Decrease in the rate of sonochemical oxidation with introduction of CO₂

Abstract

The effect of carbon dioxide (CO 2 ) in atmospheric gas on the rate of sonochemical oxidation was examined. An ultrasonic irradiation system has two types of effects, namely, physical and chemical effects. In some cases, chemical effects provide a negative performance. To suppress the chemical effect, CO 2 was introduced in a laboratory-scale setup using a syringe or a gas flow system. Sonochemical oxidation was performed at 2.4 MHz (24 W) and 200 kHz (15 W). The rate of oxidation was evaluated by potassium iodide (KI) dosimetry. The rate decreased with the introduction of CO 2 and sonochemical oxidation could not proceed at a mole fraction of CO 2 above 0.3 in the matrix. From the standpoint of practical use, in addition, a sensory test was carried out using 20% ethanol solution in a CO 2 -air atmosphere. No smell change was confirmed by the human sense of smell.

Toward understanding the mechanism of pure CO2‐quenching sonochemical processes

“…Identical comportment of CO 2 atmosphere was reported by Rooze et al . when KI solution was irradiated at 21, 41 and 62 kHz (power: 1–6 W, temperature: 20 °C) and by Harada et al . at 25 °C for 200 kHz (15 W) and 2.4 MHz (24 W).…”

“…The too high a solubility of CO 2 in water ( x CO2 =7.07 × 10 ‐4 ; 46.4‐fold much higher than that of air) makes the cavitation process a non‐inertial event due to the high extent of bubbles nucleation and coalescence, which yield bigger stable bubbles in the solution . However, some studies have pointed out that the inhibiting effect of CO 2 was due to the low collapse temperature provided from cavitation under CO 2 saturation (resulted from its lower γ = c p / c v than other gases) associated with the direct contribution of CO 2 as radical scavenger inside the bubble …”

A parametric review of sonochemistry: Control and augmentation of sonochemical activity in aqueous solutions

“…Sonochemical oxidation (of I ି ions) reduces significantly above 3% CO 2 in air, as does the sonochemical reduction of the carbon dioxide present which in atmospheres other than air follows the order Ar > He > H 2 > N 2 [223,268]. Similarly, a maximum rate of CO formation in argon with 2-3% CO 2 has been observed at 300 kHz [218].…”

“…For large amounts of CO 2 there is inhibition of radical production, however small amounts in Ar, He, O 2 , N 2 have been found to improve sonochemical rates [95,221,223,268]. Sonochemical oxidation (of I ି ions) reduces significantly above 3% CO 2 in air, as does the sonochemical reduction of the carbon dioxide present which in atmospheres other than air follows the order Ar > He > H 2 > N 2 [223,268].…”

Dispersion and coalescence of oil droplets by ultrasound and application for solvent extraction of gallium

“…When ultrasound at low frequencies below 100 kHz is irradiated into an oil-water two-phase liquid, an emulsion is formed owing to ultrasonic cavitation. Ultrasonic cavitation has physical [3][4][5][6][7][8] and chemical [9][10][11][12][13][14][15] effects. Ultrasonic emulsification is a typical physical effect of cavitation and is applied in the production of, for example, food, 3) polymers, 4) and biodiesel.…”