Research On Control Of Crystal Size Distribution Of Glycine

As an important fine chemical product,glycine has developed more and more diversifiedly with the continuous innovation of production technology for several decades.Some applications have been developed very well,such as in medicine,food and feed.However,in actual production,there exist some problems,such as uneven particle size distribution and easy agglomeration.By studying the thermodynamic properties of glycine and the effects of different operating conditions on the size of glycine,the optimal conditions for objective crystal size of glycine were obtained.The crystallizer in the laboratory was simulated by Fluent,whose conclusion was consistent with the experimental results.It provided a theoretical basis for the magnification and optimization of the industrial crystallizer.First,the solubility data of glycine in methanol-water solution with different concentration were determined by static method.The solubility of glycine increased with the increase of temperature and decreased with the increase of methanol concentration.The Apelblat equation,?h equation and CNIBS/R-K equation were used to correlate the solubility data,and the results were very good.The dissolution process is thermodynamically analyzed,indicating that the dissolution process of glycine in the experimental range is endothermic and non-spontaneous.The metastable zone width of glycine was determined by direct method,and the width of metastable zone for glycine under different conditions was researched.Then,the influence of cooling rate,stirring speed,seed addition,addition temperature and speed of anti-solvent on CSD of glycine was investigated.An orthogonal array with 16 test units was selected to optimize the crystallization parameters.A narrow CSD of glycine was obtained under the optimal condition.The optimization conditions are as follows: the cooling rate was 0.2 K/min,stirring speed was 400 r/min,the addition of seed was 8 %,the temperature of the anti-solvent was 323.15 K,and the addition of anti-solvent was 0.185 mL/min.The crystal form and morphology were determined by X-ray diffraction and optical micro-scope,and the results indicated the crystals were all ?-glycine and particle size of the products was uniform.Finally,the following rules are gained by Fluent simulation for the model of the laboratory crystallizer: the turbulent degree in the region near the impeller was stronger and the flow velocity was slower in the wall area of the mold,also the flow velocity near the stirrer was greater than the flow velocity at the bottom of the mold.Therefore,when the industrial mold was enlarged,it should be considered that adding baffles around the mold to promote mixing.The increase of mixing speed will make the mixing state of the crystallizer obviously improve,but the higher stirring speed will increase the supersaturation of the solution and increase the probability of the secondary nucleation.In actual production,all factors must be taken into account synthetically to determine the stirring speed.This work provided a good reference for the industrial crystallization of glycine.