Acoustic cavitation in water under rare gas atmosphere

Article abstract of DOI:10.1246/cl.2001.142

The results of the sonolysis of water and aqueous 2-methyl-2-propanol under a rare gas atmosphere suggest that increasing the solubility of the rare gas in water significantly enhances the rate of sonolysis but their thermal conductivity does not significantly affect the temperature of the cavitation bubbles.

Full text of DOI:10.1246/cl.2001.142

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42
Chemistry Letters 2001
Acoustic Cavitation in Water under Rare Gas Atmosphere
†
†
†
Yoshio Nagata,* Hiroshi Okuno, Yoshiteru Mizukoshi, and Yasuaki Maeda
Research Institute for Advanced Science and Technology, Osaka Prefecture University, 1-2 Gakuen-cho, Sakai, Osaka 599-8570
†
Department of Applied Materials Science, Faculty of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka 599-8531
(Received November 6, 2000; CL-001002)
The results of the sonolysis of water and aqueous 2-methyl-2-
propanol under a rare gas atmosphere suggest that increasing the
solubility of the rare gas in water significantly enhances the rate of
sonolysis but their thermal conductivity does not significantly
affect the temperature of the cavitation bubbles.
Hydrogen, oxygen, acetylene, ethylene and ethane were
determined by a gas chromatograph. Hydrogen peroxide was
determined from the amount of Fe(III) formed by the H O -oxi-
2
2
4
dation of Fe(II).
The chemical effect of ultrasounds is thought to be attrib-
uted to acoustic cavitation; the formation, growth and instanta-
neous collapse of micro bubbles in a liquid. Various physical
and thermodynamic properties of an ultrasound-exposed liquid
1
and surrounding gas would influence the cavitation efficiency.
In the sonochemical reaction, a rare gas is often used as the sur-
rounding gas due to its high polytropic index (C /C = 1.67) and
p
v
chemical inertness. A high C /C value will produce a higher
p
v
temperature and give a high reaction yield. There have been
some investigations on the dependence of rare gases on cavita-
tion and it was reported that the effectiveness of the gases on
the rate of reaction, the temperature of the bubble interior and
intensity of the sonoluminescence was in the order Xe > Kr >
Ar > Ne > He in every case. However, studies related to the
quantitative comparison of the cavitation effect among rare
gases are still limited.
The sonolysis mode of water under different rare gases is
shown in Table 1. The amount of reaction products from the water
sonolysis were proportional to the sonication time at the initial
time (over 10 min) and the rates of formation of product were in
the order Xe > Kr > Ar > Ne > He with significant difference. This
order was consistent with the results of the OH radical formation
In this paper, the sonolysis of water and aqueous 2-methyl-
5
2-propanol (t-BuOH) is carried out under an atmosphere of five
(by spin trapping measurement), H O (KI method) and OH radi-
2
2
6
rare gases, and the reaction efficiency is evaluated based on the
degradation rates and the temperature inside the cavitation bub-
bles (hereafter defined as the cavitation temperature) is estimat-
ed from the distribution of the sonolysis products. Since ultra-
sounds have become a promising tool for synthetic chemistry
cal formations (fluorescence from terephtalic acid), H O forma-
tion (titanyl sulfate method), and sonoluminescence studies.
2 2
7
8
The degradation products were hydrogen, hydrogen perox-
ide and oxygen. No other products were detected. The fact that
the H/O ratio of the products under Ar, Kr and Xe were nearly
equal to 2 indicates that the experimental results are reliable.
The degradation of water would proceed with the follow-
2
and waste degradation, the investigations about cavitation from
various view points are important for obtaining the optimum
reaction conditions as well as fundamental data.
9
ing stoichiometry:
The sonolysis experimental procedure was almost the same
3
as those previously reported. In short, a rare gas-saturated
water or aqueous t-BuOH solution was sonicated in a cylindri-
cal glass vessel. The vessel had a side arm with a silicon rubber
septum for gas bubbling or sample extraction without exposing
the sample to air. The bottom of the vessel was flat and made
as thin as possible (1 mm) because the transmission of the ultra-
sonic waves increases with decreasing thickness of the bottom.
The vessel was mounted at a fixed position relative to the nodal
plane of the sound wave (3.75 mm: λ/2 from the oscillator). A
multiwave ultrasonic generator and a barium titanate oscillator
were used for the ultrasonic irradiation and operated at 200 kHz
with an input intensity of 200 W. To fix the reaction vessel at
an exact position, a laboratory jack, clamp and holder–all the
parts used for the positioning system in optical measure-
ments–were used. During the irradiation, the vessel was closed.
Under these conditions, the temperature rise of the solution was
ca. 7 °C after a 10 min sonication.
Oxygen may be formed via eqs. 5 –7.
Eqs. 5 and 6 would occur under high temperature
10
conditions, therefore, it is postulated that the cavitation temper-
ature increased in the order Xe > Kr > Ar > Ne, He, that is, the
same order of increasing oxygen yield, but the degree of its varia-
tion was not as significant as that observed for the rate of sonoly-
sis of water.
Copyright © 2001 The Chemical Society of Japan

Chemistry Letters 2001
143
This study was financially supported by Special
Coordination Funds for Promoting Science and Technology
from the Japanese Science and Technology Agency.
References and Notes
1
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Table 2 shows the sonolysis data of the aqueous t-BuOH
solution at concentrations of 0.1, 0.5, 1, 2.5, 5 and 10 mmol/L.
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rate of water degradation.
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ethylene and acetylene are formed along with other pyrolysis
products. The cavitation temperature can be estimated from the
1
1–13
ratio [R(C H ) + R(C H )] / R(C H ).
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2
4
2
2
2
6
1
4
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2
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multi bubble sonoluminescence from Cr(CO) in octanol were
6
4
5
6
7
reported to be Xe (5100K) > Kr (4400K) > Ar (4300K) > Ne
(
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1
6
thermal conductivity. However, our results exhibited some-
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8
9
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As another factor for the effect of cavitation, the solubility
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10
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7
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2
2
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2
11 J. Warnatz, Ber. Bunsenges. Phys. Chem., 87, 1008 (1983).
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1
1
1
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1
2
1
14 –0.4
3
–1 –1
→
C H ) = 2.4 × 10 T dm mol s , k (rate constant
2
6
2
16
for 2CH → C H + H ) =1.0 × 10 exp(–134kJ/RT)
3
2
4
2
3
–1 –1
dm mol s
1
5
6
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1