Study On Recrystallization Process For Purification Of Crude1,12-dodecanedioic Acid

In this paper, recrystallization process of1,12-Dodecanedioic acid was studied for thepurpose of purification, effects of the variety of solvent, stirring speed, ethanol concentration,crystallization time, initial temperature, temperature gradient and solid-liquid ratio on it wereinvestigated and the optimum process for recrystallization was preliminarily determined.Main results were as follows:11kinds of solvent were screened to research their influence on DDA recrystallization,the results showed that four solvents, namely, acetic acid, butyl acetate, ethanol andacetonitrile, can meet the requirements of purification. After investigation, ethanol wasselected to be the most suiTable one.The esterification degree were studied with ethanol as recrystallization solvent, it isfound that temperature, time and concentration of ethanol all had effect on the degree ofesterification. Within the scope of experimental temperature and time, the production ofmonoester increased; and the monoester production first increased then decreased whenethanol concentration rising, the maximum was reached with80%ethanol concentration. Inthese factors, temperature had a significant effect on monoester production, time was thesecond, and ethanol concentration had the least effect on it. Combination of factors forminimum and maximum degree of esterification was determined with orthogonal experiments,it is to say45℃,4h,60%ethanol concentration and75℃,10h,70%ethanol concentration,respectively.Part of thermodynamic properties of DDA was studied to draw out its dissolved phasediagram in different ethanol concentration solutions. It was found that DDA solubility inethanol solution increased with the increase of temperature and ethanol concentration; whentemperature lowered an identical number under the same ethanol concentration, the higher thetemperature the greater the supersaturation; with the decrease of ethanol concentration, whentemperature lowered an identical number under the same temperature, the higher the ethanolconcentration, the greater the degree of supersaturation. Cooling crystallization method issuiTable for recrystallization of DDA in ethanol solution, according to the dissolved phasediagram of DDA in different ethanol concentration solution, it is better to choose60%or70%ethanol concentration to ensure the whole crystallization process in good operating range.Effects of operating parameters such as stirring speed, ethanol concentration,crystallization time, initial temperature, temperature gradient and solid-liquid ratio on DDArecrystallization process and the optimum process for it were investigated with single factorexperiments and multi-factors response surface experiment, the optimal condition was:stirring speed of120r·min-1,70%ethanol concentration, crystallization time of10h, initialtemperature of54.4℃, temperature gradient of1.4℃/18min and DDA capacity of9.93g (Solid-liquid ratio1:20). Under this condition, the purity of DDA can reach99.14%. Ester(mainly monoester) generated in the process of recrystallization primarily grew into crystal,both ether and acetone can wash away impurities and monoester on the surface of crystal, butneither of them can wash inside, they had a similar washing effect, the residue monoester inthe crystal was about1100mg·kg-1.According to large numbers of literatures and some phenomena in the process ofexperiment, crystal structure of DDA was speculated. In DDA crystal, a very longone-dimensional chain can be formed through hydrogen bond formation at both DDAmolecule end, then the long one-dimensional chain folded to form a paper clips structurecalled lamellae through hydrophobic force, at last, the lamellae stacked to form DDA crystalthrough hydrophobic force.