Preparation of solid acid catalyst from rice husk char and its catalytic performance in esterification

Abstract

A sulfonated carbon-based solid acid catalyst was prepared by sulfonating rice husk char with concentrated sulfuric acid. The as-prepared catalyst was characterized using X-ray diffraction, X-ray photoelectron spectroscopy, ultimate analysis, specific surface area analysis, and thermogravimetry-mass spectrometry. The effects of the sulfonation temperature and time on the catalytic performance were investigated using the esterification of oleic acid and methanol as the probe reaction. The effects of the reaction conditions on the esterification catalyzed by sulfonated rice husk char were also studied. The stability of the catalyst was examined. The results showed that 90 °C and 0.25 h were suitable sulfonation temperature and time, respectively. The catalyst prepared under these conditions had an amorphous carbon structure with a sulfonic group concentration of 0.7 mmol/g. It exhibited high catalytic performance. The conversion of oleic acid was 98.7% under the optimal reaction conditions with a catalyst amount of 5%, a methanol to oleic acid molar ratio of 4:1, and a reaction temperature and time of 110 °C and 2 h, respectively. The esterification conversion still reached 96.0% after seven cycles of successive reuse, which indicated that the catalyst stability was excellent. A solid acid catalyst with high -SO 3 H density and excellent stability was prepared from rice husk char and was used to pre-esterify materials with high fatty acid contents for biodiesel production.