Tandem production of high-purity sodium glycolate via the dual purification technology of crystallization and active carbon adsorption

Abstract

High-purity glycolic acid (GA) are highly required for the production of biodegradable polymers, pharmaceuticals, and fine chemicals. For production of bio-polyester, GA purity has emerged as a bottleneck. In this paper, we innovatively propose crystallization to dispose of purity problem and investigated the repurification of sodium glycolate crystals. Compared to traditional chemical techniques, resting cell catalysis with bio-oxidation of ethylene glycol (EG) is a promising method for the green industrial production of GA. Gluconobacter oxydans is one of the most promising strains because of its ability to ferment high GA titer from EG. However, the GA directly from fermentation broth does not meet the high purity requirements for biodegradable materials. Therefore, a tandem process was designed and experimentally verified by combining crystallization and active carbon (AC) adsorption. Sodium glycolate (SG) formation was adopted due to low-cost operation in the biological step and easy electrodialysis of GA. According to the dissociation constants (Kɑ) of glycolate, the fermentation broth was adjusted to pH 9.50 and SG saturates at 60 ℃ for SG crystallization. The macroscopic yellow plate-like crystals 91.1 g of SG with 94 % purity were produced at room temperature (25℃). In the tandem process, AC rapidly removed most pigment-like contaminants in the fermentation broth but adsorbed only a little SG (1 %), indicating selective and effective adsorption. Over 97 % of the color was removed by adding 8 % AC to a saturated solution (188 g/L). Finally, 79.2 g SG with 99 % purity was obtained at the yield of 87 % from 104 g/L SG broth. This tandem process could provide an economically-feasible approach for the industrial bioproduction of high-purity SG and GA derived from EG.