Hoechst Aktiengesellschaft

Thomas Staffel

Renate Adrian

Gunther R Schimmel

Reinhard Gradl

Wolfgang Becker

Jurgen Grosse

Horst Buhl

Herbert Neumann

Gregor Fucker

To prepare essentially water-insoluble, long-chain ammonium polyphosphate, in a first stage, ammonium orthophosphate and phosphorus pentoxide are reacted in the presence of gaseous ammonia in a reactor equipped in its interior with mixing, kneading and comminution apparatus, until the drive motor of the reactor passes through the second current peak in its current consumption/time diagram. In a second stage, the material discharged from the reactor is then fed to a disk dryer, the heating disks of which are maintained at temperatures of 240.degree. to 300.degree. C., whereas its lower cooling disk has temperatures of 5.degree. to 45.degree. C. The material, which covers the disks of the disk dryer at a layer thickness of 5 to 20 mm, has a residence time of 35 to 70 minutes in the disk dryer, while ammonia-containing gas is continuously passed through the disk dryer. Finally, the ammonia-containing gas exiting the disk dryer is freed from water vapor contained therein by condensation and the ammonia-containing gas is reheated prior to its entry into the disk dryer.

Process for the preparation of ammonium polyphosphate

In order to remove ammonia from water vapor-containing gases, in particular offgases, the gases are brought into intimate contact with warmed polyphosphoric acid, the polyphosphoric acid advantageously having a P.sub.2 O.sub.5 content of from 70 to 84% by weight and a temperature of from 120.degree. to 170.degree. C.

Process for the removal of ammonia from gases

For producing substantially water-insoluble, chain-type ammonium polyphosphate, equimolar quantities of diammonium phosphate and phosphorus pentoxide are reacted at temperatures from 170.degree. to 350.degree. C. in a zone, which effects continuous mixing, kneading and comminution, in the presence of a stream of ammonia gas. In this process, the water is separated from the ammonia gas which leaves the zone and contains water vapor, and the dried ammonia gas is caused to flow again through the zone. A plant for producing substantially water-insoluble, chain-type ammonium polyphosphate can comprise a reactor (1) into which an ammonia feed pipe (8) and pipes for feeding phosphorus pentoxide (6) and diammonium phosphate (7) lead and from which an ammonium polyphosphate discharge pipe (9) and an exit gas pipe (10) start. The exit gas pipe (10) leads into a condenser (13) which is flow-connected via a pump (14) to a heat exchanger (15). An exit gas line (18) which leads into the ammonia feed pipe (8) starts from the heat exchanger (15).

Process for producing ammonium polyphosphate

A plant for producing chain-type ammonium polyphosphate from ammonium orthophosphate and phosphorus pentoxide in the presence of gaseous ammonia comprises a reactor having rotatable mixing, kneading and comminuting tools in its interior and a feed pipe for the solid starting materials, an introduction pipe for ammonia, a gas discharge pipe and a discharge line for the reaction product, all of which are flow-connected to the interior of the reactor. The discharge line of the reactor is also connected for material flow to a mixing apparatus. A discharge device, which is controlled by the power consumption of the drive motor of the reactor, is arranged in the discharge line.

Plant for producing ammonium polyphosphate

To prepare essentially water-insoluble, chain-form ammonium polyphosphate from equimolar amounts of di- ammonium phosphate and phosphorus pentoxide in the presence of ammonia at temperatures of from 170.degree. to 350.degree. C. with constant mixing, kneading and comminution, at least some of the diammonium phosphate and phosphorus pentoxide is replaced by partially ammoniated polyphosphoric acid. A plant for carrying out this process can comprise a sealed reactor (1) which is provided with metering devices (2, 3) and feed tubes (4, 5) for phosphorus pentoxide and diammonium orthophosphate, an ammonia feed tube (8), an ammonium polyphosphate discharge tube (9) and a line for offgas. Rotatable mixing, kneading and comminution elements are provided inside the reactor (1). Furthermore, a heatable stirred tank (11) which can be charged with polyphosphoric acid via a feed line (13) is provided and can be used to remore water vapor and ammonia from the offgas flowing from the reactor (1) via the line (20) and from which partially ammoniated polyphosphoric acid can be introduced into the reactor (1) via an outlet line (17).

Alkali metal phosphate solutions having a fluorine content of less than 20 ppm, based on P.sub.2 O.sub.5, are prepared by first digesting crude phosphate using sulfuric acid, and separating the calcium sulfate from the crude phosphoric acid. An alkali metal compound is then added to the crude phosphoric acid, and the precipitated solid is filtered off. The prepurified crude phosphoric acid is neutralized to a pH of at least 7, and the solid produced during this operation is separated off. The resultant alkali metal phosphate solutions having a P.sub.2 O.sub.5 content of from 10 to 30% by weight are adjusted to a pH of between 4.8 and 6.0 using phosphoric acid. The solutions are heated to from 60.degree. to 120.degree. C., and from 1 to 6% by weight, based on the weight of the solution, of an alkaline earth metal oxygen compound are added to the alkali metal phosphate solutions with stirring. Finally, the precipitated solid is filtered off from the alkali metal phosphate solutions after a residence time of from 0.5 to 4 hours.

Process for the preparation of alkali metal phosphate solutions

A process for producing essentially water-insoluble, chain-type ammonium polyphosphates of the general formula (NH.sub.4 PO.sub.3).sub.n, in which n is a number from 10 to 1,000, whose 20% by weight aqueous suspension prepared at 60.degree. C. has a viscosity of less than 100 mPa.s at 20.degree. C., is indicated, which comprises allowing a reaction mixture of ammonium orthophosphate and phosphorus pentoxide to react fully at a high mixing intensity in a crumbly phase at a temperature from 100.degree. to 300.degree. C. over a period of from 10 to 60 minutes and then heat-treating the reaction material in a known manner over a period of from 50 to 200 minutes at a temperature from 200.degree. to 300.degree. C. under an ammonia atmosphere. Advantageously, the reaction is carried out in a kneader.

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Hurth, Germany

Thomas Staffel