| Hydroxocobalamin (VB12b), one derivative of cyanocobalamin (VB12), known as long-acting curative of vitamin B12 deficiency, is alternative of cyanocobalamin. Clinically hydroxocobalamin is cyanide antidote. The conversion rate of photocatalytic decomposition from cyanocobalamin to hydroxocobalamin is very low due to the stability of cyanocobalamin. And a reverse reaction will occur in the photolysis solution if no product separation. A method of adsorption with macroporous resin was used to separate cyanocobalamin and hydroxocobalamin in this paper. The appropriate macroporous resin was elected. Adsorption technics was optimized. And the adsorption kinetics and thermodynamics was further researched.The performances of a variety of resin (CAD45, DM1180, D150, D072, D401, D101, D418, X-5 and XAD-1180) to statically adsorb and desorb cyanocobalamin and hydroxocobalamin were measured. The macroporous resin H-D150 with better separation performance was elected through comparison with the other resins in terms of adsorption capacity, adsorption rate, adsorption selectivity and desorption ratio.The static and dynamic experiments of hydroxocobalamin adsorption and elution on H-D150 resin were conducted. The impact of hydroxocobalamin concentration, pH value, temperature, flow rate, resin regeneration on resin adsorption properties and eluent kind, acetone volume concentration in eluent, pH value, temperature, flow rate on resin elution properties was measured to determine optimal adsorption and elution conditions. Optimized adsorption and elution conditions: hydroxocobalamin initial concentration of 1000 mg·L-1, adsorption temperature 25℃, 60 % acetone-water as eluent containing 4 g sodium acetate per 100mL eluent, elution temperature 25℃, dynamic adsorption flow rate of 3.00 BV·h-1 and elution flow rate of 0.96 BV·h-1. Resin adsorption and elution properties are stable after the first regeneration. H-D150 resin was found to possess nice adsorption and desorption properties with dynamic saturation adsorption capacity of 1767 mg·g-1 wet resin and hydroxocobalamin relative purity≥99 % in the final product.SEM and IR were applied to characterize H-D150 resin before and after adsorption. SEM images show the uneven H-D150 resin surface like honeycomb structure (porous structure). Obvious protrusions exist on the resin surface as a result of a certain degree of volume expansion after adsorption. IR results show that the spectra are very similar before and after adsorption. The carbonyl absorption peak redshift indicates hydrogen bonds exist before and after adsorption. H-D150 resin adsorbs hydroxocobalamin through the hydrogen bonds breaking between the resin functional groups and the hydrogen bonds formation between resin functional groups and hydroxocobalamin molecules.Adsorption kinetics and thermodynamics of hydroxocobalamin on H-D150 resin were researched with mathematical models, and the adsorption mechanism was discussed. The Adsorption kinetics results show the adsorption rate increases with hydroxocobalamin initial concentration increasing and temperature rising in the initial stage of adsorption. And the initial adsorption rate is controlled by both intraparticle diffusion and film diffusion but mainly by the former. The thermodynamics results show the equilibrium adsorption data of hydroxocobalamin on H-D150 resin correlate with a Freundlich-type isotherm equation. Adsorption Gibbs free energy is negative indicating the spontaneous adsorption process. Adsorption enthalpy is positive implying that the adsorption is endothermic process. And raising the temperature is conducive to adsorption. The negative adsorption entropy proves the disorder degree increasing in the adsorption process.In conclusion, hydroxocobalamin and cyanocobalamin could be effective separated by adsorption and elution on H-D150 macroporous resin. In this paper, the adsorption process is simple and non-polluting. It can be applied to industry with important practical value of improving hydroxocobalamin quality and reducing production costs.
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