Addressing the influence of alkaline compounds in 5-hydroxymethylfurfural oxidation and separation towards 2,5-furandicarboxylic acid

The conversion of 5-hydroxymethylfurfural (HMF) into valuable chemicals is a critical challenge in biomass valorization. This study explores the degradation of HMF in the presence of various alkaline compounds (KOH, NaOH, Na₂CO₃, and NaHCO₃) without the use of a catalyst. The experiments showed that strong bases such as KOH and NaOH significantly accelerated HMF degradation, even under cold storage conditions, while weaker bases (Na₂CO₃ and NaHCO₃) exhibited slower degradation rates. Additionally, the aerobic oxidation of HMF to 2,5-furandicarboxylic acid (FDCA) was evaluated using a Pt-Bi/C catalyst under different alkaline conditions. Results indicated that the type and strength of the alkaline compound strongly influenced FDCA yield, with intermediate bases such as Na₂CO₃ providing the highest yields (up to 99.3 %). The study also examined the post-reaction addition of alkaline compounds, revealing that this step is essential for dissolving FDCA, which may precipitate as a solid under acidic conditions. Two methods for FDCA separation and recovery were assessed: precipitation with HCl and dissolution in isopropanol. Both methods proved effective, with the HCl method yielding crystalline FDCA and isopropanol offering a more environmentally friendly alternative. These findings provide valuable insights into optimising reaction conditions for HMF valorization and improving FDCA recovery processes.