Esterification of caprylic acid with glycerol for medium chain glycerides production catalyzed by waste coconut shell derived sulfonated carbon catalysts

Novel and sustainable biomass derived sulfonated carbon solid acid materials (SHTC-WCS-x, x refers to mL sulfuric acid g(-1) carbon) were synthesized by hydrothermal and sulfuric acid treatment of waste coconut shell, which was applied as heterogeneous catalyst for the esterification of caprylic acid with glycerol to produce medium chain glycerides (MCG). It is found that most of the aliphatic carbon structure of carbon materials was transformed into aromatic carbon structure after sulfonation modification. And the sulfonic groups (-SO3H) are well dispersed on the surface of SHTC-WCS-x through the connection of the C-S bond with carbon materials, which significantly improves the acidity and hydrophilicity of sulfonated carbon catalysts. Furthermore, the activity test results show that the SHTC-WCS-10 catalyst exhibits higher caprylic acid conversion of 77.61 % and high MCG selectivity of 99.5 %, as well as decent stability in the esterification reaction under solvent-free condition. Esterification mechanisms studies indicate that strong acid sites and surface wettability induced by introducing -SO3H species play a crucial role in enhancing the production of MCG.