The migration of imidazolidine between liquid and solid phases during the crystallization of imidacloprid.

As an intermediate in the synthesis of pesticide imidacloprid, imidazolidine is easily blended in imidacloprid products, which will lower the purity of the latter, thus affecting the using effects of it. The cooling crystallization method was used to study the distribution of imidazolidine. Taking the imidazolidine removal rate and partition coefficient as assessment criteria, the effect of the cooling rate, final crystallization temperature, crystallization time and addition of seed crystal on the migration of imidazolidine between liquid and solid phases was systematically studied, as well as the separation effect and product quality were evaluated. It was found that imidazolidine was most distributed in the solid phase at a higher cooling rate and a higher final crystallization temperature. The optimal process conditions for cooling crystallization were reached at the cooling rate of 0.2°C/min, the final crystallization temperature 15°C, the crystallization time of 5 h and the addition of seed crystal of 1%, under which the imidazolidine would remained in the liquid phase as much as possible. The final process yield was 83.62%, and the product purity was 99.70%. [ABSTRACT FROM AUTHOR]