A one-pot route to tunable sugar-derived sulfonated carbon catalysts for sustainable production of biodiesel by fatty acid esterification

Carbon-based solid acid catalysts possessing up to 1.29 mmol g(-1)-SO3H active centers were synthesized from glucose via an efficient one-pot hydrothermal carbonization-sulfonation without the need for high temperatures. Catalysts combined aromatic structure with hydrophilic-OH and-COOH groups and a high density of -SO3H centers (up to a total acid density of 5.31 mmol g(-1)). The level of -SO3H (0.81-1.29 mmol g(-1)) proved synthetically tunable. The relevance of the catalyst to the production of more sustainable fuels was tested using oleic acid (a free fatty acid whose esterification can be employed as a model for biodiesel production). Optimizing catalyst and conditions (20:1 MeOH:oleic acid molar ratio, 5 wt % catalyst loading wrt oleic acid, 80 degrees C, 120 min) enabled oleic acid esterification to the corresponding methyl oleate (a biodiesel component) with 97.5 +/- 0.4% conversion and a low 37.6 kJ mol(-1) activation energy. Activity loss upon re-use of the catalyst was proved to be by desulfonation and could be completely reversed. Hence, re-sulfonation of spent catalyst by a one-step process again delivered a 97.4 +/- 0.5% conversion of oleic acid. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

In this study, carbon-based solid acid catalysts with high density active centers were successfully synthesized via a one-pot hydrothermal carbonization-sulfonation method at low temperatures. The catalysts demonstrated great significance in the production of biodiesel, allowing efficient conversion of oleic acid with the optimized catalyst and conditions. Furthermore, the catalyst showed potential for recyclability by complete re-sulfonation.