Patent GB-658511-A (GB)
Title: Lubricating greases
Filed: 1947-03-12
Abstract: A lubricating grease comprises a mineral oil and a metal soap complex having a ratio of equivalents of metal to equivalents of fatty acids between 1.1 and 4, the excess of metal being present as carbonates or salts of low molecular weight carboxylic acids or both, and the complex being produced either by saponification of fats or fatty acids with excess of alkali or alkaline earth metal base, or by saponification with a chemically equivalent amount of base and subsequent addition of excess of base, followed by reduction of alkalinity to a free alkali content less than the equivalent of 5.0 mg. KOH per gram of soap present by oxidation, or by neutralization with lower molecular weight organic acids, with or without the introduction of carbon dioxide; the complex may also be produced by heating an oil solution of a normal metal soap with an aqueous or alcoholic solution of a metal salt of a low molecular weight carboxylic acid, with or without a metal carbonate.  The preferred ratio is between 1.2 to 1 and 2 to 1. The basic metal compounds include the oxides, hydroxides, or hydrated oxides of the alkali metals, the alkaline earth metals, beryllium, magnesium, zinc, cadmium, aluminium, indium, gallium, lead, tin, germanium, chromium, molybdenum, iron, cobalt, and nickel.  As saponifiable materials all grades of fat and also acids resulting from the oxidation of petroleum fractions, rosin, higher molecular weight naphthenic acids, saponifiable waxes such as beeswax, sperm oil, and degras may be used.  As lower molecular weight carboxylic acid salts may be used those of acids containing less than 7 carbon atoms per molecule such as formic, acetic, propionic, valeric, oxalic, malonic, and succinic acids, and low molecular weight substituted carboxylic acids such as glyceric, glycollic, and thioglycollic acids.  The reaction may be carried out in the presence of part or all of the mineral oil to be employed in the final product, or it may be carried out in the absence of mineral oil and the product compounded with oil to form a grease.  The oxidation is conducted, preferably at temperatures between 300 DEG  and 550 DEG  F., the higher temperatures favouring the formation of metal carbonates and the lower temperatures that of low molecular weight carboxylic acids.  Preferably a small proportion of between 0.5 and 4.0 per cent of water or alcohol should be present during the reaction.  Preferred methods of forming the metal soap complexes from normal metal soaps dissolved in part of the oil are (1) to mix in a solution or dispersion of the desired low molecular weight metal carboxylate in water or alcohol, boil off the water or alcohol at from 200 DEG  to 600 DEG  F., and add the remainder of the oil; (2) to add the desired amount of metal oxide or hydroxide dispersed in water or alcohol followed by the equivalent amount of lower carboxylic acid, and then heat as before; (3) to add a basically-reacting metal compound and an amount of lower carboxylic acid sufficient to neutralize a portion of the basic compound, pass carbon dioxide through the mixture to convert the remaining basic compound to carbonate, and heat; (4) to add excess of free basically-reacting metal compound and blow a gas containing free oxygen through the mixture in presence of water or an alcohol at a temperature of from 300 DEG  to 550 DEG  F. to produce acidic oxidation products sufficient to neutralize the excess basic metal compounds; any remaining basic compounds are converted to carbonates by finally blowing carbon dioxide through the mixture.  The formation of the complex greases usually requires a temperature of from 400 DEG to 550 DEG  F.  The proportion of soap complex in the oil may be from 5 per cent to 50 per cent but in some cases may be as low as 2 per cent or as high as 75 per cent.  In addition to ordinary lubricating oil, residues from the manufacture of alkylated motor fuels may be used as the oil.  The complex may contain a single metal or two or more metals, in which case one is preferably polyvalent. Antioxidants and other additives may be added.  In one example, a mixture of tallow fatty acids, glycerol, calcium oxide, and water having the calcium oxide equivalent 1.9 times that of the fatty acids is heated in a grease kettle to 240 DEG  F. and cooled.  The product is ground to powder and reheated to 300 DEG  to 350 DEG  F., when the free calcium hydroxide p  content decreases to 0.1 per cent.  The complex is finally worked up in a steam-jacketed grease kettle with mineral oil at 400 DEG  F. Other examples describe the preparation of calcium and sodium greases from tallow and hydrated lime, and tallow and sodium hydroxide respectively, strontium and lithium greases from tallow and strontium or lithium hydrate, a mixed metal grease from tallow and strontium and lithium hydrates, a lithium grease from stearic acid, sperm oil, lithium hydrate and waxy gas oil, and calcium and barium greases from tallow, acetic acid, glycollic acid, carbon dioxide, and hydrated lime or barium hydrate.