Preparation Of Glycolic Acid From Whole Cell Catalyzed Ethylene Glycol And Its Purification

As the simplest typical α-hydroxy acid,glycolic acid is an important intermediate for chemical and organic synthesis due to its special bifunctional modular properties.Among them,the fields of biomedical and polymer degradation materials are currently popular applications of glycolic acid.The commercialization processes of high quality glycolic acid crystallization are dependent on the assistance of organic solvents,and the green and efficient bioconversion technology,especially the bioreaction model for the preparation of glycolic acid by oxidation of ethylene glycol using Gluconobacter oxydans as a catalyst,is of great theoretical value and practical significance.Efficient isolation and purification of high-purity glycolic acid crystals from the fermentation broth in an economical manner remains a great challenge due to the high hydrophilicity.Therefore,in this study,glycolic acid purification is the main object of study for the catalytic and chemical crystallization process of resting cells,and the coupled cell fermentationcrystallization process is used to isolate and purify glycolic acid crystals and to obtain glycolic acid with a purity of >98% after deep purification operations such as acidification and electrodialysis treatment.This has laid a solid research foundation for the industrial preparation of high-purity glycolic acid applied to biomedical materials.The main research results are as follows:1.Screening by comparing and calculating the efficiency of resting cell catalysis and biotransformation of glycolic/ethanolic acid in five neutralizing agents,NaOH,KOH,NH₃H₂O,CaCO₃ and Ca（OH）₂.In the case of the blank control,the glycol consumption rate was low and the glycolic acid yield was significantly limited to 12.4 g/L in 24 h.The high purity goal was difficult to achieve without the modulation technique.In the regulated experimental groups of NaOH,KOH and CaCO₃,the glycolic acid yields within 9 h were 19.7 g/L,19.3 g/L and 18.7 g/L,respectively,and the glycol conversion rates were all over 2.0 g/L/h.In addition,the crystallization phenomenon of rapid enrichment was observed in the CaCO₃ and Ca（OH）2neutralization experiments,and the in situ crystallization process of glycolic acid（salt）was achieved The aim is to lay down technical support and ideas for the production of high-purity glycolic acid crystals.2.Aiming at the unique nature of calcium glycolate which is easy to crystallize,a coupled biocatalytic-crystallization process model for its continuous biopreparation of glycolic acid was established with the production of high-purity calcium glycolate crystals as the target.The model achieved in situ separation of calcium glycolate crystals using differential centrifugation at 200 g/5min with a recovery of 95 % and cell loss of only 8 %.In addition,an efficient acidification separation of glycolic acid was achieved through a comprehensive p H control strategy.Finally,0.94 L of high-purity glycolic acid-rich solution with a concentration of 74.3 g/L was collected after the coupling technique.3.To address the solid waste problem of acidification of calcium glycolate to glycolic acid,further research was conducted to develop a more environmentally friendly crystallization technology for sodium glycolate.Highly efficient precipitation of sodium glycolate crystals up to94% purity was obtained by selective crystallization treatment in concentrated fermentation broth（188 g/L）.A loading-absorbance-purity binary model was developed,and 97 % decolorization of the crystals was achieved at 8 wt% of activated carbon addition,while 99 % purity of the precipitated crystals was identified by HPLC and ¹H-NMR.This integrated process technology provides an economical and feasible method for the large-scale industrial bio-production of highpurity sodium glycolate and glycolic acid.