Study On Controllable Induced Crystallization Process In Glycine Aqueous Solution

In this paper,theoretically and experimentally studies on the induced crystallization in glycine aqueous solutions have been carried out.Based on the basic characteristics of the induced nucleation process,a new method for regulating and controlling the number of crystals in the induced nucleation process by controlling the nucleation conditions was proposed.The nucleation processes of aqueous solutions of glycine at different initial supersaturations were used as a model research system.The solid-liquid phase changes of the induced nucleation process were mainly analyzed.And a theoretical model of grain size in the induced crystallization process of glycine aqueous solution was established in combination with the mass balance equation and the original seed particle size theoretical model.Firstly,the study of the metastable properties in the crystallization process of glycine aqueous solution was systematically carried out.The crystal form of glycine during all the experiments was analyzed and determined to be a-type.The static gravimetric method and dynamic FBRM monitoring method were used to determine and verify the solubility data of a-glycine in pure water.And the empirical equations including Apelblat equation,van't Hoff equation and ?h equation were used to evaluate the fitting effect on the measured solubility data.At the same time,the crystallization metastable zone of glycine aqueous solution was determined by dynamic FBRM method.The effects of crystal seed,cooling rate and stirring rate on the width of metastable zone were respectively investigated,and the corresponding 3D metastable zone model was established.The induction period data in the different supersaturation glycine aqueous solutions at 50? was investigated.And the demarcation point S0=1.26 for primary homogeneous nucleation and primary heterogeneous nucleation was determined.Based on the experimental data of nucleation induction period,the nucleation index and interfacial tension were calculated,and the first limit supersaturation and other important information were deduced.The on-line monitoring techniques such as focused beam reflectometry measurement(FBRM)and attenuated total reflection fourier transform infrared spectroscopy(ATR-FTIR)were used to systematically investigate the induced nucleation process of glycine-water system.The results showed that the supersaturation of the crystallization system gradually decreased with the formation of nucleation and reached the fixed boundary values in the two regions of primary homogeneous nucleation and primary heterogeneous nucleation respectively.The supersaturation didn't affect the grain size of the crystal nuclei in the primary nucleation.At the same time,the mechanism of crystal nucleation and growth in the crystallization process of homogenous system was systematically studied.The primary nucleation rate and rate of secondary nucleation were calculated by crystallization experience models.Based on the above research results,a particle size control model based on induced crystallization was established,which can be used to provide basic data and theoretical basis for controlling the grain size of the glycine aqueous solution crystallization process.Finally,on the basis of this model,experiments on the induced crystallization under different initial supersaturations were conducted.These tests verified the applicability of the particle size control theoretical model and the feasibility of using controllably induced nucleation as a seeding methodology.