| A method of manufacturing potassium dihydrogen phosphate (KDP) by the directly react of wet-process phosphoric acid (H3PO4) and potassium chloride (KCl) has been studied. The process implements the direct double decomposition reation of H3PO4and KCl by using stipping removal hydrogen chloride gas. Then separating KDP based on the solubility of KDP in wet-process H3PO4in the method of crystallization. The key of this method is removed the product HCl to ensure high conversion rate of reactants. However, the HCl and water (H2O) has an azeotropic point108.6℃which is highest azeotropic point. So the effusion of HCl from the reactor must with vapour. Blowing water vapor to the reactor can remove more gas of HCl. This method can also get by-product of hydrochloric acid which is more valuable.The effects of process conditions on the percent conversion of KCl are studied. Such as reactants (the molar ratio of H3PO4and KCl), reaction temperature, reaction time, the amount of vapor, vacuum degree and so on. The purification method of recrystallization is used to decrease the content of KCl. Not only the content of KDP can reach more98%after purifying but also the mother liquor can be used as raw material recycling.The reaction system is complicated which involves different substances such as KDP, KCl, H3PO4, HCl and H2O. It can get more KDP crystal by the research of solubilities of KDP and KCl in different solvents of water, phosphoric acid and hydrochloric acid. Getting complete water salt phase diagram by study the system of K+, H+//Cl-, H2PO4-—H2O which can be used to guide the choice and optimized technological condition.Additionally, the method of preparing KDP is combined the process of double decomposition reaction with crystallization. High purity product KDP is gotten by recrystallizing of the products, and the mother liquor can be used circularly. The great merits of the process are short process flow, simple operation, low cost and environmental protection. |
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