IR Spectroscopy of the Gas Phase Formed after Interaction between CH3I and Ag-Containing Sorbents Based on Silica Gel

Article abstract of DOI:10.1134/S0036024420030140

Abstract: IR spectra of the gas phase formed during the interaction between gaseous CH₃I and SiO₂-based granular sorbents containing various silver compounds are studied. It is established that the main gaseous products formed by the

Full text of DOI:10.1134/S0036024420030140

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2020, Vol. 94, No. 3, pp. 465–470. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Zhurnal Fizicheskoi Khimii, 2020, Vol. 94, No. 3, pp. 336–341.
On the 90th Anniversary of the Russian Academy of Sciences’
Frumkin Institute of Physical Chemistry and Electrochemistry
IR Spectroscopy of the Gas Phase Formed after Interaction
between CH3I and Ag-Containing Sorbents Based on Silica Gel
S. A. Kulyukhina,*, I. A. Rumera, and V. B. Krapukhina
aFrumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow, 119071 Russia
*e-mail: kulyukhin@ipc.rssi.ru
Received June 17, 2019; revised June 17, 2019; accepted September 3, 2019
Abstract—IR spectra of the gas phase formed during the interaction between gaseous CH3I and SiO2-based
granular sorbents containing various silver compounds are studied. It is established that the main gaseous prod-
ucts formed by the interaction between CH3I and Ag-containing sorbents based on SiO2 are CH3CH2NO3,
CO2, and I2.
Keywords: methyl iodide, silver, sorbents, IR spectra, gas phase
DOI: 10.1134/S0036024420030140
INTRODUCTION
plant, CH3I is localized using inorganic Ag-contain-
ing sorbents with silver contents of 8–12 wt % [1–3].
Between 2002 and 2006, a granular sorbent based
on KSKG silica gel containing nanometer particles of
Ag compounds (trademark, Fizkhimin) was devel-
oped at the Institute for localizing radio-iodine in the
form of I2, HI, and CH3I from the vapor–gas phase [4,
The history of the Frumkin Institute’s Department
of Radiochemistry is inextricably linked to solving the
main problems of nuclear power, i.e., the safe opera-
tion of nuclear power plants, the safe handling of irra-
diated nuclear fuel, and the safe handling of radioac-
tive waste.
5]. The sorption of CH3131I from a steam–air medium
on Fizkhimin inorganic sorbents containing nanome-
ter particles of Ag or Ag and Ni was studied in [6, 7]. It
was established that the developed sorbents containing
5–6 wt % Ag or 2 wt % Ag and 4–10 wt % Ni had high
efficiency of sorption with respect to CH3131I (degree
of absorption, >99.9%). The efficiency of sorbents
remains very high (more than 99.9%) when different
parameters of both the sorbents and the medium are
altered. As part of an international Russian–Indian
contract in the field of nuclear energy, 720 kg of Fiz-
khimin sorption material was delivered in August 2007
for emergency filters of the passive filtration system to
be installed at the first and second units of the
Kudankulam nuclear power plant (India) [8–10].
There are no analogs of this passive filtration system
anywhere in the world. The work was a joint effort
between Atomstroyexport, Krasnaya Zvezda, the
Institute of Physics and Power Engineering
(Obninsk), Atomenergoproekt, the Obninsk Center
The Laboratory of Physical and Chemical Means
of Localizing Radioactive Elements, headed by Sci.
Doc. S.A. Kulyukhin, was established in 2002 as a
result of the Institute being reorganized on the basis of
two laboratories, that of the Chemistry of Transcu-
rium Elements, headed by Doc. Sci. N.B. Mikheev,
that of Technological Processes, headed by Cand. Sci.
V.B. Krapukhin. An important activity of the labora-
tory is developing novel functional materials, includ-
ing highly effective sorbents for the localization (trap-
ping) of organic and inorganic forms of radioactive
iodine in different environments. Special attention is
given to creating materials for environmental protec-
tion systems in unforeseen accidents at nuclear power
plants.
Inorganic AgNO3-containing sorbents are widely
used for the localization of volatile compounds of
radioactive iodine (below, radio-iodine) at nuclear
power facilities. Methyl iodide (CH3I) is one of the
volatile forms of radio-iodine most difficult to local- for Science and Technology, and a number of other
ize. Upon an unforeseen accident at a nuclear power organizations of Rosatom. Work is now underway to
465

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KULYUKHIN et al.
SiO2-7Ag-Amk, SiO2-3.5AgGG-3.5AgAz, and
SiO2-2Ag8Ni-NH3, the synthesis of which was
described in [4–7].
B
А
C
Sorbent SiO2-7AgAz contains Ag(I) in the form of
AgNO3; SiO2-7Ag-Amk in the form of Ag2O; and
SiO2-7AgGG and SiO2-3.5AgGG-3.5AgAz in the
form of AgNO3 and Ag0, respectively. Sorbent SiO2-
2Ag8Ni-NH3 contains Ni (II) as NiO and Ag(I) in the
form AgNO3 and Ag0, respectively.
8
2
1
3
7
4
Air
or Ar
All salts, alkalis, and acids used in the work were of
chemically pure grade.
6
5
Figure 1 shows the scheme of the setup used to
study the composition of the gas phase formed during
the interaction between gaseous CH3I and the above
sorbents in flows of Ar or air. The setup consists of
(1) a rotameter; (2) a hydraulic lock filled with glyc-
erol; (3) a reaction chamber, into which liquid CH3I
(4) is introduced; (5) a reactor, into which the investi-
gated composite material is placed; (6) a shaft furnace;
(7) a thermocouple; and (8) a storage tank for collect-
ing reaction products and unreacted CH3I.
In each experiment, 0.7 mL of CH3I (1600 mg) was
placed in reaction chamber (3) with a volume of
65 cm3, and 50 g of the sorbent was placed in specially
designed reactor (5) with a volume of 100 cm3. The
reaction chamber was connected to a hydraulic lock
filled with glycerol (2) and a reactor placed in a shaft-
type furnace (6). The output from reactor (5) was con-
nected to storage tank (8) with a volume of 1400 cm3 to
collect reaction products and unreacted CH3I. Before
an experiment, the storage tank was evacuated with a
rotary vane pump.
After assembling the setup, the entire system was
connected to the vacuum pump and air or argon was
pumped out of the system for 2−3 min with valves A
and C kept closed. Valve B was then closed, the vac-
uum pump was disconnected, and storage tank (8) was
connected to the system to collect reaction products
and unreacted CH3I.
Once assembly was complete, the sorbent was
heated to the required temperature. When it was
reached, the valves B and C were opened. The reaction
chamber was simultaneously placed in a water bath
with a temperature of 343–353 K. Opening valve B
resulted in the evacuation of the gas phase from the
system into the storage tank at a rate of 0.2 dm3/min.
After 5 min, valve A was opened to let air (or Ar) fill the
system. When the pressure in the system and the stor-
age tank reached atmospheric, valves A and B were
closed, the storage tank was disconnected, and the
reaction chamber was removed from the water bath.
Fig. 1. Schematic diagram of the setup for studying the
composition of the gas phase formed during the interac-
tion between gaseous CH I and the above sorbents in a
3
flow of Ar or air: (1) rotameter, (2) hydraulic lock filled
with glycerol, (3) reaction chamber, (4) liquid CH I,
3
(5) reactor, (6) shaft furnace, (7) thermocouple, and (8)
storage tank for the collection of reaction products and
nonreacted CH I.
3
produce 800 kg of this sorbent for the emergency fil-
ters of the passive filtration system to be installed on
the third and fourth units of Kudankulam NPP
(India).
Despite the wide range of studies of the localization
of radio-iodine on inorganic sorbents containing vari-
ous silver compounds, there is currently no data in the
literature on possible gaseous products that can form
as a result of the interaction between CH3I and inor-
ganic sorbents containing silver compounds. Solving
this problem is especially important, since the result-
ing organic form of radio-iodine (i.e., CH3I) can con-
3
tain not only radionuclides of iodine, but also H. In
14
addition, C can also be present when nitride fuel is
dissolved in gaseous products. As a result of the local-
ization of CH3I on composite materials, numerous
3
14
organic compounds containing H and C will enter
the gas phase and must then be removed. It is believed
that methyl nitrate CH3NO3 is the main product of
interaction between CH3I and inorganic sorbents con-
taining AgNO3 [11, 12]. However, the formation of
other organic compounds cannot be excluded. It is
therefore of interest to study the composition of the
gas phase formed during the interaction between gas-
eous CH3I and granular SiO2-based sorbents contain-
ing various silver compounds. The aim of this work
was to study this problem.
IR spectra were measured using spectrometric gas
cells filled with samples of the gas phase from the stor-
age tank. The cells had KBr windows; the volume of
each cell and the length of the optical path were
125 cm3 and 100 mm, respectively. In addition to sam-
EXPERIMENTAL
In this work, we used sorbents based on KSKG
brand silica gel (State Standard GOST 3956-76) with
granules of 1–3 mm: SiO2-7AgAz, SiO2-7AgGG,
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IR SPECTROSCOPY OF THE GAS PHASE FORMED
467
2.0
1.6
1.2
0.8
0.4
0
4000 3500 3000 2500 2000 1500 1000
500
ν, сm−1
Fig. 2. (Color online) IR spectrum of gaseous CH I [13].
3
pling from the storage tank, the gas phase was sampled hyde and other organic compounds as a result of inter-
into the IR spectrometric cells directly from the sys-
tem. Control background IR spectra of the used cells
were recorded before measuring the IR spectra of the
gas phase from the storage tank and the system. The
IR spectra were measured using a Specord M 80 spec-
trometer. Before measuring the spectra, the pressure
in the gas cells was adjusted to atmospheric using
nitrogen gas.
action between CH3I and SiO2-based sorbents con-
taining Ag compounds. In addition, the decomposi-
tion of organic compounds at high temperatures in the
presence of the studied sorbents can lead to the emer-
gence of CO2 in the gas phase.
Radicals I• can react either with one another
(forming I2), or with Ag compounds (forming AgI). I2
was indeed present in the gas phase in a number of
experiments with SiO2-7AgGG, SiO2-3.5AgGG-
3.5AgАz, and SiO2-2Ag8Ni-NH3.
RESULTS AND DISCUSSION
The below reactions are possible during the local-
ization of CH3I on the studied Ag-containing sor-
bents:
Different organic and inorganic compounds can
thus be present in the gas phase as a result of interac-
tion between CH3I and Ag-containing sorbents.
(1)
(2)
(3)
CH3I + AgNO3 → AgI + CH3NO3,
Figure 2 shows the IR spectrum of gaseous CH3I
[13]. There are two intense bands in the spectrum at
2980 and 1264 cm−1.
2CH3I + Ag2O → 2AgI + C2H5OH,
2CH3I + Ag2O + H2O → 2AgI + 2CH3OH.
Figure 3 shows the IR spectra of the gas phase
formed in Ar or air after interaction between gaseous
CH3I and granular SiO2 or Ag-containing sorbents.
The temperature of sorbents and SiO2 was ∼423 K.
In addition, the sorbents synthesized using hydra-
zine hydrate or NH3 contain nanometer particles of
Ag0. These particles can act as catalysts for the reaction
Ag0
•
•
(4)
CH3I ⎯⎯→ I + CH3.
Analysis of the IR spectra showed that when a flow
of air with CH3I passes through a layer of granular
SiO2 heated to ∼423 K, only the bands characteristic
of CH3I are recorded in the gas phase (Fig. 3b, spec-
trum 1), and no additional gaseous products form.
•
Radicals
formed in this reaction can interact with
CH3
organic products of reactions (1)–(3), forming more
complex compounds. For example, interaction
•
between
and CH3NO3 can result in the formation
CH3
of ethyl nitrate CH3CH2NO3. In addition, the interac-
tion between these radicals and atmospheric oxygen
can lead to the formation of formaldehyde. The gas
At the same time, passing a flow of air with CH3I
through a layer of Ag-containing sorbents based on
phase can thus contain methyl nitrate CH3NO3, ethyl SiO2 results in the formation of gaseous products, the
nitrate CH3CH2NO3, methanol, ethanol, formalde-
bands of which are clearly visible in the IR spectra
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KULYUKHIN et al.
16
(а)
(b)
10
8
14
12
10
6
8
6
5
6
4
6
5
4
3
2
4
3
2
1
4
2
0
2
0
1
4000
3000
2000
1000
ν, сm−1
4000
3000
2000
1000
ν, сm−1
Fig. 3. (Color online) IR spectra of the gas phase formed after the interaction between gaseous CH I and SiO -based sor-
3
2
bents in an atmosphere of (a) Ar or (b) air: (1) SiO , (2) SiO -7AgGG, (3) SiO -7AgАmk, (4) SiO -3.5AgGG-3.5AgАz,
2
2
2
2
(5) SiO -2Ag8Ni-NH , and (6) SiO -7AgАz.
2
3
2
(а)
(b)
5
4
500
400
300
200
100
0
500
400
300
200
100
0
5
4
3
3
2
2
1
1
4000
3000
2000
1000
ν, сm−1
4000
3000
2000
1000
ν, сm−1
Fig. 4. (Color online) IR spectra of the gas phase formed during the interaction between gaseous CH I and SiO -based Ag-con-
3
2
taining sorbents in an atmosphere of (a) Ar or (b) air (after subtracting the absorption bands of CH I): (1) SiO -7AgGG,
3
2
(2) SiO -7AgАmk, (3) SiO -3.5AgGG-3.5AgАz, (4) SiO -2Ag8Ni-NH , and (5) SiO -7AgАz.
2
2
2
3
2
(Figs. 3а, 3b, spectra 2–6). As is also seen from Fig. 3,
the IR spectra shows almost the same set of absorption
bands in both Ar and air, including those of CH3I.
Figure 5 shows the IR spectra of CH3CH2NO3
(Fig. 5, spectrum 1) [14] and the gas phase formed
after interaction between gaseous CH3I and sorbent
SiO2-2Ag8Ni-NH3 in an atmosphere of air (Fig. 5,
spectrum 2). As is seen from Fig. 5, the spectra are
almost identical, except for the 2300–2350 cm–1
region. The bands in this range of the spectrum of the
gas phase formed after the interaction between CH3I
and sorbent SiO2-2Ag8Ni-NH3 could be associated
with both the formation of CO2 during interaction and
the penetration of CO2 from the air into the IR gas
cells.
To identify the possible products of interaction
between CH3I and Ag-containing sorbents, our IR
spectra were compared to those of chemical com-
pounds that can form during this interaction [13–15].
Before comparison, the CH3I bands were subtracted
from the experimental spectra (Fig. 4).
Comparison of the experimental IR spectra and
those of the expected organic compounds listed in
[13–15] showed that the main product of interaction
between CH3I and Ag-containing sorbents was
CH3CH2NO3, and not methyl nitrate CH3NO3.
However, the similarity between the IR spectra of
the reaction products in atmospheres of Ar and air
(Fig. 4) indicates the absence of both reaction (3) and
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IR SPECTROSCOPY OF THE GAS PHASE FORMED
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4
2
400
2.0
1.5
1.0
0.5
0
3
2
300
1
200
1
100
0
4000
3000
2000
1000
ν, сm−1
4000
3000
2000
1000
ν, сm−1
Fig. 6. (Color online) IR spectra of the gas phase formed
during the interaction between CH I and a flow of air with
Fig. 5. (Color online) IR spectra of (1) CH CH NO [14]
3
2
3
3
and (2) the gas phase formed after the interaction between
SiO -2Ag8Ni-NH at different temperatures of the sor-
2
3
gaseous CH I and SiO -2Ag8Ni-NH sorbent in an atmo-
3
2
3
bent (after subtracting the absorption bands of CH I):
3
sphere of air.
(1) 293, (2) 343, (3) 383, and (4) 423 K.
that of the formation of formaldehyde. At the same
time, the IR spectra of the gas phase formed after the
interaction between CH3I and the studied sorbents
shows characteristic for CO2 bands in the region of
CONCLUSIONS
It would seem the main gaseous products formed in
the interaction between CH3I and the studied Ag-con-
taining sorbents were CH3CH2NO3, CO2, and I2.
Knowledge of the main gaseous products will help us
to find solutions for developing environmental protec-
tion systems at both nuclear power plants and nuclear
waste processing facilities.
2300–2350 cm−1 for both atmospheres [13]. Organic
compounds thus decompose under our experimental
conditions, forming CO2.
Since the sorbents intended for the localization of
CH3I must retain their efficiency in a wide range of
temperatures, we studied the composition of the gas
phase formed when CH3I interacts with the sorbents at
different temperatures in the 293–423 K range.
ACKNOWLEDGMENTS
The findings reported in this work are associated with
the behavior of radioactive elements in the gas phase and the
development of functional materials for the safety systems
of nuclear power plants in the event of foreseen and unfore-
seen reactor accidents. They are a continuation and devel-
opment of the work begun in this laboratory in 1993 under
the direction of Nikolai Borisovich Mikheev, State Prize
Laureate, Professor, and Doctor of Chemistry, and Igor’
Vital’evich Melikhov, Corresponding Member of the Rus-
sian Academy of Sciences.
Figure 6 shows the IR spectra of the gas phase after
the interaction between gaseous CH3I and SiO2-
2Ag8Ni-NH3 in an air flow, depending on the tem-
perature of the sorbent. The spectra were analyzed
after subtracting the absorption bands of CH3I.
As is seen from Fig. 6, the IR spectra of the gas
phase obtained at temperatures in the range of 343–
423 K are similar to one another, although some dif-
ferences are observed. The spectra obtained at 423 K
in particular show additional bands in the region of
2300 cm−1 that can be attributed to CO2 [13].
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