Sulfonic acid functionalized torrefied biocoal facilitates levulinates preparation: Reaction kinetics and process cost analysis

• Torrefied biocoal can be used as a heterogeneous catalyst after functionalization. • It can offer strong Brønsted acidic sites and a wide surface area for LA conversion. • The catalyst is robust and versatile for alkyl levulinates synthesis. • The catalytic setup is industrially feasible and sustainable for green energy supply. Due to the increase in population and industrialisation, the global energy demand is steeply increasing. However, the non-renewable fossil resources are in a state. Therefore, it is urgent to develop renewable resources to meet the energy demand. We employed the torrefied biomass as a porous catalyst to synthesize alkyl levulinate (a potential drop-in fuel compound) via levulinic acid esterification. The rice straw-derived torrefied solid (TRS) was functionalized with SO 3 H (TRS@SO 3 H), offering 1.23 mmol/g Brønsted acidic sites with 21 m 2 /g surface area, which are beneficial for the esterification reaction. Maximum ethyl levulinate (EL) yield of 98.9% at 60 °C within 35 min under microwave heating conditions, with a turnover frequency of 1.34x10 -2 h -1 . It also demonstrated versatility by synthesising various alkyl levulinates, with product yields varying depending on the carbon numbers. Furthermore, it exhibited robustness for reuse based on its effectiveness up to 5 cycles with a minor reduction of EL (12% relative). The techno-economic process calculation estimated the production cost of EL as low as $ 4.7/L. The acid-functionalized rice straw torrefied biocoal exhibiting a high surface area with Brønsted acidic sites facilitated a selective levulinic acid esterification to ethyl levulinate under microwave reaction conditions.