Study On The Crystallization Process Of Preparing Potassium Dihydrogen Phosphate From Wet-process Phosphoric Aci

As a very important chemical product,potassium dihydrogen phosphate is widely used in agriculture,food,chemical industry,medicine and other fields.In the preparation process of potassium dihydrogen phosphate,neutralization process has the advantages of simple process,small equipment investment and high product quality,accounting for more than 90%of the total production capacity of potassium dihydrogen phosphate in China.However,due to the neutralization method to prepare potassium dihydrogen phosphate with high energy consumption thermal phosphoric acid as raw material,using intermittent production,there are high raw material cost,small production scale,labor intensity,product lack of competitiveness and other problems,restrict its application and development,so it is necessary to improve the neutralization method.Entrusted by a company,this project uses the low-cost wet-process phosphoric acid produced by the company to replace thermal-process phosphoric acid as raw material to develop the process of producing potassium dihydrogen phosphate by crystallization method,and measures and correlates related thermodynamic data.The main research work and results are as follows:（1）The first acid provided by the company was screened as a purifying agent,and it is expected that after the simple purification of acid and potassium hydroxide reaction,the crystallization can prepare qualified potassium dihydrogen phosphate products.The results show that the effect of simple purification is limited and the desired effect is not achieved.（2）Screen the second kind of acid purifier provided by the company,and it was optimized that the potassium dihydrogen phosphate prepared by purifier 4 meets the quality requirements of HG/T 2321-2016 superior products.The process of cooling crystallization and vacuum evaporation crystallization was explored and optimized.The optimized process conditions of cooling crystallization were obtained as follows:p H of the reaction solution was 4.5-5,reaction temperature was 90℃,reaction time was 30min,cooling rate was 0.2℃/min,crystallization time was 60min,and final crystallization temperature was 40℃.On this basis,the vacuum degree,temperature and other process conditions of vacuum evaporation crystallization were studied.The results show that:When the vacuum degree is adjusted to 0.043～0.045MPa at 70℃,0.053～0.055MPa at 50℃,0.083～0.085MPa at 40℃,the yield of potassium is the highest,which is 35.97%.In order to improve the product yield,the mother liquor was concentrated and returned to the production system.The results showed that the yield of potassium could be increased to 97.75%when the amount of circulating mother liquor was increased to 100%.（3）The crystallization process of producing potassium dihydrogen phosphate from the third acid provided by the company was studied.The results showed that the product prepared by the third acid under appropriate conditions reached the quality index of HG/T 2321-2016,eliminating the purification process of phosphoric acid purification agent,and achieving the purpose of process optimization.（4）The influence of impurities on the solubility of potassium dihydrogen phosphate was investigated by single factor experiment and orthogonal experiment.The results showed that the solubility of potassium dihydrogen phosphate increased with the increase of impurity concentration at the same temperature.In addition,the solubility data of ternary system KCl-KH₂PO₄-H₂O and KH₂PO₄-CO（NH₂）₂-H₂O at353.15K were correlated to provide theoretical basis for the subsequent preparation of water-soluble fertilizer containing N-P-K nutrients.