DE1902736A1 - Magnesium ammonium phosphate - Google Patents

Abstract

Magnesium ammonium phosphate (MAP)is produced from hydrated magnesium sulphate, phosphoric acid or a conc. soln. of a very soluble salt of phosphoric acid and, if necessary, ammonia. The exit materials or their solns. are reacted at 0-60 degrees C pref. 25-30 degrees C with a satd. soln. of ammonium sulphate (AS). This soln. is heated enough, pref. 55-65 degrees C, for AS developing with the reaction, to be able to be removed from the heated soln, and for the exit material or solns. of them, to be inserted, only with such a water content that exceeds the bonding power of the MAP. The heat content of the warmed soln. increases with the heat of reaction of the final loss of evaporation sufficiently to allow the initial cold of the AS satd. mother liquor to be reachieved by water withdrawal. Either an excess of this mother liquor results which is useful for other purposes or AS results as a solid by cooling down as described, or both can occur. The MAP hydrate is led away from the AS soln. which is then cooled in a evaporation loss apparatus by water evaporation. The low water product is granulated by addition of water at a suitable temp.

Description

Process for the production of magnesium ammonium phosphate Magnesiumate Ionium phosphate, a compound that is used as a precipitation form of both magnesium and Phosphate ion has also been known for a long time from analytical chemistry also a particularly valuable fertilizer. Already before fifty Years ago it was found that magnesium phosphates are much more beneficial to grain as soluble calcium phosphates0 Among these is magnesium ammonium phosphate Particularly noteworthy because it contains both phosphoric acid and ammonium nitrogen in a form that is difficult to dissolve, that even very heavy downpours contain that Do not wash fertilizers out of light soils prematurely, and secondary heat build-up, which convert the phosphate ions into an unusable form is slowed down sufficiently will; but the phosphate ions remain the dissolving precipitates of the Plant roots and ammonium ions are easily absorbed by the nitrifying soil organisms accessible.

Due to the favorable properties of the fertilizer described, the technical production of magnesium ammonium phosphate was dealt with early on engaged. In the German patent specification 565 963 a method is already described, in which from magnesium sulfate magnesium ammonium phosphate and a solution of ammonium sulfate, which is converted secondary to potassium sulfate and ammonium chloride can be obtained. Other working methods are based on magnesium chloride or magnesium oxide (cf. U.S. Patents 1,881,195 and 1,913,539 and English Patent 379 433). In more recent times the American made an effort Company Grace about the production, as can be seen from C & En 39 (1961) 37, 83/84. About the Procedure has not yet been released. It is also in Germany worked to improve the production of magnesium ammonium phosphate (German Interpretation document 1 260 450). It has been suggested to keep the pH between Hold 5 and 8 for coarser grain. However, this thought is not new, as from the presentations in Gmelin, system no. 27 (B) S 487.

Up until now, the processing of the mother liquors was too time-consuming, the magnesium ammonium phosphate in serious competition with the usual products bring to. The invention now makes it possible to no longer directly utilize the work-up Avoid mother liquors.

According to the invention in the process for the production of magnesium ammonium phosphate from NgSO4 in the form of one of its hydrates, phosphoric acid (or phosphate) and ammonia a concentrated ammonium sulfate solution circulated. It serves as a solution or as a suspension medium for the starting materials and the end products.

The concentration of the ammonium sulfate solution at the entrance to the reactor results from the fact that at a temperature the one between Oo and 600C should be saturated. The choice of this temperature is appropriate according to the lowest temperature occurring in the process cycle. The "cold" saturated Ammonium sulfate solution is heated indirectly before entering the reactor or atch in the reactor by indirect heating and / or the heat of reaction is heated, so that they can dissolve the new ammonium sulfate that forms during the reaction a separation of the precipitated magnesium ammonium phosphate from the ammonium sulfate even when using raw materials that are low in water. After the separation of the Magnesium ammonium phosphate is the solution, e.g. by flash evaporation, cooled, whereby the ammonium sulfate formed are recovered in solid form can The mother liquor goes back to the beginning of the process But the invention writes not mandatory that the conversion of magnesium sulfate with phosphate ions and Ammonia-formed ammonium sulphate must be obtained in solid form. It becomes possible a stationary cycle only required that at the end of the cooling process a solution of the same concentration is created as entered at the reactor inlet the saturation limit should be reached at the lower temperature. The educated Ammonium sulfate is involved in this mode of operation Excess of this solution, which is withdrawn as such from the circuit The type of process control enables the use of raw materials with a higher water content0 The method according to the invention allows a better one in both cases presented Use of the heat of reaction as the previously common techniques.

The process according to the invention is illustrated by means of examples.

Example 1 Stoichiometric amounts of solid bitter salt, anhydrous Phosphoric acid and ammonia are slowly turning into such an amount of cold saturated neutral Ammonium sulfate solution, but which depends on the lower saturation temperature, e.g.

300C, is heated to almost 600C, according to the mangabe that takes place Sales gradually fed in that the heated ammonium sulfate solution formed Dissolves ammonium sulfate. Free ammonia should be in the reaction mixture leaving the reactor no longer exist.

After the precipitated Nagn.siumammoniumphosphat is separated Ammonium sulphate solution, e.g. by flash evaporation, cooled down, a large part of the evaporated water being returned to the solution to be cooled can be after it has previously been used, for example, to wash the magnesium ammonium phosphate was used. The ammonium sulfate formed falls quantitatively in solid form at.

If the procedure is correct, the cooled ammonium sulfate solution is obtained in such a concentration and amount as they correspond to the entrance to the reactor.

The reaction equation is: The water of crystallization in the magnesium ammonium phosphate drops to 4 moles of H2O when it approaches 600C in the highly concentrated ammonium sulfate solution. Above 60QC, it can drop to an average of 3 moles of effective H2O content to 1 mole of H2O content. The heat of reaction is 81 to 87 Kcal per formula conversion, depending on the water content of the end product.

If the average specific heat of the ammonium sulfate solution is taken 0.65 Kcal / kg0grd and the formula conversion is carried out in 2 530 g of this saturated Ammonium sulphate solution, which would have to be heated from 30 ° to 60 ° C, are then required 49.3 Kcal required This amount of heat is available when the ammonium sulphate solution is cooled after the magnesium ammonium phosphate has been separated off by flash evaporation available again for dehydration. That is already more than the removal of the t or 3 moles of H20 released in the reaction is required. The excess evaporated amount of water leads to the maintenance of the water balance before separation of the solid ammonium sulfate back into the cooled solution. When the solution cools if the balance is adhered to, as much solid ammonium sulphate precipitates out as passes through the reaction formed.

The heat of reaction exceeding the specified heat requirement cannot be recycled directly when using highly concentrated raw materials0 It is to be dissipated by cooling. This can include be effected by how in example 2 a larger amount of the saturated ammonium sulfate solution to the Absorbing excess heat and releasing it during relaxation cooling is circulated.

Example 2 The heat of reaction can be better used1 if not the expensive concentrated phosphoric acid is used, but one of only 52 to 53 OX; H H3P04 (approx. 38% P 0) 25 In this case there is a maximum of 8 moles of H20 to evaporate, which can easily be achieved with the amount of heat available is. In this case, however, the amount of ammonium sulfate solution is at least twice as large to recirculate as indicated in Example 1, thereby reducing the saturation limit for ammonium sulfate is not reached at the higher temperature, but nevertheless at the end of the flash evaporation the same amount of solid ammonium sulfate as in Example 1 and one in the Cooling temperature saturated ammonium sulfate solution results. Here show up the advantages of the new process compared to older working methods are very clear. By circulating the cold saturated ammonium sulfate solution on the one hand control the setting of the temperature levels very easily, and on the other hand will the heat of reaction also made usable, one of the raw materials without interference to be able to use the water balance in the cycle process in diluted form. This is especially with regard to phosphoric acid after the wet digestion process from Interest that is costly to concentrate.

Example 3 If only a very thin phosphoric acid is available, then it may be better to first convert this into one of the ammonium salts, before the concentration starts because of the corrosive effect of these salt solutions is less than that of the free acid. That is why it is of interest also the possible uses to examine the ammonium phosphate in the proposed method.

The reaction equations are: The heat of reaction is between 17 and 57 Kcal / formula. The first of the reactions mentioned here (57 Kcal) is particularly suitable for planning in the process. Both starting salts are used in solid form in a stoichiometric ratio. Despite the lower heat of reaction, the water balance does not cause any difficulties. However, if you wanted to use the triammonium phosphate, then you would have to feed additional heat into the circuit. This could be done, for example, by heating the cold, saturated ammonium sulfate solution in a heat exchanger before the solution is added to the reactor. However, it is also possible to supply heat via heating bundles in the reactor. Part of the heat converted in the flash evaporator can be recovered by preheating the cold, saturated mother liquor.

Example 4 Instead of Epsom salt, kieserite (MgSO4. H2o) can be used in a finely ground state.

However, the time required for full sales is extended Residence time of the mixture in the reactor. On the other hand, the possibility of Solutions with an even lower P205 content as listed in Example 2 than phosphate dispenser to be used

A particularly advantageous way of working on the basis of kieserite is provided represents the following variation of the inventive concept: 138.4 g of kieserite are 115.0 g NH4H2P04 in aqueous solution and 34.1 g ammonia gas in the cold but saturated Ammonium sulfate solution heated to approx. 600C to give 209.4 g of magnesium ammonium phosphate four-hydrate and 132.2 g of ammonium sulfate reacted. Here, approx. 69 Kcal of usable heat of reaction are generated free. This allows about 7 moles of water to be evaporated.

The Ammoniumdihydrogenpho sphat results for example from a Reaction to be explained later as a solution containing 48 g of salt in 100 g of water. When this solution is introduced into the reactor, then 115.0 g of ammonium dihydrogen phosphate are brought 13.4 moles of water with. Another mole of water comes from the kieserite. So it should i4.4 - 4 = 10.4 moles of water are evaporated to remove the ammonium sulfate that is formed to be obtained quantitatively in solid form. But there are only 69 Kcal available. The rest must be applied by partial heat recovery and additional heating will.

You can avoid the additional heat input if you don't use the Separation of solid ammonium sulphate is aimed at, but only the recovery of the cold saturated ammonium sulfate solution, in which case an excess of this solution results at the end of a cycle, which can be removed from the cycle can.

It has been shown that the resulting ammonium sulfate solution can advantageously be used for extracting superphosphate. The following reaction takes place between the calcium dihydrogen phosphate in the superphosphate and the ammonium sulfate: In this way, an ammonium dihydrogen phosphate solution of the above-mentioned concentration is obtained with an outlay on apparatus which is hardly greater than in the case of wet digestion for the production of phosphoric acid. At 6 to 8 washing stages, the P 205 losses are only slightly above the values known from the phosphorous acid process. On the other hand, you save up to a third of the amount of free sulfuric acid that is normally required per mole of H3PO4 (here in the form of the monoammonium salt). This fact is essential given today's sulfuric acid shortage.

To produce 115.0 g of ammonium dihydrogen phosphate from the primary Calcium phosphate of the superphosphate theoretically needs 66 g of ammonium sulfate0 If this is supplied in the form of the ammonium sulfate solution saturated at 300C, then is withdrawn from the mother liquor cycle of the magnesium ammonium phosphate process half a mole of ammonium sulfate also includes just under 4.2 moles of water. With the kieserite and the ammonium dihydrogen phosphate solution, in contrast, 14.4 moles of water are in entered the circuit and 4 moles of the four hydrate of magnesium ammonium phosphate carried out. Accordingly, there are now only 10.4 - 4.2 = 6.2 moles of water to evaporate, for which the heat of reaction is sufficient. It can then contain half a mole of (NH4) 2SO4 in Solution form that was required for the ammonium dihydrogen phosphate solution, one more half a mole of ammonium sulfate can be obtained in solid form. In principle you can too use this product to produce excess ammonium phosphate. Otherwise the ammonium sulphate is used, for example, in the production of mixed fertilizers.

In the following, the method according to the invention is to be used again The flow diagram will be explained around the technical options the implementation 0 The scheme can be used in all of the process variants presented so far adapt in a simple manner, the scheme allows a characteristic feature of the process, recognize the cycle of the mother liquor ML. In the reactor R are the starting materials or their solutions fed in.

It should be divided into individual agitator departments so that the Residence time is unified to avoid leakage of unreacted material to avoid (cascade). This is important when using the slowly reacting kieserite to attach particular importance. The temperature in the reactor R is, for example, 6o0c set0 A suspension of magnesium ammonium phosphate emerges from R in the reaction solution RL off, from which the magnesium ammonium phosphate in salt separator S1 is avoided a cooling is separated. The kare reaction solution RL is now used for the flash evaporation, for example consisting of the evaporators V1 and V2, supplied where they are below Dehydration is cooled. The evaporated water can depending on the water supply either withdrawn or through the raw materials in the reactor R after the condensation to be added again to the solution to be cooled. The for the Vacuum cooling required negative pressure can for example - by steam jet be generated. While the condenser K2 is always charged with cooling water, the condenser Ki can also be used for preheating purposes if the heat balance so requires.

As a result of the cooling in the flash evaporation system, the becomes cold saturated mother liquor ML recovered using either solid ammonium sulfate or an excess of this mother liquor can be obtained. The by-product or the excess Lye is removed from the circuit at a suitable point, e.g. at the salt separator S2.

The mother liquor ML can if necessary in the condenser K 1 and / or in Heat exchanger W before being returned to the reactor R by means of vapors or superheated steam be preheated.

The reaction heat is due to the choice of the starting materials and their Application forms specified. The heat balance can then be determined by the amount of u-rolled Mother liquor and / or connection or omission of the preheater K1 and balancers will. The heat is dissipated through K1 and, under certain circumstances, also through K2 guided cooling water.

If the addition of ammonia to the mixture in the reactor is over stoichiometric, for ammonia recovery from the vapors.

Choice of temperatures in the circuit In the examples, the Reactor specified an operating temperature close to or exactly 60 ° C, and the (NH4) 2S04 solution should be saturated at 300C. These are preferably suggested temperature settings. One can see the saturation temperature of the mother liquor but set it to a different value.

The same applies to the temperature in the reactor. This will only be thereby imposed restrictions that, for example, at temperatures above 600C form magnesium ammonium phosphates that are very low in water, which may lead to an easier release of ammonia tend. In contrast, lowering the mother liquor temperature below 300C requires a disproportionately large effort.

Conditioning of the magnesium ammonium phosphate in the vicinity of 60 ° C the magnesium ammonium phosphate falls from the concentrated ammonium sulfate solution with an average of 4 moles of crystal water. It's rough enough to be good though to be separable from the solution, but too fine for practical use.

As the low-water magnesium ammonium phosphate when treated with water Immediately accumulates up to 6 moles of H20, can be achieved by spraying with water on a granulating plate a stable granulate can be produced.

Claims (8)

Claims i. Process for the production of magnesium ammonium phosphate from magnesium sulfate hydrates, Phosphoric acid or concentrated solutions of readily soluble salts of phosphoric acid and optionally ammonia, characterized in that the starting materials or their solutions in one at a temperature between 0 ° and 60 °, preferably 25 ° to 30 ° C, solution saturated with ammonium sulfate, this solution heated to such an extent, preferably to 550 to 650C, that the reaction occurs the resulting ammonium sulfate can be absorbed by the heated solution - and, that the starting materials or their solutions only with such a water content that goes beyond the binding capacity of magnesium ammonium phosphate for water that the heat content of the heated solution, increased by the heat of reaction in the subsequent flash evaporation, which was originally cold is sufficient Mother liquor saturated with ammonium sulphate is formed again by the removal of water leave, with either an excess of this mother liquor results, that for others Purposes can be used, or in the preferred process, ammonium sulfate is obtained in solid form as a result of cooling, or both. 2. The method according to claim i, characterized in that the formed Magnesium ammonium phosphate hydrate at the elevated temperature from ammonium sulfate solution is separated, which then by water evaporation in a flash evaporator device is cooled. 3. The method according to any one of claims 1 and 2, characterized in that that solid ammonium sulfate is obtained during cooling. 4. The method according to any one of claims 1 to 3, characterized in that that the ammonium sulfate resulting from a formula conversion in solution form the process is withdrawn in such an amount that the ammonium sulfate on conversion with Ca (H2P04) 2 in sulfuric acid-treated rock phosphates ammonium dihydrogen phosphate at least in the amount necessary for the magnesium ammonium phosphate to be formed with a formula conversion Amount supplies which from the resulting plaster of paris in such a way according to techniques known per se It is left out that an ammonium dihydrogen phosphate solution in a concentration which arises when it is returned to the beginning dz s of the magnesium ammonium phosphate process does not disturb the water balance. 5o method according to claims 1 and 2, characterized in that that. the low hydrated one formed by choosing a high working temperature Magnesium ammonium phosphate is washed with water at such a high temperature that no Progression of hydration occurs, 6. The method according to any one of claims 1, 2 and ej, characterized in that the low-water magnesium ammonium phosphate in a granulator by adding water at ordinary temperature will. 7. The method according to any one of claims 1 to 6, characterized in that that the magnesium sulfate hydrate used as the starting substance as a solid salt in the reactor is entered. 8. The method according to any one of claims 1 to 7, characterized in that that the magnesium sulfate is used in the form of finely ground kieserite.