Solid acid catalyst (SAC) was synthesized via direct treatment of cacao shells (CS) with concentrated sulfuric acid at varying temperature (80, 100, 120 degrees C) and time (4, 6, 8 h) settings. The synthesized catalysts were found to have sulfonic acid density ranging from 0.6326 to 0.8500 mmol SO3H/g dry CS-SAC and total acid density from 6.0509 to 7.1165 mmol Hg dry CS-SAC. The catalytic activity is dependent on the sulfonic acid density of the catalyst. Catalyst synthesized at 120 degrees C for 6 h showed the highest sulfonic acid density (0.85 mmol SO3H/g catalyst) corresponding to highest catalytic activity (5.73 mmol OA converted/mmol SO3H center dot h) and a conversion of similar to 39% after a fixed reaction time of 4 h and carried out at 65 degrees C. Conversions of up to 76% could be achieved after 24 h. The catalyst was reused for 4 cycles and was able to retain 78% of its catalytic activity from the 2nd to the 4th cycle. Direct sulfonation may be an alternative to conventional synthesis process. (C) 2020 Elsevier Ltd. All rights reserved.