(686d) Sustainable Sulfonated Carbon Catalysts for Continuous Esterification and Production of Biochemicals

Organic esters find numerous applications in pharmaceuticals, solvents, cosmetics, lubricants, and biofuels. Conventionally, their synthesis employs homogeneous, liquid acid catalysts such as concentrated sulfuric acid, posing limitations including equipment corrosion and non-reusability. In addition, large amounts of acidic waste are generated, a major environmental concern. Sulfonated carbon catalysts have emerged as heterogeneous, solid acid substitutes for sulfuric acid, facilitating easier product separation and catalyst recyclability, and minimizing waste generation. Further, the need for green technologies has driven the chemical industry towards adopting continuous processes, owing to easier automation, safer long-term operation, high productivity, greater selectivity, and reduced energy requirements. The use of continuous-flow technology with sulfonated carbon catalysts would enable the economically viable and environmentally benign production of specialty chemicals such as esters.

We have previously devised novel and sustainable techniques for the preparation of sulfonated carbon catalysts using wood-based activated carbon and dilute sulfuric acid as the sulfonating agent. In this study, we have designed continuous processes for the esterification of certain carboxylic/hydroxycarboxylic acids with ethanol and compared the catalytic performance of our sulfonated carbons with the industrial benchmark catalyst Amberlyst-15. Several carboxylic acids have been produced fermentatively from various microbial strains and ethanol is a renewable, bio-based platform molecule. Developing continuous processes utilizing wood-based sulfonated carbon catalysts for the esterification of carboxylic acids with ethanol would create sustainable avenues for interfacing fermentation with catalysis for the continuous production of organic esters with applications in bio-based solvents and fuels.