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: Background of the Invention (1) Field of the Invention This invention relates to a method for the lubrication of an alcohol-based fuel engine, and more particularly to a method for the lubrication of a methanol- or ethanol-based fuel engine. (2) Description of the Prior Art In alcohol-based fuel engines, for example, methanol-based fuel engines, highly polar 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 crankcase to corrode and rust. Furthermore, these polar substances are the cause of wear of several parts of an engine, especially on the cylinder surfaces. Therefore, it is necessary to neutralize the formic acid immediately after it contacts with or is absorbed into the engine oil thereby deactivating the acid. For this purpose, an overbasic detergent prepared by the use of calcium carbonate has been used in conventional engine oils in order to lubricate alcohol-based fuel engines. However, the capacity of such a conventional overbasic detergent for neutralizing formic acid is insufficient, and said detergent has a tendency to form coarse-grained particles during use. Furthermore, its wear resistance is also unsatisfactory. It is an object of the present invention to overcome the problems inherent in the lubrication of alcohol-fueled engines and especially methanol- or ethanol-fueled engines, such problems originating from the specific properties of said alcohols, like a single boiling point (whereas gasoline for engines usually has a boiling point range of from about 30°C to about 200°C), a low vapour pressure and a high heat energy necessary for evaporation so that methanol is nearly introduced as a liquid phase into the cylinder(s). Furthermore, said alcohols are not soluble in oil but easily soluble in water. The present invention is based on extensive research whereby the inventors unexpectedly have found that efficient results can be attained by employing an overbasic alkaline-earth metal borate, as defined in claim 1, instead of the conventional overbasic detergents for the lubrication of alcohol-based fuel engines. By carrying out such lubrication with an engine oil composition containing an overbasic detergent in the form of an alkaline-earch metal borate there will be provided an improved capacity for neutralizing formic acid, an improved wear resistance, and the tendency to form coarse-grained particles during use will be eliminated. It is already known from DE-A1-3 607 887 to prepare alkaline-earth metal borate dispersions derived from oil soluble neutral sulfonates of an alkaline-earth metal, such dispersions having a very small particle size and a high molecular ratio of borate to alkali-earth metal. Additionally FR-A1-2 554 825 discloses oil soluble reaction products prepared from alkaline-earth metal salts of an organic acid, having been made basic by a pre-reaction with CO₂ , and a boron compound like boric acid. Since such reaction products do not comprise solid materials they can be easily compounded with luboils. Summary of the Invention The present invention provides a method for the lubrication of alcohol-based fuel engines characterized by lubricating said engines with an engine oil composition containing a major amount of mineral oil and/or synthetic oil as lubricating base oil, and 0.01 to 10% by weight of an overbasic alkaline-earth metal borate as defined in claim 1, on the basis of the total amount of the composition as an essential component. Detailed Description of the Invention Either mineral oils or synthetic oils may be used as the lubricating base oils in the present invention. Any paraffinic or naphthenic lubricating base oils may be acceptable, said base oils being manufactured by a process consisting mainly of topping a crude oil followed by vacuum distillation 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 used according to 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, perfluoralkyl ethers, and mixture thereof. The preferred kinematic viscosity of these lubricating base oils is in the range of about 3 to 20.10⁻⁶ m²/s (cSt) at 100°C. Alkaline-earth metal borates useful for the present invention have the general formula of M O .x B₂ O₃ wherein M is an alkaline-earth metal atom, x is a positive number having a value of 0.5 to 3.0. The alkaline-earth metals include magnesium, calcium, barium, with calcium being preferred. The alkaline-earth metal borates have a particle size of less than about 0.1 µm, preferably less than about 0.05 µm. The overbasic alkaline-earth metal borates are hereinafter referred to as "alkaline-earth metal borate dispersions". The overbasic alkaline-earth metal borate dispersions have a total base number (measured by the procedure presribed by JIS K 2501 5.2.3) of more than 100, preferably more than 170. The overbasic alkaline-earth metal borate dispersions are prepared by the reaction of an oil-soluble alkaline-earth metal salicylate with an oxide or a hydroxide of an alkaline-earth metal in the presence of boric acid or boric acid anhydride. Any methods for preparing the overbasic alkaline-earth metal borate dispersions may be acceptable. For example, a method has been described which comprises reacting an oil-soluble alkaline-earth metal salicylate, 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. In general, the alkaline-earth metal borate dispersions obtained by the above-mentioned procedures have a particle size of less than 0.1µm and a total base number of more than about 100, and are appropriate for the present invention. The alkaline-earth metal borate is present in the composition to be used according to the invention in an amount of 0.01 to 10% by weight, preferably 0.05 to 3% by weight, more preferably of about 0.05 to 1% by weight on the basis of the total amount of the composition. When the content is less than about 0.01% by weight, there is not observed any beneficial effect of the alkaline-earth metal borate. Inversely, when it is in excess of 10% by weight, the amount of sulfated ash is increased and therefore such an embodiment is not preferred. 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. 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, molybdenum disulfides, molybdenum dithiophosphates, molybdenum 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; defoamers 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. The viscosity index improver may be present in an amount of about 1 to 30% by weight, the defoamer in an amount of about 0.0005 to 1% by weight, the metal deactivating agent in an amount of about 0.005 to 1% by weight, and other additives in an amount of about 0.1 to 15% by weight respectively on the basis of the total amount of the composition. The engine oil compositions used for the lubrication of alcohol-based fuel engines according to 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. While the advantages of the lubrication method 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 In order to measure the capacity for neutralizing formic acid when using the present lubrication method, engine oil compositions were prepared by blending an overbasic oil-soluble salt prepared by use of calcium borate in an amount shown in Table 1 with a refined mineral oil (SAE 30, 10.0 cSt (10.10⁻⁶m²/s) @ 100°C). Formic acid in an amount shown in Table 1 was added individually to these compositions and the pH values 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-soluble metal salt, and the results are also shown in Table 1. Examples 3 to 5 and Comparative Examples 3 - 5 In order to measure the wear resistance of the compositions used acording to the invention, 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 (4.3 x 10⁻⁶m²/s) at 100°C). The tests were carried out by the high-speed four point ball method. The test conditions were as follows: Test load Engine speed Test duration 30 kg 1200 r.p.m. 30 min. 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 In order to measure the stability for hydrolysis of the compositions used according to the invention, the engine oil compositions 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 (4.3 x 10⁻⁶ m²/s) at 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. As is apparent from the results shown in Tables 1 to 3, the engine oil compositions for alcohol-based fuel engines used according to the present invention are superior to the prior art of compositions for alcohol-based fuel engines in respect of capacity for neutralizing formic acid, wear resistance, and stability against hydrolysis.

Claims: A method for the lubrication of an alcohol-based fuel engine comprising lubricating said engine with an engine oil composition comprising a major amount of mineral oil and/or synthetic oil as a lubricating base oil, and 0,01 to 10% by weight of an overbasic alkaline-earth metal borate prepared by a reaction of an alkaline-earth metal salicylate with an oxide or a hydroxide of an alkaline-earth metal in the presence of boric acid or boric acid anhydride, on the basis of the total amount of the composition as an essential component. A method according to claim 1 in which said lubricating base oil comprises an overbasic alkaline-earth metal borate dispersion with a total base number (measured according to JISK 2501 5.2.3) of more than 100, preferably more than 170. A method according to claim 1 and /or 2 in which said alkaline-earth metal borate has a particle size of less than 0,1 µm, preferably of less than 0,05 µm. A method according to anyone of the claims 1 to 3 in which said alcohol-based fuel comprises at least 10% by volume of alcohol.

Inventors: HIRATA MASAKUNI, INOUE KIYOSHI, MITO TAKASHI, HIRATA, MASAKUNI, INOUE, KIYOSHI, MITO, TAKASHI
Applicants: NIPPON OIL CO LTD, NIPPON OIL CO., LTD.
Application year: 1991
Main classification: C10M125
IPC codes: C10M125, C10M159, C10N30, C10N10, C10N40