Catalytic performance and acidic analysis of chloroaluminate ionic liquid with various impurities in the synthesis of multi-octylnaphthalene base oil

Abstract

The effects of the structure and concentration of impurities on the alkylation of naphthalene with 1-octene catalyzed by chloroaluminate ionic liquid (IL) were investigated. The presence of impurities containing oxygen and nitrogen led to a decrease in the catalytic performance of chloroaluminate IL. As the water concentration increased to 65 mg·g–1, the total selectivity of multi-octylnaphthalene gradually decreased to 42.33%, and the average friction coefficient of the multi-octylnaphthalene base oil gradually increased to 0.201. When the concentration of impurities increased to a critical value, the chloroaluminate IL began to deactivate, leading to a decrease in naphthalene conversion. The critical concentrations for ethanolamine, water, methanol, ether, and diisopentyl sulfide were 33 mg·g–1, 65 mg·g–1, 67 mg·g–1, 87 mg·g–1, and 123 mg·g–1, respectively. Impurities with higher basicity resulted in an earlier onset of chloroaluminate IL deactivation. The changes of Lewis and Brønsted acids in chloroaluminate IL under the influence of impurities were investigated using in situ IR and 27Al NMR spectroscopy. 2,6-dimethylpyridine as an indicator could detect the changes of Brønsted acid in chloroaluminate IL better, but the changes of Lewis acid were not obvious because of the overlap between the characteristic peaks. 2,6-dichloropyridine as an indicator could exclusively detect the changes of Lewis acid in chloroaluminate IL. With the increase in water concentration, the Lewis acid in chloroaluminate IL was continuously consumed and converted into Brønsted acid, and the Lewis acid gradually decreased, while the Brønsted acid showed a change of increasing first and then decreasing.