Insight into the sulfonation conditions on the activity of sub-bituminous coal as acidic catalyst during the transesterification of spent corn oil; effect of sonication waves

Abstract

The impact of the sulfonation conditions on the catalytic activity of coal as an acidic catalyst was assessed by normal stirring (NS.Coal) and sonication waves (SS.Coal) based on the Response Surface methodology. The NS.Coal exhibits acid density and surface area of 8.8 mmol/g and 27.8 m2/g, respectively. This was obtained after 90 min at sulfonation conditions of 150 °C temperature and 95% H2SO4 concentration. In the existence of sonication waves for 60 min (240 W), SS.Coal shows acid density and surface area of 14.2 mmol/g and 45.8 m2/g, respectively. This demonstrates significant efficiency for the sonication-induced sulfonation processes during the synthesis of sulfonated coal as an acidic catalyst. The activities of NS.Coal and SS.Coal acidic catalysts were evaluated during the transesterification of corn oil. The best yield was obtained by NS.Coal (4 wt, %) is 99.3% after 60 min at 60 °C in the presence of 14:1 methanol/oil ratio. The archived yields using SS.Coal at loading values of 2 wt, %, 3 wt, %, and 4 wt, % are 99.6%, 99.84%, and 99.85%, respectively after 20 min. The kinetic properties of reactions were illustrated based on the Pseudo-First order assumption. The thermodynamic studies demonstrate the endothermic properties of the corn oil transesterification reactions. The determined activation energy by NS.Coal and SS.Coal are 26.22 kJ/mol and 17.7 kJ/mol, respectively reflect the possible use of them as effective catalysts at low energy and mild conditions.