CA1190719A - Method of giving a fluid homogeneous heat and/or chemical treatment, and its application to synthesised inorganic phosphates - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A method is disclosed for applying thermal and/or chemical treatment to a dispersible fluid phase, such as in particular a liquid, semi-liquid or powder, by means of a dispersing gas phase, characterized in that the following steps take place successively and without discontinuity, by the action of the gas phase: (a) the dispersible phase is converted to a dispersion of component volumes, such as fine solid or liquid particles, which are substantially evenly distributed within said gas phase so as to give a systematically homogeneous mixture of the two phases, namely the dispersible and dispersing phases; (b) the dispersion undergoes flash treatment in a zone with plug type flow; (c) the dispersion emanating from zone of step (b) undergoes treatment which is both substantially isothermal and chemically homogeneous, in a zone with a flow which is homogeneous in the sense of the distribution of dwell times. The method of the invention overcomes some tricky problems which have plagued prior efforts in this field. The products of the method of the invention are useful in the food and detergent manufacturing industries.

Description

17~

The invention relates to ho~ogeneous heat and/or chemical treatment applied to a dispersible fluid phase~ s-uch as a liquid, which could possibly contain solids in suspension.
It applies in particular to methods of treatment which start with a liquid medium and have to produce at least one specific species, in an evolu-tion during ~hich there is a possibilit~ of parallel and parasitic reactions and/or at least the probabilit~ of intermediate compounds forming, thereby making the reaction difficult or "tricky" to perform.
A particularly good illustration of one of these problem reactions is the preparation of alkaline polyphosphates, eOg. tripolyphosphates of Na and K (triphosphates of Na and K)o In theory sodium tripolyphosphate can be obtained by the reaction:
NaH2P04 ~ 2Na2HP04 heat treatment Na5P3010 ~ 2H20, solution solution but the real position is far more complex. Neutral pyrophosphate ~Na4P207) and polyphosphates ~ith chains of varying lengths are chiefly formed~ resulting par-ticularl~ in the production of insoluble substances. It will be appreciated thatthe reaction s~stem is difficult to control, a fact which explains why there is old and extensive literature on the subject. In a diagrammatic way it can be said that one can use either two stage or single stage processes.
Thus United States 2,419,148, proposes tripolyphos~hates of Na of the ormula ~Na5P3010)x, where x is at least equal to 2 and has improved solubility in ~ater. United States 2,41~,147, also proposes forming an aqueous solution of a material comprising ~rom 5 to 6 moles of Na20 ~or every 3 moles o P205, atomizi.ng the solution, applying a flash drying treatment to said finely divided solution, and then heating the solid salt obtained to from 250 7:~

tQ 6Q0C. The sQlution i$ in fact spra~ed into a medium ~hich is hot cnough to produce a flash effect~ It is thus a ~airlr complex process and above all is difficult to control.
~ erman patent specification 649 757 descri~es a method of preparing meta and poly~hosphate from orthophosi~hates ~ treating them in a zone of ver~
hot gas, or a $1ame; and then cool~ng t~e~O
In United States 3~385,661, a phase II tripolyphosphate ~TPP) is produced ~y spraying an aqueous solution o orthophosphate ~ith an Na2O/P~05 ratio of 5/3 in a spra~ing tower which is kept at a temperature of 180 ~ 280C, so as to obtain intermediate products consisting, chiefly~ of pyrophosphate, then b~ calcining the intermediate product in a revolving furnace ~hich is kept at a tempera~ure of 150 - 450C, to convert it into phase II TPP.
B~ varying the conditions, a phase I TPP can be obtained as in United 5tates 3,387,929.
More generall~, United States 3,338,671, discloses a method of gran-ulating sodium tripolyphosphate, comprising atomizing an orthophosphate solution and then calcinating it. The patent even specifies that TPP can be obtained directlr by atomization if the atomizer is constructed in the appropriate manner, although it does not describe the appropriate construction.
Un~ortunatel~ thi$ is the essence o the ~hole problem.
German patent 1,097,421, proposes subjecting an orthophosphate solution to spraying inside a special to~er by passing it through a cro~n of flame, so as to dehydrate the individual dropletsO
This process has the disadvan~age of subjecting the droplets to different temperatures ~hen the~ are passing through ~he flame zone. Various solutions have therefore been propo~ed to remedy this, such as varying the 7~

partial pressure of the steam ~see ~erman patent 1,007,748). Unfortunatel~, as explained in Prench patent 1,535,819~ it is onl~ in ver~ special cases that these solutions are satisactory.
Researchers have therefore ~een led to propose various improvements relat~ng, e.g., to the actual zone of flame, as ln United States 3,499~476.
The prior art should, therefore, ~e considered as consis~ing of a large number Qf e$forts to resolve the ~roblem b~ dealing ei~her with the chemistry or the technology of the process, and, in more difficult ca~es, with both.
It has in fact ~een ~served that, when the dry~ng of the solution does not correspond to the formatlon of a deined compound, ~crys~alline) segregation takes place during the evaporating phaseO The composition of the graduall~ formed salid di~ers from that of the solution and evolves durlng the dry~ng processO This state corresponds to s~stems ~n thermod~namic equilibrium and can be modified b~ the kinetics of the phenomena which are brought into action during the thermal process.
Cenerall~ speaking, material transfer and heat transfer are known to take place during physico~chemical operations, and the kinetics of these transfers is kno~n to be limited~ usually b~ diffusion across the liquid-gas interface.
Ihe result is that, whatever ph~sical and/or chemical means have so far been applied, it is not known how to carr~ out some evolutions.
The perfect illustration for these remarks are the results obtained, e.g., in experiments in synthesising sodium tripolyphosphate from a solution of sodium orthophosphate with a total Na/P ratio of 1.667. Crystallisation o the solution corresponds to a mixture of orthophosphates ~ith different Na/P
ratios ~monosodium and disodiwn orthophosphates), which ma~ each evolve in a 7~L~

separate manner.
This explains the setbacks encountered when carrying out prior art methods, with the two ways of obtaining the sodium tripolyphosphate.
I~ is further known that French patent 2 257 326 claims a method of treatment including the dispersioll of a liquid or semi-liquid phase which may possibly contain solids in suspension. This is a method of bringing sub-stances in different phases into con~act, wherein a symmetrical vortical flow is formed by feeding in a gas phase, and by feeding in at least one other non-gas phase along the axis of symmetry of rotation of said flow, to substan-tially within the low pressure zone of the vortical flow.
Sufficient movement is imparted to the turbulent vortex, relative to that of the phase fed in axially, to cause that phase to be dispersed through the transfer of that much movement. Thus couples of volume components of the gas phase and the axial phase are formed, on the trajectories emanating from the gas phase and depending only on the previous history of the gas phase.
In practice, the ratio of the quantities of movement is at least 100, and preferably from 1,000 to 10,000, while the speed at which the axial phase is fed in is low, preferably less than 10 m/s. The pressure on the gas phase is also low, below 105 Pa, and preferably from 0.4 to 0.6 105 Pa above the pressure of the mixture.
The process chiefly makes it possible to use a big difference in temperature between the treatment phase (gas) and the fluid phase to be treat-ed (solution or suspension). It also has the advantage of including a zone of the plug type flow, for a description of "plug flow" see "Chemical Reaction Engineering" Second Edition, beginning at page 97 (John Wiley ~ Sons, Inc.) as far as concentrations are concerned, and a zone of the flash type in respect o temperatures The subject matter of the invention is a method of applying thermal and/or chemical treatment to at least one fluid dispersible material, under con-ditions which allow for very rapid kinetics of transfer, particularly heat transfer, between the dispersible substance or substances and at least one dis-persing phase.
The novel method of the invention comprises a method o applying heat and/or chemical treatment to a dispersible fluid phase, in particular such as a liquid, semi-liquid or powder, by means of a dispersing gas phase, and is characterized in that the following take place successively and without discon-tinuity, by the action of the gas phase:
a) the dispersible phase is converted to a dispersion of component volumes, such as fine solid or liquid particles, which are substantially evenly distributed within said gas phase, so as to give a systematically homogeneous mixture of the two phases, namely the dispersible and dispersing phases.
b) the dispersion undergoes 1ash treatment in a zone with plug type flow.
c) it is subjected to trcatment which is both substantially iso-thermal and chemically homogeneous, in a zone with a flow which is homogeneous ~0 in respect of the distribution of dwell times.
By virtue of the foregoing, it is understood that the length of the first phase is such that the mixture is formed as soon as the heat treatment begins.
Flash treatment b) (zone b) is understood as being a treatment of short duration, preferably less than 1 second, by the action of a big difference in temperature, of up to several hundreds of degrees, between the dispersing and dispersible phases, corresponding to intense heat transfer between _5_ ,:

the dispers~le and d~spersing phases~.
More p~rt~cularly~ in acc~rdance WIt~ the invention, the dispersing gas phase fulfils three functions:
lo forming the dispersion ca~rying out a ~irst flash treatment in a zone wl~h substantially plug flo~ distribu*ion 3. prcducing a second ~reatment under kinetic and thermodynamic c~ndit~orls ~hich are different from th~se in the preceding zone.
A cohesive sequence of individual operations is thus obtalned w:ithin ~hat may be an extremely short time, and the number of operations is not limited by t~e abo~e list.
A model of qualitative behaviour of such a system is sho~n diagram~
matically in ~igures 1 and 2 of the accompanying dra~ings. Figure 3 sho~s 8 alternative ab~cissae. The a~scissae of Figures 1, 2 and 3 should be considered independentl~ of one another.
Figured~ is a schematic representation of an apparatus for practlsing the method of the invention.
Pigure 1 is a hydrodynamic diagram of phases in the case of a three stage model. G represents the gas and F the dispersed fluid; the only 2Q ~unction of the time scale ~) is to indi~ate the timeO
pigure 2 lllustrates the diference in temperature ~T~T~TF~ between phas-es at the various stages. It will be seen from the diagram that, at the second stage ~zone b), the temperature difference between phases is very great for a very short time of contact, ~hereas, at the third stage ~zone c), the situation is completely diferent~
This is therefore a ne~ reactor, allo~ing for evolution of types such as shown in Figure 3, which corresponds to the special case of a liquid L
leading to a solid S. The diagram is a simple illustration of the fact that it is possible to act on stages b and c to control or determine the evolutionO
The method is particularly characterized in ~hat its thermodynamic and chemical evo]ution in zone c is defined by tha~ of TG~TF in zones a and b.
Thus, in this case where the dispersed fluid is a li~uid, zone c may correspond to a thermodynamic field of operation of a solid/gas or gas/gas reactor, where~s the substance initially introduced was a liquid and a gas.
In practice, in the method of the invention, the temperature and/or chemical compositi.on of zone c is determined by the variation of temperature of the dispersing phase in zone b~ so that heat exchange takes place selectively in zone b.
The temperature of zone c corresponds to that necessary for the kinetics of the conversion that has to be obtained from a slight temperature difference bet~een the dispersing gas phase and the dispersed phase. On the other hand, the temperature on entry into zone b is chosen so as to allow for the fact that heat exchange between the two initial phases takes place in practice in zone b.
Thus everything happens as if the method of the invention allowed for selective us!e of the energy supplied from the dispersing phase.
In fact this is allocated more specifically to the use of kinetic energy in forming the mixture in stage a, and to the use of heat energy in physico-chemically converting the dispersed phase in stage bo For example, if the dispersed phase is a solution, the heat energy is allocated more ~pecifically to the particle during its evaporation (that is to say, is allocated to a highly endothermic conversion);

this is a ne~ and unex~ected wa~ o$ treating matter, ~ urthermore, the solid o~ uid particle generated ~s protected thermall~ during and after its formation, since lt evolves, and i necessary is converted chemicall~ and/~r ph~sically~ in a su~stantially lsothermal medium.
~inall~, it evolves in a chemicall~ homogeneous ga~ phase, the composition ~e.g. t~e partial pressure of water) and temperature of which may ~ç specifically ad~usted ~zone c), for instance by the gas phase ~zone d).
Thus it ~ e acknowledgecl that undesira~le conversions of the required product cannot take place ~wlth the selected three stage model), provided that the thermodynamic conditions of the system, fixed from plug flo~
zone ~, do not allow them to happenO
It should further be emphasized that the successive flow conditions set up ~y the dispersing phase are par~icularly appropriate to continuous treatment of material in cases such as:
dr~ing follo~ed by calcination drying ~endothermic) follo~:ed by combustion ~exothermic) drying follo~ed by thermocondensation etc.
~ s a matter of ~act, the initial even distribution in zone a may ~Q include a slight spread of the various parameters about their average. This, then, takes the form of variation in the thermodynamic conditions imposed on the particle on its entry into zone c ~temperature, chemical composition of the dispersing phase, etc.).
This variation might ~e expected to cause disparit~ of treatment from one particle to another. However, zone c is found to dehomogenize the conditions of treatment.

In a s~ecial embadiment o~ the invention, endothermic conversion is carried aut in zone B, ~llawed by~furt:her endothermic conversion or exothermlc canversion in zone cO
Other treatment, such as heat treatment, may also be envisaged as the flo~ leaves zone C3 for instance by the gas phase (zone d).
As previously~mentioned, a method well adapted to procluce dispersion ~n entr~ to a zone with a piston type flow IS described in ~rench patent

2,257,326.
In one embodiment of the invention, a symmetrical vortical flow is formedJ b~ feeding in a gas phase and at least one other phase along the axis o sy~netr~ of rotation of said flow, substantiallr to within the lou pressure zone of the vortical flow; sufficient movement is imparted to said vortical flow, relative to tha~ o the phase fed in axially, ~o cause that phase to be dis.persed through transfer of that much movement, and to cause it to be treated hy-the gas phase in the plug flow zone formed by the vortical flo~, which is characterized in that the temperature at ~hich the gases enter is controlled so as- to form a substantially isothermal and chemically homogeneous zone down-stream of the piston zoneO
Thus, in accordance with the invention, the dispersing gas phase is used s.uccessively to form the mixture and to provide two reactors with diferent characteristics in seriesO This is a particularly difficult problem~ especially ~hen the operation has to take place continuously and on an industrial scale.
According to the invention this can, ho~ever, be accomplished in a simple way, ~ acting on the hydrodynamics of the dispersing phase and its initial temperature.
In practice, for economic reasonsJ the dispersible phase is given a ~9_ law initial speed, preferably less~ than 10 m/s~ and, if possible, less than 5 m/s-, so that it can reduce the initial movement of the dispersing phase.
The movement ra~io of the gas pha~e to t~e dispersi~le phase~ if it is to be ~s~ufficient, ~11 generally ~e at least 100, although it is preferablx generally ~etween 1000 and 10,000.
L~w~pres~:ures~ are also a~plied t~ the gas phas-e, Oelo~ 105 Pa, and, advantageously, from 0O~ to 0.6 105 Pa above ~he mean pressure in zone c.
However~ this pressure could ~e increased ~ithout going ~e~ond the scope of the invention, provided ~hat the ratio bet~een the amounts of movement is respectedO
Quite simply, one must obviously provide the best economic conditions ~hich will meet the technical requirementsO
A method and apparatus ~hich can also be recommended are described in ~rench patent 2,431,3~1 A typical application of the invention is in the preparation of sodium tripolyphosphate from orthophosphate solutions ~ith different Na/P
ratios.
~ Yhether in the food industr~ ~dissolved salts, salted cold, meats) or certain industrial applications such as detergent manufacture, sodium tri-~0 polyphosphate is generally used in solution. The presence of insoluble su~stances may therefore cause trouble.
The insoluble substances are introduced either upstream of theprocess for preparing the l'PP ( b~ the raw materials~, or during thermoconden-sation o~ the orthophosphates.
Before calcination, they consist mainl~ of traces of metallic phosphates which are present in the phosphoric acid and which are not completely ~recipitated when the H3PO4 is neutralized b~ Na~H~ As a general rule the amount of these insoluBle suBstances pres~ent is very small.
On the other hand, after ~he calcination of the orthophosphates~
the presence o~ ~nsolu~le ~NaPO3) is fre~uentl~ oaserved, in large quant~ties ~hich vary according to the thermocondensing conditions. This substance emanates solely rom th~ comple~e calcination of orthophosphates with an Na/P ratio of 1 ~n the following reaction:
NaH2Po4~--t N 2112P207 ~Na~H2Pn3n ~ NaP3) Any means: for forming Tpp whlch lacks homogene.ity ~at the ortho or pyrophasphate level) ~ill lead to the presence of phosphate impurities ~including the insoluble substance ~NaPO3)n~.
This is true even if the Na/P ratio is well adjusted overa.ll on the macroscopic scale.
This leads us to consider the following cases on the microscopic scale:
1) ratio NafP ~ 5/3 2~ ratio Na/P ~ 5/3 1~ Na/P - 5/3 If the mixture is homo~eneous, a TPP can be obtained ~ithout impurities b~ the currentl~ accepted mechanism as represented immediatel~ below:
2 NaH2PO4 ~ Na2H2P2O7 2 \
~ 2 Na5P3Olo ~ 4H2 4 Na2HP04 ~2Na4P27 t 2 H2O

2 NaH2PO4 ~ 4Na2H~O4 )2 Na5P3Olo 2 Another possible mechanism ~passing through p~rotrisod~um) gives the same result:

7~L~

3 2 7 2H2O \
2Na2HP04 ~ 2Na5P3010 + 4~120 2Na2HP04 ~ 4 2 7 2 2NaH2PO4 + 4Na2HP4 ~ 2Na5P31 O 2 2) Na/P ~ 5/3 If the mixture is not homogeneous, this means that thera will be local shortages or excesses relative to the total Na/P mi.xture.
2.1 With an Na/P ratio of less than 5/3, there will be found to be either insoluble substances as with the first mechanism, or short polyphosphates as with the second mechanism.
First mechanism: 2 represents the quantity mechanism of monosodium orthophos-phate corresponding to the shortage in the Na/P ratio.

2 (NaP3)n + 2H2 2 (1+E ~NaH2PO4) Na2H2P207 ~ H20 \
~ 5 3 10 4H2O
4Na2HP04 > 2Na4P2o7 2H2 2 4~ N 2HPO4 2Na5P3lo ~ 2 (NaPO3)n ~ 2 (2 ~)H2O

Second mechanism:

/ 3 2 7 2 Na6P4l3 2 2 (l+)NaH2PO4 - - 2Na3HP2O7 2 ~
2~1+)Na2HP04 ~ 2Na5P3010 + 4H20 2Na2HPO4 Na4P207 H20 2~1+)NaH2PO4 ~ 2~2-~)Na2HPO4~ 2Na5P3O1O + Na6P413 2 2.2 For Na/P ratios greater than 5/3, a calcined product Cont~;ning TPP and pyroneutral is obtained by the following reaction. (2 represents the ~v~

~uantity af disodium ortho~hos.:phate corres~onding ta the excess in the NaiP
ratio~:
2Na~ ~U4 ?Na2H2~27 H2~ \
--2Na5P3010 + ~12 . . 2~ ~Na4P27 ~ ~12 2NaH2PO~ 2(2*~)Na2H~~ ~ 2Na5P3010 * C4~)H2 ~ ENa~P27 This thus illustrates- the fact thatJ even when one starts ~ith a medium in which the total Na/P ratio is 5/3, undesirable evolutions ma~ take place and ma~ lead e.gD to the presence of insoluble substances.
The above reactions demonstrate the general acceptance that solid orthophosphates~ ~hich form the precursors o TPP and which are obtained by drying either in a revolving furnace or in a spra~, are made up respecti~ely of more or less intimate mixtures either of NaH2P0~ and Na2HP0~ or of Na3H3(P04)2 and Na2HP0~.
Depending on the processes used, these mixtures of orthophosphates, when calcined, give various pyrophosphates (Na2H2P207 + Na~P207) or ~Na3HP207 ~ Na~P207) in cr~stalline or amorphous formO The TPP is then obtained by thermocondensing these mixtures of pyrophosphates.
To the best of applicant's knowledge, whatever the processes used, the mix~ure obtained after drying alwa~s consists of at least t~o cr~stalline units which are well known and entered in the equilibrium diagram Na20 - P20 H20 o This means that prior ~rt pracesses cause cyrstalline segregation of arthophosphates- or pyrophosphates.
B~ carrring out the method o the invention ~ith a homogeneous 7~

solutign o monosodium and dîsodlum orthophosphates adjusted to the theoretical ratia of S/3, the ~ollowing important o~s~ervations have surprisingl~ ~een made:
~ ) The final product corresponds to a ne~ product virtually free from an~ insoluble compuunds;
2~ It is: possi~le to isolate a new orthophosphate xith an Na/P
ratio e~ual to 513, which is well cr~tallised and has a specific X-ray spectrum.
~ n other words, the method of the invention is not equivalent to the known mixing, dry~ng and calcining procedure, since its action is different, particularly with regard to the crystallis-ation o the phases.
At this s;tage in the work, applicant cannot give a definite e~planation of these surprising results.
They have observed, how-ever, that, in accordance ~ith the invention, crystalline segregation may be greatly minimized by:-a) imposing very rapid kinetics of evaporation, by means of instantaneous heat processes, thereby profoundly to change the nucleation and cry~tallisation conditions ~supersaturation level) and thus bring the composition af the crystals obtained closer to a mean composition corresponding to the initial solution ~action of zone b); and

4) producing a ver~ significant divided state by spra~ing the solution, in order to limit any danger of segregation to the scale of droplets of identical composition, ~hile facilitating any combination ~homogenization) bl~ diffus-ion ~ithin the particle and avoiding different evolution of the products of crystallization ~action of zone a).
Other applications of the invention have to do with the preparation of a certain num~er of phosphates in one or t~Yo stages, with an Na/P ratio ranging from 1 to 3~ corres~onding to the preparation of alkaline, particularly ~14-sodium and potassium/ orthophosphates and ;polyphos~hates,. The orthophosphates obt~ined may In turn undergo thermal reprocessIng~
According to the invention, a solution o:E alkaline phosphate$ in which the Me~P ratio corresponds, ta that In t~e f~nal product, fsrms the fluid dispersib.le phase; Me represents the alkali metal.
~ enerally~ speaking it will be noted that, in the preparation of orthophosphates ~here the Me/~ rati~ i~s less, than or equal to 2, the temperature in zone c must ~e low, advantageousl~ below 180 C and pre:Eerabl~ from 100 ~o 160C, ~hereas: in other cases the temperature in zone c will be higher and ~ill depend on the product requiredO
The ins,tallation used is shown diagrammatically in Figure 4 of the accompanying drawings.
It comprises a dispersing head 1, a doubly conical receiving vessel 2 and a cyclone 3.
The head has a conical screen 4, defining an annular space 9 with a tangential inlet 5 opening into it~ This space enables the symmetrical vortical flow to be formed, by means of apertures such as 6 and the neck 7.
The phase to be treated is introduced through an axial pipe 8, so as to bring it into the low pressure zone of the turbulent cavit~, that is to say, into the upstream part of the doubly conical vessel 2.
The gases used for treatment are fed into the annular space in a hot s.tate.

The purpose of this example is to sho~ the importance of the method of the invention in preparing TPP withaut any insoluble substances.
A solution containi.ng 20.5% P205 and 14.~% Na20 ~Na/P-1.664) is sprayed ~v~

b.y an airstream heated ~q 88Q C and flowing at SQ Nm3/h. The 1Ow rate of the solution is adjus*ed so as to bring the temperature at which the gases and product emerge to 405=420 C.
The rate af conversion to TpP is 97% and the ~roportion of insolu~le substances; i$ less than 0~01%o In a con~en~ional process (~lame or rotary dryer~ calcination of a solution with the same Na/P ratio and at the same temperature gives a mixture consisting o ~5% TPP - 3% insoluble su~stances 2% incombustible.
The proportion of insoluble substances is measured by the following method: 2Q g o product is dissolved in 400 cm3 of water and brought to the aail for 10 minutes. ~he solution is filtered after cooling, on a no. 4 frit which has previousl~ been dried for two hours at 110 C~ The frit, containing an~ washed precipitate, is dried for t~o hours at 110 C. The difference in the weight of the frit ~efore and after separation enables the proportion of insol-uble substances to be calculated.
EXAMPLE 2: Effect of the various factors on khe TPP.
The conditions under ~hich the TPP are prepared are as follows:
the solution is obtained b~ neutralizing H3PO4 with NaOH, so as to obtain an Na2O/P2O5 ratio of from 1.64 to 1 D 70 and a dry extract from 15 to 50%. The hot gases are fed in at a temperature of from 880 to 950C.
By controlling the flo~ rate of air ~of the order of 50 Nm3/h in the tests carried out) and solution, an isothermal zone can be formed, advanta-geously at from 3~Q to 450C~ corres~ponding to the temperature of the calcined product (TPP).
TPP is obtained w~thout any phosphate impurity if the ratio is properl~ adjusted to 5/3. A mixture of TPP ~ pyroacid or TPP ~ pyroneutral will ~e arrived at only i$ the Na/P is inc~r~ectly adiusted. Thus the ratio a TPP o~tained IS approximatel~ 90% in exa~ple no. 6 and over 98% when Td ~ 420C and Na/P - 5/3 ~test 0).
Tests Na2O P O5 Na/P* Dry- T Td Phase I ~ppar.
% ~ extract intaK~ o~ gas dis- % density . : : % . gas:C~ cha~ged. ~
0 15~3 21.0 lo 667 42 88Q 420 18 Q.9 E~fect Q~ Na/P ratio l 16.3 22.2 1068 42 88~ 390 19 0~7 2 14.1 1~.6 1O65 42 880 450 18 1.1 Effect of pro~d~tibn of d~ ext~act in initial solution 3 14.1 1~.6 lo 65 15 95~ 420 28 0.7 4 14.1 1~.6 1065 . 42 88Q 450 18 1.1 ~ffect o~ calcining temperature (temperature when discharged) 14 1 19 6 1 65 42 880 400 37 0.8 O
6 14~1 19.6 l.G5 42 880 420 18 1.1 7 16.3 2202 1.68 42 880 390 19 0.7 8 1603 22.2 1.68 42 88~ 450 18 0.8 * value to nearest 0~005 Tests % TPP
0 ~98%
1 ~92%
2 ~0%

37~

Furthermore, the T~ o~t~ined in tests 1 to 8 do not contain any insoluble s~stances.
It should be noted in particular that the TPP in test 5~ containing 37% of phase I7 does not lead to any solidiXication in the test described below, wi*h less than 0.05% loss of water at 150C.
In a prior art process carried ou~ under the same conditions, an anhydrous TPP containing the same proportion of phase I produces very considerable solidification.
A TPP in which the content of phase I is half the preceding one in test 7 will not lead to any solidification with the passage of time, whereas an anhydrous rPP (that is to say~ with the same loss of water at 150C) J
cont~;ning the same proportion of phase I as in prior art, will solidify.
These examples, with their surprising results, admirably illustrate that the method of the invention fulfills a new function and leads to a new re-sult.
Solubilisation test: 7 g o ~PP are added rapidly (2 seco~ds) to 20 ml of distilled ~a~er. The appearance and hardness of the non-dissolved TPP is noted 27 57 10 and 20 minutes after the addition~
EXA~PLE 3 The purpose of this example is to illustrate another important feature of the invention, namely the prevention of crystalline segregation. With this in vie~, and, as a means of recovering the orthophosphate, the temperature in the isothermal zone is reduced to prevent calcination~ and in e~ch~nge the temperature difference for the dispersing phase is kept the same at the inlet and outlet of zone b.
A solution containing 15.8% of P205 and 11.5% of Na20 ~Na/P = 1.667) 7~

and kept at 40C is sprayed, at a flcw rate of lQ litres/hourJ ~y a hot gas ~T -= 640C; 50 Nm3/h) where it is dried instan~aneously. The temperature at which the gases and solid emerge is 145C, Chromotographic analysis shows that only orthophosphate is present, and X-ray and infra-red spectra show that the cr~stalline phase is never a mixture of two phases such as NaH2P04, Na3H3~P04)20 The Na/P ratio measured by potentiometry equals 1.663. The ne~
orthophosphate can therefore be defined by the formula Na5H4(P04)3. The table below contains a list of the reticular distances and line intensities obtained by diffractometry ~Siemens Generator K 805, monochromatic radiation CuK~.
Proportional counter). This procedure makes it possible to characterize the product without any ambiguity.

Line NoO dA Estimated ~ntensities 2 5.35 vl 3 4.68 3085 a 6 3081 fl 7 3~75 a 8 3067 fh 9 3066 a 3063 a ll 3033 vl 12 3.28 fl 13 3015 vl 14 2.77 h 2072 fh 16 2.71 a 17 2.63 fh 18 2,64 vh 19 2.54 7~

N.~. vh: very high intensity h: high i~tensit~
fh: fairly high intensity a: average intensity fl: fairly lo~ intensity 1: low intensity vl. very low intensity vvl: very very low intensity The foregoing examples illustrate the importance of the invention in, as it were, making it possible to carr~ out certain types of evolution which could not otherwise be controlled, and which may be regarded as similar ~o catal~tic evolutionO
This is illustrated by the following points:
1) There are tw~ stable species in the field under consideration:
monosodium orthophosphate and disodium orthophosphate~ and metastable species which are known to varying degrees and which require higher levels of super-saturation to make them crystallizeO
The fact that a metastable species which was previously unknown is crystallized shows that considerable supersaturation levels are attained, corresponding to species being activated in the catalytic sense of the word;
2) Two species, monosodium and disodium orthophosphates, are provided with a specific stoichiometry. The fact that the initial stoichio-metry reappears in the ~inal product~ in one solid phase, suggests that under these conditions the speed at which the metastable compound crystallizes is not far below that at which the stable cQmpound crystallizes, and that it is higher khan the speed a.t which the constituents in solution are diffused. Thus the compound requiring the leas~ diffusion energy to form it ~111 have b~ far the best chance af successO This corresponds to predetermining a crystallizing species as a function of an initial stoichiometry.
Another example of the application of the method of the invention arises in the preparation of acid polyphosphates.
EXA~PLF. ~: Thermocondensation of an orthophosphate with an Na/P ratio of 1 Thermocondensation of such orthophosphates in a temperature range from 180 to 450C is known to give polyphosphates such as pyroacid or (NaPO3)n.
These latter compounds may be either soluble ~straîght or cyclic) or insolu`ble polyphosphates.
The acid polyphosphates are products of intermediate chemical stages between the pyroacid and ~NaPO3)n and comply with the general formulae Nan~[2PnO3n ~ 1 tn 2)o At the present time the acid polyphosphates can onl~ be isolated by laboratory processesO Thus Na3H2P3O10 can be prepared by taking a solution of TPP, acidified by the theoretical quantity of HCl, and precipitating it with ethanol.
~ pplicant does not know of any industrial method of preparing such a product by thermocondensation, although thermocondensation has been known 2~ per se for a long timeO
In accordance with this aspec* of the invention:
~ a) a solution of sodium orthophosphates is prepared, with the Na/P
ratio at approximately 1, and the value of that ratio is adjusted to the Na/P
ratio in the final product, ~ b) the solution is fed along the axis of a s~mmetrical vortical flow, into the low pressure zone of said flow, ~ c~ sufficient movement of the gas phase is imparted to the symmetrical vortical flow, to bring about the dispersion and treatment of the liquid phase by the gas phase ~ d) the gas phase is maintained at a temperature of from 180 to 450C, and advantageously from 230 to 320C~ in the homogeneous isothermal zone.
The proportion of acid polyphosphates ~n~2) obtained depends on the temperatureO Within the 250 - 320C range, it is of the order of at least 50% and preferabl~ 80%~ the other compounds being pyroacid, orthophosp~ate and possibly small quantities of cyclic polyphosphates.
1~ Thus the method of the invention enables a product, whicll is known per se but impossible to obtain in a simple manner, to be produced on an industrial scale.
There are special applications for such a product in the fields of food and detergentsO
The follo~ing test has been carried out:
An aqueous solution containing 370 g/l of NaH2P0~ is fed into the axial pipe 8 (see Figure 4).
The temperakure at which hot air enters the annular space is 720C.
The flow rates of air and liquid are controlled so as to produce a homogeneous isothermal zone at 286C in the doubly conical ~essel 2; this being considered as the temperature of chemical conversion for this example.
A solid is obtained, of the following composition:
-NaH2P0~ 4 %
Na2H2P207 16.2 %
-acid polyphosphates 76.4 %
-insoluble substances 0 %

The pH o~ a s~olution containing 1% of such a composition is 4.86.
Here again the whole process is determined from zone c, ma~ing allowance for the heat exchangc re~uiremen~s.
Furthermore, if a very pure acid polyphosphate is to be obtained, the thermodynamic conditions for its formation (water pressure and temperature) relating to a stable range of the compound must be st-rictly adhered ~o~
Now this stable range is very narrow. Should the limitations in operation not be respected (for example~ iE the temperature of the product should rise accidentally), an undesirable degradation compound will orm.
The endothermicity corresponding to drying is far greater than that in thermocondensation reactions; this means that a slight excess, relative to the energy which is necessary and sufficient for drying, is liable to convert and destroy all the re~uired product, unless it has been put under thermodynamic conditions which will prevent this from happening.
The above exa~ple is therefore a good illustration of the notion of speci~ic distribution of heat energy, which corresponds to the method of the inventionO
A certain number of phosphates can be prepared in accordance with the inven~ionO Examples 5, 6, 7 and 8 relate to sodium and potassium ortho-phosphates~ Examples ~, 10, 11~ 12 and 13 relate to polyphosphates. It should ~e noted that in the case of orthophosphates the discharge temperature is low, ~elow 180C~ whereas in the case of polyphosphates it is much higherO
EXA~PLE 5: Na~l2 ~ ~Sodium dihydrogenphosphate) A solution containing 17.75~ P2O5 and 7O75% Na20 ~Na ~ 1.00) is atomized by an airstream heated to 600C and flowing at 50 Nm3/hO The flow rate of the solution is adjusted ~o bring the temperature at which the gases and product are discharged to 150 C.
The resultant product consi,sts solely of monosodium orthophosphate ~sodium dih~drogen phosphate) with an apparent density of 0O7 and less than 0.3% loss of water at 150Co EXA~PLE 6: Na2 ~ ~Sodium monohydrogen phosphate~
A solution containing 15~ 0% P2O5, 13~1% Na2O (Na - 2.0~ and the following impurities: ~Na2SO~ : 3.0%; NaF : 002%; SiO2 : 001%; NaCl : 0.4%;
Ca : 500 ppm~ Mg : 4Q0 ppmg sum of other metallic impurities: 1000 ppm~, is atomized by an airstream hea.ted to 570C and flowing at 55 Nm3/h. The flow rate lQ of the solution is adjusted so as to bring the.tem~erature at which the gases and product are discharged to 125C.
The resultant product consists solely of disodium orthophosphate (sodium monohydrogen phosphate), with an apparent density of 0~57 and less than 0.6% loss of water at 150Co EXA~IPLE 7: Na7PO4 (Trisodium monophos~hate~
A solution cont~in;ng 9.1% P2O5 and 12% Na2O ~Na = 3.02) is atomi~ed by an airstream heated to 600C and flowing at 60Nm3/hO The flow rate of the solution is adjusted to bring the temperature at which the gases and product are discharged -to 170 C.
The resultant product consists solely of trisodium orthophosphate ~trisodium monophosphate) of an apparent density of 0035 and with less than 0.2% loss of water at 150Co EXA~PLE ~: K~ ~ (Potassium monohydrogen phos~hate) A solution containing 2106% K2O and 16. 3% P205 (pK - 2000) is at b~ an airstream heated to 600 Ciand flowing at 50.Nm /h. The flow rate of the solution is adjusted to bring the temperature at which the gases and product are ~2~-discharged to 150Co The resultant product contains only dipotassium orthophosphate (potassium monohydrogen phos"phate) of an apparent density of 0.50 and with less than 0.4~, 1QSS Of ~ater at 150Co EXA~PLE,~ Na2~12P2O7 (,Sodium dihydrogen diphosphate) This Na21-12P~O7 pyrophosphate is a temperature intermediate in tlle calcination of Na~l2PO4 to insoluble (NaP03)n or to cyclic (NaPO3)3 tri-methaphosphateO
When used as an acid agent~ particularly in the ood industry (yeastJ
dissolved salt)~ there must be no insoluble or cyclic phosphate present. It has been shown that, by using monosodium orthophosphate obtained by the method of the invention~ a pyroacid which is not only substantially free from insoluble su~stances (less than 0O02%) but also substantially free from trimetaphospha~e -(less than 0.2%) and monosodium orthophosphate (sodium dihydrogen phosphate) (less than 002%) can be obtained by heating in an ovenO
This unexpected result is attributed to the conjunction of several parameters~ such as the calcinating temperature, the Na molar ratio of the ~rthophosphate and the partial pressure of water in the ovenJ but also and a~ove all to the orthophosphate having a crystallinity which can only be obtained by the method of the invention.
Example: the orthophosphate Na~12PO~ is that obtained under the conditions in ~xample 5.
The orthophosphate is heated at 250 C in a tube furnace with a partial pressure of added water of 133, 10 Pa for 1 hour; this gives pyroacid (sodium dihydrogen diphosphate) substantially without any phosphate impurities, that is to say, with less ~han 00~2% insoluble substances and less than 0.2%

~25-7:~

trimetLqphOsphate and arthQphosphateO The pyroacld has an apparcnt density of 0~55 and a narrollr granulo metric distribu~ion C80% between 15 and 60 ,u).
EXA~PLE 10: Na4P207 ~retrasodlum dipllos~hate~
A solution conkaining 13~1% Na20 and 15% P205 ~Na _ 2~ Q) is atomized by an airstream heated to 815QC and flo~Ying at 45 Nm3/h. I'he flow rate of the solution i5 adjusted to bring the temperature at which the gases and product are discharged to 425C~ Neutral pyrophosphate ~tetrasodium diphosphate~ is then obtained ~over 9908~) substan~ially without any orthophosphate impurity Csodium monohydrogen phosphate and/or trisodi~un phosphate or sodium tripoly-phosphate ~sodium triphosphate) ~less than 0O2%)~ and with an apparent density of 0.4.
EXAMPLE 11: K~P207 ~Tetrapotassium diphos~hate) A solution containing 27005% K2O and 2004% P2O5 (K = 2.00) is atomized by an airstream heated to ~20C and flowing at 55 Nm3/h. The flow rate of the solution is adjusted to bring the temperature at which the gases and product are discharged to 5~10Co Neutral potassiwn pyrophosphate (tetrapotassium diphosphate) is then obtained, representing over ~9O5% of the total composition, substantially ~ithout any orthophosphate impurities (potassium monohydrogen phosphate and/or tripotassi~n phosphate) or tripolyphosphate impurities (potas-sium triphosphate) (less than 0.2%) and substantially without any insoluble substances (less than 0~02%)~ The apparent density of the product is approxi-mately 0~25 and it has a very high solubilising speed.
Calcination of orthophosphates in a furnace It is possible to obtain neutral sodium and potassium pyrophosphates ~tetrasodium and tetrapotassi~n diphosphates) of densities higher than those in examples 10 and 11; by taking the Na2HP04 and K2HP0~ orthophosphates obtained through drying by the method of the invention and calcining them in a furnace.
~XA~IPLE 12: Na~P207 (Tetrasodium dip~osphate) The orthophosphate Na2HP04 ~sodium monoh~drogen phosphate) obtained by the method described in Example 6 is placed in a tube furnace heated to 350C.
The period of heating Imder isothermal cond.itions is two hoursO This gives neutral sodium pyrophosphate Na4P207 ~tetrasodium diphosphate) substantially free from any phosphate impurities ~sodium monohydrogen phosphate and/or tri-sodium phosphate ~orthophosphates) or sodiwn tripolyphosphate ~less than 0.2%).
The apparent density of the product is approximately 0.60.
~XA~PLE 13: K~P 07 (Tetrapotassium diphosphate) The orthophosphate ~potassium monohydrogen phosphate) K2HPO4, obtained by the method described in Example 8, is placed in a tube furnace which is heated to ~50 C. The period of heating under isothermal conditions is two hours. This gives the po-tassium pyroneutral K4P207 (tetrapotassium diphosphate) substantially free from any phosphate impurities [orthophosphate (potassium monohydrogen phosphate) and/or tripotassium phosphate, or tripolyphosphate (potassium triphosphate), less than 0.2%, insoluble substances less than o.a2O~0~.
The apparent density of the product is approximately 0O4.
The invention is not of course restricted to the above examples and it ~ould be possible~ without going beyond its scopeJ to, for example, vary the exothermicity of endothermicity of the reactions which may take place in either reactive zone, or to bring about a sequence o~ more complex reactions, or to vary any particular chemical composition obtained in zone c.
This sho~s the importance of the; invention, which is based on a completely novel conceptO

Claims (11)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED FOLLOWS,

1. A method of applying thermal and/or chemical treatment to a dispersible fluid phase, such as, in particular a liquid, semi-liquid or powder, by means of a hot dispersing gas phase, characterized in that the following steps take place successively and without discontinuity, by the action of the gas phase:
a) the dispersible phase is converted to a dispersion of component volumes, such as fine solid or liquid particles, which are substantially evenly distributed within said gas phase so as to give a systematically homogeneous mixture of the two phases, namely the dispersible and dispersing phases;
b) the dispersion undergoes flash treatment in a zone with plug type flow;
c) the dispersion emanating from zone of step (b) undergoes treatment which is both substantially isothermal and chemically homogeneous, in a zone with a flow-which is homogeneous in the sense of the distribution of dwell times.

2. The method of claim 1, characterized in that the temperature of the process is controlled by the temperature and/or the chemical composition in the zone of step (c) and by the temperature gradient of the dispersing phase in the zone of step (c), so that heat exchange takes place selectively in the zone of step (b).

3. The method of claim l, characterized in that endothermic conversion is carried out in the zone of step (b), followed by a second endothermic or an exothermic conversion in the zone of step (c).

4. The method of any of claim 1, or 2, or 3, characterized in that a fourth zone d is formed by means of the gas phase.

5. The method of claim 1, characterized in that a symmetrical vortical flow is produced by means of a gas phase, that the liquid phase to be treated is fed axially into the low pressure zone of the vortical flow, by imparting sufficient movement to said vortical flow relative to the phase introduced axially, to bring about dispersion of the phase through transfer of that much movement and its treatment by the gas phase in the plug flow zone formed by the vortex, then letting the treatment continue in the agitated zone which follows the plug flow zone of the vortex; the temperature at which the hot gases enter being controlled so as to form a substantially isothermal and chemically homo-geneous zone in the zone downstream of the piston zone.

6. The method of claim 5, characterized in that the speed of the dispersible phase is less than 10 m/s, that the ratio of the quantity of movement of the gas phase to that of the dispersible phase is at least 100 to 10,000 and that the pressure in the gas phase is less than 105 Pa above the mean pressure in zone c.

applied

7. The method of claim 1 to the preparation of acid sodium polyphosphate by thermocondensation of orthophosphates, characterized in that:
(a) a solution of sodium orthophosphates in which the Na/P ratio is approximately 1, is prepared by adjusting the value of the ratio to the Na/P ratio in the final product, (b) this solution is fed along the axis of a symmetrical vortical flow, into the low pressure zone of said flow (c) sufficient movement of the gas phase is imparted to said sym-metrical vortical flow, to bring about dispersion and treatment of the liquid phase by the gas phase (d) the gas phase is maintained at a temperature of from 180 to 450°C in the homogeneous isothermal zone.

8. The method of claim 6, or 7, characterized in that the speed of the dispersible phase is less than 5 m/s.

9. The method of claim 6, or 7, characterized in that the ratio of the quantity of movement of the gas phase to that of the dispersible phase is from 100 to 10,000.

10. The method of claim 6, or 7, characterized in that the pressure in the gas phase is from 0.4 to 0.6 105 Pa.

11. The method of claim 1, or 6, or 7, characterized in that the fluid dispersible phase is an alkaline phosphate solution with an Me/P ratio cor-responding to that of the final product.