Liquid Phase Oxidation of 5-Hydroxymethylfurfural to 2,5- Results and Discussion Furandicarboxylic Acid over Co/Mn/Br Catalyst By controlled addition of the substrate solution at predetermined rates, the temperature rise due to the exothermicity of the oxidation during batch reactor operation can be

effectively limited such that burning reactions are avoided and the FDCA yield is enhanced.

Based on the optimization of reaction conditions, we have achieved nearly 90% FDCA yield at Xiaobin Zuo,1 Padmesh Venkitasubramanian,2 Daryle H. Busch1, 3 and Bala Subramaniam1, 4* 1/0.015/0.5 molar ratio of Co, Mn and Br, 7% (v/v) water as co-solvent, 30 bar (CO /O = 1/1, 1Center for Environmentally Beneficial Catalysis, University of Kansas, 2 2 mol/mol) and 180°C (entry 7, Table 1). Lawrence, Kansas 66047, United States

2Archer Daniels Midland (ADM) Company, Decatur, Illinois 62521, United States Table 1. Co/Mn/Br catalyzed oxidation of HMF 3Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, United States 4Department of Chemical and Petroleum Engineering, University of Kansas, Lawrence, Kansas 66045, United States * [email protected]

Introduction During the past decade, there has been a continuing interest in the oxidation of 5- hydroxymethylfurfural (HMF), a platform molecule derived from biomass, to 2,5- furandicarboxylic acid (FDCA) [1]. As a potential replacement for the petroleum-based terephthalic acid (TPA) that is heavily used in the production of polyesters, FDCA has been identified by DOE to be one of the twelve top value-added building blocks for future green chemical industry [2]. The Co/Mn/Br catalytic system, dubbed the Mid-century (MC) catalyst, is known to Reaction conditions: N2 (CO2)/O2 = 1/1 (mol/mol); H2O/HOAc = 7/93 (v/v); 5.0 mL HOAc convert p-xylene into TPA in acetic acid solvent with > 95% yield [3]. However, this catalyst solution of HMF (13.2 mmol) added at 0.25 mL/min; VT = 35 mL (after the addition of has also been explored for the oxidation of HMF to FDCA. Compared to p-xylene, HMF substrate solution); t = 30 min; n = 1200 rpm; Conversion of HMF > 99% for all the reactions; a contains more reactive functional groups (hydroxyl, aldehyde groups and furan ring) that can Reliable analysis not possible when CO2 is used as the inert gas undergo various side reactions (e.g. over-oxidation to CO and CO2) that lower the yield of FDCA, which is approximately 60% according to Partenheimer’s work [4]. This work reports Significance significant improvement of FDCA yield by systematically optimizing various reaction The similarity of HMF oxidation to p-xylene oxidation makes it possible for large parameters such as catalyst composition, water concentration acetic acid, reaction temperature, scale production of FDCA in existing TPA plants, provided high yield of FDCA can be pressure, and the use of zirconium as co-catalyst. obtained. Our work shows for the first time that the yield of FDCA can be made comparable to that of TPA under optimized conditions, which broadens the scope of the application of the Materials and Methods industrial MC catalytic process for FDCA production. All the chemicals were commercially available and used without further treatment. The semi-continuous oxidation was carried out in a 50 mL titanium Parr reactor. Typically, References either N2 or CO2 was added to the reactor containing the acetic acid solution of cobalt acetate, 1. Rosatella, A. A., Simeonov, S. P., Frade, R. F. M., and Afonso, C. A. M. Green Chem. manganese acetate and hydrobromic acid. The reactor contents were then heated to the reaction 13, 754 (2011). temperature following which O2 was added until the selected final pressure was reached. A 2. Bozell, J. J., and Petersen, G. R. Green Chem. 12, 539 (2010). solution of HMF in acetic acid was subsequently pumped into the reactor at a pre-defined rate 3. Tomás, R. A. F., Bordado, J. C. M., and Gomes, J. F. P. Chem. Rev. 113, 7421 (2013). to initiate the reaction. The total reactor pressure was maintained constant by continuously 4. Partenheimer, W., and Grushin, V. V. Adv. Synth. Catal. 343, 102, (2001). supplying fresh O2 from an external reservoir to compensate for the oxygen consumed in the reaction. Following the reaction, the gas phase was sampled and analyzed by GC to determine the yields of CO and CO2 produced by solvent and substrate burning. The insoluble FDCA product was separated from the liquid mixture by filtration. The solid and filtrate were analyzed by HPLC to determine the conversion of HMF and yields of products in liquid phase.