Note: Descriptions are shown in the official language in which they were submitted.
47~
The present invention relates to solid ammonium polyphosphate
compositions. More particularly, it relates to a new crystalline
form of ammonium polyphosphate possessing excellent physical properties
In recent years, there has been an increasing demand for poly-
phosphates in general and ammonium polyphosphate salts in particularwhich demand has resulted in large part to an increased use of these
salts in the fertilizer industry. As known polyphosphates substantial-
ly increase the nutrient value of phosphatic fertilizers.
Solutions based on polyphosphates have the following advantages:
- Polyphosphates sequester or dissolve the impurities present in wet
process phosphoric acid, the common starting material for their
preparation. The result will be that a crystal-clear liquid product
will be obtained.
- The solutions provide the maximum nutrient concentration available
in clear liquids. Moreover, compared with orthophosphates, they can
dissolve up to 40 times more micronutrients.
- They have an excellent quality, providing high analysls N:P:K
fertilizers in the form of suspensions or clear liquids.
- They have the property of reducing the viscosity of suspensions
and stabilizing them for easy handling and long-term storage.
The recognition of ammonium polyphosphate as a valuable fertilizer
compound, appears from the crowded prior art publications on the
subject. Most of them deal with the production of ammonium poly-
phosphates directly in solution (e.g. 10-34-0, 11-37-0 etc.),
which form the basis for N,P and N~P,K formulations. Some of these
prior art processes and methods for the production of concentrated
liquid fertilizers have proved to be indeed operative on a commercial
scale.
However production and distribution of fertilizer solutions in
general have the following drawbacks:
- Transportation of large quantities of liquid is costly and
consists a particular limitation for long distances haulage of
the finished product. This is an important consideration in
particular for international trade.
, I
~1~2~7$~
- The seasonal nature of fertilizer demand involves storage of
Large quantities of solutions by the producer or dealer.
-- Solu~ions of ammonium polyphosphate are not stable to hydrolysïs
and their polymeric phosphate content is reduced by an average of
about 5% even in mild climates.
- There exists the possibility of crystalli~ation of some of the
fertilizer solutions in extremely cold weather.
It has been recognized that producing a solid ammonium poly-
phosphate would constitute a solution to a long felt need in the
fertilizer industry, provided that the product should have the
following two main characteristics:
(a) A high content of polymeric phosphate which would ensure that
the solutions obtained would be concentrated, clear and stableO
(b) Excellent physical properties which would ensure smooth
transportation in bulk and easy handling.
Unfortunately, the various attempts to produce solid ammonium
polyphosphate have failed to provide such products which will
possess both characteristics. A commercial product containing 50%
polymeric phosphate moiety and triammonium pyrophosphate as a major
constituent, was found to be highly hygroscopic. On the other handl
reasonable physical properties (e.g. low hygroscopicity for prolonged
period of time) were found to exist mainly for solid ammonium poly-
phosphates having a low content of polymeric phosphate in the range
of 20 to 30% which result in poorly stable solutions.
According to U.S. patent 3,171.733 a new composition of matter
of ammonium polyphosphate is described. The composition consists of
about 50% by wt. monoammonium orthophosphate, at least 38% tetra-
ammonium pyrophosphate and at least 2% higher ammonium polyphosphate
polymers. It is claimed that the composition contains a total plant-
food content in the range of about 73% to about 82% by weight. In
U.S. patent 3,264.085 a similar composition is described consisting
of 14 to 16% monoammonium orthophosphate, 76 to 84% ammonium pyro-
phosphate and 2 to 8% of more highly condensed acyclic ammonium
polyphosphates from the group comprising ammonium tripolyphosphate
through ammonium nonpolyphosphate. New composition of matter of
long chain ammonium polyphosphates having a lower water solubility
are described in U.S. patent 3~342~579~ It is claimed that these
s products were found to be stable at room temperature even at high
humidity. l`he product may be varied to comprise monoammonium
orthophosphate, diammonium orthophosphate, triammonium pyrophosphate,
tetraammonium pyrophosphate and mixtures thereof, wherein the weight
ratio of N:P205 is between 0~26 to 0~475~ According to U.S. patent
3~733~191 a process is disclosed for the manufacturing of ammonium
polyphosphate comprising ammonium pyrophosphate, ammonium tripoly-
phosphate and higher acyclic ammonium polyphosphates by a vigorous
mechanical agitation of a~nonia and phosphoric acid, maintaining a
relatively small negative pressure in the reactor. It is claimed
that a simultaneously ammoniating,dehydrating and condensing occurs
in a single operation. The vigorous mixing is mentioned to eliminate
areas of over-ammoniation with excessive temperature thus resulting
in a product wherein essentially all the P205 is in an available form.
In accordance with U.S. patent No. 3J533~737J precipitated ammonium
20 polyphosphate is obtained at atmospheric pressure from polyphosphoric
acid and an aqueous ammoniating solution at temperatures below 70Co
The product contains most of the P205 as diammonium ortho- and tetra
ammonium pyrophosphate and is claimed to have good handling and
storage properties.
In spite of the large number of references dealing with ammonium
polyphosphates, it seems that there is still required an improved
solid ammonium polyphosphate product which should be instantly soluble
and free-flowing under any conditions, answering the needs of the
agricultural consumer for a solid vehicle to be transported in the
most efficient form. It is the object of the present invention to
provide a solid ammonium polyphosphate product which has improved
properties. It is another object of the present invention to provide
a solid ammonium polyphosphate product which is instantly soluble and
produces concentrated limpid fertilizer solutions. It is yet another
object of the present invention to provide a solid ammonium poly-
phosphate product, starting even with the common wet process phos-
phoric acid, thereby eliminating a prior purification step. It is
still another object of the present invention to provide a simple
method for the manufacture of an instantly soluble solid ammonium
47~0
polyphosphate product having improved properties. Thus the invention
consists of a n0w composition of instantly soluble ammonium poly-
phosphate which is obtained by reacting anhydrous ammonia with phos-
phoric acid, being characterized by the fact that the new composition
comprises diammonium pyrophosphate in orthorombic form and monoammonium
ortho-phosphate as main components, being substantially free of tri-
ammonium pyrophosphate and diammonium ortho-phosphate, the equivalent
ratio in the solid product between the nitrogen and P2O5, taking into
account the other ions, being substantially 1:1, said compositions
being characterized by a powder X'ray pattern obtained under conditions
where CuKa is equal to 1.5405, said pattern being as follows:
d I d
1.6.29 33 6. 5.32 100
2.5.64 100 7. 3.75 64
3.4.51 36 8. 3.075 89
4.3.53 92 9. 3.065 75
S.3.15 93 10. 2.66 18
It has surprisingly been found that the instantly soluble
ammonium polyphosphate composition comprising diammonium pyrophosphate
in the orthorombic form and monoammonium phosphate as the major
constituents and being substantially free of high acyclic polymers,
has improved properties being non-hygroscopic for prolonged period
of time even at high relative humidity. The ratio between the P2O5
in di = onium pyrophosphate and monoammonium phosphate constituents,
may be up to 4 to 1 and even higher and therefore the composition
will possess a relatively high concentration of polyphosphate moiety
(commonly referred to as poly content). It has also been found that
the small amounts of sulfate ion present in the wet process phosphoric
acid which are converted to diammonium sulfate do not affect the
excellent physical characteristics of the ammonium polyphosphate
composition according to the present invention. Therefore it will be
possible to utilize wet process phosphoric acid which always contains
some SO4 ions for the manufacture of the instantly soluble ammonium
polyphosphate composition, without any prior purification.
.
47~
The starting phosphoric acid may be from any known source such
as thermal phosphorus, solvent extraction process or even common wet
process acid. In the latter case a prior concentration is generally
required in order to obtain a P205 concentration of above 55%.
The main structural characteristics of the new ammonium poly-
phosphate according to the present invention are the relatively high
concentration in the polymeric phosphate contentJ mainly of the
diammonium pyrophosphate in the orthorombic form, while at the same
time being substantially free of highly condensed phosphate moietiesO
As known when wet process phosphoric acid is concentrated beyond 65%
P205, the various forms such as pyro, tripoly and more highly
condensed phosphoric acid may appear and their concentrations may
increase with the increase in concentration of the acid.
The stability of the diammonium pyrophosphate in the orthorombic
form, is completely unexpected, in view of the review of ammonium
polyphosphates given in J. Agr. Food Chem. ~Vol. 13, No. 4, 1965,
page 318), in which it is stipulated that the orthorombic form alters
rapidly to the monoclinic dimorph species.
One of the features which enables to obtain the solid ammonium
polyphosphate with the imprcved properties, according to the present
invention is to maintain the temperature in the ammoniation reactor
not above 330C. This temperature can be regulated only by controlling
the rates of the reactants as well as the concentration of the phos-
phoric acid, in view of the highly exothermic reaction of ammonia and
phosphoric acid. In case of a prior preheating of the phosphoric acid
feed, which may be desirable for a further increase in the poly
content, the preheating temperature should generally not surpass 150C.
One of the physical properties which illustrates the i~proved
properties of the instantly soluble ammonium polyphosphate composition
according to the present invention is its non-hygroscopicity. The
products obtained were found to persist in their free-flowing form
for prolonged periods of time, even at high relative humidity atmos-
phere. This would ensure an easy handling transportation and storage.
It has been discovered according to the present invention, that this
property of humidity absorption is correlated to the equivalent ratio
of nitrogen to phosphorus (N/P205) in the composition.
~1~347~C)
-- 6 --
In Figure 1 appended to the specification, two graphs are given
which show the dependency at equilibrium of humidity absorption by
the ammonium polyphosphate composition at two levels of relative
humidity (71% and 81%) as a function of the equivalent N/P ratio.
Thus we can see that when this ratio is substantially 1, the humidity
absorbed by the ammonium polyphosphate composition is very low being
in the range of 1-5% while when the ratio increases to 1.1-1.2 the
humidity absorbed is rather high reaching values of about 14 to 23%.
It should be mentioned that this dependency persists independently of
the source of phosphoric acid ~purified by solvent extraction or wet
process acid). The equivalent required ratio N/P of about 1 taking
into account the other ions present, can be maintained by a proper
treatment (so called disengagement) of the melt resulting from the
reactionJ wherein the excess of ammonia and water produced in the
condensation, are expelled.
The new composition of instantly soluble ammonium polyphosphate
can be also represented by its particular X'ray diffraction pattern
which is distinctly different than the pattern for the other known
forms of ammonium polyphosphate. All the X'ray measurements
described below were performed under conditions where Cu Ka is equal .
to 1.5405 A. In the following Table 1 are given the X'ray diffraction
data of a typical instantly soluble ammonium polyphosphate product
obtained according to the present invention from phosphoric acid
(produced by solvent extraction) and anhydrous ammonia:
TABLE 1
d I d
1. 6.29 33 6. 5.32 100
2. 5.64 100 7. 3.75 64
3. 4.51 36 8. 3.075 89
4. 3.53 92 9. 3.065 75
s. 3.15 93 10. 2.66 18
(The complete pattern contains also other lines of lesser intensity).
The pattern lines 1-5 are substantially the same as those of di-
ammonium pyrophosphate (as given in the Card 20-86, ASTM - 1974)
whereas the pattern lines 6-10 are substantially the same as those
of monoammonium orthophosphate (as given in the card 61-21,ASTM-1974).
7~0
Measurements on X'ray carried out with a conunercial ammonium
polyphosphate available on the market, show the presence of triammonium
pyrophosphate and diammonium orthophosphate monoclinic along the
monoammonium orthophosphate. The pattern lines of the first two
components are given in the following Table 2:
TABLE 2
d I d
1.9.82 29 6. 7.27 71
2.6.28 30 7. 5.57 58
3.5.43 100 8. 3.67 100
4.4.93 84 9. 3.07 52
5.3.24 69 10. 2.49 29
The complete pattern contains also other lines of lesser intensity.
The pattern lines 1-5 are substantially the same as those of tri-
ammonium pyrophosphate (as given in the card 20-87, ASTM - 1974)
whereas the pattern lines 6-10 are substantially the same as those
of diammonium pyrophosphate monoclinic (as given in the card 20-85,
ASTM - 1974),
- Some amorphous forms were also found along the above crystal-
line form in the new ammonium polyphosphate composition, their
presence being in particular noticed when wet process phosphoric
acid was utilized. The diffraction patterns of monoammonium ortho-
phosphate were the same as lines 6-lO given in Table 1, whereas the
diffraction patterns of diammonium pyrophosphate (when wet process
phosphoric acid was utilized) are given in the Table 3 below:
TABLE 3
_ I d I_
1. 6.29 27 3. 3~53 55
2. 5.64 100 4. 3.15 47
(The complete pattern contains also other lines of lesser intensity).
47~0
As we can see from Table 3 the diffraction patterns of diammonium
pyrophosphate are substantially the same to those obtained when
phosphoric acid obtained by solvent extraction was utilized~ Some
slight deviations can be observed in their intensity~ but this should
be obvious to occur in an impure starting material such as wet process
phosphoric acid.
In the following Table 4 are given typical compositions of the
instantly soluble ammonium polyphosphate prepared according to the
present invention which were obtained from phosphoric acid:
(1) produced by solvent extraction and ~2) produced by wet process
(using sulfuric acid):
TABLE 4
Source
of Phos- Analysis of Ammonium Polyphosphate
phoric __ _ _ _ . _
acid % diammonium % mono- % P205 % poly- ~ N % (NH ) SO,
phyrophos- ammonium content 4 2 -~
phate ortho- (from
(orthorombic phosphate total
+ amorphous) (Total) P20
_ _ 5
1. Solvent
extrac-
tion 71.1 25.7 65.0 75 12.5
2. Wet
process 62.5 29.1 61.7 70 12.8 5
(The products contained also small amounts of pyrophosphates and ortho-
phosphates of cations present as impurities in the acid).
We can observe from the above compositions the very high content
of polymeric phosphate in the products obtained according to the
present invention.
The ammonium polyphosphate composition obtained according to
the present invention is characterized by its high nutrient content.
Furthermore, in view of its high content of polymeric phosphateJ it
has a very low freezing point (below minus 10~.) so that no danger
of crystallization during storage would exist even in cold climate.
47~0
Instant liquid fertilizers solutions can be obtained free of
troublesome sludges. This is in view of the sequestering property
of the high content of polyphosphate in the new composition. The
product has been found to pGssess excellent physical properties
being characterized by its non-hygroscopicity property even at
relative high humidity. This enables its free-flowing easy handling
and storage for prolonged period of time. When the phosphoric acid
would contain relatively high amounts of magnesium, its prior
removal would be desirable, since as known the magnesium pyro-
phosphate has rather hygroscopic properties.
The ammonium polyphosphate composition can be mixed andgranulated with other known fertilizers such as potassium nitrate,
urea, ammonium nitrate, thus obtaining a broad range of NPK products.
Also various microelements at appropriate levels can be incorporated
in the ammonium polyphosphate composition.
The method for carrying out the manufacture of the new
composition of ammonium polyphGsphate according to the present
invention is very simple. Whereas as known the reaction between
ammonia and phosphoric acid is very rapid and exothermic, a simple
tubular reactor so called "Tee" mixer may be utilized. The reaction
temperature in the mixer is regulated not to surpass 330C and
preferable in the range between about 270 to 310C. This can be
accomplished according to the rates of the continuous feeding of
the reagents as well as the concentration of phosphoric acid.
Preferably the phosphoric acid is preheated prior to be introduced
into the reaction zone. The temperature in the preheating stage
should not surpass 150C in order not to generate high polyphosphoric
species. In the reaction zone, two reactions take place: neutrali-
zation and polymeriæation, the first generating the necessary heat
for effecting the second. The melt product issuing from the exit of
the reactor, passes to a disengagement vessel provided with a mixer
wherein ammonia and air at a proper rate are introduced, thus
controlling to obtain a solidified product with the desired equi-
valent ratio of N:P. As mentioned above the ammonium polyphosphate
can be mixed with other fertilizer or micronutrients and the solid
product being further easily granulated.
7~
- 10 -
According to one embodiment of the method, the wet process
phosphoric acid can be used such as without an intermediate step
of concentrating. The required concentration is achieved by
utilizing the free heat of ammoniation, simultaneously with a
partial ammoniation by the excess of unreacted ammonia from the
disengagement vessel, in a reactor - scrubber vessel.
The reaction between the ammonia and phosphoric acid may be
carried out either in a two stage process or in a one stage process
as known in the art. The two stages process is self-contained,
wherein in the first stage a partial ammoniation occurs utilizing
the excess of ammonia from the second stage. The one stage -
process will be more suitable for integration in a fertilizer
plant, turning the excess of ammonia into other desirable compounds
e.g. ammonium sulfate.
One of the important features required in the ammonium poly-
phosphate production is the vigorous mixing in the ammoniation
reaction. It has already been found that the "Tee" reactor is one
of the simplest suggestions which indeed gave good results, the
excellent mixing provided by this type of reactor being well known,
being also characterized by its short retention time. It seems
that the vigorous mixing enables to achieve a simultaneous ammoni-
ation and condensation for formation of the polyphosphate species,
and eliminates areas of over ammoniation with the accompanying
excessive temperature. As mentioned in the prior art it is
preferred to use the "Tee" reactor in a vertical position in order
to prevent channelling of NH3 past the fluid melt.
The hot liquid mass fromthe "Tee" reactor enters in a separate
vessel for disengaging water vapour and excess ammonia entrapped in
the heavy viscous melt of ammonium polyphosphate so as to obtain the
right N:P ratio. The melt is further conveyed, generally by over-
flow, to a final vessel wherein the melt is solidified. As known in
the art the solidification of a melt can be more easily accomplished
with a system containing minimum components. Thus, when pure phos-
phoric acid will be utilized in the reaction with ammonia, the solid-
ification of ammonium polyphosphate will be more easily achievedthan with wet process phosphoric acid. The solution which was found
347~0
- 11
in order to obtain solid product even with arl impure ammonium poly-
phosphate obtained from wet process phosphoric acid, is to mix
vigorously the molten mass together with recycled final solid product.
Although the output energy provided to the molten mass may be varied
in a very bToad range depending on the degree of impurities present
in the phosphoric acid, it has been found that the solidification
would be most easily accomplished when the energy output pro~ided
by the mixer will be at least 0.002 Kwh/Kg melt. As could be expected,
an easier solidification would also be manifested by a clear picture
of the X'ray patterns of the crystalline orthorombic diammonium
pyrophosphate. The dry solid product can be easily granulated,
either alone or admixed with other common fertilizers.
In order to further illustrate the nature of this invention and
the manner of practising it, the following Examples are pTesented
for clearness of understanding only and no limitation should be
understood therefrom.
Example 1
An amount of 2500 kg per hour of phosphoric acid (produced by
solvent extraction) was fed continuously into a "Tee" reactor together
with 500 kg/hr of gaseous ammonia. The composition of the phosphoric
acid was as follows:
68% P2o5 33 ppm Mg
0.63% Fe 395 ppm Zn
700 ppm Ca 395 ppm Na
49 ppm K
The phosphoric acid was preheated to about 80C prior to its
entering into the"Tee"reactor. The temperature in . e"Tee"reactor
was about 310C. The melt issued from the"Tee"reactor was poured
into a disengagement vessel and further conveyed c-) a mixer vessel
wherein recycled product was also introduced. White granulated
ammonium polyphosphate containing 65% P205 ~total) and 12.5~ N was
obtained. It was fount that 75% of the total P205 was in a poly-
phosphate form. The ratio N:P was about 0.975. The composition
of the product was 71.1% ammonium pyrophosphate orthorombic and
.~
- 12 -
amorphous and 25.7% monoammonium orthophosphate. The final product was
free-flowing and did not absorb humidity even after storage for
prolonged period of time. The X'ray diffraction patterns is given in
Table 1 in the present specification.
Example 2
An amount of 2250 kg/hr of wet process phosphoric acid was fed
continuously into a "Tee" reactor together with 500 kg/hr of gaseous
ammonia. The composition of the phosphoric acid was as follows:
61.9 % P205 0.6 % Mg 22.1 ppm Ca
1() 3.8 % S04 0.3 % Al 70 ppm Cu
0.18% F 0.11% Na 510 ppm Zn
0.57% Fe
The phosphoric acid was preheated to about 100C prior to its
entering into the "Tee" reactor. The temperature in the"Tee''reactor
lS was about 320C. After about 2 minutes residence time the melt issued
from the"Tee"reactor was poured into a disengagement vessel where it
was vigorously mixed (420 rpm, output energy of the mixer 0.5 HP/l).
The composition of the product was as follows:
62.5% diammonium pyTophosphate (orthorombic and amorphous)
29.1% mono a onium orthophosphate
5 % ammonium sulfate
The product contained 61.7% P205 (total) and 12.8% N. It was
found that about 70% of the total P205 was in a polyphosphate form.
The ratio N:P was about 1.05. The product was granulated using
recycled end product obtained in a previous cycle. The final product
had a greenish colour and was free-flowing. The X'ray diffraction
pattern is given in Table 3 in the present specification.
Example 3
The wet process phosphoric acid utilized in this experiment had
the following composition:
55 % P205 0.53% Mg 20 ppm Ca
3.4% S04 0.27% Al 62 ppm Cu
0.16% F 0.10% Na 450 ppm Zn
0.51% Fe
.
7~0
An amount of 2500 kg~hr o the acid preheated to about 100C was
introduced continuously at the top of an absorption column, counter-
currently to a stream of gases resulting from the neutralization of
a mixture of monoammonium orthophosphate and phosphoric acid with
gaseous ammonia. The stream of gases contained 99 kg/hr of free
ammonia. A mixture of monoammonium orthophosphate, ammonium poly-
phosphate and concentrated phosphoric acid resulted at the bottom
of the column and having a temperature of about 160C was fed into
a "Tee" reactor together with 359 kg/hr of gaseous ammonia. The
temperature in the "I`ee"reactor was about 270 C. After a residence
time of about 2 minutes, the melt resulted was poured to a disengage-
ment vessel where it was vigorously mixed (420 rpm, output energy of
the mixer 0.5 HP/l). The composition of the product was as follows:
53.0% diammonium pyrophosphate (orthorombic and amorphous).
38.3% monoammonium orthophosphate
5.0% ammonium sulfate
The ammonium polyphosphate product contained 61% P205 (total) and
12.7% N. It was found that about 60% of the total P205 was in a poly-
phosphate form. The ratio N:P was about 1.06 The product was
granulated using recycled end product obtained in a previous experiment~
The final product had the same appearance as in Example 2 and its X'ray
diffraction pattern as given in Table 3 in the present specification