Frauscher, M.; Besser, C.; Allmaier, G.; Dörr, N. Oxidation Products of Ester-Based Oils with and without Antioxidants Identified by Stable Isotope Labelling and Mass Spectrometry. Appl. Sci. 2017, 7, 396.

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