Photochemical oxidation of methyldiethanolamine (MDEA) in aqueous solution by UV/K2S2O8 process
Int J Ind Chem
Photochemical oxidation of methyldiethanolamine (MDEA) in aqueous solution by UV/K2S2O8 process
G. Samira Molareza 0 1 2
Mojtaba Ahmadi 0 1 2
A. A. Zinati Zadeh 0 1 2
0 Applied Chemistry Department, Faculty of Chemistry, Razi University , Kermanshah , Iran
1 Chemical Engineering Department, Faculty of Engineering, Razi University , Kermanshah , Iran
2 & Mojtaba Ahmadi
Methyldiethanolamine (MDEA) as an organic material is a hazardous contaminant in the aquatic environment because of its adverse effects on aquatic life, environment, and humans. In this study, a batch reactor of ultraviolet (UV) light and peroxydisulfate was performed to investigate the degradation of MDEA in aqueous media. The effect of different experimental parameters such as UV irradiation, peroxydisulfate concentration, MDEA concentration, temperature, and solution pH on removal of MDEA was evaluated precisely. No significant degradation was observed with a separate UV light. Adding peroxydisulfate to the solution increased the removal performance more than 75 %.
Peroxydisulfate; MDEA; Advanced oxidation processes; Wastewater treatment
Introduction
Raw natural gas includes some acidic gases such as H2S
and CO2. These acidic gases are very corrosive and toxic
to the environment, and therefore required to be removed.
Different alkanolamines such as monoethanolamine
(MEA), diethanolamine (DEA), methyldiethanolamine
(MDEA) and diisopropanolamine (DIPA) are used for the
removal of acidic gases in the sweetening gas units [
1
]. In
addition N-methyldiethanolamine (MDEA) as
metalMDEA complexes have as propertysignificant ultraviolet
(UV) absorption. New photosensitive precursors was
prepared as thin films by N-methyldiethanolamine
complex [
2, 3
]. Usually during cleaning, protecting and
scheduled control of absorption and desorption column,
high concentration of alkanolamine is generated into the
wastewater [4]. Nevertheless, due to its toxicity the
conventional biological treatment cannot be used for this
wastewater [
5
].
During recent two decades, advanced oxidation
processes (AOPs) have been considered as popular techniques
to treat the high concentration of organic contaminant in
the wastewater [
6
]. AOPs are of the most alternative
techniques for destruction of many other organic matters in
wastewater and effluents. These processes generally
involve UV/H2O2, UV/O3, UV/S2O82- or UV/Fenton’s
reagent for degradation of contaminants [
7–9
].
A large number of experimental works have been
performed on the application of AOPs to treat wastewater. The
Fenton’ reagent in the AOPs was used to degrade MEA
[
10
], DEA [
11
], N,N-diethyl-p-phenylenediamine [
12
] and
DIPA [
13
]. Also, the use of UV/H2O2 in the AOPs for
degradation of MEA and MDEA [
4, 14
] and ozonation for
degradation of DEA [15] have been studied.
Because of its high reactivity of UV/S2O82- process,
high solubility, relatively low cost of peroxydisulfate and
benign end products, recently the application of UV/
S2O82- in wastewater treatment was investigated in
numerous studies [
16
]. Peroxydisulfate (S2O82-) is a strong
oxidant (E0 = 2.05 V) which has been used widely in the
petroleum industry for the treatment of hydraulic fluids or
as a reaction initiator [
17
].
It has also been reported to be effective for degrading
organic matters in hazardous wastewaters in acidic or basic
media through direct chemical oxidation, where
peroxydisulfate is used as a sacrificial reagent [
17–19
]. However,
since the reactions of peroxydisulfate are generally slow at
normal temperature. The thermal or photochemical
activated decomposition of S2O82- ion to SO4- radical has
been proposed as a method of accelerating the process [
19,
20
], as summarized in the following reactions (Eqs. 1–12):
2 hv=heat
S2O8 ! 2SO4
SO4 þ RH2 ! SO24 þ Hþ þ RH
2
RH þ S2O8
! R þ SO24 þ Hþ þ SO4
SO4 þ RH ! R þ SO24 þ Hþ
2R ! RRðdim erÞ
SO4 þ H2O ! HSO4 þ OH ð500
60 S 1Þ
HSO4 ! Hþ þ SO24
2
OH þ S2O8
SO4 þ OH
1
! HSO4 þ SO4 þ 2 O2
1
! HSO4 þ 2 O2
2OH
! H2O2 ðexpect in alkaline solutionÞ
1
H2O2 ! H2O þ 2 O2 ðmostly in acidic solutionÞ
S2O8 þ H2O2 ! 2Hþ þ 2SO24 þ O2
2
ð1Þ
ð2Þ
ð3Þ
ð4Þ
ð5Þ
ð6Þ
ð7Þ
ð8Þ
ð9Þ
ð10Þ
ð11Þ
ð12Þ
As can be seen in the above reactions, the oxidation
process is begun by production of the sulfate and hydroxyl
radicals (Eqs. 1 and 2). These radicals are powerful
oxidizing agents which may attack the organic matters (R) in
the contaminated water. It causes, ultimately, complete
decomposition of toxic and bioresistant compounds to
harmless species (like CO2, H2O, etc.). Sulfate ion will be
generated as the end product, which is practically inert and
is not considered to be a pollutant. It is worth to mention
that the United States Environmental Protection Agency
(USEPA) has listed SO42- under the secondary drinking
water standards. A maximum concentration of sulfate ion is
250 mg l-1 (1.43 mM), based on sanitary reasons such as
taste and odor [
1 (...truncated)