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Volatile organic compounds (VOCs) may frequently contaminate groundwater and pose threat to human health when migrating into the unsaturated soil zone and upward to the indoor air. The kinetic of chemical oxidation has been investigated widely for dissolved VOCs in the saturated zone. But, so far there have been few studies on the use of in situ chemical oxidation (ISCO) of vapour phase contaminants. In this study, batch experiments were carried out to evaluate the oxidation of trichloroethylene (TCE), ethanol, and toluene vapours by solid potassium permanganate. Results revealed that solid potassium permanganate is able to transform the vapour of these compounds into harmless oxidation products. The degradation rates for TCE and ethanol were higher than for toluene. The degradation process was modelled using a kinetic model, linear in the gas concentration of VOC [ML(-3)] and relative surface area of potassium permanganate grains (surface area of potassium permanganate divided by gas volume) [L(-1)]. The second-order reaction rate constants for TCE, ethanol, and toluene were found to be equal to 2.0×10(-6)cms(-1), 1.7×10(-7)cms(-1), and 7.0×10(-8)cms(-1), respectively.
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Oxidation of volatile organic vapours in air by solid potassium
Mojtaba Ghareh Mahmoodlu
, Niels Hartog
, S. Majid Hassanizadeh
, Amir Raoof
Utrecht University, Department of Earth Sciences, The Netherlands
Soil and Groundwater Systems, Deltares, Utrecht, The Netherlands
KWR Watercycle Research Institute, Nieuwegein, The Netherlands
Oxidation of chlorinated and non-chlorinated hydrocarbon vapours by solid potassium permanganate was investigated.
A linear kinetic oxidation model effectively predicted the degradation rate of TCE, ethanol, and toluene.
The reaction rate constants for TCE, ethanol, and toluene in gas phase by solid pot assium permanganate were calculated.
article info
Article history:
Received 31 July 2012
Received in revised form 12 December 2012
Accepted 15 December 2012
Available online 26 January 2013
Solid potassium permanganate
VOC vapour
Kinetic parameters
Chemical oxidation
Volatile organic compounds (VOCs) may frequently contaminate groundwater and pose threat to human
health when migrating into the unsaturated soil zone and upward to the indoor air. The kinetic of chem-
ical oxidation has been investigated widely for dissolved VOCs in the saturated zone. But, so far there
have been few studies on the use of in situ chemical oxidatio n (ISCO) of vapour phase contaminants.
In this study, batch experiments were carried out to evaluate the oxidation of trichloroethylene (TCE),
ethanol, and toluene vapours by solid potassium permanganate. Results revealed that solid potassium
permangan ate is able to transform the vapour of these compounds into harmless oxidatio n products.
The degradation rates for TCE and ethanol were higher than for toluene. The degradation process was
modelled using a kinetic model, linear in the gas concentration of VOC [ML
] and relative surface area
of potassium permangan ate grains (surface area of potassium permanganate divided by gas volume)
]. The second-order reaction rate constants for TCE, ethanol, and toluene were found to be equal to
2.0 10
cm s
, 1.7 10
cm s
, and 7.0 10
cm s
, respectively.
Ó2013 Elsevier Ltd. All rights reserved.
1. Introduction
Volatile organic compound s (VOCs) are defined as organic com-
pounds with boiling points (at 1 amt) below 260 °C(De Nevers,
2000). VOCs have high vapour pressures under normal conditions,
so they can easily vapourize into the atmosphere or form vapour
plumes in the soil (Kim et al., 2007 ). VOCs are present in some
household products and automobile liquids (Berscheid et al.,
2010). Releases of VOCs to the environment have occurred through
surface spills, leaking underground storage tanks, and inadequate
disposal practices (Berscheid et al., 2010 ).
Small quantities of VOCs may contaminat e large volumes of
water. When released as free product, VOCs may migrate down-
ward to significant depths through the soil. In addition, VOC va-
pours can migrate upwards to the surface through diffusion and
produce elevated concentratio ns within indoor air spaces (Bersc-
heid et al., 2010 ). Exposure to some VOCs might affect central ner-
vous system and internal organs, and might cause symptoms such
as headache , respiratory tract irritation, dizziness and nausea,
known as the Sick Building Syndrome (SBS) (Yu and Lee, 2007 ).
We have chosen TCE, ethanol, and toluene, as model VOCs (tar-
get compound s) for chlorinat ed solvents, biofuel, and mineral oil,
respectivel y, for the reasons explained below.
TCE is one of the most common man-made chemicals found in
soil (Albergaria et al., 2012 ). It has been widely used as a dry clean-
ing solvent, degreasing agent, and chemical extraction agent. Since
TCE is carcinogenic, its movement from contaminated groundwa-
ter and soil into the indoor air of overlying buildings is of serious
concern (EPA, 2011 ).
Ethanol is being increasingly used in (renewable) fuel alterna-
tives and as replacemen t for methyl tertiary-b utyl ether (MTBE),
which, despite helping to accomplis h Clean Air Act goals, has
caused widespread water contaminat ion problems (Johnson
et al., 2000; Capiro et al., 2007 ). Ethanol can reduce the biodegra -
0045-6535/$ - see front matter Ó2013 Elsevier Ltd. All rights reserved.
Corresponding author.
E-mail address: (M.G. Mahmoodlu).
Chemosphere 91 (2013) 1534–1538
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dation rate of light non-aqueous phase liquid (LNAPL) such as ben-
zene, toluene, ethylbenzene, and xylene isomers (BTEX) in ground-
water and soil (Mackay et al., 2007; Freitas et al., 2010 ).
Toluene is found frequently in indoor environments. Toluene is
mainly used as an additive to improve the octane number of gaso-
line (Yu and Lee, 2007 ).
One of most common treatment techniques for unsaturated
zone polluted with VOCs is soil vapour extraction (SVE). This is a
long-term operation and does not convert a contaminan t to less
toxic compounds . A promising alternative is in situ oxidation of
VOC that can lead to favourab le results in less time. Oxidation of
VOCs may convert hazardous contaminan ts to harmless com-
pounds. The oxidizing agents most commonl y used for the treat-
ment of hazardous contaminants are potassium permanganate ,
ultraviolet radiation, ozone, chlorine dioxide, hydrogen peroxide,
sodium persulfate, and Fenton’s reagent (H
oxidation in the
presence of ferrous iron, Fe
Among these oxidants, potassium permanganate has been
receiving increased attention for the treatment of liquids, slurry
soils, and sludges polluted with VOCs (Kao et al., 2008 ). Early lab-
oratory studies have indicated that dissolved potassium perman-
ganate can remediate a variety of organic compounds ,
chlorinated alkanes (Waldeme r and Tratnyek, 2006 ), chlorinated
ethylenes (Huang et al., 1999; Hood et al., 2000; Yan and Schwartz ,
2000; Waldeme r and Tratnyek , 2006; Kao et al., 2008; Urynowicz,
2008), oxygenates (Jaky et al., 2000; Damm et al., 2002; Waldemer
and Tratnyek, 2006 ), BTEX (Gardner, 1996; Rudakov and Lobachev,
2000; Waldeme r and Tratnyek, 2006 ), substituted phenols (Jin
et al., 2003; Waldemer and Tratnyek, 2006 ) and PAHs (Forsey,
2004), in aqueous phase. However, the potential of solid potassium
permanganate to oxidize VOC vapours in unsaturated zone is cur-
rently unknown .
In this study, we demonst rate the ability of solid potassium per-
manganate to oxidize VOC vapours.
Currently, the literature lacks data on the reaction between so-
lid oxidants such as permanganate and vapour phase of contami-
nants. Therefore, we planned a series of batch experiments with
two objectives: (1) to evaluate the ability of solid potassium per-
manganate to fully oxidize vapour phase contaminants, (2) to
determine kinetic parameters for TCE, ethanol, and toluene oxida-
tion by solid potassium permang anate.
2. Materials and methods
2.1. Materials
We used 4.8 10
, 3.5 10
, 2.3 10
mole of TCE, etha-
nol, and toluene vapours, respectively. These values were calcu-
lated based on 1.5 mL of gas samples (under normal condition s)
which were obtained from the headspace of their highly pure li-
quid phases. Solid potassium permanganate of 99% purity was ob-
tained from Sigma–Aldrich. The required potassium permanganate
for complete oxidation of VOCs was calculated based on the fol-
lowing reactions for TCE, ethanol, and toluene, respectively:
þ4KM nO
The required amount of potassiu m permangana te for oxidizin g
4.8 10
mole of TCE, 3.5 10
mole of ethanol, and 2.3 10
mole of toluene were estimated to be 1.25, 2.22, and 4.44 mg,
respective ly. These were calculated based on reactions in aqueou s
environm ent, assuming a full dissolution of crystals. In dissolved
form, potassium permangana te may be fully available for oxidation.
But, in the solid form only the surface of potassium permangana te
grains is in contact with the gas phase. Accordingly , more potas-
sium perman ganate is needed to avoid limitation in the degrada tion
rate. Hence, excess amount of potassium permangana te (2.703 g)
was used for each batch.
Potassium permanganate grains were put inside12- mL trans-
parent glass vials, which were capped with a hard septum to pre-
vent any leakage. VOC vapour was injected using a gas tight
syringe (2.5 mL Hamilton, SGE) and 16 mm disposab le needles
(£0.5 mm, Terumo).
In order to get kinetic parameters, three batch experiments at
three different initial amounts of vapour and potassium permanga-
nate were performed for all compounds (Table 1). All experiments
were carried out in duplicate. For each experiment, we prepared
several identical batches and each batch was allocated to a given
sampling time.
A control experiment was also performed in duplicate for each
compound to ensure that the loss of target compound due to leak-
age was negligible over the course of the experiments . To prepare a
control batch, a 12-mL transparent glass vial was capped with a
hard septum. Then VOC vapour was injected into the vial.
All experiments were carried out in a vertical rotary shaker, at
room temperat ure, 20 ± 2 °C, and air humidity of 37 ± 2%, which
is also the initial humidity inside the vials.
2.2. Sampling and measurem ents
Reaction and control batches were periodically sampled using a
gas tight syringe until no detectable concentr ation was found in
the reaction vial. To eliminate the effect of pressure drop due to
sampling , each vial was used only once.
The concentratio ns of target compounds , TCE, ethanol, and tol-
uene were measure d by a gas chromatograp h (GC). Gas samples of
Table 1
Initial experim ental conditions for each compound.
Compound Experiment n(mol) M
(g) A(cm
TCE 1 4.8 10
2.703 2703 10.5 257.43
2 2.4 10
2.703 2703 10.5 257.43
3 4.8 10
1.351 1351.5 11.25 120.13
Ethanol 1 3.5 10
2.703 2703 10.5 257.43
2 1.75 10
2.703 2703 10.5 257.43
3 3.5 10
1.351 1351.5 11.25 120.13
Toluene 1 2.3 10
2.703 2703 10.5 257.43
2 1.15 10
2.703 2703 10.5 257.43
3 2.3 10
1.351 1351.5 11.25 120.13
n= Initial number of VOC moles. M
= mass of solid potassium permanganate. A= surface area of potassium permanganate, V= volume of the gas phase. S
= initial
relative surface area.
M.G. Mahmoodlu et al. / Chemosphere 91 (2013) 1534–1538 1535
2 mL were taken using the headspace syringe of the GC from each
vial. Then, samples were injected into the GC. The GC (Agilent
Technologie s 6850) equipped with a capillary column
(0.25 mm 60 m), a flame ionization detector, and a purge and
Specific surface area of potassium permang anate was measured
using 10-point Brunauer–Emmett–Teller (BET) method by a Nova
3000 from Quantachrome . Performa nce of this machine was con-
trolled using reference 173 from Community Bureau of Reference.
Samples were degassed at 120 °C overnight before measureme nts.
The relative surface area was calculated as the surface area per vol-
ume of gas (Table 1).
To calculate the amount of the potassium permanganate con-
sumption, at end of experiment potassium permanganate grains
were dissolved in deionized (DI) water and its concentr ation was
measured using a UV-spectrop hotometer (UV-1800, Shimadzu) at
a wavelength of 525 nm.
3. Results and discussion
3.1. Oxidation study
Fig. 1 depicts the normalized concentr ation (C/C
) of the target
compounds as a function of time, where Cdenotes the observed
concentratio n of the target compound for a given time and C
the initial concentratio n of the target compound . Degradat ion of
target compound s shows an exponential trend, as indicated by
the fitted formula in the graph (Fig. 1). These results also show that
solid potassium permang anate was able to rapidly oxidize the va-
pour phase of TCE and ethanol. Toluene was also degraded but less
No VOC intermedi ates or by-products were found in vapour
samples. During the experiment, potassium permang anate crystals
turned into dark colour, which is the colour of a coating layer of
produced manganese dioxide (MnO
3.2. Kinetics analysis of data
Since the degradat ion of three reactants showed an exponential
trend, we assumed that the kinetics followed a first-order reaction
rate. We also assumed that only surface of solid potassium per-
manganate reacts with compounds . So, to a proper calculation of
the reaction rate coefficient, we should have an equation that in-
volves the physical properties of potassium permanganate , such
as the surface area and mass of potassium permanganate . Such
an equation may be written as:
dt ¼kCS ð4Þ
where kdenotes the reaction rate constant, Cis the vapour concen-
tration of compound [ML
], tis time [T], and Sis the relative sur-
face area of solid potassiu m permangana te [L
], which is defined
where Ais the surface area of the potassium permangana te [L
] and
Vis the volume of the gas phase [L
First, we assumed the relative surface area not to alter signifi-
cantly during the course of the reaction. To validate this assump-
tion, we determined the amount of potassium permanganate that
was consumed, at the end of the experime nt. This was done by dis-
solving potassium permanganate grains which were used in the
experiments in DI water and then using a spectrophot ometer to
determine its mass. We compared this to the initial mass and the
result showed that there was no significant consump tion of solid
potassium permanganate during our experiments .
With Sset equal to S
Eq. (4) can be solved to obtain:
Ln C
¼kt ð6Þ
where S
denotes the initial relative surface area of potassium per-
mangan ate [L
According to Eq. (6), plot of 1/ S
Ln C/C
vs. time should yields a
straight line. Then, the reaction rate constant kcan be obtained
from the slope of this line.
We used all data from Experiments 1, 2, and 3 to estimate kfor
each compound. Fig. 2 shows that the plots of 1/ S
Ln C/C
vs. time
for all compounds . The square of linear correlation coefficients (R
obtained for TCE, ethanol, and toluene were 9.6 10
, 9.9 10
and 9.9 10
, respectively . Results suggest that the degradation
of the target compound s can be modelled by Eq. (6) as long as suf-
ficient relative surface area of potassium permanganate is avail-
able. These results also show the accuracy of reaction rate
constant s which are given in Table 2.
Fig. 1. Degradation of TCE, ethanol, and toluene vs. time using experiment 1 (exp.
xy:xdenotes number of experiment and yis the experiment repetition).
1536 M.G. Mahmoodlu et al. / Chemosphere 91 (2013) 1534–1538
We compared results of our experiments with the oxidation of
VOCs in aqueous phase reported in the literature (Waldemer and
Tratnyek, 2006 ). We found that the oxidation process in both
phases follows a first-order model. This comparison also revealed
that the oxidation rates for VOCs in vapour phase are much smaller
than for aqueous phase. However, in both phases, the reaction rate
for TCE is higher than for ethanol and toluene.
As mentioned above, as a result of oxidation, MnO
is produced
and coats the grains. This may affect the efficiency of oxidation
process. To analyze the effect of surface coating, we accounted
for the reduction of the relative surface area during the experi-
ment. This was done by supplem enting Eq. (4) with an equation
relating the relative surface area to the MnO
concentr ation. This
resulted in the following equation:
dt ¼kC S
 ð7Þ
is the number of moles of MnO
produced per mole of tar-
get compound (based on stoichiom etry reaction) and
is the coat-
ing factor (number of moles of produce d MnO
per area of
potassiu m permangana te grains) [ML
The numerical solution of Eq. (7) was fitted to the TCE experi-
mental data. Results showed a maximum reduction of around 4%
in the relative surface area. This confirms the validity of our
assumpti on that there is a negligible change in the relative surface
area of potassium permang anate during our TCE experiments.
Although the largest amount of MnO
was produced during
degradat ion of ethanol and toluene (based on stoichiomet ry reac-
tion), there was still a large excess of the relative surface area dur-
ing the ethanol and toluene experime nt (based on the amount of
potassium permanganate we used). Moreover, we calculated the
amount of used potassium permanganate for all three compounds.
On all cases, this was found to be small fraction of initial amount
(around 4%).
4. Conclusion s
In this study, we investiga ted the kinetic paramete rs of both
chlorinat ed and non-chlorin ated hydrocarbo n vapours by solid
potassium permanganate under room temperature and humidity
condition s. Results showed that potassium permanganate is able
to oxidize the vapour of TCE and ethanol, and toluene. We also
found that TCE and ethanol in vapour phase can be rapidly oxi-
dized by solid potassium permanganate . However, toluene was de-
graded slower. A linear kinetic oxidation model, based on the
concentr ation of VOC in gas and a constant relative surface area,
effectively predicted the rate of TCE, ethanol, and toluene degrada-
tion. Results revealed that the reaction rate constant s for TCE, eth-
anol, and toluene are 2.0 10
cm s
, 1.7 10
cm s
, and
7.0 10
cm s
, respectivel y. Results also showed that the
amount of used potassium permanganate for all three compounds
was small fraction of initial amount (around 4%).
These findings will be helpful in designing a horizontal perme-
able reactive barrier with solid potassium permang anate in unsat-
urated zone for vapour intrusion. The performance of such
methodol ogy may be affected by moisture content, pH, and tem-
perature of the soil matrix. Also, one has to consider the health ef-
fects of by-product gases such as ethane (Pant and Pant, 2010 ) and
methane (Freitas et al., 2010 ) that can be produced under anaero-
bic biodegradat ion of TCE and ethanol, respectively .
Acknowled gments
The authors would like to thank Jan Kubiak (Wageningen Uni-
versity), Pieter J. Kleingeld (Utrecht University) and Pieter Van Rij-
wijk (NIOO-CEME) for their technical assistance, Dr. Kotai Laszlo
(Hungarian Academy of Sciences) and Dr. Hamid Nick (Utrecht
Universit y) for providing critical comments throughout the course
of this research and Tom Bosma (Utrecht University) for his
thoughtful review of this manuscript. Through review comments
by two anonymous referees helped to improve the manuscr ipt.
This work was supported by Ministry of Science, Research and
Technolo gy of Iran.
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Ethanol 1.7 10
9.8 10
Toluene 7.0 10
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... where c w O2 and c a O2 are oxygen concentrations in water and air, respectively, t is time, s is local volume fraction of water, D w O2 and D a O2 are the diffusion coefficients of oxygen in water and air, respectively, and J O2 provides a sink term due to oxygen consumption in the electrochemical reactions. The concentration field is continuous and Henry's law may be applied to couple oxygen concentration at the air-water interfaces as [49,50]: ...
The production of liquid water in cathode catalyst layer, CCL, is a significant barrier to increase the efficiency of proton exchange membrane fuel cell. Here we present, for the first time, a direct three-dimensional pore-scale modelling to look at the complex immiscible two-phase flow in CCL. After production of the liquid water at the surface of CCL agglomerates due to the electrochemical reactions, water spatial distribution affects transport of oxygen through the CCL as well as the rate of reaction at the agglomerate surfaces. To explore the wettability effects, we apply hydrophilic and hydrophobic properties using different surface contact angles. Effective diffusivity is calculated under several water saturation levels. Results indicate larger diffusive transport values for hydrophilic domain compared to the hydrophobic media where the liquid water preferentially floods the larger pores. However, hydrophobic domain showed more available surface area and higher oxygen consumption rate at the reaction sites under various saturation levels, which is explained by the effect of wettability on pore-scale distribution of water. Hydrophobic domain, with a contact angle of 150, reveals efficient water removal where only 28% of the pore space stays saturated. This condition contributes to the enhanced available reaction surface area and oxygen diffusivity.
... Possible contamination of soil and groundwater by volatile organic compounds (VOCs) is a major environmental concern at many sites currently or formerly occupied by large-scale chemical industries or smallscale users such as dry cleaners or gasoline stations (Han et al., 2016;Rivett et al., 2011;Schubert et al., 2011). VOCs frequently contaminate soil and groundwater and pose a potential threat to human health when migrating upward through the unsaturated soil to indoor air (Berscheid et al., 2010;Han et al., 2016;Mahmoodlu et al., 2013;Rivett et al., 2011). ...
In this study we performed batch experiments to investigate the dissolution kinetics of trichloroethylene (TCE) and toluene vapors in water at room temperature and atmospheric pressure. The batch systems consisted of a water reservoir and a connected headspace, the latter containing a small glass cylinder filled with pure volatile organic compound (VOC). Results showed that air phase concentrations of both TCE and toluene increased relatively quickly to their maximum values and then became constant. We considered subsequent dissolution into both stirred and unstirred water reservoirs. Results of the stirred experiments showed a quick increase in the VOC concentrations with time up to their solubility limit in water. VOC vapor dissolution was found to be independent of pH. In contrast, salinity had a significant effect on the solubility of TCE and toluene vapors. VOC evaporation and vapor dissolution in the stirred water reservoirs followed first-order rate processes. Observed data could be described well using both simplified analytical solutions, which decoupled the VOC dynamics in the air and water phases, as well as using completely coupled solutions. However, the estimated evaporation (ke) and dissolution (kd) rate constants differed by up to 70% between the coupled and uncoupled formulations. We also numerically investigated the effects of fluid withdrawal from the small water reservoir due to sampling while decoupling the VOC air and water phase mass transfer processes produced unreliable estimates of kd, the effects of fluid withdrawal on the estimated rate constants were found to be less important. The unstirred experiments showed a much slower increase in the dissolved VOC concentrations versus time. Molecular diffusion of the VOCs within the aqueous phase became then the limiting factor for mass transfer from air to water. Fluid withdrawal during sampling likely caused some minor convection within the reservoir, which was simulated by increasing the apparent liquid diffusion coefficient.
... The concentration of H 2 O 2 and persulfate were measured using the iodide-spectrophotometric method described by Zhong et al [30]. The concentration of permanganate ion (MnO 4 − ) was measured with a UV-spectrophotometer (UV-2250, Shimadzu) at a wavelength of 525 nm [69,70]. Sulfate, ferrous ion and total dissolve iron were measured using a Hach DR2800 spectrophotometer (Loveland, CO) based on the modulated Hach methods ( No. 8051, 8146, 8008). ...
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In this study, batch and column experiments were conducted to evaluate the feasibility of using persulfate oxidation to treat groundwater contaminated by landfill leachate (CGW). In batch experiments, persulfate was compared with H2O2, and permanganate for oxidation of organic compounds in CGW. It was also compared with the potential of biodegradation for contaminant removal from CGW. Persulfate was observed to be superior to H2O2 and permanganate for degradation of total organic carbon (TOC) in the CGW. Biodegradation could cause partial removal of TOC in CGW. In contrast, persulfate caused complete degradation of the TOC in the CGW or aged CGW, showing no selectivity to the contaminants. Magnetite (Fe3O4) enhanced degradation of leachate compounds in both CGW and aged CGW with limited increase in persulfate consumption and sulfate production. Under dynamic flow condition in 1-D column experiment, both biodegradation and persulfate oxidation of TOC were enhanced by Fe3O4. The enhancement, however, was significantly greater for persulfate oxidation. In both batch and column experiments, Fe3O4 by itself caused minimal consumption of persulfate and production of sulfate, indicating that magnetite is a good persulfate activator for treating CGW in heterogeneous systems The results of the study show that the persulfate-based in-situ chemical oxidation (ISCO) method has great potential to treat the groundwater contaminated by landfill leachate.
Applying ozone removal devices in ventilation systems is an effective way to reduce building occupant exposure to ozone. However, little is known about the performance of commercially-available ozone removal devices under realistic usage conditions, especially for technologies that have recently emerged for general ventilation such as ultraviolet photocatalytic oxidation (UV–PCO) and catalysis (without UV). A total of 14 ozone removal devices that are representative of products on the market were selected: 11 activated carbon filters, 2 UV-PCO devices, and 1 catalyst filter without UV. We tested these devices with an “ozone stress test” by exposing them to 70 ppb, 107 ppb, and 500 ppb of ozone at 25 °C, 50% RH, and 2.5 m/s face velocity. The device performance was evaluated by the average efficiency at each ozone level, degradation rate at 500 ppb, pressure drop, and a quality factor that combines efficiency and pressure drop. Results show a wide range of single-pass removal efficiency from 3% to 93% at 70 ppb. All devices degraded at a slow rate; at 500 ppb, most devices degraded at 1.5%/h relative to their efficiency at the beginning of this period. The catalyst (no UV) and three 12″ activated carbon devices achieved high efficiency at the least cost of pressure drop. The loading and source of carbon had a significant impact on the efficiency of activated carbon filters. A two-fold increase in carbon loading led to nearly a two-fold higher single-pass removal efficiency. Coal-based carbon degraded 20 times faster than coconut shell-based carbon.
Permanganate (MnO4−) ions were adsorbed on the surface of MoS2 nanosheet and then reacted with it. In this work, effects of pH, temperature, initial MnO4− concentration and ionic strength on this process were studied. The adsorption sites of MoS2 were Mo(IV)–S pairs located in its micropores (abbreviated as MI). Before starting reaction, MoS2 acted as a high capacity adsorbent for MnO4− ions at a certain time. Under various conditions, MnO4− ions were adsorbed on the surface of MoS2 during different time periods (20–180 min) and then reacted with it. The maximum adsorption capacity of MnO4− ions on MoS2 surface in water at 328 K was 368.3 mg g⁻¹ (2.33 mmol g⁻¹). Adsorption isotherms were analyzed by the ARIAN model and it was recognized that in the pH range of 1–11, adsorption isotherms were composed from regions I and II and ΔH values of the process for regions I and II in neutral water were 31.4 kJ mol⁻¹ and 9.9 kJ mol⁻¹, respectively. At pH = 12, adsorption isotherm was only formed from region I. In the pH range of 1–12, after completion of adsorption process, reaction of adsorbed MnO4− ions with adsorbent obeyed ARIAN–Hinshelwood mechanism. In the pH range of 1–11, water molecules and at pH = 12, OH− ions and water molecules acted as nucleophiles, respectively. Finally, MoS2 adsorbent was used for separation of Cr2O72− and Ni²⁺ ions from MnO4− ions in water.
Chromium oxide (VI), (Cr (VI)) has been used in gas detector tubes as an indicator to detect alcohols. However, it is toxic and regulated to prevent environmental pollution. In this report, potassium manganate (VII) was chosen instead of Cr (VI). A hundred milliliter sample of vapors of ethanol, methanol and 2-propanol were passed through the tube respectively with the aspirating pump. Sampling time was 3 minutes. The stain length on the tube was in a range of 20-300 ppm. A novel detector tube for alcohols was developed without Cr (VI).
Background Potassium permanganate is a green and versatile industrial oxidizing agent. Due to its high oxidizing ability, it has received considerable attention and extensively used for many years in the synthesis, identification, and determination of inorganic and organic compounds. Objective Potassium permanganate is one of the most applicable oxidants, which has been applied in a number of processes in several industries. Furthermore, it has been widely used in analytical pharmacy to develop analytical methods for pharmaceutically active compounds using chemiluminescence and spectrophotometric techniques. Result This review covers the importance of potassium permanganate over other common oxidants used in pharmaceuticals and reported its extensive use and analytical applications using direct, indirect and kinetic spectrophotometric methods in different pharmaceutical formulations and biological samples. Chemiluminescent applications of potassium permanganate in the analyses of pharmaceuticals using flow and sequential injection techniques were also discussed. Conclusion This review summarizes the extensive use of potassium permanganate as a chromogenic and chemiluminescent reagent in the analyses of pharmaceutically active compounds to develop spectrophotometric and chemiluminescence methods since 2000.
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Many environmental and agricultural applications involve the transport of water and dissolved constituents through aggregated soil profiles, or porous media that are structured, fractured or macroporous in other ways. During the past several decades, various process-based macroscopic models have been used to simulate contaminant transport in such media. Many of these models consider advective-dispersive transport through relatively large inter-aggregate pore domains, while exchange with the smaller intra-aggregate pores is assumed to be controlled by diffusion. Exchange of solute between the two domains is often represented using a first-order mass transfer coefficient, which is commonly obtained by fitting to observed data. This study aims to understand and quantify the solute exchange term by applying a dual-porosity pore-scale network model to relatively large domains, and analysing the pore-scale results in terms of the classical dual-porosity (mobile-immobile) transport formulation.
The performance of a proton exchange membrane fuel cell, PEMFC, is significantly affected by the rate of oxygen diffusion through the cathode catalyst layer, CCL. Continuum-scale modelling of PEMFCs requires knowledge of the effective oxygen diffusivity as a function of CCL porosity and its water saturation. To provide this functionality, we used three-dimensional pore-scale modelling to simulate the diffusion of oxygen under different liquid water saturations in CCLs having different porosity values. Solving the governing equations for immiscible two-phase flow, fluid distributions at different saturation levels were obtained. We show that the presence of liquid water initiates a hindering effect by decreasing the diffusive transport of oxygen. Oxygen diffusion, including dissolution of oxygen into the liquid water phase, was taken into account to calculate effective diffusivity values of the entire domain. The resulting effective diffusivity values showed good agreement with values reported in the literature, which are often based on quasi-empirical relationships. Utilizing a large number of simulation results, a correlation equation was developed for the effective diffusivity of oxygen as a function of porosity and liquid water saturation, which is appropriate to be used for macroscopic modelling of flow and transport in CCLs.
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The decomposition of volatile organic compounds (VOCs) was investigated using a flow-type plasma-driven catalysis (PDC) system and a cycled system. In the flow-type PDC reactor a trade-off relation was observed between the formation of nitrogen oxides and the decomposition of VOCs. Complete decomposition of VOC to CO2 was achieved with the cycled system without forming CO, aerosol, and any nitrogen oxides. The oxygen-partial pressure dependence of different catalysts on the decomposition of benzene and toluene was investigated. The influence of VOC concentration and the temperature of oxygen plasma on the equivalent energy in the cycled system will be also discussed.
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The competitive interactions between target (e.g., dissolved trichloroethene) and nontarget (e.g., dissolved humic acid) compounds during chemical oxidation by permanganate were evaluated using syringe reactor experiments. The experiments were performed in phosphate buffered de-ionized water at ambient temperature (∼ 20°C). The dissolved humic acid exerted a significant and almost instantaneous permanganate demand reducing the mass of oxidant available for the destruction of the target compound. At the high humic acid concentration (246 mg/L as Total Organic Carbon), competition between the target and nontarget compounds for the available permanganate significantly reduced the rate of trichloroethene (TCE) degradation and the mass degraded. A pseudo first-order model was shown to effectively predict the rate of TCE degradation as long as sufficient permanganate was available to maintain an oxidant residual while overcoming the demand exerted from the target and nontarget compounds.
The widely used gasoline additive MTBE has been found in ground- and surface waters and poses a threat to the nation's community water supply wells. Richard Johnson, James Pankow, David Bender, Curtis Price and John Zogorski make the case for an improved understanding of factors affecting the magnitude of the problem.
Bioassay-directed chromatographic fractionation of an ethyl acetate extract from leaves of sweet potato (Ipomoea batatas L.) afforded six quinic acid derivatives: 3,5-epi-dicaffeoylquinic acid (1), 3,5-dicaffeoylquinic acid (2), methyl 3,5-O-dicaffeoylquinate (3), methyl 3,4-dicaffeoylquinate (4), methyl 4,5-dicaffeoylquinic acid (5),4,5-dicaffeoylquinate (6), and two phenolic compounds: caffeic acid (7) and caffeic acid methyl ester (8) together with three flavonoids: quercetin 3-O--D-glucopyranoside (9), quercetin 3-O--D-glucopyranoside, isoquercitrin (10) and kaempferol 3-O--D-glucopyranoside (11). The structures of these compounds were elucidated by the aid of spectroscopic methods. These compounds were assessed for antioxidant activities using three different cell-free bioassay systems. All isolates except 11 showed potent DPPH and superoxide anion radicals scavenging, and lipid peroxidation inhibitory activities. 3,5-epi-DCQA (1) and methyl quinates (3-5) along with flavonoide 9 were isolated for the first time from this plant.
The kinetics of oxidation of trichloroethylene (TCE) by potassium permanganate (KMnO4) was investigated in a phosphate buffer solution of pH 7 and ionic strength (I) of 0.05 M at three different temperatures (10, 15, and 20 degrees C), The results indicate that the oxidation of TCE by KMnO4 at a constant pH and temperature may be modeled as an irreversible second-order (first-order individually with respect to KMnO4 and TCE) reaction. The second-order rate constant and the activation energy, determined using the initial rate method for the reaction between TCE and KMnO4, were 0.89 +/- 0.03 M(-1)s(-1) and 35 +/- 2.9 kJ/mol, respectively. The results of this study also confirmed the assumed reaction stoichiometry, i.e., 2 mol of KMnO4 are required for the mineralization of 1 mol of TCE.
The kinetics and mechanism of the oxidation of ketones with permanganate ions were studied in aqueous acidic and alkaline media for acetone, hydroxyacetone, butan-2-one and butane-2,3-dione. Acid catalysed nucleophilic addition of the permanganate to the carbonyl C-atom is suggested. In alkaline media, parallel with electron abstraction from the enolate, a concerted mechanism is proposed. Intermediates and end products were determined. Comparisons between halogenation and oxidation have been made.
The gas-phase toluene removal efficiencies by photocatalytic oxidation (TiO2/UV), the combination of ozone and photocatalytic oxidation (TiO2/UV/O3), and the UV/O3 reaction were tested using a quartz tube photoreactor. The experiments were conducted under various ozone concentrations (3.3–15 ppm), toluene concentrations (1–9 ppm), relative humidity (5–80%), and gas flow rates (200–1200 mL/min). The toluene oxidation rates (TORs) of TiO2/UV/O3, and UV/O3 reactions were proportional to the ozone concentrations. The TORs of TiO2/UV, TiO2/UV/O3, and UV/O3 reactions increased with toluene concentration. However, there were negative correlations between the toluene removal efficiencies of these three kinds of reactions and the toluene concentrations. The order of the TORs and the CO2 yield rates of these three reactions were TiO2/UV/O3 > TiO2/UV > UV/O3. The kinetics of TiO2/UV, and TiO2/UV/O3 reactions fit the Langmuir–Hinshelwood rate form. The rate constants (k) and Langmuir adsorption constants (K) are as follows: TiO2/UV: k = 0.0102 ppm m/s, K = 0.146 ppm−1; TiO2/UV/O3: k = 0.0268 ppm m/s, K = 0.0796 ppm−1. The reciprocal of UV/O3 reaction rate showed a positive linear relationship with the reciprocals of humidity and of toluene concentration. Ozone, also an air pollutant, was removed in the TiO2/UV/O3, and UV/O3 reactions. The ozone removal efficiency of TiO2/UV/O3 reaction in the presence and absence of toluene ranged from 61.1 to 99.5% and 38.1 to 95.1%, respectively.
The oxidation of trichloroethylene (TCE) by permanganate proceeds in three sequential reaction steps. In the initial step, a cyclic hypomanganate ester is formed via an activated organometallic complex. The activation parameters for this step were determined to be Ea = 41.46 kJ/mol, ΔH = 39 kJ/mol, and ΔS = −14 J/mol. The initial reaction is a rate-limiting step (second-order rate constant k1p = 0.65−0.68 M-1 s-1 at 21 °C) and independent of pH. In the second step, the decomposition of the cyclic ester with complete chlorine liberation proceeds quickly via various reaction pathways to form four carboxylic acids. Approximately 77% of the TCE was transformed to formic acid at pH 4, while 95−97% of the TCE was transformed to oxalic and glyoxylic acids at pH values of 6−8. Kinetic data suggest that the decomposition rate of the cyclic ester is at least 100 times higher than its formation rate. In the final step, all carboxylic acids are oxidized by permanganate to the final product, CO2. Second-order rate constants of k3ap = 0.075−0.35 M-1 s-1, k3bp = 0.13−0.37 M-1 s-1, and k3cp = 0.073−0.11 M-1 s-1 over a pH range of 4−8 at 21 °C were estimated for oxidation of formic, glyoxylic, and oxalic acids, respectively. The oxidation rate of carboxylic acids and accumulation rate of CO2 increase with decreasing pH. The kinetic model that was developed, formulated, and solved analytically on the basis of the understanding of various processes is consistent with results obtained in the kinetic experiments.
Data on the kinetics, kinetic isotope effects, substrate selectivety, and activation parameters for the first step of oxidation of alkylbenzenes by permanganante in acidic aqueous solutions are surveyed. The MnO4 −, HMnO4, and MnO3 + species serve as oxidants at different acidities. The increase in the positive charge in this series enhances the electrophilicity of the reagent, which manifests itself as an increase in the reaction rate and a change in the site of attack on the alkylbenzene molecule (either the aromatic ring or C−H bond in the alkyl group). The oxidation of the alkyl C−H bonds in alkylbenzenes and in alkanes follows similar mechanisms, while the attack on the aromatic ring proceedsvia the electrophilic aromatic substitution mechanism with a transition state intermediate between the charge transfer complex and σ-complex.
This paper presents the study of the remediation of sandy soils containing six of the most common contaminants (benzene, toluene, ethylbenzene, xylene, trichloroethylene and perchloroethylene) using soil vapour extraction (SVE). The influence of soil water content on the process efficiency was evaluated considering the soil type and the contaminant. For artificially contaminated soils with negligible clay contents and natural organic matter it was concluded that: (i) all the remediation processes presented efficiencies above 92%; (ii) an increase of the soil water content led to a more time-consuming remediation; (iii) longer remediation periods were observed for contaminants with lower vapour pressures and lower water solubilities due to mass transfer limitations. Based on these results an easy and relatively fast procedure was developed for the prediction of the remediation times of real soils; 83% of the remediation times were predicted with relative deviations below 14%.