Process For Preparation Of Sodium Hexametaphosphate From Wet Process Phosphoric Acid

In the two traditional routes of prepare phosphoric acid, the thermal process phosphoric acid mainly used for the preparation of the phosphate salt due to its high quality. But the high cost and the energy consumption are limiting its development potential. In the same time, the cost of wet process phosphoric (WPA) production is low, while because of its high impurity content, it is difficult used for industrial phosphoric acid or phosphoric acid foods directly, and shoule undergo purification treatment. The wet process phosphoric acid is near the thermal phosphoric acid in purity by solvent extraction purification, and the cost is still low. The tendency to replace the thermal phosphoric acid as raw material for preparation of fine phosphate products.are more and more popular in recent yearsIn this paper, the target is the production of sodium hexametaphosphate, investgated the process of wet phosphoric acid phosphate to prepare the phosphoric salt. And get the products from the the solvent phase which load the phosphoric directly. The steps included Solvent extraction purification process, stripping the purification phosphoric acid, the crystallization of sodium dihydrogen phosphate, and the sodium hexametaphosphate polymerization. Mainly study about the suitable extraction system, the influence of concentration, temperature and time on the extraction of the raw phosphoric acid. Study about the stripping process time, temperature and other appropriate operating conditions, Analysis the stirring rate, cooling rate and other conditions in the crystallization process. And the influence of the anions, cations come from phosphoric acid to the metastable zone of sodium dihydrogen phosphate crystals. Fit the equation between SO42-, F-, Fe3+, Al3+, Mg2+et al Impurity ion contents and the metastable zone width of the sodium dihydrogen phosphate crystals. The experiments studied the relationship between reaction time, temperature and the molten polymer molecular weight in the process of the polymerize sodium dihydrogen phosphate to sodium hexametaphosphateThrough the experiment, we used the TBP+kerosene as the extraction solvent, extraction at 50℃; and stripping at 25℃by using lmol/L of NaOH in chemical equivalent; after the separation of the extraction agent, concentrated the solution which load the sodium dihydrogen phosphate, and then cooling crystallization it in the stirring energy consumption of 0.1w/L and the cooling rate is 0.2℃/min, melt polymerization the crystals at a high temperature, got sodium hexametaphosphate products.Under the optimal extraction, stripping, crystallization, polymerization conditions, the sodium hexametaphosphate in the molecular weight range of 6000-7000 can be obtained, in which Fe, As, Pb, F and other impurities to achieve national food grade requirements.Compared to the thermal acid process, this process route can reduce the energy consumption, and fully guarantee the quality of the product, thereby reducing the economic pressure.