US2047780A - Manufacture of lubricating oils - Google Patents

Description

Patented- July 14. 1936 TES" UNITED ST aormso MANUFACTURE OF LUBRICATING oILs Victor Henny, London, England, assignor to Universal Oil Products Gcmpany, Chicago, 111., a corporation of Delaware No Drawing. Application March 5, 1934,

' Seriall No. 714,114

4 Claims. (oi. 196-142) The invention relates more particularly to the manufacture of lubricating oil blends of a special character in relation to oxidizabllity under conditions of service.

In a more specific sense the invention has reference to a process forthemanufacture of compound lubricating oils comprising both straight run and cracked petroleum stocks;

Pioneer experiments to determinethe properties of lubricating oil films between moving surfaces such as, for example, ajournal and its bearing were made under conditions of complete fluid lubrication, with a film of microscopic dimensions so that the principal factors influencing the coeflicient of friction were the viscosity of the oil and its "oiliness, no phenomena involving boundary lubrication being involved. In addition to the fact that extreme conditions of pressure and temperature were seldom used simultaneously, the oil used to flood the bearing was not circulated, that is, a fresh supply of oil was constantly fed. In general the temperatures in the case of journal bearing experiments were held well below that corresponding to any appreciable amount of oxidation of the oil by the air with which it was in contact.

Later investigations involving both the lubrication of internal combustion engines and of exposed shaft bearings have indicated that more effective lubrication, as evidenced by a lower coefficient of friction, is obtained if oxidation of the oil is allowed to take place or is artificially produced, the degree of oxidation corresponding to greatest improvement in lubricating efiiciency varying naturally with the speed and temperature of, and the pressure on, the bearing, the type of oil used and whether it is circulated, and other factors.

Under severe conditions of lubrication corresponding to pressures of about 2000 pounds per square inch of actual bearing arc and temperatures as high as 300 C., it has lately been ob-' served that the coefficient of friction becomes lower and the temperature of seizure becomes higher as lubricants become oxidized, and it has been tentatively assumed that these phenomena the activity of the oxidized portion of the oils upon the metal surfaces. These effects have been observed on various types of lubricants of a mineral, vegetable and animal origin.

In one specific embodiment the present inve tion comprises the manufacture of composite lubricants by blending lubricating fractions made from cracked products, and possessing varying degrees of oxidizability, with straight run petroleum lubricants which are deficient in this property.

In the manufacture of so-called straight run lubricants, crude petroleum is distilled under atmospheric pressure using steam until distillates of appreciable viscosity appear in the overhead, after which a vacuum may be applied and fractions of varying viscosity segregated. These fractions may. be further distilled or reduced to insure a sufiiciently high flash point and they are then commonly treated with moderately strong sulphuric acid to coagulate and precipitate asphaltic colloids and material which is readily polymerized so that the final product is comparatively stable and shows little tendency to deposit gum and carbonize in service. Some viscosity may be lost by the acid treatment but since it is seldom possible to obtain a lubricant having a good color from a sales standpoint without acid treatment, this is seldom dispensed with. Following the acid treatment the sludge is settled either by gravity or by centrifuging and neutralization is effected by the use of finely divided contact clays either alone or mixed with a small amount of lime. The clay treatment also improves color and color stability when properly applied.

The foregoing brief outline of the main steps employed in straight-run lubricant manufacture shows that the final product, owing to the necessity for having a good color for sales purposes, has very little tendency toward oxidation, principally on account of the previous removal of readily reactive and possibly olefinic molecules by the acid. Oils thus'produced in many cases show poor adherence to surfaces which they are called upon to lubricate even though their viscosity and other properties may be correct.

The use of corresponding fractions of lubricants produced from heavy cracked residua in I a straight run lubricants constitutes the principal feature of the present process. Owing to the general character of the cracking reaction which involves loss of hydrogen and the production of unsaturated products, corresponding lubricating fractions of a given viscosity produced from cracked residua will be in general more readily susceptible to oxidation than the fractions of a straight run character. Consequently the blendadaptable to use under a wide range of operating conditions involving different exposure of oxidizingconditions. I

Cracked lubricating stocks to be thus blended with straight run may be produced from cracked residua by the same general steps as those em-' ployed in the manufacture of straight run lubricants as briefly outlined above. The residua may be subjected to vacuum distillation with recover! of cuts of varying viscosity which are then mildly refined to produce fractions of variable oxidize.- bility. The treatment may be made more or less selective in regard to the elimination of asphalt or tar-forming constituents while conserving the less reactive but still oxidizable constituents which do not go of! color or gum rapidly under average storage conditions and still furnish in service oxidizable products of a character capable of producing" improved lubricating effects.

Thus in the manufacture of these cracked blending stocks some minimum amount of sulphuric acid may be employed and treatment may be conducted upon a solution of the residuum in a lightpetroleum distillate which has a minimum.

' solubility for distinctly asphaltic or pitchy substances. After such treatments the sludge may be settled as usual and the stock reduced to flash and viscosity after distilling off the solvent. The

neutralization-step may be effected as before and in respect to a final treating step it may be found advantageous 'to lightly oxidize thestocks to instigate the formation of peroxidic compounds which will facilitate the required degree of oxidation under the conditions to which the oil will be exposed later in service. This step, however, is not of general application and must be used with caution since the tendency toward oxidation of different cracked fractions having appreciable viscosity variesgreatl'y. For the same reason the amounts of cracked lubricating stocks to be mixed with straight run will vary over a considerable range due to their varying tendencies to oxidation.

It is within the scope of the invention to start the manufacture of the oxidizable lubricants with blends of straight run and cracked stocks, which are then subjected simultaneously to regulated sulphuric acid or other treatment and later if found desirable pre-oxidized to a limited extent before being put into service.

In testing lubricating oil blends containing bo straight run and crackedcomponents, use may be made of standard testing equipment consisting of a journal revolving in a bearing lined with a soft metal such as Babbitt metal, means being provided toincrease the temperature of the journal by internal heating to any point which is safe in consideration of the flash of the lubricant. Determinations may be made ofthe coefficient of friction by noting the angle of rest of a suspended pendulum with a given weight, etc., such a set-up conforming to the original type of Thurston lubricant testing machine. In the case of pressure experiments, pressure may be applied by springs or weights so that accurate conditions may maintained.

The efliciency of a lubricant may then be determined by noting the change in the coeflclent of friction with change in temperature and pressure and by noting the "seizure" temperature corresponding to a given load. As the coeflicient of oil obtained from an uncracked hydrocarbon 011.

friction decreases and the seizure temperature increases it may be assumed that'the lubricant is more effective.

It has been found by tests and under service conditions that suitably proportioned blends of straight run and cracked lubricants give extremely low coefiicients of friction and relatively high seizure temperatures and that constant values for these two properties are attained in a much shorter time than with straight run lubricants, l particularly those which have been subjected to extensive reflning to produce a light colored oil and one which is low in carbon content and resistant to sludging.

In one case a highly refined commercial lul bricant when used upon a test bearing was found to show a minimum coeflicient of friction of 0.002 and a seizure temperature of 0., when .the bearing pressure was 1000 pounds per square uum distillation of a cracked residuum, a period 30 of approximately 6 hours of continuous use was suilicient to develop oxidized components which reduced the minimum coeflicient of friction to 0.0012, while the seizure temperature was then as high as 250' c. 3

The foregoing specification has described in detail the character and objects ,of the invention andthe single example is suflicient to show its merits butneither is to be construed in the light of imposing undue limitations uponits generally broad scope.

I claim as my invention:

1. A process for the manufacture of lubricating oils having lower coeflicients of friction and exhibiting more eilicient lubrication, which comprises subjecting the liquid residue produced in a cracking process to the action of an oxidizing agent and reflning the same to produce a 1ubrieating oil, and blending therewith a lubricating 2. A process for the treatment of lubricating oils derived from cracked liquid residues which comprises subjecting the same to the-action of an oxidizing agent, and blending therewith a lubricating oil obtained from an uncracked hydrocarbon oil.

3. A process for improving straight-run petroleum lubricating oil which comprises blending therewith a miidly oxidized lubricating oil derived from the liquid ruidue. of hydrocarbon oil 00 cracking.

4. A lubricant comprising a blend of sil'aigntrlm petroleum lubricating oil and a mildly oxidised lubricating oil derived from the liquid residueofhydroca'rbonoilcraeking.

CI-03m.