The influence of a quartz surface on the transformation of molybdenite under the action of hydrogen oxidation

Article abstract of DOI:10.1023/A:1010473619760

The process of the transformation of powdered molybdenite (MoS₂) under the action of hydrogen oxidation is studied under the conditions of adding quartz pieces, different in shape and size. The investigation is carried out in flow-type conditions at an atmospheric pressure and 873 K. The time of contact with the gas phase, where the hydrogen oxidation takes place, is 38 s. The ratio of initial compounds is P_H2 : P_air = 3 : 1. It is shown that the presence of quartz pieces increases the degree of molybdenite desulfurization.

Full text of DOI:10.1023/A:1010473619760

Kinetics and Catalysis, Vol. 42, No. 2, 2001, pp. 243–245. Translated from Kinetika i Kataliz, Vol. 42, No. 2, 2001, pp. 271–273.
Original Russian Text Copyright © 2001 by Kosoyan, Niazyan.
The Influence of a Quartz Surface on the Transformation
of Molybdenite under the Action of Hydrogen Oxidation
A. Zh. Kosoyan and O. M. Niazyan
Institute of Chemical Physics, National Academy of Sciences of Armenia, Erevan, Armenia
Received June 9, 1998
Abstract—The process of the transformation of powdered molybdenite (MoS ) under the action of hydrogen
2
oxidation is studied under the conditions of adding quartz pieces, different in shape and size. The investigation
is carried out in flow-type conditions at an atmospheric pressure and 873 K. The time of contact with the gas
phase, where the hydrogen oxidation takes place, is 38 s. The ratio of initial compounds is PH2 : P = 3 : 1. It
air
is shown that the presence of quartz pieces increases the degree of molybdenite desulfurization.
Earlier, it has been shown [1–4] that the gas phase
As a result, the gas phase where the hydrogen oxi-
chain reactions of hydrocarbon and hydrogen oxidation dation took place continuously contacted the solid inor-
can cause the transformation of inorganic compounds ganic compound. The rate of supply and the ratio of ini-
and, in particular, can induce the formation of hydrogen tial gas components were controlled with flow meters.
sulfide if this chain reaction takes place in contact with The gas mixture was sampled directly from the first
metal sulfides. It was shown in [5–7] that these pro- reactor using a quartz capillary (Fig. 1a) and from the
cesses involve atoms and radicals and, particularly, that gas outlet of the second reactor (Fig. 2b). The weight of
sulfur-containing paramagnetic species are formed in the molybdenite sample was 2 g in all experiments. The
these complex coupled processes. It is also necessary to contact time in the gas phase reaction was 38 s. Hydro-
note that hydrogen sulfide is not formed under these gen sulfide and sulfur dioxide (SO ) were analyzed by
2
conditions if only hydrogen or only hydrocarbon is in chromatography as described in [2, 5, 9].
contact with metal sulfides metals.
The first set of experiments was carried out in the
However, a comparison of experimental data first reactor (1.8 cm in diameter, Fig. 1a). The quartz
obtained in the study of the action of the same chain boat was placed into the reactor and filled with: (1) the
reactions on copper chalcopyrite and molybdenite molybdenite sample, (2) the molybdenite sample with
shows some difference between these two processes. rectangular quartz pieces buried in the powder to half-
For example, a decrease in the reactor diameter, in length, (3) the molybdenite sample with horizontal
which the gas phase chain reaction takes place, leads to quartz cylinders buried in the powder to 2/3 of the
an increase rather than to a decrease in the intensity of length, and (4) the molybdenite sample with relatively
the process of molybdenite transformation, as was small quartz pieces put onto the sample surface.
observed for copper chalcopyrite [3] and expected from
the general laws of chain reactions [8].
(‡)
1
This work deals with the influence of a quartz sur-
face on the formation of sulfur-containing compounds
and particularly hydrogen sulfide during the transfor-
2
mation of molybdenite (MoS ) under the action of
2
hydrogen oxidation.
H : air
2
Experiments were carried out in reactors made of
quartz tubes of different diameters. The first reactor
was a cylindrical quartz tube, 1.8 cm in diameter.A spe-
cial quartz boat with molybdenite powder was placed
into the tube. The second reactor was a U-shaped tube,
(b)
H : air
2
0
.8 cm in diameter, and filled with molybdenite powder
1
(
Fig. 1). The reactors were placed into a temperature-
controlled heater. Experiments were carried out under
flow conditions at 873 K and atmospheric pressure. The
initial mixture of hydrogen with air with the composi-
Fig. 1. Schematic of the reactor assembly: (a) cylindrical
reactor (d = 1.8 cm) with a boat for the molybdenite sample,
(
b) a U-shape reactor (d = 0.8 cm) filled with molybdenite
sample. (1) a heater with a temperature controller, (2) a cap-
tion PH2 : P = 3 : 1 passed through the reactors.
illary for gas sampling for chromatographic analysis.
air
0
023-1584/01/4202-0243$25.00 © 2001 MAIK “Nauka /Interperiodica”

2
44
KOSOYAN, NIAZYAN
P, kPa
tion increases in this case from 1.67% (Fig. 2, curve 1)
to 3.1%.
This effect could have been associated with an
increase in the total quartz surface area, which is equal
to the area of the quartz reactor surface and the area of
quartz pieces S + Squartz, and with respective increase in
the ratio of S + Squartz to the reactor volume. Indeed,
when comparing data obtained in reactors with differ-
ent diameters (see the table), we see the correlation
between the extent of desulfurization and the ratio
between the reactor surface area and its volume (S/V).
However, in the experiments with cylindrical quartz
pieces, the ratio of the quartz surface area to the reactor
volume increases insignificantly (from 2.22 to 2.31),
but the efficiency of the process almost doubles (Fig. 2,
curves 1 and 3).
1
1
5
4
0
1
5
3
The degree of molybdenite desulfurization also
2
increases when the rectangular pieces of quartz (S
=
quartz
2
1
.25 cm ) are placed onto the molybdenite sample and
buried in the powder to half-length (Fig. 2, curve 2).
0
10
20
The desulfurization degree increases from 1.67 to
Time, min
2
.2%, that is, by a factor of 1.3, but the ratio S/V
increases by only 2.5%. The degree of molybdenite
desulfurization also increases when relatively small
Fig. 2. Kinetics of hydrogen sulfide formation in the reactor
1.8 cm in diameter). PH2 : Pair = 3 : 1. The boat with the
(
pieces of quartz with the surface total area S
=
quartz
2
following sample was placed into the reactor: (1) the molyb-
denite sample; (2) the molybdenite sample with rectangular
quartz pieces buried in the powder to half-length, (3) the
molybdenite sample with horizontal quartz cylinders buried
in the powder to 2/3 of the length, and (4) the molybdenite
sample with relatively small quartz pieces put onto the sam-
ple surface.
2
.16 cm are placed onto the sample surface. In this
case, the maximal concentration of hydrogen sulfide is
achieved (Fig. 2, curve 4). However, if these quartz
pieces are not placed onto the molybdenite sample sur-
face but mixed with molybdenite powder, the effect is
small. The kinetic curve of hydrogen sulfide formation
changes insignificantly compared to the curve obtained
in the experiment with molybdenite without quartz.
Figure 2 presents the curves showing a change in
hydrogen sulfide amounts in the reacting gas during the
If quartz pieces are mixed with molybdenite at a
weight ratio of 1 : 1, the process of desulfurization fol-
process. The total amount of H S formed in the process
2
lows another route: only SO is formed in this case.
2
and, correspondingly, the degree of desulfurization cal-
culated using these curves are presented in the table.
The results presented in Fig. 2 and the table show that
This experimental result requires a detailed study.
It was shown in [10–12] that not only radical decay
[
10] but other processes with their participation take
the conversion is highest if cylindrical quartz pieces
place on the reactor surface [11]. In [12], it was exper-
2
(
Squartz = 2.26 cm ) are partially buried into the powder imentally confirmed that active species (for example,
sample (Fig. 2, curve 3). The percentage of desulfuriza- hydrogen atoms) are very mobile on the surface and can
The degree of desulfurization of molybdenite in reactors with different diameters after the addition of different quartz pieces
to molybdenite
Diameter
of the
reactor, cm
Weight
Surface area
Volume
Surface area of
quartz pieces
(
S + Squartz)/V,
Degree of des-
ulfurization, %
–
1
of molybdenite of the reactor of the reactor S/V, cm
2
3
2
cm–1
sample, g
S, cm
V, cm
Squartz, cm
1.8
1.8
1.8
1.8
3.6
0.8
2
2
2
2
2
2
56.52
56.52
56.52
56.52
113.04
47.22
25.43
25.43
25.43
25.43
50.86
7.98
2.22
2.22
2.22
2.22
1.11
5.92
*
1.25
2.26
2.16
*
–
2.27
2.31
2.30
–
1.67
2.20
3.10
2.00
0.86
3.90
*
–
*
Without the addition of quartz pieces.
KINETICS AND CATALYSIS Vol. 42
No. 2 2001

THE INFLUENCE OF QUARTZ SURFACE
245
easily migrate from one active site to another. There-
fore, we assume that quartz pieces placed onto the
molybdenite surface promote the heterogeneous forma-
tion of active sites leading to the further formation of
hydrogen sulfide.
3. Bagdasaryan, V.R., Niazyan, O.M., and Mantashyan, A.A.,
Arm. Khim. Zh., 1986, vol. 39, no. 9, p. 553.
4. Kosoyan, A.Zh., Niazyan, O.M., and Mantashyan, A.A.,
Prevrashchenie molibdenita pod vozdeistviem tsepnoi
reaktsii okisleniya vodoroda (Molybdenite Transforma-
tions under the Action of the Chain Oxidation of Hydro-
gen), Erevan, 1987 (Preprint).
The experiments showed that for any method of intro-
ducing the quartz pieces of any shape and size to molyb-
denite in the U-shaped reactor (Fig.1b, d = 0.8 cm) filled
completely with sample powder, only a small increase
in the process intensity is observed. This is expectable
because the area of the quartz reactor surface that con-
tacts molybdenite is much larger than the area of quartz
pieces.
5
6
7
. Bagdasaryan, V.R., Khachatryan, L.A., Niazyan, O.M.,
et al., Kinet. Katal., 1986, vol. 27, no. 1, p. 16.
. Kosoyan, A.Zh., Niazyan, O.M., and Mantashyan, A.A.,
Arm. Khim. Zh., 1986, vol. 39, no. 4, p. 208.
. Bagdasaryan, V.R., Khachatryan, L.A., Niazyan, O.M.,
and Mantashyan, A.A., React. Kinet. Catal. Lett., 1986,
vol. 30, no. 2, p. 391.
Therefore, according to the experimental data and
the data presented in [10–12], we suppose that the pro-
cess of hydrogen sulfide formation under the action of
the reaction of hydrogen oxidation on molybdenite is
affected considerably by the quartz surface contacting
the molybdenite sample directly, that is by heteroge-
neous factors.
8. Semenov, N.N., O nekotorykh problemakh khimicheskoi
kinetiki i reaktsionnoi sposobnosti (On Some Problems
of Chemical Kinetics and Reactivity), Moscow: USSR
Acad. Sci., 1958.
9
. Bernatosyan, A.G., Niazyan, O.M., and Mantashyan, A.A.,
Arm. Khim. Zh., 1990, vol. 43, no. 2, p. 81.
1
0. Nalbandyan, A.B. and Vardanyan, I.A., Sovremennoe
sostoyanie problemy gazofaznogo okisleniya organ-
icheskikh soedinenii (The Present State of theArt in Gas-
Phase Oxidation of Organic Substances), Arm. SSR
Acad. Sci., 1986, p. 277.
REFERENCES
1
. Mantashyan, A.A. and Niazyan, O.M., Arm. Khim. Zh.,
1
1. Grigoryan, G.L., Arm. Khim. Zh., 1996, vol. 49, no. 4,
1
981, vol. 34, no. 6, p. 523.
p. 118.
2
. Karapetyan, A.Z., Niazyan, O.M., and Mantashyan, A.A., 12. Poladyan, E.A., Gukasyan, P.S., and Nalbandyan, A.B.,
Arm. Khim. Zh., 1984, vol. 37, no. 1, p. 3.
Dokl. Akad. Nauk SSSR, 1984, vol. 247, no. 6, p. 1417.
KINETICS AND CATALYSIS Vol. 42 No. 2
2001