Crystal Growth Kinetics Of Pronamide

Kinetics of an industrial crystallization process directly determines the size,shape,particle size distribution and flow characteristics of the products,which then affects the subsequent unit operations such as filtration,drying and storage.Obviously,the kinetic study is of great significance to the crystallization process.However,the relevant theory is still lacking,and needs more supplements.In this work,pronamide was picked as the model compound,and the bulk diffusion and surface integration in crystal growth process was systematically investigated by the comparison of crystal surfaces {100} and {10(?)}.It was revealed that the crystal face {100} grew according to "2D nucleation and growth" mechanism while the mechanism of {10(?)} was "normal growth".Kinetic functions were obtained through a large number of experiments on various factors.The details are as follows :The growth habit that determined by the inner crystal structural was simulated by using the Materials Studio(MS)software.The growth rule for indivi dual crystal face was,for the first time,theoretically predicted by the single solute growth method from the energy perspective.It was estimated that the relatively smooth {100} followed the "2D nucleation and growth" mechanism,while the rough {10(?)} tended to "normal growth" mechanism.The surface integration process was investigated by the microscopic structural characterization of the crystal faces.It was determined that the growth mechanism of face {100} was "2D nucleation and growth" and face {10(?)} was "normal growth" in acetone solution,which verified the correctness of the theoretical prediction.The effects of solvent,supersaturation and impurity on the surface integration process were studied through the further experiments.The result s showed that the strong interactions between solvent molecules and the crystal surface made solvents bonded with crystal surface firmly,and correspondingly the solute molecules were difficult to grow on the crystal surface.The effect of acetone on cryst al face {100} of pronamide was significantly higher than that of methanol,which resulted that the "2D nucleation and growth" mechanism of the {100} crystal face was transformed from "polynuclear growth" in methanol to "mononuclear growth" in acetone.The bulk diffusion process of crystal growth was studied by molecular simulation.The distribution of solvent layers on different crystal faces was first obtained by dynamic simulation and then the bulk diffusion process of solute through the solvent layer to the crystal surface was studied in details.Furthermore,the effect of different solvents,temperatures,concentrations and impurities on the solute diffusion coefficient were examined.The results indicated that the radial distribution density of solvent acetone was greater than that of methanol on the same {100} crystal surface,so the diffusion resistance of acetone was larger which reduced the diffusion coefficient of solute.From the comparison of crystal faces {100} and {10(?)},it was found that the density of acetone solvent layer on the {10(?)} crystal surface was significantly greater than that of {100},and the diffusion rate was obviously lowered when the solvent reached close to the {10(?)} face.