Study On The Liquid Phase Catalytic Oxidation Of 5-hydroxymethylfurfural

2,5-furandicarboxylic acid(FDCA),which is currently prepared by catalyzing the oxidation of 5-hydroxy methylfurfural(HMF),is a bio-based platform compound with broad market prospects.For the liquid-phase oxidation system catalyzed with Co/Mn/Br catalyst,this paper optimized the process conditions for HMF oxidation via systematic experimental study,investigated the kinetics of main and side reactions,and explored the reaction path and the mechanism of the chemical oscillation phenomenon in this system.The main research work and results of the paper include:1.Firstly,the possibility of liquid phase oxidation of HMF was explored.To optimize the process conditions,the influence of substrate concentration,reaction temperature,reaction pressure,catalyst concentration and by-product content on HMF oxidation was investigated.The results show that lower reaction pressure is beneficial to promote the highly selective conversion of HMF to FDCA.Although increasing the reaction temperature and catalyst concentration can accelerate HMF oxidation,the instability of the furan ring and the high reactivity of the substituents on the ring make HMF prone to undergo a variety of side reactions at high reaction temperature and substrate concentration.After optimization,the yield of FDCA obtained by the liquid phase oxidation of HMF can reach 91.5%,and the purity can exceed 99.8%.2.Based on the mechanism of Co/Mn/Br synergistic catalysis and the detection results of oxidation products,the main and side reaction paths and mechanisms for the liquid-phase oxidation of HMF were proposed.For the main reaction,HMF was successively oxidized to 2,5-furandiformaldehyde(DFF),5-hydroxymethylfurfuric acid(HMFCA),5-formyl-2-furancarboxylie acid(FFCA),and finally oxidized to FDCA.During the liquid phase oxidation of HMF,the hydroxymethyl group of HMF exhibited higher reactivity than the aldehyde group.In addition to the combustion side reactions to COx(CO and CO2)and the condensation side reactions to HMF polymers,a small amount of HMF can undergo ring-opening side reactions to form maleic acid(MA)and fumaric acid(FA).The experimental results for the investigation of oxidation kinetics at different concentrations found that the oxidation reaction rate is not sensitive to the changes of substrate concentration.Based on this concentration effect,the hyperbolic kinetic model was used to carry out the data fitting and parameter regression.3.The reaction oscillation behavior is first reported in the HMF liquid-phase oxidation system.Based on the experimental investigation of the chemical oscillation law under different reaction conditions,it is found that the oscillation phenomenon is the result of the coupling effect of reaction and diffusion.The sufficient gas-phase oxygen concentration and the steady-state reaction condition is the prerequisite for the periodic fluctuations of the tail oxygen concentration and COx generation rate in the process.The experimental results confirm the non-linearity kinetic behavior of the process is related to the oxidation of aldehyde group on FFCA in the series reactions of HMF oxidation.Based on the two-stage oscillation model of aldehyde self-oxidation and the radical chain reaction process of aldehyde groups,the oscillation reaction mechanism in the liquid-phase oxidation of HMF catalyzed by Co/Mn/Br was proposed.