Generation of Methanol and Ethanol from Inhibited Mineral Oil

Transcription

1 Generation of Methanol and Ethanol from Inhibited Mineral Oil Presenter: Shanika Matharage 1 Date: May 20 Authors: S. Y. Matharage 1, Q. Liu 1, Z.D. Wang 1, G. Wilson 2, P. Dyer 3 and P. Mavrommatis 4 1 The University of Manchester, Manchester, M13 9PL, UK 2 National Grid, Warwick, CV34 6DA, UK 3 UK Power Networks, Crawley, RH10 0FL, UK 4 TJ/H2b Analytical Services Ltd, Bromborough, CH62 4SU, UK

2 Content 2

3 Paper Ageing Indicators in Oil Also generated from oil oxidation CO 2 affected by air ingress Carbon oxides Methanol Paper Ageing Indicators Generated from cellulose Increased linearly with paper ageing Related to normal paper ageing Also generated from 2-Furfural components other than cellulose (hemicellulose, levoglucosan) Suitable at the later stage of paper ageing Ethanol Generated from levoglucosan Related to abnormal paper ageing (abnormally high temperatures) 3

4 Methanol to Indicate Early Stage of Paper Ageing Figure shows the variation of methanol and 2-FAL in a mineral oil and a gas-to-liquid oil against the DP of paper. Laboratory ageing experiments were conducted at 80, 100 and 120 C. Methanol in oil was higher than 2-FAL until the DP reduces below 400. Result shows that methanol is better than 2-FAL to indicate early stage of paper ageing. MeOH>2-FAL 2-FAL>MeOH Variation of methanol and 2-FAL against the DP of paper 4 S. Y. Matharage, Q. Liu, and Z. D. Wang, "Ageing Assessment of Kraft Paper Insulation through Methanol in Oil Measurement," IEEE Transactions on Dielectrics and Electrical Insulation, vol. 23, pp , June 2016.

5 Ethanol to Indicate Abnormal Paper Ageing Ethanol was largely generated from the ageing of levoglucosan, which is a pyrolysis by-product of paper ageing. Therefore, it was suggested to use ethanol to indicate abnormal paper ageing. Case Study Abnormal paper ageing due to arcing was found during post-mortem analysis of a distribution transformer that had high amount of ethanol than methanol. Concentration of the chemical indicators and the DP of paper MeOH (ppm) EtOH (ppm) 2-FAL Winding DP Lead <DL * DL=detection limit (a) Paper samples obtained from windings (b) Damaged paper insulation 5 E. Rodriguez-Celis, J. Jalbert, S. Duchesne, B. Noirhomme, M. C. Lessard, and M. Ryadi, "Chemical markers use for the diagnosis and life estimation of power transformers: a preliminary study of their origins," presented at the CIGRE Canada Conference, Montreal, Quebec, 2012.

6 Methanol & Ethanol Generation from Oil Methanol and ethanol measurements obtained from oil-only and oil-paper ageing experiments conducted with an inhibited mineral oil and kraft paper at 120 C under sealed conditions were compared. Methanol measured at the end of the oil-only ageing experiments was less than 10% of that measured during the oil-paper ageing experiment. Ethanol measured at the end of the oil-only ageing experiments was more than twice of that measured during oil-paper ageing experiments. (a) Oil-only> oil-paper (b) Oil-paper> oil only Variation of (a) methanol and (b) ethanol during oil-only and oil-paper ageing experiment 6 S. Y. Matharage, Q. Liu, and Z. D. Wang, "Ageing Assessment of Kraft Paper Insulation through Methanol in Oil Measurement," IEEE Transactions on Dielectrics and Electrical Insulation, vol. 23, pp , June 2016.

7 Gas Chromatography/ Mass Spectrometry Unit Auto sampler unit (CTC Combi Pal) Headspace vials Gas tight syringe with heater 1 Heater with the agitation unit GC unit (Varian CP 3800) with 60 m VF-624ms column 2 3 MS unit (Varian Saturn 2200) 7

8 Identification of Methanol & Ethanol Total Ion Chromatogram is used to identify the retention time of methanol and ethanol. Mass spectra of the peaks are compared with a library of mass spectra to identify the peaks of methanol and ethanol. m/z=31 Background Measurement Technique Experiments m/z=31 Total ion count Each peak represents a compound 8 Retention time (minutes) Relationship between Total ion chromatogram and mass spectra

9 Quantification of Methanol and Ethanol Calibration curves obtained from the samples prepared with known concentration of methanol and ethanol in oil are used for the quantification. Polar by-products in aged oil may create bonds with methanol and ethanol reducing their volatility in aged oil than in new oil Therefore, measuring the chemical indicators in aged oil using the calibration curves prepared with new oil may create errors. More MeOH MeOH New oil MeOH from new oil > oil MeOH from aged Disadvantage of the external standard calibration method Less MeOH Acids MeOH Alcohols water Aged oil 9

10 Internal Standard Calibration A chemical compound that behaves similarly to the chemical indicators and not generated in oil is injected into both calibration samples and the samples are to be subsequently measured. Peak height ratio between the chemical indicators and the internal standard is then used to obtain the calibration curves (called as internal standard calibration method). Following literatures ethanol d-6 was selected as the internal standard compound. More MeOH More Ethanol d-6 MeOH Ethanol d-6 New oil New oil MeOH Ethanol d-6 Less MeOH Aged oil Less Ethanol d-6 = MeOH Ethanol d-6 Acids water Ethanol d-6 MeOH Alcohols Aged oil Overcoming the disadvantage with an internal standard 10

11 Quantification of Methanol and Ethanol Peak height ratio between the chemical indicators and the internal standard is used to obtain the calibration curves. Calibration curves for methanol and ethanol 11

12 Effect of Temperature on Methanol Generation Ageing experiment was conducted with a naphthenic type high grade inhibited mineral oil. 80 g of oil samples were aged inside 100 ml sealed glass bottles at different temperatures including 110, 120 and 130 C. The initial rate of production of methanol increased with the temperature. However, Methanol showed a levelling off at the later stage of the ageing, which could be due to the lack of oxygen in the system. 12 Variation of methanol in oil at different temperatures Variation of acidity in oil at different temperatures

13 Ageing Experiments with an Intermittent Air Supply A laboratory ageing experiment was conducted with an intermittent air supply to increase the rate of oxidation of oil without losing the volatile compounds. Ageing experiment was conducted at 130 C for up to 154 days. Once every two weeks the samples were taken out from the oven and cooled down for three hours before leaving the caps open for one minute to add fresh air into the bottles. Oil type Details of the ageing experiment Temperature ( C ) Sampling interval (Days) Naphthenic type high grade inhibited mineral oil , 28, 42, 56, 70, 84, 98, 126, Variation of acidity in oil

14 Variation of Methanol and Ethanol in Oil Against Acidity Methanol in oil reached a peak of 0.98 mg/kg and reduced down to 0.51 mg/kg at the end of the experiment. Ethanol in oil increased with ageing and reached a peak of 2.14 mg/kg at 126 days of ageing Results indicate the possibility of two reactions contributing to the concentration of alcohols in oil; one generates the alcohols from oil while the other consumes them. 14 Variation of methanol in oil Variation of ethanol in oil

15 Variation of Methanol and Ethanol in Oil Against Acidity Three different stages can be identified: 1. (Low acidity values): Alcohols are generated from oil (oxidation) 2. (Moderate to high acidity values): Some of the alcohols generated react with the acids (esterification) resulting in a level-off or a reduction in the rate of increase. 3. (Very high acidity values): Consumption starts to dominate the generation resulting in a reduction of the alcohols in oil Variation of methanol against acidity in oil Variation of ethanol against acidity in oil

16 Conclusions Inhibited mineral oils investigated in this work generate methanol and ethanol during their ageing process. Generations of methanol and ethanol from oil are affected by different factors such as temperature, the amount of air in the system. Under similar ageing conditions the amount of ethanol generation from oil is higher than the amount of methanol generation from oil. Alcohol generation from the oils can be categorised into three stages 1. At low acidity values alcohols are generated from oil through oil oxidation. 2. At moderate to high acidity values the esterification process starts to consume the alcohols resulting in a level-off or a reduction in the rate of increase of the alcohols. 3. At very high acidity values the consumption process dominates the generation process resulting in a reduction of alcohols in oil. 16

17 Generation of Methanol and Ethanol from Inhibited Mineral Oil Presented by: Shanika Matharage School of Electrical & Electronic Engineering The University of Manchester. Linkedin:uk.linkedin.com/in/shanikamatharage