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Патент USA US2412607

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Patented Dec. 17, 1946
Henry V. Farr, Ferguson, Mo., and John R.
Ruho?, Bronxville, N. Y., assignors to Mallin
ckrodt Chemical Works, St. Louis, Mo., a cor
poration of Missouri
No Drawing. Application October 21, 1943,
I Serial No. 507,178
7 Claims.
(Cl. 23-115)
This invention relates to ammonium thio
sulfate, and more particularly to methods for
the preparation of this compound.
Among the objects of this invention are the
provision of an improved method for the prepara
tion of ammonium thiosulfate; the provision of
an improved method for preparing ammonium
thiosulfate in crystalline form; the provision of
an improved method for the provision of a stable
will not undergo decomposition under ap
propriate storage conditions.
Ammonium thiosulfate is prepared in accord
ance with the present invention by the reaction
ammonium thiosulfate solution; the preparation
of anhydrous ammonium thiosulfate; the prepa
ration of anhydrous ammonium thiosulfate in
stable form; and the provision of anhydrous
ammonium thiosulfate and ammonium thiosul
fate‘ solutions, bothcf which are stable and do
not decompose under appropriate conditions‘of
storage. Other objects will be in Part obvious
and in part pointed out hereinafter.
The invention accordingly comprises the steps
of ammonium sul?te and sulfur in the presence
of sul?de ions. The probable course of the re
action is as follows when ammonium sul?de is
(NH4)2SOa+S —'—_> (N?dzszos
Ammonium sul?te may be prepared by any
convenient means, such as by the reaction of
sulfur dioxide with ammonia in the presence of
water to produce ammonium sul?te solution.
' Where ammonium thiosulfate has in the past
been prepared by the reaction of ammonium
sul?te and sulfur, the reaction has not pro
ceeded smoothly. The reaction is extremely slow,
and apparently requires conditions of tempera
and sequence of steps, and features of manipu 20 ture and concentration which make it economi
lation, which will be exempli?ed in the methods
cally unfeasible. It has been found, however,
and products hereinafter described, and the scope
that where, as in the present invention, the re
of the application of which will be indicated in
action is carried out in the presence of sul?de
the following claims.
ions, the reaction itself takes place easily in a
comparatively short time interval and may be
,. Ammonium thiosulfate has long been known
to be awsuperior photographic ?xing agent. It
carried out at a wide range of temperatures.
Since, as indicated in the foregoing reaction, the
ammonium sul?de is not consumed by the re
sodium thiosulfate, the customarily employed ?x 30 action, only a relatively small proportion is re
quired. The ammonium sul?de apparently acts
ing agent. Ammonium thiosulfate, however, has
as a carrier or solubilizer for the sulfur which
not been widely used because it has been ex
reacts with the ammonium sul?te to form am
pensive to produce and because a product su?i
ciently free from impurities for photographic use
monium thiosulfate.
The above reaction is, however, preferably car
has not been available. Such small quantities 35
ried out by keeping the reaction temperature
of ammonium thiosulfate as have been used have
low, and by having present in the reaction mix
customarily been marketed in the form of a con
ture an excess of ammonium hydroxide. The
centrated solution, chie?y because economical
reaction is preferably carried out between sulfur,
methods of preparing a stable crystalline product,
particularly one in the anhydrous state, have not 40 ammonium sul?de and ammonium sul?te in the
presence of such an amount of ammonium hy
been known. The transportation of a solution
droxide that the ?nal reaction solution is about
is difiicult because it has, in the case of am
1N in ammonium hydroxide. Ammonium sul?de
monium thiosulfate, been shipped in glass car
is preferably employed to provide the sul?de ions,
boys, which adds greatly to the cost because the
carboys themselves are expensive and must be 45 since it does not introduce an undesired cation.
Other sul?des could be substituted but would in
shipped back to the manufacturer when empty.
e?ect contaminate the reaction product. The
This greatly increases transportation costs.
reaction is preferably carried out at a tempera
It has now been found that in accordance with
ture of from 30 to 55° C.
the present invention, ammonium thiosulfate can
At the end of the reaction, ‘the liquors con
be easily and economically prepared as a product 50
tain ammonium hydroxide, ammonium sul?de
of great purity, and that it may, if desired, be
or polysul?de, and excess sulfur, in addition to
made in the iormof an anhydrous crystalline
the ammonium thiosulfate product, the am
solid. The ammonium thiosulfate prepared in
monium sul?te, having been substantially com
accordance with the present invention, either in
has the advantage that it will ?x the photo
graphic image at a much more rapid rate than
the‘form of a solution or as a solid, is stable and 55 pletely converted to the thiosulfate.
The am
monium thiosulfate could be isolated directly
proves the stability of the ammonium thiosulfate,
and also aids in the subsequent drying step. The
from this solution. However, from an economic
viewpoint it is preferable to treat the solution
so that more ammonium thiosulfate is formed at
the expense of the impurities present in the
reaction solution. This is accomplished by the
careful addition of ammonium bisul?te solution
to the reaction mixture. This addition neutral
ammonium sul?te need not be present in the
mother liquor, but the salt can be washed with
ammonium sul?te solution if it is desired to
introduce additional proportions of ammonium
sul?te to stabilize the drying step.
The factors pointed out above for the evapora
tion of ammonium thiosulfate solutions also
sul?te, and the ammonium sul?te is converted to 10 apply to the drying of moist crystalline am
monium thiosulfate. Ammonium thiosulfate is
ammonium thiosulfate by reaction with the am
not a stable product, and dissociates substan
monium sul?de remaining in the solution. Neu
tially over normal drying temperature ranges.
tralization of the ammonia favors the reaction of
It has been customary therefore, where such
the ammonium sul?de and the ammonium sul?te,
which may thereby be made to take place readily 15 drying has been carried out, to effect it in a
izes the excess ammonia to form ammonium
and substantially completely.
By proper selec
tion of the reaction conditions and concentra
tions, and by careful addition of the ammonium
vacuum over a drying agent, such as sulfuric
acid, and at a temperature of about room tem
bisul?te, the ?nal solution will contain " insig
In accordance with the present invention it
ni?cant amounts of ammonium sul?de, am
20 has been found that ammonium thiosulfate can
be dried at temperatures above those at which
monia, and ammonium sul?te, when considered
decomposition would ordinarily occur, if am
in the light of commercial speci?cations for am
monia is present in suf?cient quantity in the
monium thiosulfate. The percentages may be of
atmosphere in the drying chamber. The higher
the order of from O to 1% ammonium sul?de,
from 0 to 1.5% ammonia, and from 0.5 to 1% 25 the temperature of drying, the greater the pro
portion of ammonia which must be present in
ammonium sulfite.
the atmosphere in order to prevent the dissocia
The solution may contain a small amount- of
tion of the ammonium thiosulfate. We believe
colloidal sulfur, and is preferably therefore ?l
that the partial pressure of the ammonia present
tered, with or without a prior adjustment by
the addition of ammonium bisul?te. At this 30 must be at least as great as the dissociation
pressure of the ammonium thiosulfate at the tem
point a controlled amount of ammonium hy
perature of treatment in order to prevent dis
droxide is preferably also added to aid in the
sociation of the ammonium thiosulfate. As long
preservation and stabilization of the ammonium
as the ammonia is present to at least this ex
thiosulfate. The ?ltered solution is hen ready
tent, the ammonium thiosulfate will dry with
for sale as such, or may be used as feed for .
out decomposition. However, whatever the cor
the evaporator if crystalline anhydrous am
rect explanation may be, this drying may be
monium thiosulfate is desired.
carried out at atmospheric pressures, or under
Ammonium thiosulfate solutions are unstable
vacuum, or by placing the thiosulfate in a cabi
in the presence of heat, and concentration of
such solutions has in the past been carried out 40 net containing trays of a drying agent, such
as calcium oxide or merely in an ordinary heated
usually at temperatures in the neighborhood of
pipe drier, provided always that su?icient am
30° C. by operation under a high vacuum.
monia is present in the atmosphere.
It has been found, however, that in accord~
In all of the above processes in which ammonia
ance with the present invention, ammonium
is employed, the ammonia. is of course preferably
thiosulfate solutions can be concentrated at at
recovered from the moisture-laden atmosphere
mospheric pressure if this is carried out in the
removed from the concentrating or drying cham
presence of ammonia, or of ammonium sul?te
or both.
Pressures below atmospheric may be
employed if desired, but this is not necessary.
The following description is given by way of
Ammonium thiosuliate solutions may thus be
concentrated under atmospheric pressure by
heating and simultaneously blowing ammonia
example to indicate one form in which the in
vention can be carried out:
In general, ammonium thiosulfate is prefer
mixture, allowing the mixture to stir for about
1800 pounds of water, 2890 pounds of am
monium white and 140 pounds of 28% ammo
gas into the solution. The ammonia is recovered
nium hydroxide solution are placed in a tank of
from the vapors. If ammonium sul?te is pres
560 gallons capacity equipped with an agitator.
ent, the solution can be heated to a higher tem
90 pounds of ammonium sul?de solution of 40%
perature and hence less ammonia is required to
concentration and 800 pounds of sulfur are then
evaporate the same quantity of water, and the
added, and the mixture is vigorously agitated.
higher the percentage of ammonium sul?te, the
The temperature at which this agitation takes
hotter the solution can be heated. Ammonium
sul?te is not essential, and the evaporation can 60 place may vary over fairly wide limits, but it
is preferred to maintain the temperature between
be carried out with ammonia alone in the sub
30 and 50° C. As the agitation proceeds the
stantially complete absence of ammonium suliite
liquid gradually turns yellow due to the forma
if desired.
tion of ammonium polysul?de, and the appear
If the concentration is carried out under re
ance of this yellow color indicates that the main
duced pressure, a smaller proportion of ammonia
reaction is terminated since the ammonium poly
is required. The lower the pressure, the less
sul?de can only form after the ammonium sul?te
ammonia will be necessary. Likewise, if am
has been completely converted to ammonium
monium sul?te is present, less gaseous ammonia
thiosulfate. With the agitation continuing, am
is needed. Aqueous ammonia may be substituted
for gaseous ammonia, but in this event more 70 monium bisul?te solution of any suitable con
centration, but preferably of about 66% strength,
water will have to be evaporated, although the
is then added in small portions to the reaction
concentration can be carried out.
ably crystallized from liquors containing of the
10. minutes between each addition.
order of 3% of ammonium sul?te. This'im
tion mixture is tested from time to time for the
The reac
absence of sul?te ions, and the presence of sul
?de ions. This is simply accomplished by allow
containing eiiiuent vapors from the drying
chamber through a scrubbing tower, or by any
ing the reaction mixture to stir for a time and
other convenient means.
observing whether the yellow color reappears.
The reappearance of the yellow color indicates
obtained is substantially stable over an inde?
absence of sul?te, and also presence of ammonium
sul?de. The total acidity of the solution is also
nitely long period of time, when stored in gas
tight containers. If stored in ammonia-tight
periodically checked to determine the amount
of excess ammonium hydroxide. When the point
containers containing an atmosphere of am
The anhydrous ammonium thiosulfate thus
monia the anhydrous salt is substantially free
is ?nally reached at which the addition of a small 10 from any tendency to decompose.
It has been found in addition that the solution
of ammonium thiosulfate is likewise stable, and
may be stored for extended periods. The solution,
test is shown to be free from sul?de, the reac
if this is the desired ?nal form, is preferably con
tion is considered to be completed.
This solution is then ?ltered through a ?lter 15 centrated to contain 60% of ammonium thio'sul
amount of ammonium bisul?te gives a perma
nently water white solution which by additional
press in order to remove such excess sulfur and
colloidal sulfur as may be present, and dis
charged into a second tank. At this point su?i
fate. Such a 60% solution will not deposit crys
tals unless it is subjected to low temperatures, and
is quickly and easily mixed with other ingredi
ents to form a photographic ?xing bath, for ex
remove from the solution all of the remaining 20 ample.
Attention is directed to our copending applica
sul?de ion, and during this stage a slight amount
of colloidal sulfur may precipitate out. Am
tion, Serial No. 666,811, ?led May 2, 1946.
monium hydroxide is then added to preserve and
In view of the above, it will be seen that the
several objects of the invention are achieved and
stabilize the ammonium thiosulfate. The amount
other advantageous results attained.
to be added at this point is largely optional,
As many changes could be made in the above
but suf?cient to produce a solution of about pH 8
cient ammonium sul?te is added to completely
is preferred.
The solution is again ?ltered
through a ?lter press to remove any solid ma
terial, and is then ready for sale as such, or is
suitable for feed to the evaporator.
About 400 gals. of 60% ammonium thiosulfate
solution are placed in a 500 gal. stainless steel
tank equipped with a stainless steel internal heat
ing coil and a stainless steel agitator. The liquor
methods and products Without departing from
the scope of the invention, it is intended that all
matter contained in the above description shall
be interpreted as illustrative and not in a lim
iting sense.
We claim:
1. The method of concentrating ammonium
thiosulfate solutions which comprises evaporat
is agitated to avoid local overheating and is heated
ing such solutions in contact with ammonia.
as rapidly as possible. When the temperature
2. The method of concentrating ammonium
reaches about 80° C‘. anhydrous ammonia is
thiosulfate solutions which comprises evaporat
bubbled into the solution through a stainless steel
ing said solution in contact with ammonia and
tube extending nearly to the bottom of the tank.
ammonium sul?te.
The solution is heated to approximately 105° C. 40
3. The method of dehydrating ammonium
and the anhydrous ammonia is bubbled in at the
thiosulfate which comprises evaporating water
rate of approximately 1 lb. per hour. After about
from hydrous ammonium thiosulfate in contact
3 hours the rate of addition of ammonia is in
creased to about 11/2-2 lbs. per hour. The
with gaseous ammonia.
temperature is not allowed to exceed 105° 0. Gen
erally 6 or 7 hours evaporation will concentrate
the solution to such an extent that crystals of
ammonium thiosulfate will separate from it on
cooling. The concentrated solution is then ?l
thiosulfate which comprises evaporating Water
from hydrous ammonium thiosulfate in contact
4. The method of dehydrating ammonium
with gaseous ammonia at a partial pressure at
least equal to the dissociation pressure of the
ammonium thiosulfate under the dehydration
tered while still hot and permitted to crystallize. 50 conditions.
The crystals are separated from the liquors by
5. The method of making stable anhydrous
any convenient means. In the moist state the
ammonium thiosulfate which comprises mixing
crystals are subject to accelerated rates of de
ammonium vsul?te and sulfur in the presence of
composition and should preferably be exposed to
a substantial proportion of ammonium sul?de
air as short a time as possible.
55 and of ammonium hydroxide, neutralizing the re
The mother liquors from the crystallization may
sulting solution with ammonium bisul?te and
be returned to the evaporator and again con
evaporating the resulting solution in the pres
centrated to yield further crops of ammonium
ence of ammonia and ammonium sul?te.
6. The method of dehydrating ammonium
thiosulfate, or, if desirable, they can be mixed
with fresh feed solution prior to evaporation.
60 thiosulfate crystals which contain water, which
Drying the moist ammonium thiosulfate crys
comprises evaporating water from said crystals
tals may be accomplished following conventional
in contact with gaseous ammonia from an out
drying practices, if, as has been pointed out, salt
side source.
7. The method of dehydrating ammonium
is maintained in an ammonia-containing atmos
phere throughout the drying operation. We have 65 thiosulfate crystals which contain water, which
comprises evaporating water from said crystals
found it convenient to place trays of ammonium
thiosulfate in a drying chamber, gradually heat
ing the chamber to a temperature in the neigh
borhood of 50° C. while continually passing a
stream of gaseous ammonia into the chamber 70
during the drying operation. The ammonia may
be recovered by passing the moist, ammonia
in contact with gaseous ammonia from an out
side source at a partial pressure at least equal
to the dissociation pressure of ammonium thio
sulfate under the dehydration conditions.
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