Effects of thermal treatment on carbon cryogel preparation for catalytic esterification of levulinic acid to ethyl levulinate

- Thermal effects on carbon cryogel production via carbonization and calcination were investigated.
- Carbon cryogel with microsphere structure was synthesized from lignin and furfural.
- Characteristic and properties between carbonized and calcined cryogel were compared.
- Calcined carbon cryogel gave high performance for levulinic acid esterification.

Organic catalyst, especially derived from lignocellulosic biomass, is currently being developed for application in reaction engineering. Lignin, a major constituent in biomass, is highly potential as carbon- based -derived catalyst. Carbon cryogel was prepared from acidic lignin-furfural mixtures via sol-gel polycondensation. The effect of carbonization and calcination on carbon cryogel preparation has been investigated in this study. The carbon cryogels were characterized using surface area analyzer and NH3-TPD. Based on the carbonization and calcination studies, the total surface area and acidity of the selected carbonized cryogel were 214.2 m2/g and 11.3 mmol/g, respectively while calcined cryogel were 426.5 m2/g and 16.1 mmol/g, respectively. The selected carbon cryogels were further characterized using TGA, FTIR, XRD and FESEM-EDX. Overall, the characterization results revealed calcined cryogel has higher thermal stability and stronger acid sites. Subsequently, the performance of calcined carbon cryogel prevailed in catalytic esterification of levulinic acid to ethyl levulinate. The esterification reaction was further investigated at different catalyst loading (5 to 35 wt%), molar ratio of ethanol to levulinic acid (5 to 30), time (1 to 8 h) and temperature (78 to 170 °C). At the optimum conditions, calcined cryogel evinced 87.2% and 86.5 mol% of levulinic acid conversion and ethyl levulinate yield, respectively.