US3367869A

US3367869A - Alkaline lubricating oil

Info

Publication number: US3367869A
Application number: US554700A
Authority: US
Inventors: Silver Howard Bernard; Dennison Alan Charles
Original assignee: BP PLC
Current assignee: BP PLC
Priority date: 1965-06-18
Filing date: 1966-06-02
Publication date: 1968-02-06
Anticipated expiration: 1985-02-06
Also published as: NO120154B; CH481209A; SE339967B; GB1142195A; DE1594355A1; NL6608326A; BE682705A; AT270033B; ES328225A1

Description

United States Patent 3,367,859 ALKALINE LUBRICATING OIL Howard Bernard Silver, Esher, Surrey, and Alan Charles Dennison, Twickeuham, England, assignors to The British Petroleum Company Limited, London, England, a corporation of Great Britain No Drawing. Filed June 2, 1966, Ser. No. 554,700 Claims priority, application Great Britain, June 18, 1965, 25,847/ 65 '7 Claims. (Cl. 252-35) This invention relates to an alkaline lubricating oil that is capable of being water washed without serious loss of alkalinity, and to the preparation of additives for such oils.

In recent years there has been a big increase in the use of residual fuels for the operation of certain types of internal combustion engines, particularly slow-speed diesel engines, such as are commonly used to drive ships. The use of these fuels is attractive owing to their low cost compared with distillate fuels but it has been found that their use gives rise to certain problems one of which is an increase in crankcase oil acidity which influences crankshaft corrosion. This trouble is believed to be due to the presence in residual fuels of certain materials, particularly those containing sulphur, which form acidic products on combustion, some of which acidic products find their way into the crankcase oil.

During the operation of slow-speed marine diesel engines it is customary to circulate used crankcase oil from the pump through a filter and cooler and to subject a proportion of the circulating oil to a cleansing operation. The cleansing operation comprises a water-Wash which has the effect of coagulating insoluble materials (e.g., carbon) which are then more easily removed by subsequent centrifuging. It is customary to rely on this washing operation to reduce mineral acidity in the oil but this is not always very satisfactory.

Another approach to the problem of oil acidity is to incorporate an alkaline-reacting additive in the oil but, generally speaking, the additives that have been found to give adequate neutralisation of acids from cylinder drainings, tend to suffer from the drawback that they are too readily extracted from the oil by the Water Washing operation referred to above. Examples of such additives are certain amines and certain overbased calcium phenates and sulphonates.

In most large marine diesel engines the crankcase oil is also used for piston cooling where it may be subjected to piston temperatures in the region of 180 to 200 C. On many ships the same oil is also used for the total lubrication of auxiliary trunk-piston medium speed diesel engines. For both these applications an improvement in oxidation stability would be an advantage.

We have now found a particular type of compound which is etfective in reducing the problem of lubricating oil acidity in slow-speed engines and which is not readily removed from the oil by water washing. In addition the additives impart improved oxidation stability to lubricating oil base stocks rendering them more suitable for use in both types of diesel engine.

According to the invention, there is provided a lubricating composition comprising a lubricating base oil, which may be mineral or synthetic, having blended therein from 0.01 to 20% wt., preferably 0.l-5% wt., of the composition, of a compound having the empirical formula (RCOO) Zn O where R is an alkyl, cycloalkyl, aryl, aralkyl or alkaryl group preferably having not more than 24 carbon atoms, the compound having a tetrahedral structure with the four zinc atoms at the corners, the oxygen atom in the centre and the six carboxylate groups arranged along the sides. Most suitably R is an alkyl group having up to 18 carbon atoms.

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Compounds of this type may be prepared, according to another aspect of the invention, by reacting one molar proportion of zinc oxide with one and a half molar proportions of an acid of the formula RCOOH, where R is as specified above, and removing all of the water formed during the reaction. The reaction is preferably carried out by refluxing with an azeotroping agent such as benzene or toluene. Excess zinc oxide may be used in the reaction but if the water formed is removed this excess does not react and it has to be filtered off from the product.

The reaction may be represented as follows:

However the reaction is believed to proceed in two stages as follows:

The base oil used in the compositions according to the invention is usually a refined lubricating oil obtained from petroleum, e.g., one having a viscosity in the range 3-50 centistokes at 210 F. and a viscosity index in the range -110.

The amount of the additive should preferably be such as to give the composition a total base number of 0.05- 100, preferably 0.5100, mg. KOH/ g.

It is to be understood that the lubricating composition may contain more than one of the zinc compounds and that more than one carboxylic acid may be used in the preparation of the compounds with the result that a given molecule of the product may contain more than one type of carboxylic group.

A number of examples of the preparation of the zinc compounds will now be given. In all cases the reaction was carried out by heating a mixture of four moles of zinc oxide with six moles of carboxylic acid in toluene, re-

moving the water formed during the reaction and filtering the reaction product. The acids used in the preparation of the compounds are shown in Table 1 which also gives certain data on the products. The inspection data is in all cases consistent with the expected properties of the compounds.

TABLE 1 Total Z Compound Acid used in preparation Base No. Percent n mg. wt. KOH/g.

2-ethy1 hexanolc 383. 1 22. 8 Versatie 9, 11* 325 19.1 3,5,5-trimethyl hexanoic 363 21. 4 Oleie 203 11.8 Gyclohexyl carboxylic 432 23. 9 n-Octauoic 378 22. 5 Z-ethyl hexauoic, 50% 463 27. 2

molar; Grotonic, 50% molar. H. 2-ethyl hexanoie, 50% 435 25. 9 1. 4555 molar; Pivalle, 50% molar.

Versatic 9, 11 i s a. commercially available Cry-C11 branched tertiary carboxylic acid.

As is seen from the foregoing table, the number of carbon atoms present in the carboxylic acids employed in the reaction ranges from 4 carbon atoms, as represented by crotonic acid, up to 18 carbon atoms, as represented by oleic acid.

In a further example, six moles of versatic 9, ll acid were reacted with eight moles of zinc oxide (i.e., a molar excess). The reactants were refluxed in toluene, the water being removed as it was formed. The theoretical amount of water appropriate to the amount of acid was obtained. On filtering the reaction product, approximately half of the zinc oxide originally used was separated from a toluene solution of basic zinc versatate 9, 11. The [01- uene was evaporated from the basic zinc salt which was found to have a TBN of 322.5.

The TBN of all the compounds prepared according to the invention was found to be very close to the theoretical value calculated from the empirical formula given above.

A number of lubricating compositions according to the invention Were prepared using Compounds A and B in refined petroleum base oils. The compositions are shown in Table 2 which gives percentages by Weight of the ingredients and also the 210 F. viscosity (centistokes) and viscosity index of the base oils.

Composition P had a total base number (TBN) of 2.0 mg. KOH/ g. It did not form stable emulsions with Water and after two washings with 20% distilled water at 60 C. its TBN was 1.7 mg. KOH/ g. which is considered to be very satisfactory.

Composition R had a TBN of 1.38. It was given a much more severe water wash using ten times its volume of distilled water at 70 C. After one Wash the TBN was 1.14 and after two washes it was 0.96, i.e., 83% and 70% respectively of the original TBN. A commercially available water-Washable oil for marine engines gave figures of 44% and 13% when subjected to the same test.

An anti-wear test was carried out on compositions Q and S using the Four Ball test with a 15 kg. applied load. The results given in Table 3 indicate that the zinc compounds improve the anti-wear properties of base oils.

TABLE 3 Wear soar diameter after 30 minutes 45 minutes 60 minutes SAE 90 base oil... 0. 70 0. 70 0.80 Composition Q-.. 0.46 0. 52 0. 52 Liquid parafiin. 0.59 0.72 0.81 Composition S 0. 34 0.46 0.56

being water-washed Without serious loss of alkalinity comprising a major amount of a lubricating base oil and from 0.01 to 20% by weight of the composition of a compound having the empirical formula (RCOO) Zn O, where R is selected from the group consisting of alkyl, cycloalkyl, aryl, aralkyl and alkaryl groups having up to 24 carbon atoms, the compound having a tetrahedral structure with the four zinc atoms at the corners, the oxygen atom in the center and the six carboxylate groups arranged along the sides.

2. A composition according to claim 1, in which the proportion of the said compound in the composition is from 0.1 to 5% wt.

3. A composition according to claim 1, in which the proportion of the said compound in the composition is" such that the composition has a total base number of from 0.05 to mg. KOH/g.

4. A composition according to claim 1, in which the proportion of the said compound in the composition is such that the composition has a total base number of from 0.5 to 100 mg. KOH/g.

5. A composition according to claim 1, in which R is an alkyl group having 4 to 18 carbon atoms.

6. A method of preparing a compound suitable for use as a lubricating oil additive and having the empirical formula (RCOO) Zn O, wherein R is selected from the group consisting of alkyl, cycloalkyl, aryl, aralkyl and alkaryl groups having up to 24 carbon atoms which comprises reacting one molar proportion of zinc oxide with one and a half molar proportions of an acid of the formula RCOOH, refluxing the reactants with an azeotroping agent, and removing all of the water formed during the reaction.

7. A method according to claim 6, in which R is an alkyl group having 4 to 18 carbon atoms.

References Cited UNITED STATES PATENTS 1,767,076 6/1930 Jarman 252-35 2,362,233 11/1944 Bannon 25235 2,384,551 9/1945 Jehle 25235 2,501,127 3/1950 Kebrich 260429 9 3,017,361 1/1962 Morris et al. 25235 FOREIGN PATENTS 891,858 3/1962 Great Britain.

OTHER REFERENCES Koyama et a1.: Crystal Structure Zinc Oxyacetate, in Chemical Abstracts of J.A.C.S., vol 49 (1955), page 12909h.

DANIEL E. WYMAN, Primary Examiner.

C. F. DEES, Assistant Examiner.

Claims

1. AN ALKALINE LUBRICATING OIL COMPOSITION CAPABLE OF BEING WATER-WASHED WITHOUT SERIOUS LOSS OF ALKALINITY COMPRISING A MAJOR AMOUNT OF A LUBRICATING BASE OIL AND FROM 0.01 TO 20% BY WEIGHT OF THE COMPOSITION OF A COMPOUND HAVING THE EMPIRICAL FORMULA (RCOO)6ZN4O, WHERE R IS SELECTED FROM THE GROUP CONSISTING OF ALKYL, CYCLOALKYL, ARYL, ARALKYL AND ALKARYL GROUPS HAVING UP TO 24 CARBON ATOMS, THE COMPOUND HAVING A TETRAHEDRAL STRUCTURE WITH THE FOUR ZINC ATOMS AT THE CORNERS, THE OXYGEN ATOM IN THE CENTER AND THE SIX CARBOXYLATE GROUPS ARRANGED ALONG THE SIDES.

6. A METHOD OF PREPARING A COMPOUND SUITABLE FOR USE AS A LUBRICATING OIL ADDITIVE AND HAVING THE EMPIRICAL FORMULA (RCOO)6ZN4O, WHEREIN R IS SELECTED FROM THE GROUP CONSISTING OF ALKYL, CYCLOALKYL, ARYL, ARALKYL AND ALKARYL GROUPS HAVING UP TO 24 CARBON ATOMS WHICH COMPRISES REACTING ONE MOLAR PROPORTION OF ZINC OXIDE WITH ONE AND A HALF MOLAR PROPORTIONS OF AN ACID OF THE FORMULA RCOOH, REFLUXING THE REACTANTS WITH AN AZEOTROPING AGENT, AND REMOVING ALL OF THE WATER FORMED DURING THE REACTION.