China Petroleum Processing and Petrochemical Technology
Catalyst Research
2015, Vol. 17, No. 2, pp 57-63
June 30, 2015
Adsorptive Desulfurization of Propylmercaptan and
Dimethyl Sulfide by CuBr2 Modified Bentonite
Cui Yuanyuan; Lu Yannan; Yi Dezhi; Shi Li; Meng Xuan
(The State Key Laboratory of Chemical Engineering, East China University of Science and Technology,
Shanghai 200237)
Abstract: Adsorptive desulfurization for removing propylmercaptan (PM) and dimethyl sulfide (DMS) over CuBr2 modified bentonite was investigated under ambient conditions in this work. A saturated sulfur capacity as high as 196 mg of S per
gram of adsorbent was demonstrated. The influence of loading amount of Cu (II) and calcination temperature on adsorptive
desulfurization was investigated. Test results revealed that the optimum loading amount of Cu (II) was 15%, and the calcination temperature was 150 ℃. The pyridine-FTIR spectroscopy showed that a certain amount of Lewis acid could contribute
to the increase of adsorption capacity. Spectral shifts of the ν(C-S) and ν(Cu-S) vibrations were detected from the Raman
spectra of the Cu (II) complex which was a reaction product of CuBr2 with DMS. According to the hybrid orbital theory and
the complex adsorption reaction, the desulfurization of PM and DMS over the CuBr2 modified bentonite is ascribed to the
formation of S-M (σ) bonds.
Key words: desulfurization; bentonite; propylmercaptan; dimethyl sulfide; mechanism
1　Introduction
Sulfides often exist as the main pollutants in liquid fuels
and natural gas and its oxidation can bring about the formation of tropospheric sulfur dioxide (SO2), which would
cause acid rains[1]. The presence of sulfur compounds will
reduce the purity of petrochemical products, deteriorate
the service performance, and severely poison the noble
metal catalysts used in subsequent processes[2-4]. The deep
desulfurization of gasoline and diesel is becoming more
and more difficult, since the sulfur content of crude oil
is becoming higher and the permitted sulfur limits in oil
product are becoming stricter. Therefore, it is a worldwide
urgent challenge to produce increasingly cleaner fuels[5-11].
Hydrodesulfurization (HDS) process is a conventional
method to remove sulfur compounds using Co-Mo/
Al 2O 3 or Ni-Mo/Al 2O 3 catalysts at high temperature
(300—340 ℃) and high pressure (2.0—10.0 MPa of H2).
However, the hydrogenation of olefins would take place
simultaneously during the HDS process, which will reduce
the octane number of gasoline[7, 9, 12-15]. Compared with HDS,
adsorptive desulfurization is a more economical method[14]
and has attracted researchers’ interest extensively.
Bentonite is a relatively economical material used for
adsorptive desulfurization. Its partial-amorphous nature
provides mesopores with a wide range of pore sizes and
some peculiar physical and chemical properties (i.e., large
specific surface area and satisfactory adsorptive affinity
for organic and inorganic ions) and has been attracting
more and more attention as effective separating agents or
adsorbents[4,7-10, 14, 16].
The primary objective of this study is to investigate the
adsorptive desulfurization efficiency of the Cu (II)-modified bentonite for removing propylmercaptan (PM) and
dimethyl sulfide (DMS). The adsorbents, raw bentonite
and Cu (II)-modified bentonite, are characterized by X-ray
diffractometry (XRD), thermogravimetric analysis (TGA)
and pyridine-FTIR spectroscopy. Raman spectroscopy is
used to characterize the Cu (II) complex. Finally, combined
with the hybrid orbital theory and complex adsorption reaction, the adsorption mechanism is discussed briefly.
2　Experimental
2.1　Adsorbents and feedstocks
In this work, the raw bentonite was bought from the
Received date: 2014-08-22; Accepted date: 2015-01-09.
Corresponding Author: Dr. Meng Xuan, Telephone: +86-2164252274; E-mail: [email protected].
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Cui Yuanyuan, et al. China Petroleum Processing and Petrochemical Technology, 2015, 17(2): 57-63
Hangzhou Yongsheng Catalyst Co., Ltd, Zhejiang province, China. It was used directly without further treatment. The composition analysis of the raw bentonite is
shown in Table 1.
D-500 X-ray diffractometer equipped with Ni-filtered
CuKα radiation (40 kV, 100 mA). The 2θ scanning angle
range was 10°—70° with each step of 0.02(°)/s.
Table 1　The composition of the raw bentonite
2.2.2　Thermogravimetric analysis
SiO2
67.8
Al2O3
16.3
Thermogravimetric analysis (TGA) was carried out using a
STA 449F3 thermal analyzer, made by Netzsch, Germany.
The instrument was heated at a heating rate of 10 ℃ /min
to 700 ℃ in air with an air flow rate of 100 mL/min.
Fe2O3
4.0
2.2.3　Acidity characterization
TiO2
0.4
CaO
1.1
MgO
1.7
K2O
1.6
The amount of acids, the acid density, and the acid variety
were measured via the Fourier transform infrared (FT-IR)
spectroscopy (Magna-IR550, Nicolet Company), using
pyridine as the probe molecule.
Na2O
0.9
Other compounds
6.2
Components
Mass fraction, %
The chemical reagents (CH3COO)2Cu, Cu(NO3)2, CuSO4,
CuBr and CuBr2 were purchased from the Sinopharm
Chemical Reagent Co., Ltd. PM and DMS were purchased from the Shanghai Chemical Reagent Co., Ltd.
The adsorbents in this work were prepared by means of
the kneading method. The raw bentonite was mixed
2.2.4　Raman spectra
The Raman spectroscopic studies were conducted on a
Renishaw System 100 Raman spectrometer. The laser
power was 3 mW at the sample position. The Raman scattered light was detected perpendicular to the laser beam
with a Peltiercooled CCD detector, and the spectral resolution for all measurements was 1 cm−1.
2.3　Adsorption experiments
with (CH 3 COO) 2 Cu, Cu(NO 3 ) 2 , CuSO 4 , CuBr and
2.3.1　Dynamic tests
CuBr2 for 0.5 h, respectively. Dilute nitric acid used as
The adsorptive desulfurization capacity of the adsorbents
a liquid binder was added into the mixture to make the
for PM and DMS was measured using dynamic tests on a
fixed-bed reactor under ambient conditions in a custommade quartz tube (with an internal diameter of 9 mm, a
length of 500 mm and a bed volume of 1.25 cm3). The
slurry. Pellets were formulated by an extruder with an
outer diameter of 1 mm. All of the adsorbents were dried
at 120 ℃ overnight and calcined in a muffle furnace at
150 ℃ for 4 h in air. The mass fraction of Cu (II) species
in all adsorbents was 15%. In the follow-up experiments,
the CuBr2 modified bentonite with different Cu (II) contents
and at different calcination temperature were prepared in the
similar way.
The model oil for adsorptive desulfurization was prepared
by adding PM and DMS into n-hexane simultaneously,
and the sulfur content of PM and DMS in the mixture was
2 000 μg/g each.
2.2　Characterization of adsorbents
2.2.1　X-ray diffraction
The crystal structure of powder adsorbents was characterized by X-ray diffraction (XRD) method, using a Siemens
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58 ·
weight hourly space velocity (WHSV) of the model oil
was 5 h-1. Reaction products were sampled every halfhour and analyzed with a HP5890 gas chromatograph
equipped with FID and GC–MS (type GC6890-MS
5973N, made by the Agilent Co.).
Desulfurization rate = [(C0 − C)/C0] × 100%
where C 0 is the initial molar concentration of sulfur
(mol/L), C is the final molar concentration of sulfur (mol/L).
2.3.2　Static tests
The saturated desulfurization capacity of the adsorbents
for DMS and PM was evaluated by static tests at ambient temperature. 0.1 g of adsorbent and 10 g of model oil
were put into an airtight container to enter into reaction
for 24 hours. The concentration of sulfur was analyzed by
Cui Yuanyuan, et al. China Petroleum Processing and Petrochemical Technology, 2015, 17(2): 57-63
a gas chromatograph.
Sulfur capacity (mg S/g of adsorbent) = 1 000×(C0 – C)VM/m
where C0 is the initial molar concentration of sulfur (mol/L),
C is the final molar concentration of sulfur (mol/L), V is
the volume of solution (L), M is the molar mass of sulfur
(g/mol), and m is the mass of adsorbent (g).
ples had a better DMS removal performance than the raw
2.3.3　Preparation of the Cu (II) complex
samples. Therefore, CuBr 2 was selected as the active
The Cu (II) complex was prepared by static complex
adsorption of CuBr2 and an excess of DMS in an airtight
container for 24 hours. The deposit formed during the reaction was filtered and extensively washed with n-hexane
subsequently. The product was obtained after drying at
room temperature.
component.
bentonite. The CuBr2 modified bentonite showed the best
DMS desulfurization performance, which could maintain
a complete elimination of DMS for 4 h. As a result, the
CuBr2 modified bentonite had a better desulfurization
performance for both PM and DMS compared with other
3　Results and Discussion
3.1　D esulfurization performance of the modified
bentonite
The desulfurization performance of the (CH3COO)2Cu,
Cu(NO3)2, CuSO4, CuBr and CuBr2 modified bentonite
(BE for short) were evaluated via dynamic tests at room
temperature. Breakthrough curves for PM and DMS are
shown in Figure 1 and Figure 2, respectively.
It can be seen from Figure 1 that all of the modified
bentonite samples could absorb more PM than the raw
bentonite. Among them, the CuBr2, Cu(NO3)2, and CuSO4
modified bentonite samples showed more excellent PM
removal performance, which could achieve a complete
elimination of PM for 5 h. Figure 2 shows that except the
(CH3COO)2Cu modified bentonite sample, the other sam-
Figure 1　Breakthrough curves for PM adsorption on
modified bentonite calcined at 150 ℃
■—BE; ●—CuBr-BE; ▲—(CH3COO)2Cu-BE;
▼—CuBr2-BE; ◆—Cu(NO3)2-BE;
—CuSO4-BE
Figure 2　Breakthrough curves for DMS adsorption on
modified bentonite calcined at 150 ℃
■—BE; ●—(CH3COO)2Cu-BE; ▲—Cu(NO3)2-BE;
▼—CuSO4-BE; ◆—CuBr-BE;
—CuBr2-BE
3.2　Effects of the amount of Cu (II) loading on adsorption of PM and DMS
A correlation between desulfurization performance and
contents of Cu (II) on bentonite had been tested. The results presented in Figure 3 and Figure 4 denote the breakthrough curves for PM and DMS.
Figure 3　Breakthrough curves for PM adsorption on
CuBr2 modified bentonite with different contents of Cu (II)
calcined at 150 ℃
■—20%; ●—15%; ▲—10%; ▼—5%; ◆—BE
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Cui Yuanyuan, et al. China Petroleum Processing and Petrochemical Technology, 2015, 17(2): 57-63
solid. Excessive CuBr2 content would block the pores of
the bentonite adsorbents, which could affect the adsorptive desulfurization efficiency.
Figure 4　Breakthrough curves for DMS adsorption on
CuBr2 modified bentonite with different contents of Cu (II)
calcined at 150 ℃
■—20%; ●—15%; ▲—10%; ▼—5%; ◆—BE
Figure 5　X-ray diffraction patterns of CuBr2 modified
bentonite with different Cu (II) contents calcined at 150 ℃
It can be seen from the curves shown in Figure 3 and
Figure 4 that the bentonite loaded with CuBr2 could adsorb more sulfur than the raw bentonite. The desulfurization performance increased gradually with an increasing
amount of Cu (II) loading. When the amount of Cu (II)
loading was 15%, the sulfur adsorption capacity reached
a maximum for both PM and DMS. If the Cu (II) loading increased to 20%, as presented in Figure 3, there was
no significant change in the desulfurization efficiency
compared with the case using the 15% of Cu (II) loading.
The results showed that the CuBr2 modified bentonite with
15% of Cu (II) loading could be the proper adsorbent for
removal of PM and DMS from the model oil.
The X-ray diffraction analysis in Figure 5 was carried
out to identify the mineralogical structure of the raw bentonite and the CuBr2 modified bentonite adsorbents with
different contents of Cu (II) species. The XRD patterns of
the bentonite adsorbents loaded with CuBr2 showed the
characteristic reflections for CuBr2 at 2θ = 14.42°, 24.64°,
29.08°, 29.44°, 35.94°, 46.34°, 47.24° and 60.32° cor_
_
_
responding to the planes (101), (101), (202), (011), (211),
_
_
(211), (213) and (404) of cubic CuBr2 crystal, respectively. Figure 5 confirms that the strength of the peaks
of CuBr2 increased with an increasing Cu (II) content,
and the crystallinity of the modified bentonite adsorbents
slightly decreased. These facts suggested that CuBr2 on
the bentonite existed as an amorphous material with a low
Cu (II) content of less than 5%. With the increase of Cu (II)
content, CuBr2 on the bentonite existed as a crystalline
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60 ·
To investigate the type and number of surface acidic sites
of the adsorbents, FT-IR spectra for the adsorption of
pyridine at 200 ℃ and 450 ℃ were obtained as shown in
Figure 6 and Figure 7. It can be seen from Figure 6 that
Figure 6　FT-IR spectra at 200 ℃ for Cu (II)-bentonite
(containing 15 % of Cu (II) calcined at 150 ℃) and bentonite
Figure 7　FT-IR spectra at 450 ℃ for Cu (II)-bentonite
(containing 15 % of Cu (II) calcined at 150 ℃) and bentonite
Cui Yuanyuan, et al. China Petroleum Processing and Petrochemical Technology, 2015, 17(2): 57-63
the spectra presented the adsorption band at 1 450 cm−1,
which was attributed to the ν(C-C) vibration of pyridine
adsorbed at the Lewis acid sites[14, 17] in the Cu (II)-bentonite. When the temperature rose up to 450 ℃, as shown in
Figure 7, no peak could be found. Therefore, it could be
concluded that the Lewis acid sites would be increased by
the addition of CuBr2 on bentonite, and a certain amount
of weak Lewis acid sites could contribute to the adsorption of sulfur compounds.
intense signals were located at 2θ of 35.48°, 38.66° and
48.76°, respectively. This suggests that most of CuBr species have been transformed to CuO.
3.3　Effects of calcination temperature on adsorption
of PM and DMS
A correlation between the desulfurization performance
and the calcination temperature of the CuBr2 modified
bentonite has been tested. As shown in Figure 8, the sulfur adsorption capacity decreased with an increase of the
calcination temperature.
Figure 9　X-ray diffraction patterns of CuBr2 modified
bentonite at different calcination temperatures
In order to get more structural information, the thermogravimetric analysis method under air flow was conducted to further evaluate the effect of calcination temperature
on the desulfurization performance. The differential
scanning calorimetry-thermogravimetric analysis (DSCTGA) curves for raw bentonite and the CuBr2 modified
bentonite adsorbents, which were dried at 120 ℃ for 24
h, are shown in Figure 10 and Figure 11, respectively. In
the curve of raw bentonite, no single remarkable peaks in
TG and endothermic or exothermic curves were found.
This phenomenon indicated that the framework of the
Figure 8　Effects of calcination temperature on
bentonite was stable in this temperature range and most of
desulfurization performance of Cu (II)-bentonite (containing
the adsorbed water would be evaporated during the pre-
15 % of Cu (II) species)
treatment of the sample at 120 ℃. Being different from
The modified bentonite samples calcined at different
temperatures were characterized by X-ray diffraction,
the raw bentonite, a considerable weight loss and two
endothermic peaks were observed for the CuBr2 modi-
as shown in Figure 9. The samples calcined at 150 ℃
showed the presence of the CuBr2 phase. The intensity
of the peaks corresponding to CuBr2 decreased with an
increasing calcination temperature. When the sample
was calcined at 250 ℃, the XRD peaks for CuBr were
noticed at 2θ=27.08°, 44.98° and 53.30°, respectively,
which were attributed to the planes (111), (220) and (311),
respectively. The intensity of these characteristic peaks
decreased or even disappeared when the calcination temperatures went up to 350 ℃ and 450 ℃. In addition, new
crystallite phases of CuO were observed and the most
Figure 10　TGA-DSC curves of the raw bentonite obtained
under air flow
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Cui Yuanyuan, et al. China Petroleum Processing and Petrochemical Technology, 2015, 17(2): 57-63
peak in the range of 200—400 ℃ was resulted from the
ing the vacant s-orbitals and p-orbitals[14]. As a result, the
usual S-M (σ) bonds could be obtained if sulfur atoms of
DMS could provide lone pair electrons to Cu (II) [14, 18]. As
shown in Figure 12, the distinct peaks of Cu-S stretching
vibrations at 300 cm-1and C-S vibration at 700 cm-1 were
detected in the Cu (II) complex, which suggested that
DMS could bind to the Cu (II) species without breaking
up its C-S bonds in its molecule[19, 20].
transformation of CuBr2 to CuBr and CuO.
5　Conclusions
fied bentonite, as it can be seen in Figure 11. Combined
with XRD characterization, the weight loss peaks formed
in the modified bentonite were typically attributed to the
stepwise decomposition of CuBr2·xH2O, denoting that
the peak in the range of 50—150 ℃ was caused by the
evaporation of water adsorbed in the bentonite and the
dehydration of crystalline water in CuBr2·xH2O, while the
CuBr2gxH2O
150 ć
CuBr2
250 ć
CuBr
350 ć
CuO
Figure 11　TGA-DSC curves of the CuBr2 modified
bentonite adsorbent obtained under air flow
4　Raman Characterization of the Cu (II) Complex
With the purpose of discovering the reaction mechanism
of DMS and Cu (II), the Cu (II) complex was prepared
thereby. The Raman spectra of the products are presented
in Figure 12.
The XRD and TGA results have synergistically demonstrated that the bentonites loaded with CuBr2 are excellent adsorbents for the removal of PM and DMS from
liquid fuels. Moreover the bentonite, which was loaded
with 15% of Cu (II) and baked at 150 ℃, exhibited a
sulfur adsorption capacity of about 200 mg-S/g of adsorbent during the desulfurization of model oil containing
about 2 000 μg/g of PM and 2 000 μg/g of DMS. The
FT-IR analyses indicated that a certain amount of weak
Lewis acid sites could contribute to the adsorption of sulfur compounds. The characteristics of the Cu-S and C-S
stretching vibrations were simultaneously identified in
the Raman spectra of the Cu (II) complex. On the basis of
complex adsorption reaction and hybrid orbital theory, the
adsorption of DMS on the CuBr2 modified bentonite occurred via the formation of S-M (σ) bonds. More studies
such as the performance of the CuBr2 modified bentonite
prepared by different methods or the reaction of CuBr2
with bentonite excavated from different regions will be
needed in order to fully understand the effect of copper
loading and the combination mechanism of Cu (II) species with sulfur.
Acknowledgments: This work is financially supported by
the National Natural Science Foundation of China (No.
21276086).
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