Marine engine lubrication

Abstract

A low S marine fuel trunk piston diesel engine lubricant includes an overbased metal detergent; a zinc dihydrocarbyl dithiophosphate; optionally an aminic antioxidant; and a borated ashless dispersant. The lubricant exhibits improved thermal and oxidative stability and improved high temperature detergency.

Claims

1. A low sulfur marine fuel trunk piston diesel engine lubricating oil composition comprising or made of admixing (A) a Group I base oil in a major amount; and in respective minor amounts; (B) an overbased detergent consists essentially of an overbased calcium salicylate and an overbased calcium sulfonate; wherein the soap level of the composition is from 1.49 to 1.747 mass %; (C) a primary and/or secondary zinc dialkyldithiophosphate in an amount of 352 to 387 ppm by weight in terms of P atoms; the aminic antioxidant is an alkylated diphenylamine; (D) a borated ashless dispersant comprising a borated succinimide and is present in an amount of 50 to 65 ppm by weight in terms of B atoms; and wherein the TBN of the composition is from 11.9 to 15 mg KOH/g; and wherein the composition is essentially free of aminic antioxidant.

2. The composition of claim 1, wherein the composition exhibits three or more of the following characteristics: a Komatsu Hot Tube Test (KHTT) score at 320° C. of at least 1.5; a peak area increase (PAI) after 216 hours in a GFC Oxidation Test of less than 505; a % KV100 increase after 216 hours in a GFC Oxidation Test of less than 60.5; a % TBN remaining after 216 hours in a GFC Oxidation Test of greater than 40; and a wear protection temperature, as measured using a High Frequency Reciprocating Rig (HFRR), of greater than 295° C.

3. The composition of claim 2, wherein the composition exhibits four or more of the characteristics.

4. The composition of claim 2, wherein the composition exhibits a peak area increase (PAI) after 216 hours in a GFC Oxidation Test of 361 or less, a % KV100 increase after 216 hours in a GFC Oxidation Test of 36 or less, and/or a wear protection temperature, as measured using HFRR, of 354° C. or higher.

5. The composition of claim 3, wherein the composition exhibits a peak area increase (PAI) after 216 hours in a GFC Oxidation Test of 361 or less, a % KV100 increase after 216 hours in a GFC Oxidation Test of 36 or less, and/or a wear protection temperature, as measured using HFRR, of 354° C. or higher.

6. A method for operating a four-stroke trunk piston engine comprising the steps of: (i) providing the engine fueled with a low sulfur marine fuel; and (ii) lubricating the engine with a lubricating oil composition as claimed in claim 1.

7. The method of claim 6 where the low sulfur marine fuel is a distillate fuel.

8. The method of claim 6 where the fuel has a sulfur content of equal to or less than 0.5 mass % in terms of S atoms of sulfur.

9. The method of claim 6 where the low sulfur marine fuel is a distillate fuel and the fuel has a sulfur content of equal to or less than 0.5 mass % in terms of S atoms of sulfur.

10. A method for operating a four-stroke trunk piston engine comprising the steps of: (i) providing the engine fueled with a low sulfur marine fuel; and (ii) lubricating the engine with a lubricating oil composition as claimed in claim 2.

11. A method for operating a four-stroke trunk piston engine comprising the steps of: (i) providing the engine fueled with a low sulfur marine fuel; and (ii) lubricating the engine with a lubricating oil composition as claimed in claim 3.

12. A method for operating a four-stroke trunk piston engine comprising the steps of: (i) providing the engine fueled with a low sulfur marine fuel; and (ii) lubricating the engine with a lubricating oil composition as claimed in claim 4.

13. A method for operating a four-stroke trunk piston engine comprising the steps of: (i) providing the engine fueled with a low sulfur marine fuel; and (ii) lubricating the engine with a lubricating oil composition as claimed in claim 5.

14. The composition of claim 2, wherein the composition exhibits a Komatsu Hot Tube Test (KHTT) score at 320° C. of up to 3.

15. The composition of claim 1, wherein the composition exhibits three or more of the following characteristics: a Komatsu Hot Tube Test (KHTT) score at 320° C. of at least 1.5; a peak area increase (PAI) after 216 hours in a GFC Oxidation Test of less than 505; a % KV100 increase after 216 hours in a GFC Oxidation Test of less than 71; a % TBN remaining after 216 hours in a GFC Oxidation Test of greater than 40; and a wear protection temperature, as measured using a High Frequency Reciprocating Rig (HFRR), of greater than 295° C.

16. The composition of claim 15, wherein the composition exhibits four or more of the characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The features of the invention will now be discussed in more detail below.

(2) Oil of Lubricating Viscosity (A)

(3) The lubricant composition contains a major proportion of an oil of lubricating viscosity. Such lubricating oils may range in viscosity from light distillate mineral oils to heavy lubricating oils. Generally, the viscosity of the oil ranges from 2 to 40, such as 3 to 15, mm.sup.2/sec, as measured at 100° C., and a viscosity index of 80 to 100, such as 90 to 95. The lubricating oil may comprise greater than 60, typically greater than 70, mass % of the composition.

(4) Natural oils include animal oils and vegetable oils (e.g., castor oil, lard oil); liquid petroleum oils and hydro refined, solvent-treated or acid-treated mineral oils of the paraffinic, naphthenic and mixed paraffinic-naphthenic types. Oils of lubricating viscosity derived from coal or shale also serve as useful base oils.

(5) Synthetic lubricating oils include hydrocarbon oils and halo-substituted hydrocarbon oils such as polymerized and interpolymerized olefins (e.g., polybutylenes, polypropylenes, propylene-isobutylene copolymers, chlorinated polybutylenes, poly(1-hexenes), poly(1-octenes), poly(1-decenes)); alkybenzenes (e.g., dodecylbenzenes, tetradecylbenzenes, dinonylbenzenes, di(2-ethylhexyl)benzenes); polyphenyls (e.g., biphenyls, terphenyls, alkylated polyphenols); and alkylated diphenyl ethers and alkylated diphenyl sulphides and derivative, analogues and homologues thereof.

(6) Alkylene oxide polymers and interpolymers and derivatives thereof where the terminal hydroxyl groups have been modified by esterification, etherification, etc., constitute another class of known synthetic lubricating oils. These are exemplified by polyoxyalkylene polymers prepared by polymerization of ethylene oxide or propylene oxide, and the alkyl and aryl ethers of polyoxyalkylene polymers (e.g., methyl-polyiso-propylene glycol ether having a molecular weight of 1000 or diphenyl ether of poly-ethylene glycol having a molecular weight of 1000 to 1500); and mono- and polycarboxylic esters thereof, for example, the acetic acid esters, mixed C.sub.3-C.sub.8 fatty acid esters and C.sub.13 oxo acid diester of tetraethylene glycol.

(7) Another suitable class of synthetic lubricating oils comprises the esters of dicarboxylic acids (e.g., phthalic acid, succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkylmalonic acids, alkenyl malonic acids) with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycol monoether, propylene glycol). Specific examples of such esters includes dibutyl adipate, di(2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate, didecyl phthalate, dieicosyl sebacate, the 2-ethylhexyl diester of linoleic acid dimer, and the complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene glycol and two moles of 2-ethylhexanoic acid.

(8) Esters useful as synthetic oils also include those made from C.sub.5 to C.sub.12 monocarboxylic acids and polyols and polyol esters such as neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol and tripentaerythritol.

(9) Silicon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy- or polyaryloxysilicone oils and silicate oils comprise another useful class of synthetic lubricants; such oils include tetraethyl silicate, tetraisopropyl silicate, tetra-(2-ethylhexyl)silicate, tetra-(4-methyl-2-ethylhexyl)silicate, tetra-(p-tert-butyl-phenyl) silicate, hexa-(4-methyl-2-ethylhexyl)disiloxane, poly(methyl)siloxanes and poly(methylphenyl)siloxanes. Other synthetic lubricating oils include liquid esters of phosphorus-containing acids (e.g., tricresyl phosphate, trioctyl phosphate, diethyl ester of decylphosphonic acid) and polymeric tetrahydrofurans.

(10) Unrefined, refined and re-refined oils can be used in lubricants of the present invention. Unrefined oils are those obtained directly from a natural or synthetic source without further purification treatment. For example, a shale oil obtained directly from retorting operations; petroleum oil obtained directly from distillation; or ester oil obtained directly from esterification and used without further treatment are unrefined oils.

(11) The American Petroleum Institute (API) publication “Engine Oil Licensing and Certification System”, Industry Services Department, Fourteenth Edition, December 1996, Addendum 1, December 1998 categorizes base stocks as follows: a) Group I base stocks contain less than 90 percent saturates and/or greater than 0.03 percent sulphur and have a viscosity index greater than or equal to 80 and less than 120 using the test methods specified in Table E-1. b) Group II base stocks contain greater than or equal to 90 percent saturates and less than or equal to 0.03 percent sulphur and have a viscosity index greater than or equal to 80 and less than 120 using the test methods specified in Table E-1. c) Group III base stocks contain greater than or equal to 90 percent saturates and less than or equal to 0.03 percent sulphur and have a viscosity index greater than or equal to 120 using the test methods specified in Table E-1. d) Group IV base stocks are polyalphaolefins (PAO). e) Group V base stocks include all other base stocks not included in Group I, II, III, or IV.

(12) Analytical Methods for Base Stock are tabulated below:

(13) TABLE-US-00001 PROPERTY TEST METHOD Saturates ASTM D 2007 Viscosity Index ASTM D 2270 Sulphur ASTM D 2622 ASTM D 4294 ASTM D 4927 ASTM D 3120

(14) The present invention can be used with all of the above base oils. The present invention is particularly suited to oils containing greater than or equal to 90% saturates and less than or equal to 0.03% sulphur as the oil of lubricating viscosity, e.g. Group II, III, IV or V. They also include basestocks derived from hydrocarbons synthesised by the Fischer-Tropsch process. In the Fischer-Tropsch process, synthesis gas containing carbon monoxide and hydrogen (or ‘syngas’) is first generated and then converted to hydrocarbons using a Fischer-Tropsch catalyst. These hydrocarbons typically require further processing in order to be useful as a base oil. For example, they may, by methods known in the art, be hydroisomerized; hydrocracked and hydroisomerized; dewaxed; or hydroisomerized and dewaxed. The syngas may, for example, be made from gas such as natural gas or other gaseous hydrocarbons by steam reforming, when the basestock may be referred to as gas-to-liquid (“GTL”) base oil; or from gasification of biomass, when the basestock may be referred to as biomass-to-liquid (“BTL” or “BMTL”) base oil; or from gasification of coal, when the basestock may be referred to as coal-to-liquid (“CTL”) base oil.

(15) Preferably, the oil of lubricating viscosity in this invention contains 50 mass % or more said basestocks. It may contain 60, such as 70, 80 or 90, mass % or more of said basestock or a mixture thereof. The oil of lubricating viscosity may be substantially all of said basestock or a mixture thereof.

(16) A TPEO may employ 5-35, preferably 7-20, more preferably 12-15, mass % of a concentrate or additives package, the remainder being base stock.

(17) Preferably, the TPEO has a compositional TBN (using D2896) of 7-30, such as 7-20, most preferably 8-15.

(18) The following may be mentioned as typical proportions of additives in a TPEO.

(19) TABLE-US-00002 Mass % a.i. Mass % a.i. Additive (Broad) (Preferred) detergent(s) 0.5-12  2-8 dispersant(s) 0.5-5   1-3 anti-wear agent(s) 0.1-1.5 0.5-1.3 oxidation inhibitor 0.1-2   0.5-1.5 rust inhibitor 0.03-0.15 0.05-0.1  pour point dispersant 0.03-1.15 0.05-0.1  base stock balance balance

(20) These proportions are, however, modified in the present invention in accordance with the limitations stated herein.

(21) The TBN of the TPEO of the invention is in the range of 5 to less than 20, such as 5 to 18, such as 8 to 15.

(22) Overbased Metal Detergents (B)

(23) A detergent is an additive that reduces formation of deposits, for example, high-temperature varnish and lacquer deposits, in engines; it has acid-neutralising properties and is capable of keeping finely divided solids in suspension. It is based on metal “soaps”, that is metal salts of acidic organic compounds, sometimes referred to as surfactants.

(24) A detergent comprises a polar head with a long hydrophobic tail. Large amounts of a metal base are included by reacting an excess of a metal compound, such as an oxide or hydroxide, with an acidic gas such as carbon dioxide to give an overbased detergent which comprises neutralised detergent as the outer layer of a metal base (e.g. carbonate) micelle.

(25) The detergent is preferably an alkali metal or alkaline earth metal additive such as an overbased oil-soluble or oil-dispersible calcium, magnesium, sodium or barium salt of a surfactant selected from phenol, sulphonic acid and hydroxybenzoic acid, wherein the overbasing is provided by an oil-insoluble salt of the metal, e.g. carbonate, basic carbonate, acetate, formate, hydroxide or oxalate, which is stabilised by the oil-soluble salt of the surfactant. The metal of the oil-soluble surfactant salt may be the same or different from that of the metal of the oil-insoluble salt. Preferably the metal, whether the metal of the oil-soluble or oil-insoluble salt, is calcium. The acids are hydrocarbyl-substituted, such as alkyl-substituted, as is known in the art.

(26) The TBN of the detergent may be low, i.e. less than 50 mg KOH/g, medium, i.e. 50-150 mg KOH/g, or high, i.e. over 150 mg KOH/g, as determined by ASTM D2896. Preferably the TBN is medium or high, i.e. more than 50 TBN. More preferably, the TBN is at least 60, more preferably at least 100, more preferably at least 150, and up to 500, such as up to 350 mg KOH/g, as determined by ASTM D2896.

(27) The soap mass in the TPEO may be 0.1 to 4, such as 0.4 to 3.3, mass %. Preferably, the surfactant is in the form of a hydroxybenzoic acid such as a hydrocarbyl-substituted salicylic acid. The surfactant may be a single acid, a mixture of acids, or a complex of different acids. Advantageously, the detergent may be a mixture of a salicylate and a sulfonate.

(28) Zinc Dihydrocarbyldithiophosphate (C)

(29) Dihydrocarbyl dithiophosphate metal salts may be prepared in accordance with known techniques by first forming a dihydrocarbyl dithiophosphoric acid (DDPA), usually by reaction of one or more alcohols or a phenol with P.sub.2S.sub.5 and then neutralizing the formed DDPA with a metal compound. For example, a dithiophosphoric acid may be made by reacting mixtures of primary and secondary alcohols. Alternatively, multiple dithiophosphoric acids can be prepared where the hydrocarbyl groups on one are entirely secondary in character and the hydrocarbyl groups on the others are entirely primary in character. To make the metal salt, any basic or neutral metal compound could be used but the oxides, hydroxides and carbonates are most generally employed. Commercial additives frequently contain an excess of metal due to the use of an excess of the basic metal compound in the neutralization reaction.

(30) At least 50 mole % of component (C) is a zinc alkyl dithiophosphate where the alkyl group is a C.sub.6 primary alkyl group and may be represented by the following formula:

(31) ##STR00001##
wherein R.sup.1 and R.sup.2 may be the same or different and are primary alkyl groups containing 6 carbon atoms, such as n-hexyl.

(32) Preferably, at least 60, at least 70, at least 80, or at least 90, mole % of component (C) is the zinc dialkyl dithiophosphate. More preferably, all of component (C) is the zinc dialkyl dithiophosphate.

(33) Preferably, (C) constitutes 50 to 800, such as 100-800, such as 100-500, or 50 to 500 such as 200-400, ppm by weight in terms of P content of the TPEO. (C) may be a primary and/or secondary zinc dialkyldithiophosphate.

(34) Aminic Antioxidant (D)

(35) As examples of aminic antioxidants there may be mentioned secondary aromatic amines such as diarylamines, for example diphenylamines wherein each phenyl group is alkyl-substituted with an alkyl group having 4 to 9 carbon atoms.

(36) Preferably, the anti-oxidant is provided in the composition in an amount of 10-400, such as 10-300, such as 10-200, such as 50-200, ppm by weight in terms of N content. In an embodiment of the invention, such as anti-oxidant is not present.

(37) Borated Ashless Dispersant (E)

(38) Ashless dispersants are non-metallic organic material that form substantially no ash on combustion. They comprise a long chain hydrocarbon with a polar head, the polarity being derived from inclusion of e.g., an O, P or N atom. The hydrocarbon is an oleophilic group that confers oil-solubility and has, for example 40-500 carbon atoms. Thus, ashless dispersants may comprise an oil-soluble polymeric backbone having functional groups that are capable of associating with particles to be dispersed.

(39) Noteworthy, examples of ashless dispersant are succinimides, e.g., polyisobutene succinic anhydride and polyamine condensation products.

(40) In this invention, borated ashless dispersants are used in order to provide the defined boron content. Preferably, it is 10-200, such as 10-150, such as 50-150, ppm by weight in terms of B content.

(41) Other additives such as other dispersants, pour point depressants, anti-foamants, metal rust inhibitors, and/or demulsifiers may be provided, if necessary.

(42) The terms ‘oil-soluble’ or ‘oil-dispersable’ as used herein do not necessarily indicate that the compounds or additives are soluble, dissolvable, miscible or capable of being suspended in the oil in all proportions. These do mean, however, that they are, for instance, soluble or stably dispersible in oil to an extent sufficient to exert their intended effect in the environment in which the oil is employed. Moreover, the additional incorporation of other additives may also permit incorporation of higher levels of a particular additive, if desired.

(43) The lubricant compositions of this invention comprise defined individual (i.e. separate) components that may or may not remain the same chemically before and after mixing.

(44) It may be desirable, although not essential, to prepare one or more additive packages or concentrates comprising the additives, whereby the additives can be added simultaneously to the oil of lubricating viscosity to form the lubricating oil composition. Dissolution of the additive package(s) into the lubricating oil may be facilitated by solvents and by mixing accompanied with mild heating, but this is not essential. The additive package(s) will typically be formulated to contain the additive(s) in proper amounts to provide the desired concentration, and/or to carry out the intended function in the final formulation when the additive package(s) is/are combined with a predetermined amount of base lubricant.

(45) Thus, the additives may be admixed with small amounts of base oil or other compatible solvents together with other desirable additives to form additive packages containing active ingredients in an amount, based on the additive package, of, for example, from 2.5 to 90, preferably from 5 to 75, most preferably from 8 to 60, mass % of additives in the appropriate proportions, the remainder being base oil.

(46) The final formulations may typically contain about 5 to 40 mass % of the additive packages(s), the remainder being base oil.

EXAMPLES

(47) The present invention is illustrated by, but not limited to, the following examples.

(48) Preparations

(49) Three trunk piston engine oils (TPEOs) were blended to comprise one or more of

(50) a Group I base oil a succinimide dispersant an overbased calcium salicylate detergent a zinc dialkyldithio phosphate anti-wear agent (ZDDP) an alkylated diphenyl amine anti-oxidant (DPA)

(51) These components were identical except that examples of the invention (1 and 2) each contained a borated succinimide dispersant whereas a comparison example (A) contained a non-borated dispersant.

(52) The compositions of the three TPEOs are set out in the table below.

(53) TABLE-US-00003 TABLE 1 A (comparison) 1 2 TBN 13.56 13.36 13.21 ppm B 0 120 120 ppm N from DPA 260 180 180 ppm N from 250 320 250 dispersants ppm P from ZDDP 550 360 350 ppm Zn from ZDDP 610 390 390

(54) The main differences are that Examples 1 and 2 each contain B whereas Example A does not; and that Example 1 and 2 contain less DPA and less ZDDP than Example A.

(55) Testing and Results

(56) Each of compositions A, 1 and 2 was subjected to three tests: the Komatsu Hot Tube Test (KHTT) which is a lubrication industry bench test that measures the degree of high temperature detergency and thermal and oxidative stability of a lubricating oil. The test was carried out at 320° C. and results are expressed as a rating where a higher number indicates a better performance. the Differential Scanning Calorimeter Test (PDSC) is used to evaluate the evaluate the thin film oxidative stability of lubricating oils and is carried out in accordance with ASTM D-6186. Tests were carried at 210° C. and results expressed in time (in minutes) at which the oxidation of the oils starts. Thus, a greater time indicates a better performance. The GFC Oxidation Test is carried out in accordance with GFC Tr-21-A-90. PAI (peak area increase) is measured after 216 hours, % KV100 increase measured also after 216 hours, and % TBN remaining after 216 hours calculated. Lower figures indicate better performance.

(57) The results are summarized in the table below.

(58) Tests

(59) TABLE-US-00004 GFC % KV 100 TBN Examples KHTT P DSC PAI increase Change A 0 21.8 507.5 60.5 −7.3 1 2 25.0 317.10 31.30 −5.9 2 1.5 25.0 321.30 32.50 −5.8

(60) In the results, the examples of the invention (1 and 2), which contained B and lower levels of ZDDP and DPA, gave better performance in all of the tests than the comparative example (A).

(61) A second set of TPEOs was prepared and tested.

(62) Preparations

(63) Five TPEO's were blended to comprise one or more of a Group I base oil a succinimide dispersant an overbased calcium salicylate and/or an overbased calcium sulfonate detergents a zinc dialkylthiophosphate anti-wear agent (ZDDP) optionally, an alkylated diphenylamine anti-oxidant (DPA).
The compositions of the five TPEO's are set out in the table below, examples B and C being comparison examples and examples 3-5 of the invention.

(64) TABLE-US-00005 TABLE 2 B C (comparison) (comparison) 3 4 5 TBN 11.9 11.9 12.1 11.9 14.9 metal salicylate salicylate sulfonate Salicylate Salicylate detergent and and sulfonate sulfonate soap level 1.53 1.123 1.085 1.49 1.747 (mass %) ppm B 0 78 78 65 59 ppm N from 260 0 50 0 0 DPA ppm N from 250 310 240 210 240 dispersant ppm P from 896 560 320 352 387 ZDDP ppm Zn 985 616 352 388 425 from ZDDP
Testing and Results

(65) Each of the five compositions was subjected to the KHTT and GFC Oxidation Test as described and also to the high frequency reciprocating rig test (HFRR) described as follows.

(66) Samples of the above formulations were tested using a PCS Instruments high frequency reciprocating rig (HFRR) on a standard protocol comprising the following conditions: 15 minutes 20 Hz reciprocation of 1 mm stroke length 400 g load using standard equipment manufacturer-supplied steel substrates 80° C. to 380° C. at 20° C. per minute

(67) The temperatures reported (in ° C.) were taken from the point at which a consistent frictional response is no longer received from the test sample (onset of scuffing), as measured by the HFRR equipment software. Once this has occurred, the oil is deemed to no longer be able to provide sufficient wear protection. Onset of scuffing correlates to minimum friction coefficient. Higher results are better.

(68) The results are summarized in the table below.

(69) TABLE-US-00006 % kV100 TBN Examples KHTT HFRR PAI increase change B 0 295 636 111 37 C 0 290 560 86 40 3 3 >375 505 71 40 4 2 354 429 34 60 5 1.5 361 450 36 65

(70) In the results, B-containing and lower ZDDP-level examples of the invention (3-5) performed better and the presence of Ca sulfonate in Examples 4 and 5 gave rise to improved performance; in particular, improved high temperature stability and improved oxidation resistance.