Design Of Immobilized Metal Porphyrin Biomimetic Enzyme And Its Application In Hydroxymethylfurfural Oxidation Process

Hydroxymethylfurfural?HMF?is a substance that produced by foods with high sugar through Maillard reaction or thermal degradation.It was shown that when HMF content reaches a certain dose,it would cause harm to human health.In many food quality tests,the content of HMF can be used as an important indicator.Therefore,when the content of hydroxymethylfurfural in foods is too high,foods can not be eaten by humans,but in order to save resources,hydroxymethylfurfural in foods can be converted into valuable chemicals.It was shown that foods rich in fructose and glucose can be easily transformed into HMF.Therefore,it is necessary and important to study the conversion pathway of hydroxymethylfurfural in foods.2,5 furandicarboxylic acid?FDCA?can be obtained through HMF oxidation reaction.Due to the similarity of its Structure to polymer monomer terephthalic acid,it can be used as a renewable substitute monomer of petroleum-based terephthalic acid in the process of synthesizing food contact materials.Therefore,it is very meaningful to explore the oxidation process of HMF to FDCA.There are some problems in the synthesis process of 2,5-furandicarboxylic acid by HMF oxidation.Firstly,the oxidation of HMF to FDCA requires base to remove the acidic oxidation product that is adsorbed on the surface of the catalyst so that the oxidation reaction continues,but homogeneous base is added to the reaction system presently and can seriously pollute the environment.Secondly,the catalysts currently used in the oxidation of HMF to FDCA are basically accompanied by high pressure and other harsh environments to obtain high FDCA yield.In summary,this paper is based on two aspects of the control of alkaline environment and the design of catalyst as the basic research content,the main conclusions are as follows:?1?The control of alkaline environment:Solid base catalyst was designed?Pd/C-OH^-?to catalyze the oxidation of HMF,creating an environmental friendly and safe reaction system.The conversion of HMF reached 100%and the yield of FDCA reached 82.39%when 40 mg Pd/C-OH^-1catalyst was added into water at 373 K for 24 h.At the same time,the surface structure and properties of the catalyst were characterized by SEM,XRD,TG,FT-IR and CO₂-TPD techniques.It was proved that the alkaline ionic liquid was successfully loaded on the surface of Pd/C catalyst,the ionic liquid loading of Pd/C surface was 18.13 wt.%,the base amount of Pd/C-OH^-1was 2.54 mmol·g^-1within the range of the ionic liquid loading.I?2?The design of catalyst:metal acetates are mixed with porphyrin compounds to form metal porphyrin complex compounds,and the obtained metal porphyrin compounds are loaded onto support which was modified by surface modifiers to form immobilized metal porphyrin mimetic enzyme catalyst.The catalysts were characterized by SEM,XRD,TG,FT-IR,XPS,BET,et al.Finally,the characterization results showed that the metal porphyrins were successfully loaded onto the surface of the mesoporous materials.After the catalyst was applied to the oxidation reaction,the immobilized palladium porphyrin was proved to be the optimal catalyst.Finally,the effect of HMF oxidation conditions were studied.The immobilization of palladium porphyrin as the catalyst and oxygen as the oxidant gave the best results after reacting in water at 373 K for 24 h:100%HMF conversion and 97.34%FDCA yield.Furthermore,the reaction kinetics of the immobilized palladium porphyrin catalyst catalyzing HMF oxidation was studied.The results showed that the oxidation reaction pathway of HMF to FDCA was:HMF?HFCA?FFCA?FDCA.The reaction step in which the aldehyde group in FFCA was oxidized to the carboxyl group in FDCA was a rate-limiting step.