Solid acid carbon catalysts for sustainable production of biofuel enhancers via transesterification of glycerol with ethyl acetate

SO3H-bearing carbons prepared from sugars or glycerol were used as catalysts for the production of acetins via a transesterification route. Two methods of preparation of functionalized carbon catalysts were compared: a) an energy-efficient, one-pot synthesis including partial carbonization of precursors with H2SO4 coupled with simultaneous in-situ functionalization and b) a two-step method including template synthesis of carbon followed by functionalization of the obtained product with sulfuric acid or diazonium salt. The synthesized carbons were used in an eco-friendly process of glycerol transesterification with ethyl acetate under different reaction conditions. All the prepared samples were found to effectively catalyze the reaction, producing a mixture of mono-, di- and triacetins (MA, DA and TA, respectively); however, the efficient production of the target compounds, namely DA and TA, which are valuable biofuel additives, was found to be strongly dependent on the content of sulfonic groups on the surface of these catalysts. A direct correlation between -SO3H concentration and glycerol conversion, as well as the yield of higher esters was established. Moreover, the applied method of one-pot combined partial carbonization and functionalization with H2SO4 was shown to be a convenient way to obtain carbonaceous solid acid catalysts that can be used as promising alternatives to modified carbons produced by conventional two-step techniques.