Note: Descriptions are shown in the official language in which they were submitted.
'7~
This invention relates to the prod~lction of ~erki-
lisers and is particularly concerned with the production o~
potassium dihydrogen phosphate and/or soluble polym~rised
forms of this sal~. These materials are of great value
as sources of both potassium and phosphor~us and can be used
as fertilisers directly o~ together with other components.
Potassium dihydrogen phosphate can be obtained by
the reaction of phosphoric acid with potassium chloride
according to the well-known reaction:
KCl + H3PO4 ~ KH2PO4 + HCl
The removal of the hydrogen chloride quantitatively from
the reaction mass is extremely difficult in practice, unless
high temperatures or a large excess of phosphoric acid
are used. In the former case, the water-insoluble potas-
sium metaphosphate is preferentially formed and, in the
latter case, the isolation of the s~lt from the acid is
difficult and expensive in practice.
According to our invention we provide a process for
the production of potassium phosphate or polyphosphate in
which potassium chloride and phosphoric acid or a poly-
phosphoric acid are reacted together in a molar ratio of
1.25:1 inclusive and the entire reaction being at a
temperature in the range of 220 C. to 250~C" air being
blown through the reaction mixture to facilitate the
removal of hydrochloric acid and either cooling the
reaction product to form a glass-like solid with a'
chloride content of less than 1.5% and a free acid
content of less than.l5% P205 or hydrol.~sing the
reaction product by heating with water an~ recovering
the hydrolysis product as a crystalli.ne solid.
- 2 -
s&~
The preferre~ n,~lar ratio of pho~phoru~ to potas3ium
i~ sub~tantially l.l:l.
The resulting reaction product is itself a valuable
fertiliser product which may be used without further treat-
ment. Alternatively, the reaction product may be hydrolysed
by heating with water at temperatures in the neighbourhood
of 100 C., e.g. 100-120 C the product of hydrolysis being
thereafter recovered. The reaction product when cooled
is a glass-like solid which dissolves in water to give
~olutions of high analysis which can be used for the
production of liquid fertili~ers. The hydrolysis product
can be recovered as a crystalline solid and can likewise
be dissolved in water for the produckion of liquid
fertilizers.
The phosphoric acid employed in this reaction is
normally commercial phosphoric acid containing from 50 to
54~ P2O5. We may, however, use instead as the phosphoric
acid reactant dehydrated commercial phosphoric acid con-
taining more than 54% and less than 75% of P205.
;) In general, phosphoric acid with a P205 content in
the range of from 30% to 75% may be used.
Liquid fertilisers with a very low chloride content
may be manufactured by dissolving the hydrolysed product
in water or alternatively in an ammonia solution or by
forming a solution of the reaction product of the hydro-
lysis product in water and khereafter passing gaseous
ammonia through the solution.
The process of the invention involves the production
of pota3sium dihydrogen pho3phate and polymer3 of this
~0 salt by the reaction of phosphoric acid with pota3sium
chloride accordlng to the well-known reaction:
D
: . .
`-`` 10~8582
KCl + H3PO4 -~ KH2PO4 + HCl
Dehydration of the orthophosphate takes place at the
elevated temperature to yield pyrophosphate and higher
polymeric phosphates. The temperature of reaction
(220-250C) is sufficiently low however, to avoid the
formation of insoluble metaphosphate.
We have found in accordance with our invention that
the removal of chloride from the reaction mass can be
easily and effectively carried out with stoichiometric or
near stoichiometric quantities of reagents, the P to K mol
ratio varying from 1.0 : 1 to 1.25:1 without the use of
very high temperatures or large excesses of acid, by
sparging the reaction mass with air.
The process of the invention has the advantage o
avoiding the preferential formation of water insoluble
metaphosphate and also the difficult and expensive
isolation of the desired potassium dihydrogen phosphate
salt from large excesses of accompanying acid.
2~
~.,
' .
.
~785~Z
The phosphoric acid employed may be the we-t process
phosphoric acid of commerce with potassium pentoxide
content in the range of from 30 to 54% or it may be
dehydr~ted phosphoric acid with a P205 content of
substantially 75~, or the superphosphoric acid of
commerce or various other grades of phosphoric acid
which are commercially available.
The resulting glass-like product is a polymerised
mixture of phosphates with a small amount of free acid
present varying from 5% to 15~ P205 depending on the
relative quantities o~ acid and potassium chloride used,
which can be ground up to yield fertiliser material of
high P205 and K20 analyses or dissolved in water to
yield a liquid fertiliser of high analysis and low
chloride content.
The mass is hydrolysed by heating with water at
temperatures of substantially the boiling point of water
so as to yield the solid potassium dihydrogen phosphate
product. This product can be dried to yield a friable
-powder or dissolved in water to yield a liquid fertiliser
of high analysis containing potassium and phosphate with ~-
a very low chloride content.
According to one embodiment of the process according
to the invention, the reaction product is recovered as a
glass-like solid with a chloride content of less than 1.5
and a free acid content of less than 15~ P205.
Factors whic~ affect the chloride content of the
product are the reaction temperature and the ratlo of
phosphoric acid to potash. Other reaction conditions which
influence the chloride content are the reaction time and
1C~';'8~i~Z
the air sparging of the reaction mass as illustrated
in the following Examples 3 and 2 respectively. Thus
in the following Example 1, a product having a chloride
content of below 1.5~ could be obtained if the mole ratio
of P to K was raised above 1.1, or if the temperature
was raised above 250C, or if the residence time was
increased.
The solution of either the reaction or hydrolysis
product can be ammoniated to give a stable solution with
analyses for N, P and K which are much higher than it has
been possible to achieve up to now with commercial materials.
We have found that although high analysis solutions
can be obtained with the hydrolysed product, whiah is
an orthophosphate, solutions having even higher
- .
~ . .
.. ..
- ~0'785~
analyses can be obtained by dissolving the polytler~c reaction
product in water. The reaction ~roduct is therefore a u~eul
material for the production of llquid fertilisers. For those
purposes in which handling and transport of the product is necessary
or in which a solid product is required the hydrolysed product is
advantageously used.
An apparatus which may be used ~or carrying out the
process according to the invention is described with reference
~ to the accompanying flow-sheet of a process for making potassium
phosphate from muriate of potash.
The apparatus shown in the drawing comprlses a reactor
3 which is fed with phosphoric acid from a storage vessel 1 and
muriate of potash from a storage vessel 2. Air is fed in at 12.
Hydrochloric acid together with some water vapour is evolved at `
4. The product of the reactor 3 may be ~ed to a hydration
apparatus 5 where it is mixed with water from a conduit 6. The
hydrated product from the hydration apparatus 5 is fed to a `
drying unit 7 and thence to storage 8.
Alternatively, the product from the reactor 3 may be fed
2Q to a cooler 9 and thence to a crusher 10 from which is passed to
storage 11.
According to another modification, the product from
reactor 3 goes to a second reactor where it is again treated with
air. The product from the second reactor then continues on the same
paths described above.
- 7 -
': . ' ,
3S8~
EX~PLE 1
Fertiliser yrade potassium chloride (Muriate of
Potash 60~ K20) was fed at a constant rate 11800 g/hr) with
phosphoric acid to an air sparyed reactor maintained at
250C. The ratio o~ phosphoric acid to potash in the
feeds was suc'n as to give a reactor product containing
1.10 ~oles P per mole K. The reactor was sparged with
air at the rate of 15 litres/minute, The product from
this reactor was allowed to flow con-tinuously to a second
reactor where the temperature was 250 C. and the air sparging
rate was again 15 litres/min. The resulting product was
analysed at intervals and contained an average free acid
content, expressed as P205 of 7.7% and an average chloride
content of 1.5%. The average analysis was:
54.5% total P205 32.6~ total K20 48.5% sol. P205
29.4% sol. K20
The reactor product was divided into two streams,
one of which was chilled, crushed and bagged. The other
stream was heated with water at 110C. for 2i hours to
hydrolyse the phosphates and the hydrolysed product was
cooled, vacuum dried and stored. The hydrolysed product
had an analysis of 49.2% total P20~, 29.4% total K20.
The glass like reactor product and the hydrolysed
product were dissolved in water and saturated solu-tions at
20C. obtained. The saturated solutions had potassium
analyses given below:
Reactor product solution (~K20) 1~.5
Hydrolysed product solution (%IC20) 7.9
,~
. i : - .
)78SBZ
EX~PLE 2
Fertiliser yrade potassium chloride (Muriate of
Potash 60% K20) ~00 g was reacted at 220C. wi-th stirring
with wet process phosphoric acid (~S2 g) which had been
heated to 250C. and concentrated to 58.8% P205. This
corresponds to a mole ratio of P to K of 1.4 to 1Ø
When the evolution of hydrochloric acid ilad ceased the
reaction mass was divided into two p~rts and each part
heated at 220C. for 120 mlnutes. One portion was
sparged with air through a glass tube. The other portion
was unsparged. The reaction mass was analysed as
follows:
Air Sparged Unsparged
Residual chloride %Cl 1.64 3.21
Total P205~ 55.6 54.5
Total K20~ 26.4 25.9
EX~'~PLE 3
Fertiliser grade potassium chloride (Muriate
of Potash 60% K20)200 g was reacted at 220C. with
stirring with wet process phosphoric acid 356 g which had
been concentrated to 58.8% P205. This is equal to a mole
ratio of P to K of l.l to 1Ø- When the evolution of
hydrochloric acid gas had ceased, as indicated by
the cessation of effervescence, the mixture was
sparged with air and the temperature maintained at
220C. Samples were removed for chloride analysis at
intervals. The results of these analyses are yiven below:
Time after cessation
of effervescence (mins) 120 1~0 2~0 300
Residual chloride % Cl 6.56 ~.g6 3.5~ 2.6
The analysis of ~he final product was Total P205% 53.1
Total K20~ 31.9
g _
:
:'. ,:,
.
The glass-like reaction product and
the hydrolysis product thereof may be ammoniated to
produce products with valuable K, N, P contents.
Thus, for example, 150 ml of a 20% aqueous ammonia
solution was mixed with 203 g of reactor product. The
resulting solution containing 4.2~N, 33~ P205 and
17.8% K20 was formulated as a valuable fertiliser.
-- 10 --
.
. . . :
.
