Investigation of sulfonated solid acid catalysts derived from oil palm kernel shell, corncob, and diatomaceous earth for esterification of ethanol and propanoic acid, characterisation and their performance

In this study, solid acid catalysts were prepared from different sources including oil palm kernel shell, corncob, and diatomaceous earth. Then, the raw materials were sulfonated and further activated by a microwave-induced reactor. Characteristics of sulfonated oil palm kernel shell (OPS-AC), corncob (CK-AC), and diatomaceous earth (DE-AC) were analysed using FTIR, XPS, NH3-TPD, XRD, SEM, BET, and TGA to establish their physical and chemical properties. The CK-AC and DE-AC showed high potential to be used as solid acid catalysts consisting of the strong acid site (-SO3H and -COOH) with 2344 and 3098 μmol/g for CK-AC and DE-AC, respectively. The DE-AC exhibited better thermal stability by only 7% of mass loss observed. The ester yields of 54.2 and 60.4% were achieved over CK-AC and DE-AC, respectively. Moreover, DE-AC shows the outstanding reusability for five successive times, which is promising as the potential solid catalysts for ethyl propanoate production.