FI72057C - Process for homogeneous, thermal and / or chemical treatment of flowing materials and application thereof to the preparation of acidic polyphosphates to sodium. - Google Patents

Description

1 72057

Method for homogeneous, thermal and / or chemical treatment of a fluid and its application to the production of sodium acid polyphosphates

The present invention relates to a process for treating a dispersible, flowable phase, such as in particular a liquid, semi-liquid or powder, with a thermally and / or chemically dispersing gas phase.

It is particularly directed to treatment methods which start from a liquid medium and which result in at least one clearly defined product and which offer the possibility of side and side reactions and / or the formation of at least probable intermediates.

These sensitive types of problems are illustrated in particular by the cases of the preparation of alkaline polyphosphates such as Na and K tripolyphosphates.

Theoretically, sodium tripolyphosphate can be obtained according to the following formula:

Nal ^ PO ^ + 2Na2HPO ^ heat treatment ^ Na ^ P ^ O ^ + 21 ^ 0 solution solution but the reality is much more complicated. Namely, neutral pyrophosphate and more or less long-chain polyphosphates are formed, which manifests itself in particular in the formation of insoluble substances. It is easy to understand that the reaction system is difficult to control, which explains the existence of an extensive and ancient literature on this subject. Schematically, it can be said that recourse is made to either two-step methods or one-step methods.

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Thus, U.S. Patent No. 2,419,148 proposes tripolyphosphates of the formula (Na 2 P 2 O 2) x wherein x is at least equal to 2 and is more soluble in water. U.S. Pat. No. 2,419,147 also proposes the formation of an aqueous solution of a substance containing 5-6 moles of Na 2 O per 3 moles of decomposition of a P2 ° 5 'solution, and the abrupt drying of the resulting fine solution and then heating of the solid salt thus obtained to 250-600 ° C: C.

In fact, the solution is sprayed into an environment hot enough to cause sudden drying. However, this is a rather complex and difficult-to-manage method.

DE-PS 649 757 also describes a process for the preparation of meta-polyphosphate starting from ortho-phosphates, by treatment in a very hot gas or flame and then by cooling.

According to U.S. Pat. No. 3,385,661, a stage II tripolyphosphate is prepared by spraying an aqueous solution of orthophosphate with a Na 2 O / P 2 O 2 ratio = 5/3 in a spray tower maintained at a temperature between 180 and 280 ° C to give an intermediate consisting mainly of pyrophosphate and calcium then picking up this intermediate in a rotary kiln maintained at a temperature between 150-450 ° C to convert it to a stage II tripolyphosphate.

By changing the conditions, a stage I tripolyphosphate can be obtained, as in U.S. Patent No. 3,387,929.

More generally, U.S. Patent No. 3,338,671 discloses a process for granulating sodium tripolyphosphate comprising spraying an orthophosphate solution and subsequently calcining. This patent even specifies that tripolyphosphate can be obtained directly by spraying if the sprayer is constructed in a proper manner, without, however, explaining this proper manner.

Il 3 7205 7

Unfortunately, the whole problem is there.

It has also been proposed in German Patent 1,097,421 that an orthophosphate solution be sprayed inside a special tower, passing it through a ring of flame, to remove water from private little droplets.

The disadvantage of this method is that the droplets, as they pass through the flame zone, are exposed to various high temperatures. Therefore, various solutions have been proposed to remedy this, such as varying the partial pressure of water vapor, see German Patent 1 007 748. Unfortunately, as made clear in French Patent 1 535 819, these solutions are not satisfactory except in very special cases.

As a result, various improvements have had to be proposed, for example for the flame zone itself, as in U.S. Pat. No. 3,499,476. However, it should be noted that the prior art consists of a large number of attempts to solve this problem, either in process chemistry or technology, both.

In fact, it has been found that when the solution does not correspond to the formation of a single, specific compound by drying, (crystalline) separation occurs during the evaporation step. The composition of the gradually forming solid is different from that of the solution and it develops during drying. This state corresponds to thermodynamic equilibrium systems and can be modified by the kinetics of the phenomena used during the thermal process.

In general, it is known that during physico-chemical work steps, transfers of matter and heat take place and that the kinetics of these transfers are mostly limited by diffusion through the liquid-gas interface.

This is evident from the fact that whatever physical and / or chemical means have been used so far, it has not been possible to implement certain developments.

These observations are fully illustrated by the results obtained, for example, in an attempt to synthesize sodium tripolyphosphate from a solution of sodium orthophosphates with a total Na / P ratio of 1.667. The crystallization of this solution corresponds to a mixture of orthophosphates with different Na / P ratios (orthophosphates, mono- and disodium phosphates) and which can develop in an isolated manner.

This explains the failures observed in the use of prior art methods for the preparation of said tripolyphosphate.

In addition, it is known that there is a patented process in which a liquid or semi-liquid phase, which may optionally contain suspended solids, is treated with the dispersion, according to French Patent 2,257,326. It comprises a method of contacting substances in different phases, forming a symmetrical gap-vortex flow by introducing a gas phase, and introducing at least one other non-gas phase along the symmetry center line of said flow rotation substantially into the vacuum zone of said shaft vortex flow. This shaft vortex flow is given such a large magnitude of motion as compared with the motion of the axially fed phase that dispersion of the latter phase occurs due to the displacement of the motion variable. In this way, volume pairs are formed from the gas phase and the axial phase, for the paths starting from the gas phase, regardless of the previous history of this gas phase.

In practice, the ratio of the motion variables is at least 100, preferably 1000-10,000, and the feed rate of the axial phase is small, preferably less than 10 m / sec. The pressure in the gas phase is also low, less than 10 Pa, and preferably 0.4-0.6 10 Pa higher than the pressure of the mixture.

In particular, this method allows the use of a large temperature difference between the treatment phase (gas) and the liquid phase to be treated (solution or suspension). It further has the advantage that it comprises a piston-type zone in terms of concentrations and a sudden drying type in terms of temperatures.

The present invention relates to a process for the thermal and / or chemical treatment of at least one dispersible fluid under conditions which allow very rapid, in particular thermal transition kinetics, between the dispersant or dispersants and the at least one dispersant.

This method constitutes a new and unexpected means of material handling.

It is a process for the thermal and / or chemical treatment of a dispersible, flowable phase, such as in particular a liquid, semi-liquid or powdered phase, with a dispersing gas phase, characterized in that under the action of the gas phase, successively and without discontinuity: a) the dispersible phase is as a dispersion of liquid particles substantially evenly distributed in said gas phase in such a way as to obtain a systematically homogeneous mixture of the two dispersible and dispersing phases, b) this dispersion is subjected to a flash-drying process in the flow is homogeneous with respect to the distribution of residence times, subjected to a treatment that is simultaneously substantially both isothermal and chemically homogeneous.

The duration of the first stage must be such that the mixing takes place from the beginning of the heat treatment.

By sudden drying treatment (in zone b) is meant a treatment of short duration, preferably less than one second, under the influence of a large temperature difference which may be several hundred degrees between the dispersing and dispersible phases and corresponding to a strong heat transfer between the dispersing and dispersing phases.

More specifically, according to the invention, the dispersing gas phase performs three functions: 1. to form a dispersion, 2. to carry out the first flash-drying treatment in a substantially piston-type zone, and 3. to carry out the second treatment under conditions which are kinetically and thermodynamically different from the above-mentioned zone.

This results in a very cohesive chain of unit work steps, which can be extremely short and the number of which is not limited to the list above.

Figures 1 and 2 below schematically show a model of the qualitative behavior of such a system. The abscissae in Figures 1, 2 and 3 must be considered independent of each other.

Figure 1 shows, in the case of a three-stage model, a hydrodynamic diagram of the phases, in which G represents the gas and F the dispersed fluid, and not on the time scale (s)

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7 72057 has no meaning other than to indicate the direction of the passage of time.

Figure 2 shows the temperature difference between the phases (T = TG - TF) at different stages. Schematically, it can be considered that in the second step (b) the temperature difference between the phases is very large for a very short time, while in the third step (zone c) the situation is completely different.

Thus, this is a novel reactor that allows developments of the type shown in Figure 3, corresponding to the special case that liquid L leads to solid S. This diagram illustrates that steps b and c can be influenced in a simple manner to control or stabilize these developments. This method is characterized in particular by the fact that its thermodynamic and chemical development in zone c is determined by the development of (TG -TF) in zones a and b.

In this way, in the case where the dispersed fluid is a liquid, zone c may correspond to a thermodynamic region which functions as a solid / gas reactor, or as a gas / gas reactor when one liquid and one gas are initially fed to it.

In practice, according to the method of the invention, the temperature and / or the chemical composition of zone c is determined by the temperature variations of the dispersing phase in zone b in such a way that the heat exchange takes place in zone b.

The temperature in zone c corresponds to the temperature required for the kinetics of the change to be achieved from the small difference between the temperature of the dispersing gas phase and the temperature of the dispersible phase. In contrast, the inlet temperature to zone b is determined taking into account that the heat exchange between the two initial phases takes place in practice in zone b.

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Thus, everything happens as if the method according to the invention would allow the selective utilization of the energy obtained from the dispersing phase.

In fact, it is more specifically affected in zone a by the utilization of kinetic energy for the formation of the mixture, and in zone b by the utilization of thermal energy for the physicochemical change of the dispersed phase.

If the dispersible phase is a solution, the thermal energy acts especially on the particle during evaporation (i.e. as a strong endothermic change), which constitutes a new and unexpected means of material treatment.

In addition, the resulting solid or liquid particle is protected during and after its formation because it develops and, if necessary, chemically and / or physically changes in a substantially isothermal environment. Finally, it develops in a chemically homogeneous gas phase, the composition (e.g. its water partial pressure) and temperature can be explicitly set (zone c).

It can therefore be acknowledged that adverse changes to the target product cannot occur (in the chosen 3-step model) insofar as the thermodynamic conditions of the system, which are fixed from the piston zone b, do not allow them to occur.

In addition, it should be emphasized that successive flow conditions stabilized by the dispersing phase are particularly suitable for continuous treatment of the substance in cases such as: - drying followed by calcination, - drying (endothermic) followed by (exothermic) combustion, 72057 drying followed by thermal condensation, etc. ...

In fact, the initial even distribution in zone a may involve a slight dispersion of the various parameters on either side of its mean. This then manifests itself as a distribution of the thermodynamic conditions (temperature, chemical properties of the dispersing phase ...) applied to the particle as it enters zone c.

Based on this, one would expect that this distribution would cause differences in treatments from one particle to another. Instead, it is observed that zone c causes re-homogenization of the processing conditions.

According to a particular embodiment of the invention, an endothermic change is performed in zone b, followed by another endothermic or exothermic change in zone c.

After zone c, another, for example thermal treatment * can also be carried out, for example with the gas phase (zone d).

As previously stated, one method which is well suited for carrying out dispersion at the inlet of the piston flow zone is described in French Patent 2,257,326.

According to an embodiment of the invention, a symmetrical shaft vortex flow is obtained by supplying a gas phase, and at least one other phase, up to the center line of rotation of said flow, substantially up to the vacuum zone of the shaft vortex flow. Said shaft vortex flow is given a motion magnitude so large as that of the axially fed phase that the dissipation of this phase occurs due to the displacement of the motion variable and its treatment in the gas phase takes place in the downstream piston zone of a substantially isothermal and chemically homogeneous zone.

Thus, according to the invention, the dispersing gas phase is used successively to form a mixture and to provide two reactors connected in series with different characteristics, which is a particularly difficult problem when it is desired to operate continuously and on an industrial scale.

According to the invention, it is instead solved in a simple manner by influencing the hydrodynamics of the dispersing phase and its initial temperature.

In practice, for economic reasons, the dispersed phase is given a low initial velocity, preferably less than 10 m / s and if possible less than 5 m / s, so that the initial motion of the dispersing phase can be reduced. The ratio of the gas phase to the displacement of the dispersed phase must, in order to be sufficient, usually be at least 100, but generally preferably between 1000 and 10,000.

The gas phase is also subjected to low pressures which are c 5 less than 10J Pa and substantially 0.5 to 0.6 Pa n greater than the average pressure in zone c. However, the scope of the invention is not deviated from if this pressure is increased, in so far as the ratio of the motions is taken into account.

It is simply clear that the economically best conditions that meet the technical requirements must be chosen.

An equally preferred method and apparatus is described in French Patent 2,431,321.

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One illustrative embodiment of the invention is the preparation of sodium triphosphate from orthophosphate solutions of different Na / P ratios.

As for the nutrient industry (melting salts, saline cuts) or for some industrial applications such as detergents, sodium tripolyphosphate is generally used as a solution; the presence of insoluble substances can then be disturbing.

The latter are fed either upstream of the tripolyphosphate (from its starting materials) production stage, or during the thermal condensation of the ortho-phosphates.

Prior to calcination, these are mainly traces of metal phosphates present in phosphoric acid, which precipitate only incompletely in the neutralization of H 2 PO 4 with NaOH. In general, the relative amount of these insoluble substances is very small.

In contrast, after calcination of orthophosphates, the presence of insoluble (NaPO 3) n is often observed in significant amounts, which vary according to thermal condensation conditions. This insoluble matter results exclusively from the complete calcination of orthophosphates with a Na / P ratio of 1 according to the following reaction:

NaH2PO4 — MJa2H2P207— «anH2Pn03; rrT-» (NaPO3) n

Any mechanism of tripolyphosphate formation in which there is a lack of homogeneity (in the region of ortho or pyrophosphates) results in the presence of phosphate impurities (of which insoluble (NaPO 3) n) is present.

This is true even if the Na / P ratio as a whole is well regulated on a macroscopic scale.

12 72057 This must be considered on a microscopic scale in the following cases: 1) Na / P ratio = 5/3 2) Na / P ratio / 5/3 3. °) Na / P = 5/3

If the mixture is homogeneous, a tripolyphosphate free of impurities is obtained according to the following currently accepted mechanism: 2 NaH2PO4 - ^ Na2H2P207 + H2O 2 Na5P3 ° 10 + 4H2 °

4 Na2HPO4 -> 2Na4P2Oy + 2 H2CK

2 NaH2PO4 + 4Na2HPO4 - ^ 2 Na5P3 ° 10 + 4H2O

Another possible mechanism (passage through pyrotrin sodium phosphate) leads to the same result: + 4H 2 O 2 °) Na / P

If the mixture is not homogeneous, this means that either a smaller or a larger relative to the total Na / P ratio has to be found locally.

2.1. When the Na / P ratio is greater than 5/3, the presence of either insoluble substances according to the first mechanism or short polyphosphates according to the second mechanism is detected.

The first mechanism: 2 £ represents the amount of monosodium orthophosphate, which corresponds to a lower Na / P ratio.

2 (l + f) NaH2PO4 - ^ Na2H2P20? + H2Ov ^> 21 (NaPO3) n + 2 £ H2O "> 2Na5P30io + 4H2O

4Na2HPO4 - »2Na4p207 + 2H2CT

2 (1 + f) NaH2PO4 + 4Na2HPO4 -> 2Na5p3O10 + 2i (NaPO3) n + 2 (2 + £) H2O

Second mechanism: ^ - * 2 £ Na3Hp2O7 + 2tH2O cNa6p4013 + 3 £ H2O2 (1 + £) NaH2PO4-2Na3Hp207 + 2H2O4.

2 (1 + E) Na 2 HPO 2 2 Na 5 P 3 O 10 + 4H 2 O 2 Na 2 HPO 4 -> Na 4 P 2 O 7 + H 2 O 2 (1 + t) NaH 2 PO 4 + 2 (2 + £) Na 2 HPO 4 -> 2Na5p301C) -t: £ Na6P4013 + (4 + 3 £) H2O 2.2. When the Na / P ratio is greater than 5/3, a calcined product containing tripolyphosphate and pyroneutria is obtained according to the reaction. (2 £ represents the amount of disodium orthophosphate corresponding to the greater of the Na / P ratio): 2NaH2PO4 Na2H2p207 + H2 (K.

-> 2Na5p3O10 + 4H2O 2 (2 + £) Na2HPO4 ^^ ~ »2Na4p207 + 2H2O ^ 2eS> £ Na4p207 + £ E20 2NaH2PO4 + 2 (2+ <£) Na2HPO4 -> 2Na5p301Q + (4 + £) H2O + £ 4 Na 14 72057 This thus illustrates that even starting from a substance with an overall Na / P ratio of 5/3, harmful developments may occur, which may lead to the presence of insoluble substances, for example.

In fact, the above reactions show that it is generally accepted that solid orthophosphates, tripolyphosphate precursors obtained by drying in either a rotary oven or an atomizer, consist of NaH 2 PO 4 and Na 2 HPO 4 on the one hand and Na 2 H 2 (PO 4) 2 on the other. more or less thorough mixtures of n and Na 2 HPO 4.

These mixtures of orthophosphates, depending on the methods, lead to various pyrophosphates (Na 2 H 2 P 2 O 2 + Na 4 P 2 O 2) or (Na 3 HP 2 O 7 + Na 4 P 2 O 2), which are crystalline or amorphous, via calcination. The tripolyphosphate is then obtained by thermal condensation of these pyrophosphate mixtures.

To the best of the applicant's knowledge, whatever the methods, the mixture obtained after drying always consists of at least two crystalline, well-known and well-known compounds of the formula Na20 -P2 ° 5 - H2 °.

This means that the methods according to the prior art cause the crystalline separation of orthophosphates or pyrophosphates.

Thus, surprisingly, when using the process according to the invention to a homogeneous solution of mono- and disodium orthophosphates set at a theoretical ratio of 5/3, the following significant observations can be made: 1) the final product corresponds to a new product which is practically insoluble * 2 ) makes it possible to isolate a well-crystallized new orthophosphate with a Na / P = 5/3 ratio and a characteristic X-ray spectrum.

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In other words, the process according to the invention does not correspond to the known combination of mixer, dryer and calciner, because its behavior is different, especially with regard to the crystallization of the phases.

At the present stage of the studies, the applicant is not in a position to provide a definite explanation for these surprising results.

The Applicant has found that according to the invention the crystalline separation can be greatly reduced: by causing very fast evaporation kinetics to thoroughly modify the sudden-heat-drying-fogging and crystallization conditions (at the supersaturation level) and to cause the composition of .

. by causing a very high state of fineness by spraying the solution to limit possible separation risks on the scale of mist particles of identical composition, thus facilitating all coalescence (homogenization) through diffusion within the particle and avoiding developments different from the crystallization products.

Surprisingly, the applicant has isolated a new product containing a single crystalline phase with a Na / P ratio substantially equal to 5/3.

The following formula can be given for this new product: Na5H4 (PO4) 3

In addition, its X-ray spectrum is as follows as measured by reflection diffractometry.

72057 16 Radius No. dÄ 1 8.9 2 5.35 3 4.68 4 4.63 5 3.85 6 3.81 7 3.75 8 3.67 9 3.66 10 3.63 11 3, 33 12 3.28 13 3.15 14 2.77 15 2.72 16 2.71 17 2.68 18 2.64 19 2.54

More specifically, the product of the invention can be prepared by a process consisting of the following steps: a) preparing a solution of mono- and disodium orthophosphates in such a way that the total Na / P ratio will be substantially 1.667 + 0.01.

b) forming a gap-vortex flow from a hot gas phase with a large motion.

c) feeding said orthophosphate solution to the vacuum zone of the gap-vortex flow so as to cause said orthophosphate solution to disperse under the action of the gas phase, and to crystallize the dispersion.

In practice, the shaft-vortex flow is given a large momentum in the gas phase which is at least 100 times, preferably 1000 to 10,000 times, relative to the orthophosphate solution.

In addition, the solution is given a low velocity (less than 10 m / sec) and a small overpressure relative to the gas (less than 105 Pa).

Finally, the thermal profile of the gas phase crystallization reaction is adjusted.

Il 17 72057 In practice, in the process according to the invention, the gas gap-vortex flow and the liquid phase form, from the contact of the phases, three successive zones in space without discontinuity, which are as follows: a) a very short dispersion zone, b) a zone with a gas volume droplets form gas / liquid pairs along the paths determined by the gas and which substantially follow the piston flow background, c) the isothermal zone.

According to the invention, the entire heat exchange and crystallization between the phases must be effected in zone b).

For this purpose, the temperature in zone c) must be sufficiently low, in the order of 100 to 160 ° C, preferably between 120 and 130 ° C.

Instead, the gas inlet temperature must be high enough because all water in the zone must be removed from the solution. Its determination depends on the other operating conditions of the process, but is several hundred degrees higher than the temperature of the iso-thermal zone, and preferably 400 to 600 ° C higher than the latter under normal operating conditions.

By acting as above, the solution droplets are homogeneously distributed. The thermodynamic conditions of the system are such that the parasitic development costs are completely prevented and that the composition of the solid remains identical to the composition of the liquid during crystallization. This is a completely new and unexpected result.

In addition, as far as sodium tripolyphosphate is concerned, in general the starting solution can be prepared by neutralizing 18 72057 H 2 PO 2 with NaOH or a mixture of orthophosphates Na 2 PO 3 + 2 Na 2 HPO 4. This solution is then treated with heat by generally known methods: spraying, rotary kiln, Lei bed or flame in one step (or in two steps if the intermediate orthophosphate is separated). Depending on the thermal condensation conditions (temperature, partial pressure of water, Na / P ratio, impurities), tripolyphosphates are obtained either 100% phase I, or 100% phase II or a mixture of phases I and II.

It is known that in some applications, specifically in the nutrient and detergent industry, dissolving tripolyphosphate in a non-turbid or poorly agitated medium generally results in the formation of sparingly soluble lumps or mass curing. In this case, the anhydrous phases I and II form partial hardenings.

Aqueous phase II results in complete and sudden curing. While the aqueous phase I does not cause any hardening. A tripolyphosphate with good solubility is a tripolyphosphate which contains less than 40% of phase I and is prehydrated (according to the test to be explained below).

Prehydration can be accomplished by spraying water after synthesis or by natural attachment of atmospheric water. The amount of prehydration required to allow dissolution without mass curing in an unstirred medium is at least 0.6% as measured at a loss at 150 ° C.

Accordingly, the applicant has invented a new sodium tripolyphosphate having a Na / P ratio of 1.667 + 0.01 and a water loss at 150 ° C of less than 0.6% and preferably 0.02%, characterized in that it has no mass curing at all. in an undisturbed medium according to the test described below.

Test 7 g of tripolyphosphate are added rapidly (2 sec) to 20 ml

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19 72057 distilled water. The appearance and hardness of the insoluble tripolyphosphate precipitate is observed after 2.5, 10 and 20 min of addition. Curing can be zero, partial or complete and can develop more or less rapidly.

This product is all the more surprising when solubility is observed regardless of the relative concentration of phase I and the particle size of the product, and this despite the fact that the water loss at 150 ° C is less than 0.6%.

Chemically, the Na / P ratio is 1.667 + 0.01.

The ratio of phase I to phase II therein can vary.

According to a preferred embodiment of the present invention, the tripolyphosphate has an apparent density of 0.5 to 1.1, agglomerates having a size of less than 100 microns and preferably between 90 and 60 microns and a phase I content of between 15 and 60%, and free of insoluble matter.

The product according to the invention can be obtained by using a process according to which: a solution of alkali phosphates with a Na / P ratio of between 1.64 and 1.70 is prepared, setting this ratio to the value desired in the final product, - this solution is fed in a symmetrical gap-vortex flow downstream of said flow to the vacuum zone, the heat transfer takes place in the piston-zone formed by the shaft-vortex flow, - the reaction is allowed to continue in the isothermal zone, - the product obtained is recovered.

In practice, the ratio of the motion variables of the gas phase to the liquid phase is more than 100 and preferably between 1000 and 10,000.

The feed rate of the starting solution is low and preferably less than 10 m / sec.

The overpressure relative to the gas phase is also small, less than 10 ^ Pa, and preferably between 0.4 and 0.6 10 Pa.

As stated above, the Na / P ratio is between 1.64 and 1.70. Preferably, the starting solution contains 15 to 50% dry matter.

Preferably, the starting solution is obtained by neutralization with H 2 PO 4 and NaOH.

The treatment temperature of the solution is between 380 and 450 ° C.

There are other embodiments of the present invention relating to the 1- or 2-step preparation of certain phosphates, in which the Na / P ratio varies between 1 and 3, and which correspond to the preparation of alkali, especially sodium and potassium orthophosphates and polyphosphate. The resulting orthophosphates can in turn be re-treated with heat.

According to the invention, a solution of alkali phosphates with a Me / P ratio corresponding to the same ratio of the final product forms a dispersible phase in which Me represents an alkali metal.

In general, for the preparation of orthophosphates with a Me / P ratio of 2, the temperature in zone c must be low, preferably less than 180 ° C, and preferably between 100 and 160 ° C, while in other cases the temperature in zone c is higher and depends on the product being sought.

Il 21 72057 The plant used is schematically shown in Figure 4 below.

It comprises a dispersing head 1, a receiving double cone and a cyclone 3.

At the end there is a perforated basket 4 delimiting an annular space 9 into which the tangential inlet pipe 5 opens. In this space a symmetrical gap-vortex flow can be achieved by means of the openings 6 and the neck 7.

The phase to be treated is fed along the axial line 8 so that it is conducted up to the sub-pressure zone of the shaft-vortex flow, i. to the upstream portion of the double cone 2.

The treatment gases are fed hot into the annular space. Example 1 The purpose of this example is to demonstrate the interest of the process of the invention in the preparation of insoluble tripolyphosphate.

A solution containing 20.5%? 2 ° 5 3a 14'9% Na 2 ° (Na / p-sulfur = -1.664) is sprayed with an air stream heated to 880 ° C 3 with a flow rate of 50 Nm / h. The flow of the solution is adjusted so that the outlet temperature of the gases and the product is 405 to 420 ° C.

The conversion to tripolyphosphate is 97% and the relative amount of insoluble matter is less than 0.01%.

In the conventional flame or rotary kiln process, calcining a solution with the same Na / P ratio at the same temperature gives a mixture of 95% tripolyphosphate and 3% insoluble and 2% pyroneutral.

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The relative amount of insoluble matter is measured by the following method: 20 g of product are dissolved in 400 cm of water and boiled for 10 min. After cooling, the solution is filtered through a sintered filter No. 4, which has been dried for 2 hours at 110 ° C. The sinter filter containing any precipitate is washed and dried for 2 hours at 110 ° C. From the difference between the weights obtained before and after the separation of the sinter filter, the amount of insoluble matter is calculated.

Example 2: Effect of different factors on tripolyphosphate. The preparation conditions of the tripolyphosphate are as follows: the solution is obtained by neutralizing H 2 PO 4 with NaOH in such a way that the ratio of Na 2 O / P 2 O 2 - will be between 1.64 and 1.70 and the dry content between 15 and 50%. Hot gases are fed at a temperature between 880 and 950.

By adjusting the air flow (on the order of 50 Nm / h in the experiments performed) and the solution flow, an isothermal zone can be obtained, the temperature of which is preferably between 390 and 450 ° C, which corresponds to the temperature of the calcined product (tripolyphosphate).

A tripolyphosphate is obtained which is free of phosphate impurities if the ratio is well set at 5/3. We end up with a mixture of tripolyphosphate plus pyroacid or tripolyphosphate plus pyroneutral only if the Na / P ratio is poorly set. The relative amount of tripolyphosphate thus obtained is about 90% in Experiment 6 and more than 98% when Ts = 420 ° C and Na / P ratio = 5/3 (Experiment 0).

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Co- Na 2 O ° 2 ° 5 Na / P Dry Gas Gas Phase Examples V concentration inlet outflow flow temperature temp. %%% ° C% 0 15.3 21.0 1.667 42 880 420 18 0.9

Effect of the Na / P ratio 1 16.3 22.2 1.68 42 880 390 19 0.7 2 14.1 19.6 1.65 42 880 450 18 1.1 Effect of the dry concentration of the starting solution 3 14.1 19.6 1.65 15 950 420 28 0.7 4 14.1 19.6 1.65 42 880 450 18 1.1

Effect of calcination temperature (outlet temperature) 5 14.1 19.6 1.65 42 880 400 37 0.8 6 14.1 19.6 1.65 42 880 420 18 1.1 7 16.3 22.2 1.68 42 880 390 19 0.7 8 16.3 22.2 1.68 42 880 450 18 0.8 X) value to the nearest 0.005

Experiments% TPP

0> 98% 1> 92%

2> 90 S

In addition, the tripolyphosphates obtained according to Experiments 1 to 8 do not contain an insoluble matter.

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In particular, the tripolyphosphate of Experiment 5 with 37% phase I does not result in any mass cure according to the test described below when the water loss at 150 ° C is less than 0.05%.

Under the same conditions, according to a previously known method, anhydrous tripolyphosphate containing the same amount of phase I results in a very high mass cure.

The tripolyphosphate according to Experiment 7, which contained phase I half of the above, does not lead to any mass curing over time, while the anhydrous tripolyphosphate according to the prior art (having the same water loss at 150 ° C) containing Phase I hardens to a mass.

These examples of surprising results are a good illustration of the fact that the co-operation of the means according to the invention results in a new type of function which leads to a new type of result.

Solubility test: 7 g of tripolyphosphate are added rapidly (in 2 seconds) to 20 ml of distilled water. The appearance and hardness of insoluble tripolyphosphate are observed at 2, 5, 10 and 20 minutes after addition.

Example 3 The purpose of this example is to illustrate another advantage of the invention which makes it possible to avoid crystalline separation. To this end, in order to recover the orthophosphate, the temperature of the isothermal zone is lowered to avoid calcination, while the temperature difference of the dispersing phase remains the same between the inlet of zone b and the u-outlet.

A solution containing 15.8% P2 ° 5 3a% Na 2 O (Na / P = 1.667) and a temperature of 40 ° C is sprayed at 10 l / h

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25 72057 flow to hot gas (temperature = 640 ° C; 50 Nm3 / h) where it is suddenly dried. The outlet temperature of the gases and solid product is 145 ° C. Chromatographic analysis shows that it is only orthophosphate, and the X-ray and infrared spectra show that this crystalline phase is in no way a mixture of two phases such as NaH2PO4 and Na.jH3 (PO4) 2. Na / P ratio, measured potentiometrically is 1,663. The formula Na 2 H 4 (PO 4) 3 can therefore be written for this new orthophosphate. · The following table lists the network distances and line line intensities determined by reflection diffractometry (Siemens K 805 generator with CuK monochrome radiation and relative calculator); These allow this product to be unambiguously in nature.

Radius No. Estimated intensities 1 8.9 ttf 2 5.35 tf 3 4.68 f 4 4.63 f 5 3.85 m 6 3.81 mf 7 3.75 m

Δ 3.67 mF

9 3.66 m 10 3.63 m 11 3.33 vol 12 3.28 m 13 13 3.15 vol

14 2.77 F

15 2.72 mF

16 2.71 m

17 2.68 mF

18 2.64 FF

19 2.54 f 26 72057

Note. FF - intensity very high F - intensity high mF - intensity moderately high m - intensity average mf - intensity moderately weak f - intensity weak tf - intensity very weak ttf - intensity very, very weak These examples therefore illustrate well the advantage of the invention that it makes it possible in some way to carry out certain types of developments which are impossible to control in any other way and which, by analogy, can be limited to catalytic developments.

This can be illustrated by the following considerations: 1) there are two stable compound species in the region in question: monosodium orthophosphate and disodium orthophosphate, as well as more or less known metastable compound species that require higher levels of supersaturation to crystallize.

The crystallization of a hitherto unknown metastable compound species indicates that high levels of supersaturation have been achieved, corresponding to species that are activated in the catalytic sense of this word; 2) batching two types of compounds, namely mono- and disodium orthophosphate, in a given stoichiometry. The fact that the same stoichiometry is observed in the final product as on departure, as a single solid phase, suggests that under these conditions the rate of crystallization of the metastable compound is not much lower than the rate of crystallization of the stable compound and that it is higher than the diffusion rate of the solution components. In this case, the compound whose formation requires less diffusion energy is in the most preferred position.

Il 27 72057 This corresponds to the predetermination of the type of crystallizing compound corresponding to the starting stoichiometry.

Another example of the application of the method concerns the preparation of acidic polyphosphates.

Example 4; thermal condensation of an orthophosphate with a Na / P ratio of 1.

It is known that the thermal condensation of such orthophosphates at 180-450 ° C results in polyphosphates such as pyroic acid or (NaPO 4) n. The latter compounds can be either soluble (linear or cyclic) polyphosphates or insoluble polyphosphates.

Acidic polyphosphates are the products of the central chemical intermediates of pyroic acid and (NaPC> 3) n and correspond to the general formulas Na H ^ P O- (n J ^ 2).

J n 2 n 3n +1

At present, acidic polyphosphates cannot be isolated other than by laboratory methods. Thus Ν33Η2Ρβ0 ^ φ can be prepared by ethanol precipitation of a tripolyphosphate solution acidified with a theoretical amount of HCl.

The applicant does not know of any industrial method for producing such a product by thermal condensation, although thermal condensation has long been known per se.

According to the invention: - a solution of sodium orthophosphates with a Na / P ratio of about 1 is prepared, setting this ratio to correspond to the Na / P ratio of the final product, - this product is fed along the center line of the symmetrical shaft-vortex flow to the vacuum zone of said flow, the shaft vortex flow is given 28 72057 such a large phase motion that it is sufficient to cause the gas phase to disperse and treat the liquid phase, - the gas phase is given a temperature in the homogeneous isothermal zone between 180 and 450 ° C and preferably 230 and 320 ° C between.

The relative amount of acidic polyphosphates (n 2) obtained depends on the temperature. In the temperature range of 250 to 320 ° C, it is of the order of at least 50% and preferably 80%, the other compounds being pyroacid, orthophosphate and possibly small amounts of cyclic polyphosphates.

Thus, the process according to the invention makes it possible to obtain in an industrial manner a product which is known per se but impossible to obtain in a simple manner.

Such a product has applications especially in the field of nutrients and detergents.

In practice, the following test has been performed:

An aqueous solution of 370 g / l NaH 2 PO 4 is fed to the axial line 8.

The hot air inlet temperature to the annular space is 720 ° C.

By adjusting the air and liquid flows, an isoternic homogeneous zone with a temperature of 286 ° C can be obtained in the double cone 2, which is considered to be the temperature of chemical change in this example.

A solid product is obtained with a composition of: - NaH2PO4 4% - NaH2P207 16.2% - acidic polyphosphates 76.4% - insoluble 0%

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29 72057 The pH of a 1% solution of such a combination is 4.86.

Here again, the whole method is prescribed for zone c of the bays, taking into account the requirements of heat exchange.

In addition, obtaining a highly pure acidic polyphosphate is conditional on strict observance of the thermodynamic conditions (temperature and water pressure) associated with the stability range of this polyphosphate.

This area of stability is quite narrow. If this limitation of operation is not taken into account (the temperature of the product accidentally rises), the formation of an undesirable decomposition product will occur.

Namely, the endotherm corresponding to drying is clearly higher than that of thermal condensation reactions, which means that even a small excess of the amount of energy necessary and sufficient for drying easily alters and destroys the entire desired product, unless this is maintained under thermodynamic conditions that avoid this possibility. .

The above example illustrates quite well the specific distribution of thermal energy corresponding to the method according to the invention.

In addition, a certain amount of phosphates can be prepared according to the invention. Examples 5, 6, 7 and 8 illustrate sodium and potassium orthophosphates. It should be noted that in the case of orthophosphates the starting temperature is low, below 180 ° C, while in the case of polyphosphates it is much higher.

Example 5: NaH 2 PO 2 (sodium dihydrogen phosphate)

A solution containing 17.75% P2 ° 5 9a 7'7 ^% Na2 ° (Na / p = 1Ό0) »is sprayed with a stream of air at a temperature of 600 ° C and a flow of 50 Nm / h. The flow of the solution is adjusted so that the outlet temperature of the gas and the product will be 150 ° C.

30 72057

The resulting product consists exclusively of monosodium orthophosphate (sodium dihydrogen phosphate) with an apparent density of 0.7 and a water loss at 150 ° C of less than 0.3%.

Example 6: Na 2 HPO 2 (sodium monohydrogen phosphate)

A solution containing 15,0% P2 O 5 ', 1% Na2O (Na / p = 2.00) and the following impurities: - (Na2SO4: 3.0%; NaF: 0.2%; ΞίΟ ^ ίΟ, Ι%, NaCl: 0,4%, Ca: 500 ppm, Mg: 400 ppm, total other metallic impurities: 1000 ppm), - sprayed with a stream of air at a temperature of 570 ° C and a flow rate of 55 Nm3 / h. The flow of the solution is set so that the outlet temperature of the gases and the product becomes 125 ° C.

The resulting product consists exclusively of disodium orthophosphate (sodium monohydrogen phosphate) with an apparent density of 0.57 and a water loss at 150 ° C of less than 0.6%.

Example 7: Na 2 PO 2 (trisodium monophosphate)

A solution containing 9.1% P2 ° 5 3a 12% Na2 ° (Na / P = 3 »02)» is sprayed with a stream of air at a temperature of 600 ° C and a flow rate of 60 Nm / h. The flow of the solution is adjusted so that the outlet temperature of the gases and the product becomes 170 ° C.

The resulting product consists exclusively of trisodium orthophosphate (trisodium monophosphate) with an apparent density of 0.35 and a water loss at 150 ° C of less than 0.2%.

Example 8: Κ ^ ΗΡΟ ^ (potassium monohydrogen phosphate)

A solution containing 21.6% K 2 O and 16.3% Ρ2 ° 5 (K / p = 2.00) is sprayed with a stream of air at a temperature of 600 ° C and a flow rate of 50 Nm / h. The flow of the solution is then adjusted so that the outlet temperature of the gases and the product becomes 150 ° C.

The resulting product contains only dipotassium orthophosphate (potassium monohydrogen phosphate) with an apparent density of 0.50 and a water loss at 150 ° C of less than 0.4%.

Il 31 72057

Example 9: Μ ^ 2-2-2-2-7 This pyrophosphate is a temperature intermediate of Na2H2P20y ° obtained as NaH-PO. calcined to insoluble (NaPO 4) or 2 4 3 n cyclic trimetaphosphate, (NaPO 4) ^ ·

Its application, especially in the food industry, as an acidic agent (raising agent, melting salt) requires the absence of insoluble or cyclic phosphate. It is shown that the monosodium orthophosphate obtained by the process of this invention can, by heating in an oven, give pyroacid which is both insoluble (less than 0.02%), trimetaphosphate free (less than 0.2%) and monosodium orthophosphate free. (sodium dihydrogen phosphate) (less than 0.2%).

This unexpected result is calculated due to the combined effect of several parameters, such as the calcination temperature, the Na / P molar ratio of the orthophosphate and the partial pressure of the water in the furnace, but also and above all the crystallinity of the orthophosphate which cannot be achieved by the process.

Example: the orthophosphate Na 2 PO 2 is that obtained under the conditions of Example 5.

This orthophosphate is heated to 250 ° C in a tubular furnace to which the added water has a partial pressure of 133 10 Pa for one hour; this gives pyroacid (sodium dihydrogen phosphate) which is free of phosphate impurities, i.e. wherein the relative amount of insoluble matter is less than 0.2% and the relative amounts of trimetaphosphate and orthophosphate are less than 0.2%. This pyroacid has an apparent density of 0.55 and a narrow particle size distribution (80% between 15 and 60).

Example 10: Na 2 P 2 O 7 (tetrasodium diphosphate)

A solution of 13.1% Na 2 O and 15% P 2 O 5 (Na / p = 2.0) is sprayed with a stream of air at 815 ° C and

O

flow 45 Nm / h. The flow of the solution is adjusted so that the outlet temperature of the gases and the product becomes 425 ° C.

32 72057 This gives neutral pyrophosphate (tetrasodium diphosphate) (more than 99.8%) without orthophosphate (sodium monohydrogen phosphate) and / or trisodium phosphate or sodium polyphosphate (sodium triphosphate), 2%) and has an apparent density of about 0.4.

Example 11; Κ4Ρ20 ^ (tetrapotassium diphosphate)

A solution containing 27.05% K 2 O and 20.4% P2 ° 5 (K / p = 2.00) is sprayed with a stream of air at a temperature of 920 ° C and a flow rate of 55 Nm / h. The flow of the solution is adjusted so that the outlet temperature of the gases and the product becomes 500 ° C.

In this case, neutral potassium pyrophosphate (tetrapotassium triphosphate) is obtained in a yield ratio of more than 99.5%, without orthophosphate (sodium monohydrogen phosphate and / or tripotassium phosphate) or tripolyphosphate (potassium triphosphate) 0.2% insoluble matter (less than 0.02%). The product has an apparent density of about 0.25 and a very high dissolution rate.

Calcination of phosphates in the furnace

It is possible to obtain neutral sodium and potassium pyrophosphates (tetrasodium and tetrapotassium diphosphates) having a density higher than that of Examples 10 and 11 by carrying out oven calcination according to the process of the invention on the dried orthophosphates Na2HPO4 and K2HPO4, respectively.

Example 12; Na ^ P20., (Tetrana tr iumdif phosphate)

Orthophosphate Na 2 HPO 4 (sodium monohydrogen phosphate) obtained by the method of Example 6 is fed to a tubular furnace with a temperature of 350 ° C. The heating time under isothermal conditions is 2 hours. This gives neutral sodium pyrophosphate Na 2 P 2 O 2 (tetrasodium diphosphate) which is free of phosphate impurities (sodium monohydrogen phosphate and / or trisodium phosphate (orthophosphates) or sodium tri-polyphosphate (less than about 0.2%). 60.

Il 33 72057

Example 13: (tetrapotassium diphosphate)

An orthophosphate (potassium monohydrogen phosphate) K 2 HPO 4 obtained by the method described in Example 8 is fed to a tubular furnace at a temperature of 450 ° C. The heating time under isothermal conditions is 2 hours. This gives potassium pyroneutria (K 2 P 2 O 2 (tetrapotassium diphosphate) free of phosphate impurities orthophosphate (potassium monohydrogen phosphate and / or tripotassium phosphate or tripolyphosphate (potassium triphosphate) (less than 0,2%) and less than The apparent density of the product is about 0.4.

The above examples are, of course, not limiting of the invention, and the scope of the invention is not varied if the exotherm or endotherm of the reactions in one or the other reaction zone is altered, or by a series of more complex reactions, or by modification of a specific chemical compound in zone c.

Thus, all the advantages of the present method, which is carried out in a completely new way, are seen.

Claims (2)

34 72057 1. For use in thermal and / or chemical treatment of dispersants, fly ash, special t.ex. Vätska, halv-vätska eller Pulver, med en dispersand qasfas, kän nne -tecknat av att man manivivt och oavbrutet med hjälp av gasfasen these gases have, in particular, a homogeneous mixture of these particles, such as dispersants and dispersants; b) utstäten denna dispersion för snttorkningsbehandling i en strömningszon av kolvtyp; (c) utilizing the above-mentioned dispersions in a zone which is homogeneous with the addition of quaternary teas, for example, having the same viscous and chemically homogeneous levels. A process for treating a dispersible, flowable phase, in particular a liquid, semi-liquid or powder, with a thermally and / or chemically dispersing gas phase, characterized in that successively and without interruption by the gas phase: a) the dispersible phase is converted to elemental volumes such as finely divided solids or fines , which are substantially evenly distributed in said gas phase so as to obtain a systematically homogeneous mixture of the two phases, namely the dispersible and the dispersing phase; b) subjecting this dispersion to a sudden drying treatment in a piston-type flow zone; c) subjecting the dispersion from zone b, in a zone where the flow is homogeneous with respect to the distribution of residence times, to a treatment which is at the same time substantially both isothermal and chemically homogeneous. Process according to Claim 1, characterized in that the temperature of the dispersing phase entering zone b is adjusted according to the desired temperature and / or chemical composition of zone c and the temperature gradient of the dispersing phase of zone b so that the heat exchange takes place selectively in zone b. Process according to Claim 1 or 2, characterized in that an endothermic change is carried out in zone b, followed by a second endothermic or exothermic change in zone c. Method according to one of Claims 1 to 3, characterized in that the velocity of the dispersible phase is less than 10 m / sec and preferably less than 5 m / sec, that the ratio of the motion of the gas phase to the motion of the dispersible phase is at least 100 and preferably between 100 and 10,000 and that the pressure of the gas phase is less than 10 Pa and is preferably 5 (0.4-0.6) x 10 Pa higher than the average pressure in zone c. Il 35 72057 Application of a process according to any one of claims 1 to 4 for the preparation of sodium acid polyphosphates by thermally condensed orthophosphates, characterized in that: a solution is prepared from sodium orthophosphates having a Na / P ratio of about 1, setting this value to the Na / P value of the final product; the solution is fed along the center line of the symmetric shaft-vortex flow to the vacuum zone of said flow, said symmetrical shaft-vortex flow is given a gas phase motion sufficient to cause dispersion and treatment of the liquid phase at 180 ° C in the homogeneous phase, and the gas phase C and preferably between 230 and 320 ° C. 2. A patent according to claim 1, which can be used for temperature control