A roundabout strategy for high-purity glycolic acid biopreparation via a resting cell bio-oxidation catalysis of ethylene glycol

Abstract

High-purity glycolic acid (GA) is a necessary building block unit of medical materials which provides a promising value-added utilization of ethylene glycol (EG). Almost all currently applied commercial processes for GA crystallization depend on organic solvent assistance, such as flammable and combustible alcohols, ketones, and alkanes, with great pitfalls of high industrial production cost and safety issues. The green and effective bioconversion technology, based on the resting cell catalysis of EG to GA by Gluconobacter oxydans, grabs the spotlight. However, the efficient separation of purified GA crystals from the fermentation broth in an economical manner is still a big challenge owing to their strong hydrophilicity. In this study, a roundabout strategy was proposed and established to prepare high-purity GA by taking full advantage of the poor hydrophilicity and easy crystallization of calcium glycolate (CG). By processing-module integration, we designed a novel and prospective bio-based technology to integrate resting cell catalysis and the crystallization step, acidification step, and electrodialysis purification step – named RC&CR-AF-ED technology – to achieve continuous and efficient GA bio-preparation. Herein, we first prepared CG crystals, followed by their in situ separation from the fermentation broth, which somewhat relieved the GA end-product inhibition of resting cell catalysis and promoted productivity. Furthermore, the high-purity CG was obtained by the recrystallization operation and acidified to GA solution with sulfuric acid, from which high-purity GA was finally prepared by electrodialysis separation. In contrast to the conventional industrial technology, this roundabout strategy is environmentally friendly for high-grade GA bio-production from EG without any organic solvent processing.