Study On The Crystallization Process Of Imidacloprid

Imidacloprid is a super efficient insecticide,which has a strong control effect on stinging and sucking mouthparts pests,and is widely used in the planting of rice,wheat,cotton and other crops.At present,imidacloprid products generally have problems such as uneven particle size distribution,incomplete crystal habit,low purity and low packing density,and the product quality needs to be improved.Crystallization is an important process in the production of imidacloprid,which has a great influence on the crystal shape,particle size and purity of the product.The crystallization process of imidacloprid crystal was systematically studied in this paper.The solid-liquid distribution and migration of imidazolidine were explored by cooling crystallization.Taking the imidazolidine removal rate and partition coefficient as assessment criteria,the effects of the cooling rate,final crystallization temperature,crystallization time and addition of seed crystal on the migration of imidazolidine between liquid and solid phases were systematically studied,as well as the separation effect and product quality were evaluated.The solubility and supersolubility of imidacloprid form Ⅱ in methanol-water mixed solution were determined by using laser dynamic laser method,and the solubility data were correlated by applying Apelblat model,l h model and Van’t Hoff model.Akaike information criterion analysis was used to identify the best model.Afterwards,thermodynamics parameters including enthalpy change,entropy change and Gibbs free energy change of imidacloprid in binary mixed solvents were calculated,which provided basic data for crystallization process optimizing.The Form I and Form II of imidacloprid were prepared by cooling crystallization.The effects of cooling rate,initial concentration of solution and final crystallization temperature on crystal form were investigated.The Form I and Form II of imidacloprid were analyzed by X-Ray diffraction,Differential scanning calorimeter and scanning electron microscope.The characteristic peaks of X-Ray diffraction,crystal habits and melting points about them were determined.The solubility of the two forms in methanol was measured respectively,which provided a theoretical basis for the study of the the crystal forms of imidacloprid.The cooling crystallization process of imidacloprid was optimized by single factor experiment,and the effects of solvent types,initial concentration of crystallization solution,cooling rate,stirring rate,final crystallization temperature,crystallization time,seed crystal addition amount and seed addition timing on product yield and quality were explored.The optimal process parameters were determined.It can be used to prepare imidacloprid crystals with uniform particle size distribution,complete crystal habit and good fluidity.In view of the low bulk density and high porosity of imidacloprid powder,the relationship between particle size distribution and bulk density of imidacloprid powder was investigated.The effects of sieving and grinding on powder size and bulk density were investigated by microscope analysis,particle size analysis and density determination.The bulk density of the imidacloprid powder was effectively improved,thereby improving the product quality.