Study On The Synthesis Of 2,5-furandicarboxylic Acid From Biomass-based 5-chloromethylfurfural By Consecutive Hydrolysis And Oxidation

Biomass is a renewable resource with abundant reserves.The development of biomass instead of fossil raw materials to produce chemicals,materials and fuels necessary for human society can reduce carbon dioxide emissions and conform to the concept of green and sustainable development.Lignocellulosic biomass can be converted into some platform compounds with great potential through a series of biological or chemical methods.Among them,biomass based 2,5-furandicarboxylic acid has similar physical and chemical properties with petroleum based Terephthalic acid,so FDCA can replace PTA with dialcohol and diamine to synthesize polyester and polyamide materials,and will have a wide application prospect in the fields of renewable packaging materials,engineering plastics,textile materials and other fields.Catalytic oxidation of the biomass-based platform molecule 5-hydroxymethylfurfural is the most promising path for FDCA synthesis.However,the direct preparation of HMF with cheap raw materials such as cellulose and glucose has low selectivity,and it is difficult to separate and purify HMF and high energy consumption.Therefore,the cost of preparing HMF by the above methods is high,which further hinders the largescale production of FDCA from cellulosic biomass.It was found that 5chloromethylfurfural could be efficiently converted from cellulose raw materials by hydrolytic chlorination,and CMF with relatively stable chemical properties could be easily separated and purified by traditional distillation.It is worth noting that CMF is easy to prepare HMF through hydrolysis reaction.Therefore,the hydrolysis and oxidation of cellulosic biomass via CMF is an important way to efficiently prepare HMF and FDCA.In this paper,the high concentration of CMF(10 wt%)hydrolysis reaction system and the separation and purification method to improve the stability of HMF were explored and established,and Ru/Al2O3 catalytic high concentration of HMF(10 wt%)selective oxidation synthesis of FDCA was designed and synthesized,which has a certain theoretical and practical significance for the large-scale production of FDCA in the future.Firstly,in order to solve the problem of low selectivity of HMF in high concentration CMF hydrolysate in pure water system,this paper studied the hydrolysis of CMF to HMF by alkali promoter in water/acetone system.The results showed that alkali promotors such as CaCO3 could neutralize HCl produced by CMF hydrolysis in time and reduce HMF side reactions caused by acid catalysis.On the other hand,the water/acetone system has the effect of stabilizing HMF relative to the pure water system,so it can also reduce the side reaction of HMF.In this paper,the effects of the ratio of water to acetone,reaction temperature and time on the hydrolysis of HMF to HMF were systematically studied.The optimized yield of HMF could reach 85%(10 wt%CMF,water:acetone=1:4,353.15 K,24 min).The kinetic studies show that the activation energies of CMF hydrolysis and HMF hydrolysis in water/acetone system are 12.3 kJ/mol and 22.9 kJ/mol,respectively,and the kinetic constants of the former are one order of magnitude higher than that of the latter.Therefore,the hydrolysis of CMF in water/acetone system is easier than that of HMF,which is conducive to improving the selectivity of the target product HMF.Secondly,Al2O3 supported precious metal ruthenium(Ru)catalyst(Ru/Al2O3)was designed and synthesized,and used in dioxane/water system to catalyze the selective oxidation of high concentration HMF to FDCA.The results of catalyst characterization and catalytic experiments show that Ru/Al2O3 is a highly efficient oxidation catalyst with good dispersion of active site,good oxidation stability and easy regeneration and reuse.In the dioxane/water system(dioxane:water=9:1),Ru/Al2O3 catalyzed HMF oxidation to FDCA yield up to 99.2%(10 wt%HMF,140℃,3 h,40 bar O2).The prepared Ru/Al2O3 catalyst has strong ferromagnetism at room temperature,and the ferromagnetism does not decrease after the use of high temperature reaction.Therefore,the catalyst can be easily recovered by external magnetic field.Finally,in view of the problem that side reactions of HMF in CMF hydrolysates are likely to occur in the process of heating and decompressing concentration and distillation separation,it was found in this paper that adding a small amount of sodium disulfite in the hydrolysate of CMF can effectively inhibit the generation of humus and other by-products of HMF in the above process.With 1,2-dichloroethane will reaction liquid extraction and the extraction solvent evaporation,found no Na2S2O4 coarse product in black,results of its content is 50%,used in dioxane/water system Ru/Al2O3 preparation FDCA catalytic oxidation rate was 18%,and after adding Na2S2O4 coarse product to orange transparent,results of its content is 84%,used in dioxane/water system Ru/Al2O3 preparation FDCA catalytic oxidation rate was 91%.In addition,in the vacuum distillation process,adding Na2S2O4 to the crude HMF product can also improve the separation rate of HMF,without Na2S2O4,the separation rate of HMF is 50%,after adding Na2S2O4,the separation rate is 86%.The results showed that Na2S2O4 could inhibit the loss of HMF at high temperature in the process of rotary distillation and vacuum distillation,so as to improve the separation rate of HMF.