SODIUM TRIPOLYPHOSPHATE HEXAHYDRATE PRODUCTION PROCESS Russian patent published in 2000 - IPC

FIELD: industrial inorganic synthesis. SUBSTANCE: sodium tripolyphosphate hexahydrate used as synthetic detergent component is prepared from phosphoric acid and soda. The two reactants form anhydrous sodium tripolyphosphate, which is then hydrated in aqueous salt solution in presence of seed and alkali metal and/or ammonium sulfates, the content of the latter in liquid phase of suspension constituting 0.05 to 0.5 mol %. Suspension is separated into mother solution and final product which is further dried at 55 to 110 C. To improve quality of product, precipitate after separation of suspension is washed with saturated aqueous solutions of sodium tripolyphosphate hexahydrate in amounts 0.7 to 2 wt parts per 1 wt part of liquid phase. Utilization of liquid part of suspension after separation of phases and wash water is made in the course of sodium tripolyphosphate formation. According to one of embodiments of process, presence of sulfate salts in liquid phase of suspension is provided by formation of anhydrous sodium tripolyphosphate from extraction phosphoric acid and soda ash obtained from raw nepheline material. In this case, in order to lower level of alkali-earth metals in final product, suspension, prior to be separated, is treated with alkali metal and/or ammonium nitrates in amounts 4 to 12 mol per 100 mol of sodium tripolyphosphate hexahydrate, ammonium nitrate being added to suspension at pH value thereof 7.7-8.2. EFFECT: intensified process to 2 1/5 to 5 h due to reduced hydration time and raised drying temperature without tripoly form degradation. 6 cl, 3 tbl, 4 ex