CHEMICAL ENGINEERING TRANSACTIONS
VOL. 78, 2020
A publication of
The Italian Association
of Chemical Engineering
Online at www.cetjournal.it
Guest Editors: Jeng Shiun Lim, Nor Alafiza Yunus, Jiří Jaromír Klemeš
Copyright © 2020, AIDIC Servizi S.r.l.
ISBN 978-88-95608-76-1; ISSN 2283-9216
Esterified Durian Peel Adsorbents with Stearic Acid for Spill
Removal
Thai Van Nam*, Trinh Trong Nguyen, Dao Ngoc Dung, Pham Thi Hoai Phuong
Ho Chi Minh City University of Technology (HUTECH), 475A Dien Bien Phu Street, Ward 25, BinhThanh District, Ho Chi
Minh City, Vietnam
tv.nam@hutech.edu.vn
The treatment of oil spill using natural adsorbents is considered as an eco-friendly and cost-effective way.
Agriculture waste is preferred as an oil cleanup technology due to its biodegradation and buoyancy. The goal
of this study is to examine the diesel oil adsorption efficiency, the capacity of raw peels and stearic acid
esterified peels for three durian types: Ri6, CB, and 6H, which are the most popular in Vietnam. The oil
adsorption capacity in artificial oil-polluted water depends on the oil content, particle size, and adsorption time.
Analytical techniques of durian peel, such as microstructure and morphology using FTIR spectrometry and
scanning electron microscopy are also studied. The result shows that Ri6 raw powder has the highest oil
adsorption capacity. The oil adsorption capacity of raw and esterified durian peels are 0.2340 g/g and 0.3780
g/g. The results explain that the best conditions were established at 0.15 – 0.3 mm particle size of modified
absorbents and pH ranging from 6.5 – 9.3 for 20 min. Adsorption capacity of esterified durian peel absorbent
confirms to a Langmuir isotherm adsorption line with maximum adsorption capacity of 453.9 mg/g.
1. Introduction
In recent years, there have been many oil spills, oil-polluted wastewater causing serious impacts on the
environment and ecosystems (Chuong, 2008). According to the statistics of Vietnam Environment
Department, more than 90 oil spills from 1987 to 2007 in estuarine and coastal areas had caused great
economic losses as well as serious environmental pollution for a long time (Thang, 2016). Oil-polluted
wastewater affects fisheries, aquaculture, and tourism (Thung et al., 2007) and kills fish, especially causing
serious consequences to health (Wardley-Smith, 1983).
In addition, pollution of mineral oil at some seaports in Vietnam is also a concern. Oil concentration in surface
water of all 91 ports exceeded the allowable Vietnam standard of 0.1 mg/L, i.e., 0.42 mg/L in Hai Phong port
and 0.6 mg/L in Cai Lan port (VASI, 2018). Therefore, it is necessary to take effective measures to recover oil
quickly on a large surface area of water, without affecting to aquatic organisms.
The methods used to remove oil in the water can be divided into three groups: chemical methods
(solidification, dispersion), biological methods and mechanical methods (skimmers, oil seals, adsorption) (El-
Din et al., 2018). Chemical methods cause secondary pollution due to the addition of chemicals to the
environment, affecting the aquatic organism, high cost and inefficient in trace level (El-Din et al., 2018).
Biological methods have not yet met the requirements of the emergency response because they take so much
time. The adsorption methods are still the most preferred techniques for oil clean-up because it is the most
rapid (Gheorghiu et al., 2014), a simple method, friendly to the environment (El-Nafaty et al., 2013), and low
cost (Nurul et al., 2011). Although organic polymer products such as polypropylene, polyethylene
polyurethane have been widely used to adsorb oil in surface water, there are major disadvantages due to the
difficulty to biodegrade (Gerald et al., 2003). In recent years, many researchers have focused on the use of
agricultural residues natural adsorbents for oil clean-up such as banana peel (El-Din et al., 2018), duckweed,
corn cob, peanut shell, bagasse (Lan, 2016), rice husk (Nui and Thuy, 2012), or greasy raw wool as natural
adsorbent materials (Periolatto and Gozzelino, 2015).
To improve oil capacity adsorption, making the material surface hydrophobic is necessary (Bannerjee et al.,
2006). Hence, there are many methods to increase the hydrophobic, oil-loving of adsorbents such as
DOI: 10.3303/CET2078046
Paper Received: 15/04/2019; Revised: 07/09/2019; Accepted: 30/10/2019
Please cite this article as: Nam T.V., Nguyen T.T., Dung D.N., Phuong P.T.H., 2020, Esterified Durian Peel Adsorbents with Stearic Acid for
Spill Removal, Chemical Engineering Transactions, 78, 271-276 DOI:10.3303/CET2078046
271
https://www.sciencedirect.com/topics/engineering/saline-water
pulverization to increase the contact area of the material (El-Din et al., 2018), treating with fatty acid (Sayed et
al., 2006) or base (Tham et al., 2010), and esterification (Bannerjee et al., 2006).
In this study, the oil adsorbent used is durian peel (DP). It has high porosity, contains composition of cellulose
being suitable to adsorb many organic pollutants (Uyen, 2012). DP waste has a volume about 115,816 to
117,992 tons/year in the southern provinces of Vietnam, showing great potential to producing natural
adsorbents for oil clean-up. However, DP contains many hydroxyl groups (-OH) which are hydrophilic groups
that need to convert into oil-loving tails through an esterification reaction (Bannerjee et al., 2006). Esterified
DP adsorbent is easier to float on surface water so it is convenient for oil collection to recycle, and recover.
This paper demonstrates the efficacy of surface modification of DP by stearic acid, which is the most common
saturated fatty acid in nature, for oil adsorption.
2. Experimental
2.1 Materials
Durian has many types in Vietnam, but there are three popular types: Ri6, 6 Huu (6H) and Chuong Bo (CB).
This three types of (DP) were collected from the market in Ho Chi Minh City, washed several times with tap
water to clean up mud and soil. Then, the exterior thorn was removed and cut into small pieces, 1-2 cm, oven-
dried to constant mass at 80 °C. Samples after drying were crushed and sieved to particles with different
sizes. Dried powders in different sizes were stored and preserved in plastic containers at room temperature.
Adsorbents were denoted by DP-Ri6, DP-6H, and DP-CB.
Diesel oil (DO) 0.05S was purchased at a gas station in Ho Chi Minh City used as an oil-contaminant in water
(d = 0.84 g/mL). The chemicals used were of analytical grade (E. Meck).
The oil-polluted water was created by adding the appropriate amount of diesel oil into glass beakers (volume
250 mL) containing 100 mL distilled water. Tested mineral oil concentrations were based on actual oil levels at
Vietnam seaports (Vietnam Administration of Seas and Islands, 2018).
Through analysis of DP with the highest oil adsorption capacity, DP-Ri6 was selected, then grafted with stearic
acid according to the research of Banerjee et al. (2006). The sample of DP-Ri6 dried powder (1.00 g) was
treated with 0.1 - 0.6 g of stearic acid in 100 mL of n-hexane containing one drop of concentrated H2SO4 as a
catalyst. The mixture was refluxed in a Dean - Stark apparatus at 65 ± 2 °C for 6 h. After the reaction, the
esterified DP-Ri6, named as DP-Ri6AS, was washed repeatedly with n-hexane. The material is dried in an
oven at 80 °C for 24 h and stored in a plastic container.
2.2 Research methods
On the surface of untreated DP, many groups -OH (of alcohol and phenol) make materials that tend to be
hydrophilic resulting in oil absorption capacity reduction. When the oil-loving tails of stearic acid were grafted
to the material, they help to attract the oil molecules in the water towards the material to increase the oil
absorption capacity in the water. The esterification reaction scheme is shown in Eq(1).
𝐷𝑃 −𝑂𝐻 + 𝐶17𝐻35 −𝐶𝑂𝑂𝐻
H+
↔ 𝐶𝑒𝑙𝑙 −𝑂𝐶𝑂𝐶17𝐻35 +𝐻2𝑂
(1)
Surface morphology of adsorbents before and after modification with stearic acid was investigated by
scanning electron microscopy (SEM), JEOL JSM-5300. The oscillation frequency of molecules is analyzed by
Fourier transform infrared spectroscopy (FTIR) using FTIR spectrometry, JASCO-4700.
The oil content in the water is determined by the extraction method with n-hexane solvent (Bien, 2011). The
emulsion is completely dehydrated by passing anhydrous sodium sulfate, and finally, n-hexane in the mixture
was removed by drying at 85 °C. The remaining oil is determined by the weighing method.
The amount of oil adsorbed on adsorbents is determined by taking the amount of initial oil minus the amount
of remaining oil in water after the adsorption (g oil/g material).
To determine the highest oil adsorption potential of DP waste, SEM and FTIR were used. Also, the mineral oil
adsorption capacity of three types of DP waste was also investigated by adding 1.00 g each of raw DPs to a
beaker (volume 250 mL) containing 100 mL of distilled water polluted with 0.42 g of oil for 30 min (Bien and
Thoi, 2011). Then, the oil absorption capacity of DPs was calculated and compared.
DP-Ri6 with suitable particle size (0.15 to 0.3 mm) was selected because of the highest oil adsorption
potential to conduct the esterification reaction with stearic acid. The oil adsorption capacity and the amounts of
sunk adsorbents were compared to determine the best ratio of acid and DP-Ri6. Experimental conditions:
poured 0.42 g of oil into 100 mL of distilled water, at pH 6.5, and adsorption time of 30 min (Nam and Nguyen,
2016). FTIR spectrometry was used to verify the ester bond formation of DP-Ri6AS.
In this study, factors were investigated by the single-factor method. Specifically, factors independently
surveyed were the oil content in the water, particle size, contact time, and maximum adsorption capacity.
272
When a factor was surveyed, the remaining factors were fixed at selected levels. Evaluation criteria are the
mineral oil adsorption and capacity of adsorbents. Through these experiments the best value of each factor
affecting the oil adsorption capacity was determined.
3. Results and discussion
3.1 Determination of drying time and moisture of DP waste
The moisture of the three DP types has little change after 8 h, from 76.31 % to 83.40 %, the highest is in DP-
Ri6. Therefore, the selected drying time for the next experiment is 8 h.
3.2 Determination of the highest oil adsorption potential of DP waste
DP-Ri6, DP-6H and DP-CB with suitable particle size (0.15 to 0.3 mm) were recorded by FTIR. Figure 1
shows that the three types of DPs have the bands in the region 3,400 cm-1 indicating the presence of
stretching of strong hydroxyl groups. In addition, the stretching C – O can be seen at 1,205 cm-1, while the
bands at 1,715 cm-1 correspond to the stretching of a carbonyl group, C=O (hemicellulose) (Bannerjee et al.,
2006). DP-Ri6 has stronger and broader peaks of -OH and -C=O, so they have higher moisture and the ability
to form an esterification reaction is also better. Table 1 indicates that the oil adsorption efficiency of DP-Ri6
was significantly higher than that of DP-CB and DP-6H at 1.67 and 1.73 times. Because this efficiency is still
low, DP-Ri6 was chosen to graft with stearic acid through esterification.
Figure 1: FTIR spectra of the three DP types
Table 1: The amount of oil adsorption of the three DPs waste
DP types g oil/100 mL Amount adsorbed (g oil/g adsorbent)* Efficiency (%)
6H 0.42 0.1541 ± 0.0107b 36.69
CB 0.42 0.1679 ± 0.007b 37.99
Ri6 0.42 0.2670 ± 0.089a 63.57
* Oil adsorption capacity with different superscripts (a, b) are significantly (p < 0.05) different.
3.3 Comparison of oil adsorption capacity of DP-Ri6 and DP-Ri6AS
The levels of adsorbed oil increased from 0.234 to 0.3780 g/g when the dose of stearic acid mixed up to 0.4 g
stearic/1g DP-Ri6, and the weights of adsorbents sunk decreased from 0.6068 g (DP-Ri6) to 0.0227 g (0.4 g
stearic acid) (Figure 2). Thus, the ratio of acid and adsorbent (w/w) at 0.4 is the highest oil adsorption capacity
and the floating ability is the best.
Figure 2: Effect of stearic acid dose to oil adsorption capacity and floating capacity of adsorbents
273
This result explained the fact that raw DP-Ri6 contains a lot of hydroxyls (-OH) groups on the surface, causing
hydrophilic capacity, and easily settle-down; hence, the oil adsorption capacity is poor. When stearic acid
levels increase, many bonds of DP-OCOC17H35 formed lead to improve the capacity of the oil adsorption and
material buoyancy (Bannerjee et al., 2006) (Eq(1)). However, higher levels of stearic acid would cover the
surface of DPs so that the oil molecules could not be adsorbed. In addition, the alkane strings (C17H35-) may
limit each other because they could roll instead of forming tentacles in the water environment, thereby
reducing the oil adsorption capacity of DP-Ri6AS. To verify this identification, the SEM image and the FTIR
spectrum of DP-Ri6 and DP-Ri6AS were analyzed. It was found that both adsorbents have porous surfaces to
allow oil and water to penetrate into the internal parts of the materials easily. After grafting with stearic acid,
the material surface appears yarns of the C17H35 strings without covering pores.
Figure 3a shows a broad and strong peak at ~3,300 cm-1 corresponding to O-H group (alpha – cellulose). The
intensity of O-H groups of DP-Ri6AS declines due to forming of carboxyl bonds (-COO-) in esterification.
Some new bonds created provide evidence that the esterification occurred. The band at 2,930 cm-1
corresponds to C–H asymmetric stretching of –CH2- groups (from stearic acid). Stronger peak intensity at
1,730 – 1,740 cm-1 of DP-Ri6AS indicates that the number of C=O groups increased. In addition, the presence
of C–O stretching shows that stearic acid has been esterified with –OH groups of DP to form DP-OCOC17H35
(Figure 3b). This result is similar with the analysis of infrared spectrometry of DP cellulose that converts
cellulose to carbon methyl cellulose (CMC) (Uyen, 2012).
Figure 3: FTIR spectra of (a) DP-Ri6 and (b) DP-Ri6AS
3.4 Factors affecting oil adsorption capacity of DP-Ri6AS
3.4.1. Effect of oil content in water
The amount of oil adsorption increased from 0.2486 to 0.4474 g/g when the volume of oil increased from 0.3
to 0.9 mL (corresponding from 0.252 g to 0.756 g), and the oil adsorption efficiency decreased from 99.86 %
to 59.18 % (Figure 4). When the volume of oil increased and proceeded to saturation state, oil in water cannot
well adsorb to DP-Ri6AS; hence oil adsorption efficiency would decrease. This rule is similar to previous
results (Duong et al., 2010) about the oil adsorption capacity.
Figure 4: The effect of oil content to adsorption capacity of DP-Ri6AS
(a) (b)
274
If compared with the Vietnam standard of oil content in coastal seawater, 0.1 mg/L is an allowable limit. When
the oil content ranges from 0.254 g to 0.42 g (0.3 mL - 0.5 mL), oil-polluted water after adsorption is below the
standard in the most suitable conditions. With a higher oil volume, the water quality after treatment is not
guaranteed. Adsorption efficiency of oil content at 0.42 g (0.5 mL) is about 90 % and oil content in water is
below the allowable limit after treatment.
3.4.2. Effect of particle size
With the oil content of 0.42 g in 100 mL of distilled water and 1.00 g of DP-Ri6AS material, the oil adsorption
efficiency descends according to the particle size of the material, 99.5 % - 81.67 % corresponding to the
amount of oil adsorbed 0.418 g/g - 0.343 g/g. This result is completely consistent with the study of Nui and
Thuy (2012), which shows that the oil adsorption capacity increases as the size of the material decreases.
There were no significant differences (p < 0.05) between < 0.15 mm and 0.15 - 0.3 mm. If the particle size is
small, it would be affected by wind in practical application. Therefore, the best particle size from 0.15 to 0.3
mm is selected, smaller than the particle size of banana peel adsorbent, 0.3625 mm (El-Din et al., 2018).
3.4.3. Effect of adsorption time
The oil adsorption capacity reached 0.3193 g/g within 10 min and 0.3987 g/g (94.93 %) after 20 min, showing
that oil is trapped so fast. It is highly potential for oil spill removal and interruption of oil getting away farther
into the sea (Bannerjee et al., 2006). After 20 min, the oil adsorption efficiency was nearly constant and the
material reached a saturation state. As a result, the most suitable adsorption time is 20 min for the next
experiments.
3.4.4. Maximum adsorption capacity of DP-Ri6AS
The data obtained in this experiment, i.e., Ce and Ce/qe, were analyzed using a Langmuir isotherm model to
identify qm. Figure 5 shows the Langmuir equation with the correlation coefficient, R2 = 0.9996. The adsorption
data of DP-Ri6AS could be best fitted by the Langmuir model. Therefore, the adsorption could be described as
monolayer coverage and the maximum adsorption capacity of DP-Ri6AS was found, qm = 453.9 mg/g.
Figure 5: Langmuir isotherm of DP-Ri6AS
Compared with some research results on the oil adsorption capacity of natural adsorbents in previous studies
(Duong et al., 2010; Sayed and Zayedb, 2006), the oil absorption capacity of DP – Ri6AS is higher, but still
lower than that of the results of Bannerjee et al. (2006), and El-Din (2018) (Table 2). The difference is that
those authors gave the adsorbent materials directly contacting with crude oil. In addition to assessing the oil
adsorption capacity, this research also assessed adsorption efficiency of oil content after treatment.
Table 2: Comparison between DP-Ri6AS and other organic sorbents
Sorbents Adsorption capacity (g/g) Oil type Reference
Banana Peel
Stearic Grafted Saw Dust
Untreated Saw Dust
Onion Peel
DP-Ri6AS
Garlic Peel
Duckweed
Coconut Fiber
Corn Cob
5 – 7
5.23
3.77
0.455
0.454
0.385
0.29
0.21
0.178
Crude oil
Crude oil
Crude oil
Crude oil
Oil in water
Crude oil
Oil in water
Oil in water
Oil in water
EL-Din et al. (2018)
Benerjee et al. (2006)
Benerjee et al. (2006)
Sayed and Zayedb (2006)
This study
Sayed and Zayedb (2006)
Duong et al. (2010)
Duong et al. (2010)
Duong et al. (2010)
275
4. Conclusion
Study on the oil adsorption capacity of the three DP types showed that DP-Ri6 has the highest potential in
adsorption of mineral oil. The best mixing ratio between DP and stearic acid is 0.4 g acid/1g of DP-Ri6 to
create the product of esterification process, DP-Ri6AS, having the highest oil adsorption capacity. Oil
adsorption capacity of DP-Ri6AS is higher than that of DP-Ri6 1.61 times. Experimental results of oil
adsorption capacity of 1.00 g of VSR-Ri6AS showed the maximum contaminant oil content in water that the
adsorbent may treat to meet the standard is 0.42 g in 100 mL distilled water, with an optimal particle size of
0.15 - 0.3 mm, optimal adsorption time of 20 min. The maximum oil adsorption capacity of VSR-Ri6AS is
453.9 mg/g and the oil adsorption process of VSR-Ri6AS follows the isothermal Langmuir equation.
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