SU7516A1 - The method of obtaining solid diammonium phosphate - Google Patents

Description

Direct preparation of diammonium phosphate in solid form poses great difficulties, since this salt is distinguished by considerable solubility, in comparison with poorly soluble monoi, especially tri-ammonium phosphate, and may exist under limited conditions. Another disadvantage is that significant amounts of ammonia are split off when the solutions are heated.

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{upon receipt of this salt, it always happens more or less, the review according to the conditions of work is contaminated by the admixture of mono- or tri-ammonium phosphate. Therefore, to obtain pure diammonium phosphate, it is usually preferred to go over easily crystallized tri-ammonium phosphate, which can be easily transferred to the diammonium salt by careful heating.

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The inventors said that ammonium phosphate, which is practically free of the above mentioned impurities, can be obtained directly by neutralizing it so that 1.5–2–2 ammonia molecules fall on each molecule of phosphoric acid. It is most expedient to proceed from a solution of pure diammonium phosphate saturated at the ordinary temperature. The solution is first poured in, with vigorous placement, as much concentrated phosphoric acid as possible so that the molecular weight ratio reaches 1: 1.5. Concentrated phosphoric acid and ammonia gas are then introduced simultaneously, keeping the molecular weight ratio of 1: 1.5 in order to maintain the indicated ratio of components in the solution and not switch to the more acidic side. Finally, cooling is carried out to an ordinary temperature, passing ammonia gas at the same time or thereafter, until the molecular weight ratio reaches 1: 2. This precipitates, in the form of pure diammonium phosphate, phosphoric acid almost completely taken over. To establish the molecular relationship boundaries required for proper operation, you can use a titration method with suitable indicators or an electrical method. Example. In a cold saturated solution of diammonium phosphate, which gives a neutral reaction with cresol red and containing about 630 K1 phosphate in 1 Kij6.M water, first pour in pb / p-phosphoric acid until the solution gives color from brominerespurpura; to achieve this coloration it is usually required per cubic meter. About 240 kg of the above acid is added to the solution. Then ammonia gas and phosphoric acid are simultaneously introduced in amounts corresponding to a molecular weight ratio of 1.5: 1. The correct ratio of the amounts of these reagents can be controlled in the following way: a sample is taken from time to time, and, if necessary, diluting and cooling it, is tested for staining with bromineresol. Although the solution itself, due to the considerable heat of neutralization, is heated very strongly with the evaporation of water introduced with phosphoric acid, but there is no loss of ammonia. To avoid also the evaporation of large quantities of water, it is advisable to maintain the temperature not higher than 80-90, adding to each. m of a basic solution of 150 kg of ammonia gas and another 880 kg of phosphoric acid, or a multiple of these quantities, are gradually cooled to an ordinary temperature, and then ammonia gas is reintroduced until then. while the solution will again change color with cresol red; this will require 105 kg of ammonia gas or a multiple thereof, in accordance with the amount of phosphoric acid used for the reaction. When This diamonium phosphate falls in an amount approximately equivalent to the amount of phosphoric acid consumed; it is free of mono-ammonium tri-ammonium phosphate, is in the form of large, easily separated | j from each other crystals and, after {released from water and dried, is a finished product. The mother liquor again goes to work, as the starting material. If a higher concentration of phosphoric acid is used for this work, then to achieve the volume of the initial solution, a more significant cooling is performed to neutralize it, or ammonia is added to part i i as an aqueous solution. When using dilute phosphoric acid: a slightly higher temperature is chosen for the reaction; can also be used to enhance | evaporation of water to arrange additional firebox. Working with a dilute solution in some cases is preferable to using more concentrated phosphoric acid, since it is obtained by evaporation, since when a partially neutralized liquid is evaporated, there is no significant eating of the dishes; in addition, impurities can be simultaneously isolated and, moreover, ammonia losses are very insignificant if evaporation is carried out in a vacuum. In particular, to evaporate water from solutions that are not very weak, cooling in vacuum is sufficient. At present, it has been proposed to use solutions of phosphoric acid or mono-ammonium phosphate and the like to obtain ammonia from ammonia-containing gases or vapors, for example, gases from coke ovens;