Novel Solvent Systems for the Base-Free Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid Using Pt/C Catalysts

Efficient production of 2,5-furandicarboxylic acid (FDCA), a key monomer in the production of bioplastics, is hindered by low solubility in common solvents and limited selectivity during 5-hydroxymethylfurfural (HMF) oxidation. In this study, base-free oxidation of HMF was performed using a 5% Pt/C catalyst in various pure and mixed aqueous/organic solvent systems to evaluate the solvent effects on FDCA production. Organic solvents tested included sulfolane, dimethyl sulfoxide, γ-valerolactone, γ-butyrolactone, tetrahydrofuran, and acetonitrile. Binary solvent blends with 20–80% water consistently outperformed pure solvents, with FDCA yields exceeding 70% in several mixtures. Sulfolane/water mixtures uniquely maintained high FDCA yields at up to 50 wt % sulfolane and achieved higher mass recoveries and FDCA yields at initial HMF concentrations up to 10 wt %. In the 50/50 sulfolane/water system at a 7.5 wt % HMF concentration, there was 94% product recovery including a 25% FDCA yield. The effects of reaction temperature were also studied, with the increasing temperature correlating to improved yields but lower mass balances at temperatures greater than 373 K. These findings show that sulfolane/water mixtures are promising solvents for high-concentration, base-free oxidation of HMF.