GB736890A - Improvements in or relating to lubricating greases and method of making same - Google Patents

Abstract

Lubricating greases of high dropping point and soft consistency over a wide temperature range are prepared by saponifying, in a lubricating oil, a saponifiable material consisting of saturated or hydrogenated glyceride fats and oils, or unsaturated fats and oils other than rapeseed oil, or mixtures of glycerine and C12-C30 saturated or unsaturated fatty acids, the saponification being effected with an excess of alkali, heating the mixture after saponification until gas is evolved, maintaining the temperature until gas evolution ceases, and then cooling the mixture. Suitable lubricating oils are mineral oils or unsaponifiable synthetic oils, but when the reaction mixture has been cooled to a temperature below 300 DEG F., following gas evolution, further lubricating oil may be added and this may be of any type, including ester lubricating oils. The preferred alkali p used for saponifying is caustic soda. Saponifiable materials mentioned are tallow, hog-fat and mixtures of glycerides with fatty acids and glycerine. Lauric, myristic, palmitic, stearic and behenic acids are examples of saturated fatty acids which may be employed. The preferred unsaturated fatty acids are C18 to about C22 acids, but those acids containing conjugated bonds such as the acids of oiticica, tung and similar drying oils should be used, if at all, only in small quantities. The lubricating greases may contain additional ingredients such as antioxidants (especially amines), dispersants, and sulphur-containing extreme pressure agents, while an oil-soluble petroleum sulphonic acid or alkali metal salt thereof may be present during saponification to increase the soft consistency and the stability of the greases. After the gas evolution, at least a portion of the free alkali in the grease may be neutralized by the addition of a fat or an organic acid, particularly a fatty acid, and sufficient acid may be added to ensure the presence of free acid in the final grease. If the acid is added after the grease has been cooled to a temperature below the transition temperature where it becomes a short-fibred unctuous mass (about 325-375 DEG F.), to produce a slight excess of free acidity in the finished grease, the cooling time may be reduced to about 1-10 hours, slow cooling being necessary otherwise. Suitable acids for neutralization of excess alkalinity are C2-C11 saturated aliphatic monocarboxylic acids such as acetic, propionic, butyric and valeric acids; C12-C30 saturated or unsaturated fatty acids such as palmitic, stearic, behenic, oleic and erucic acids; acrylic acid or hydroxy-substituted acids such as lactic, hydroxy-stearic and dihydroxy-stearic acids; and the acid employed may be the same as those employed in the initial saponification. It is believed that the evolution of gas mentioned above is caused by the dehydration of glycerine to acrolein and the reaction of the latter with alkali to form the alkali metal salt of acrylic acid and hydrogen. In the examples, lubricating greases are prepared according to the process of the invention from mineral oil, caustic soda and (1) hydrogenated tallow, further hydrogenated tallow being added after gas evolution to partially neutralize alkalinity; (2) oleic acid, with or without "Hydrofol A.B." acids, glycerine, sodium petroleum sulphonates, phenyl alpha-naphthylamine and condensation product of salicylal and ethylene diamine; and (3) hydrogenated tallow and sodium petroleum sulphonates, with the addition of hydrogenated fish oil acids and phenyl alpha-naphthylamine after gas evolution to produce a final grease containing free acids. The preparation of various rapeseed oil greases is also described for comparison purposes.