Note: Descriptions are shown in the official language in which they were submitted.
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
--2--
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
--3--
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
-- 4 --
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
-6-
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);
-7
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.
8-
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
-10-
~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~
2 4
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
- 12 -
~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
-13-
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.
EXAMPLE 1
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
-16-
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%
-17-
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)
-18-
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
809
2 5.35 vl
3 4.68
4 4063
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
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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,
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~ 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 %
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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
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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
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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
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