Concave carbon-microsphere-based solid acid catalysts for transesterification and epoxidation

Abstract

In this study, concave carbon microspheres (CCMSs) were synthesized using glucose as the raw material in the presence of an anionic surfactant sodium dodecyl sulfate (SDS) by a hydrothermal method. Sulfonic acid groups (−SO3H) were attached on the CCMSs surfaces by sulfonation using concentrated sulfuric acid, affording a solid acid catalyst (CCMSs catalyst). Scanning electron microscopy (SEM) results revealed that the diameters of the microspheres are 1–3 μm, and the diameters of the concave are 1–2 μm; hence, micron or submicron reaction cells can be formed Furthermore, sulfonation did not change the morphology of the carbon microspheres. N2-BET measurement results revealed that at a hydrothermal temperature and time of 180 °C and 8 h, respectively, and an SDS dosage of 0.10 g, the Brunauer-Emmett-Teller (BET) surface area of CCMSs could reach up to 7.7 m2/g. X–ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) results confirmed that CCMSs are successfully modified by sulfonation. The surface acid amounts of CCMSs before and after sulfonation were 3.7 and 5.6 mmol H+/g, respectively. CCMSs catalyst was used to catalyze the transesterification of waste frying oil, affording fatty acid methyl ester in 93% yield. CCMSs catalyst was used to catalyze the epoxidation of waste frying oil, achieving a double-bond conversion of 79% and a relative epoxy yield of 57%.