Note: Descriptions are shown in the official language in which they were submitted.
CA 02239253 1998-10-02
TflANSLATION OF PCT APPLICATION AS FILED (18 PAGES)
1
PREPARATION OF AQUEOUS SOLUTIONS
OF FREE HYDROXYLAMIHE
The present invention relates to a process for the preparation of
aqueous solutions of free hydroxylamine.
Hydroxylamine is an important intermediate for the chemical
industry. However, particular caution is required in handling it
because it irritates the eyes, the skin and the mucous membranes
and can cause allergies. In particular, however, it is thermally
unstable, ie. it decomposes slowly to explosively, especially in
the presence of metal ions, in a basic medium in relatively high
concentration, and at relatively high temperatures.
Hydroxylamine is produced on a large industrial scale as
hydroxylammonium salt, usually as hydroxylammonium sulfate, and
is also used as such. Frequently, however, it is necessary to use
a highly concentrated salt-free aqueous solution of free
hydroxylamine. In order to avoid the abovementioned problems and
in particular the instability of the hydroxylamine, those skilled
in the art have avoided the use of traditional methods of
large-scale chemistry for concentrating distillable substances,
for example distillation, in the recovery of salt-free
hydroxylamine solutions. The distillation of hydroxylamine, even
on the laboratory scale, is even said to be a particularly
dangerous operation; cf. Roth-Weller: Gefahrliche Chemische
Reaktionen, Stoffinformationen Hydroxylamin, page 3, 1984, 2,
Ecomed-Verlag. The distillation of hydroxylamine on an industrial
scale has therefore also never been considered in technical
publications. Instead, special methods have been used, although
all of them have serious disadvantages.
Attempts were thus made to isolate free hydroxylamine from
aqueous salt solutions with the aid of ion exchangers; cf., for
example, US-A-4,147,623, EP-A-1787, EP-A-237052 and Z. Anorg. Ch.
288, 28-35 (1956). However, such a process leads only to dilute
solutions with low space-time yields. Moreover, hydroxylamine
reacts with many ion exchangers or is decomposed by them.
A further method comprises the electrodialysis of an aqueous
hydroxylammonium salt solution in electrolysis cells with
semipermeable membranes, as described, for example, in
DE-A-33 47 259, JP-A-123771 and JP-A-123772. However, such a
process is technically complicated and expensive and has to date
not become established in industry.
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2
DE-A-35 28 463 discloses the preparation of free hydroxylamine
from hydroxylammonium sulfate by treatment with calcium oxide,
strontium oxide or barium oxide and removal of the insoluble
alkaline earth metal sulfates. In this method, the removal of the
sulfates obtained in finely divided form presents considerable
difficulties. In addition, only dilute solutions are obtained
and, when calcium oxide or calcium hydroxide is used, free
hydroxylamine still contains undesirably large amounts of ions
owing to the relatively good solubility of the calcium sulfate.
I0 When strontium compounds and barium compounds are used, the
relatively high price and especially the toxicity are moreover
disadvantages with regard to an industrial production process.
DE-A-12 47 282 describes a process in which alcoholic solutions
of free hydroxylamine are obtained by reacting hydroxylammonium
sulfate with ammonia in alcohol as a solvent and removing the
ammonium sulfate. A similar process is described in EP-A-108 294.
However, alcoholic solutions are unsuitable and undesirable for a
number of applications. For example, particular precautions must
be taken during the handling of such solutions, owing to their
flammability. Furthermore, the alcohol used must as a rule be
recovered by an expensive procedure, since the discharge of
relatively large amounts of alcohol into waste water treatment
plants or into outfalls is prohibited.
Finally, DE-A-36 01 803 describes a process for obtaining aqueous
solutions of free hydroxylamine, in which hydroxylammonium
sulfate is reacted with ammonia in lower alcohols, the
precipitated ammonium sulfate is separated off, water is added to
the alcoholic solution of free hydroxylamine and the alcohol is
distilled off from the solution thus obtained. The abovementioned
disadvantages of working with alcohol are applicable to this
process too. Moreover, owing to the instability of the
hydroxylamine in conjunction with the flammability of the
alcohols, particular caution is required in the final
distillation stage. Common to all prior art processes is that
they are not suitable for being carried out on an industrial
scale or give rise to uneconomically high additional safety
costs.
For the decomposition of hydroxylamine, a temperature above 65'C
is regarded as <:ritical. In a differential thermal analysis, the
onset temperature of a 50% strength by weight aqueous
hydroxylamine solution (in a glass crucible) was determined as
70~C. The amount of heat liberated, vie. about 2.2 kJ/g of 50%
strength by weight solution, confirms the high thermal potential
of the material. Differential thermal analysis is a
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3
microthermoanalytical method which is employed for screening to
estimate the thermal stability and the thermal potential. The
onset temperature is the lowest ambient temperature at which a
noticeable exothermic reaction proceeds in the sample at a
heating rate of 1 K/min, commencing at 30°C. For safety reasons,
the processing temperature should be significantly below the
onset temperature.
In the context of the preparation of hydroxylamine nitrate,
US-A-4,956,168 describes the preparation of a slurry of
hydroxylamine sulfate in alcohol at a temperature which does not
exceed 65°C. This slurry is then treated with ammonia at <_ 65°C
to produce an alcoholic hydroxylamine solution.
US-A-5,472,679 describes a process for preparing an alcohol-free,
aqueous hydroxylamine solution by reacting a hydroxylamine
sulfate solution with a suitable base at up to about 60°C. The
mixture obtained is then subjected to distillation under reduced
pressure at below 65°C. This gives a solid residue (the salt
formed in the liberation of the hydroxylamine) and as distillate
an aqueous hydroxylamine solution containing 16-23% by weight of
hydroxylamine. This process has the disadvantage that it requires
working under reduced pressure and the temperature has to be
controlled carefully.
In addition, the process requires working with solids. In a
continuous process, the solid would accordingly have to be
removed continuously. This can present great problems in terms of
process technology if the solid is one which tends to cake, eg.
in the case of Na2S04xH20.
Furthermore, the "distillation" proceeds to dryness, more
correctly described as evaporation, such that the low-boiling
water evaporates first. The high-boiling hydroxylamine
accumulates. It is known that the decomposition tendency of
hydroxylamine increases with the concentration of hydroxylamine,
and together with it the losses of hydroxylamine during the
process. There is an increasing risk that, because of the high
concentration of hydroxylamine, explosive decomposition will
occur. It is known that pure hydroxylamine or hydroxylamine > 70%
by weight decomposes explosively. Thus, appropriate safety
requirements must be fulfilled f~~r the process mentioned.
Finally, the remaining solid still contains residues of
hydroxylamine (hydroxylamine adsorbed on the surface,
hydroxylamine in interstitial spaces in the solid). The solid
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4
therefore has to be decontaminated in a separate disposal
process.
It has now surprisingly been found that the hydroxylamine
solution obtained after partial or complete liberation of
hydroxylamine from a hydroxylammonium salt in an aqueous phase
cam be separated into an aqueous hydroxylamine fraction and a
salt fraction by treatment with Water or steam at.above 65~C,
without noticeable decomposition of the hydroxylamine occurring.
The present invention therefore relates to a process for the
preparation of an aqueous solution of free hydroxylamine, in
which
a) a hydroxylammoniurn salt is treated with a suitable base in
water,
b) any insoluble components are separated off from the solution
obtained,
c) the solution obtained in stage (a) or stage (b) is separated
into an aqueous hydroxylamine fraction and a salt fraction by
treatment with water or steam at ? 80~C, and
d) if desired, the aqueous hydroxylamine solution obtained is
concentrated by distillation.
Stage (a) of the novel process is carried out in a conventional
manner. Hydroxylamrnoniurn salts generally used are the
hydroxyl-ammonium salts of mineral acids, for example of sulfuric
acid, phosphoric acid or hydrochloric acid, usually in aqueous
solution. The hydroxylammonium salt is reacted with a suitable
inorganic base, for example ammonia, sodium hydroxide, potassium
hydroxide or calcium hydroxide, in aqueous solution. The amount
of the base is chosen so that the hydraxylammonium salt is
converted completely or at least partially into free
hydroxylarnine. This may be carried out continuously or batchwise
and at from about 0 to 100~C. The resulting aqueous solution
contains free hydroxyl-amine and the salt which originates from
the base cation and the anion present in the hydroxylammonium
s-alt.
More specifically, the present invention relates to a process for the
preparation
of an aqueous solution of free hydroxylamine, wherein
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4a
a) a hydroxylammonium salt is treated with a suitable base in water,
b) any insoluble components are separated off from the solution
obtained,
c) the solution obtained in stage (b) is separated into an aqueous
hydroxylamine fraction and a salt fraction by passing water or
steam countercurrently into the bottom of the column and with the
aid of a stripping column at a temperature of >_ 80°C.
Depending bn the type arid concentration of the hydroxylammoniurn
salt, the base used for liberating the hydroxylamine and the
temperature at which the reaction is carried out, some of the
salt formed may be precipitated. If necessary, the solution may
also be cooled in order to precipitate a relatively large amount
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of the salt. If such insoluble components, ie. salt precipitates,
are present, they are advantageously separated off in a
conventional manner before stage (c). Depending on the process
conditions, for example with the use of ammonia as the base or
5 the use of sodium hydroxide as the base and relatively low
concentration of the reactants, no precipitate is formed and
stage (b) can therefore be dispensed with.
The separation (stage c)) of the solution obtained from stage (a)
or stage (b) into an aqueous hydroxylamine solution and a salt
fraction is preferably carried out by treatment with water or
steam in a stripping column. This is a conventional plate column,
eg. bubble tray column or sieve plate column, or is provided with
a.conventional packing, for example Raschig rings, Pall rings,
saddle elements, etc., and preferably has from 5 to 70
theoretical plates. The stabilized solution, to which further
stabilizer may, if required, be added, is fed directly to the top
of the column (upper part of the packing or uppermost plate).
In the stripping column, the solution is separated in such a way
that the salt fraction is taken off at the bottom of the column
and an aqueous hydroxylamine solution is taken off at the height
of the feed plate or above it, in particular via the top. In
order to achieve this, it is preferable to treat the solution by
passing water and/or steam countercurrent into the bottom of the
column. At a hydroxylamine concentration of from 5 to 45% by
weight in the feed solution, the flow rate of water or steam is
generally from 1 to 8, in particular from 1 to 5, times the feed
rate. The temperature of the water or steam introduced is in
general from 80 to 180'C. If required, the bottom of the column is
additionally heated.
The pressure in the stripping column is in general from 5 to
300 kPa (from 0.05 to 3 bar), preferably from 50 to 300 kPa (from
0.5 to 3 bar). It is particularly preferable to operate the
stripping column at from 50 to 150 kPa (from 0.5 to 1.5 bar).
The temperatures prevailing at the top of the stripping column
depend on the pressure at which the column is operated. They are
in general 80-130'C, preferably 90-120'C. The temperature of the
steam passed in can be significantly higher, eg. 150'C. However,
it should advantageously not be so high that too much water is
also vaporized from the salt solution and the salt begins to
precipitate in the bottom of the column.
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6
The aqueous (vaporous or liquid) hydroxylamine fraction taken off
via the top of the stripping column usually contains 10-200 g of
hydroxylamine/1 and may, if desired (stage d), be concentrated in
one or more stages which differ from one another in their
operating pressure. Advantageously, a conventional packed column
containing the abovementioned packings or a suitable plate column
or another apparatus suitable for distillation is used. A column
having from 4 to 20 theoretical plates is preferred.
In general, the distillation column is operated at from 1 to
200 kPa (from 0.01 to 2 bar), preferably from 5 to 120 kPa (from
0.05 to 1.2 bar), particularly preferably from 30 to 110 kPa
(from 0.1 to 1.1 bar). The higher the intended final
ccncentration of hydroxylamine, the gentler (low pressure and low
temperature) the distillation must be. The distillation may be
carried out continuously or batchwise.
The water taken off via the top of the distillation column can be
recirculated as stripping steam to the stripping column or can be
conveyed as wastewater to wastewater treatment.
If desired, a droplet precipitator (demister) is additionally
installed above the feed plate or in the vapor take-off in such a
way that entrainment of the salt by droplets is prevented.
In a particularly preferred embodiment, stripping of the
hydroxylamine from the salt solution and partial concentration of
the hydroxylarnine solution are carried out in only one column,
ie. a stripping/distillation column. Water is distilled off via
the top and the concentrated hydroxylamine solution is removed
about 1 to 3 plates above the feed of the
hydroxylamine-containing salt solution from stage (a) or stage
(b). The salt solution is fed in roughly in the middle of the
column (about 5-30 theoretical plates above the bottom). The
hydroxylamine-free salt fraction is taken off at the bottom of
the column. The number of theoretical plates of the
stripping/distillation column is in general from 10 to 50 and the
reflux ratio is adjusted so that it is from 0.5 to 3. Otherwise,
the stripping/distillation column is operated as described above.
In a further preferred embodiment, stripping of the hydroxylamine
from the salt solution and partial concentration of the
hydroxylarnine solution are carried out in the above
stripping/distillation column with an inserted dividing wall. As
described above, water is distilled off via the top and the
hydroxylamine-free salt fraction is taken off at the bottom. The
hydroxylamine-containing salt solution is fed in, as described,
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roughly in the middle of the column (about 5-30 theoretical
plates above the bottom). At the height of this feed, a dividing
wall is mounted in the column over a height of from 1 to 10,
preferably from 1 to 5, theoretical plates, so that the column is
divided vertically into two separate sections, the feed taking
place roughly in the middle of the dividing wall. The solution
enriched in hydroxyl-amine can thus be removed in salt-free form
in the region of the dividing wall, on the side opposite the feed
point. The dividing wall separates the removal point from the
feed point. However, identical concentrations of hydroxylamine
are present on both sides of the dividing wall, but salt is
present in the solution only on the feed point side. The
salt-free solution enriched with hydroxylamine can be removed
within the height of the dividing wall, at the height of maximum
concentration of the hydroxyl-amine, preferably at the height of
the feed or, if required, slightly below. Otherwise, the
stripping/distillation column having a dividing wall is operated
as described above.
Alternatively to the embodiment with a dividing wall, it is also
possible to attach a side column to the stripping/distillation
column described above, in such a way that this side column is
connected on the gas and liquid side, above and below one or more
plates from the feed point, to the stripping/distillation column,
and the hydroxylamine-richer solution is removed via this side
column and the latter is designed so that passage of salt-
containing solution into the removal point of the side column is
avoided.
In order to keep the risk of decomposition of the hydroxylamine
very low, all solutions which contain free hydroxylamine are
stabilized by adding a decomposition stabilizer. Suitable
stabilizers are known, for example hydroxyquinaldines, such as
8-hydroxyquinaldine, flavones, such as morin, hydroxyquinolines,
such as 8-hydroxyquinoline, hydroxyanthraquinones, such as
quinalizarine, which are used, if desired, in combination with
polyhydroxy-
phenols, such as pyrogallol. Further suitable stabilizers are
benzonitrile, benzamidoxime, N-phenylthiourea, N-hydroxythiourea,
reductones and/or reductonates, for example 2,3-didehydro-
hexano-1,4-lactone, and alkali metal salts of ethylenediamine-
tetraacetic ac.~d. The concentration of stabilizers is
advantageously from 5 x 10-4 to I, in particular from 5 x 10-3 to
5 x 10-2, $ by weight, based on free hydroxylamine. Stabilizers
which have proven particularly useful are 8-hydroxyquinaldine,
8-hydroxyquinoline and also polyethylenimine or polypropylenimine
and compounds of the formula RlRzN-A-NR3,R4, where A is
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8
cycloalkylene or alkylene and R1 to R4 are, independently of one
another, CH2COOH or a benzyl radical which is unsubstituted or
substituted on the phenyl ring by OH, NH2 or COOH. Examples of
these compounds are trans-1,2-diaminocyclohexane-N,N,N',N'-
tetraacetic acid and N,N'-di(2-hydroxybenzyl)ethylene-
diamine-N, N'-diacetic acid.
The novel process has the advantage that it can be carried out in
a simple and gentle manner. The use of flammable substances and
working with solids containing free hydroxylamine can be avoided.
The concentration of hydroxylamine is low over the entire
process. For example, it is less than 45% by weight in the
solution obtained from stage (a) or (b) and less than 30, in
general less than 15, % by weight in the stripping column or
stripping/distillation column. Owing to the mode of operation of
the stripping column or stripping/distillation column, the liquid
hold-up is minimal and the residence time in the process is
relatively short. Moreover, the mode of operation of the
stripping column or stripping/distillation column makes it
possible to employ higher pressures, in particular atmospheric
pressure.
Higher hydroxylamine concentrations occur only during
concentration in the distillation column (stage d). The
hydroxylamine.concentration of the solution in stage d) can be
adjusted as desired, for example in the range from 20 to 70% by
weight. In order to reduce the risk of decomposition, further
stabilizer may additionally be introduced into the solution to be
distilled.
The apparatuses required for the novel process can be produced
from nonmetallic materials, such as glass, ceramic and plastics.
The decomposition initiated by metal ions is thus ruled out.
Surprisingly, it has been found that parts of the apparatuses may
also be produced from metallic materials without significantly
higher decomposition of the hydroxylamine being observed.
Owing to the simple but at the same time safe process design,
only a small capital cost is necessary for carrying out the novel
process on an industrial scale. Moreover, the process can be
scaled up virtually as desired.
The novel process is illustrated further with reference to the
flow charts shown in Figures 1 and 2:
In stage a), a suitable container 12, for exampple a stirred
vessel, a static mixer or a container equipped with a reaction
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9
mixing pump, is charged with hydroxylammonium salt or a
hydroxylammonium salt solution 3, the base 2 used and a
stabilizer 1 (cf. Figure. 1 and 2). Mixing results in an aqueous
solution 4 which contains free hydroxylamine and the salt which
originates from the base cation and the anion present in the
hydroxylammonium salt.
If insoluble components are present in the solution 4, these are
separated off in stage (b) with the aid of a filtration apparatus
13, the salt 11 and a solution 4' being obtained (cf. Figures 1
and 2).
If required, further stabilizer 1' is then added to the solution
4 or 4'. The separation into an aqueous hydroxylamine fraction
and a salt fraction is then carried out according to stage (c).
According to Figure 1, the separation is carried out in a
stripping column 14, the solution 4 or 4' being introduced at the
top of the column. For this purpose, steam 10 is passed into the
bottom of the column. The separation is effected in such a way
that the substantially hydroxylamine-free salt solution 5 is
taken off at the bottom of the column, and a salt-free aqueous
hydroxylamine fraction 6 (in vapor or liquid form) is taken off
via the top (heat exchangers 15 not described in more detail are
provided in each of stages (c) and (d)).
According to Figure 2, the solution 4' is fed into a
stripping/distillation column 16. The lower part of the column
consists of a stripping section 16' and the upper part of a
distillation section 16". The solution 4' is fed in between these
two sections, ie. at the top of the stripping section. The
separation in the stripping/distillation column 16 is effected in
such a way that the substantially hydroxylamine-free salt
solution 5 is taken off at the bottom of the column and
substantially hydroxylamine-free water 9 via the top. The
salt-free hydroxylamine solution 6 is removed via a side
take-off.
The hydroxylamine solution 6 obtained from stage (c) can, if
desired, be concentrated in a distillation column 18 (stage d).
Advantageously, further stabilizer 1" (Figures 1 and 2)
is added before the distillation. The hydroxylamine
solution 6 is fed in at about the height of theoretical plates 1
to 5 of the distillation column 18. In the distillation,
substantially hydroxylamine-free water 7 is obtained via the top,
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and a hydroxylamine solution 8 whose concentration is dependent
on the distillation conditions is obtained at the bottom.
In the examples which follow, all hydroxylamine-containing
5 solutions contain 0.01% by weight, based on free hydroxylamine,
of stabilizer, eg. 8-hydroxyquinoline, 8-hydroxyquinaldine,
trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid or a
branched polyethylenimine having a molecular weight of 800,
unless stated otherwise.
Example 1
Liberation of hvdroxylamine from.hydroxylammonium sulfate with
ammonia
538.3 g of hydroxylammonium sulfate, 330 g of water and 0.1 g of
8-hydroxyquinaldine as a stabilizer were initially taken in a
water-cooled glass 3 1 double-jacketed vessel having a stirrer.
446 g of 25% strength ammonia solution were slowly added dropwise
at room temperature while stirring. A clear solution containing
16.4% by weight of hydroxylamine was obtained.
Example 2
Liberation of hydroxylamine from hydroxylammonium sulfate with
sodium hydroxide solution
538.3 g of hydroxylammonium sulfate, 920 g of water and 0.1 g of
8-hydroxyquinaldine as a stabilizer were initially taken in a
water-cooled glass 3 1 double-jacketed vessel having a stirrer.
1008 g of 25% sodium hydroxide solution were slowly added
dropwise at room temperature while stirring. A clear solution
containing 8.4% by weight of hydroxylamine was obtained.
Example 3
Liberation of hydroxylamine from h~droxylammonium sulfate with
sodium hydroxide solution
1500 g/h of a 37% strength by weight hydroxylammonium sulfate
solution at 50~C together with the stoichiometric amount of 50%
strength by weight sodium hydroxide solution at room temperature
were introduced continuously into a glass stirred vessel having a
capacity of 100 ml. The required amount of stabilizer (600 ppm)
was dissolved in the sodium hydroxide solution. The reaction
volume in the stirred vessel was 70 ml, giving a calculated
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11
residence time of 2 minutes. The clear product solution at about
70'C was taken off continuously via an overflow. The sodium
sulfate formed remained in solution. The aqueous solution
obtained contained 11% by weight of HA, 23.6% by weight of sodium
sulfate and the required amount of stabilizer in the region of
100 ppm. A mass balance was carried out on the streams and no HA
decomposition was observed.
Example 4
Obtaininct an aqueous hydroxylamine ~ HA) solution from a hyd-
roxvlamine (HAl/ammonium sulfate (AS1 solution using a stripping
column
An aqueous solution containing 218 g of HA/1 and 680 g of AS/1
was added at a rate of 300 ml/h to the uppermost plate of a
stripping column. The glass stripping column having a height of
2 m and a diameter of 35 mm was filled with 3 mm glass Raschig
rings over a height of 1.8 m. 1000 ml/h of distilled water were
fed to the bottom of the column. The column was at 40 kPa. The
bottom temperature was 84~C. 1000 ml/h of aqueous, salt-free HA
solution containing 39.0 g of HA/h, corresponding to 59.6% of the
total HA in the feed, were distilled off via the top of the
column. 300 ml/h of ammonium sulfate solution containing 86.0 g/1
of HA were taken off from the bottom of the column. This
corresponds to 39.4% of the total HA in the feed.
The concentration of HA in the column was not more than i00 g/1.
The amount of liquid in the column was 20-225 ml, depending on
the loading. The residence time of the liquid in the column was
thus only 1.5-10 min. At this low concentration and within the
short time, the decomposition rate is low.
Further experiments are listed in the table below.
40
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12
Table 1
Separation of an acrueous HA solution from an agueous HAAS
solution.
Feed HA H20 Pres- Top HA via HA
con- steam sure tem- the in
tent pera- top the
ture bottoms
ml/h g/1 ml/h kPa C
g/1 (%) g/1 (%)
318 222 1156* 50.0 81.0 40.5 66.9 48.6 21.2
170 222 1060* 70.0 90.5 22.8 65.6 45.2 I7.2
370 219 1475" 100.4 100.9 32.4 62.2 75.6 47.8
179 105.5 1530" 100.8 100.6 9.0 70.5 29.0 27.6
245 220.0 1530" 100.8 100.6 28.0 73.3 54.0 42.2
150 4 990" 100.8 100.0 0.4 68.1 0.8 15.7
150 5.6 990" 100.8 99.9 0.6 73.0 0.4 5.6
119 204 1063" 101.5 100.4 15.4 67.6 40.5 19.7
* The bottom of the column Was heated by means of a thermostat.
" The water was fed in as superheated steam for simultaneous
heating of the bottom.
Example 5
Separation of an aqueous HA solution from an aqueous HA/Na2S04
solution using a stripping column
The aqueous solution from Example 3, containing 11% by weight of
HA and 23.6% by weight of Na2S04, was added at a rate of 978 g/h
to the uppermost plate of a stripping column. The enamel
stripping column having a height of 2 m and a diameter of 50 mm
was filled with 5 mm glass Raschig rings. The column was at
atmospheric pressure. Steam at 2.5 bar absolute was passed into
the bottom of the column. The steam/feed ratio was 2.9:1. 985 g/h
of sodium sulfate solution containing 1.7 g/1 of HA were taken
off from the bottom of the column. This corresponds to 1% of the
total HA in the feed. 3593 g/h of aqueous, salt-free solution
containing 36.8 g of HA/1, corresponding to 99.2% of the total HA
in the feed, were distilled off via the top of the column.
Further experiments are listed in the table below.
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13
Table 2:
Separation of an aqueous HA solution from an aqueous HA/sodium
sulfate solution
Feed HA Steam/ Pres- Top HA via HA
the in
bottoms
con- feed sure tem- top
tent pera-
ture
10g/h g/1 kg/kg kPa 'C g/1 (%) g/1 (%)
945 135 2.6 200 125.4 34.0 84.0 7.8 17
970 136 2.7 101 106.3 35.5 96.2 3.3 2.5
980 8.0 2.8 101 107.0 2.1 95.5 0.45 5.7
Example 6
Obtaining an aQUeous HA solution from an aaueous HA/sodium
sulfate solution using a striDpinc~/distillation column
An aqueous solution containing 221 g of HA/1 and 540 g of AS/1
was added at a rate of 202 ml/h to the llth plate of a glass
bubble tray column having a diameter of 35 mm, a total height of
1.6 m and 21 plates (lowermost plate = plate 1). 1300 ml/h of
steam (about 125~C) are fed to the bottom of the column. The
pressure in the column was 99 kPa. 180 mm/h of substantially
HA-free water (0.6 g of HA/1) were taken off at the top of the
column at a top temperature of 99.8~C and a reflux ratio of 1:3
(reflux:feed). The aqueous HA solution (product solution) was
taken off at a rate of 1180 ml/h and a concentration of 44 g/1
via a side stream from plate 12. 400 ml/h of salt solution were
taken off at the bottom of the column.
Example 7
Obtaining an aqueous HA solution from an aqueous HA/sodium
sulfate solution using a stripping/distillation column With
concentration via a side take-off
An aqueous HA solution as described in Example 3, containing 11%
by weight of HA and 23.6% by weight of Na2S04, was added to the
11th theoretical plate of a glass bubble tray column having a
diameter of 50 mm (number of pates corresponding to 30
theoretical plates). Steam at 2.5 bar absolute and about 125'C was
fed to the bottom of the column. The pressure in the column was
101 kPa. Substantially HA-free water (0.05 g of HA/1) were taken
off at the top of the column. The aqueous, salt-free HA solution
(product solution) was taken off at a concentration of 8.3% by
CA 02239253 1998-10-02
14
weight via a side stream from plate 12. The salt solution having
a residual HA content of 0.2% by weight was taken off at the
bottom of the column.
Example 8
Concentration of a salt-free aqueous hydroxylamine solution by
distillation
1600 g/h of an 8.3% strength by weight aqueous, salt-free,
stabilized hydroxylamine solution were fed continuously onto the
8th plate of a glass bubble tray column having a diameter of 50
mm and 30 bubble trays. A small amount of stabilizer dissolved in
hydroxylamine solution was additionally metered into the column
onto the uppermost plate, plate No. 30. The reflux ratio was set
to 0.5. Water was distilled off via the top of the column. The
distillate still contained a residual amount of hydroxylamine of
0.07% by weight. About 240 ml/h of a 50% strength by weight
hydroxylamine solution were discharged from the bottom of the
column via a pump.
30
40
