Crystallization Kinetics Of Glycine And MgCl₂-Ethanol Adduct With Thermodynamic Approach

Glycine is an important organic compound used in food,pharmaceutical,chemical,and agricultural industries.The separation process used in biochemical industries such as,fractional precipitation,crystallization,and ion exchange are conventional,and the cost associated in these processes is almost 50%higher than the total cost of manufacturing.To develop efficient separation techniques,a thorough knowledge of thermodynamic properties in different medium,and at different temperatures and concentrations are essential.Polymorph control of the crystalline products is important especially in pharmaceutical industries where a wrong polymorph of a drug can pose a danger.Study for nucleation and growth/polymorphic transformation of glycine in different media will provide insight into the riddle of glycine polymorphism.The study will be useful in understanding polymorphism for other amino acids.MgCl2 supported heterogeneous Ziegler-Natta catalyst is used in the polymerization reaction in the polyolefin industries.MgCl2 is first treated with alcohol(mostly ethanol)and then TiCl4 is impregnated on it.The MgCl2/EtOH ratios in the precursor determine,among other features,the activity and the isotacticity degree of the resulting polymer.The crystallization kinetics of MgCl2 nEtOH will contribute to a deeper understanding,and thereby to a greater control,of the structure of crystalline adduct.The solubility determination by dynamic method was carried out of glycine(?-form)in different solutions.In electrolyte solutions,the solubility of glycine in MgCl2—H2O solutions from molality 0.5 to 3.5 and in mixed NaCL-MgCl2 solutions at MgCl2(0.5,1.0.and 1.5 mol-kg-1)from 283.15 to 333.15 K were carried out.In acid solutions,the solubility of glycine in HCl H2O upto molality 4.0 and in mixed HCl-MgCl2 solutions at MgCl2(0.25,0.5,and 0.75 mol·kg-1)from 283.15 to 343.15 K were carried out.In alcohol solutions,the solubility of glycine in alcohol(ethanol/1-propanol)-H2O,in ethanol-NaCl-H20 solutions at NaCl(0.5,1.0,and 2.0 mol·kg-1)and 1-propanol-NaCl-H2O solutions at NaCl(0.5 mol-kg-1)from 283.15 to 333.15 K were carried out.The solubilities of glycine in MgC1h and HC1 solutions show large increment,in mixed systems MgCl2—NaCl and HCl-MgCl2 solutions show moderate increase and in alcohol(ethanol/I-propanol)solutions show decrease in solubility with increasing temperature and concentration.Also,solubilities study for bischofite(MgCl2-6H2O)in glycine-H2O,and NaCl in alcohol(ethanol/I-propanol)-glycine-H2O were measured.The OLI System Software was used to thermodynamically model all the systems that were measured in the laboratory.Initial predictions by Stream Analyzer for all the three systems showed large deviations from the experimental data.Environmental Simulation Program was used to regress the solubility data by two different models,Bromley-Zemaitis(B-Z),and Mixed solvent electrolytes(MSE)model.B-Z model was used in mixed electrolyte(glycine-MgCl2—NaCl-H2O),and MSE model was used in mixed solvent(glycine-HCl-MgCl2—H2O)and glycine-alcohol(ethanol/1-propanol)-NaCl-H2O systems.Newly obtained model parameters were successful in representing the respective systems with low average absolute deviations.Supersaturations for glycine in different media(H2O,MgCl2-H2O,HCl-H2O,HCl-MgCl2-H2O)at different concentrations level were obtained with the aid of newly obtained model parameters from glycine-HCl-MgCl2-H20 systems.Supersaturation for MgCl2-6C2H5OH in MgCl2-6C2H5OH solutions were also obtained at different temperatures.These calculations were obtained with the aid of OLI Stream Analyzer.Polymorphic transformation of ?-glycine was experimentally studied in different solutions,such as H2O,MgCl2(1.5 mol kg-1)-H2O,HCl(1.0 mol-kg-1)-H2O,NaOH(1.0 mol-kg-1)-H2O,glycine-HCl(1.0 mol·kg-1)-MgCl2(0.75 mol kg-1)-H2O,and glycine-HCl(2.0 mol kg-1)-MgCl2(1.5 mol-kg-1)-H2O systems.The respective solutions were heated to 70? and then cooled and hold at different supersaturation level until the crystallization.In this way,the effects of medium,temperature,supersaturation,and time on the crystallization of glycine were investigated.Single y-glycine phase was achieved only in the HCl solution under all the investigated temperature and holding time.In the NaOH solution,y-glycine phase was observed at certain conditions.In other systems,such as H2O,MgCl2(1.5 mol·kg-1)-H2O,and HCl-MgCl2(1.5 mol kg-1,2.0 mol kg-1)-H2O,ca-glycine or its mixture with y-glycine or C4H-8N2O4 HC1 was produced depending on the conditions.Morphological investigation showed a-glycine with prismatic shape in pure water,y-glycine with polar morphology in MgCl2 solution,y-glycine with bipyramid and polar structure in HC1 solution,y-glycine with bipyramid shape in NaOH solution,and combination of bipyramid and polar shapes crystals formed in HCl-MgCl2 mixed system.An experimental study was carried out to determine the metastable zone width(MSZ W)and induction time for the crystallization of MgCl2-ethanol adduct.The metastable zone(MSZW)width and induction period were measured by polythermal method at various temperatures.The crystallization kinetics was calculated by Nyvlt and Sangwal approach.The effect of temperature,and supersaturation were studied by the induction time measurement.It was observed that induction period decreases as either temperature or supersaturation increases.The homogeneous and heterogeneous mechanisms were identified by the dependence of the induction period on temperature and supersaturation.From the induction period data,the interfacial energy and other various nucleation parameters were calculated.