Preparation of a carbon microsphere–based solid acid application to waste frying oil transesterification

Abstract

The present work designed a new strategy incorporating oxidation, amidation and sulfonation to prepare carbon microsphere–based solid acids having a high density of sulfonic acid group. The carboxyl group concentration of the microspheres was increased through an oxidation process to provide grafting sites for amidation. Subsequently, p–phenylenediamine was introduced via an amidation reaction to provide more active sites for sulfonation. Finally, a sulfonic acid–type solid acid with an amount of surface acidic site of 11.3 mmol/g was obtained using a sulfonation process. Analyses by X–ray photoelectron and Fourier transform infrared (FTIR) spectroscopy confirmed the introduction of amino groups followed by sulfonic acid groups. These results were in agreement with thermogravimetric data. This material exhibited good catalytic performance during the transesterification of waste frying oil (WFO) and gave a fatty acid methyl ester yield of 92.2% after 4 h at 140 °C. This synthetic strategy is expected to provide a new approach to the preparation of sulfonic acid solid acids.