Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
` ` ` 110(~2~39
The present invention relates to a process for re-
fining a gas which contains hydrogen sulfide, sulfur oxides
and nitrogen oxides and may contain hydrogen cyanide. The
present invention relates more particularly to a wet process
for treatment of a gas by which desulfurization of the gas is
achieved simultaneously with the removal of nitrogen oxide and
hydrogen cyanide, if the latter is present, from the gas by
absorbing such contaminant gases into the specified absorp-
- tion medium.
Although a variety of processes are known for wet~
desulfurization of a gas, the known processes still suffer from
some disadvantages. For example, in the Seaboard process, the
absorbed hydrogen sulfide is discharged into the air during
regeneration of the absorption medium. Consequently, this
process results in air pollution, causing decay and damage-in
- animals and plants and, furthermore, in discoloration and cor-
rosion of metals. In the Thylox process handling of the materi-
als and operation of the process involve dangers since a poison-
ous arsenite is employed for desulfurization. Moreover, this
process involves complicated operations, such as one for extrac-
tion of the arsenite from the sulfur obtained. The Giammarco
process is even more disadvantageous in that yreater care must
be taken in handling the catalyst and removing arsenite from
the sulfur than in the Thylox process since the former employs
an absorption medium containing an arsenite of higher concen-
tration than that in the latter.
Recently, several processes have been proposed in
which an absorption medium containing a quinone type compound
is employed. For example, a desulfurization process using
benzoquinone has been proposed. However, in this process, the
catalytic activity of benzoquinone i9 SO high that the catalytic
life is insufficiently short since the oxidation-reduction
~. `
--1--
110~J2~99
potential of benzoquinone is as high as about 0.7 volt. As
another example of the processes using a quinone type compound,
mention can be made of the Stretford process which employs
anthraquinone-2,5 or 2,6-di-sulfonate thereof as a catalyst
component. However, since such component has a low oxidation-
- reduction potential of about 0.228 volt, sufficient desulfuriz-
ing effect cannot be obtained even when it is used in a very
large quantity. In order to obviate the disadvantage of the
Stretford process, there is proposed a process in which a
metal, such as vanadium, arsenic or iron, an alkali salt and
a tartarate are used in combination. This process is con-
sidered to be one in which the desulfurization principles in
each of the Thylox, Gia~marco and Vetrocoke processes are com-
bined and a certain effect is attained therewith. (See Cana-
dian Patent No. 672,084). However, the Stretford process or
its modification is nothing more than a mere combination of
the Thylox process with other known techniques, and still
suffers from the need for removal of vanadium or the like and
arsenic. Furthermore, the desulfurizing effect attained by
the Stretford process or its modification is not sufficiently
high.
It is of course noted that the above-mentioned pro-
cesses are essentially directed only to desulfurization of a
gas, and no process has yet been proposed which is effective
in desulfurization of a gas simultaneously with the removal
of nitrogen oxides.
The present inventor has already proposed an effec-
tive process for desulfurization of a gas which employs, as
catalytic component in the absorption medium, a specified
quinone or its derivative (see U. S. Patent No. 3,459,495,
Japanese Patent No. 427,094), or a quino-chelate compound (see
U. S. Patent No. 3,937,795 or Japanese Patent No. 805,456),
_~ -2-
11002~9
; these compounds having suitable oxidation-reduction potential
` in the range of from 0.45 to 0.7 volt.
This process employing a specified quinone or its
derivative, or quino-chelate will provide an effective wet
- process for desulfurization of a gas so as to overcome the
disadvantages and defects of the above-mentioned conventional
processes, but it is not thoroughly effective in removing
nitrogen oxides simultaneously with sulfur-bearing contaminant
such as hydrogen sulfide or sulfur dioxide.
` 10 Nowadays, environmental pollution due to nitrogen
oxides has become as serious a problem as that caused by sul-
fur-bearing gases, and several methods have been proposed for
: removing nitrogen oxides and/or converting such gases into
materials harmless to human beings, plants.and animals. Among
. these, mention can be made of a process which meets the re-
quirements to a certain degree, wherein No is converted to N2
or to N02 at a temperature exceeding 130C in the presence of
ammonia or methane over alumina, silica, or alumina- or silica-
supported noble metal. However, this process is applicable to
à gas in which nitrogen oxides are contained in a considerable
high amount, and is` disadvantageous in that it must be used in
treating an extremely high volume of gas if this process is to
. be employed in treating a gas containing nitrogen oxides on the
order to several ppm or several hundred ppm such as coal gas
or the waste gas from the Claus process.
It is the main object of the present invention to
provide a process by which desulfurization of a gas can be ef-
fectively accomplished simultaneously with the removal of
nitrogen oxides, and, if present, hydrogen cyanide.
It is another object of the present invention to
provide a novel absorption medium for wet gas refining process
which comprises à specified quinone or its derivative or a
-3-
110C~289
specified quino-chelate as a catalytic component in combina-
` tion with a specified solvent for the catalytic component.
These and other objects of the present invention
and the advantages and merits achieved by the present inven-
tion will be readily apparent from the following detailed des-
cription thereof.
In accordance with the practlve of the process of
the present invention, a gas, which contains nitrogen oxides
as well as hydrogen sulfide and/or sulfur oxides and may fur-
ther contain hydrogen cyanide, can be refined by contactingthe gas with the absorption medium so that such contaminants
contained in the gas are absorbed in the medium. The absorp-
tion medium contains as catalytic component a naphthoquino-
chelate formed from naphthoquinone or a derivative therefrom
having the general formula
O(or OH)
C~x
O(or OH)
or naphthodiquinone or a derivative therefrom having the gen-
eral formula
O(or OH)
~ O(or OH)
.. ~ X
O(or OH)
O(or OH)
llOOZ~39
- in which X represents hydrogen atom, hydroxyl group, a lower
alkyl group, a lower alkoxy group, sulfonic group (-S03H),
carboxylic group (-COOH), an alkaline metal or alkaline earth
metal salt of sulfonic or carboxylic group (such as -SO3Na,
-COONa), thioglycol group (-S-CH2-COOH) or thiol group (-SR
in which R is a lower alkyl group). The naphthoquino-chelate
- is prepared by mixing (A) said quinone or quinone derivative
with (B) a precursor of a chelating agent which is selected
from the group consisting of the reaction product of a metal
selected from the group consisting of the metals of groups V,
VI, VII and VIII in the fourth period of the Periodic Table,
arsenic and selenium with an acid selected from the group
consisting of oxalic, citric tartaric and glutaric acids, and
aging the mixture of (A) and (B) to form a naphthoquino-chelate
compound.
The process of the present invention is character-
ized by the fact that the absorption medium contains as the
solvent for the above-mentioned catalytic component (1) a
- specified diamine selected from among cyclohexadiamine and
diamines having the chemical formula NH2(C H2n)NH2 in which
n is 2, 3 or 4 and (2) mono-, di-, tri- or tetra-acetate,
mono-, di-, tri- or tetra-propionate, or mono-, di, tri- or
tetra-buthylate of the diamine.
In carrying out the process of the present invention,
the absorption medium which has absorbed the contaminants is
then treated in a suitable manner for obtaining sulfur from
hydrogen sulfide and sulfur oxides and thiocyanate from hydro-
gen cyanide, if such were present in the gas, while producing
gas having high nitrogen oxides concentration.
The present invention is based on the discovery that
the absorption medium, which comprises the specified quino-
chelate in combination with the specified diamine and acetate,
--5--
llOCl Z~39
propionate or buthylate thereof, highly absorbs not only sulfur-
bearing compound such as hydrogen sulfide and sulfur dioxide
but also nitrogen oxides such as nitric oxide.
Acetate, propionate or buthylate of the diamine of
the formula NH2(CnH2n)NH2 or cyclohexadiamine forms in the
absorption system a chelate compound such as (acetate, pro-
pionate or buthylate of NH2-CnH2n.NH2)Fe++ or (acetate, pro-
pionate or buthylate of NH2 CnH2n NH2)Fe++* (hereinafter re-
fered to as "the diamine-chelate"). Such chelate will absorb
nitrogen oxides such as nitric oxide to produce a relatively
stable compounds which may be expressed, for example, by the
formula (acetate, propionate or buthylate of NH2-CnH2n-NH2)Fe++ NO.
This compound then liberates, when treated in a suitable man-
ner such as heating, in the manner as expressed by the follow-
ing equation, so that the nitrogen oxides concentrated gas is
obtained.
(acetate, propionate or buthylate of NH2CnH2nNH2)Fe++-NO--
~(acetate, propionate or buthylate of NH2 CnH2n NH2~Fe++ + NO~
In addition, the presence of the diamine-chelate is
advantageous in that the precipitation of a metal sulfide such
as FeS is prevented. On the other hand, the presence of hydro-
gen sulfide and sulfur dioxide per se is advantageous in ren-
dering such chelate more suitable form for absorbing nitrogen
oxides. For example, it is found that the ferrous chelate is
more effective than the ferric chelate in absorbing nitrogen
oxides, and hydrogen sulfide and sulfur dioxide serve, because
of their capacity for reduction, to convert Fe+++ to Fe+*.
The diamine selected from NH2(CnH2n)NH2 and cyclo-
hexadiamine and acetate, propionate, or buthylate thereof will
of course work as a good solvent for dissolving hydrogen sul-
fide and sulfur dioxide. Because of their high dissolving
capacities, hydrogen sulfide and sulfur dioxide in the gas to
--6--
llO~Z~9
be refined are transferred in the solvent to cause a reaction
therebetween in the following manner:
S 2 H2 H20 + 2S~
Excess hydrogen sulfide is oxidized by the quino-chelate to
precipitate sulfur.
The metal in forming the diamine chelate may be fed
from the excess metal in preparing the quino-chelate, the
preparation of which will be described in details later. Thus,
~ the diamine-chelate may be formed together with the preparation
10 of the quino-chelate, in which a metal salt is added in excess
of the amount that is necessary to prepare the quino-chelate
and the diamine and the acetate (or propionate or buthylate~
-- thereof is added. Alternatively, the diamine and the acetate
-~ (or propionate or buthylate) thereof may be added into the
- aqueous or non-aqueous solution containing the quino-chelate,
where the metal for forming the diamine-chelate is fed from
the excess metal left in the preparation of the quino-chelate.
The amount of the diamine and the acetate ~or pro-
pionate or buthylate) is optional mainly depending on the
amount of nitrogen oxides present in the gas to be refined. In
- most cases, as the amount of nitrogen oxides is rather small,
the amount of the acetate (or propionate or buthylate) of the
diamine may be small.
The naphthoquinone or naphthodiquinone or the deriva-
tive thereof for forming the naphthoquino-chelate suitable for
use in the absorption medium in the present invention are set
forth in the above-mentioned patents issued to the present
inventor, which is herein repeated in the following. These
quinones and quino-chelates should have high solubility in water
or an organic solvent. As suitably useful compounds meeting
such conditions, there can be mentioned those having a group
such as those set forth below and having an oxidation-reduction
.- ,1
~ 7-
`\ llOo~g
potential ranging from about 0.3 to about 0.8 volt, measured
at 25C.
Goups to be introduced:
(a) hydrogen atom (-H)
(b) hydroxyl group (-OH)
(c) lower alkyl group (-CH , -C2H5, -C H , etc.)
(d) lower alkoxy group (-OCH3, -OC2H5, -OC3H7, etc.)
(e) sulfonic group (-SO3H)
(f) carboxylic group (-COOH)
(g) alkali metal or alkaline earth metal salts of
acid groups (e) and (f) (-SO3Na, -COONa, etc.)
(h) thioglycol group (-S-CH2-COOH)
(i) thiol group (-SR in which R is an alkyl group)
These groups (a) to (i3 are hereinafter referred to merely as
"radicals". The naphthoquinone and naphthodiquinone and deri-
vatives thereof which can be used in forming the naphthoquino-
chelate are represented by the following general formulae:
O(or OH)
O(or OH) I O(or OH)
~ - X or~ ~ X
O(or OH) O(or OH)
O(or OH)
wherein O (or OH) stands for a quinone (or hydroquinone) struc-
ture and X designates a radical such as those mentioned above.
In the above formulae, the position of O (or OH) is
merely a typical illustrative instance and it can be attached
to any optional position. For example, theo~-type is shown
above with respect to the naphthoquinone, but the ~-type is
included in the naphthoquinones which can be used in this inven-
tion. Further, the radical X can be attached to any optional
. .
llOOZ89
position other than the position to which O(or OH) is attached.
Moreover, the number of the radical X present is also optional.
Specific examples of the radical-introduced quinones and hydro-
quinones or derivatives thereof that can be used in this inven-
tion are as follows:
Compound Structural Formula
1,4-naphthoquinone o
O
1,2-naphthoquinone o
~\ O
1,4-naphthoquinone-2-sulfonic
acid and its salt - o
~ r
1,2-naphthoquinone-4-sulfonic
acid and its salt o
0
S03M'
1,4-naphthoquinone-2-carboxylic
acid and its salt
~COOM'
O
_g _
. 1:10~289
Compound Structural Formula
1,2-naphthoquinone-4-carboxylic
acid and its salt
ro
COOM'
2-methyl-1,4-naphthoquinone O
1~
O
2,3-dimethyl-1,4-naphthoquinone
- ~ ~ CH3
~' , o
2,5-dimethyl-1,4-naphthoquinone
CH3
CH3
2,6-dimethyl-1,4-naphthoquinone
CH
--10--
` . 1100289
Structural Formula
Compound
2-methyl-1,4-naphthoquinone-3-
sulfonic acid and its salt O
503M'
O
'
2-alkylthio-1,4-naphthoquinone
~ \ SR
2-carboxymethylmercapto-1,4-
naphthoquinone
~ ~ ~ S-CH2-COOM'
o
1,4,5,8-naphthodiquinone
O O
O O
1,2,3,4-naphthodiquinone
O
IJ
~CF
110~2~39
Compound Structural Formula
2-hydroxy-1,4-naphthoquinone
o
0~1
5-hydroxy-1,4-naphthoquinone
~"' `3
OH O
6-hydroxy-1,4-naphthoquinone
OH \~ ' \
; 2,5-dihydroxy-1,4-naphthoquinone
OH
OH O
2,6-dihydroxy-1,4-naphthoquinone
HO ~ ~ OH
` .` 110~289
. .
- Compound Structural Formula
2,7-dihydroxy-1,4-naphthoquinone
O
2,8-dihydroxy-1,4-naphthoquinone
- OH O
~J,~I~,~,r OH
5,6-dihydroxy-1,4-naphthoquinone
.. , ~,JI,. .
HO ~ ~ ~ ~ J
OH O
5,8-dihydroxy-1,4-naphthoquinone
OH O
OH O
2,5,8-trihydroxy-1,4-
naphthoquinone OH o
ro~
-13-
llOl~lZ~39
Compound Structural Formula
3,5,7-trihydroxy-1,4-
naphthoquinone O
Ho ~ OH
OH o
2,3-dihydroxy~1,4-naphtho-
quinone - O
6,7-dihydroxy-1,4-naphtho-
quinone o
HO
o
2,3,6-trihydroxy-1,4- O
naphthoquinone ll
/ ~ , ~ OH
HO
2,3,5,8-tetrahydroxy-1,4-
naphthoquinone OH
OH
OH o
-14-
` 110C12139
Com~ound Structural Formula
.:
5,6,8-trihydroxy-1,4-naphtho-
quinone OH o
OH o
2-methoxy-1,4-naphthoquinone
(~
o
2-methoxy-3-hydroxy-1,4-
naphthoquinone
~ OH
': ' O
. _
: 2-methyl-1,4,5,8-naphthodi-
quinone
~ , CH3
: O o
.
2-methoxy-1,4,5,8-naphtho-
diquinone O
OCH3
O O
-15-
- llO~Z89
Compound Structural Formula
2-ethyl-1,4,5,8-naphthodi-
quinone
3~ C 2H5
O O
2-ethoxy-1,4,5,8-naphthodi-
quinone O - O
~r Oc2 5
O O
2-propyl-1,4,5,8-naphthodi-
quinone
~ 3 7
- O O
2-propoxy-1,4,5,8-naphthodi-
quinone O O
/~ roc~H7
O O
-16-
```~ ` l~O~Z~99
In the present invention, the above-mentioned quinone
or the quinone derivative may be used as the catalytic com-
ponent in the absorption medium. However, the refining effect
for a gas is improved when as the catalytic component the
quino-chelate is employed which is prepared by mixing the
above-mentioned quinone or quinone derivative with the chel-
` ating agent precursor described below, and aging the mixture.
The aging is conducted over a wide time range generally from
as short as about 10 minutes to about 12 hours and preferably
about 30 minutes to about 3 hours. The resulting naphtho-
quino chelate compound:is used as an absorption medium in the
form of an aqueous solution of a concentration of 0.01 to
500 mole/kl.
In preparing the naphthoquino-chelate suitable for
use in this invention, there may be employed as metals of
Groups V, VI, VII or VIII in the fourth period of the Periodic
Table and arsenic and selenium, for example, vanadium, arsenic,
chromium, selenium, manganese, iron, cobalt and nickel, Vana-
dium and iron are especially preferred.
As the aliphatic carboxylic acid or hydroxycarboxylic
acid that can be employed in carrying out the process of this
invention, there can be mentioned, for example, oxalic acid,
citric acid, tartaric acid, glutaric acid and the like.
The reaction of a compound of the above-mentioned
metals, such as a hydroxide or chloride, with the aliphatic
carboxylic acid or hydroxycarboxylic acid is conducted in water
or in any other suitable solvent at an appropriate pH, general-
ly ranging from 4 to 10 according to customary methods. The
so formed chelating agent precursors are represented by the
following general formula:
(Alk-Y)nM
wherein Alk stands for an alkali metal or ammonium group, M
' ` 11(11~2~39
designates a metal belonging to Groups V, VI, VII or VIII in
the fourth period of the Periodic Table, arsenic or selenium,
n represents a number from 1 to 3 and Y is an acid or hydroxyl
residue of the aliphatic carboxylic acid or hydroxycarboxylic
acid.
Examples of the chelating agent precursor obtained
by employing tartaric acid or its alkali salt as the starting
material are as follows:
COOM' M'OOC COOM' MII
- ,CHO~ MII OHC (I) CHO (II)
CHO ~ M'OHC CHOM'
COOM' M'OOC COOM' 3
10, MII__--- M'OOC ,CO - MII - OOC
CHO ~ ~ --OHC (III) CHO ~ M'OHC (IV)
CHOM' M'OHC CHOM' M'OHC
.COOM' M'OOC COOM' M'OHC
COOM OOC COO M'OOC
. CHO MII ~ OHC (V) CHOM' MII , (VI)
. CHOM' M'OHC CHOM' M'OHC
COOM' 2 M'OOC ~CHOM'M'OOC
.
COO OOC 'COO~
CHOM ~ ~ OHC CHOM'
' MII , (VII) l MII (VIII)
CHOM ~ M'OHC CHOM'
COO M'OOC COOM'
wherein M' is hydrogen, ammonium or an alkali metal such as
sodium and potassium and M is as defined above and prefer-
ably vanadium or iron.
The amount of the chelating agent precursor employed
in accomplishing the process of this invention can vary widely
-18-
llO(~Z~9
being optionally chosen, and sufficient and satisfactory re-
sults can be obtained when it is added in an amount of from
about 0.01 to about 5~/O by weight, based on the quinone or
hydroquinone compound employed.
The utilization of a chelating agent precursor, such
as mentioned above provides a further advantage in that even
when the metal has come into contact with hydrogen sulfide in
the absorption liquid, precipitation of a metal sulfide is
- prevented by its protective activity.
One of the features of this invention is that the
absorption medium can have a pH value of a broad range of gen-
erally from about 3 to about 10. In view of the fact that in
the conventional methods known desulfurization is possible
only in an alkaline solution, it will readily be understood
that the process of this invention can be applied broadly in
various fields.
According to the present-invention, with the use
of the diamine as solvent which has high dissolving capacity both
~- for sulfur-bearing compounds such as hydrogen sulfide or sul-
fur dioxide and nitrogen oxides such as nitric oxide, particles
of p~ecipitated sulfur is formed from hydrogen sulfide or sul-
fur dioxide while the relatively stable adduct such as ~acetate,
propionate or buthylate of NH2 CnH2n-NH2)Fe~+-NO is formed.
Thus, by treating the absorption medium, after having been con-
tacted with the gas to be refined, in a suitable manner such
as by heating the medium or by blowing a gas stream into the
medium, and subjecting the medium to~a settling treatment in
a suitable device, the gas in which the nitrogen oxides such
as nitric oxide is highly concentrated is discharged from the
top of the device while the precipitated sulfur is extracted
from the bottom. Such nitrogen oxides concentrated gas may be
subjected to the above-mentioned process by which NO can be
--19--
-` 110~289
converted into N2. Such treatment of the absorption medium
may be conducted after or before the oxidizing step of the
medium for a reuse of the medium.
It should be mentioned that according to the present
invention since the high-boiling organic solvent is employed,
it is possible to use the temperature of the absorption liquid,
say, over the melting point of sulfur (120C), and hence, the
fine particles of sulfur can be melted to form coarse particles
which then settle down so as to be recovered as pure melted
sulfur. Thus, the process of this invention is advantageous
in that sulfur is recovered in the most desirable form while
the loss of the liquor and the catalyst is prevented. In a
conventional wet process for desulfurization of sulfur-con-
taining gas, the precipitated sulfur is recovered by using a
filter-press. However, with such filter-press, the water can-
not be removed as much as over 60~/o. This fact can be easily
; understood from a simple calculation of the volume of gap
among the particles of the sulfur. Thus, such process is dis-
advantageous in that it results in degradation of sulfur re-
covered as well as loss of alkaline, acid, organic solvent or
even catalyst to be used in an absorption medium.
In addition, when hydrogen cyanide is contacted with
sulfur of ordinary form, it hardly reacts with the sulfur,
and hence, there is practically no conversion to thiocyanate.
In contrast, if sulfur is in the atomic state, hydrogen cyanide
reacts with it very readily and it is easily converted to a
thiocyanate. When the quinone or its derivative or quino-
chelate compound of this invention is present, atomic sulfur is
readily formed and in a particle size distribution in which the
maximum particles size is within a range of from about 0.01 to
about 2,u. As may be readily understood from this fact, sulfur
is in a highly active state, and it reacts with hydrogen cyanide
-20-
` . 11~2~39
to form a thiocyanate as follows:
NCN + atomic S NCNS
An instance of the sulfur particle size distribution
in the absorption liquid observed when the operation is con-
tinued for 15 hours is as follows
particle size (jU) amount of particles (%)
- below 0.1 80
0.1 to 1 15
1 to 2 5
The oxidation-reduction state and the deposition
of sulfur are provided in the following table with respect to
typical quinone compounds for showing the effects of the pre-
sent invention.
TABLE
E as measured
at 25C State of Sulfur
~xidized Form (volt) Deposition
o-benzoquinone 0.787 no sulfur precipitate,
extreme formation of
thionic acid
3-hydroxy-o-benzo- small amount of sulfur
quinone 0.713 precipitate
p-benzoquinone 0.699 "
1,4-naphthoquinone0.484 sulfur precipitate
9,10-anthraquinone0.154 no sulfur precipitate
1,2-naphthoquinone-0.628 sulfur precipitate
- 4-sulfonic acid
1,4-naphthoquinone-0.533 good precipitation of
2-sulfonic acid sulfur
1,4-naphthoquinone- - sulfur precipitate
2,3-dicarboxylic acid
2-hydroxy-1,4-naphtho- 0.351 "
quinone
5-hydroxy-1,4- 0.452
naphthoquinone
4-amino-1,2-naphtho-0.352 sulfur precipitate
qulnone
.
-21-
~10~2~39
.
TABLE (cont'd)
E as measured
at 25C State of Sulfur
Oxidized Form (volt) ~eF,osition
_ .
- 9,10-anthraquinone- 0.187 very slow and insuffic-
2-sulfonic acid ient precipitation
- of sulfur
1,2-anthraquinone- - "
4-sulfonic acid
anthraquinone-2,6- 0.228 "
disulfonic acid
l-hydroxy-9,10- 0.132 no sulfur precipitate
anthraquinone
Naphthoquinone or naphthodiquinone or the derivative
therefrom as above listed per se serves as a catalytic com-
ponent in an absorption medium although not so effective as the
naphthoquino-chelate. Thus, as a modified embodiment of the
invention, a gas which contains nitrogen oxides as well as
hydrogen sulfide and/or sulfur dioxides and may contain hydro-
gen cyanide may be absorbed in an absorption medium containing
such quinone or quinone derivative and the diamine-chelate,
wherein such diamine chelate has been externally prepared.
The absorption medium for use in the present inven-
tion may contain other organic solvents such as glycerin,
ethylene glycol, diethylene glycol, or a compound represented
by the formula RO-(CH2)2-OH in which R is alkyl group having
1 to 4 carbon atoms, depending on the types and the amounts of
the contaminants contained in the gas to be refined. With the
use of such a solvent, the refining effect may be occasionally
higher.
The present invention will be understood more readily
with reference to the following examples. However, the exam-
ples are intended to illustrate the invention and are not to
be construed to limit the scope of the invention.
EXAMPLE 1
A naphthoquino-chelate was prepared by mixing 0.5 mol
-22-
-- . 110C~2~39
of ammonium 1,4-naphthoquinone-2~sulfonate in 1 kl of water
with 0.6 mol of the iron salt of the compound (I) as a chelat-
ing agent precursor and aging for 2 hours. The solu~ion con-
taining the naphthoquino-chelate thus obtained was added with
ethylene-diamine and ethylene-diamine-tetraacetate to form an
absorption medium according to the invention. In the medium
ethylene-diamine was contained in the amount of l~/o by weight
and ethylene-diamine-tetraacetate was contained in the amount
of 10 mol/kl of the medium.
- 10 A glass tube having the inner diameter of 50 mm and
the length of 1000 mm was packed with synthetic resin fillers
- having the diameter of 15 mm. The absorption medium was
sprinkled into the tube from the top of the tube while a gas
to be treated was introduced from the bottom of the tube to
flow in counter-current contact with the absorption medium.
The gas to be treated was composed of 1000 ppm of H2S, 500 ppm
of S02, 300 ppm of No, 5% of 2 and the remainder of N2. The
gas treatment was conducted at 60C and at pH of 8 with the
flow rates of the gas and the absorption medium of 150 l/hr
and 2 l/hr, respectively. As results, the percentages of the
removal of H2S, S02 and N0 from the gas were 99.95%, 99.8% and
98%, respectively. During the operation, the formation of
amine sulfanilate expressed by NH(SO3Na) was observed with
- the increase of the amount of N0 absorbed.
EXAMPLE 2
.--
An aqueous mixture of 5% of ethylene diamine, 5% of
2-ethoxyethanol and 5 mol of propylene-diamine-tetraacetate in
1 kl of the mixture was added with 0.5 mol of sodium 1,4-naphtho-
quinone-2-sulfonate. The solution thus formed was mixed with
the iron salt of the above-mentioned compound (I) in an amount
of 0.6 mol in 1 kl of the solution and aged for 1.5 hours to
obtain an absorption medium of the present invention.
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ll(~G289
The gas treatment was carried out in the same manner
as in Example 1 for the gas composed of H2S 1800 ppm, SO2
800 ppm, NO 280 ppm, 2 8%, CO2 15% and the remainder of N2
under the conditions of pH 6.7 at 40C, with the result that
the percentage of H2S, SO2 and NO removal were 99.3%, 98% and
97% respectively.
EXAMPLE 3
A quino-chelate was prepared by mixing 1 mol of
naphthodiquinone in 1 kl of water with 1 mol of ferrous citrate
as a chelating precursor. The quino-chelate solution thus
obtained was added (ethylene-diamine-tetraacetate)Fe++ in an
- amount of 5% in the solution. With the absorption medium thus
obtained, the gas composed of 20,000 ppm of H2S, 9850 ppm of
SO2, 283 ppm of NO, 3% of 2~ 1% of HCN and the remainder of
N2, was treated using the test tube as in Example 1 at 40C and
pH 8Ø The result is that the percentages of H2S, S02, NO
and HCN removals were 99.1%, 98%, 97% and 98%, respectively.
The process of the present invention is effective in
refining a gas which contains sulfur- and/or nitrogen-bearing
compounds and will throw impediments in an industrial pro-
cess and cause environmental pollution, such as coal gas, the
waste gas from the Claus process or any other industrial waste
gas.
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