Studies on the oxidation of mineral lubricating oils

Beaton, John (1962) Studies on the oxidation of mineral lubricating oils. PhD thesis, University of Glasgow.

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The work carried out under this research programme was primarily concerned with the effect of the composition of a lubricating oil fraction on its oxidation behaviour, Before commencement of this work, however, it was first of all necessary to device a method for the determination of resins and to modify methods for the determination of molecular weight and oxygen content. The method used to determine the amount of resins produced on oxidation wart their selective adsorption on Fullers Earth, the adsorption process being carried out in a petroleum ether solvent. It has been shown that this method can accurately determine the quantity of oxidised pro ducts remaining in an oil after oxidation and that the treatment does not affect the unoxidised part of the oil In so far as its average structural composition is concerned. Molecular weight was determined by an ebullioscopic method involving the use of a thermistor sensing element. A modification was made in the condensing system of the apparatus. A removable cold finger condenser was replaced by a permanently fixed Leibig type condenser which has boon shown to give more accurate results. Modifications were made to the Unterzaucher oxygen determination apparatus and method and were concerned with the temperature used, the flow rate of nitrogen and the time of analysis. The modified technique is satisfactory for use with oxidised oils. It has been shown that the differences between oxidation behaviour of oils of different composition are principally ones of degree rather than of kind, the amount of total sludge, for instance, being a function of the aromatic content of the original oil. The total acidity Produced on oxidation was found to be a function of the sludging tendency of the oil while the acidity of the nonsludging part of the oil was found to be a function of the paraffinic content of the original unoxidised oil. The amount of deterioration of the lubricant and the effect of the oxidised materials on its properties was found to be related to the aromatic content of the original oil. Under normal I.P. oxidation test conditions, the amount of material removed on oxidation and treatment with Fullers Earth was found to be fairly evenly spread over the various hydrocarbon types in the oil, with a slight tendency for the aromatics to be preferentially attacked. This effect was found to ho emphasised with oils of higher aromaticity. A stirring method of oxidation was devised which accelerated oxidation and under those conditions it was found that oxidation was more widely spread over the various structural types, with the tendency for preforential attack on aromatics much lessened. A considerable amount of evidence has been obtained indicating that the oxidative deterioration of the lubricants followed the pattern of: hydrocarbons -> resins -> oil soluble sludge oil insoluble sludge. The extent to which this sequence of reactions is carried wan found to be dependent upon the aromatic content of the original oils. Oils low in aromatics form only resins while oils high in aromatics form all the reaction products through to oil insoluble sludge. Some evidence has been obtained indicating that the acidity of the oil insoluble sludge is related to its insolubility and it is suggested that this in due to the formation of hydroxy acids, produced by oxidation of aromatics present in the oil soluble sludge, which are known to be insoluble in petroleum oils.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: William Gibb
Keywords: Chemical engineering
Date of Award: 1962
Depositing User: Enlighten Team
Unique ID: glathesis:1962-72449
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 24 May 2019 15:12
Last Modified: 24 May 2019 15:12

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