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CHEMICAL ENGINEERING TRANSACTIONS

VOL. 43, 2015

A publication of

The Italian Association
of Chemical Engineering
Online at www.aidic.it/cet

Chief Editors: Sauro Pierucci, Jiří J. Klemeš
Copyright © 2015, AIDIC Servizi S.r.l.,
ISBN 978-88-95608-34-1; ISSN 2283-9216

Degradation of Aqueous Diethanolamine (DEA) solutions
using UV/H2O2 Process

Nur Madihah Bt Yaser, Fareeda Chemat, Tazien Rashid, Murugesan Thanabalan*
Department of Chemical Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750, Perak, Malaysia.
murugesan@petronas.com.my

Aqueous diethanolamine (DEA) solutions are commonly used for the absorption/scrubbing of acidic gases
(CO2 and H2S) from natural gas apart from its wide applications in the formulations of consumer chemicals
namely, soaps, shampoos, emulsifiers etc. During these processes high concentrations of DEA are released
into the atmosphere in the form of waste water/effluents causing a severe pollution to the environment. Hence
these stable organic compounds need to be treated/degraded/mineralized before being released into the
atmosphere. Hence in the present research an attempt was made to employ UV/H2O2 based advanced
oxidation process for the degradation of DEA. Experiments were conducted using a synthetic solution of DEA
with a concentration range of 500 - 2000 ppm. The other variables used for the DEA degradation experiments
were, the initial concentrations of H2O2, pH and the temperature. Experiments were conducted in a glass
reactor, using UV lamp (8W) as radiation source. The DEA removal efficiencies were estimated based on the
TOC measurements. Based on the experimental results the optimum conditions for the maximum removal
efficiency were obtained by using the Box-Behnken Response Surface Methodology (RSM). A quadratic
regression model was developed to represent the present experimental results on the degradation efficiency
as a function of the variables. The experiments conducted based on the estimated optimum conditions
showed a satisfactory agreement with the predicted values.

1. Introduction

Emission of carbon dioxide (CO2) which is one of the greenhouse gases lead to serious environmental
problem such as global warming and greenhouse effect. The emission of carbon dioxide released to the
atmosphere has the largest percentage that cause global warming which is about 84 % compared to the other
gases such as nitrous oxide, fluorinated gases and methane which are 5 %, 2 % and 9 % (Mariz,1998). Other
than its contribution towards global warming and greenhouse effect, presence of CO2 in the gas stream also
will cause interference to the process and reduce the quality of the product (Barchas and David, 1992).
Releasing untreated flue gas to the atmosphere is becoming an issue because it violates the hazardous air
pollutants under the Clean Air Act (Shah et al., 2013). DEA is an organic compound which has primary amine
due to the presence of amino group in the molecule. It is a weak base, toxic, flammable, corrosive, colourless
and has an odour which similar to ammonia (Razali et al., 2010), which has been used for the scrubbing of
acid gases. However, other than being used as CO2 scrubber, DEA is also widely being used in cutting oils,
soaps, shampoos, cleaners, polishers, cosmetics, pharmaceuticals and as an intermediate in the rubber
chemical industry. During the processing of the above, high concentrations of DEA in solutions are released in
to the atmosphere in the form of wastewater/effluents, particularly during the periodic maintenance and
cleaning of the absorber/stripper units. In order to maintain the environmental regulations these effluents
containing high concentration of DEA must be treated before their release into atmosphere. Advanced
Oxidation Process is one of the common techniques used for the treatment of such stable highly organic
compounds (Ghaly et al., 2001). Due to the disadvantages of sludge formation, Fenton’s reagents are not
preferable, whereas the combination of UV/H2O2 is the most preferred AOP’s for the treatment of amine
solutions (Fauzi, 2010). The main advantages of the UV/H2O2 process are: no formation of sludge during the

DOI: 10.3303/CET1543378

Please cite this article as: Nur Madihah Bt Yaser B.Y., Fareeda C., Tazien R., Thanabalan M., 2015, Degradation of aqueous diethanolamine
(dea) solutions using uv/h2o2 process, Chemical Engineering Transactions, 43, 2263-2268 DOI: 10.3303/CET1543378

DOI: 10.3303/CET1543378

2263

treatment, high ability to produce hydroxyl radicals and applicability of the process for a wide pH range. The
combination of UV/H2O2 treatments can create a very fast and efficient for degradation. This is because if UV
treatment alone is used, the range of contaminants UV can degrade by itself is very limited, thus slowing
degradation and increase the time to degrade (Rinker et al., 1996). For H2O2, it is very strong oxidizing agent
where it is capable to destroy some halogenated and most non halogenated compounds in aqueous media
(Sohrabi and Ghavami, 2008). The combination of UV/H2O2 is one of the best known AOP’s and their
combination will form two free hydroxyl radicals, OH- which is potential oxidizing agent. The degradation
mechanism of DEA could be explained as follows:

DEA + H2O2 + hv → deg. product (1)

The free hydroxyl radicals are not in the stable state because they are at excited state species since they are
characterized by a one-electron deficiency. Therefore, because of its instability, hydroxyl radicals, OH- will
tend to react with the first chemical that it comes in contact with and tend to completely oxidize dissolved
organic contaminants in aqueous media (Peters et al., 2011).

H2O2 + hv →2•HO (2)

DEA + •OH → H2O + deg. products (3)

Hence in the present work an attempt has been made to study the effect of UV/H2O2 process on the
degradation of aqueous solutions of DEA.

2. Materials and Methods

The chemicals used in the present research namely, Diethanolamine (DEA), hydrogen peroxide (H2O2),
sodium hydroxide (NaOH), concentrated hydrochloric acid (HCl), were purchased from Merck (Germany). All
the experiments were conducted in a stirred jacketed glass reactor (700 mL) with a working volume of 400 mL.
Provisions were made in the reactor to monitor and also to collect samples for follow the degradation process.
NaOH/H2SO4 solutions were used to adjust the pH accordingly. The radiation source is a UV lamp (8 W, UV-C
manufactured by Philips, Holland) and was protected by a quartz tube. The degradation of the process were
followed by measuring the Total Organic Carbon (TOC) of the samples. The TOC were measured using TOC
analyzer (Shimadzu TOC-VCSH) and the H2O2 concentration was estimated by KMnO4 titration (Harimurti et
al, 2013). Reaction between diethanolamine (DEA) and hydrogen peroxide is as follow:

C4H11NO2 + 10H2O2  4CO2 + 14H2O + NH3 (4)

Degradation percentage of DEA will then be analysed by using TOC analyzer equipment in order to measure
the total organic carbon present in the solution. The detailed experimental procedures were discussed
elsewhere for oxytetracycline (Rahmah et al., 2014) and MDEA (Harimurti et al, 2013).

3. Results and Discussion

In the present research, preliminary experiments were conducted to study the individual effect of UV, H2O2
and the combination of both UV/H2O2. The effect of initial concentration of DEA (500 – 2,000 ppm), effect of
initial H2O2 concentration (500 – 2,000 ppm), effect of pH (3 - 9) and the effect of temperature (30 - 50 oC) on
the degradation of DEA were studied. Based on the present results, the optimized conditions for the
degradation process were established. The present results are discussed in detail in the following sections.

3.1 Individual effect of UV radiation and H2O2
Three experiments were carried out in order to study the TOC removal differences by using UV radiation only,
H2O2 and the combination both UV radiation plus H2O2 and the obtained results are shown in Figure 1. It can
be seen that the UV/H2O2 combination shows higher TOC removal, which could be attributed to the enhanced
production of hydroxyl radicals due the presence of UV in the system. The capacity of H2O2 to degrade the
stable organic compound is mainly due to its high redox potential i.e., +1.8 V. This reduction potential
indicates the high tendency of H2O2 to act as an oxidant, which refers to direct electron transfer reaction
between the organic compound and H2O2. However, a very high reduction of DEA and the total organic
carbon was found, when the combination of UV/H2O2 were applied. Nearly a complete degradation of DEA
was achieved at 240 min of reaction time. Hence it can be concluded that the combination of UV/H2O2 will
generate more hydroxyl radical, which has a major role to play in the degradation of DEA.

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3.2 Effect of initial H2O2 concentration
The effect of initial H2O2 concentration on the degradation efficiency is investigated by adding different
concentration of H2O2 ranging from 500 ppm to 2,000 ppm. The degradation efficiency is increasing from 500
ppm to 1,500 ppm of initial H2O2 concentration Figure 2. However, as the initial H2O2 concentration increases
to 2,000 ppm, the degradation efficiency is decreasing. As the initial H2O2 concentration increases, the
production of hydroxyl radical also increases as well which lead to a faster rate of degradation of DEA.
However, when initial H2O2 concentration increases to 2,000 ppm, the hydroxyl radicals produced were
preferred to react with the excess H2O2 rather than reacting with DEA molecule, and hence the reduction in
degradation efficiency (Zang and Farnood, 2005). As the H2O2 concentration increases, hydroperoxyl radicals
which are less reactive compare to hydroxyl radicals also are being produced.

Figure 1: Effect of UV radiation and H2O2 on
degradation of DEA (DEA = 1000 ppm, H2O2 =
1500 ppm, pH = 5)

Figure 2: Effect of initial H2O2 concentration with
irradiation time (DEA = 1000 ppm, pH = 5,
Temperature = 30 ºC)

3.3 Effect of initial diethanolamine (DEA) concentration
The effect of initial DEA concentration (500 ppm to 2,000 ppm) on the degradation efficiency is shown in
Figure 3. As the irradiation time increases, the TOC removes decreases, hence resulting increases in the
degradation efficiency for initial DEA concentration from 500 ppm to 1,000 ppm. However, after 1,000 ppm of
DEA concentration (1,000 – 2,000 ppm), it shows that the degradation efficiency of DEA is decreasing which
is from 97.8 % to 70.2 %. The reason could be that, as the concentration of DEA increases, there is not
sufficient hydroxyl radicals available to degrade DEA molecule.

3.4 Effect of initial pH
In order to study the effect of initial pH (3 - 9) on the degradation of DEA four different experiments were
conducted. The value of pH were adjusted by adding concentrated hydrochloric acid or sodium hydroxide to
the sample solution (Arslan and Balcioğlu, 1999). As the pH increases, the TOC removal increases up to pH =
5 within 4 hours of irradiation time, indicating that the degradation of DEA is more effective at acidic condition
than at alkaline condition, since at acidic condition more hydroxyl radicals are being produced compared to at
alkaline condition (Sohrabi and Ghavami, 2008). Further increase in pH beyond 5, resulted in decrease in
percentage TOC removal, which might be due to the decomposition of H2O2 itself at higher pH levels. At high
pH conditions H2O2 tend to ionize to form hydroperoxide anion, which is a well-known strong scavenger to
hydroxyl radical. The reaction between hydroperoxide anion and hydroxyl radical generates a less reactive
hydroperoxyl radical and hence in the reduction in degradation of DEA/TOC removal

3.5 Effect of temperature
Experiments were conducted at 30 °C to 50 °C, at a pH of 5. The initial concentrations of DEA and H2O2 were
1,000 ppm and 1,500 ppm concentration respectively. The percentage degradation increased with increasing
temperature. Heating has either increased the generation rate of hydroxyl radicals or directly affected the
reaction rate with DEA (Razali et al., 2010). Since the overall rate appears to be limited by the availability of
hydroxyl radicals, it is likely that the higher temperature increased the activation energy for the H2O2 reaction
to hydroxyl radicals. An increase in degradation efficiency with temperature could be attributed to the reason
that may be due to an increase in collision frequency between DEA and the hydroxyl radical in the system.

0 30 60 90 120 150 180 210 240
0

100

T
O

C
r

e
m

o
v
e

,
(%

)

Irradiation time, (min)

UV/H2O2
UV
H2O2

0 30 60 90 120 150 180 210 240
0

100

T
O

C
r

e
m

o
v

e
,

(%
)

Irradiation time, (min)

500 ppm
1000 ppm
1500 ppm
2000 ppm

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Figure 3: Effect of initial DEA concentrations with
irradiation time (H2O2 = 1500 ppm, pH = 5,
Temperature = 30 ºC)

Figure 4: Effect of initial pH with irradiation time
(DEA = 1000 ppm, H2O2 = 1500 ppm,
Temperature = 30 ºC)

3.6 Optimization studies
Optimization of Diethanolamine (DEA) degradation process was carried out by using Portable Statgraphic
Centurion 15.2.11.0 statistical software which then compared with the experimental values. The range and
level of the factors (initial concentration of H2O2, initial pH and temperature) were determined based on the
initial screening results while the other factors (DEA concentration, UV intensity and irradiation time) were kept
constant. Based on the analysis, using the Pareto chart of standardized effect at p = 0.05 (Figure 6, which
shows that all the three factors namely., initial concentration of H2O2, initial pH and temperature have a
significant contribution to the degradation percentage of DEA. The optimum response and relationship
between the factors and response were obtained by using Response Surface Methodology (RSM). The
quadratic regression model for representing the present experimental data on the percentage degradation on
DEA is shown in the following form of equation: = 44.9531 + 0.05475 + 5.90417 − 0.219167 − 0.0000187167 − 0.000375 + 0.00013 − 0.532292 − 0.0075 + 0.00145833 (5)
Where Y is the response , percentage degraded; X1 is H2O2 concentration; X2 – pH; X3 is temperature. The
proposed empirical correlation represents the present data with an R2 = 0.989. The comparison of the

predicted percentage degradation of DEA with those obtained experimentally are shown in Figure 7, which
indicates a satisfactory agreement.

Figure 5: Effect of temperature with irradiation time
(DEA = 1000 ppm, H2O2 = 1500 ppm, pH = 5)

Figure 6: Pareto chart of standardized effect for
percentage of degradation

0 30 60 90 120 150 180 210 240
0

100
T

O
C

r
e
m

o
v
e
,
(%

)

Irradiation time, (min)

500 ppm
1000 ppm
1500 ppm
2000 ppm

0 30 60 90 120 150 180 210 240
0

100

T
O

C
r

e
m

o
v
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,
(%

)

Irradiation time, (min)

pH3
pH5
pH7
pH9

0 30 60 90 120 150 180 210 240
0

100

T
O

C
r

e
m

o
v
e
,

(%
)

Irradiation time, (min)

30
o
C

40
o
C

50
o
C

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Figure 7: Comparison of the predicted (Eq(5)) and experimental values

4. Conclusions

Based on the present study, it can be concluded that the aqueous DEA solution could be effectively degraded
using UV/H2O2 process. Initial concentration of H2O2, pH and temperature of the system control the
degradation efficiency of the process. The optimized parameters for the degradation process are:
concentration of H2O2 = 1590.13 ppm, pH = 4.63 and temperature = 50 ºC. Under these optimized conditions
the degradation efficiency was found to be 99.14 %. However, in order to confirm the validity of regression
equation, another two experiments were conducted at optimum conditions, and the average degradation was
found to be 98.99 %, which satisfactorily agree with the predicted values. All the present experiments were
conducted in a batch mode, further experimentation in continuous mode is necessary for establishing the
scale up parameters towards its commercial applications.

Acknowledgements

The authors would like to thank Universiti Teknologi PETRONAS for financial support provided for conducting
the research.

References

Arslan, I. Balcioğlu, I. A. 1999. Degradation of commercial reactive dyestuffs by heterogenous and
homogenous advanced oxidation processes: a comparative study. Dyes and pigments, 43, 95-108.

Barchas, R., Davis, R. 1992. The Kerr-McGee/ABB Lummus Crest technology for the recovery of CO2 from
stack gases. Energy Conversion and Management, 33, 333-340.

Fauzi, I. 2010. Studies on the oxidation of monoethanolamine using UV and H2O2 with post-biological
treatment. MS Dissertation, Universiti Teknologi PETRONAS, Perak, Malaysia

Ghaly, M. Y., Härtel, G., Mayer, R., Haseneder, R. 2001. Photochemical oxidation of p-chlorophenol by
UV/H2O2 and photo-Fenton process. A comparative study. Waste Management, 21, 41-47.

Harimurti, S., Rahmah, A. U., Omar, A. A., Murugesan, T. 2013. Kinetics of Methyldiethanolamine
Mineralization by Using UV/H2O2 Process. CLEAN–Soil, Air, Water, 41, 1165-1174.

Mariz, C. L. 1998. Carbon dioxode recovery: Large scale design trends. Journal of Canadian Petroleum
Technology, 37, 42-47.

Peters, L., Hussain, A., Follmann, M., Melin, T., Hägg, M. B. 2011. CO2 removal from natural gas by
employing amine absorption and membrane technology-A technical and economical analysis. Chemical
Engineering Journal, 172, 952-960.

Rahmah, A. U., Harimurti, S., Omar, A. A., Murugesan, T. 2014. Kinetics and Thermodynamic Studies of
Oxytetracycline Mineralization Using UV/H2O2. CLEAN–Soil, Air, Water.

Ramli, R. M., Chong, F. K., Omar, A. A., Murugesan, T. 2014. Performance of Surfactant Assisted Synthesis
of Fe/TiO2 on the Photodegradation of Diisopropanolamine. CLEAN–Soil, Air, Water.

Razali, M., Yunus, R., Jemaat, Z., Alias, S. 2010. Monoethanolamine Wastewater Treatment via Adsorption
Method: A Study on Comparison of Chitosan, Activated Carbon, Alum and Zeolite. Journal of Applied
Sciences (Faisalabad), 10, 2544-2550.

Rinker, E. B., Ashour, S. S., Sandall, O. C. 1996. Kinetics and modeling of carbon dioxide absorption into
aqueous solutions of diethanolamine. Industrial & Engineering Chemistry Research, 35, 1107-1114.

88 90 92 94 96 98 100
88

100
P

re
d

ic
te

d
v

a
lu

e
s
,
(%

)

Experimental values, (%)

R
2
= 0.989

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Shah, A. D., Dai, N., Mitch, W. A. 2013. Application of ultraviolet, ozone, and advanced oxidation treatments to
washwaters to destroy nitrosamines, nitramines, amines, and aldehydes formed during amine-based
carbon capture. Environmental Science & Technology, 47, 2799-2808.

Sohrabi, M., Ghavami, M. 2008. Photocatalytic degradation of Direct Red 23 dye using UV/TiO2: Effect of
operational parameters. Journal of Hazardous Materials, 153, 1235-1239.

Zang, Y., Farnood, R. 2005. Effects of hydrogen peroxide concentration and ultraviolet light intensity on
methyl tert-butyl ether degradation kinetics. Chemical Engineering Science, 60, 1641-1648.

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