US2370228A - Method of treating lubricating oils - Google Patents

Description

Patented Feb. 27, 1945 METHOD OF TREATING LUBRICATING Johannes H. Bruun and Mildred M. Hicks-Bmun, I Swarthmore. Pa., asslgnors to Sun 011 Company, Philadelphia, Pa.

, a corporation of New Jersey I No Drawing. Application April 1, 1942,

Serial No. 437,164

4 Claims. (6K. 196-142) The invention relates to the treatment of lubricating oils in order to improve the quality thereof.

Among the many processe which have been suggested and used for improving lubricating oils are hydrogenation and controlled partial oxidation of the oil. It is well known that either hydrogenation or controlled partial oxidation of lubricating oils will impart to the oil, thus treated, improved properties in certain desired characteristics of the oil. This improvement in the quality of the oil is most clearly reflected in the im-' provement or increase in its viscosity index, although other properties and characteristics are simultaneously improved.

We have discovered that if an oil is first partially oxidized and the partially oxidized oil then hydrogenated until all the oxidized products are converted to neutral hydrocarbons, the viscosity index of the oil is improved to a much greater extent than is the case when either hydrogenation or oxidation is employed alone. We have also discovered that certain less desirable properties and characteristics which are imparted to lubricating oils which are treated by either hydrogenation or oxidation alone are not imparted to the oil when the two processes are combined in accordance with our invention.

While our improved process is applicable to and results in substantial improvement in qual- :lty of all types of mineral oils, a particularl remarkable improvement, distinct in character as well as greater in degree, is brought about in naphthenic base oils. Oils which are extremely naphthenic in character, when treated in accordance with the present invention, produce oils having characteristics closely approaching those of the best grade of parafiinic base oils. The

l amount of improvement in the quality of naphthenic base oil that can be efiected by meanaof our improved process increases as thhaphthenic content of the oil increases. The discovery that the process is particularly adapted to the treatment of naphthenio base oils-that it does not merely improve the oil but imparts thereto qualities closely approximating those possessed by the best grade of paraffinic base oilsis deemed by us to be specifically novel and patentable. We have therefore specifically described the use of the process in connection with the treatment of such oils. However, since oils of the para'flimc type can be subjected to similar treatment with resultant less marked improvement, the invention, in its broader aspect, is not limited to the treatment of naphthenic base oils; 7

Briefly stated, our invention, as applied to naphthenic base oils, comprises, first oxidizing a mineral oil until the oil has a saponification number of from 8 to 12, say about 10. Any desired method of oxidation may be employed, but we prefer to so control the oxidation that the ratio of saponification number and acid number in oil being oxidized is maintained at from (say) 2:1 to 3:2. During the course of oxidation a portion of the oil is converted into esters, acids, alcohol, aldehydes, ketones and similar products of oxidation and a considerable increase in the viscosity of the oil is effected, without, however, any effect on the molecular weight of the oil. The partially oxidized oil is then hydrogenated and the partial oxidation products therein, esters, acids, alcohol, aldehydes, ketones, and similar products formed by the oxidation reaction and any unsaturated compounds present therein are converted into hydrocarbons. This hydrogenation may be eifected in any desired or known manner. Hydrogenation is continued until the products of oxidation in the oil have been converted substantially completely into neutral hydrocarbons, as will be evidenced by the oil obtaming a saponification number of zero. This hydrogenation results in a material decrease in the viscosity of the oil, the viscosity of the hydrogenated oil being at least as low as that of the oil charged to the process, and also in a slight decrease in the apparent molecular weight of the oil.

In the case of an oil having decided naphthenic properties, the finished product of oxidation followed by hydrogenation will have a lower vis cosity than the oil charged to the process. This is an advantageous change, however, since one objection to naphthenic oils is that they have a lower boiling range than parafiinic oils of i the same viscosity. Therefore, as a result of the change in viscosity effected in naphthenic oils treated in accordance with our invention,.we are able to produce from naphthenic oils improved lubricating oils having a boiling range approximating that of paramnic oils of the same viscosity. Even more remarkable is the improvement in the viscosity index of an oil.

The exact nature of all the various reactions which take place in an oil treated in accordance with an invention is not fully understood. However, the following probable explanation is oiiered as an aid to a better understanding of our invention, it being understood, however, that we do not wish to be limited thereby. It appears that the oxidation causes some breakdown, particularly in the compounds presentin the oil. which impart to it a'low viscosity index. The subsequent hydrogenation of the oil converts the partial oxidation products of these low viscosity index constituents back into hydrocarbons which, however, have a substantially better viscosity .in-.

dex than the compounds from which they were;

passing air therethrough at a pressure of 145 pounds per square inch and at a'rate of 0.17 literof air per minute per kilogram of oil. At the end 01"8 hours, the oil had the properties listed below in Column B of the table. The partially oxidized oil was then hydrogenated by shaking in an autoclave in the presence of Raney nickel catalyst under an initial pressure of 2,000 pounds per square inch but which gradually dropped to 1,800 pounds per square inch during the hydrogenating period'of 10 hours and at a temperature of 300 C. The product obtained by hydrogenation of the partially oxidized oil was found to have the properties listed below in Column C of the table.

Table I A B C D Naph- Same oil g fifi 011A tained after hym by hydrogencharged gs drogenating 9 ating only process tion on B 0 9.2 0 0 0 5.9 0 0 Hydroxyi No 0 4 0 0 Carbonyl No. 0 l2 0 0 Iodine No..... 6.6 15.9 0 0 Reiractive index "0 l. 5094 l. 5099 M 1. 4826 l. 4879 Viscosity at 100F. centistokes 49. G9 00. 150 30. 153 47. D18 Viscosity at 210 F. centistokes 5. l6 6. 04 4. 58 5. 53 Viscosity index 31. 80 13. 9 53 34 Calculated molecular weight 341 351 330 346 It is, therefore, apparent that the oil had been substantially improved by increasing its viscosity index from -31.8 to +53. This increase in viscosity index was accompanied, asnoted above, by a decrease in the viscosity of the oil and also by a decrease in the apparent molecular weight of the oil, the molecular weight of the charging stock having been calculated as being 341, while the calculated molecular weight of the product was 330.

while ior the p 'p se l fully disclosing our invention, particular methods of oxidation and"- hydrogenation have been described above, it is to be understood that the invention is not to be limited to these particular methods or to the precise degree of partialoxidation that is specified as giving the best results. The amount of oxidation to be eifected prior, to hydrogenation will vary somewhat with the character of the oil being treated. The more naphthenic the character of the oil being treated, the greater is the amount of oxidation necessary in order to effect improvement in quality of the oii'on'subsequent hydrogenation thereof. Thus. a highly naphthenic oil .swshould be oxidized until it has a saponiflcation number-oi about 10 and an acid number or about 5 in order that subsequent hydrogenation of this oil may effect the maximum improvement in the viscosity index of the oil, while the maximum improvement in the viscosity of a highly paraffinic oil may be efiected if the oil is oxidized until it has a saponiiication number of about 3. It

shouldbe noted, however, that somewhat more oxidation of an oil'than is necessary to bring about the maximum improvement in the viscosity index of the oil on subsequent hydrogenation does not appear to adversely affect the oil but such excessive partial oxidation is merely economically undesirable. Thus, we have oxidized highlyparaiilnic oils until they had a saponification number of about 10 and then hydrogenated such partially oxidized oil and have obtained a product having substantially the same viscosity index as did the product produced from this same parafhnic base oil when the oil was oxidized only until it had a saponification number of about 3 and then hydrogenated. It is, therefore, apparent that with parafllnic base oils somewhat less oxidation may be used than with naphthenic base oils in order to obtain the maximum improvement in viscosity index. It is also apparent that slightly more oxidation than is absolutely necessary appears to exercise no detrimental eifects on the finished product. However, greater oxidation than is necessary n'ecessitates more hydrogenation than is necessary, and thereiore, increases the cost of treating the oil. It is, therefore, desirable to test each oil in order to determine the minimum amount of oxidation necessary to eiiect the desired improvement in the viscosity index of the oil on such hydrogenation.

Among the advantages of our invention over presently known methods of treating and improving lubricating oiis are the following:

There is practically no loss of oil treated in accordance with our process. Unlike many extraction. processes currently employed for improving naphthenic base oils in which a material amount of the oil charged to the process is removed as an undesirable and low priced naphthenic extract, in the present process the undesirable constituents are converted into desirable and improved constituents of the finished oil and, therefore, are not lost. The improved flnished product which is obtained from our process is substantially equal in amount to the oil charged thereto. It should also be noted that oils produced in accordance with our process do not have imparted thereto certain less desirable characteristics which are frequently imparted to oils treated in accordance with other processes.

What we claim and desire to protect by Letters Patent is:

1. A method of improving the quality of lubricating oil which consists of subjecting a lubricating oil stock characterizedby relatively low a free-oxygen containing gas for so limited a time as to convert a minor but substantial proportion of the oil to products of oxidation and hydrogenating the mixture of oil and oxidation products to convert substantially all oxygenated material therein to hydrocarbons and produce a substantially neutral hydrocarbon oil characterized by relatively high viscosity index.

2. The method defined in claim 1 in which the starting lubricating oil stock is a naphthenic base lubricating oil. to thereby produce a resultant oil product having a viscosity-boiling range relationship comparable to that of parafllnic base 0 3. A method of improving the quality of lubrieating oil which consists of subjecting a lubricating oil stock characterized by relatively low viscosity index to oxidation by treating it with a free-oxygen containing gas for so limited a time as to efiect only such partial conversion of the oil toproducts of oxidation that the oxidation oil saponification number will be between 3 and 12 and hydrogenating the mixture of oil and oxidation products to convert substantially all oxygenated material therein to hydrocarbons and produce a substantially neutral hydrocarbon oil characterized by relatively high viscosity index.

4. A method of improving the quality of naphthenic base lubricating oil which consists of subjecting a. naphthenic base lubricating oil stock to oxidation by treating it with a free-oxygen 'containing gas for so limited a time as to eflect only such partial conversion of the oil to products of oxidation that the oxidation oil saponification number will-be between 8 and 12 and. hy-

-dr0genating the mixture of oil and oxidation products to convert substantially all oxygenated material therein to hydrocarbons and produce a resultant oil product having a viscosity-boiling range relationship comparable to that of Dar-- afiinic base oil.

J OHANNES H. BRUUN. MILDRED M. HICKS-BRUUN.