DE1767156A1 - Process for the production of ammonium phosphates - Google Patents

Description

Dr. Walter Beil "κ add Alfred Hoeppener -5. APR.

Dr. H? R, s Joadtfin Wolff Dr. Hans Chr. BeU

FUchUinw .-. Lte Frankfurt a. M. - Hddut Adelootir. 58 IeL 3010 94

Our no.14620

SINCAT - Soeietä Industriale Catanese S.p.A. Palermo / Italy

Process for the production of ammonium phosphates .

The invention relates to a process for the production of ammonium phosphates. In particular, it relates to a method for the production of crystalline Diamaoniumphosphat and a concentrated solution of Asamoniumphosphaten, which for the Production of fertilizers is suitable, wherein «an from an impure, aqueous solution obtained by a wet process starts from phosphoric acid.

The phosphoric acid obtained by reacting phosphate rock with sulfuric acid by the wet process contains more or less large amounts of impurities depending upon the composition of Phosphorus "The most common and occur most impurities consist of Fe ₂ O ,, AIpO- * HgSiPg, HP, CaSO. and free H ₂ SO ..

Up to now it has been impossible to obtain ammonium phosphates from these contaminated phosphoric acid solutions, except by using complicated and expensive processes, all the more so, than the ammonia treatment of the solutions leads to the formation of a very fine and gelatinous precipitate, which both desired ammonium phosphate as well as some insoluble salts

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contains, which originate from the impurities, in particular basic bis and aluminum phosphates, calcium sulfate, ammonium fluoride and silica · · ** »» ·. This Hiedersohlag is extreme difficult to filter or centrifuge, which is why it is not possible to separate it from the mother liquor or to separate the ammonium phosphate from its impurities

A goal of this SHfindung is therefore a method for Production of diammonium phosphate of high purity, which is particularly suitable for the chemical industry and for the production of high quality fertilizers using impure solutions of Phosphoric acid runs out.

Another object of this invention is to produce diammonium phosphate in the form of a crystalline precipitate excellent grain size distribution.

Another aim of the invention is a method with which Help one with great ease and at low cost the diammonium phosphate formed from its mother liquor and can separate from its impurities " A final aim of the invention is the recovery of pure, crystalline diammonium phosphate in addition to a concentrated solution of diammonium phosphate and monoammonium phosphate, which is suitable for the production of fertilizers.

These and other objects are achieved with the method according to the present invention in which crystalline diammonium phosphate and a concentrated solution of Dianaaonium phosphate and monoammonium phosphate, which is suitable for crew guilding of fertilizers, from one to one Impure phosphoric acid solution obtained by wet process; this process is characterized by the following stages:

1.) The phosphoric acid solution is mixed with a water-soluble Treating compound of an alkali metal to precipitate the silicic acid in the form of an alkali fluosilicate;

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2.) The alkali fluorosilicate is used together with the, if necessary, in the Solid calcium phosphate contained in the solution separated from the solution by decanting;

3 ·) the solution is then treated with ammonia until a pH value between 6.9 and 7 »2 is reached, with a solid phase, which consists of dianonium phosphate and very fine insoluble salts derived from the impurities, and a concentrated solution of diamaonium phosphate and monoammonium phosphate is obtained}

4 ·) the diammonium phosphate is derived from its mother liquor and separated from the very fine salts originating from the impurities.

It has been found that, according to the invention, the precipitation of the Fluosilicic acid in the form of an alkali fluosilicate facilitates the separation of the greater part of this salt is made possible by simple decanting, and that the presence of this salt in the ammoniacalization phase, whether it is not during the decanting separated smaller part or occasionally a larger amount, in no case interferes with the crystallization of the diammonium phosphate and in particular does not interfere with the formation of colloidals Hydrated silica precipitates. It has also been found that if you are in the Ammoniakalisierungsphaee in a limited pH range between 6.9 and 7.2 works, the iron, aluminum and the other cationic impurities precipitate in the form of microcrystalline phosphates, which in no way interfere with the precipitation of the diammonium phosphate, which is in the form of a crystalline precipitate is obtained, which can be easily separated from its mother liquor and its impurities by simple centrifugation.

It has also been found that the solution, when working in this pH range, has a relatively low viscosity, whereby both the crystallization of the ^ ammonium phosphate and the impurities, as well as the subsequent separation

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dee ^ ammonium phosphate are very relieved from the mother liquor and from the impurities In addition, the solubility of diammonium phosphate is relatively low at a pH value between 6.9 and 7.2 , which is why at least half of the P? ^ 5 of ^the starting phosphoric acid is generally found in the form of crystalline diammonium phosphate without the need for external Apply heat to concentrate the solution.

The starting phosphoric acid, which is obtained by the conventional wet process by the action of sulfuric acid on phosphorite, generally has a PgOc content of about 27 up to 32 wt. Ji. Their HgSiFg content is generally between 2,3 and 3 »0 wt.

The precipitation of the fluosilicic acid can according to the invention by means of any soluble alkali metal compound, d. H. one Oxide, hydroxide, carbonate or sulfate are carried out · These compounds are preferably used in stoichiometric amounts used with reference to the fluosilicic acid or in a slightly larger amount. Generally a hydroxide is taken.

The solution is then left to stand to decant, wherein most of the alkali fluosilicate and almost all of it, Calcium sulphate still contained in the output acid is deposited "

The ABRo & lateli0i®r »ac is preferably made of gaseous ammonia by means of FJtäri _i . Oilers with liquid immonislr or aqueous kWmnLttkl'asm & ^ m. ,, Ms a pH value between 6.9 and 7.2 is reached »Below, ^s ''.: .- I ^ tingangen is the oil ratio of clay IHyIjPO ^; -; - Rtactionfemisch, ie dft «global molar ratio for the solid phase and the saturated X & sunc ®wii» e! I * n 1, B and 1.9.

The at ier Uaseisnaf swieehan the gaseous Immoniiir and phosphoric acid WKxse formed allows the evaporation of 55 to 65 f of the water contained in the AusganfesKure.

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Under these conditions, the amount of precipitated diammonium about 50 i "of P contained in the starting acid makes ₂ ⁰ C ^from" while the remaining, remaining in the solution PPOC to 80 i> in the form of Diammoniuaphosphat and 20 i> in the form of mono-ammonium phosphate is present.

The ammoniacization is carried out in an apparatus which is suitable for concentrating and crystallizing out solutions is, for example, in a saturator of the type used for the production of crystalline ammonium sulfate from sulfuric acid and Ammonia is used.

The ammonia alkalization is preferably carried out under vacuum and in. carried out in such a way that the temperature of the solution is between 65 ° and 75 ° C, under these conditions flows in Part of the HH, along with the water vapor from the reactor. It it is therefore necessary to bind the HEU by placing it in the Countercurrent with the acid fed in, e.g. B, in Venturi washers or wash towers react.

The diammonium phosphate crystals obtained at the end of the ammoniacalization have a size of about 65% and a size of more than 1 mm.

The cationic impurities are found in the form of basic iron and aluminum phosphates and calcium phosphates and sulfates. They emerge as microcrystals less than 0.1 mm in size.

These differences in grain size allow the diammonium phosphate easy to separate from its mother liquor and from the impurities. The separation is preferably carried out by means of centrifugation accomplished.

The weight ratio between the solid phase and the mother liquor at the end of the ammoniacalization is generally about 1.0. This ratio is particularly suitable for centrifugation. Because of the very small dimensions, the crystals of the impurities almost completely pass through the centrifuge. The centrifuged diammonium phosphate has a low water content, ie from 1.5 to 3.0 wt. ^. His ¹ ^ ⁰ S "salary, calculated on dry product, is $ 53.

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Comparable results are also obtained when using other methods to separate the phosphate from the mother liquor and the impurities, e.g. by piltrating and decanting, if such Procedures are carried out properly.

Because of its high purity, the diammonium phosphate obtained by the process according to the invention is very suitable for the production of highly concentrated fertilizers. Applied alone, after it has been dried in a conventional drying chamber, it is a two-component fertilizer with an average content of 20.8-53, ie the weight ratio of the two nutrients is: N / P ₂ O ₅ m 20.8 / 53.

By mixing the salt with other components and granulating and drying the mixture, one can produce highly concentrated binary and ternary fertilizers, especially those with a nutrient _{ratio of N / P 2} 0 ₅ A ₂ 0 >> 1.0, ie binary 26-26 and ternary Manufacture 18-18-18 fertilizers. These products, which previously could not be made based on phosphoric acid, the only P ₂ Oc SOURCE with which these products could be made at a reasonable price, are extremely valuable, because because of their purity they give high nutrient contents and because they are completely soluble in water. The 26-26 binary mixtures can be obtained by mixing the diamnonium phosphate produced by the process according to the invention with solutions of ammonium nitrate of any concentration or with molten ammonium nitrate.

The 18-18-18 ternary mixtures can be obtained by the Diammonium phosphate is mixed with solutions of ammonium nitrate of any concentration or molten ammonium nitrate and with potassium chloride.

A very advantageous feature of the invention is that the impurities contained in the centrifuged diammonium phosphate not enclosed in the crystal lattice, but rather deposited on the outer surface of the crystals. As the crystals of impurities, As already mentioned, are much smaller than the diammonium phosphate crystals, it is very easy to remove the centrifuged phosphate from the to separate remaining impurities by taking advantage of the different settling rates of the crystals.

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E.g. it is possible to put the phosphate coming from the centrifuge in Stir in the presence of a saturated solution of diammonium phosphate to separate the microcrystals of the impurities from the diammonium phosphate crystals, whereupon, either by fractional sedimentation or by centrifugation, the diammonium phosphate is separated from the solution containing the solutions Contains Buspened. This solution is then freed from the impurities by filtration and then added to the stirred phase of the phosphate coming from the centrifuge.

The diammonium phosphate purified in this way has a content of impurities which does not exceed 0.1% by weight. It puts a very inexpensive PgOc source, which is used for chemical-technical Purposes in all those areas of application that require a starting material of a purity that of after phosphoric acid produced by the thermal process.

The mother liquor separated from the diaemonium phosphate can on can be exploited in various ways for the production of fertilizers. According to a preferred embodiment of the invention, browns one does not resort to any method of separating the impurities from the mother liquor, as these impurities in no way hinder the further processing of the mother liquor,

These impurities are therefore found in the outside of the mother liquor obtained fertilizers again.

One of the most convenient ways to use the mother liquor is in using them to produce granulated diammonium phosphate.

For this purpose »the mother liquor is ammoniacized further until a NHy ^ HJPO ^ -MoI ratio between 1.9 and 2.0, i.e. a pH value between 6. θ and 8.0 is reached. AmmoniaJtalization is preferably carried out at a molar ratio of 1.9, i.e., a pH between 6.9 and 7.2 is reached. The disamoniuaphosphate produced on dl · ·· catfish contains one • Bestieetea Prestmtsfttz from Monoasmoniumphoephat. The ammoniacization takes place during the final granulation carried out.

The Qanulleren and the drying are carried out, for example, in Troissslgrtnulatoren and -Trookern. The granulated diassionium phosphate obtained in this way has a nitrogen titer between 17 and 18 and a P ₂ O ₅ titer between 46 and 43.

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Another very interesting field of application for the mother liquor of the crystalline diammonium phosphate is the production of ammonium sulfophate. For this purpose, the mother liquor is in a second plant suitable for saturation and crystallization processes is, together with ammonia, sulfuric acid and the mother liquors coming from the previous stage of the sulfophosphate division fed in.

The addition of sulfuric acid is calculated so that the heat of the Nftutrasiation by ammonia is sufficient to remove the in the circulated ammonium phosphate solution and, if necessary, in the other reactants, namely to evaporate the sulfuric acid itself and the ammonia contained water.

The ammonia alkalization is preferably carried out with gaseous ammonia until a pH value between 3.9 and 4.5, preferably between 3.9 and 4.1, is reached. The reaction is preferably carried out under vacuum and at temperatures of the solution between 60 ° and 80 ⁰ C.

The impurities present do not hinder crystallization in any way of the phosphate phosphate. On the contrary, it has been observed that they promote the crystallization of the latter because they act as crystallization nuclei.

After completion of the ammoniacalization, the sulfophosphate is from his The mother liquor is separated, preferably by centrifugation, and the mother liquor is returned. The one in a closed one Circulating amount of mother liquor is measured so that it corresponds to the most suitable solids / liquid ratio for centrifugation, namely corresponds to 1.0.

That part of the microcrystalline impurities that is not within the Sulphophosphate crystals have been entrapped, also in this case passes through the centrifuge, and the impurities therefore accumulate in the mother liquor at the beginning of a continuous process. After a certain number of repatriations the content of impurities in the mother liquor becomes constant, and

enema

the impurities in the process cycle can therefore be found quantitatively in the sulfophosphate produced. After centrifugation, the sulfophosphate can, if desired, be dried will.

The sulfophosphate produced in this way generally has a nitrogen titre of 15 and a P ₂ O of 26.

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The mother liquor of the crystalline mammonium phosphate can also be used with advantage as an intermediate product for the production of complex binary and ternary fertilizers. For this purpose it is combined with other compounds that are used in solid or liquid state or as a slurry. The mixture is granulated and dried, for example in drum or disk granulators. In this way binary and ternary products of various kinds are obtained. By adding NH ₄ NO, a 24-24 fertilizer is obtained, by adding CNH. ^ SO. a 20-20 fertilizer. By means of suitable mixtures with ammonium nitrate, potassium chloride or potassium sulphate and optionally inert substances, it is possible to put together formulations of the types 17-17-17, 16-16-16, 14-14-14, 13-13-13 etc.

Although it is generally not expedient to separate the impurities from the mother liquors, these can nonetheless be separated before processing the mother liquors. If the mother liquors are processed in a closed cycle, then it is preferred to use a periodic method of separating the contaminants by filtration, e.g. hit a rotary filter, or by decanting or removing part of the mother liquors. This is how you get products with a high titer.

From these explanations it is clear that all phases of the process can be carried out without external heat input, if one disregards the heat required to finally dry the crystalline diammonium phosphate and to dry the granular one Product from the mother liquors is required. The equipment required is also extremely simple and cheap, because it comprises practically only measuring devices for the reactants, a reactor for the addition of the alkaline compound, apart from a device for decanting, a device for ammoniacalization and crystallization and a centrifuge the equipment required for the recovery of the diammonium phosphate mother liquors. All phases of the process are suitable for continuous operation and can easily be automated.

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The following examples illustrate the invention. example 1

This example relates to a continuous process: 1.) An open circuit of diammonium phosphate with an NH -, / H ₃ PO ₄ molar ratio of about 2.0 with a titer of 20.7 $ of ammoniacal nitrogen and 53 # of P ₂ OcJ 2.) a closed cycle of ammonium sulfophosphate with a nitrogen titer of 15 and a P ₂ ° 5 ^of ^ * For reasons of convenience, all quantities are based on 1000 kg of phosphoric acid solution introduced into the circuit.
1000 kg Fhc-phosphoric acid solution, which contained the following:

H ₃ PO ₄ 405 kg

H ₂ SO ₄ 20 »

H ₂ SiP ₆ 19 "

gO-J-Fe ₂ O, and others metal oxides 20 ⁿ

HF 3 "

ASO ₄ 20 -

H ₂ P 513 ^M.

was treated continuously with constant stirring at tree temperature with 26 kg of an aqueous solution of 50% strength by weight RaOH. The whole thing was then decanted. The purified acid, which was roughly the following:

H ₃ PO ₄ 415 kg

H ₂ SO ₄ 20 «

HF 3 ^H

Na ₂ SiF ₆ 7 "

Al ₂ O ₃ , Fe ₂ O _{3 and} other metal oxides 20 "

H ₂ O 535 -

was continuously introduced into a first saturator. 139 kg of gaseous ammonia were then continuously fed into the saturator until an HHyIi ₃ PO ₄ molar ratio of 1.89 was achieved.

The temperature inside the saturator was 65 ° to 70 ⁰ C, the negative pressure about 600 mm of mercury. The pH was kept between 6.9 and 7 »2. The vapors coming from the saturator contained approximately 345 kg of H ₂ O.

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The slurry was then transferred to the centrifuge. The centrifuged Diammonium phosphate contained approximately:

(NH ₄ ) ^ iPO ₄ 282 kg

Metal phosphates 5 "

H ₂ O 4 "The mother liquor contained approximately:

) ₂ HP0 ₄ 195 kg

₄₄
NH ₄ H ₂ PO ₄ 48 »

₄ Y ₂ SO ₄ 27 "

Metal phoephates. 35 "

H ₂ O 255 "

with about 70 kg H «0 added for washing the two centrifuges had been.

This mother liquor was then about 800 kg in circulation; led mother liquor (Mr. 2), which came from the previous process stage, and then, together with 204 kg of concentrated sulfuric acid containing <196.5 kg of 100% H ₂ SO ₄ , introduced into a second saturator. 40.8 kg of gaseous ammonia were continuously fed into the saturator. The temperature was 65 ° to 70 ⁰ C, the negative pressure about 600 mm Hg, the pH is about 4.0. The vapors emerging from the saturator contained about 225 kg of water. The slurry was then transferred to the centrifuge. The centrifuged product contained approximately:

HH ₄ H ₂ PO ₄ 218 kg

(NH ₄ ) ₂ SO ₄ '285 "

Metal Phosphates 35 "

H ₂ O 30 ";

the mother liquor contained approximately:

NH ₄ H ₂ PO ₄ 230 kg

(NH ₄ J ₂ BO ₄ 200 »

Metaphosphates 64 "

H ₂ O 305 ·.

This mother liquor was fed back into a second ammonia alkalization phase, without ever having been freed from its defilements.

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Example 2

This example explains the use of the mother liquors obtained during centrifugation of the diammonium phosphate for the production of granular binary 24-24 products or ternary 17-17-17 products. The mother liquor from the centrifugation of the diammonium phosphate (Example 1) has the following composition:

(NH ₄ ) ₂ HPO ₄ 195 kg

KH ₄ H ₂ PO ₄ 48 »

(NH ₄ ) ₂ SO ₄ 27 "

Metal phosphates 35 "■

H ₂ O 220 "

with about 35 kg of water added to wash the centrifuge.

This mother liquor was ammonium nitrate solutions or molten Ammonium nitrate and ammonium sulfate solutions or crystalline ammonium sulfate added in the following proportions: Mother liquor 845 kg

NH ₄ NO, (10096) 400 "

(NH ₄ J ₂ SO ₄ (100 ^) 90 ".

The resulting slurry was granulated and dried using one of the methods known in fertilizer technology, a binary product with a titer of 24-24 being formed. Adding about 955 kg of a slurry having the same composition as that used to prepare the binary 24-24 product, about 285 kg of potassium chloride with a K ₂ O titer of 61.5 wt. #, Then a ternary product with a 17-17-17 titer is obtained.

By adding inert materials, such as limestone or calcium sulfate, or by appropriately modifying the recipe, it is possible to produce other types of binary or ternary products, such as 20-20-, 16-20-, 14-14-14-, 10-10 -10- and 13-13-20 fertilizers. Example 3

This example explains the use of the mother liquors obtained when centrifuging diammonium phosphate to obtain granular diammonium phosphate.

The mother liquors, which tie in Example 2 given composition had, been granulating and drying in drum granulators uo & dryers. During the granulation

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the ammonia was carried out until a pH - '. Vert between 6.9 and 7.2 was reached. Granular diammonium phosphate with a titer of 17-48 was obtained.

In all of the embodiments described above, the process according to the invention is always carried out without the external supply of heat in order to concentrate the solutions subjected to ammoniacalization. However, in order to find a larger amount of P ₂ ^ r - ^ ¹¹ £ ' ^{orm of} crystalline diammonium phosphate at the entrance of the circuit, it is also possible to add heat during the ammoniacalization phase. If you add heat during the formation phase of the sulfophosphate, you can use smaller amounts of HpSO. and in this way obtain a product with a higher P ^ Oc titer. A higher concentration of diammonium phosphate can also be obtained by pre-concentrating the phosphoric acid until an acid with a PgQc titer of, for example, 36 to 40 Qevi.% Is obtained.

The mother liquors resulting from the production of the diammonium phosphate can also be partially or completely returned to the production phase of the diammonium phosphate. In this particular case it is necessary to add some heat during the ammoniaizing phase or to pre-concentrate the acid. In the case of total circulation, it is also necessary to periodically clean the mother liquor by drawing it off or filtering or decanting it, in order to prevent the diammonium phosphate from being contaminated by the impurities.

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Claims (11)

Claims 1. Process for the production of crystalline diammonium phosphate and a concentrated solution of diammonium phosphate and honoammonium phosphate, which are suitable for the production of fertilizers, wherein an impure phosphoric acid solution obtained by the Haß process is used as the starting point, characterized in that the phosphoric acid solution is treated with a soluble compound of an alkali metal detail in such a way that the silicic acid precipitates in an alkali fluorosilicate, and the alkali fluorosilicate is removed from the solution together with any solid calcium sulfate present Separate decanting, whereupon the solution is treated with ammonia until A pH value between 6.9 and 7.2 is reached, whereby one is fixed Phase consisting of diammonium phosphate and very fine insoluble, of the impurities derived salts, and a concentrated solution of diammonium and MonosjoMsdueqfeoephat, and that the diammonium phosphate from the solution and the very fine, separating salts originating from the impurities. 2. Process according to claim 1, characterized in that the diaemonium phosphate is separated from the solution and the impurities by centrifugation. 3. The method according to claim 1 or 2, characterized in that old soluble alkali metal compound a hydroxide is used. 4. The method of claim 1,2 or 3, characterized in that the Ammonikalisierung under vacuum at "performs a temperature between 60 ° and 8O ⁰ C. 5. A process for the preparation of fertilizers using the process according to claims 1 to 4, characterized in that the concentrated solution of diammonium phate and monoammonium phate is further ammoniacalized until a pH of 6.9 to 7 _t 2 is reached, and then granulated and dried, whereby granular diammonium phosphate with a titer of H between 17 and 18 and of P ₀ Oc- between 46 and 43 is obtained. 109834/1306 ; £ - ■■■ · " 6. A process for the preparation of fertilizers using the process according to claim 1 to 4, characterized in that the concentrated solution of diammonium phosphate and monoammonium phosphate in the presence of a mother liquor derived from a previous process stage with HpSO ₁ , and NH- treated until one pH between 3.9 and 4.5 is reached, ammonium sulfophosphate being obtained as a precipitate, which is separated from the mother liquor by centrifugation, and that the mother liquor is circulated, using a binary fertilizer with a titer of H and P ₂ ^{receives 0} K from J 5-26. 7. The method according to ANapruch 1 to 4, characterized in that one the concentrated solution of diammonium phosphate as an intermediate in the manufacture of complex binary and ternary fertilizers used. . ·, .- 8. Binary and ternary fertilizers of type 20-53, 26-26 or 18-18-18, which contain crystalline diammonium phosphate obtained by the process of claims 1 to 4. 9. Concentrated solutions of dianmonium and honoammonium phosphate, obtained by the method of claims 1-4. 10. Crystalline Diaieoniumphosphat, which according to the method of claims 1 to 4 has been obtained. 11. Binary and ternary fertilizers obtained according to the method of claims 5 to 7 have been made. Pure SIKCAT Societä Industriale Catanese S.p.A. Palermo, Italy 4 * 1 * W BATH ORIGINAL