GB1442780A - Process for the manufacture of ammonium polyphosphate - Google Patents

Abstract

1442780 Ammonium polyphosphates VEBACHEMIE AG 28 Dec 1973 [30 Dec 1972] 60103/73 Heading C1A In a process for the continuous production of ammonium polyphosphates by the reaction of gaseous ammonia and aqeuous phosphoric acid at elevated temperature in a single stage or multiple stage falling film reactor, aqueous wet process phosphoric acid is introduced into the top of the reactor and gaseous ammonia, optionally with a diluting gas, is introduced into the bottom of the reactor, the amount of ammonia introduced being a large excess over the amount corresponding to a molar ratio NH 3 : P 2 O 5 from 0À5 to 4À5 in the intended end product, the reaction temperature being between 120‹ and 260‹ C., the pH of the resulting ammonium polyphosphate solutions when diluted to a solution of 10% by weight being between 2À5 and 6À0, and the heat of neutralization of the reaction being utilized for the evaporation of water to concentrate the ammonium polyphosphate product and to condense the phosphate to polyphosphate in the reactor, and to heat thermal fluids which are used to regulate the temperature of the reaction, the thermal fluids possibly being preheated in a heat exchanger intermediate two reactor stages of a multi-stage reactor by condensing vapour from the gaseous phase. Condensation promoters such as urea may be present. When a multiple stage reactor is used, the vapour passing from one stage is preferably treated to condense out water vapour, and the remaining gas is preheated and passed to the next stage. Preferred products contain 12-16% by weight of ammonium N and 54-70% by weight of P 2 O 5 .