Continuous flow tube-in-tube oxidation of HMF to FDCA using heterogeneous manganese catalyst under mild conditions

Abstract

The shift from a petrol-based to a bio-based society and economy is already underway. Continuous development is required to seek increasingly efficient methodologies capable of being competitive with the current production chain. 2,5-furan dicarboxylic acid (FDCA) currently represents, together with its precursor 5-hydroxymethylfurfural (HMF), among the major players in the sector of products derived from biomass due to their potential use as building blocks for the synthesis of bio-plastics or bio-polymers in general. Among the many methods reported for the selective oxidation of HMF to FDCA, the use of heterogeneous catalysts based on noble metals is widely studied. However, these catalysts represent a problem in terms of resource scarcity and are often synthesised using complex procedures. In addition, most systems for the oxidation of HMF to FDCA make use of oxygen at high pressures and high reaction temperatures. In this contribution, we report our efforts to develop a continuous flow apparatus for the selective oxidation of HMF to FDCA using an easy-to-synthesize manganese-based catalyst. By sequentially evaluating the design, construction, and use of different flow systems, we finally were able to propose a system that allowed the use of the manganese catalyst at relatively low temperatures and pressures, comparable to or even better than those utilised for noble-metal catalysts, with excellent efficiency and productivity.