Fundamental Study On Chromatographic Separation Of The Glycolic Acid Solution Containing Salt

Glycolic acid（GA）,a kind of important organic acid,is widely used in chemical cleaning,daily chemicals,organic synthesis and other fields.GA is mostly prepared by chemical synthesis method in industry,and obtained GA solution contains inorganic salts,organic by-products and other substances,which requires subsequent separation and purification operations.Traditional methods of separating GA still have disadvantages such as high energy consumption and multiple separation procedures,and chromatography can overcome above disadvantages to a certain extent.But the current studies on separating GA by chromatography are not sufficient,and exploration of preparative grade separation of GA remains a long-term and arduous task.This paper mainly studied the separation process of GA and Na Cl by ligand exchange chromatography,and established chromatographic model of separation process for design of SMB and optimization of operating parameters.The main work and conclusions are as follows:Firstly,separation performance of different ligand exchange resins was compared through static adsorption experiment and fixed-bed pulse experiment.Then,adsorption characteristics of GA and Na Cl on the resin with better performance were studied in thermodynamics and kinetics.Results indicated that sulfonic-acid groups,Ca²⁺loaded,gel type pore and small particle size are favorable for separation,and UBK555-Ca²⁺is determined as the separation medium with better performance.Two-component M-Langmuir model can reasonably describe adsorption characteristics of GA and Na Cl on UBK555-Ca²⁺.△H<0、△S<0、△G<0,which indicate that UBK555-Ca²⁺is feasible to separate GA and Na Cl.The adsorption is in accordance with pseudo-second-order kinetics model.The mass transfer of GA is mainly controlled by liquid film diffusion step,and which of Na Cl is affected by both liquid film diffusion and intra-particle diffusion.Secondly,breakthough curves and elution curves under different chromatographic conditions were obtained by single column experiments.Based on the above,chromatographic separation process was modeled.Results indicated that mass transfer diffusion model（TD model）is more applicable.When axial diffusion coefficient is determined by empirical formula method and total mass transfer coefficient is determined by chromatographic model fitting method,TD model has a better fitting effect on breakthough curves and elution curves.Relationship between total mass transfer coefficient and chromatographic operating conditions was established by using the fitting results of elution curves.Then,TD model can predict the elution curves of different column lengths or liquid volume,which proves the reliability of chromatographic model and determined results of model parameters.Finally,simulation and experiment of separating GA and Na Cl by SMB were carried out.SMB model was established based on single column TD model.Simulation results indicated that separation effect and productivity are optimal when configuration is three zones of 2-2-2,flow ratio of I-zone is 1.156,and switching time is 7.5 min,and operation point should not be selected at the boundary of separation region.The optimized operating conditions were used for SMB experiment,and finally purity and recovery of GA were respectively 95.75%and92.92%,which were closer to the simulated separation effect compared with that before optimization.