(509b) Sustainable Sulfonated Carbons as Esterification Catalysts for the Production of Biochemicals

Organic esters have been commercially employed in pharmaceuticals, solvents, cosmetics, lubricants, and biofuels. Conventionally, their synthesis employs liquid acids such as sulfuric acid, posing limitations including reactor corrosion, non-reusability, and treatment of the effluent. Sulfonated carbons (SC) have emerged as efficient, heterogeneous, solid acid substitutes for sulfuric acid, facilitating easier product separation, catalyst recyclability, and minimizing waste generation. Conventionally, these catalysts are synthesized by the
hydrothermal sulfonation of carbon with concentrated H2SO4 (18M), or treatment with toxic gaseous SO3, necessitating more environmentally benign preparation methods. Plasma
technology is gaining attention for catalyst fabrication, permitting synthesis at low temperatures and pressures, in shorter durations, and could be a valuable tool for designing SC catalysts. Further, most SC are synthesized from carbon in powdered/granular forms, which limits their use in continuous processing as the particles undergo attrition, affecting catalyst recovery and longevity. High pressure drop and mass transfer limitations are among other concerns. Activated carbon monolith(ACM), a structured carbon support, confers the advantages of high mass transfer rates, low pressure drop, and easy scale-up, facilitating its use in continuous processes. In this study, we devised a novel and more sustainable hydrothermal technique for the sulfonation of wood-based activated carbon in granular(GAC) and monolith(ACM) forms using dilute(2M) sulfuric acid as the sulfonating agent. We have also demonstrated the sulfonation of activated carbon(GAC and ACM) using an argon-water vapor plasma. The catalytic activity of the hydrothermal and plasma sulfonated carbon catalysts was compared to an industrial benchmark catalyst, Amberlyst-15, in batch esterification reactions of 2-hydroxyisobutyric acid(2HIBA) with ethanol. 2-HIBA has been produced fermentatively from several recombinant microbial strains and ethanol is a renewable, bio-based platform molecule. Developing green solid acids for the esterification of 2-HIBA with ethanol would create sustainable avenues for interfacing fermentation with catalysis for the production of organic esters.