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Molecule
(10/ 39)
[5][_]
water
(15)
[6][_]
nitrate of ammonia
(8)
[7][_]
potassium
(4)
[8][_]
nitrate
(3)
[9][_]
ammonium chloride
(2)
[10][_]
chloride
(2)
[11][_]
mercury
(2)
[12][_]
NO3NiF4
(1)
[13][_]
ammonium nitrate
(1)
[14][_]
appa
(1)
[15][_]
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Physical
(15/ 23)
[16][_]
reduced pressure
(6)
[17][_]
700 mm
(3)
[18][_]
85 percent
(2)
[19][_]
0.5 percent
(1)
[20][_]
60 mm
(1)
[21][_]
680 mm
(1)
[22][_]
700mm
(1)
[23][_]
720 mm
(1)
[24][_]
83.3 percent
(1)
[25][_]
84 percent
(1)
[26][_]
86 percent
(1)
[27][_]
87 percent
(1)
[28][_]
88 percent
(1)
[29][_]
95 percent
(1)
[30][_]
atmospheric pressure
(1)
[31][_]
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Generic
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[32][_]
salt
(6)
[33][_]
salts
(5)
Publication
_________________________________________________________________
Number GB403240A
i»?
Title
_________________________________________________________________
EN Title Improvements relating to the crystallization of substances
that crystallize exothermically
Abstract
_________________________________________________________________
Substances which crystallize exothermically' e[[g]] ammonium nitrate
are crystallized from their hot solutions by applying and maintaining
a sufficiently reduced pressure to cause evaporation of the solvent,
resulting in saturation and consequently partial crystallisation of
the solution. The heat thus produced exothermically causes further
evaporation of the solvent followed by further crystallisation and the
cycle is repeated until complete crystallisation and desiccation are
obtained. Two or more such salts or a salt mixed with an insoluble
suspension may be crystallised in this manner. Specification 301,496,
[Class 32, Distilling and c.], is referred to.
Description
_________________________________________________________________
COMPLETE SPECIFICATION.
Improvements relating to the Crystallization of Substances that
Crystallize Exothermically.
We, APPAREILS ET EVAPORATEURS
KESTNER, a Body Corporate duly incorporated under the laws of France,
of 7, rue de Toul, Lille, France, (Nord), do hereby declare the nafure
of this inven tion and in what manner the same is to be performed, to
be particularly described and ascertained in and by the following
statement
This invention relates to the crystalliza tion of substances that
crystallize exothermically and has for its main object to fur- nish an
improved process whereby crystallization and -the elimination of
surplus
water
may be economically effected. The invention is
particularly applicable, though not confined, to nitrate of ammonia .
It has been proposed to crystallize solu tions by passing a solution
through a series of chambers in each of which the vacuum is
progressively increased, and thus to obtain the solution with the
crystals in suspension +herein.
It is known that, hitherto, in order to obtain a very dry product,
containing for example 0.5 percent of water , it was necessary to
start with a concentrated solution, in the case of nitrate of ammonia
say 95 percent
NO3NH4. This
pulverization
operation.
generally involved cry stallization accompanied by
in a chamber, and drying with hot air a very costly
Applicants previously effected appreci able economy by utilising the
exothermic heat of crystalliza-tion, or at least seme of it, to obtain
gratuitous evaporation of the latter percentages of water this pro
cess formed the subject of their British
Patent No. 301,496 dated 2nd December, 1927. Even in that case,
however. owing to the loss of calories by ventilation, it was
necessary to start with fairly concentrated solutions.
The present invention likewise utilises the heat of crystallization,
but in a more effective manner, thus permitting less concentrated
starting solutions to be employed, for example 85 percent NO2NIT4.
In
accordance
with the present invention an aqueous solution
containing a substance that crystallizes exothermically, and which may
be a solution of comparatively low concentration, has applied to it a
sulliciently reduced pressure (or strong vacuum) to cause evaporation
of water and consequent cooling of the liquid resulting in saturation
and
crystallization, whereupon the exothermically produced heat
eliminates further water , and so on to the extent. desired. By this
means practically complete crystallization and desiccation can be
obtained
even when starting with solutions of low degrees of
concentration.
The invention. is applicable to an aqueous solution containing one or
more salts alone or to such a solution containing also in suspensioa a
finely divided solid.
It will be appreciated that in carrying the invention into effect the
liquid, which is hot preferably from preliminary concentration, is
introduced into a crystallizer where the reduced pressure is applied
to cause the repetitious phenomenon of cooling by evaporation, and
crystallization disengaging a considerable number of calories causing
the further elimination of water , in such a way that substantially
all the heat of crystallization can be utilised in the elimination of
the remaining water .
By way of further explanation some
nitrate of ammonia will now be given:
data
respecting solutions of
The solution of nitrate of ammonia at a strength of 88 percent ' of
NO3NiF4 and an initial temperature of 1300 C. may be considered, and
this solution at atmospheric pressure has a boiling temperature of
1430 G., and under a vacuum of 700 mm .
(pressure of 60 mm .) of mercury , it has a boiling temperature of 770
C. When this solution has a vacuum of 700 mm . applied to it
evaporation takes place owing to the heat contained therein, and this
evaporation tends to lower the temperature-of the solution to that at
which it would boil under the chosen vacuum.
Owing to this evaporation, however, the strength of the solution is
increased, and consequently the temperature of crystallization which
was 87 for initial solution, is raised. Consequently when the pressure
is reduced saturation and the formation of salt resulte. From this
moment the temperature will tend to rise owing to the dis-engagement
of calories by exothermic crystallization, but rise of temperature is
not possible as long as there remains present -in the product water to
evaporate, since all calories added by crystallization cause fresh
departure of water by evaporation. In fact, under a given vacuum and
for a product in course of crystallization which still contains water
, there is produced a fised temperature of the medium; the water
remaining in the'product and moisteaing the formed crystals is present
in the state of a solution at a fixed strength corresponding to the
saturation point under the temperature determined by the vacuum.
As soon as all the water is evaporated, crystalization then taking
place is accompanied by a rise in the temperature anhydrous mass. The
final temperature of the product is however limited by the temperature
of fusion of the anhydrous - nitrate (1520 C.).
Applicants have determined the temperatures obtained under different
vacuums for solutions of nitrate of ammonia in the course of
crystallization and still containing water as follows:
For a vacuum of 720 mm . - - 62 C.
For a vacuum of 700 mm . - - 73 C.
For a vacumm of 680 mm . - - 84 C.
The precedent temperature are the minimum ones at which the anhydrous
products can be obtained. Graphe made by Applicants show that if for
example one employs a solution at:
83.3 percent at a temperature of 133 C.
84 percent at a temperature of 1240 C.
85 percent at a temperature of 113 C.
86 percent at a temperature of 100 C.
87 percent at a temperature of 90 C. there should be obtained by
crystalization under a vacuum of 700mm . of mercury and without any
addition of exterior heatm an anhydrous product at a final temperature
of 73.
While
the
present
process is very easily applicable to the
crystallization of nitrate of ammonia , it lends itself just as easly
to the crystallization of a mixture of ammonium chloride and of
nitrate of potassium or to a solution containing in suspension a salt
that is not itself dissolved in the solution, for example chloride of
potassium . A mixture of nitrate of ammonia and gypsum or of limestone
could likewise be crystallized by the present process. It is only
necessary that the solid insoluble substance should be contained in
the liquid in a finely divided or pulverized state and that the liquid
should be -a solution of a kind adapted to crystallize exothermically
and thus produce the calories necessary for the desired elimination of
the motherwaters.
The -process can, of course, be carried into effect in many different
ways and is not limited to any of them.
The
vacuum
or reduced pressure applied may 'be progressively
increased, or if de sired it may be increased stage by stage but in
any
case
it
is
desirable that the apparatus in which the
crystalization is effected should be furnished with an agitator or
stirrer.
Where it is desired to feed continuously the product or the muxtures
to be crystallized, pulverization tubes may be replaced by mechanical
means for pulverizing the product, such for example as a rotable disc
or a perforated scuttle rotating rapidly. In continuously working appa
ratus the concentrated liquid may be pulverized by any appropiate
means as above indicated in a chamber subjected to a strong vacuum. On
the other hand the -process may be operated in apparatus of the
dis-continuous kind, by introducking the liquid charge iby charge and
applying the vacuum progressively so iliat it attains its masimum
strength at the last stage of the crystal lization. Obyiously also any
desired apparatus may be provided adapted for continuous, stage bv
stage, or charge by charge operation and appropriate means may be
provided for applying and regulating the reduction of pressure as
desired.
The mode in which the vacuum is applied is immaterial in practice,
because the final result obtained is not dependent upon the pressures
intermediate between the initial one and the final reduced pressure .
Thus, the full vacuum desired may be applied at once, or on the
contrary if desired the vacuum could be increased pro gressively. In
either case the plant must comprise apparatus designed to create and
maintain the required vacuum, such as a pump.
Having now particularly described and ascertained the nature of our
said invention and in what manner the same is to be performed, we
declare that what we
Claims
_________________________________________________________________
claim is:
1. An improved process for the crystallization of substances that
crystallize exothermically which consists in applying a sufficiently
reduced pressure (or strong vacuum) to cause evaporation of water and
consequent
cooling
of the liquid resulting in saturation and
crystallization, the exothermically produced heat then eliminating
further water , and so on again and again, whereby practically
complete crystallization and desiccation can be obtained even when
starting with solutions of low degrees of concentration.
2. A process as claimed in claim 1, applied to the solution of a
single salt , such as nitrate of ammonia , to produce a very dry salt
.
3. A process as claimed in claim 1, applied to a solution of two or
more salts , such as ammonium chloride and nitrate of potassium , to
produce the salts in a very dry form.
4. A process as claimed in claim 1, applied to a solution of one or
more salts erystallizing exothermically and containing in suspension a
finely divided solid product, such as a salt insoluble in the
solution, for example chloride of potassium .
5. The substantially dried product of any of the preceding claims.
6. The improved process for the crystallization land dehydration of
solutions
containing substances that crystallize exothermieally,
substantially as hereinbefore described.
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