Selective esterification of glycerol with acetic acid or lauric acid over rod-like carbon-based sulfonic acid functionalized ionic liquids

Abstract

A series of rod-like nitrogen-containing carbon-based sulfonic acid functionalized ionic liquids, [PrSO3HN][SO3CF3]/C, with tunable Brønsted acid site densities are fabricated by quaternary ammonization of hydrothermally prepared nitrogen-containing carbon nanorods with 1,3-propanesultone followed by anion exchange with trifluoromethanesulonic acid. The materials are successfully applied in the selective esterification of glycerol with acetic acid or lauric acid to the value-added glycerol esters including triacetain, glycerol monolaurate and glycerol dilaurate. The excellent esterification activity of the [PrSO3HN][SO3CF3]/C nanorods strongly depends on their Brønsted acid nature; additionally, the morphological characteristics, surface hydrophilicity and flexible polycyclic aromatic carbon structure influence the catalytic activity to some extent. The [PrSO3HN][SO3CF3]/C-2 nanorod with high density of super strong Brønsted acid sites and perfect rod-like nanostructure exhibits the highest esterification activity, and its activity outperforms Amberlyst-15, propylsulfonic acid functionalized SBA-15, the [PrSO3HN][SO3CF3] group functionalized carbonaceous framework obtained by high temperature (600°C) calcination as well as homogeneous p-toluenesulfonic acid. Moreover, the catalyst can be reused three times without significant activity loss, attributing to the chemical interactions between the [PrSO3HN][SO3CF3] groups and the carbon framework.