Mesoporous activated carbon from sunflower shells modified with sulfonic acid groups as solid acid catalyst for itaconic acid esterification

Abstract

Mesoporous activated carbon from sunflower shells (SAC) modified with sulfonic acid groups (SACSO3H-XX) was synthesized by grafting the sulfonic groups on the carbon surface to produce novel heterogeneous and reusable solid acid catalysts. The mesoporous carbon was prepared by chemical (H3PO4) and thermal (600 °C) activation of sunflower seed shells. Four materials with increasing SO3H content (SACSO3H-5, SACSO3H-10, SACSO3H-15, and SACSO3H-20) were obtained using rising chlorosulfonic acid:SAC ratios. They were texturally and physicochemically characterized by SEM-EDX, BET, FT-IR, and TGA-DSC. Potentiometric titration with n-butylamine technique was used to evaluate their acidic properties. The results showed that both the acid strength and the number of acid sites increased with the SO3H content in the SACSO3H-XX samples. The FT-IR spectra of SACSO3H-XX samples confirmed the successful functionalization of SAC with the sulfonic acid group. TGA-DSC diagrams of SACSO3H-20 showed that the elimination of the sulfonic groups takes place in the range 250–350 °C. The activity and selectivity of SACSO3H-XX in the esterification reaction of itaconic acid with absolute ethanol to form the diester derivative depended strongly on their acidic properties. Furthermore, the effective separation of the product combined with the use of a recyclable catalyst resulted in a clean and environmentally friendly strategy for the synthesis of diethyl itaconate, a bioproduct of relevance to the biorefinery industry.