Use of cobalt(II) phthalocyanine sulfonates in gas purification to remove hydrogen sulfide

Article abstract of DOI:10.1023/B:RJAC.0000022444.05065.00

Experiments on liquid-phase oxidation of H₂S with oxygen in the presence of catalysts, cobalt phthalocyanine sulfonates [CoPc(SO ₃Na)_n], were performed on a laboratory static installation in order to find conditions under which a stationary oxidation mode can be established at pH ≥ 8. The influence exerted by additional introduction of a soluble salt of Mn²⁺ (MnSO₄, MnCl₂) into the reaction mixture at various pH values was studied.

Full text of DOI:10.1023/B:RJAC.0000022444.05065.00

Russian Journal of Applied Chemistry, Vol. 76, No. 12, 2003, pp. 1946 1950. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 12, 2003,
pp. 1995 1999.
Original Russian Text Copyright
2003 by Faddeenkova, Kundo.
CATALYSIS
Use of Cobalt(II) Phthalocyanine Sulfonates in Gas Purification
To Remove Hydrogen Sulfide
G. A. Faddeenkova and N. N. Kundo
Boreskov Institute of Catalysis, Siberian Division, Russian Academy of Sciences, Novosibirsk, Russia
Received August 12, 2002
Abstract Experiments on liquid-phase oxidation of H2S with oxygen in the presence of catalysts, cobalt
phthalocyanine sulfonates [CoPc(SO3Na)n], were performed on a laboratory static installation in order to
find conditions under which a stationary oxidation mode can be established at pH 8. The influence ex-
erted by additional introduction of a soluble salt of Mn2+ (MnSO4, MnCl2) into the reaction mixture at var-
ious pH values was studied.
Cobalt(II) phthalocyanine sulfonates [CoPc(SO3Na)n]
are active catalysts for liquid-phase oxidation of H2S
with oxygen [1 3], which can be successfully used in
liquid oxidative processes for purification of various
gases to remove hydrogen sulfide. Liquid oxidative
methods for gas purification include H2S absorption
with an aqueous solution that contains an alkaline
agent and a catalyst and catalytic oxidation of the thus
caught H2S with atmospheric oxygen.
In this case, the catalyst activity is more than an or-
der of magnitude lower [1], with sulfites and sulfates
formed as a result of oxidation. It should be noted
that, in gas purification to remove H2S, it is important
to obtain elementary sulfur, since it is easily separated
from the absorbing solution.
At pH 8 11, lower rates of liquid-phase oxidation
of H2S are commonly observed in the presence of
CoPc(SO3Na)n, compared with those at pH 7.3 8.0
and pH > 11. The rate of oxidation and the composi-
tion of the oxidation products formed at pH 8 11 are
even affected by minor changes in the process param-
eters {pH value, presence of oxidation (semi)products,
such as S0 and SO23 ions [6]}.
In a weakly alkaline medium (pH 7.3 8.0), the ab-
sorbed H2S, which is in the form of HS ions, is
oxidized in the presence of CoPc(SO3H)n at a high
rate by the polysulfide mechanism [1]. The main ox-
idation products are elementary sulfur and thiosul-
fates [1]. HS ions are oxidized via redox transitions
In gas purification to remove H2S, it is necessary to
maintain a stationary oxidation mode of oxidation of
H2S being caught. The purification process should be
stable in an as wide fluctuation range of the purifica-
tion process parameters as possible, and, primarily,
it should be stable against accumulation of oxidation
products and semiproducts.
Co(II)Pc(SO3H)n + HS
Co(I)Pc(SO3H)n The ox-
idation mechanism is described by the scheme
Co(II)Pc(SO3Na)n + HSn
Co(I)Pc(SO3Na)n
.
+ HSn + H+,
(1)
(2)
.
2HSn
S22n + 2H+,
The aim of this study was to find conditions that
make it possible to establish a stationary mode of li-
quid-phase oxidation of H2S with oxygen in the pres-
ence of catalysts CoPc(SO3Na)n at pH 8 11, to select
optimal oxidation conditions, and to perform test pu-
rification of petroleum gas to remove H2S on a pilot
installation.
2Co(I)Pc(SO3Na)n + 0.5O2 + 2H+
2Co(II)Pc(SO3Na)n + H2O,
(3)
(4)
HS + S22n
HSn + S2(n + 1)
.
In alkaline solutions (pH > 11), HS ions are ox-
idized through oxygen activation via formation of
[Co(III)Pc(SO3Na)n O2 ] complexes [4], i.e., via the
redox transitions [1, 4, 5]
EXPERIMENTAL
Experiments on liquid-phase oxidation of H2S
were performed on a static laboratory installation [6].
Co(II)Pc(SO3Na)n
Co(III)Pc(SO3Na)n.
1070-4272/03/7612-1946 $25.00 2003 MAIK Nauka/Interperiodica

USE OF COBALT(II) PHTHALOCYANINE SULFONATES IN GAS PURIFICATION
For the experiments, Na2S and Na2SO3 solutions
1947
and solutions of the catalysts Co(II)Pc(SO3Na)2 and
Co(II)Pc(SO3Na)4 were prepared. The content of
Na2SO3 and Na2S2O3 in the working solutions was
determined by iodometry [7], and the concentration
of the catalysts, cobalt(II) phthalocyanine sulfonates,
by spectrophotometry [6]. The pH value of a solution
being oxidized was maintained constant by introduc-
ing a phosphate buffer solution.
The rate of NaHS oxidation in the static installation
was determined volumetrically from the oxygen ab-
sorption, and also from changes in the iodometrically
found concentration of NaHS in the reaction mixture
[7]. The completion of NaHS oxidation was indicated
both by termination of oxygen absorption and by the
absence of HS ions in the reaction mixture, which
was determined using lead indicator paper [8]. The
content of oxidation products, Na2SO3 and Na2S2O3,
in the reaction mixture was found iodometrically [7].
The presence of elementary sulfur in the oxidation
products in the static installation was determined vi-
sually, and the amount of sulfur formed, spectropho-
tometrically [9]. The overall balance of oxidation
products in the static installation correlated with the
amounts of oxidized NaHS and oxygen consumed
for oxidation.
Fig. 1. Kinetics of liquid-phase oxidation of H S with
2
oxygen in the presence of a catalyst, (1 3) CoPc(SO Na)
3
4
or (1 3 ) CoPc(SO Na) at pH value of (a) 8.0 and
3
2
(b) 10.2. T = 25 C, P
= 101 kPa, V = 20 ml,
O
21
[CoPc(SO Na) ] = 5 mg l . (V ) Oxygen volume and
3
n
O2
( ) process duration; the same for Figs. 2 4. Concentration
2
[H S] (M): (1, 1 ) 2.4 10 , (2, 2 ) 4.8, and (3, 3 ) 7.2.
2
0
the initial concentration of H2S (curves 1 and 1 ),
the main oxidation product was Na2S2O3 and, in part,
elementary sulfur. The increase in the oxidation rate
and sulfur yield upon repeated introduction of the sub-
strate being oxidized into the oxidized reaction mix-
ture (curves 2 and 2 ) is due to the fact that the ele-
mentary sulfur formed in the initial experiments
maintains a high concentration of polysulfide ions
in the reaction mixture through the reaction
The concentration of H2S in an unpurified petro-
leum gas was found by means of chromatography.
The absence of H2S in a purified gas was established
visually, using a lead indicator paper moistened with
water and placed in the gas flow [8]. The content of
the products formed in oxidation of the H2S caught,
Na2SO3 and Na2S2O3, was determined iodometrically
[7], and the absence of Na2SO4 in the absorbing solu-
tion was established using BaCl2 [10]. The content
of elementary sulfur in the absorbing solution was
found spectrophotometrically [9], and the concentra-
tion of soda (NaHCO3 + Na2CO3), by titration with
sulfuric acid [11]. The overall balance of the amount
of products formed in oxidation of the H2S caught
in the absorbing solution correlated with the total
amount of H2S caught by the installation for purifica-
tion of petroleum gas to remove H2S.
HS + (n
1)S0 = HSn.
(5)
The high running concentration of polysulfide ions
in the reaction mixture favors the liquid-phase oxida-
tion of H2S by the polysulfide mechanism. The yield
of S0 in NaHS oxidation is about 60%, and that of
Na2S2O3, approximately 40% (curves 2 and 2 ). The ki-
netic curves 2, 3 and 2 , 3 , which describe liquid-phase
oxidation of H2S, are very close. This is accounted for
by the fact that the oxidation products S0 and Na2S2O3,
which are accumulated in the solution, have no in-
hibiting effect on the liquid-phase oxidation of H2S
[6]. Thus, a stationary mode of liquid-phase oxida-
tion of H2S in the presence of catalysts, cobalt(II)
phthalocyanine sulfonates CoPc(SO3Na)n, is ensured
at pH 8.0.
Figures 1a and 1b show the results of experiments
on liquid-phase oxidation of H2S in the presence of
catalysts, CoPc(SO3Na)2 and CoPc(SO3Na)4, at pH
8.0 and 10.2, performed on the static installation.
As can be seen from Fig. 1a, introduction of al-
ready a second portion of the substrate results in that
the process becomes steady-state, being characterized
by rather high oxidation rate [especially in the pres-
ence of CoPc(SO3Na)4]. In the experiments with
The process of liquid-phase oxidation of H2S at
pH 10.2 (Fig. 1b) does not become steady-state upon
repeated charging of the substrate: the time of oxida-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 12 2003

1948
FADDEENKOVA, KUNDO
Table 1. Calculated equilibrium compositions of an ab-
sorbing solution of soda in purification of an H2S-contain-
ing gas ([H2S] = 0.3, [CO2] = 2.5 vol %; Pgas = 101 kPa)
The disodium salt of disulfonic acid of cobalt
phthalocyanine, CoPc(SO3Na)2, is used in air puri-
fication to remove H2S [12, 13]. In this case, a suffi-
cient capacity of a weakly alkaline absorbing solution
for H2S is ensured both by the alkalinity of the ab-
sorbing solution and by the high activity of the cat-
alyst CoPc(SO3Na)2. In purification of oxygen-free
gases, the capacity of the absorbing solution for sulfur
depends solely on the alkalinity of the absorbing so-
lution. Table 1 lists calculated equilibrium composi-
tions of a soda solution at various pH values of the
solution in purification of a gas containing H2S.
Concentration, M
pH
value
NaHCO3
Na2CO3
NaHS
Na2S
2
4
3
7
6
5
4
3
8.0 3.17 10 1.47 10 2.22 10 1.6 10
3
2
3
8.5
9.0
9.5
0.100
0.317
1.00
1.47 10
7
10 1.6 10
2
1.47 10 2.22 10 1.6 10
0.147
1.47
0.07
1.6 10
1
10.0
3.17
2.22 10 1.6 10
As follows from the data in Table 1, raising the pH
of the absorbing solution from 8.0 to 10.0 leads to
an increase in the equilibrium content of H2S being
caught in the absorbing solution by two orders of
magnitude (H2S is present in solutions at pH 8 10
mainly as HS and S2 ions). Therefore, it is necessary
to use absorbing solutions with the highest possible
pH value in purification of oxygen-free gases to re-
move H2S with CoPc(SO3Na)n. Consequently, it is
important to select the conditions at which H2S is ox-
idized in solutions with the highest possible pH value
in the stationary mode by the polysulfide mechanism,
to give elementary sulfur as a result of oxidation.
tion increases upon introduction of each subsequent
portion of the substrate into the reaction mixture.
The elementary sulfur formed in the initial experi-
ment (curve 1) dissolves afterwards (curves 2 and 3):
in runs with the CoPc(SO3Na)2 catalyst, no sulfur was
formed at all. At pH 10.2, an intermediate oxidation
mechanism is operative [4], in which a major part of
polysulfide ions formed in reactions (1) (4) is non-
catalytically oxidized to SO23 ions. Sulfite ions ac-
cumulated in the absorbing solution increasingly dis-
rupt the polysulfide oxidation mechanism by decom-
posing the sulfide ions:
The process of liquid-phase oxidation of H2S at
pH 10.2 (Fig. 1b) does not become steady-state be-
cause of the accumulation of the oxidation semiprod-
uct Na2SO3 in the absorbing solution. To pass to
a stationary oxidation mode, it is necessary to restrict
the accumulation of SO23 ions in the reaction mixture.
(n
1)SO23 + HSn = (n
1)S2O23 + HS .
(6)
In the experiments performed at pH 10.2, the li-
quid-phase oxidation of H2S did not become steady-
state. Therefore, absorbing solutions of this composi-
tion cannot be recommended for use in gas purifica-
tion to remove hydrogen sulfide.
It is known that manganese compounds are active
catalysts for liquid-phase oxidation of H2S and oxi-
dation of sulfite ions to sulfate ions. In this study,
it is suggested to introduce soluble Mn2+ salts into
the reaction mixture in addition to the CoPc(SO3Na)n
catalyst.
Figure 2 shows data on oxidation of alkaline aque-
ous solutions of NaHS with oxygen in the presence
of the CoPc(SO3Na)2, CoPc(SO3Na)4, and MnSO4
catalysts.
Addition of Mn+2 salts to the CoPc(SO3Na)4 cata-
alyst (Fig. 2, curve 4) makes shorter the time of
complete NaHS oxidation, from 48 to 14 min. Also,
the composition of the oxidation products is changed:
the volume of oxygen consumed for complete oxidation
of the reaction mixture decreases from 19.6 to 16.4 ml.
In the simultaneous presence of CoPc(SO3Na)4 and
MnSO4, elementary sulfur is formed in NaHS oxidation.
In the presence of only one of these catalysts, MnSO4
(Fig. 3, curve 1) or CoPc(SO3Na)4 (Fig. 3, curve 3),
no elementary sulfur is formed in NaHS oxidation.
Fig. 2. Kinetics of oxidation with oxygen of alkaline
aqueous solutions of NaHS in the presence of catalysts,
CoPc(SO Na) , CoPc(SO Na) , and MnSO . T = 25 C,
3
2
3
4
4
P
10
= 101 kPa, pH 11.3, V = 20 ml, [H S] = 2.4
M. Concentration (M): (1) [MnSO ] = 0.5 10 ,
4
O
2 0
22
3
(2) [CoPc(SO Na) ] = 10, (3) [CoPc(SO Na) ] = 10;
3
2
3
4
1
3
(4) [CoPc(SO Na) ] = 10 mg l , [MnSO ] = 0.5 10 M.
3
4
4
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 12 2003

USE OF COBALT(II) PHTHALOCYANINE SULFONATES IN GAS PURIFICATION
1949
Table 2. Results obtained in purification of petroleum gas on the pilot installation (amount of petroleum gas being pu-
1
1
1
rified 0.76 m3 h , air flow rate 2.4 m3 h , solution circulation rate 47 l h , time of oxidative regeneration of solution
1
12.8 min, MnCl2 concentration 80 mg l , purified gas contains no H2S, regenerated solution contains HS ions)
H2S content Amount of
in unpurified H2S caught
Solution pH
Content of indicated substance in absorbing solution
,
min
gas,
by 1 l of
after
after
NaHCO3,
Na2CO3,
Na2S2O3 , CoPc(SO3Na)4 ,
1
1
1
1
vol %
solution, g absorber regenerator
g l
g l
g l
mg l
135
495
180
505
960
2.34
1.36
1.63
2.55
1.99
0.57
0.38
0.4
0.64
0.49
8.4
8.8
8.6
8.5
8.7
8.8
9.0
9.0
8.8
8.9
14.9
10.8
4.77
5.3
111
102
22
22
6.89
6.84
4.62
3.68
108
112
8.0
8.4
The elementary sulfur formed as a a result of oxida-
tion was floated to the solution surface in the regen-
erator and was removed therefrom as sulfur foam.
Figures 3 a 4 show the kinetic curves obtained in
experiments on NaHS oxidation in the presence of
MnSO4 and CoPc(SO3Na)4 catalysts at pH 11.0 and
11.85, respectively. In these experiments, the stage of
oxidative regeneration of the absorbing solution was
simulated by multiple introduction of the substrate
into an oxidized solution.
Table 2 presents the results obtained in purification
of petroleum gas to remove H2S with CoPc(SO3Na)4
and MnCl2 catalysts.
At pH 11.0 and 11.85, the process of liquid-phase
oxidation of H2S becomes steady-state already after
a second introduction of the substrate. The main
oxidation products are elementary sulfur and thio-
sulfates. Thus, simultaneous use of two catalysts,
CoPc(SO3Na)4 and Mn2+, must ensure a stationary
mode of liquid oxidative purification of oxygen-free
gases to remove H2S.
Fig. 3. Kinetics of NaHS oxidation with oxygen in the pres-
ence of CoPc(SO Na) and MnSO catalysts. T = 25 C,
Petroleum gas was purified to remove H2S by the
liquid oxidative method on the pilot installation. The
initial absorbing solution contained CoPc(SO3Na)4
and MnCl2 catalysts, and also sodium thiosulfate,
carbonate, and bicarbonate.1
3
4
4
P
= 101 kPa, pH 11.0, V = 20 ml, [CoPc(SO Na) ] =
O2
3 4
1
3
10 mg l , [MnSO ] = 0.5 10
M. (1) [NaHS]
=
4
0
2
2.4 10 M, (2 7) reaction mixture after the preceding
experiment, into which NaHS was introduced in amount
equal to its initial content in the reaction mixture.
The gas to be purified was fed into the bottom
part of an absorber packed with iron chips and was
washed there in the counterflow mode with the ab-
sorbing solution.
The gas purified to remove H2S was directed from
the upper part of the absorber through a spray catcher
to the flare, and the absorbing solution saturated with
hydrogen sulfide was delivered to the bottom part of
the regenerator, an apparatus with a continuous bubbl-
ing bed. In the regenerator, air was bubbled through
the solution and the H2S caught was oxidized. The re-
generated solution was delivered from the upper part
of the regenerator to the upper part of the absorber.
Fig. 4. Kinetics of oxidation of aqueous alkaline solutions
of NaHS with oxygen in the presence of CoPc(SO Na)
3
4
and MnSO catalysts. T = 25 C, P = 101 kPa, pH 11.85,
4
O2
1
V
= 20 ml, [CoPc(SO Na) ] = 10 mg l , [MnSO ] =
0.5 10 M. (1) [NaHS] = 2.4 10 M, (2 4) reaction
3 4 4
3
2
0
1
The tests were performed by staff members of the VNIPIgaz-
mixture after the preceding experiment, into which NaHS
was introduced in amount equal to its initial content in
the reaction mixture.
pererabotka Institute (Krasnodar) with participation of one of
the authors of this paper.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 12 2003

1950
FADDEENKOVA, KUNDO
3. Stuchinskaya, T.L., Maizlish, V.E, Kundo, N.N., and
It follows from the data in Table 2 that complete gas
purification was observed at sufficiently high loads
in terms of H2S to be purified (up to 0.6 g H2S l ).
At solution pH 8.4 9.0, the purification mode was
stable. The yield of sulfur was about 90%.
Smirnov, R.P., Zh. Prikl. Khim., 1993, vol. 66, no. 5,
pp. 1039 1043.
1
4. Abel, E.W., Chem. Commun., 1971, no. 9,
pp. 449 450.
5. Wagnerova, D.M., Schwertnerova, E., and Veprek-
Šišska, J., Coll. Czech. Chem. Commun., 1974, vol. 39,
no. 8, pp. 1980 1988.
CONCLUSIONS
6. Faddeenkova, G.A. and Kundo, N.N., Zh. Prikl. Khim.,
(1) It was shown that the process of liquid oxida-
tive purification of oxygen-free gases to remove H2S
with cobalt phthalocyanine sulfonates as catalysts is
stable if accumulation of SO23 ions in the absorbing
solution is prevented.
1979, vol. 52, no. 10, pp. 2161 2165.
7. Karyakin, Yu.V. and Angelov, I.I., Chistye khimiches-
kie veshchestva (Pure Chemical Substances), Moscow:
Khimiya, 1974.
8. TU (Technical Specification) 2061 49, Lead Indica-
tor Paper.
(2) If manganese chloride MnCl2 was used, together
with the CoPc(SO3Na)4 catalyst, on a pilot installation,
petroleum gas containing 1.4 to 2.6 vol % H2S was
completely purified to remove H2S. In this case, the
capacity of the absorbing solution for H2S was up to
9. Lazarev, V.I. and Kostrikov, V.I., Zh. Anal. Khim.,
1970, vol. 25, no. 3, pp. 553 555.
10. Kreshkov, A.P., Osnovy analiticheskoi khimii (Fun-
damentals of Analytical Chemistry), Moscow: Khi-
miya, 1976, vol. 1, 4th ed.
1
0.6 g l , with the yield of elementary sulfur obtained
in the process of purification equal to about 90%.
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11. Kreshkov, A.P., Osnovy analiticheskoi khimii (Fun-
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