Liquid-Phase Oxidation of Inorganic Sulfides in Aqueous Media in the Presence of a Homogeneous Catalyst Based on 3,3′,5,5′-Tetra-tert-Butyl-4,4′-Stilbenequinone

Article abstract of DOI:10.1134/S0036023618020109

The rates and factors influencing the rates of liquid-phase oxidation of inorganic sulfides by oxygen in aqueous media in the presence of a homogeneous catalyst based on 3,3′,5,5′-tetra-tert-butyl-4,4′-stilbenequinone dissolved in the kerosene fraction ha

Full text of DOI:10.1134/S0036023618020109

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2018, Vol. 63, No. 2, pp. 256–261. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © H.Y. Hoang, R.M. Akhmadullin, F.Yu. Akhmadullina, R.K. Zakirov, A.G. Akhmadullina, 2018, published in Zhurnal Neorganicheskoi Khimii, 2018, Vol. 63,
No. 2, pp. 245–250.
PHYSICAL METHODS
OF INVESTIGATION
Liquid-Phase Oxidation of Inorganic Sulfides in Aqueous Media
in the Presence of a Homogeneous Catalyst Based
on 3,3',5,5'-Tetra-tert-Butyl-4,4'-Stilbenequinone
a,
b
a
H. Y. Hoang *, R. M. Akhmadullin , F. Yu. Akhmadullina ,
a
b
R. K. Zakirov , and A. G. Akhmadullina
a
Kazan State University of Research and Technology, Industrial Biotechnology Department, Kazan, 420015 Russia
b
Ahmadullins—Science and Technologies, Kazan, 420029 Russia
*
e-mail: nhochieny@gmail.com
Received November 25, 2016
Abstract⎯ The rates and factors influencing the rates of liquid-phase oxidation of inorganic sulfides by oxy-
gen in aqueous media in the presence of a homogeneous catalyst based on 3,3',5,5'-tetra-tert-butyl-4,4'-stil-
benequinone dissolved in the kerosene fraction have been studied.
DOI: 10.1134/S0036023618020109
Sulfur compounds are undesirable components in and the contents were heated to 70°С under stirring.
oils, as they sharply impair the quality of petroleum After the reaction mass was heated for 30 min, 42 mL
products and pollute the environment when used. of 35% aqueous hydrogen peroxide was dropped in,
Purification of petroleum products from sulfur com- and the reaction was continued for 9 h at 70–75°С.
The resulting mixture was cooled to room tempera-
ture; the precipitated crystals were filtered off and
dried. The 3,3',5,5'-tetra-tert-butyl-4,4'-stilbenequi-
none yield was 98%.
An aqueous ammonium sulfide solution was pre-
pared as described in [4]; sodium hydrosulfide solu-
tion was prepared as described in [5].
pounds often produces sulfurous alkaline wastes
SAWs) that contain inorganic sulfides in high con-
centrations. Being toxic, SAWs cannot be discharged
to water bodies or collected and purified together with
the other industrial sewages even though considerably
diluted.
There are various methods for decontaminating
SAWs, the most promising being the liquid-phase oxi-
dation of SAW by air oxygen in the presence of a cata-
lyst [1–3]. In the present study, we propose a new
homogeneous catalyst based on 3,3',5,5'-tetra-tert-
butyl-4,4'-stilbenequinone (hereafter, referred to as
stilbenequinone) dissolved in the kerosene fraction,
for the liquid-phase oxidation of sulfide–hydrosulfide
derivatives; this catalyst has high catalytic activity and
selectivity and is stable in alkaline media. In choosing
the kerosene fraction, we were guided by its low solu-
(
The sodium sulfide used corresponded to the
GOST (State Standard) 2053-77. Sodium sulfide
solutions were prepared by dissolving Na S · 9H O in
2
2
distilled water.
Also used were: technical grade oxygen in cylinders
(
GOST 5583-78), aqueous ammonia (GOST 3760-79),
technical grade argon in cylinders (GOST 10157-79),
kerosene fraction (GOST 10227-2013), and technical
grade toluene (GOST 14710-78).
The oxidation of inorganic sulfides was performed
3
bility in water, low volatility, and a satisfactory solubil- in a 150-cm glass three-necked cylinder-shaped reac-
ity of stilbenequinone in kerosene.
tor. To the reactor, 40 mL of a solution of an inorganic
sulfide and 20 mL of kerosene were poured in the pres-
ence of a calculated amount of the catalytic compo-
nent. The oxygen was fed from a cylinder to the reac-
EXPERIMENTAL
–1
The catalytic component, 3,3',5,5'-tetra-tert- tion solution at 0–625 h . The solution in the reactor
butyl-4,4'-stilbenequinone, was prepared by following was stirred at 1400 rpm. The temperature of the reac-
3
method: a 500-cm cylinder-shaped glass reactor was tion solution was maintained at 90°C by a tempera-
loaded with 30 g of 2,6-di-tert-butyl-4-methtlphenol, ture-controlled stirrer. In certain periods during an
3
g of potassium iodide, and 120 mL of isopropanol, experiment, oxygen feeding was stopped, the magnetic
256

LIQUID-PHASE OXIDATION OF INORGANIC SULFIDES
257
stirrer was switched off, and samples were taken to
RESULTS AND DISCUSSION
determine the sulfides by potentiometric titration
according to GOST 22985-90. Sodium thiosulfate and
sodium sulfite were determined by the method pro-
posed in [6]; sodium sulfate was determined spectro-
photometrically [7].
Oxidation of Sodium Sulfide in the Presence
of a Homogeneous Catalyst Based on a Stilbenequinone
Sodium sulfide oxidation in the presence of a
homogeneous catalyst based on a stilbenequinone has
a complex scheme and comprises several stages. Men-
The 3,3',5,5'-tetra-tert-butyl-4,4'-stilbenequinone kovsky and Yavorsky [6] proposed a reaction scheme
was determined by a photocolorimetric method: From for the liquid-phase oxidation of sulfide sulfur in the
the three-necked cylinder-shaped reactor, a 0.5-mL presence of benzoquinone. According to these authors
sample of the kerosene phase was taken without pre- [6], mechanism of sulfide sulfur oxidation in the pres-
cooling, then the sample was diluted with toluene to ence of stilbenequinone can occur as follows (Scheme 1):
5
0 mL in a volumetric flask. The kerosene phase with the first stage involves the hydrolysis of sodium sul-
the stilbene quinone dissolved therein colors toluene fide; at the second stage, the sodium hydrosulfide pro-
bright yellow, the color intensity increasing as the stil- duced at the first stage reacts with stilbenequinone to
bene quinone concentration increases. Light absorp- reduce it to 1,2-bis(3,5-di-tert-butyl-4-hydroxyphe-
tion was determined on an Ecros PE5300V spectro- nyl) (hereafter in the text, hydrostilbenequinone); and
photometer at the wavelength λ = 500 nm using a the third stage involves the regeneration of the catalyst
1
0-cm cell, followed by the determination of catalyst by oxidizing the hydrostilbenequinone to stilbenequi-
concentration from a calibration plot.
none in an alkali medium.
k3
O2 +
CH3O H C
3
H3C
H3C
CH3
CH3
H C
3
CH3
OH
H C
CH3
CH3
3
H C
3
H3C
H3C
CH3
+
H2O
k1+
CH3 O H C CH3
Na2S
NaHS
P +
k1−
k2
H C
CH3
CH3
3
H C
3
CH3
H C
3
OH
Scheme 1. Oxidation of sodium sulfide in the presence of a homogeneous catalyst based on a stilbenequinone. k , k , and
1
2
k3 denote rate constants; P denote oxidation products.
The alkali-metal sulfides are well soluble in water certain minimal value and then increases again after
and are strongly hydrolyzable, so the oxidation rate is the sodium sulfide is exhausted.
controlled by the second or third stage.
Our results provide evidence that the rates of sul-
In studying the rate of catalytic sodium sulfide oxi- fide sulfur oxidation by stilbenequinone are higher
dation as a function of oxygen concentration, we than the catalyst regeneration rates. Therefore, cata-
found that, initially, the reaction was independent of lyst regeneration is the rate-controlling step in the
variations in oxygen concentration (Fig. 1a), but was reaction of sodium sulfide oxidation in the presence of
determined only by the presence of stilbenequinone.
stilbenequinone.
In studying the effect of oxygen amount on the cat-
alytic oxidation of sodium sulfide, we also proved the
absence of this effect on the initial reaction rate and on
the complete exhaustion of sulfide sulfur at oxygen
Influence of the Induction Period and the Catalyst
Amount on the Sulfide Sulfur Oxidation Rate
in the Presence of a Homogeneous
–1
flow rates higher than 45 h in an ideal mixing reactor
Table 1). From Fig. 1b one can infer that the stilbene
Catalyst Based on Stilbenequinone
(
quinone concentration in the oxygen-saturated reac-
The kinetic curve for the studied catalytic reaction
tion solution decreases in the course of reaction to a is affected by two more factors, namely, the induction
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 63 No. 2 2018

2
58
HOANG et al.
(a)
0
0
0
0
0
0
0
.8
.7
.6
.5
.4
.3
.2
0
.1
α
0
50
100
150
200
Time, min
1
0% O2
20% O2
40% O2
60% O2
80% O2
(b)
0.8
0
.47
.43
.39
.35
0
0
0
.6
.4
.2
B
0
0
A
0
0
60
120
Time, min
180
240
Fig. 1. Panel (a): kinetics curves for catalytic sodium sulfide oxidation with various initial oxygen concentrations in the carrier
gas. Panel (b): (A) rate curves for catalytic sodium sulfide oxidation and (B) variation in stilbenequinone concentration. The initial
–1
sodium sulfide concentration: 0.7 mol/L; reaction temperature: 90°C; stilbenequinone amount: 0.5 g; oxygen flow rate: 300 h
stirrer rotation velocity: 1400 rpm; kerosene volume: 20 mL; and aqueous sodium sulfide solution volume: 40 mL.
;
–
period and the amount of catalyst. Figure 2a shows step) and the amount of ОН ions that catalyze the
rate curves for the oxidation of sulfide sulfur and reduction of stilbenequinone (the 3rd step) [10–12]. A
hydrosulfide sulfur at various initial concentrations.
consequence of this is a decrease in the number of ele-
mentary reaction acts and the associated lowering of
the reaction rate.
It is apperent from Fig. 2a that, in sodium sulfide
oxidation, induction periods lengthen as the initial
sodium sulfide concentration increases. The observed
Sodium hydrosulfide oxidation (Fig. 2b) has no
effect may be explained by a nearly complete hydroly- induction period, but the effect of the catalyst
sis of sodium sulfide upon its dissolution in water to amount is manifested at low initial hydrosulfide con-
form sodium hydrosulfide [8] (the 1st step). According centrations. This is likely to arise from high proton
to the Ostwald dilution law, the degree of dissociation concentrations in sodium hydrosulfide solutions
–
+
2–
of sodium hydrosulfide is reduced as its concentration (HS + H O ꢀ H O + S ), the protons having a
2
3
rises [9]. Therefore, an increase in the initial sodium far higher electrophilicity index [13] and a small
sulfide concentration in the reaction solution radius, which is responsible for an attack on the car-
+
–
decreases the amount of Na and HS ions that enter bonyl group of sterically hindered quinone and the
the elementary reaction with stilbenequinone (the 2nd more facile formation of an activated complex with
Table 1. Average rates of catalytic sodium sulfide oxidation in the presence of stilbenequinone at various oxygen flow rates
(
the initial sodium sulfide concentration: 0.7 mol/L; reaction temperature: 90°C, stilbene quinone amount: 0.5 g; stirrer
velocity: 1400 rpm; kerosene volume: 20 mL; aqueous sodium sulfide solution: 40 mL; reaction time: 120 min)
Oxygen flow rate, h–1
0
45
75
125
300
475
625
Average oxidation rate, mol/(L min)
0.0026
0.0099
0.0103
0.0105
0.0106
0.0106
0.0106
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY
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LIQUID-PHASE OXIDATION OF INORGANIC SULFIDES
259
(a)
(b)
1
00
100
80
60
40
20
8
0
0
0
0
6
4
2
τ
ind-2 ind-3 ind-4
τind-5
τ
τ
0
60
Time, min
120
0
60
120
Time, min
1
.75 mol/dm3
1.4 mol/dm3
1.05 mol/dm3
0.70 mol/dm3
0.35 mol/dm3
Fig. 2. (a) Sodium sulfide and (b) sodium hydrosulfide oxidation rates at various initial concentrations. Stilbenequinone amount:
.42 g; the other experimental conditions are as in the legend to Fig. 1.
0
sulfide sulfur (Scheme 2). As a result, the rate of the stilbene quinone; the newly formed hydrostilbene-
second step is accelerated. The lower the pH, the quinone has not enough time to oxidize to stilbene-
more rapidly this reaction proceeds. On the rate quinone upon subsequent oxidation, thereby being
curves with initial NaHS concentrations of 0.35 and responsible for the slowed down rates of sulfide sulfur
0
.70 mol/L, one can see that, the higher the dilution oxidation. At higher initial sodium hydrosulfide con-
of the initial concentration, the lower the pH. Due to centrations, its oxidation rate and catalyst regenera-
this, stilbenequinone first rapidly converts to hydro- tion rate increase as pH rises.
d−
H C
2+
CH3
3
H C
CH3
3
OH
CH3 H C
CH3
O
3
OH
CH3
H3C
CH3
CH3
H3C
H C
3
CH3
H C
3
d+
H C
3
CH3
HS
HS
H C
3
+
2HS−
2H+
CH
CH
+
CH
CH
CH
CH
H C
3
H C
CH3
CH3
CH3
CH3
3
H C
3
d+
CH3
CH3
H C
3
CH OH
3
H C
3
OH
CH3
H C
3
CH3
O
H3C
H C
H C
3
3
−
d
Scheme 2. Formation of an activated complex of stilbenequinone with proton.
Influence of an Inhibitor on the Sulfide Sulfur Oxidation philes. As mentioned above, the action of a stilbene-
Rate in the Presence of a Homogeneous
Catalyst Based on a Stilbenequinone
quinone–based homogeneous catalyst consists pri-
marily of the attack of an electrophile on the quinone
Quinones are unsaturated cyclic diketones with carbonyl group, which is due to the formation of an
fused structure, so they are very sensitive to electro- activated complex with sulfide sulfur. In order to assess
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 63 No. 2 2018

2
60
HOANG et al.
0
1
00
.011
7
5
5
0
5
0
0
.009
2
0.007
40
50
60
0
0.05
0.10
0.15
0.20
0.25
Temperature, °C
NH OH concentration, mol/L
4
With kerosene
Catalytic component + kerosene
Fig. 4. Average rate of catalytic sodium sulfide oxidation in
the presence of stilbenequinone versus aqueous NH OH
4
concentration. The initial sodium sulfide concentration:
0
.7 mol/L; reaction temperature: 70°C; stilbene quinone
Fig. 3. Ammonium sulfide conversion versus temperature
in the presence and absence of stilbenequinone. Stilbene
quinone amount: 0.45 g (for the catalytic experiment);
aqueous ammonium sulfide solution: 40 mL; the other
experimental conditions are as in the legend to Fig. 1.
–1
amount: 0.5 g; oxygen flow rate: 125 h ; stirrer rotation
velocity: 1400 rpm; kerosene volume: 20 mL; total volume
of the aqueous sodium sulfide solution and aqueous
ammonia: 40 mL; and reaction time: 120 min.
the effect of the electrophile on the catalytic oxidation
process in the presence of stilbenequinone, we studied
the oxidation rate of sulfide sulfur depending on its
type. The results of these studies show that the rate of
catalytic ammonium sulfide oxidation does not
change compared to the noncatalytic process (Fig. 3).
There is the following possible explanation: as known,
in aqueous solutions of ammonium sulfide (NH ) S,
which is formed by a weak base cation and a weak acid
anion, there exist ammonium and hydroxide ions, sul-
fide and hydrosulfide ions, neutral molecules of
ammonia, hydrogen sulfide, etc. [14].
0
.084
0
.064
.044
0
4
2
0
.024
0.004
0
40
80
120
Time, min
NH ) S
Ammonium ions are strong electrophiles and have
a tetrahedral spatial configuration, hampering their
addition at the carbonyl group of the sterically hin-
dered stilbenequinone, and thereby inhibiting com-
plexation with sulfide sulfur. In addition, neutral
ammonia molecules with their lone pairs are nucleop-
hiles that compete with sulfide ions for complexation
(
Na2S
4
2
Fig. 5. Kinetics curves for noncatalytic sulfide sulfur oxi-
dation by stilbenequinone. The initial sulfide sulfur con-
centration: 0.09 mol/L; reaction temperature: 80°C; stil-
bene quinone amount: 1.25 g; stirrer rotation velocity: 1400
rpm: kerosene volume: 20 mL; aqueous sodium sulfide
solution: 40 mL.
(Scheme 2).
Figure 4 makes it clear that, when aqueous ammo-
nia is added to a sodium sulfide solution, the catalytic the presence of stilbenequinone and depends on pH.
oxidation rate is reduced. The higher the ammonia We have found that ammonium ion inhibits the oxida-
concentration, the lower the sodium sulfide oxidation tion of sulfide sulfur in the presence of stilbenequi-
rate.
Compared to sodium sulfide, ammonium sulfide is
oxidized by stilbenequinone (second stage) slowly
none.
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Translated by O. Fedorova
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 63 No. 2 2018