Preparation of potassium dihydrogen phosphate with N-methyldiethanolamine as extractant

Abstract

Potassium dihydrogen phosphate (KH2PO4) is an important compound. Using KCl and H3PO4 as raw materials, N-methyldiethanolamine (MDEA) as extraction agent, an efficient and profitable route of preparing KH2PO4 was proposed. MDEA selectively extracts HCl to shift the reaction equilibrium, and the intermediate N-methyldiethanolamine·hydrochloride (MDEA·HCl) is an excellent precipitant for the crystallization of KH2PO4. The coupling of reaction and separation was realized and the process was intensified by the presence of MDEA. The effects of operation parameters on the product yield, product purity and the chlorine content in the solid-product KH2PO4 were investigated systematically. The optimal operation conditions were: H3PO4/KCl molar ratio of 1.4:1, MDEA/KCl molar ratio of 1:1, reaction time of 10 min, reaction temperature of 30 °C, H3PO4 concentration of 52.04 wt %. Under the optimal operation conditions, the product yield was 98.64%, product purity was 99.37% and the chlorine content in the solid-product KH2PO4 was only 0.15 wt %. The obtained product satisfies the industrial grade standard of KH2PO4. Compared with existing processes of KH2PO4 production, the proposed process has the advantages of high product purity, high product yield, mild reaction conditions and profitable.