Известия Томского политехнического университета: Инжиниринг георесурсов (Sep 2017)
Production of potassium-nitrogen sulfate fertilizer by conversion of potassium chloride with sulfuric acid
Abstract
The relevance of the research is caused by the necessity to obtain complex potassium sulfate fertilizers, which do not contain chloride ion. The accumulation of the latter in soil leads to lower yields and increases the level of soil salinity. The main aim of the work is to investigate potassium chloride conversion with sulfuric acid and potassium hydrogensulfate neutralization stages by ammonia solution in production of potassium-nitrogen sulfate fertilizer; to define optimal parameters of these stages. The methods used in the study: theoretical analysis of the processes, modeling of technological process in laboratory conditions, definition of hydrochloric acid concentration by chloride ion argentometric titration, study of changes in the content of ion HSO 4 - by titration of product with sodium hydroxide, X-ray analysis of product, obtained by neutralization. The results. The authors have studied the production of potassium-nitrogen sulfate fertilizer by vacuum potassium chloride conversion with sulfuric acid with further neutralization of the obtained potassium hydrogensulfate by ammonia solution. At conversion it was determined that the residual pressure and sulfuric acid concentration in reaction mixture influence on the output of basic products - potassium hydrogen sulfate and hydrogen chloride, and on concentration of the obtained hydrochloric acid as well. Studying the potassium hydrogensulfate neutralization with the ammonia solution the authors determined the dependence of neutralization degree on the process duration at 25, 40 and 60 °C. The findings. It was ascertained that application of rarefaction at the potassium chloride conversion stage with sulfuric acid allows reducing the reaction mixture boiling temperature, thereby decreasing the conversion temperature, and increasing as well the output of the basic conversion products - potassium hydrogensulfate and hydrogen chloride. It was revealed that the output of potassium hydrogensulfate and hydrogen chloride increases with the increase of sulfuric acid concentration in reaction mixture. The conversion should be carried out at sulfuric acid excess from stoichiometry, as the sulfuric acid, being the dehydrating agent, binds a part of water and reduces the solubility of reaction products. Application of sulfuric acid excess more than 20 % of stoichiometric amount is inappropriate, as it leads to accumulation of sulfuric acid in mother liquor and raw material losses. Sulfate of potassium and ammonium KNH 4 SO 4, is the product of potassium hydrogensulfate neutralization by ammonia solution. It can be used as a complex potassium and nitrogen fertilizer. Based on the carried out researches the authors determined the optimal parameters of potassium chloride conversion with sulfuric acid (Т=90 °С, residual pressure 40 kPa, ratio Н 2 О/КСl=1,5, concentration H 2 SO 4 46 wt. %) and potassium hydrogensulfate neutralization with ammonia solution (Т=60 °С, t=40 minutes) in technology for obtaining potassium and nitrogen sulfate fertilizer.
