Note: Descriptions are shown in the official language in which they were submitted.
--` 1058830
FIELD OF THE INVENTION-
This invention relates to a method of efficiently
removing nitrogen oxides from a gas containing nitrogen
oxides, and more particularly to a method of removing
nitogen oxides from the gas efficiently in the form of a
solid salt of imidodisulfonic acid.
BACKGROUND OF THE INVENTION:
Examples of gases containing oxides of nitrogen
(hereinafter referred to as NOX) are exhaust gases from
combustion apparatuses such as boilers, nitric acid
manufacturing plants, various metal treating processes and
other nitrogen oxide generating plants.
In recent years, it is known that a so-called photo-
chemical smog is generated frequently. One of the main
causes of such photochemical smog is that a large quantity
of NOX is present in the atmosphere. There is, there-
fore, a great need to reduce the quantity of NOX
contained in such exhaust gases and/or to remove NOX
from such exhaust gases. -
In combustion apparatuses such as boilers, for
example, the NOX content in the exhaust gas has been
reduced conventionally by employment of burners and
furnaces of improved design. These methods, however, are
not very desirable because they allow the reduction of
NOX only within narrow limits for both theoretical and
economical reasons.
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1!--` -
`` 1058830
. .
In this connection, it is also well known in the art
to employ the so-called wet type processes, for the removal of
NOx contained in an exhaust gas, using an alkaline aqueous
solution including an aqueous solution of sodium hydroxide or
sodium sulfite; an aqueous solution of potassium permanganate;
an aqueous solution of hypochlorite or chlorite; or an aqueous
solution of ferrous salt and sulfurous acid alkali salt (alkali
sulfite). The present inventors disclosed in their copending
application Serial No.212,631. filed October 30 1974, as a new
wet type process, a method for removing nitrogen oxides from a
gas containing nitrogen oxides, which is characterized by bring-
ing the nitrogen oxides-containing gas into contact with an
aqueous solution containing an organic acid alkali salt and a
salt of metal selected from the group consisting of Fe, Co, Ni,
Cu and Mn in the presence of sulfurous acid alkali salt. In the
above-mentioned wet type processes, as a matter of fact, there
has been no established method for effectively treating an
absorption solution which has absorbed therein NOx and therefore,
there i~ a great need for a method which is more efficiently
capable of removing NOx from a gas containing NOx by effectively
treating the absorption solution.
It is therefore an object of the present invention to
provide a method of removing NO efflciently from a gas containin~ 1
. ,
1~58830
NOX in the wet pr~cess, by effectively treating an NOX-
absorbed solution for the removal therefrom of NOX in
the form of ammonium sulfate which is valuable as a
fertilizer.
The present inventors have found that when a nitrogen
oxides-containing gas is contacted with an aqueous
solution which contains a ferrous and a sulfurous acid
alkali salt, NOX are absorbed in the solution in the
form of an alkali salt of imidodisulfonic acid. They have
also found that the imidodisulfonic acid alkali salt can
be converted into ammonium sulfate by hydrolysis at a
temperature higher than 100C under an acidic range after
separation and recovery of.the salt from the absorption
solution.
Thus, according to the present invention, there is
provided a method of removing nitrogen oxides from a gas
containing nitrogen oxides in the form of ammonium
sulfate, comprising the ste~s of contacting a nitrogen
oxides-containing gas with an aqueous solution which
contains at least a ferrous salt and sulfurous acid alkali
salt to form therein an alkali salt of imidodisulfonic
acid by.absorption of said nitrogen oxides, and converting
said alkali salt of imidodisulfonic acid into ammonium
sulfate by hydrolysis at a temperature higher than 100C
after separation and recovery of said salt from said
solution.
The above and other objects, features and advantages
of the invention will become clear from the following
description and the claims.
D
1058830
DESCRIPTIOW OF THE PREFERRED EMBODIME~TS:
The aqueous solution referred to herein as containing
at least ferrous salt and sulfurous acid alkali salt is, for
example, (1) an aqueous solution which contains a ferrous salt
and a sulfurous acid alkali salt, (2) an aqueous solution which
contains a ferrous salt, an organic acid alkali salt and a
sulfurous acid alkali salt, (3) an aqueous solution which con-
tains a ferrous salt, an organic acid alkali salt, an organic
acid and a sulfurous acid alkali salt, (4) an aqueous solution
which contains a ferrous sait of organic acid and a sulfurous
acid alkali salt, or (5) an aqueous solution which contains a
ferrous salt of organic acid, an organic acid alkali salt, an
organic acid and a sulfurous acid alkali salt. Examples of the
ferrous salts include inorganic salts such as ferrous sulfate,
ferrous nitrate and ferrous chloride, and various water-soluble
ferrous salts of organic acids such as acetic acid, propionic
acid, butyric acid, malonic acid, succinic acid, ethylenediamine
tetracarboxylic acid and nitrilo-tricarboxylic acid. In this
connection, when an iron salt of ethylenediamine tetra-
carboxylic acid or nitrilo-tricarboxylic acid is used,
the iron salt may not be in the form of ferrous salt but may be
a ferric salt. More particularly, the ferric salt is easily
reduced into the form of ferrous salt by a coexisting sulfurous
acid alkali salt, forming an aqueous solution which contains
substantially a ferrous salt. The organic acid alkali salts are
. .
L ' ~ ..~
I ` 1058830
¦ water-soluble salts of organic acids, for example: salts of
organic acids with alkali metals such as Li, Na and K; salts of
organic acids with alkali earth metals such as Mg and Ca; or
ammonium salts of organic acids. The organic acids forming
S ¦ these organic acid alkali salts include, for example: monobasic
I acids such as acetic acid, propionic acid and butyric acid;
¦ dibasic acids such as malonic acid and succinic acid; polybasic
l acids such as ethylenediamine tetracarboxylic acid and nitrilo-
¦ tricarboxylic acid. A typical example of ethylenediamine
l tetracarboxylic acid is ethylenediamine tetraacetic acid (here-
¦ inafter referred to as EDTA) and a typical example of nitrilo-
¦ tricarboxylic acid is nitrilo-triacetic acid (hereinafter
¦ referred to as NTA). The carboxylic acids forming ethylenedi-
¦ amine tetracarboxylic acids and nitrilo-tricarboxylic acids may
~15 I be, for example, propionic acid, butylic acid or both of these
¦ acids. It should be understood, however, that the carboxylic
l acids are not limited only to these acids but other suitable
¦ acids may also be employed. The sulfurous acid aIkali salt is
¦ in the form of M2S03 or MHS03 (wherein, _ represents an alkali
l as in the organic acid alkali salt) and includes, for example,
¦ sodium sulfite, potassium sulfite, ammonium sulfite, sodium
¦ bisulfite, potassium bisulfite, ammonium bisulfite and the
¦ like.
~ ¦ It is assumed that, when an N0x-containing gas is
¦ contacted with an aqueous solution which contains at least
I . . `'
I ` - - 6 -
` 1~58~330
ferrous salt and sulfurous acid alkali salt as mentioned
hereinabove, the NOX and the ferrous salt form a complex
in the aqueous solution and the complex thus produced
forms an alkali salt of imidodisulfonic acid by reaction
with the sulfurous acid alkali salt, according to the
following reaction formulae (1) and (2) (where the ferrous
salt is represented by ferrous sulfate, NOX is rep-
resented by NO, and the sulfurous acid alkali salt is
represented by sodium sulfite, respectively).
FeSO4 + NO ) Fe(NO)SO4 . . . . . . . . . . (1)
Fe(NO)S04 + 2Na253 + 2H20 ~ Fe(OH)3 + Na2S04 ~ NH(S03Na)2
. . . . . . . . . . (2)
It will be clear from the foregoing reaction formulae
(l) and (2) that the absorption of NOX becomes difficult
with an insufficient amount of ferrous salt and that it
becomes difficult to satisfactorily produce the alkali
salt of imidodisulfonic acid with an insufficient amount
of sulfurous acid alkali salt. Therefore, the aqueous
solution should contain the ferrous salt and sulfurous
acid alkali salt in sufficient amounts. In the present
invention, the aqueous solution should contain the ferrous
salt in an amount, in terms of moles, equal to or greater
than the amount of NOX to be absorbed, preferably in an
amount at least 0.02% by weight. Moreover, the aqueous
solution to be employed in the present invention should
contain the sulfurous acid alkali salt in an amount, in
terms of moles, two times greater than that of the ferrous
salt, preferably in an amount at least 0.2% by weight. In
this connection, if the amount of sulfurous acid alkali
salt in the aqueous solution enhances, the alkali salt of
imidodisulfonic acid is produced in an increased amount.
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.. . . . .
1058830
When the content of the sulfurous acid alkali salt in the
aqueous solution is equal to or greater than 1~ by weight,
approximately 9Q% of the NOX which have been absorbed in
the solution is converted into alkali salt of imidodi-
sulfonic acid. In this manner, when the alkali salt of
imidodisulfonic acid is produced, a portion of the NOX
which is absorbed in the aqueous solution forms a nitrilo-
trisulfonic acid alkali salt (N(SO3MJ3) and a sulfamic
acid alkali salt (NH2SO3M). The thus formed nitrilo-
trisulfonic acid alkali salt and sulfamic acid alkali saltare converted easily into ammonium sulfate by hydrolysis
when the alkali salt of imidodisulfonic acid is hydrolyzed
as will be discussed hereinafter. Therefore, the
production of such nitrilo-trisulfonic acid alkali salt
and the sulfamic acid alkali salt can impose no adverse
ef f ects in the present invention.
It usually takes a relatively lon~ time for the NOX
- in the gas to produce an alkali salt of imidodisulfonic
acid after absorption in the aqueous solution. For
example, where the NOX are absorbed in the aqueous
solution at 55C and the absorption solution, which has
absorbed therein NOX, is left standing still at that
temperature, it usually takes 3 to 4 hours before a major
portion of the absorbed NOX is converted into an alkali
salt of imidodisulfonic acid. The reaction time is
reduced at a higher temperature level, for example, at
90C, 90~ of the absorbed NOX is converted into an
alkali salt of imidodisulfonic acid in 30 minutes. Thus,
it is desirable to heat the absorption solution for the
purpose of shortening the working time.
The alkali salt of imidodisulfonic acid thus formed in
,; .~
, ...
1058830
the absorption solution shows the least solubility when it
is in the form of potassium or calcium salt, allowing easy
separation from the absorption solution. Therefore, where
the aqueous soluti~n to be used for the absorption of
NOX contains a potassium salt as the sulfurous acid
alkali salt, the alkali salt of imidodisulfonic acid which
has been formed in the absorption solution is easily
caused to precipitate in the form of potassium salt for
separating purposes simply by condensing or cooling the
absorption solution. On the other hand, where the
potassium salt is not employed as the sulfurous acid
alkali salt in the aqueous solution, the alkali salt of
imidodisulfonic acid is also easily caused to precipitate
in the form of a potassium or calcium salt for separation
purposes simply by adding a potassium or calcium compound
such as potassium sulfate, potassium chloride, potassium
nitrate, calcium hydroxide, calcium carbonate, calcium
oxide, calcium chloride or the like to the resultant
absorption solution before condensation or cooling the
absorption solution. In case a potassium compound is
added to the absorption solution for separating the alkali
salt of imidodisulfonic acid in the form of potassium
salt, it is preferable to employ potassium sulfate as the
potassium compound. This is because potassium sulfate has
a relatively low solubility as compared with other
potassium co~pounds to allow easy recovery and cyclic
reuse. In case a calcium compound is added to the
absorption solution for separating the alkali salt of
imidodisulfonic acid in the form of calcium salt, it is
preferable to employ calcium hydroxide as the calcium
compound. This is because calcium hydroxide has a proper
_ g _
__ . . _ _. .. .... .. ... . .. . ~ . __ ; _ ... _ _ .
1058830
solubility as compared with other calcium compounds to
allow easly conversion of the alkali salt of imidodi-
sulfonic acid to calcium salt. Moreover, potassium sulfate
or calcium hydroxide is completely free from accumulation
of anions which occurs in the absorption solution when
. other potassium or calcium compound such as potassium
chloride, potassium nitrate or calcium chloride is used
while such anions do not exist originally in the absorption
solution. The filtrate obtained after separating the
imidodisulfonic acid alkali salt from the absorption
solution in the form of potassium or calcium salt may be
used again as the aqueous solution for the absorption of
NOX. In such a case, there occur no inconveniences even
if a portion of the alkali salt of imidodisulfonic acid
remains in the filtrate. When the alkali salt of imidodi-
sulfonic acid is formed in the absorption solution,
precipitation of a ferric salt (Fe(OH)3) takes place in
the absorption solution as shown by reaction formula (2)
above. It is therefore necessary to remove the ferric
salt by filtration from the absorption solution. Further-
more, in a case where the filtrate which has been obtained
after separating the alkali salt of imidodisulfonic acid
in the form of potassium or calcium salt is reused as an
aqueous solution for the absorption of NOX, it is
necessary to supplement the ferrous salt for the filtrate
in an amount suitable for compensating the loss. However,
this is not necessary when a polybasic acid such as EDTA
or NTA is contained in the ~queous solution to be used for
the absorption of NOX, since the ferric salt which has
been formed in the absorption solution and which has been
in the form of a complex based on the polybasic acid is
-- 10 --
lOS8830
easily reduced by the sulfurous acid alkali salt coexisting
in the absorption solution, without calling for the need
for the removal of the ferric salt nor the supplementation
of the ferrous salt. As a portion of the sulfite ions in
the NOx-absorbed solution (absorption solution) is
consumed by the production of the alkali salt of imidodi-
sulfonic acid, it is necessary to supplement the sulfite
ions to the filtrate which is obtained after separation of
the alkali salt of imidodisulfonic acid from the absorption
solution in the form of potassium or calcium salt, before
recirculating the filtrate as the aqueous solution for the
absorption~of NOX. However, where the gas under treat-
ment contains sulfur oxides along with NOX, the sulfur
oxides are also absorbed in the absorption solution
simultaneously with the NOX to produce sulfite ions in
the absorption solution. In such a case, the addition of
supplementary sulfite ions to the filtrate is not always
necessary.
The alkali salt of imidodisulfonic acid thus formed in
the absorption solution is, after separation therefrom,
hydrolyzed into ammonium sulfate in an acidic range,
preferably at a pH value of below 5Ø In this case, the
minimum pH value to be employed may be preferably
determined with due consideration to the relationship
between the velocity of hydrolyzation for the alkali salt
of imidodisulfonic acid and the quantity of an acid to be
consumed since a large amount of the acid is required with
the lowering of the pH value. The excess lowering of
below pH 1.5 cannot be expected ato bring about any effect
for promoting hydrolyzation. In this connection,
hydrolyzation of the alkali salt of imidodisulfonic acid
-- 11 --
D
~`1058830
is preferably performed at a pH value of from 5.0 to 1.5,
- and at a temperature higher than 100C. As shown by the
reaction formulae (3) and (4) given below, it is assumed
that the alkali salt of imidodisulfonic acid is firstly
converted into a sulfamic acid alkali salt (or sulfamic
acid), which is then converted into ammonium sulfate by
further hydrolysis.
2NH(S03M)2 + 2H2 t 2NH2SO3M + M2SO4 + H2 4
2 3M 2H20 ~ (NH4)2SO4 + M2SO4 ....................... (4)
(where M represents an alkali as mentioned hereinbefore).
The hydrolytic reaction of the alkali salt of imidodi-
sulfonic acid which has been formed in the absorption
solution does not proceed substantially to the stage as
shown by the reaction formula (4) at a temperature below
100C and, as a result, a sulfamic acid alkali salt or
sulfamic acid is produced in the solution. On the other
hand, when the reaction temperature is higher than 370C
which is almost at the level of the critical temperature
of water, the reaction does not occur because water can
not exist in the form of liquid. Therefore, in the
present invention, it is necessary to maintain the
hydrolytic temperature higher than 100C, preferably
within a range of from 110 to 200C. In this instance, as
mentioned hereinbefore, the absorption solution has formed
therein nitrilotrisulfonic acid alkali salt and sulfamic
acid alkali salt, which are also converted into ammonium
sulfate as shown by the following reaction formula (5) and
the afore-mentioned reaction formulae (3) and (4).
3 )3 2H2 ~~~ 2NH(SO3M)2 + M2S4 + H2S4 (5)
(where M represents an alkali as mentioned hereinbefore).
The hydrolyze-formed solution thus obtained which
contains ammonium sulfate is acidic due to the production
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~..,~'
lOS8830
o~ sulfuric acid, which, however, may be neutralized with use
of ammonia, thereby converting the sulfuric acid in the
hydrolyze-formed solution also into ammonium su}fate as shown
by the following reaction formula (6).
2H2S4 + 4NH3 --t 2 (N~4)2so4 ~ -----(6)
On the other hand, the hydrolyze-formed solution thus
obtained, which contains ammonium sulfate, may be alkalized,
for example, by addition of an alkaline substance such as
sodium hydroxide thereto, in order to generate ammonium gas
and recover same.
The thus obtained ammonium sulfate can be advan-
tageously used, for example, as a fertilizer, after
separation and recovery from the hydrolyze-formed solution.
The filtrate as obtained after recovery of the ammonium
sulfate may be used again to form potassium or calcium
imidodisulfonate. In this connection, where potassium
sulfate is added to the NOx-gas absorbed solution
~absorption solution) in order to produce the alkali salt of
imidodisulfonic acid in the form of potassium salt and the
thus produced potassium imidodi- sulfonate is hydrolyzed
-after separation from the solution, the hydrolyze-formed
solution contains therein potassium sulfate which may be
separated and recovered from the hydrolyze-formed solution
with the ammonium sulfate, so that it becomes possible to add
`recircularly the recovered potassium sulfate to the
absorption solution. In view of this advantage, it is
preferred in the present invention to add potassium su~fate
to the absorption solution to produce the alkali salt of
imidodisulfonic acid in the form of potassium salt. In
connection with the formation of the potassium salt, the
NOx-gas absorbed solution should preferably be added
with a suitable amownt of potassium sulfate even where
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~ lOS8830
,: I
the aqueous solution for the absorption of NOX contains a
potassium salt as the sulfurous acid alkali salt. Further, the
ammonium sulfate and the potassium sulfate may be separated
from the hydrolyze-formed solution individually by precipitating
S them one after the other utilizing the difference in solubility.
Alternatively, the ammonium sulfate and the potassium sulfate
may be precipitated as a mixture and separated from each other
- after recovery from the hydrolyze-formed solution.
It will be appreciated from the foregoing description
that, according to the present invention, the NOX which are
contained in a gas are efficiently removed therefrom in the form
of useful ammonium sulfate. The invention can thus contribute
greatly to the treatment of NOx-containing gases, particularly
to the treatment of NOx-containing exnaust gases.
The invention will be illustrated more particularly
by the following examples, which are given only by way of
example and therefore should not be construed as limitative of
the invention.
.' , , ,.
EXAMPL~ 1:
FeSO4 ............... 2.0% by weight
Na2SO3 .............. 3.2% by weight
CH3COONa ........... l0.0% by weight
CH3COOH ............. 2.4~ by weight
H2O ................ 82.4% by weight
.,
Il ~058830-
300 mi~ of NO gas was contacted at a normal temperature
' with lO0 m~ of an aqueous solution having the above composition
absorbing therein 290 m~ of the NO gas. --
~ ~he gas absorbed-liquid was heated up to 95C and
maintained at that temperature for 30 minutes. As a result, a
precipitate of an iron compound appeared in the liquid, and a
supernatant liquid was obtained by removing the precipitate.
In order to separate NH(SO3Na)2 which was dissolved in the
supernatant liquid, 10 g of KCl was added thereto, followed
by cooling to room temperature, to obtain 4.5 g of a precipitate.
i An infrared absorption spectrum analysis revealed
that the precipitate separated from the supernatant liquia con-
, tained NH(SO3K)2. It was found by an analysis that the nitrogen
Il content in the precipitate corresponded to 70% of the absorbed5 ~ NO gas. A further infrared quantitative analysis revealed that
the precipitate contained 47~ by weight of NH(SO3K)2.
Thereafter, the filtrate which was obtained after the !
filtration of the precipitate from the supernatant liquid was
I heated and condensed to precipitate a mixture of N(SO3K)3 and
NH2~SO3K) which were found, as a result of a quantitative
analysis, to have nitrogen contents corresponding to about 20
of absorbed NO. As a result, it was confirmed that about 90%
of absorbed NO gas was recovered and fixed.
., I
i; - 15 -
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.,,, , . ~
1058830
EXAMPLE 2:
~eSO4 ........ ~.- ----- 2.0~ by weight
KHSO3 .................. 3.0% by weight
CH3COOK ................ 5.0~ by weight
CH3COOH ................ 1.0% by weight
H2O - ................... 89% by weight
300 mQ of NO gas was contacted at 55C with 100 m~ of
an aqueous solution having the above composition absorbing
therein 280 mQ of the NO gas. The gas absorbed-liquid was left
standing at that temperature for 180 minutes. As a result,
a precipitate of an iron compound appeared in the liq'uid.
10 g of KCl was added to the separated supernatant liquid, fol-
lowed by cooling, to obtain another precipitate.
, As a result of an infrared absorption spectrum analysis
it was revealed that the precipit,ate separated from the superna-
tant liquid contained NH(SO3K)2. The precipitate had a nitrogen
content corresponding to about 70% of the absorbed NO gas.
EXAMPLE 3: , ,
FeSO4 ................ ~.0%-by weight
Na2SO3 ............... 5.0~ by weight
CH3COONa ............. 5.0% by weight
CH3COOH .............. 3.0% by weight
H2O .................. 85.0% by weight
; ~ 1058830
300 mQ of NO gas was contacted at 60C with 100 mQ
of an aqueous solution having the above composition absorbing
therein 290 mQ of the NO gas. The gas absorbed-liquid was left
standing at 60C for 180 minutes. As a result, a precipitate
of an iron compound appeared in the liquid. The iron compound
was separated and 25 g of KCl was added to the supernatant
liquid, followed by cooling, to obtain another precipitate.
As a result of an infrared absorption spectrum analy-
sis, it was revealed that the precipitate from the supernatant
liquid contained NH(S03K)2 which had a nitrogen content cor-
responding to about 90% of the absorbed NO gas.
.. , ' , . .
EXAMPLE 4:
FeS04 ................ 2.0% by weight
Na2S03 ................ 2.0% by weight
CH3COONa ............. 10.0% by weight
CH3COOH .............. 2.4~ by weight
EDTA-Na .............. 2.0% by weight
~ethylenediamine sodium tetraacetate)
- H20 ................... 81.6~ by weight
, ' . .
300 mQ of NO gas was contacted at room temperature
with 100 mQ of an aqueous solution having the above composition
absorbing therein 280 mQ of the NO gas. The gas absorbed-
liquid was heated at 80C for 1 hour and thereafter 8 g of
K2S04 dissolv d in the liquid, followed by cooling to room
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1058830
temperature, to obtain 3 g of a precipitate. An infrared
spectrum absorption analysis and an elementary analysis revealed
that the precipitate consisted of NH(SO3R)2 and R2SO4. Accord-
ing to a quantitative analysis by the infrared spectrum absorp-
tion method, NH (S03K)2 component in the precipitate contained
apparoximately 50~ of the nitrogen of the absorbed NO gas.
After removal of the precipitate, the remaining liquid was mixed
with Na2SO3 in a proportion of about 2~, followed by
contact with 300 me of NO gas in the same manner as described
hereinbefore and absorbed therein 270 me of the N0 gas.
The gas absorbed-liquid was heated to 80C and then added with
4 g of K2SO4, followed by cooling, to obtain a precipitate of
approximately 2.6 g of NH(S03K)2. The precipitate corresponded
in nitrogen content to approximately 89% of the NO gas which
was absorbed during the second contact absorption.
.. .
EXAMPLE 5:
FeSO4 ................ .4% by weight
Na2SO3 ............... .4% by weight
NTA-Na ............... .4% by weight
(nitrilo sodium triacetate)
H20 .................. 88% by weight
300 mQ of N0 gas was contacted at 50C with 100 mQ
of an aqueous solution having the above composition absorbing
therein 275 m~ of the NO gas. The gas absorbed-liquid was left
... . . .
1058830
standinq for 4 hours at 50C and then 10 g of CH3COOK was
dissolved in the liquid, followed by cooling to 10C, to obtain
2.8 g of a precipitate. The precipitate, after centrifugal
separation, was studied under the infrared absorption spectrum
analysis and found to contain NH(SO3K)2. Under a further
quantitative analysis also employing the infrared absorption
spectrum method, the 2.8 g of the precipitate was determined to
contain 1.7 g of NHtSO3K)2, which corresponded to 58% of the
absorbed NO gas. Presumably, the balance of the absorbed NO gas
remained, as shown in Example 4 , as a dissolved state of
NH(SO3K)2 in the gas absorbed-liquid. It is thus possible to
increase the recovery rate of imidodisulfonic acid alkali salt
by repeated use of the gas absorbed-liquid.
. ,,.
EXAMPLE 6:
EDTA-Fe chelate compound... 5% by weight
Na2SO3 .................... 4% by weight
H2O ....................... 91% by weight
Acetic acid was added to an aqueous solution having
the above composition to adjust the pH value to 5.5. The thus
prepared solution was placed in a gas absorption bottle with
a blowing pipe. After heating the solution to 60C, a nitrogen
gas containing 300 ppm of NO was passed through the bottle
at a rate of 100~/h for 10 hours. The gas which was discharged
from the bottle had an average NO content of 20 ppm.
i -
'i ' . lOS8830
! The gas absorbed-liquid was heated at 80C for 4 hours, followed
, by addition of 4 g of K2SO4. Upon cooling the liquid, 1.4 g of
i~ NH~SO3K)2 precipitated. The precipitated NH(S03K)2 corresponded
!' in nitrogen content to 54% of the absorbed NO gas. In view of
!I the fact that it was possible to precipitate more NH(S03K)2
, by further concentration of the liquid, the balance of the
absorbed NO gas was presumably dissolved in the gas absorbed-
, liquid in the form of NH(SO3K)2.
l,i , , '.
I' EXAMPLE 7:
I
, FeSO4 ................ 3.0% by weight
CH3COONa ............. 10.0~ by weight
CH3COOH .............. 4.5% by weight
Na2SO3 ............... 5.0% by weight
1 H2O --------------- 77.s% by weight
i 8500 mQ of NO gas was absorbed at 50C in 2000 mQ
of an aqueous solution having the above composition. The gas- 1,
absorbed solution was heated at 80C for 1 hour. As a result,
, a precipitate of iron hydroxide appeared in the solution. The
~ precipitate was filtered out and 180 g of potassium sulfate was
l added to the filtrate, followed by cooling down to 30C, to
', precipitate crystals.
The crystals were in the form of a mixture consisting
!~ mainly of NH(SO3K)2 and K2SO4 and containing a small amount of
', sodium acetate and NH2SO3K. A quantitative analysis by the
,.
! i
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.; . . I
.. . .
~ ~058830
¦ infrared absorption spectrum method revealed that the crystals
¦ contained 44.3 g of NH(S03K)2. After filtering out the crystals,
¦ part of the filtrate was treated to have a pH value of 2.0 and
¦ then heated for 4 hours. Sodium nitrite was added thereto to
S ¦ generate nitrogen gas.~ AS a resùlt of calculation based on the
amount of nitrogen gas generated from the filtrate, it was
¦ found that 33.4 g of NH(S03K)2 still remained in the filtrate
¦ as a whole. This brought the total amount o~ NHtS03K)2 to 77.7 g ,
which corresponded in nitrogen content to 95.7% of the absorbed
N0 gas.
The above-mentioned crystals were washed with a small
amount of cold water to obtain crystals which contained 42.1 g
of NH(S03X)2 and 6.8 g of K2S04. The entire amount of the
just-mentioned crystals, 0.1 g of concentrated sulfuric acid
L5 and 100 m~ of water were put in an autoclave for reaction at
120C for 8 hours underagitating. After the reaction, ammonia
was added thereto little by little to adjust the pH value to
6.5, followed by cooling to 20C, to obtain 25.9 g of K2S04
crystals which was 92~ in purity.
~he just-mentioned R2S04 crystals were filtered out
and the filtrate was dried under reduced pressure to obtain
32.8 g of crystals which contained 2.1 g of NH2S03K, 19.3 g of
~NH4)2S04 and 8-6 g of K2 4
As a result, it was confirmed that NH(S03K)2 had been
!5 hydrolyzed 100~, and NH2S03K, the product of the hydrolysis,
~058830
., ' . .
was further hydrolyzed 91%. Thus, (N~4)2S04 was produced from
NH~S03K)2 at a rate of 96%. That is to say, 91.7% of the
absorbed NO gas was recoverea in the form of (NH4~2S04.
; I , ,I E ~ ~LE 8:
Feso4.~ 2~o% by weight .
Na2S03~.......... ~3.2% by weight
- C~3COONa........... 10.0~ by weight
C~3COOB............ 2.4% by weight
; ~20................ 82.4% by weight
10; 300 mQ of NO gas was contacted at room temperature
with 100 m~ of an aqueous solution having the above composition,
absoxbing therein 290 mQ of the NO gas. The gas absorbed-liquid
was heated at 95C for 30 minutes to form therein a precipitate
of an iron compound. After separating the precipitate from the
liquid, CaC03 and (CH3C00)2Ca were added to the resultant filt-
rate to adjust the pH value thereof to 6.2, converting Na2S04
and Na2S03 which existed therein into CaS04 and CaS03, respectiv _
ly. This is because there occur firstly the precipitates of
. ~hese CaS04 and CaS03 in the filtrate in converting imidodi-
sulfonic acid alkali salt into the form of calcium salt.
Thereafter, Ca~OH)2 was added little by little to the solution
obtained by separating the thus precipitated CaS04 and CaS03
from the filtrate to adjust finally the pH value thereof to 8.0,
followed by leaving standstill, to precipitate 3.3 g of crystals.
The crystals werc analyzed after recrystallization
fxom water. The analysis revealed that the crystals had the
. ' .. ~. ', -.
-22- . .
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,
...... .. . .
` lOS8~330
chemical composition of NS206NaCa~3EI20. In this connection,
94% of the absor~ed N0 gas was recovered as NS~06NaCa 3H20.
A liquid comprising 2.0g of NS206NaCa 3H20 and 100 m~
. ~f O.lN H2S04 was heated at a temperature of 160C for 4 hours,
followed by alkalizing the liquid, to recover 158 m~ of NH3.
. . Accordingly, 0.033 mol/L of (NH4)2S04 was contained in the
.. . hydrolyze-formed solution. .
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