Method for reducing piston deposits in marine diesel engines

Abstract

To provide a method for reducing an incidence rate of deposits on a piston of a four-stroke marine diesel engine during its operation when the engine is powered by a marine residual fuel that meets the ISO8217 / 2017 fuel standard for marine residual fuels and has a sulfur content of more than 0.1 mass% to less than 0.5 mass%.SOLUTION: A method comprises lubricating an engine with a lubricant composition, wherein the lubricant composition comprises: (a) an oil having a lubricating viscosity of at least 50 mass% based on the mass of the composition; (b) 5-25 mass% of oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent based on the mass of the composition, or mixtures of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents; and (c) 0.1 to 10 mass% of one or more oil-soluble or oil-dispersible ashless dispersants based on the mass of the composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for reducing piston deposits in engines, and in particular to a method for reducing the incidence of deposits on pistons in four-stroke marine diesel engines powered by marine residual fuels having low levels of sulfur. [Background technology]

[0002] Currently, residual fuels used to power marine diesel engines for offshore shipping operations must have a sulfur content of 3.5% or less by mass, based on the mass of the fuel. However, as with other transportation sectors, there is environmental pressure to reduce harmful emissions resulting from commercial and leisure shipping. The sulfur present in residual fuels is a major cause of environmental pollution. Since January 2015, various regions around the world have implemented Emission Control Areas (ECAs), primarily in coastal areas. In these ECAs, ships may only burn bunker fuels with a sulfur content of 0.1% or less by mass. Because ECA-compliant fuels are relatively expensive, mandating their use for offshore shipping would economically damage the global shipping industry. Instead, the International Maritime Organization (IMO) mandated a global reduction in the sulfur content of residual fuels used in offshore shipping to 0.5% or less by mass, based on the mass of the fuel. The cap on sulfur levels is scheduled to come into effect on January 1, 2020.

[0003] The IMO's new regulations (called IMO 2020) pose challenges not only for shipowners and operators but also for fuel refiners and manufacturers. Shipowners will have a choice: either all ships must begin operating on fuels with a lower sulfur content, or alternatively, they may continue to use existing higher-sulfur (<3.5% by mass) fuels, provided that measures are taken to eliminate air pollution resulting from their combustion. This latter option requires the use of exhaust gas cleaning systems (often called "scrubbers") capable of removing over 95% of sulfur oxides and most particulate matter from exhaust gases. However, there are significant financial costs to shipowners, both for purchasing and installing the scrubbers and for the loss of vessel availability while the upgraded equipment is installed. While some shipowners and operators may find it more attractive over time to retrofit their ships to continue using higher-sulfur fuels, for others, it will be more cost-effective to switch to lower-sulfur residual fuels. This will have ramifications for fuel refiners and manufacturers. Currently, there are no commercially available residual fuels with a sulfur content of 0.5% by mass or less, as there is no commercial incentive to produce such fuels until it is mandated by IMO regulations.

[0004] After January 1, 2020, there will be a market for the fuel, but the size of this market will depend on the ratio of shipowners and operators who choose to use the new fuel to those who choose to install scrubbers. Fuel refiners and manufacturers will have to determine both how much low-sulfur residual fuel will be needed and the exact type of fuel that will comply with IMO regulations. For example, there are many different ways to produce compliant residual fuel, for example, by utilizing a combination of various refinery streams appropriately treated to reduce sulfur content as needed. The new fuel will also have to meet the existing International Standard Specification for Marine Residual Fuels, ISO 8217 2017, which specifies properties such as maximum kinematic viscosity, density, and flash point for various categories of marine residual fuel. The present invention relates to an engine powered by residual fuel that meets the ISO 8217 2017 specification for marine residual fuel and has a sulfur content of 0.5% by mass or less. ISO 8217 2017 also specifies international standards for marine distillate fuels, but these are not relevant to the present invention.

[0005] The new low-sulfur residual fuels will also necessitate changes to the lubricants used to lubricate marine diesel engines. Traditionally, lubricant manufacturers have formulated their products to operate on fuels with higher sulfur contents. These fuels produce significant amounts of sulfur oxides upon combustion, which can lead to high levels of acidic species building up in the lubricant. Therefore, lubricants have contained chemical species that can neutralize these acids to prevent corrosion of engine parts and deterioration of the lubricant. Particulate matter and soot levels have also been quite high, requiring species that can disperse them in the lubricant. Therefore, the upcoming move to lower sulfur content presents new challenges to lubricant formulators: lubricants designed to lubricate engines powered by high sulfur fuels will not perform optimally in the same engines when powered by the new fuels. Previous experience with lubricants designed to lubricate engines powered by high-sulfur marine residual fuels has shown that ashless dispersants adversely affect piston cleanliness in the presence of overbased metal detergents, which are always present to neutralize acidic combustion products. This is due to a reduced ability of the lubricant to process asphaltenes, which are always present in high-sulfur marine residual fuels, and has been observed in both bench and real-world engine tests. As a result, the use of ashless dispersants in lubricants designed to lubricate engines powered by high-sulfur marine residual fuels has been limited to date.

[0006] New marine residual fuels that meet the IMO 2020 regulations will have reduced sulfur content, but will still contain asphaltenes because the processes used to remove sulfur typically do not also remove asphaltenes. Based on previous experience, it could be predicted that including ashless dispersants in lubricants used in engines powered by these low-sulfur fuels would similarly result in poor piston cleanliness. Surprisingly, however, the inventors have discovered that the combination of a metal detergent and an ashless dispersant in a lubricant used to lubricate an engine powered by a marine residual fuel that meets the IMO 2020 regulations (and the ISO 8217 2017 specification for marine residual fuels) actually results in reduced piston deposits compared to a similar lubricant that does not contain any ashless dispersant. Furthermore, they have discovered that the metal detergent and ashless dispersant combination can be "boosted" with the addition of certain compounds to "boost" this effect, thereby providing even improved piston cleanliness. Summary of the Invention

[0007] Accordingly, in a first aspect, the present invention provides a method of reducing the incidence of deposits on pistons of a four-stroke marine diesel engine during operation of the engine when the engine is powered on a marine residual fuel that meets the ISO 8217 2017 fuel standard for marine residual fuels and has a sulphur content of more than 0.1% and less than 0.5%, by mass, based on the mass of the fuel, comprising lubricating the engine with a lubricating oil composition comprising: (a) at least 50% by weight of an oil of lubricating viscosity, based on the weight of the composition; (b) from 5 to 25 weight percent, based on the weight of the composition, of an oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents, wherein the oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or each oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent in the mixture, has a total base number (TBN) of from 0 to 500 mg KOH / g as measured by ASTM D2896; (c) 0.1 to 10 wt. %, based on the weight of the composition, of one or more oil-soluble or oil-dispersible ashless dispersants; and optionally, (d) 0.1 to 10% by weight of a polyalkylene-substituted succinic anhydride, based on the weight of the composition The present invention provides a method comprising:

[0008] Preferably, the oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents, is present in an amount of 6 to 20% by weight based on the total weight of the composition, more preferably 7 to 15% by weight based on the total weight of the composition. When a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents is used, these amounts refer to the weight percentage of the mixture present in the composition.

[0009] The method includes supplying a marine residual fuel to a four-stroke marine diesel engine, the marine residual fuel meeting the ISO 8217 2017 fuel standard for marine residual fuel and having a sulfur content greater than 0.1% and less than 0.5% by mass, based on the mass of the fuel. While any residual fuel meeting these criteria is suitable for practicing the process of the claimed invention, preferably the marine residual fuel is selected from the group consisting of atmospheric tower bottoms, vacuum tower bottoms, light cycle oil, heavy cycle oil, fluid catalytic cracked cycle oil, fluid catalytic cracked slurry oil, thermal cracking residue, thermal tar, unfluxed tar, thermally cracked heavy distillates, Group I slack wax, deasphalted oil, thermally cracked kerosene gas-to-liquid wax, hydrotreated light cycle oil, hydrotreated heavy cycle oil, hydrotreated fluid catalytic cracked cycle oil, hydrotreated thermally cracked heavy distillates, hydrotreating residue, hydrocracker Preferably, the residual marine fuel comprises one or a mixture of two or more residual refinery streams selected from the group consisting of sulphur dioxide (SDS), ...

[0010] More preferably, the marine residual fuel consists essentially of one or a mixture of two or more residual refinery streams selected from atmospheric tower bottoms, vacuum tower bottoms, light cycle oil, heavy cycle oil, fluid catalytic cracking cycle oil, fluid catalytic cracking slurry oil, thermal cracking residue, thermal tar, unfluxed tar, thermally cracked heavy distillates, Group I slack wax, deasphalted oil, thermally cracked kerosene gas-to-liquid wax, hydrotreated light cycle oil, hydrotreated heavy cycle oil, hydrotreated fluid catalytic cracking cycle oil, hydrotreated thermally cracked heavy distillates, hydrotreated residue, hydrocracked hydrowax, and hydrotreated hydrocracked deasphalted oil. Even more preferably, the marine residual fuel consists essentially of a mixture of two or more of these residual refinery streams. DETAILED DESCRIPTION OF THE INVENTION

[0011] IMO 2020 compliant fuels must meet the ISO 8217 2017 fuel standard for marine residual fuels and have the required low sulfur content, but their composition and physical properties are variable and depend on the residual stream used in their production. The selection of which blend components to use requires complex calculations based on factors including availability, cost, compatibility and stability effects, and refinery design. The lubricating oil composition comprises (b) an oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents, which detergents are well known in the art. Detergents are additives that reduce the formation of piston deposits in engines, such as low-temperature varnish and lacquer deposits; they usually have acid-neutralizing properties and are capable of holding finely divided solids in suspension. Most detergents are based on "soaps," which are metal salts of acidic organic compounds. Thus, the lubricating oil composition of the present invention contains as the soap an alkali metal or alkaline earth metal salt of salicylic acid, i.e., a salicylate soap. Preferably, the oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents, provides the lubricating oil composition with 30 to 100, preferably 40 to 90, more preferably 50 to 80 mmol of salicylate soap per kg of lubricating oil composition. When two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents are used, these ranges refer to the amount of salicylate soap provided by the mixture.

[0012] By the term "salicylate soap" we mean the amount of alkali metal or alkaline earth metal salicylate contributed by one or more alkali metal or alkaline earth metal salicylate detergents, excluding any overbasing materials. The moles of alkali metal or alkaline earth metal salicylate (salicylate soap) can be derived using titration methods, including two-phase titration, total acid number (TAN) determined using ASTM D664, dialysis, and other well-known analytical techniques. The total amount of metal must be determined and allocated to salicylic acid and inorganic acid using a metal ratio. The total amount of metal present is usually conveniently determined by inductively coupled plasma atomic emission spectroscopy (ASTM D4951). The metal ratio is defined as the total amount of metal present divided by the amount of metal in excess of the amount required to neutralize any salicylic acid present, i.e., the amount of metal neutralizing the inorganic acid. Metal ratios are provided by manufacturers of commercial detergents and can be determined by the manufacturer with knowledge of the total amount of salt present and the average molecular weight of the salicylic acid. The amount of alkali metal or alkaline earth metal salicylate present in a detergent can be determined by dialyzing the detergent and quantifying the amount of residue. If the average molecular weight of the salicylate salt is unknown, the residue from the dialyzed detergent can be treated with a strong acid to convert the salt to its acid form, which can then be analyzed by chromatography, proton NMR, and mass spectrometry to correlate with the known property of salicylic acid. More specifically, the detergent can be dialyzed, and then the residue can be treated with a strong acid to convert any salts to their respective acid forms. The hydroxide number of the mixture can then be measured using the method described in ASTM D1957. Because salicylic acid contains hydroxyl functional groups, a separate analysis must be performed to quantify the amount of these hydroxyl groups so that the hydroxide number determined by ASTM D1957 can be corrected. Alternatively, a second method for deriving the moles of alkali metal or alkaline earth metal salicylate (salicylate soap) assumes that all of the salicylic acid added to make the detergent is actually converted to the salt. Both of these methods allow for the determination of the amount of salicylate soap present in a detergent.

[0013] Salicylic acid is typically prepared by carboxylation of phenoxides, for example by the Kolbe-Schmitt process. Methods for overbasing salicylic acid are well known to those skilled in the art. Detergents generally comprise a polar head and a long hydrophobic tail, with the polar head comprising a metal salt of an acidic organic compound. The salts, generally described as normal or neutral salts, can contain substantially stoichiometric amounts of metal and will typically have a total base number (TBN) of 0 to 80 at 100% active mass (as measured by ASTM D2896). Large amounts of metal base can be incorporated by reacting excess metal compound, e.g., oxide or hydroxide, with an acidic gas, such as carbon dioxide. The resulting overbased detergent contains neutralized detergent as the outer layer of a metal base (e.g., carbonate) micelle. The overbased detergent can have a TBN of 100 or greater, typically 200 to 500 or greater, at 100% active mass. Suitably, the one or more alkali metal or alkaline earth metal salicylate detergents may be neutral or overbased. The one or more alkali metal or alkaline earth metal salicylate detergents have a TBN (as measured by ASTM D2896) of 0 to 500 mgKOH / g, based on 100% active mass. Preferably, the one or more alkali metal or alkaline earth metal salicylate detergents are overbased alkali metal or alkaline earth metal salicylate detergents. Preferably, the one or more overbased alkali metal or alkaline earth metal salicylate detergents have a TBN (as measured by ASTM D2896) of 50 to 500 mgKOH / g, based on 100% active mass, preferably 100 to 500 mgKOH / g, more preferably 150 to 500 mgKOH / g, even more preferably 200 to 500 mgKOH / g, for example 250 to 500 mgKOH / g.

[0014] Preferably, the oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents, is one or more alkali metal or alkaline earth metal C8-C30 alkyl salicylate detergents, more preferably one or more alkali metal or alkaline earth metal C10-C20 alkyl salicylate detergents, and most preferably one or more alkali metal or alkaline earth metal C14-C18 alkyl salicylate detergents. The alkyl group may be linear or branched, and examples of suitable alkyl groups include octyl, nonyl, decyl, dodecyl, pentadecyl, octadecyl, eicosyl, docosyl, tricosyl, hexacosyl, and triacontyl. The salicylate detergents defined herein may also include their sulfurized derivatives.

[0015] Preferably, the one or more alkali metal or alkaline earth metal salicylate detergents are one or more alkaline earth metal salicylate detergents. Calcium salicylate and magnesium salicylate detergents, especially calcium salicylate detergents, are especially preferred. Preferably, the oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents, contributes at least 0.3, more preferably at least 0.4, and even more preferably at least 0.5, mass % of metal to the lubricating oil composition, based on the total mass of the lubricating oil composition, as measured by ASTM D 5185. Preferably, the oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents, contributes at most 1.5, more preferably at most 1.3, and even more preferably at most 1.2, mass % of metal to the lubricating oil composition, based on the total mass of the lubricating oil composition, as measured by ASTM D 5185.

[0016] Other metal-containing detergents may be present in the lubricating oil composition, including oil-soluble salts of metals, particularly alkali or alkaline earth metals, such as sodium, potassium, lithium, calcium, and magnesium, such as neutral and overbased sulfonates, phenates, sulfurized phenates, thiophosphonates, and naphthenates. The most commonly used metals are calcium and magnesium, and mixtures of calcium and / or magnesium with sodium, both of which may be present in detergents used in lubricants. The detergents may be used in various combinations. In a preferred embodiment, the oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents, is the only metal-containing detergent in the lubricating oil composition.

[0017] The lubricating oil composition includes (c) one or more oil-soluble or oil-dispersible ashless dispersants. Ashless dispersants useful in the present invention suitably comprise an oil-soluble long-chain polymeric backbone having functional groups capable of associating with particles to be dispersed. Typically, the dispersants have amine, amine-alcohol, or amide polar moieties attached to the polymer backbone, often via a bridging group. Suitable ashless dispersants may be selected, for example, from oil-soluble salts, esters, amino-esters, amides, imides, and oxazolines of long-chain hydrocarbon-substituted mono- and polycarboxylic acids or their anhydrides; thiocarboxylic acid derivatives of long-chain hydrocarbons; long-chain aliphatic hydrocarbons having a polymeric portion directly attached thereto; and Mannich condensation products formed by the condensation of long-chain substituted phenols with formaldehyde and polyalkylenepolyamides. Dispersants suitable for use in the lubricating oil compositions of the present invention are preferably derived from polyalkenyl-substituted mono- or dicarboxylic acids, anhydrides, or esters, having polyalkenyl moieties of number average molecular weight of at least 900 and greater than 1.3 to 1.7, preferably greater than 1.3 to 1.6, and most preferably greater than 1.3 to 1.5 functional groups (mono- or dicarboxylic acid-producing moieties) per polyalkenyl moiety (medium functionality dispersants). The functionality (F) can be determined according to the following formula:

[0018] F=(SAP×Mn) / ((112,200×AI)-(SAP×MW)) (1) where SAP is the saponification number (i.e., the number of milligrams of KOH consumed in the complete neutralization of the acid groups in one gram of reaction product, as determined according to ASTM D94); Mn is the number average molecular weight of the starting olefin polymer; AI is the percent actives of the reaction product (the remainder being unreacted olefin polymer, carboxylic acid, anhydride or ester, and diluent); and MW is the molecular weight of the carboxylic acid, anhydride, or ester (e.g., 98 for succinic anhydride). Generally, each mono- or dicarboxylic acid generating moiety will react with a nucleophilic group (the polar portion of an amine, alcohol, amide, or ester), and the number of functional groups in the polyalkenyl-substituted carboxylic acylating agent will determine the number of nucleophilic groups in the finished dispersant. The polyalkenyl moiety of the dispersant preferably has a number average molecular weight of at least 450, suitably at least 700, preferably at least 900, for example from 450 to 3000, preferably from 700 to 3000, more preferably from 900 to 2400. As the exact molecular weight of the dispersant will depend on a number of parameters including the type of polymer used to derive the dispersant, the number of functional groups, and the type of nucleophilic group available, the molecular weight of the dispersant is generally expressed in terms of the molecular weight of the polyalkenyl moiety. Polymer molecular weight, specifically

[0019]

number

[0020] can be determined by a variety of known techniques. One convenient method is gel permeation chromatography (GPC), which also provides number average molecular weight distribution information (see W.W. Yau, J.J. Kirkland and D.D. Bly, "Modern Size Exclusion Liquid Chromatography", John Wiley and Sons, New York, 1979). Another useful method for determining molecular weight, especially for low molecular weight polymers, is vapor pressure osmometry (see, e.g., ASTM D3592). Polyalkenyl moieties suitable for forming dispersants useful in the lubricating oil compositions of the present invention preferably have a narrow molecular weight distribution (MWD), also known as polydispersity, determined by the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn). Polymers having an Mw / Mn ratio of less than 2.2, preferably less than 2.0, are most desirable. Suitable polymers have a polydispersity of 1.5 to 2.1, preferably 1.6 to 1.8. Suitable hydrocarbons or polymers for use in forming dispersants include homopolymers, interpolymers, or low molecular weight hydrocarbons. One family of such polymers comprises polymers of ethylene and / or at least one C3-C28 alpha olefin having the formula HC=CHR1, where R1 is a straight or branched chain alkyl group containing from 1 to 26 carbon atoms, and the polymers contain carbon-carbon unsaturation, preferably a high degree of terminal ethenylidene unsaturation. Preferably, the polymer comprises an interpolymer of ethylene and at least one alpha olefin of the above formula, where R1 is alkyl of from 1 to 18 carbon atoms, more preferably alkyl of from 1 to 8 carbon atoms, and even more preferably alkyl of from 1 to 2 carbon atoms.

[0021] Another useful class of polymers is polymers prepared by cationic polymerization of isobutene, styrene, and the like. A typical polymer in this class is polyisobutene, obtained by polymerization of a C4 refinery stream having a butene content of 35 to 75% by weight and an isobutene content of 30 to 60% by weight in the presence of a Lewis acid catalyst, such as aluminum trichloride or boron trifluoride. A preferred monomer source for making poly-n-butenes is a petroleum feedstream, such as Raffinate II. These feedstreams are disclosed in the art, for example, in U.S. Pat. No. 4,952,739. Polyisobutylene is the most preferred backbone of the present invention because it is readily available from butene streams by cationic polymerization (e.g., using AlCl3 or BF3 catalysts). The polyisobutylene typically contains residual unsaturation along the chain in an amount of one ethylenic double bond per polymer chain. A preferred embodiment utilizes polyisobutylene prepared from a pure isobutylene stream or a raffinate I stream to prepare reactive isobutylene polymers having terminal vinylidene olefins. Preferably, these polymers, also referred to as highly reactive polyisobutylenes (HR-PIB), have a terminal vinylidene content of at least 65%, e.g., 70%, more preferably at least 80%, and most preferably at least 85%. Methods for producing such polymers are described, for example, in U.S. Pat. No. 4,152,499. HR-PIB is known and is commercially available under the trade names Glissopal™ (from BASF) and Ultravis™ (from BP-Amoco).

[0022] Available polyisobutylene polymers are generally based on hydrocarbon chains of 450 to 3000. Methods for producing polyisobutylene are known. Polyisobutylene can be functionalized by halogenation (e.g., chlorination), thermal "ene" reactions, or free radical reactions using catalysts (e.g., peroxides), as described below. The hydrocarbon or polymer backbone can be functionalized with, for example, carboxylic acid-producing moieties (preferably acid or anhydride moieties) selectively at sites of carbon-carbon unsaturation on the polymer or hydrocarbon chain or randomly along the chain using any of the above three processes or combinations thereof, in any order. Processes for reacting polymeric hydrocarbons with unsaturated carboxylic acids, anhydrides or esters and the preparation of derivatives from such compounds are disclosed in U.S. Pat. Nos. 3,087,936; 3,172,892; 3,215,707; 3,231,587; 3,272,746; 3,275,554; 3,381,022; 3,442,808; 3,565,804; 3,912,764; 4,110,349; 4,234,435; 5,777,025; 5,891,953; and EP 0 382 450 B1; CA-1,335,895 and GB-A-1,440,219. Polymers or hydrocarbons can be functionalized with carboxylic acid-producing moieties (preferably acids or anhydrides) by reacting the polymer or hydrocarbon under conditions that result in the addition of functional moieties or functional agents, i.e., acids, anhydrides, ester moieties, etc., onto the polymer or hydrocarbon primarily at sites of carbon-carbon unsaturation (also called ethylenic or olefinic unsaturation), for example, using a halogen-assisted functionalization (e.g., chlorination) process or a thermal "ene" reaction. Selective functionalization can be achieved by halogenation, e.g., chlorinating or brominating unsaturated α-olefin polymers to 1 to 8 weight percent, preferably 3 to 7 weight percent, chlorine or bromine, based on the weight of the polymer or hydrocarbon, by passing chlorine or bromine through the polymer at temperatures from 60 to 250°C, preferably 110 to 160°C, e.g., 120 to 140°C, for 0.5 to 10 hours, preferably 1 to 7 hours. The halogenated polymer or hydrocarbon (hereinafter backbone) is then reacted with sufficient monounsaturated reactant, e.g., monounsaturated carboxylic acid reactant, to add the required number of functional moieties to the backbone, so that the resulting product contains the desired number of moles of monounsaturated carboxylic acid reactant per mole of halogenated backbone, at temperatures from 100 to 250°C, typically 180 to 235°C, for 0.5 to 10 hours, e.g., 3 to 8 hours. Separately, the backbone and monounsaturated carboxylic acid reactant are mixed and heated as chlorine is added to the hot material.

[0023] The hydrocarbon or polymer backbone can be functionalized by random attachment of functional moieties along the polymer chain by a variety of methods. For example, the polymer may be grafted with a monounsaturated carboxylic reactant, as described above, in solution or solid form, in the presence of a free radical initiator. When carried out in solution, grafting occurs at elevated temperatures ranging from 100 to 260°C, preferably from 120 to 240°C. Preferably, free radical-induced grafting will be accomplished in a mineral lubricating oil solution containing, for example, 1 to 50 wt. %, preferably 5 to 30 wt. %, of polymer, based on the initial total oil solution. Monounsaturated reactants that can be used to functionalize the backbone include mono- and dicarboxylic acid materials, i.e., acids, anhydrides, or acid ester materials, such as (i) monounsaturated C4-C10 dicarboxylic acids, where (a) the carboxyl groups are vicinal (i.e., located on adjacent carbon atoms) and (b) at least one, preferably both, of the adjacent carbon atoms is part of the monounsaturation; (ii) derivatives of (i), such as anhydrides or mono- or diesters derived from C1-C5 alcohols; (iii) monounsaturated C3-C10 monocarboxylic acids in which the carbon-carbon double bond is conjugated with the carboxy group, i.e., the structure -C=C-CO-; and (iv) derivatives of (iii), such as mono- or diesters derived from C1-C5 alcohols. Mixtures of monounsaturated carboxylic acid materials (i)-(iv) can also be used. Upon reaction with the backbone, the monounsaturation of the monounsaturated carboxylic acid reactant becomes saturated. Thus, for example, maleic anhydride becomes backbone-substituted succinic anhydride, and acrylic acid becomes backbone-substituted propionic acid. Typical examples of such monounsaturated carboxylic acid reactants are fumaric acid, itaconic acid, maleic acid, maleic anhydride, chloromaleic acid, chloromaleic anhydride, acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, and the lower alkyl (e.g., C1-C4 alkyl) acid esters of the foregoing acids, such as methyl maleate, ethyl fumarate, and methyl fumarate.

[0024] To provide the required functionality, the monounsaturated carboxylic reactant, preferably maleic anhydride, will typically be used in an amount ranging from an equimolar amount to a 100% weight excess, preferably a 5 to 50% weight excess, based on moles of polymer or hydrocarbon. Excess unreacted monounsaturated carboxylic reactant can be removed from the final dispersant product, for example, by stripping, usually under vacuum, if desired. The functionalized oil-soluble polymer hydrocarbon backbone is then derivatized with a nucleophilic reactant, such as an amine, amino-alcohol, alcohol, metal compound, or mixtures thereof, to form the corresponding derivative. Amine compounds useful for derivatizing the functionalized polymer contain at least one amine and can contain one or more additional amine or other reactive or polar groups. These amines can be hydrocarbyl amines, or primarily hydrocarbyl amines, but the hydrocarbyl group can contain other groups, such as hydroxy groups, alkoxy groups, amide groups, nitrile groups, imidazoline groups, and the like. Particularly useful amine compounds include mono- and polyamines, such as polyalkenes and polyoxyalkylene polyamines having 2 to 60, e.g., 2 to 40 (e.g., 3 to 20), total carbon atoms and 1 to 12, e.g., 3 to 12, preferably 3 to 9, and most preferably 6 to 7, nitrogen atoms per molecule. Mixtures of amine compounds, such as those prepared by the reaction of alkylene dihalides with ammonia, can be advantageously used. Preferred amines are saturated aliphatic amines, such as 1,2-diaminoethane; 1,3-diaminopropane; 1,4-diaminobutane; 1,6-diaminohexane; polyethyleneamines, such as diethylenetriamine; triethylenetetramine; tetraethylenepentamine; and polypropyleneamines, such as 1,2-propylenediamine; and di-(1,2-propylene)triamine. The polyalkylenepolyamine mixture known as PAM is commercially available. A particularly preferred polyalkylenepolyamine mixture is the mixture obtained by distilling light ends from PAM products. The resulting mixture, known as "heavy" PAM or HPAM, is also commercially available. The properties and characteristics of both PAM and / or HPAM are described, for example, in U.S. Patent Nos. 4,938,881; 4,927,551; 5,230,714; 5,241,003; 5,565,128; 5,756,431; 5,792,730; and 5,854,186.

[0025] Dispersants used in lubricating oil compositions according to the method of the present invention may be borated by conventional means, as generally taught in U.S. Patent Nos. 3,087,936, 3,254,025, and 5,430,105. Boronation of the dispersant is readily accomplished by treating the acyl nitrogen-containing dispersant with a boron compound, such as boron oxide, boron halides, boric acids, and boric acid esters, in an amount sufficient to provide a 0.1 to 20 atomic ratio of boron for each mole of acylated nitrogen component. The boron, found in the product as dehydrated boric acid polymers (primarily (HBO2)3), is believed to be attached to the dispersant imides and diimides as amine salts (e.g., the metaborate salt of the diimide). Borylation can be accomplished by adding a sufficient amount of a boron compound, preferably boric acid, to the acyl nitrogen-containing compound, usually as a slurry, and heating at 135°C to 190°C, e.g., 140°C to 170°C, for 1 to 5 hours, followed by nitrogen stripping. Alternatively, boron treatment can be accomplished by adding boric acid to a hot reaction mixture of the dicarboxylic acid material and the amine while removing water. Other post-reaction processes known in the art can also be applied. When a boronated dispersant is present in the lubricating oil composition, the amount of boron contributed by the boronated dispersant to the lubricating oil composition is suitably at least 10, such as at least 30, for example at least 50 or at least 65 ppm of boron, based on the total weight of the lubricating oil composition. When present, the boronated ashless dispersant suitably contributes no more than 1000 ppm, preferably no more than 750 ppm, more preferably no more than 500 ppm of boron to the lubricating oil composition, based on the total weight of the lubricating oil composition.

[0026] In a preferred embodiment, the one or more oil-soluble or oil-dispersible ashless dispersants comprise a succinimide formed by the reaction of a polyisobutylene-substituted succinic anhydride with a polyalkylene polyamine, preferably a mixture of polyalkylene polyamines. The number average molecular weight of the polyisobutylene group is suitably at least 450, preferably at least 700, more preferably at least 900, for example, 450 to 3000, preferably 700 to 3000, more preferably 900 to 2400. In embodiments utilizing multiple oil-dispersible ashless dispersants, each is preferably a succinimide formed by the reaction of a polyisobutylene-substituted succinic anhydride with a polyalkylene polyamine, preferably a mixture of polyalkylene polyamines, with the polyisobutylene group having a number average molecular weight of 900 to 1500 in one dispersant and the polyisobutylene group having a number average molecular weight of 1800 to 3000 in another dispersant. In a particularly preferred embodiment, two oil-soluble or oil-dispersible ashless dispersants are used, each a succinimide formed by the reaction of a polyisobutylene-substituted succinic anhydride with a mixture of polyalkylene polyamines, wherein the number average molecular weight of the polyisobutylene group of one dispersant is 900-1000, and the number average molecular weight of the polyisobutylene group of the other dispersant is 2000-2500. Preferably, the one or more oil-soluble or oil-dispersible ashless dispersants are present in the lubricating oil composition in an amount from 0.4 to 10 mass %, preferably from 0.5 to 8 mass %, more preferably from 1 to 5 mass %, based on the mass of the composition.

[0027] The lubricating oil composition may optionally further comprise (d) a polyalkylene-substituted succinic anhydride. These compounds include those described above with respect to component (c) as the functionalized oil-soluble polymeric hydrocarbon backbone prior to derivatization with a nucleophilic reactant. Preferred are polyisobutylene-substituted succinic anhydrides in which the polyisobutylene group has a number average molecular weight of at least 450, preferably at least 700, more preferably at least 900, for example, 450 to 3000, preferably 700 to 3000, more preferably 900 to 2400. Preferred compound (d) is a polyisobutylene-substituted succinic anhydride in which the polyisobutylene group has a number average molecular weight of 900 to 1000. In a preferred embodiment, the lubricating oil composition further comprises (d) a polyalkylene-substituted succinic anhydride, preferably the polyisobutylene-substituted succinic anhydride described above. When present, the polyalkylene-substituted succinic anhydride (d) is preferably present in the lubricating oil composition in an amount of from 0.1 to 10 mass %, preferably from 0.2 to 8 mass %, more preferably from 0.5 to 6 mass %, based on the mass of the composition.

[0028] At least 50 mass % of the lubricating oil composition used in the present invention comprises (a) an oil of lubricating viscosity. The oil may range in viscosity from a light distillate mineral oil to a heavy lubricating oil. Typically, the oil has a viscosity in the range of 2 to 40, e.g., 3 to 15 mm / s, measured at 100°C, and a viscosity index of 80 to 100, e.g., 90 to 95. Natural oils include animal and vegetable oils (e.g., castor oil, lard oil); liquid petroleum oils of the paraffinic, naphthenic, and mixed paraffinic-naphthenic types, and hydrorefined, solvent-treated, or acid-treated mineral oils. Oils of lubricating viscosity derived from coal or shale also serve as useful base oils. Synthetic lubricating oils include hydrocarbon oils and halo-substituted hydrocarbon oils, such as polymerized and copolymerized olefins (e.g., polybutylene, polypropylene, propylene-isobutylene copolymers, chlorinated polybutylene, poly(1-hexene), poly(1-octene), poly(1-decene)); alkylbenzenes (e.g., dodecylbenzene, tetradecylbenzene, dinonylbenzene, di(2-ethylhexyl)benzene); polyphenyls (e.g., biphenyl, terphenyl, alkylated polyphenols); and alkylated diphenyl ethers and alkylated diphenyl sulfides and their derivatives, analogs, and homologs.

[0029] Alkylene oxide polymers and interpolymers and derivatives thereof in which 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 the polymerization of ethylene oxide or propylene oxide, and the alkyl and aryl ethers of polyoxyalkylene polymers (e.g., methyl polyisopropylene glycol ether having a molecular weight of 1000 or the diphenyl ether of polyethylene glycol having a molecular weight of 1000 to 1500); and their mono- and polycarboxylic acid esters, such as the acetate ester of tetraethylene glycol, mixed C3-C8 fatty acid esters, and C13 oxoacid diesters.

[0030] Another suitable class of synthetic lubricating oils comprises the esters of dicarboxylic acids (e.g., phthalic acid, succinic acid, alkyl and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkyl malonic acids, alkenyl malonic acids) and various alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycol monoether, propylene glycol). Specific examples of such esters include dibutyl adipate, di(2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate, didecyl phthalate, dieicosyl sebacate, 2-ethylhexyl diester of linoleic acid dimer, and the complex ester formed by reacting 1 mole of sebacic acid with 2 moles of tetraethylene glycol and 2 moles of 2-ethylhexanoic acid.

[0031] Esters useful as synthetic oils also include those made from C5-C12 monocarboxylic acids and polyol and polyol esters such as neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, and tripentaerythritol. Silicon-based oils, such as polyalkyl, polyaryl, polyalkoxy or polyaryloxy silicone oils and silicate oils, constitute another useful class of synthetic lubricating oils; these 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)siloxane and poly(methylphenyl)siloxane.Other synthetic lubricating oils include the liquid esters of phosphorus-containing acids (for example, tricresyl phosphate, trioctyl phosphate, decylphosphonic acid) and polymeric tetrahydrofurans. Unrefined, refined, and re-refined oils can be used in the lubricants of the present invention. Unrefined oils are those obtained directly from natural or synthetic sources without further refinery treatment. For example, shale oil obtained directly from retorting operations and used without further treatment; petroleum oil obtained directly from distillation and used without further treatment; or ester oil obtained directly from esterification and used without further treatment are unrefined oils.

[0032] The American Petroleum Institute (API) publication "Engine Oil Licensing and Certification System," Industry Services Department, Fourteenth Edition, December 1996, Addendum 1, December 1998, classifies base stocks as follows: a) Group I base stocks contain less than 90 percent saturates and / or greater than 0.03 percent sulfur 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 sulfur 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 sulfur 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 (PAOs). e) Group V base stocks include all other base stocks not included in Group I, II, III, or IV. The analysis method for base stock is shown in the table below.

[0033] TIFF0007721605000002.tif4772

[0034] The present invention preferably encompasses oils of lubricating viscosity, such as those described above, containing 90% or more saturates and 0.03% or less sulfur, e.g., Group II, III, IV, or V. These include basestocks derived from hydrocarbons synthesized by the Fischer-Tropsch process, in which synthesis gas (or "syngas") containing carbon monoxide and hydrogen is first purified and then converted to hydrocarbons using a Fischer-Tropsch catalyst. These hydrocarbons typically require further processing to be useful as base oils. For example, they may be hydroisomerized; hydrocracked and hydroisomerized; dewaxed; or hydroisomerized and dewaxed by methods well known in the art. Syngas may be produced, for example, from natural gas or other gaseous hydrocarbons, e.g., by steam reforming, when the base stock may be referred to as a gas-to-liquid ("GTL") base oil; or from the gasification of biomass, when the base stock may be referred to as a biomass-to-liquid ("BTL" or "BMTL") base oil; or from the gasification of coal, when the base stock may be referred to as a coal-to-liquid ("CTL") base oil. However, the present invention is not limited to the use of the above base stocks; and thus may include, for example, the use of Group I base stocks and the use of bright stock. Preferably, the oil of lubricating viscosity in the present invention contains 50 mass % or more of said base stock. It may contain 60, e.g., 70, 80, or 90 mass % or more of said base stock. The oil of lubricating viscosity may be substantially all of said base stock or mixtures thereof. Preferably, the lubricating oil composition used in the method of the present invention comprises at least 60 mass %, such as at least 70 mass %, or at least 80 mass %, of oil of lubricating viscosity, based on the mass of the composition.

[0035] Other additives may optionally be present in the lubricating oil composition used in the method of the present invention. In an embodiment, the lubricating oil composition further comprises one or more anti-wear additives. Anti-wear agents reduce friction and excessive wear and are typically based on sulfur- or phosphorus-containing compounds, or both, which can, for example, cause the buildup of polysulfide films on the involved surfaces. Of note are dihydrocarbyl dithiophosphate metal salts, where the metal can be an alkali or alkaline earth metal, or aluminum, lead, tin, molybdenum, manganese, nickel, copper, and preferably zinc. Metal dihydrocarbyl dithiophosphate salts can be prepared by first forming a dihydrocarbyl dithiophosphoric acid (DDPA) according to known techniques, usually by reacting P2S5 with one or more alcohols or phenols, and then neutralizing the resulting DDPA with a metal compound. For example, a dithiophosphoric acid can be prepared by reacting a mixture of primary and secondary alcohols. Alternatively, multiple dithiophosphoric acids can be prepared in which the hydrocarbyl groups on one dithiophosphoric acid are entirely secondary in nature and the hydrocarbyl groups on the others are entirely primary in nature. While any basic or neutral metal compound can be used to make the metal salt, oxides, hydroxides, and carbonates are most commonly utilized. Commercially available additives often contain an excess of metal due to the use of an excess of basic metal compound in the neutralization reaction. The preferred zinc dihydrocarbyl dithiophosphates (ZDDPs) are oil-soluble salts of dihydrocarbyl dithiophosphates and can be represented by the formula:

[0036] [ka]

[0037] wherein R and R' may be the same or different hydrocarbyl groups containing 1 to 18, preferably 2 to 12, carbon atoms, including, for example, alkyl, alkenyl, aryl, arylalkyl, alkaryl, and alicyclic groups. Alkyl groups of 2 to 8 carbon atoms are particularly preferred for the R and R' groups. Thus, the groups may be, for example, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl, amyl, n-hexyl, i-hexyl, n-octyl, decyl, dodecyl, octadecyl, 2-ethylhexyl, phenyl, butylphenyl, cyclohexyl, methylcyclopentyl, propenyl, or butenyl. To achieve oil solubility, the total number of carbon atoms in the dithiophosphoric acid (i.e., R and R') will generally be about 5 or greater. Thus, the zinc dihydrocarbyl dithiophosphate can include a zinc dialkyldithiophosphate. ZDDP is added to the lubricating oil composition in an amount sufficient to provide not more than 1200 ppm by weight, preferably not more than 1000 ppm, more preferably not more than 900 ppm, and most preferably not more than 850 ppm of phosphorus by weight, based on the total weight of the lubricating oil composition, as measured in accordance with ASTM D 5185. ZDDP is suitably added to the lubricating oil composition in an amount sufficient to provide at least 100 ppm, preferably at least 200 ppm, e.g., 200 to 400 ppm, of phosphorus by weight, based on the total weight of the lubricating oil composition, as measured in accordance with ASTM D 5185. Mixtures of more than one antiwear additive may be used, for example, mixtures of two or more different ZDDP compounds. Other additives (or co-additives) that may be present in the lubricating oil composition used in the method of the present invention are described below, and when present, the amount of co-additive is as set forth below in mass percent of the active ingredients in the lubricating oil composition.

[0038] TIFF0007721605000004.tif43138

[0039] As is known in the art, some additives can provide a variety of benefits. Rust inhibitors selected from the group consisting of nonionic polyoxyalkylene polyols and esters thereof, polyoxyalkylene phenols, and anionic alkylsulfonic acids may be used. Copper and lead-containing corrosion inhibitors may be used, but are typically not required in the formulations of the present invention. Typically, these compounds are thiadiazole polysulfides containing 5 to 50 carbon atoms, their derivatives, and polymers thereof. Derivatives of 1,3,4-thiadiazole are typical, such as those described in U.S. Patent Nos. 2,719,125; 2,719,126; and 3,087,932. Other similar materials are described in U.S. Patent Nos. 3,821,236; 3,904,537; 4,097,387; 4,107,059; 4,136,043; 4,188,299; and 4,193,882. Other additives include thio- and polythiosulfenamides of thiadiazoles, such as those described in UK Patent Specification No. 1,560,830. Benzotriazole derivatives also fall within this class of additives. When these compounds are included in a lubricating oil composition, they are preferably present in an amount not exceeding 0.2 wt.% active ingredient.

[0040] A small amount of a demulsifying component may be used. A preferred demulsifying component is described in EP 330522. It is obtained by reacting an alkylene oxide with an adduct obtained by reacting a bis-epoxide with a polyhydric alcohol. The demulsifier should be used at a level not exceeding 0.1% by weight active ingredient. Treat rates of 0.001 to 0.05% by weight active ingredient are convenient. Foam control can be achieved by many compounds, including polysiloxane type antifoam agents, such as silicone oil or polydimethylsiloxane. The individual additives, both essential components (b) and (c), optional component (d), and any co-additives can be incorporated into the oil of lubricating viscosity by any convenient means. Thus, each component can be added directly to the oil of lubricating viscosity by dispersing or dissolving it in the oil of lubricating viscosity at the desired concentration. The blending can occur at ambient or elevated temperatures. Preferably, all components are blended into a concentrate or additive package which is subsequently blended into an oil of lubricating viscosity to produce the finished lubricating oil composition. Concentrates will typically be formulated to contain precise amounts of additives to provide the desired concentration in the final formulation when combined with a predetermined amount of oil of lubricating viscosity. The concentrate formulations are preferably prepared according to the method described in U.S. Pat. No. 4,938,880, which describes making a premix of ashless dispersants and metal detergents that are preblended at a temperature of at least about 100° C. The premix is then cooled to at least 85° C. and additional ingredients are added.

[0041] In a second aspect, the present invention provides the use of a lubricating oil composition as defined in relation to the first aspect for reducing the incidence of deposits on pistons of a four-stroke marine diesel engine during operation of the engine when the engine is powered with a marine residual fuel that meets the ISO 8217 2017 fuel standard for marine residual fuel and has a sulphur content of more than 0.1% and less than 0.5% by mass based on the mass of the fuel. [Example]

[0042] The present invention will now be described by way of example only. Lubricating oil compositions were prepared as shown in Table 1 below. The amounts given are in wt % based on the total weight of the oil composition.

[0043] TIFF0007721605000005.tif5380

[0044] The ingredients used were as follows: Disp 1: A borated (1.3 wt. % B) ashless dispersant that is a succinimide formed by the reaction of a polyisobutylene-substituted succinic anhydride with a polyalkylene polyamine, where the polyisobutylene group has a number average molecular weight of 950. Disp 2: A non-boronated ashless dispersant which is a succinimide formed by the reaction of a polyisobutylene-substituted succinic anhydride with a polyalkylene polyamine, the polyisobutylene group having a number average molecular weight of 2225. Det 1: A calcium salicylate detergent having a TBN of 350 mg KOH / g and a calcium content of 12.5 wt. % as measured by ASTM D2896. Det 2: A calcium salicylate detergent having a TBN of 225 mg KOH / g as measured by ASTM D2896 and a calcium content of 8 wt. %. ZDDP: zinc dialkyldithiophosphate in which 60% of the alkyl groups are 10 C4 groups and 40% are 10 C5 groups, and the zinc content is 8.8% by weight. PIBSA: Polyisobutylene-substituted succinic anhydride, where the polyisobutylene group has a number average molecular weight of 950. Gp II oil: API Group II mineral oil.

[0045] Lubricating oil compositions were evaluated for asphaltene dispersancy using the Focused Beam Reflectance Method (FBRM), a technique that provides a measure of asphaltene aggregation and therefore indicates the tendency of a lubricating oil to form piston deposits when used to lubricate an engine. The FBRM test method utilizes a fiber optic probe. The tip of the probe houses optics that focus laser light to a small spot. The optics rotate so that the focused beam scans a circular path across a window through which the oil sample to be measured flows. As asphaltene particles in the oil flow past the window, they cross the scanning light path, and backscattered light from the particles is collected. The scanning laser beam moves much faster than the particles, meaning that the particles are effectively stationary compared to light. When the focused beam intersects one end of the particle, the amount of backscattered light collected increases and decreases again when the beam reaches the other end of the particle. The instrument determines the time during which an increase in backscattered light is detected. This time is multiplied by the laser scanning speed to obtain the distance. This distance is the chord length, which is actually the linear length between two points on the particle edges. FBRM technology measures tens of thousands of chord lengths per second, providing a chord length distribution, usually expressed in microns. This provides an accurate measure of the particle size distribution of asphaltene particles in the sample. The FBRM instrument used was a model Lasentec G400 supplied by Mettler Toledo, Leicester, UK. It was configured to provide particle size resolution between 1 μm and 1 mm. While the data obtained can be presented in several ways, our studies have shown that the average counts per second can be used as a quantitative measure of asphaltene dispersity. This value is a function of both the average particle size and the degree of aggregation. Five different marine residual fuels were used, which are detailed in Table 2 below.

[0046] TIFF0007721605000006.tif43154

[0047] Fuels 1 to 3 are examples of marine residual fuels that meet current regulations for such fuels in that they have a sulfur content of less than 3.5% by mass and that meet the ISO 8217 2017 fuel standard for marine residual fuels. These fuels will not be usable after 1 January 2020 unless ships using them are fitted with appropriate exhaust gas cleaning systems. Fuels 4 and 5 are examples of marine residual fuels that have a sulphur content that is less than 0.5% by mass and therefore can be used after 1 January 2020. They also meet the requirements of the ISO 8217 2017 fuel standard for marine residual fuels. It is noteworthy that both high and low sulfur fuels have appreciable and similar asphaltene content, which was determined by the "pentane in-solubles" method presented in Appendix X1 of ASTM D2007-11. As a first step, individual samples (880 g) of each lubricating oil composition detailed in Table 1 were artificially aged by heating at 140°C with stirring in a multi-necked flat-bottom flask and passing air through the oil through a sintered glass tube at a flow rate of 45 liters / hour for 48 hours. Individual samples (49.5 g each) of the lubricating oil compositions aged as described above were then heated to 60°C and maintained at that temperature with stirring. A weighed sample (9.90 g) of each fuel shown in Table 2 was added to each oil sample. An FBRM probe was inserted into each mixture and measurements were collected for 15 minutes. The results obtained, expressed as average counts per second, are detailed in Table 3 below. Each data point is the average of two individual measurements for each sample.

[0048] TIFF0007721605000007.tif35156

[0049] A unique pattern of behavior was evident for fuels with high sulfur content (Fuels 1-3). Comparing the results for Oil 1 and Oil 2, it was clear that the addition of dispersant greatly reduced the ability of the oil to disperse asphaltenes, as evidenced by the large increase in the average counts per second recorded. Further addition of PIBSA resulted in some improvement (compare Oils 2 and 3), but Oil 3 still performed significantly worse than Oil 1 in each case. A similarly unique but contrasting trend was observed for fuels with low sulfur content (Fuels 4 and 5), where the addition of dispersant (compare Oil 1 and Oil 2) resulted in a significant increase in the oil's ability to disperse asphaltenes, and this behavior was further improved by the addition of PIBSA (compare Oils 2 and 3). These data demonstrate that the method of the present invention allows for a reduction in the incidence of piston deposits in a four-stroke marine diesel engine when running on residual fuels in compliance with the upcoming IMO 2020 regulations. Oils 1, 2 and 3 listed in Table 1 above were evaluated for purification performance in a Ricardo Atlas II four-stroke, single-cylinder, medium-speed engine, running at full engine load and maximum rated speed for a duration of 60 hours each under the following conditions:

[0050] TIFF0007721605000008.tif48101

[0051] This test allows for the measurement of a lubricating oil's ability to prevent deposits. A commercially available very low sulfur heavy fuel oil (VLSFO) meeting the RMG380 specification was used for these tests (Fuel 6). It had a sulfur content of less than 0.5% by mass and met the requirements of the ISO 8217 2017 fuel standard for marine residual fuels.

[0052] TIFF0007721605000009.tif23146

[0053] At the completion of the test, the top of the piston and ring components were visually assessed (according to DIN 51349-3) for deposits formed during operation. The results are given in Table 6.

[0054] TIFF0007721605000010.tif37142

[0055] Comparing Oil 1 with Oil 2 and Oil 3, it is clear that the addition of dispersant reduced deposit levels in the engine when running with marine residual fuel having a sulfur content of less than 0.5% by mass and meeting the requirements of the ISO 8217 2017 fuel standard for marine residual fuels. Another aspect of the present invention may be as follows. [1] A method for reducing the incidence of deposits on pistons of a four-stroke marine diesel engine during operation of the engine when the engine is powered by a marine residual fuel that meets the ISO 8217 2017 fuel standard for marine residual fuels and has a sulfur content of more than 0.1% and less than 0.5% by mass, based on the mass of the fuel, comprising lubricating the engine with a lubricating oil composition, wherein the lubricating oil composition has a sulfur content of: (a) at least 50% by weight of an oil of lubricating viscosity, based on the weight of the composition; (b) from 5 to 25 weight percent, based on the weight of the composition, of an oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents, wherein the oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or each oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent in the mixture, has a total base number (TBN) of from 50 to 500 mg KOH / g as measured by ASTM D2896; (c) 0.1 to 10 wt. %, based on the weight of the composition, of one or more oil-soluble or oil-dispersible ashless dispersants; and optionally, (d) 0.1 to 10% by weight of a polyalkylene-substituted succinic anhydride, based on the weight of the composition. The method comprising: [2] The method according to [1], wherein the marine residual fuel comprises one or a mixture of two or more residual refinery streams selected from atmospheric tower bottoms, vacuum tower bottoms, light cycle oil, heavy cycle oil, fluid catalytic cracking cycle oil, fluid catalytic cracking slurry oil, thermal cracking residue, thermal tar, unfluxed tar, thermally cracked heavy distillates, Group I slack wax, deasphalted oil, thermally cracked kerosene gas-to-liquid wax, hydrotreated light cycle oil, hydrotreated heavy cycle oil, hydrotreated fluid catalytic cracking cycle oil, hydrotreated thermally cracked heavy distillates, hydrotreated bottoms, hydrocracked hydrowax, and hydrotreated hydrocracked deasphalted oil. [3] The method according to [1], wherein the marine residual fuel consists essentially of one or a mixture of two or more residual refinery streams selected from atmospheric tower bottoms, vacuum tower bottoms, light cycle oil, heavy cycle oil, fluid catalytic cracking cycle oil, fluid catalytic cracking slurry oil, thermal cracking residue, thermal tar, unfluxed tar, thermally cracked heavy distillates, Group I slack wax, deasphalted oil, thermally cracked kerosene gas-to-liquid wax, hydrotreated light cycle oil, hydrotreated heavy cycle oil, hydrotreated fluid catalytic cracking cycle oil, hydrotreated thermally cracked heavy distillates, hydrotreated bottoms, hydrocracked hydrowax, and hydrotreated hydrocracked deasphalted oil. [4] The method according to any one of [1] to [3] above, wherein the alkali metal or alkaline earth metal is calcium. [5] The method according to any one of [1] to [4] above, wherein the oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents, is present in an amount of 6 to 20 mass % based on the total mass of the composition, more preferably 7 to 15 mass % based on the total mass of the composition. [6] The method according to any one of [1] to [5], wherein the one or more oil-soluble or oil-dispersible ashless dispersants include a succinimide formed by the reaction of a polyisobutylene-substituted succinic anhydride with a polyalkylene polyamine. [7] The method according to any one of [1] to [6] above, wherein the lubricating oil composition further contains (d) a polyalkylene-substituted succinic anhydride, preferably a polyisobutylene-substituted succinic anhydride. [8] The method according to any one of [1] to [7], wherein the lubricating oil composition further contains one or more anti-wear additives. [9] The method according to [8], wherein the one or more anti-wear additives comprise a dihydrocarbyl dithiophosphate metal salt, preferably a dihydrocarbyl dithiophosphate zinc salt.

[10] A lubricating oil composition comprising: (a) at least 50% by weight of an oil of lubricating viscosity, based on the weight of the composition; (b) 5 to 25 weight percent, based on the weight of the composition, of an oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents, wherein the oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or each oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent in the mixture, has a total base number (TBN) of 0 and 500 mg KOH / g as determined by ASTM D2896; (c) 0.1 to 10 wt. %, based on the weight of the composition, of one or more oil-soluble or oil-dispersible ashless dispersants; and optionally, (d) 0.1 to 10% by weight of a polyalkylene-substituted succinic anhydride, based on the weight of the composition. The lubricating oil composition comprising 1. Use of a four-stroke marine diesel engine for reducing the incidence of deposits on pistons of the engine during operation of the engine when the engine is powered by a marine residual fuel that meets the ISO 8217 2017 fuel standard for marine residual fuels and has a sulphur content of more than 0.1% and less than 0.5% by mass based on the mass of the fuel.

Claims

1. 1. A method of reducing the incidence of deposits on pistons of a four-stroke marine diesel engine during operation of the engine when the engine is powered on a marine residual fuel that meets the ISO 8217 2017 fuel standard for marine residual fuels and has a sulfur content of greater than 0.1% and less than 0.5%, by mass, based on the mass of the fuel, comprising lubricating the engine with a lubricating oil composition, the lubricating oil composition comprising: (a) at least 50% by weight of an oil of lubricating viscosity, based on the weight of the composition; (b) from 5 to 25 weight percent, based on the weight of the composition, of an oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents, wherein the oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or each oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent in the mixture, has a total base number (TBN) of from 0 to less than 50 mg KOH / g, as determined by ASTM D2896; and (c) 0.1 to 10 wt. %, based on the weight of the composition, of one or more oil-soluble or oil-dispersible ashless dispersants. The method comprising:

2. The lubricating oil composition further comprises: (d) 0.1 to 10% by weight of a polyalkylene-substituted succinic anhydride, based on the weight of the composition.

2. The method of claim 1, comprising:

3. 3. The method of claim 1 or 2, wherein the residual marine fuel comprises one or a mixture of two or more residual refinery streams selected from atmospheric tower bottoms, vacuum tower bottoms, light cycle oil, heavy cycle oil, fluid catalytic cracking cycle oil, fluid catalytic cracking slurry oil, thermal cracking residue, thermal tar, unfluxed tar, thermally cracked heavy distillates, Group I slack wax, deasphalted oil, thermally cracked kerosene gas-to-liquid wax, hydrotreated light cycle oil, hydrotreated heavy cycle oil, hydrotreated fluid catalytic cracking cycle oil, hydrotreated thermally cracked heavy distillates, hydrotreated bottoms, hydrocracked hydrowax, and hydrotreated hydrocracked deasphalted oil.

4. 3. The method of claim 1 or 2, wherein the residual marine fuel comprises one or a mixture of two or more residual refinery streams selected from atmospheric tower bottoms, vacuum tower bottoms, light cycle oil, heavy cycle oil, fluid catalytic cracking cycle oil, fluid catalytic cracking slurry oil, thermal cracking residue, thermal tar, unfluxed tar, thermally cracked heavy distillates, Group I slack wax, deasphalted oil, thermally cracked kerosene gas-to-liquid wax, hydrotreated light cycle oil, hydrotreated heavy cycle oil, hydrotreated fluid catalytic cracking cycle oil, hydrotreated thermally cracked heavy distillates, hydrotreated bottoms, hydrocracked hydrowax, and hydrotreated hydrocracked deasphalted oil.

5. 5. The method according to claim 1, wherein the alkali metal or alkaline earth metal is calcium.

6. 6. The method of any one of claims 1 to 5, wherein the oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents, is present in an amount of 6 to 20% by weight, based on the total weight of the composition.

7. The method of claim 1, wherein the oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents, is present in an amount of 7 to 15% by weight, based on the total weight of the composition.

8. 6. The method of any one of claims 1 to 5, wherein the one or more oil-soluble or oil-dispersible ashless dispersants comprises a succinimide formed by the reaction of a polyisobutylene-substituted succinic anhydride with a polyalkylene polyamine.

9. The method of claim 2, wherein (d) the polyalkylene-substituted succinic anhydride comprises polyisobutylene-substituted succinic anhydride.

10. The method of any one of claims 1 to 9, wherein the lubricating oil composition further comprises one or more anti-wear additives.

11. 11. The method of claim 10, wherein the one or more anti-wear additives comprise a dihydrocarbyl dithiophosphate metal salt.

12. The method of claim 10, wherein the one or more anti-wear additives comprise a zinc dihydrocarbyl dithiophosphate.

13. 1. A lubricating oil composition comprising: (a) at least 50% by weight of an oil of lubricating viscosity, based on the weight of the composition; (b) from 5 to 25 weight percent, based on the weight of the composition, of an oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents, wherein the oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or each oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent in the mixture, has a total base number (TBN) of from 0 to 500 mg KOH / g, as measured by ASTM D2896, but the TBN is neither 0 nor 500 mg KOH / g; and (c) 0.1 to 10 wt. %, based on the weight of the composition, of one or more oil-soluble or oil-dispersible ashless dispersants. The lubricating oil composition comprising 1. Use of a four-stroke marine diesel engine for reducing the incidence of deposits on pistons of the engine during operation of the engine when the engine is powered by a marine residual fuel that meets the ISO 8217 2017 fuel standard for marine residual fuels and has a sulphur content of more than 0.1% and less than 0.5% by mass based on the mass of the fuel.

14. The lubricating oil composition further comprising: (d) 0.1 to 10% by weight of a polyalkylene-substituted succinic anhydride, based on the weight of the composition.

14. The use according to claim 13, comprising:

15. The use of claim 14, wherein (d) the polyalkylene-substituted succinic anhydride comprises polyisobutylene-substituted succinic anhydride.

16. The use according to any one of claims 13 to 15, wherein the alkali metal or alkaline earth metal is calcium.

17. The use according to any one of claims 13 to 16, wherein the oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergent, or a mixture of two or more oil-soluble or oil-dispersible alkali metal or alkaline earth metal salicylate detergents, is present in an amount of 6 to 20% by weight, based on the total weight of the composition.

18. The use of any one of claims 13 to 17, wherein the one or more oil-soluble or oil-dispersible ashless dispersants comprises a succinimide formed by the reaction of a polyisobutylene-substituted succinic anhydride with a polyalkylene polyamine.

19. The use according to any one of claims 13 to 18, wherein the lubricating oil composition further comprises one or more anti-wear additives.

20. The use of claim 19, wherein the one or more anti-wear additives comprise a dihydrocarbyl dithiophosphate metal salt.

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