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Lipase-catalyzed esterification and transesterification reactions of selected phenolic acids with lipids were investigated in organic solvent media. The esterification of linoleyl alcohol with dihydrocaffeic acid (DHA) in neat hexane medium resulted in highest esterification yield (EY) of 17% when a Candida antarctica lipase (Novozym 435) was used to catalyze the reaction. The use of co-solvents t-butanol and 2-butanone with hexane resulted in a dramatic increase in EY. The highest EY of 83% was obtained in hexane:2-butanone mixture of 85:15 (v/v) using Novozym 435; however lower EY (40%) was obtained when a lipase from Rhizomucor meihei (Lipozyme IM 20) was used. Increasing the amount of the co-solvent 2-butanone in the hexane:2-butanone mixture to 75:25 (v/v) resulted in a lower EY of 75% with Novozym 435; using the same enzyme, the esterification of a more unsaturated alcohol, linolenyl alcohol, with DHCA in the hexane:2-butanone mixture of 75:25 (v/v) resulted in EY of 76% which was similar to that obtained with linoleyl alcohol as lipid substrate. The esterification of DHCA and ferulic acid with linolenyl alcohol in the hexane:2-butanone mixture of 65:35 (v/v) resulted in an EY of 58 and 16%, respectively. Both linoleyl and linolenyl alcohols demonstrated mass action effects with EY of 99% in DHCA: fatty alcohol ratio of 1:8. Using a molar ratio of 1:2, the transesterification reactions of DHCA with trilinolein (TLA) and trilinolenin (TLNA) in hexane:2-butanone mixture of 75:25 (v/v) resulted in total transesterification yields (TYs) of phenolic lipids of 66 and 62%, respectively. The TYs of phenolic monoacylglycerols was higher than that of phenolic diacylglycerols for both TLA and TLNA transesterification reactions. A lower molar ratio of DHCA to TLA of 1:4 resulted in a lower TY of 53%. Using a molar ratio of 1:2, the TY of TLA and TLNA with ferulic acid in hexane:2-butanone mixture of 65:35 (v/v) was 16 and 14%, respectively. An equal molar transesterification reaction of DHCA with flaxseed oil, in a hexane:2-butanone mixture of 75:25 (v/v), resulted in the production of only phenolic monoacylglycerols (19%); however, decreasing the molar ratio resulted in the production of both phenolic mono and diacylglycerols. A molar ratio of DHCA to flaxseed oil (1:8) resulted in a TY of 76%, with 43 and 33% phenolic mono and diacylglycerols, respectively. Changing the solvent mixture of hexane:2-butanone from 65:35 to 85:15 (v/v) resulted in an increased in the TY of phenolic diacylglycerols from 24 to 55% with no significant effect on the TY of phenolic monoacylglycerols. The transesterification reaction resulted in a change in the composition of the C18:3 FA from 53% in the unmodified oil to 60 and 65% in the phenolic mono and diacylglycerols. Transesterification reaction of DHCA with fish liver oil in the solvent mixtures of hexane:2-butanone of 75:25 and 85:15 (v/v) resulted in TY of 56 and 65%, respectively. Transesterification in solvent: mixture of 75:25 resulted in a 40 and 16% TY of phenolic mono and diacylglycerols, respectively, whereas that in the solvent mixture of 85:15 (v/v) resulted in a 38 and 37% TY of phenolic mono and diacylglycerols, respectively. The structures of phenolic lipids of linoleyl and linolenyl alcohols with DHCA were confirmed by LC/MS analysis likewise for the phenolic mono and diacylglycerols from transesterification of DHCA with TLA and TLNA as well as flaxseed and fish liver oils. The phenolic esters of the fatty alcohols demonstrated radical scavenging properties similar to that of alpha-tocopherol but less than for DHCA; however, the phenolic lipids obtained with the use of TLA and TLNA as substrate as well as flaxseed and fish liver oil, demonstrated significant radical scavenging effects but less than that of alpha-tocopherol and DHCA.

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This study is focused on the analysis of transformer oil commonly used in South African transformers and the characterisation of the blends of these oils with either synthetic antioxidants or those extracted from natural sources. The virgin naphthenic based uninhibited transformer oil was shown to have no acidic or saponifiable constituents. Although the oil used in this study is naphthenic based it was found to contain bicyclic compounds identified as tetralin (aromatic) and decalin by GC-MS. The oils were void of typical wear metals and only additive metals/non-metals were present. The blending of transformer oils with synthetic antioxidants was successful as confirmed by ¹H NMR, ¹³C NMR and FT-IR data. The blending showed increased antioxidant activity of the oils as well as thermal stabilities (DPPH assay and TGA respectively). Apparent activation energy for the decomposition reaction was determined by means of the Ozawa, Flynn and Wall (OFW) and Kissinger models. The apparent activation energy for BHT-B, DBP-B and VO were found to be 57.0, 63.7 and 69.3 kJ molˉ¹ , respectively for 10% mass conversion obtained from TGA data (OFW model). The dissipation factor for the oil blends was established to be favourably lower than that of unblended oils; however an undesirable decrease in the dielectric breakdown voltage of the blends was observed (16, 26 and 50 kV for BHT-B, DBP-B and VO respectively). The blending of transformer oil with synthetic antioxidants is a common practice, however greener approaches are always favoured. In this study, a greener approach was employed by blending the transformer oil with turmeric plant extract in an effort to improve the oil’s performance. Turmeric is known for its antimicrobial, antioxidant and anticarcinogenic properties. Solvent extraction of turmeric powder and subsequent blending into transformer oils, revealed the dissolution of 5 components from turmeric into the oil, viz., curcumene, sesquiphellandrene, ar-turmerone, α-turmerone and β-turmerone (curlone). In this work, we analysed novel turmeric-oil blends in terms of oxidation and thermal stability in comparison to that of virgin transformer oil. The DPPH assay confirmed that addition of these blends into the oil increased its ability to scavenge the free radical DPPH. Thermogravimetric analysis showed an increase in thermal stability when compared to that of virgin unblended oil. Evidently blending of synthetic antioxidants/turmeric extract has potential to enhance the performance and increase the life-span of transformer oils. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2012.

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No description available.

In this work, a rapid Fourier transform near infrared (FT-NIR) spectroscopic peroxide value (PV) method was developed and a prototype Continuous Oil Analysis and Treatment (COAT) system was assessed for monitoring and analytical purposes. High erucic acid rapeseed oil, a principle representative of triglyceride based oils suitable for biodegradable lubricating applications and mineral oil were used to test the methodology developed. / The FT-NIR PV method is based on a well defined stoichiometric reaction of triphenylphospine (TPP) with hydroperoxides to form triphenylphospine oxide (TPPO). A partial least squares calibration model for the prediction of PV was developed using the NIR spectral region where TPP and TPPO co-absorb. The resulting calibration was highly linear over the analytical range of 100PV. Validation of the method carried out by comparing the PV of PLS prediction to the results of AOCS iodometric procedures indicated an excellent concurrence between the two methods. By programming the FT-NIR spectrometer, the analytical procedure simply consists of the addition of TPP stock solution to oil sample, mixing, taking its spectrum and predicting PV value. Through selected testing procedures, the prototype COAT system utilizing FTIR spectroscopy, advanced sample handling system designs, and computer programming was proved to be effective in monitoring the oil quality and behavior of antioxidants in real time. / Both approaches offer combined advantages of speed, accuracy, low labor cost, automation, and environmental friendliness mainly derived from FTIR spectroscopy, and can serve as convenient means for routine quality control applications in oils and fats industry. Potential application based on the joint usage of the two methods in the obtaining of true value of oil stability was also presented in this text. (Abstract shortened by UMI.)

The application of Fourier transform infrared (FTIR) spectroscopy in the assessment of oil quality and stability and the determination of the degree and type (cis or trans) of unsaturation of fats and oils was investigated. FTIR spectroscopy was shown to provide a rapid means of monitoring changes in oils undergoing oxidation or subjected to thermal stress. Absorption bands associated with common primary and secondary oxidation products were identified by relating them to those of spectroscopically representative reference compounds, and a quantitative approach based on the use of oils spiked with these reference compounds as calibration standards was proposed. A sample-handling accessory based on a heated 25-mum transmission flow cell and heated input and output lines was developed to facilitate the rapid analysis of oils and premelted fats in their neat form. Using this system, an FTIR edible oil analysis package was developed to simultaneously analyze for trans content, cis content, iodine value (IV), and saponification number (SN) of neat fats and oils, using partial-least-squares (PLS) calibrations based on pure triglycerides. An automated transmission-based peak height method for isolated trans isomer determination using the characteristic trans absorption band at 967 cm -1 in the spectrum of a neat fat or oil, ratioed against the spectrum of a trans-free oil, was also developed. A subsequent validation study involving the analysis of more than 100 oil samples demonstrated concurrence between the trans data obtained by the PLS and peak height FTIR methods as well as between IV results obtained by FTIR analysis and gas chromatography. In addition, the internal consistency of the IV, cis, and trans FTIR predictions provided strong experimental evidence that the FTIR edible oil analysis package measures all three parameters accurately. A PLS-based IV/trans method was developed for a heated single-bounce horizontal attenuated total reflectance (SB-HATR) sample-

Three new quantitative Fourier transform infrared (FTIR) spectroscopic methods were developed to measure key lubricant condition monitoring parameters; total acid number (TAN), total base number (TBN), and moisture (H2O). All methods employ a common sample-handling accessory and are based on the addition of specific reagents designed to react stoichiometrically with target species in oils, with quantification being carried out using differential FTIR spectroscopy. The combined use of a stoichiometric reaction and differential spectroscopy overcomes the need for a reference oil, which has traditionally hindered quantitative analysis of lubricants by FTIR spectroscopy. Potassium hydroxide, trifluoroacetic acid (TFA) and 2,2-dimethoxypropane (DMP) were the stoichiometric reagents used to develop the FTIR TAN, TBN and H2 O methods, respectively. Calibrations were developed using either peak height measurements or partial least squares (PLS) regression and the methods were validated using standard addition techniques, as the ASTM (American Society of Testing and Materials) standard methods were not sufficiently reproducible to make valid comparisons. Validation of the methods indicated that the TAN, TBN and H2O methods had accuracies of +/-0.095 mg KOH/g, +/-0.5 mg KOH/g and +/-32ppm respectively and corresponding reproducibilities of +/-0.05 mg KOH/g, +/-0.17 mg KOH/g and +/-22 ppm. The TAN, TBN and H2O methods were implemented on a Continuous Oil Analysis and Treatment (COATRTM) System, integrating instrumentation, software and sample handling so as to provide packaged, user and environmentally friendly analytical methods that are alternatives to conventional ASTM wet chemical methods.

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