Using nuclear magnetic resonance to assist in calculating the structure of Fischer-Tropsch lubricant

Hu Li¹Tengfei Jiang²Yushan Jiang²Xuemei Liang¹Xingyu Su¹Liangcheng An¹Nana Fan¹Likun Yang¹Linhua Song^2*

• ¹Ningxia Coal Industry Co., Ltd, Yinchuan, Henan Province, China
• ²School of Chemistry and Chemical Engineering, China University of Petroleum (East China), Qingdao, Shandong Province, China

Research on Fischer-Tropsch (FT) synthetic lubricant base stock products is expected to fill a global gap in high-quality lubricants. However, the lack of identifiable characteristic functional groups in their pure hydrocarbon compositions makes it difficult to accurately analyze their compositions using existing methods. In this study, we propose a method combining nuclear magnetic resonance (NMR) and high-temperature gas-phase analysis to achieve a simple and accurate calculation of the structural information of lubricant base oils. Four structural parameters of FT lubricant base oilsnamely, the average carbon number (C*), the number of branched chain nodes (B), the degree of branching (BI), and the structural index (BC*)-were successfully calculated using a series of empirical equations. Subsequently, we correlated the molecular structure parameters of the oils with their density, viscosity, viscosity index, and condensation point. Effective fitting equations were developed and quantitatively verified. Studies have shown that the physicochemical properties of lubricant base oils can be related to the structural parameters BC* or BBC*. BBC* fits better, with an R 2 value of up to 0.91 or more, except for the condensation point. Density correlates well with viscosity, with a calculation error of less than 5%. This method of calculating the structural information of lubricant base oils can be applied to the structural determination of many hydrocarbon base oil molecules, while the simulation equations can simultaneously be used as a reference for the structurefunction relationship of distillate base oils.