Research On The Cooling Crystallization Process Of Hydroxyacetic Acid

Hydroxyacetic acid is the simplest and smallest organic molecule in the α-hydroxycarboxylic acid family and is an important chemical intermediate.At present,hydroxyacetic acid is widely used in organic synthesis,chemical cleaning,polymer materials,medical engineering and other fields,especially in the polymer polymer materials and medical engineering.With the development and application of the biodegradable material,polyglycolic acid,which takes glycolic acid as the raw material,the purity,particle size and water content of raw materials will have certain influence on the subsequent polymerization process and finally determine the performance of polymers.However,study of the purification method for crude hydroxyacetic acid mainly focuses on the solvent extraction method,which is not suitable for the crude hydroxyacetic acid obtained by hydrolysis of methyl glycolate.In addition,domestic hydroxyacetic acid product generally have the problems of high water content,poor stability,irregular crystal habit,small particle size,serious coalescence,prone to deliquescence,difficult to dry and save,which are limiting the subsequent application of hydroxyacetic acid products.Therefore,the purification method of hydroxyacetic acid in this paper has been systematically studied in order to provide the basis for the production of hydroxyacetic acid with excellent performance.In this paper,firstly,the single crystal of hydroxyacetic acid was obtained by single crystal culture and its structure was analyzed.The crystal habit of hydroxyacetic acid was predicted by BFDH model and AE model,which provided some guidance for the crystal morphological regulation of hydroxyacetic acid.Secondly,the solubility of hydroxyacetic acid in six common organic solvents,including acetone,ethanol,isopropanol,n-butanol,ethyl acetate and acetonitrile,and two mixed solvents,acetone + ethyl acetate and ethanol + ethyl acetate,was determined by the dynamic method.The solubility data of pure solvent was fitted by the Apelblat equation,λh equation,NRTL equation and Wilson equation,while the solubility data in binary solvents was fitted by Jouyban-Acree equation.In addition,the thermodynamic properties of the solute in the pure solvents were estimated.In addition,the nucleation induction time of hydroxyacetic acid were determined by using of the randomness of crystal nucleation.The data was fitted by the nucleation probability equation.Then the nucleation parameters of hydroxyacetic acid in ethanol,acetone,ethyl acetate and acetonitrile were calculated.The nucleation difficulty of hydroxyacetic acid in these four solvents was found.Finally,on the basis of the above research,the effects of some key parameters of crystallization solvent were systematically studied,including the initial solution concentration,whether to add seed or not,addition amount of seed and seeding time.By taking control of the nucleation process of hydroxyacetic acid,the optimal operating parameters of the cooling crystallization process of hydroxyacetic acid were obtained.The product from the new process has high purity,regular crystal morphology,high average particle size,low water content,easy to dry,and the process of one-way yield can reach 72.9%,which are a greater extent to solve the problems of domestic products.