Propyl-SO3H functionalized graphene oxide as multipurpose solid acid catalyst for biodiesel synthesis and acid-catalyzed esterification and acetalization reactions

A graphene based acid catalyst, GO-PrSO3H, was prepared through a simple two-step process. Surface modification with (3-mercaptopropyl) trimethoxysilane followed by oxidation of sulfide groups led to the production of sulfonic acid sites on graphene oxide nanosheets. The results of various physicochemical techniques approved the synthesis of desired catalyst. The amount of acid sites was measured via the acid-base treatment with triethylamine which exhibited 1.07 mmol/g H+ in the catalyst structure. Two kinds of acid-catalyzed reactions i.e. esterification and acetalization were adopted to evaluate the catalytic performance of prepared catalyst. More than 90% conversion was achieved for butyl acetate production in acetic acid esterification with n-butanol. Moreover, methyl oleate as one of the main components of biodiesel was produced with good yield over the prepared catalyst via oleic acid esterification with methanol. The 1H NMR technique was also conducted to characterize and determine the amount of produced methyl oleate. Finally, the benzaldehyde acetalization with ethylene glycol was performed which high conversion (92%) was obtained at 3 h. The catalyst reusability for both esterification and acetalization reactions demonstrated the catalyst stability after five reaction cycles.