| 摘要 |
<p>Potassium metaphosphate, (KPO3)n, is prepared by partially reacting phosphoric acid and KCl at 120-300 DEG C. and completing the reaction by running the partly reacted mass into a fused bath of (KPO3)n maintained at 560-850 DEG C. The acid may be -ortho, meta or super phosphoric acid, preferably containing over 25% P2O5. Equimolar proportions, or excess of either reactant, may be used, and H2SO4 may be added to provide K2SO4/sBKCl in the product. The first step may be carried out in a rotary kiln or tank furnace, to which the reactants are fed separately or as a suspension of KCl in the acid, heat being supplied by HCl gases from the second step and optionally by a burner. 45-75% of the KCl is allowed to react, and the fluid mass is then fed into a second rotary or tank furnace containing a (KPO3)n melt, heated directly by a burner above the surface of the melt or by a radiant roof, and/or by resistance heating of the melt. The m. pt. of the bath may be reduced by adding KCl, K2SO4, CaCl2, MgCl2 or oxides, e.g. of Ca, Mg, Fe, Al or Si. The melt may be cooled slowly, or rapidly, e.g. by tapping on to a water-cooled metal conveyer or rotary drum, to give a water-insoluble or -soluble product respectively, which may then be ground and screened. Alternatively, the melt may be sprayed to give granules. The HCl evolved in both steps may be fed to an aqueous absorber.</p> |
