Method for lubricating alcohol-based engines

Abstract

 The present invention provides an engine oil composition for alcohol-based fuel engines characterized by containing a major amount of mineral oil and /or synthetic oil as a lubricating base oil, and about 0.01 to 10 % by weight of an alkaline-earth metal borate on the basis of the total amount of the composition as an essential component.

Description

2. Background of the Invention

(1) Field of the Invention

[0001] This invention relates to an engine oil composition for alcohol-based fuel engines, and more particularly to an engine oil composition for alcohol-based, such as methanol- or ethanol-based, fuel engines.

(2) Description of the Prior Art

[0002] In alcohol-based fuel engines, for example, methanol-based fuel engines, oxidation products of alcohol such as formic acid and water are easily formed. A problem associated with the formation of such oxidation products has been the blowing of the products through the crankcase as a blow-by gas thus causing the cranckcase to corrode and rust . Furthermore, these polar substances are the causes of wear of several parts of an engine. Therefore, it is necessary to neutralize the formic acid immediately after it enters into the engineoil to deactivate the acid. For the purpose, an overbasic detergent prepared by use of calcium carbonate has been used in conventional engine oils. However,the capacity of such a conventional overbasic detergent for neutralizing formic acid is insufficient, and said detergent has a tendency to become a coarse-grained particle during use. Furthermore, its wear resistance is also unsatisfactory.

[0003] The present invention is based on a discovery whereby efficient results can be attained employing an alkaline-earth metal borate instead of the conventional overbasic detergents.

[0004] The present invention provides for an engine oil composition for alcohol-based fuel engines containing an overbasic detergent having improved capacity for neutralizing formic acid, improved wear resistance and no tendency to form coarse-grained particles during use.

3. Summary of the Invention

[0005] The present invention provides an engine oil composition for alcohol-based fuel engines characterized by containing a major amount of mineral oil and/or synthetic oil as a lubricating base oil, and about 0.01 to 10 % by weight of an alkaline-earth metal borate on the basis of the total amount of the composition as an essential component.

4. Detailed Description of the Invention

[0006] Either mineral oils or synthetic oils may be used as the lubricatong base oils of the present invention. Any paraffinic or naphthenic lubricating base oils may be acceptable wherein said base oils are manufactured by a process consisting mainly of topping of crude oil followed by vacuum distilation to give a lubricating oil fraction, and refining said lubricating fraction by a process selected from the group consisting of solvent deasphalting, solvent extraction, hydro-cracking, solvent dewaxing, catalytic dewaxing, hydro-refining, sulfuric acid treating, and clay treating. The synthetic oils of the present invention include, for example, α -olefin polymers (polybutenes, octene-1 oligomers, decene-1 oligomers, and the like), alkylbenzenes, alkylnaphthalenes, diesters (ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, di-3-ethylhexyl sebacate, and the like), polyol esters (trimethylolpropane caprilate, trimethylolpropane pelargonate, pentaerythritol- 2-ethyl hexanoate, pentaerythritol pelargonate, and the like), polyoxyalkylene glycol, polyphenyl ether, silicon oils, perfluoroalkyl ethers, and mixture thereof.

[0007] Preferred kinematic viscosity of these lubricating base oils is in a range of about 3 to 20 cSt at 100°C.

[0008] Alkaline-earth metal borates of the present invention have a general formula of M O · x B₂ O₃ wherein M is an alkaline-earth metal atom, x is positive having a value of 0.5 to 3.0. The alkaline-earth metals include magnesium, calcium, barium, with calcium being preffered. The alkaline-earth metal borates have a particle size of less than about 0.1 µ m, preferably less than about 0.05µ m. Although alkaline-earth metal borates in pure state can be used, so-called overbasic alkaline-earth metal borates (hereinafter referred to as " alkaline-earth metal borate dispersions") prepared by reacting oil-soluble metal salts with alkaline-earth metal borates may also be utilized in the present invention. The alkaline-earth metal borate dispersions have a total base number (measured by the procedure prescribed by JIS K 2501 5.2.3) of more than 100, preferably more than 170. The alkaline-earth metal borate dispersions are prepared by a reaction of an oil-soluble metal salt such as an oil-soluble alkaline-earth metal sulfonate, alkaline-earth metal saricylate, alkaline-earth metal pheneate, alkaline-earth metal phosphonate with an oxide or a hydroxide of an alkaline-earth metal in the presence of boric acid or boric acid anhydride. Among oil-soluble metal salts, alkaline-earth metal saricylates are most appropriate. Any methods for preparing the alkaline-earth metal borate dispersions may be acceptable. For example, a method has been known which comprises reacting an oil-soluble metal salt aforesaid, a hydroxide or an oxide of alkaline-earth metal, and boric acid or boric acid anhydride in the presence of water, an alcohol such as methanol, ethanol, propanol, or butanol, and a diluent such as benzene, toluene or xylene at a temperature of about 20 to 200°C for about 2 to 8 hours, heating the mixture at about 100 to 200°C to remove water, followed by removing the alcohol and the diluent if necessary, to give a dispersion. The reaction conditions may be employed suitably depending on the raw materials to be used, the amount of reactants and the like. Typical of such prior art practices are those disclosed in Japanese Patent Publication Nos. 116688/60 and 204298/61 and the disclosures of which are incorporated by reference. In general, the alkaline-earth metal borate dispersions obtained by the above-mentioned procedures have a particle size of less than 0.1µ m and a total base number of more than about 100, and are appropriate for the present invention.

[0009] A content of the alkaline-earth metal borate in the present composition is in an amount of 0.01 to 10 % by weight, preferably 0.05 to 3 % by weight, more preferably about 0.05 to 1 % by weight on the basis of the total amount of the composition.

[0010] When the content is less than about 0.01 % by weight, there is no merits of alkaline-earth metal borate. Inversely, when it is in excess of 10 % by weight, an amount of sulfated ash is increased unpreferably.

[0011] In the present invention, the following conventional lubricating oil additives can be additionally used to improve further the performance of the present composition if necessary, in so far as they do not deviate from the gist of the present invention. Examples of these additives include oiliness improvers such as higher alcohols, higher fatty acids, esters and the like ; extreme pressure agents and friction modifiers such as tricresyl phosphate, triphenyl phosphate, zinc dithiophosphates, molibdenum disulfides, molibdenum dithiophosphates, molibdenum dithiocarbamates and the like; rust preventives such as petroleum sulfonates, dinonyl naphthalene sulfonates and the like; metal deactivating agents such as benzotriazole and the like; metal-based detergents such as alkaline-earth metal sulfonates, alkaline-earth metal salicylates, alkaline-earth metal pheneates, alkaline-earth metal phosphonates and the like; ashless dispersants such as succinimide, succinic esters, benzylamine and the like; deformers such as silicon oils and the like; viscosity index improvers and pour point depressants such as polymethacrylates, polyisobutylenes and polystyrenes and the like; antioxidants such as zinc dithiophosphates, hindered phenols, aromatic amines and the like; and mixtures thereof. A content of the viscosity index improver is in an amount of about 1 to 30 % by weight, the deformer is in an amount of about 0.0005 to 1 % by weight, the metal deactivating agent is in an amount of about 0.005 to 1 % by weight, and other additives is in an amount of about 0.1 to 15 % by weight respectively on the basis of the total amount of the composition.

[0012] The engine oil compositions for alcohol-based fuel engines of the present invention are suitable for spark-ignition or compression-ignition engines in which said alcohol-based fuel is selected from the group consisting mainly of methanol, ethanol, propanol, mixtures thereof, and the mixture of at least 10 % by volume of one of these alcohols with a petroleum-based fuel such as gasoline, kerosene, and gas oil.

[0013] While the advantages of the compositions according to the present invention will be described in detail hereinbelow in conjunction with the following examples, it is to be noted that the scope of the present invention should not be limited to these examples.

Examples 1 - 2 and Comparative Examples 1 - 2.

[0014] In order to measure the capacity for neutralizing formic acid of the present compositions, engine oil compositions were prepared by blending an overbasic oil-soluble metal salt prepared by use of calcium borate in an amount shown in Table 1 with a refined mineral oil (SAE 30, 10.0 cSt 100°C). Formic acid in an amount shown in Table 1 was added individually to these compositions and pH of these compositions after 30 Sec. were measured. Table 1 gives the results. For reference, the same procedures were repeated except that calcium carbonate was used to prepare the overbasic oil-souble metal salt, and the results are also shown in Table 1.

Examples 3 - 5 and Comparative Examples 3 - 5.

[0015] In order to measure the wear resistance of the present compositions, engine oil compositions were prepared by blending 2 % by weight, on the basis of the total amount of the composition, of overbasic oil-soluble metal salt prepared by use of calcium borate with a refined mineral oil (SAE 10, 4.3 cSt @ 100 °C). The tests were carried out by the high-speed four point ball method. The test conditions were as follows;

[0016] Table 2 shows the test results. For reference, the same procedures were repeated except that calcium carbonate was used to prepare the overbasic oil-soluble metal salt, and the results are also shown in Table 2.

Examples 6 - 8 and Comparative Examples 6 - 8.

[0017] In order to measure the stability for hydrolysis of the present compositions, the engine oil compositions of the present invention were prepared by blending 15 % by weight, on the basis of the total amount of the composition, of an overbasic oil-soluble metal salt prepared by use of calcium borate with a refined mineral oil (SAE 10, 4.3 cSt @ 100 °C). The tests were carried out by the method prescribed by ASTM D 2619. Table 3 gives the test results. For reference, the same procedures were repeated except that calcium carbonate was used to prepare the overbasic oil-soluble metal salt, and the results are also shown in Table 3.

[0018] As is apparent from the results shown in Tables 1 to 3, the engine oil compositions for alcohol-based fuel engines of the present invention are superior to the prior arts of compositions for alcohol-based fuel engines in capacity for neutralizing formic acid, wear resistance, and stability for hydrolysis.

Claims

1. An engine oil composition for alcohol-based fuel engines comprising a major amount of mineral oil and / or synthetic oil as a lubricating base oil, and about 0.01 to 10 % by weight of an alkaline-earth metal borate on the basis of the total amount of the composition as an essential component.