Studies On The Preparation Process Of 2,5-Furandicarboxylic Acid By Cyclodehydration Of Hexaric Acids

With the increasing depletion of fossil resources,the preparation of chemicals from biomass has become an important solution to cope with the shortage of non-renewable resources.2,5Furandicarboxylic acid(2,5-FDCA)is an important biomass-based platform compound that can be polymerized with diols to produce high-performance biobased polyester materials,which has enormous market potential.There are many synthetic routes for 2,5-FDCA,including the oxidation of hexose to obtain hexaric acid,then cyclodehydration of hexaric acid to form 2,5-FDCA.The competitiveness of this route has been greatly improved due to the advantages of non-grain biomass as raw materials,stable intermediate product hexaric acid,and short process route.Currently,the synthesis of hexaric acid is relatively mature,so the process of preparing 2,5-FDCA by cyclodehydration of hexaric acid has received some attention.The research team previously constructed a hydrogen halide-metal halide composite catalytic system for the cyclodehydration reaction and screened an efficient HBr-LiBr system.However,there are still problems such as unoptimized process conditions,unclear decomposition of by-products,and incomplete process flow.To address these issues,this paper selected the HBr-LiBr catalytic system,optimized the process for the cyclodehydration of hexaric acids,studied the kinetics and mechanism of the decomposition reaction of the by-product 2-furoic acid,then scaled up the reaction and explore the separation and purification methods of the product and the performance of the recycling of the mother liquor.Finally,the industrialization of 2,5-FDCA prepared by hexaric acid was envisioned,and a complete process flow was proposed.The main work and research results of this paper are as follows:By screening reaction solvents and optimizing process parameters such as HBr-LiBr concentration ratio,stirring speed,and substrate concentration,the optimal process conditions for the HBr-LiBr-catalyzed reaction of potassium bisaccharate were obtained:using sulfolane as the solvent,2%HBr-5%LiBr,300 rpm,120℃,and 24 h,a 75.2%yield of 2,5-FDCA was obtained from 4%potassium bisaccharate.The effect of water content on the reaction was also investigated,and the results showed that water enrichment was detrimental to the reaction,and to maintain a yield of no less than 60%,the water content in the system should be controlled below 5.2%.The by-product of the cyclodehydration reaction of hexaric acid is 2-furoic acid,which has poor stability and its decomposition products may introduce impurities into the system.Therefore,the decomposition reaction of 2-furoic acid was studied for its kinetics and mechanism.By comparing with standard samples and mass spectrometry analysis,the main decomposition products of 2-furoic acid were determined to be furan,2,3-benzofuran,and dibenzofuran.The differences in the decomposition rates of 2-furoic acid in different catalytic systems were compared,and the order from fast to slow was 10%H2SO4,3%HBr-2%MgBr2,3%HBr,and 3%HBr-2%LiBr.The activation energy of the 2-furoic acid decomposition reaction was fitted to be 98.74 kJ/mol in the optimal catalytic system 2%HBr-5%LiBr,and the possible pathway for the decomposition of 2furoic acid was proposed:2-furoic acid first undergoes decarboxylation to form furan,furan then undergoes Diels-Alder reaction to form relatively stable 2,3-benzofuran,which can further react with furan through Diels-Alder reaction to form dibenzofuran.The reaction was scaled up by 100 times to investigate the effects of stirring method,stirring speed,substrate concentration,and water content on the reaction after scaling up,and the results were compared with those of the small-scale experiment.The results showed that mechanical stirring at 120 rpm could better eliminate mass transfer differences,the effect of substrate concentration was the same before and after scaling up reaction,and the reaction after scaling up was more sensitive to the change of water content.The optimal process conditions obtained in the small-scale experiment were verified by scaling up,and a 73.7%yield of 2,5-FDCA was achieved,which was a successful result for scaling up by 100 times.To complete the entire process,a cooling crystallization,water washing,and one-time recrystallization process was used to obtain a purity of 99.7%or higher for the 2,5-FDCA product.Under the conditions of water removal and recycling of hydrobromic acid,the mother liquor was recycled 10 times without any significant decrease in performance,and the average yield of 2,5-FDCA was 68.8%.Finally,based on the above research,a complete industrial process flow for the preparation of 2,5-FDCA from hexaric acids was proposed.This paper will promote the industrialization of the hexaric acid route.