ISSN 0018ꢀ1439, High Energy Chemistry, 2014, Vol. 48, No. 1, pp. 60–61. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © E.S. Bobkova, A.V. Sungurova, 2014, published in Khimiya Vysokikh Energii, 2014, Vol. 48, No. 1, pp. 82–83.
PLASMA CHEMISTRY
SHORT COMMUNICATIONS
Formation of Formaldehyde in Aqueous Solution
under AtmosphericꢀPressure DirectꢀCurrent Discharge
E. S. Bobkova and A. V. Sungurova
Research Institute of Chemical Thermodynamics and Kinetics, Ivanovo State University of Chemical Technology,
pr. F. Engel’sa 7, Ivanovo, 153000 Russia
eꢀmail: esbobkova@isuct.ru
Received June 10, 2013; in final form, August 30, 2013
DOI: 10.1134/S0018143914010044
The possibility of degradation of organic comꢀ
The figure (curve
1) shows the kinetics of formaldeꢀ
pounds in water by treatment with discharges of variꢀ hyde formation in water by the action of the discharge.
ous types has become a subject matter of intensive The concentration of formaldehyde increases to
research. Regardless of the discharge type, the comꢀ 0.24 mg/L as the treatment time increases to 6 min;
mon products of decomposition of a variety of organic then, its degradation begins, which results in СО2 and
compounds (phenol, synthetic surfactants, carboxylic Н2О as the final product [5]. The shape of the kinetic
acids) are aldehydes and carbon dioxide [1, 2]. By curve indicates that there is a competition of the synꢀ
plasma treatment of water, not only species having a thesis and degradation of formaldehyde and different
high oxidizing power (OH radicals), but also good active species are involved in these the processes. The
reducing agents (H radicals) are generated [3]. Thus, it hydrogen carbonate ion concentration measured in
may be assumed that reduction reactions can occur distilled water prior to treatment was 16.6 mg/L,
along with the oxidative degradation processes. The which is quite sufficient for the formation of formaldeꢀ
purpose of this study was to test this hypothesis using hyde in the amount found.
distilled water as the object of treatment.
The next step of the research was to study the influꢀ
Analyses showed that water has pH ~ 6.8, and its
potentiometric titration with hydrochloric acid
revealed the presence of hydrogen carbonate ions at a
concentration of 16.6 mg/L. That is, the acidity is due
to the presence of dissolved CO2 in the water.
ence of the amount of dissolved СО2 on the concenꢀ
tration of formaldehyde. For this purpose, the water
was preliminarily either boiled and purged with argon
to reduce the concentration of dissolved carbon dioxꢀ
ide or saturated with СО2. In the former case, both the
rate of formation and the amount of formaldehyde
The experimental setup was described earlier [4].
An atmosphericꢀpressure air dc discharge was excited
by applying dc voltage across a metal anode and the
surface of the solution. The anode–electrolyte surface
distance was 4 mm. The discharge current was 40 mA.
The volume of the electrolyte (distilled water) was
80 mL. After a certain time of discharge treatment, the
solution was analyzed for formaldehyde. A fresh porꢀ
tion of the solution was used for each run.
decreased (curve
water. In the latter case (curve
2
) as compared with the untreated
3), the formaldehyde
concentration and formation rate increased. Thus, the
source of formaldehyde was dissolved СО2 indeed.
The formaldehyde formation process can involve
the following wellꢀknown reactions:
Н2О + discharge
СО2 + •Н
→
•ОН + •Н,
СО + •ОН,
•СОН,
НСОН.
The aldehyde concentration was determined by
measuring the intensity of fluorescence, excited at the
maximum absorption band, with a Fluoratꢀ02 fluoꢀ
rometer (Russia). The luminescent compound was the
product of the formaldehyde reaction with 1,3ꢀcycloꢀ
hexanedione in the presence of ammonium ions. The
random error was determined for five measurements
→
СО + •Н
→
•СОН + •Н
→
In summary, this type of discharge ensures the synꢀ
using a confidence level of 0.95. The error did not thesis of formaldehyde in water in the presence of disꢀ
exceed 10%.
solved carbon dioxide. Moreover, the CO2 content
60