Preparation of High Purity of Complex Lithium and Discussion on the Structure of its Prefabricated Thickener and Recombination Process

Complex lithium grease can be used under high temperature conditions that traditional lithium grease cannot be applied to, it has been widely used in countries around the world since its development in the 1960s. Although there are many kinds of complex lithium base greases, the most advanced one is the compound lithium grease prepared by fatty dibasic acid and 12-hydroxy-stearic acid or stearic acid. The drop point and various physicochemical indexes are mainly affected by the content of thickening agent, additives and compound agent. The excellent recombination process is one of the main factors to determine the performance of complex lithium grease, so it has always been the difficulty and focus of people's research. Domestic and foreign scholars have carried out a lot of research work on the essence and mechanism of compound lithium grease recombination process. Researchers believe that the key factor for the formation of high drop point of complex lithium grease lies in the formation of appropriate hydrogen bond or lithium bond association similar to hydrogen bond between the two thickeners, dicarboxylate and 12-hydroxy-stearate. However, most of the reported research work is based on the direct oil-soap preparation method and process of traditional composite lithium grease, which is usually affected by the large viscosity of the base oil used and the complex parameter variables of the preparation process, so it is difficult to explore the compounding process and mechanism. Therefore, in order to study the composite process of lithium complex grease, and different from the traditional oil-soap mixing system, ethanol was used as the reaction medium to prepare high-purity lithium 12-hydroxy-stearate, lithium sebacate and prefabricated lithium complex thickener powders of different dibasic acids indirectly by the two-step preparation process of lithium complex grease. The structure and morphology of the compound lithium grease were determined by infrared and scanning electron microscopy, and the substance of the compound process was revealed by means of X-ray powder diffractometer, in-line infrared and solid/liquid nuclear magnetic field. The results showed that the prepared soap powder had a good double helix fiber structure, and there was a process of strong acid replacement of weak acid in the compound process of lithium complex grease, which essentially involved the mutual conversion and chemical interaction between 12-hydroxy-stearic acid, 12-hydroxy-stearate lithium and sebacic acid, and lithium sebacate. By monitoring the change of microstructure during the preparation of prefabricated thickener, it was further verified that there was an interaction between strong acidic dibasic acid and formed 12-hydroxy-stearate lithium salt in the compound lithium base grease. The performance of indirect lithium compound grease was better in appearance and colloid stability than that of traditional lithium compound grease prepared by direct method, and other properties are comparable. This work provided theoretical support and data accumulation for further research on the compounding process of complex lithium grease and development of high-performance grease.