Fe-ethylenediamine tetraacetate complexes immobilized on fibrous anionite and their catalytic activity in H2S oxidation

Article abstract of DOI:10.1023/A:1020936222090

The effect of the complexonate solution pH on the nature and amount of ethylenediamine tetraacetate complexes of iron, immobilized on a FIBAN A-5 fibrous anionite, and their catalytic activity in H₂S oxidation by molecular oxygen was studied.

Full text of DOI:10.1023/A:1020936222090

Russian Journal of Applied Chemistry, Vol. 75, No. 8, 2002, pp. 1231 1233. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 8, 2002,
pp. 1257 1259.
Original Russian Text Copyright
2002 by Potapova, Volkovinskaya, Soldatov, Egiazarov.
SORPTION
AND ION-EXCHANGE PROCESSES
Fe Ethylenediamine Tetraacetate Complexes Immobilized
on Fibrous Anionite and Their Catalytic Activity
in H S Oxidation
2
L. L. Potapova, T. V. Volkovinskaya, V. S. Soldatov, and Yu. G. Egiazarov
Institute of Physicoorganic Chemistry, Belarussian National Academy of Sciences, Minsk, Belarus
Received December 18, 2000; in final form, January 2002
Abstract The effect of the complexonate solution pH on the nature and amount of ethylenediamine tetra-
acetate complexes of iron, immobilized on a FIBAN A-5 fibrous anionite, and their catalytic activity in
H S oxidation by molecular oxygen was studied.
2
Purification of gas mixtures to remove hydrogen
sulfide is commonly carried out by sorption or oxida-
tion techniques with the use of solid or liquid sorbents
and catalysts. High activity in liquid-phase oxidation
24.3 g of FeCl3 6H O in 50 ml of H O. The re-
2 2
sulting solution was acidified with 2 ml of conc. HCl
and heated to 80 90 C, with 30 ml of a 25% NH OH
4
solution added dropwise under constant stirring. Then
of H S by molecular oxygen to sulfur is exhibited
50 ml of hot water was added to the Fe(OH) pre-
2
3
by ethylenediamine tetraacetate complexes of iron
cipitate formed, the mixture was stirred and allowed
to stay for 1 h for particle coagulation to occur, and
the precipitate was separated by filtration.
(Fe EDTA) [1 4].
Previously (5 7), catalytic systems with Fe EDTA
complexes immobilized on some fibrous anionites
have been synthesized and the effect of various factors
on their activity has been studied. The catalysts were
prepared using a complexonate solution obtained by
To obtain iron complexonate, 32 g of Trilon B was
placed in a beaker, 150 ml of water was added, and
the mixture was heated on a water bath, with Fe(OH)3
paste gradually added at 80 90 C. The obtained com-
mixing solutions containing stoichiometric amounts of plexonate solution (of brown color) was filtered to
an iron salt and a disodium salt of ethylenediamine
tetraacetic acid (Trilon B). The complexonate solution
was strongly acidic (pH 0.5) and contained, together
remove a minor amount of unreacted hydroxide and
then a complex salt was precipitated. For this purpose,
dimethylacetamide was added to the complexonate
solution (1 : 2 : 5 by volume) and the mixture was
heated on a water bath. The dark yellow crystals pre-
cipitated at 60 90 C were separated by filtration and
dried in air. The yield of the product was 90% of
the theoretically calculated value ( 30 g).
with complex anions, NO or Cl anions. All other
3
conditions being the same, the presence of competing
anions in the system puts limitation on the content
of complexes immobilized on the fibrous anionite,
which is associated with the ion-exchange equilibrium.
Therefore, it was of interest to obtain a solution of
iron complexonate without foreign ions and to study
the effect of the complexonate solution pH on the con-
tent and nature of Fe EDTA complexes immobilized
on the ionite and also on the catalytic activity of
the samples obtained.
The complexonate synthesized was used to prepare
a 0.1 M solution for treatment of ionite samples:
1
6
1.6 g of complexonate in 300 ml of solution, pH 6
.5. To vary the solution pH within the prescribed
limits (2.5 10.5), concentrated NH OH or HCl solu-
4
tions were added.
EXPERIMENTAL
The catalysts were prepared from the chloride form
of the FIBAN A-5 anionite, which is an ionite with
weakly basic tertiary amino groups and low content of
Iron(III) hydroxide and iron(III) complexonate
were prepared using conventional procedures. An
iron(III) chloride solution was prepared by dissolving
1
carboxy groups (exchange capacity 4.3 mg-equivg ,
1
that of carboxy groups 0.6 mg-equiv g ). The an-
1
070-4272/02/7508-1231 $27.00 2002 MAIK Nauka/Interperiodica

1232
POTAPOVA et al.
It can be seen that the dependence of the amount
of the complex immobilized on the samples (wt %)
on the solution pH is complex: with increasing pH,
the amount of the complex decreases from 21 to
1
3 wt % in the pH interval 3 5, then increases steeply
at pH 6 8, and again decreases at pH > 8 (Fig. 1).
The working life till H S breakthrough of the cat-
2
alysts synthesized also depends on the pH of the com-
plexonate solution (Fig. 2). It can be seen that samples
obtained from a sufficiently acid solution (pH 3 4) are
low-active: H S breakthrough is observed in the very
2
first minutes of experiment. Higher catalytic activity
is exhibited by samples obtained at pH > 5, and
the highest activity, by those prepared at solution
pH 7 8.5. With the pH increasing further, to 10, the
sample activity decreases somewhat. Noteworthy is
the fact that a sample obtained at complexonate solu-
tion pH equal to 3 shows low activity despite the rel-
atively high content of the complex (21 wt %).
Fig. 1. Content of Fe EDTA complexes in anionite, c, vs.
complexonate solution pH.
It should be kept in mind in interpreting the results
obtained that the complexonate solution pH simulta-
neously affects the following factors: composition and
degree of ionization of the functional groups of the
anionite, composition and charge of ethylenediamine
tetraacetate complexes with iron and their quantitative
relationship, and the degree of dissociation of hy-
drogen sulfide molecules.
Fig. 2. Working life of samples, , vs. complexonate solu-
tion pH.
The known constants of the acid-base equilibria
[8, 9] allow calculation of the fractions of various
fiber with N,N-dimethylaminopropylamine used as forms of the starting reagents at 20 C:
ionite was obtained on the basis of a polyacrylonitrile
aminating agent. Approximately 2 g of anionite swol-
Fe HEDTA + OH
[Fe EDTA(H O)] ,
len in water and squeezed on filter paper ( 0.8 g
of air-dry fiber) was poured over with 15 ml of a so-
lution with prescribed pH value, kept for 30 min,
and then removed from the solution and squeezed
on filter paper. The treatment was repeated several-
fold, until the ionite was saturated with the complex.
The amount of the complex in the fiber was deter-
mined gravimetrically: by burning a weighed portion
2
K1 = 0.5 1013 M 1;
[Fe EDTA(H O)]
[Fe EDTA(OH)]2 + H+,
2
K2 = 2.88 10 8 M;
Fe EDTA(OH)]2 + OH
3
[
[Fe EDTA(OH) ] ,
2
K3 = 3.47 104 M 1;
of the sample (1000 C, 1 h) and weighing the Fe O3
2
formed.
H2S
HS
HS + H+, K4 = 0.91 10 7 M;
H+ + S2 , K5 = 0.11 10 11 M.
Experiments on oxidation of hydrogen sulfide with
molecular oxygen were carried out in a flow-through
reactor at room temperature. Composition of the re-
action mixture (vol %): H S 0.4, O 12.2, and N the
The results of the calculations were used to plot
the dependences of the fraction of acid-base forms of
the reagents on the pH of the medium (Fig. 3). It can
be seen that the degree of hydroxylation of the com-
plexes and their charge grow with increasing pH. At
pH equal to 4, 8.5, and 12, the solution contains the
maximum amounts of, respectively, single-, double-,
and triple-charged anions of iron ethylenediamine tet-
2
2
2
rest. The sample weight in swollen state was 0.21 g
2
(cross-sectional area of the catalyst bed 0.6 cm , bed
height 1 cm), and the flow rate of the gas mixture,
1
2
7 ml min . To evaluate the efficiency of a catalytic
system (relative activity), the working life of the sam-
ples till H S breakthrough, which was recorded chro-
matographically, was determined.
2
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 8 2002

Fe ETHYLENEDIAMINE TETRAACETATE COMPLEXES IMMOBILIZED ON FIBROUS ANIONITE 1233
raacetate. According to the electroselectivity rule,
an increase in the charge of the complex favors a rise
in its content in the anionite. At the same time, the
degree of ionization of the functional groups decreases
with increasing complexonate solution pH. As a re-
sult, the absorption of the complex anion decreases.
In the pH range 3 5, only a hydrated single-charged
complex [Fe EDTA(H O)] is present in solution
2
(
Fig. 3), and the decrease in the content of the com-
plex introduced by ion exchange (Fig. 1) is apparently
due to a decrease in the degree of ionization of the
functional groups of the ionite. At pH 6 8.5, an in-
crease in the content of the supported complex is ob-
served, which correlates with the increase in the frac-
tion of the hydroxylated double-charged complex ion
2
[
Fe EDTA(OH)] , and at solution pH 8.5 10.5
Fig. 3. Fraction of acid-base forms of the reagents, , vs. the
the content of the complex in the anionite decreases.
Apparently, the charge of the counter ion affects more
strongly the ion-exchange equilibrium in the first case
pH of the medium. (1) HFe EDTA, (2) [Fe EDTA(H O)] ,
2
2
3
(
(
3) [Fe EDTA(OH)] , (4) [Fe EDTA(OH) ] , (5) H S,
2
2
2
6) HS , and (7) S
.
(
region of transition from weakly acid to weakly alka-
line medium), whereas in the second case (strongly
alkaline medium) stronger influence is exerted, con-
versely, by the decrease in the content of ionized func-
tional groups of the anionite, which results from the
increase in the concentration of OH ions.
(3) The necessary condition for effective operation
of the catalytic systems studied is high degree of H2S
dissociation to form the hydrosulfide ion, which can
be achieved at pH 8 10.
Hydrogen sulfide virtually does not dissociate in
the acid medium (pH 3 5), and, therefore, the system
is low-active, irrespective of the amount and compo-
sition of the complex introduced into the anionite.
REFERENCES
1. US Patent 4 014 983.
2. US Patent 4 278 646.
With increasing pH, the H S dissociation becomes
2
3. Gritsenko, A.I., Galanin, I.A., Zinov’eva, L.M., and
Murin, V.I., Ochistka gazov ot sernistykh soedinenii pri
ekspluatatsii gazovykh mestorozhdenii (Gas Purification
To Remove Sulfides in Exploitation of Gas Fields),
Moscow: Nedra, 1985.
more pronounced (Fig. 3, curves 5 and 6) and, corre-
spondingly, the activity of the catalytic system grows.
It is noteworthy that the content of the complex anion
in the ionite falls markedly (from 30 to 13 wt %,
Fig. 1) at pH 8.5 10.5, whereas the working life of
4
. Martell, A.E., Motekaitis, R.J., Chen, D., et al., Canad.
J. Chem., 1996, vol. 74, no. 10, pp. 1872 1879.
the samples to H S breakthrough decreases only slight-
2
ly (Fig. 2). The latter indicates that the activity of the
2
3
5. Potapova, L.L., Egiazarov, Yu.G., Soldatov, V.S., and
Elinson, I.S., Dokl. Nats. Akad. Navuk Belarusi, 1998,
vol. 42, no. 3, pp. 54 57.
[
Fe EDTA(OH)] and [Fe EDTA(OH)2] hydroxo
complexes in oxidation of hydrogen sulfide is suf-
ficiently high and dissociation of hydrogen sulfide,
rather than HS oxidation on active centers of the cat-
alyst, is the rate-limiting stage of the process.
6. Potapova, L.L., Shunkevich, A.A., Akulich, Z.I., and
Egiazarov, Yu.G., Zh. Prikl. Khim., 2000, vol. 73,
no. 5, pp. 780 784.
CONCLUSIONS
7. Yegiazarov, Yu.G., Soldatov, V.S., Radkevich, V.Z.,
et al., Proc. 16th Mendeleev Congr. on General and
Applied Chemistry, St. Petersburg, 1998, vol. 2, p. 292.
(
1) The amount of Fe EDTA complexes immobi-
lized on a fibrous anionite depends on the charge of
the complex anion and the degree of ionization of
the functional groups.
8
. Neyaglov, A.A., Digurov, N.G., Bukharkina, T.V.,
et al., Kinet. Kataliz, 1991, vol. 32, no. 3, pp. 548 552.
9
. Dyatlova, N.M., Temkina, V.Ya., and Popov, K.I.,
Kompleksony i kompleksonaty metallov (Complexones
and Complexonates of Metals), Moscow: Khimiya,
1988.
(
2) Catalytic activity in oxidation of H S by mo-
2
lecular oxygen is exhibited by the complex anions
2
3
[
Fe EDTA(OH)] and [Fe EDTA(OH) ] .
2
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 8 2002