PROCESS FOR PREPARING A CONTROLLED-RELEASE MICROENCAPSULATED CHEMICAL FERTILIZER

摘要

The invention relates to a process for preparing a controlled-release microencapsulated chemical fertilizer. According to the invention, the process consists in the prepolymerization of a 37% formaldehyde aqueous solution and technical urea granules at a formaldehyde : urea molar ratio of 1:1, while stirring and heating continuously for 2 h at 65...70°C, while maintaining the pH value of the reaction mass within the range of 8.5...9 by repeatedly dosing a 40% KOH solution, after which the reaction mass is cooled down to the ambient temperature and is admixed, while stirring vigorously, to a microemulsion of the water-in-oil type consisting of a cyclohexane which contains a non-ionic surfactant and an aqueous solution containing mono-ammonium phosphate and potassium chloride, the resulting fine dispersion being brought to a pH value of 4...5, when urea is admixed again until a final ratio of 2...2.4 :1 is reached and the controlled heating starts for the polycondensation of the reaction mass at 60...75°C, for 2 h, with pH correction to 3.0...4.5, after which water is removed azeotropically and the fertilizing precipitate is filtered at the ambient temperature and dried in a drying chamber, at 70°C, until a constant mass is reached.