Deep hydrodenitrification of pyridine by solid catalyst coupling with ionic liquids under mild conditions

Article abstract of DOI:10.1039/c6gc03432b

A new route for deep hydrodenitrification (HDN) by solid catalyst coupling with ionic liquids (ILs) under mild conditions was proposed. Ni₂P/SBA-15 activated at different temperatures were characterized with XRD, XPS, TG/DTA, and TEM and studied for further improvement. The deep HDN catalyzed by Ni₂P/SBA-15 coupling with different ILs was evaluated. [Bmim]BF₄ was selected as the best one compared with [Emim]BF₄, [Bmim]Cl and [Bmim]Br. The effect of reaction temperature, hydrogen pressure and the amount of IL on denitrification efficiency was investigated with parallel experiments using Ni₂P/SBA-15 coupling with [Bmim]BF₄. The N-removal efficiency increased from 27.09% to 73.48% after optimization. The IL system could be recycled for three times without a significant decrease in HDN activity. The coupled catalyzed HDN process and mechanism were also proposed and evaluated preliminarily through molecular simulation.

Full text of DOI:10.1039/c6gc03432b

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Deep Hydrodenitrification of Pyridine by Solid
Catalyst Coupling with Ionic Liquid under Mild Conditions
Haoyu Yaoa,b, Gang Wanga,b, Cuncun Zuob, Chunshan Lib, Erqiang Wanga,*, Suojiang
Zhangb,*
a College of Chemistry and Chemical Engineering, University of Chinese
Academy of Sciences, Beijing 100049, People’s Republic of China
b Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of
Multiphase Complex System, Institute of Process Engineering, University of Chinese
Academy of Sciences, Beijing 100190, People’s Republic of China
Corresponding author: Suojiang Zhang, TEL/FAX: +86ꢀ10ꢀ82627080
E-mail: sjzhang@ipe.ac.cn
Erqiang Wang, TEL/FAX: +86ꢀ 010ꢀ88256093
E-mail: wangerqiang@ucas.ac.cn
Abstract
A new route for deep hydrodenitrification (HDN) by solid catalyst coupling with
ionic liquid (IL) under mild conditions was proposed. Ni2P/SBAꢀ15 activated under
different temperatures were characterized with XRD, XPS, TG/DTA, and TEM and
studied for further improvement. The deep HDN catalyzed by Ni2P/SBAꢀ15 coupling
with different ILs was evaluated. [Bmim]BF4 was selected as the best one compared
with [Emim]BF4, [Bmim]Cl and [Bmim]Br. The effect of reaction temperature,
hydrogen pressure and the amount of IL on denitrification efficiency was investigated
with parallel experiments using Ni2P/SBAꢀ15 coupling with [Bmim]BF4. Nꢀremoval
efficiency increased from 27.09% to 73.48% after optimization. The IL system could be
recycled in three times without a significant decrease in HDN activity. The coupled
catalyzed HDN process and mechanism were also proposed and evaluated
preliminarily through molecular simulation.

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1. Introduction
Petroleum products such as gasoline and diesel have been widely used as an
effective engine fuel around the world. However, nitrogenꢀbased compounds in fuel
will produce nitrogen oxides during combustion, leading to a series of environmental
problems such as acidic rain and photochemical smog. With the growing trend of the
decreasing quality of crude oil and increasing stringent environmental legislation, the
deep denitrogenation of oil should be paid more attention.
The elimination of nitrogen compounds from fuels by catalytic/noncatalytic, ion
exchange, alkylation, metalcomplexation, and extraction process were reported in the
past years[1ꢀ13]. HDN, as one of the most efficient technologies, was used to remove
nitrogen element in the form of NH3 while S and O could also be removed.
In the last decades, HDN technology had been extensively studied and widely
used in industrial manufacture. Marc [14] studied the HDN reaction of cyclic amines on
MoO3/Al2O3 catalyst under normal hydrogen pressure, and reported a denitrification
efficiency of 43.1 %. Lu et al.[15] found that during HDN process of quinoline catalyzed
by nickel phosphide supported on MCMꢀ41, the HDN efficiency was only about 13 %
at 300 oC. Zhang [16] also reported that unsaturated aromatic nitrogen compounds could
not be effectively removed by conventional conditions due to the sterical hindrance.
Meanwhile, Ibrahim [17] discovered that with the increasing temperature from 348 °C to
375 °C, the HDN activity of Co0.4Ni2P/Al2O3 catalyst would reach up to 50 % under the
hydrogen pressure of 8.8 MPa. Conventional HDN technology shows good efficiency
in removing nitrogen compounds, but the operating conditions are very severe
because of high temperature and hydrogen pressure. In all, to meet the requirements
of deep HDN, a new route should be developed for undergoing at mild conditions.
In recent years, with the rapid development of ionic liquids (ILs), it has attracted
the researchers attention in various applications due to its unique physical and
chemical properties [18ꢀ27]. As IL has the advantages of low vapor pressure, cannot
dissolve with the oil, a good selectivity with nitrogen compounds, it was already used

Page 3 of 22
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for deep denitrogenation under mild operation conditions through the way of
extraction [28ꢀ33]. However, the extraction process required a large amount of extraction
agent and produced a series of byꢀproducts, enterprises tend to use the process of
HDN. Combine IL and HDN catalyst to achieve mild conditions process, has become
[34]
a new research direction. In 1995, Chauvin et al.
firstly reported the case of
catalytic hydrogenation using IL. [Rh nbd(Ph3P)2]PF6 complex in [Bmim]PF6 or
[Bmim]SbF6 had catalytic effect on the biphasic hydrogenation of pentꢀ1ꢀene. Liu et
al. [35] synthesized a kind of catalyst that using Pd (II) supported on mesoporous silica
promoted by ILs of Nꢀheterocyclic carbene (NHC) with different alkyl chain lengths.
The catalysts had high activity and selectivity for the hydrogenation of allyl alcohol
and alkenes. Meanwhile, the operation conditions were very mild: the reaction
o
temperature, 40 C; hydrogen pressure, 4.00 MPa. However, it was not suitable for
industrial application as the complication and high cost in catalysts synthesis. To
alleviate the existed problems, Dai et al. [36] found that IL coupling with conventional
o
catalyst had high efficiency under the reaction temperature, 150 C and hydrogen
pressure, 3.00 MPa in hydrodesulfurization (HDS) reaction. This method provides a
good application prospect for HDN reaction under mild conditions.
In this study, solid catalyst coupling with IL was used for deep HDN reaction.
The reaction was carried out in a batch reactor and the efficiency was measured with a
sulfur and nitrogen analyzer. The solid catalysts Ni2P/SBAꢀ15 were designed and
optimized. Meanwhile, different solid catalysts were characterized by XRD, XPS,
TG/DTA, and TEM. Ni2P/SBAꢀ15 coupled with different ILs, such as [Bmim]BF4,
[Bmim]Cl, [Bmim]Br, and [Emim]BF4, were studied in the HDN experiments. The
optimization of experimental conditions such as reaction temperature, hydrogen
pressure and the amount of IL were conducted. The process and mechanism of HDN
were also systematically studied. At last, the IL used in the experiments was separated
and used repeatedly for several times to evaluate its recyclability.

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2. Experimental details
2.1Chemicals and raw materials
Commercial SBAꢀ15 with a surface area of 550 m2/g and an average pore size of
7 nm was purchased from Nanjing XFNANO Materials Tech Co., Ltd, China. The
metal precursor Ni(H2PO2)2 was obtained from Sinopharm Chemical Reagent Beijing
Co., Ltd, China. ILs including [Emim]BF4, [Bmim]BF4, [Bmim]Cl, and [Bmim]Br
were provided by Linzhou Keneng Material Technology Co., Ltd. The compounds of
pyridine and nꢀhexane were obtained from Sinopharm Chemical Reagent Co.,Ltd. All
materials were used directly without further treatment.
2.2 Preparation of catalyst
All the catalysts used in this study were prepared by equivalentꢀvolumetic
ultrasonic impregnation method. Nickel hypophosphite was dissolved into water at
room temperature and the nickel hypophosphite was totally impregnated onto SBAꢀ15
by several times. Maintain the impregnation precursor in an ultrasonic machine (50
kHz) for 3h and dried at 100 oC overnight. Then the precursor was activated in tubular
furnace under nitrogen atmosphere at temperatures of 200 oC，300 oC，400 oC，500 oC
and 600 oC for 4 h.
2.3 Characterization of catalyst
The physical and chemical properties of prepared catalysts were characterized by
some traditional characterization methods.
(1) XꢀRay Diffraction (XRD)
The XRD were obtained from a diffractometer and the model of the
diffractometer is X’Pert PRO MPD, PAN analytical Co., Ltd. The equipment was
operated with CuKα radiation (λ=0.154187 nm) at 40 kV and 30 mA. It was recorded
at steps of 10 o/min and in the scanned 2θ ranged from 5 to 90 °.
(2) XꢀRay Photoelectron Spectroscopy (XPS)
The XPS measurements were obtained on an ESCA Lab220iꢀXL electron
spectrometer (VG Scientific). The machine was operated with Al anode

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(AlKα=1486.3 eV) at 300 w. The base pressure was about 3*10ꢀ9 mbar. C 1s line at
284.5 eV was using as the reference line.
(3) Thermo Gravimetric Analysis (TGA)
TGA was carried out with Thermo Plus EVO purchased from Rigaku
Corporation. The temperature was raised from room temperature to 700 oC under
nitrogen flow.
(4) Transmission electron microscopy (TEM)
TEM analysis was carried out with a JEOL JEMꢀ2100 system. The acceleration
voltage of the system is 200 kV. Samples were dispersed in ethanol by ultrasonic and
a drop of resultant suspension was evaporated after dripping on the special grid.
2.4 Activity evaluation of the catalyst
Pyridine was dissolved in nꢀhexane to obtain the model oil with N of 100ppm.
Deep HDN reaction of model oil was conducted in a batch reactor (as shown in Fig. 1).
The reactor volume was 200 mL with the inner diameter of 6 cm and design pressure
was 15 MPa. After adding a certain percentage of catalyst, IL and model oil, the reactor
was sealed. Then hydrogen was injected into the reactor to replace the air for three
times and then the reactor was heated to the specified temperature. After completion of
the reaction, the upper phase of model oil was collected and analyzed.
Fig. 1 Batch reactor
The product was analyzed with sulfur and nitrogen analyzer (SH / T0704ꢀ2001

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standard for nitrogen element): carrier gas, O2, 150~200 ml/min; combustion
temperature, 1050 °C.
The nitrogen removal efficiency for reaction could be calculated using Eq. (1):
ꢀꢁꢂ − ꢁ ꢄ
ꢃ ꢅ
N − removal efficiency = {
} × 100%
（1）
ꢁꢂ
Where Co and Cf represent the nitrogen concentration (ppm) before and after
reaction respectively.
The products were also analyzed by GC–MS (Agilent 6890 N with a 30 mm×0.25
mm×0.25 mm HPꢀ5MS capillary column). The oven temperature was programmed
from 30 to 320 oC (20 oC/min).
2.5 Regeneration of the IL
The recycle of IL was crucial in the HDN process, so the reuse of IL was
investigated. After the completion of the reaction, solid catalyst was separated from the
mixture with a funnel and washed several times with distilled water. After that, the
separating funnel was used for the separation of liquid phase. IL was purified with a
rotary evaporator at the temperature of 80 °C for 5 h. Meanwhile, a comparison of the
fresh and the recycled IL was made based on the structure by FTꢀIR.
3. Results and discussion
3.1 The optimization of solid catalysts
3.1.1 The selection of active component
Series of catalysts with different active component were studied and the
corresponding results of Nꢀremoval efficiency were shown in Fig. 2. When the solid
catalyst combined with [Bmim]BF4, the Nꢀremoval efficiency was followed the order
of Ni2P > CoP > WP > CrP > MoP > Fe2P. Ni2P coupling with [Bmim]BF4 has higher
catalytic activity than other metal phosphides. Thus, the solid catalyst Ni2P/SBAꢀ15
was selected as a reference.

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70
60
50
40
30
20
10
0
Fe2P
MoP
CrP
CoP
WP
Ni2P
Different metal phosphide loaded on SBAꢀ15
Fig.2 Effect of different catalysts on HDN reaction
Conditions: hydrogen pressure, 3 MPa; reaction temperature, 150 °C; reaction time, 3 h; the
amount of model oil, 50 g; the amount of catalyst, 0.2 g; IL ([Bmim]BF4), 5g.
3.1.2 The evaluation of catalysts activated in different temperatures
The effect of different activation temperatures on the decomposition of nickel
hypophosphite and corresponding decomposition reaction has been reported by Shi [37]
.
Fig. 3 shows the effect of activation temperature of solid catalyst on HDN reaction
under the same reaction conditions. Different activation temperatures will lead to
different catalytic activity of catalysts. Nꢀremoval efficiency reaches the highest of
73.48% at the activation temperature of 300 °C. With temperature raising from 200 to
300 °C, Nꢀremoval efficiency shows an increasing trend, i.e. from 67.90% to 73.48%.
When the activation temperature is above 300 °C, the Nꢀremoval efficiency begins to
decrease. It can be concluded that the activation temperature has effect on the activity
of catalysts. Compared the HDN reaction without [Bmim]BF4 and with [Bmim]BF4
using the same solid catalyst Ni2P/SBAꢀ15 (activated at 300 °C), Nꢀremoval
efficiency is increased from 27.09% to 73.48%. Thus, the combination of solid catalyst
Ni2P/SBAꢀ15 with IL [Bmim]BF4 is possible to reduce the HDN reaction conditions

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o
and the results shows that the solid catalyst Ni2P/SBAꢀ15 which activated at 300 C
has the best Nꢀremoval efficiency.
74
72
70
68
66
64
62
60
200
300
400
500
600
Activation temperature
Fig. 3 Effect of activation temperature on Nꢀremoval efficiency
Conditions: hydrogen pressure, 3 MPa; reaction temperature, 150 °C; reaction time, 3 h; model oil,
50 g; catalyst, 0.2 g; IL （[Bmim]BF4）, 5g.
Fig.4 shows the TG and DTA curves of solid catalysts precursor. With the
increase of temperature from 30 °C to 190 °C, the heat absorbed by the sample and the
quality reduced. This process is dehydrated of the sample. As the temperature raising to
230 °C, TG curve still have declining trend. At this point, the bound water of the sample
was removed. After 230 °C, a distinct exothermic peak appeared on the DTA curve and
when the temperature is about 250 °C, TG curve reached its lowest point, due to the
decomposition of nickel hypophosphite as shown in following reactions (1) to (3).
Subsequently, TG curve presented an upward trend accompanied with the increasing
temperature and it can be explained as the reaction showed in reaction (4) and (5). PH3
could react with Ni5P4 at first and the Ni2P could react with excess HPO3. Thus, to
control the generation of Ni2P and Ni5P4, the activation temperature of 300 °C was
selected as the best.
Ni(H2PO2)2→Ni2P+ Ni5P4+ H3PO3
(1)

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H3PO3→H3PO4+ PH3
H3PO4→HPO3+H2O
Ni5P4+ PH3→Ni2P+ H2
(2)
(3)
(4)
(5)
Ni2P+HPO3+PH3→Ni(PO3)2+Ni5P4+H2O
10
100
98
96
94
92
0
ꢀ10
ꢀ20
ꢀ30
ꢀ40
ꢀ50
0
100
200
300
400
500
600
700
Temperature /oC
Fig.4 TGꢀDTA curves of 25%Niꢀ Ni2P/SBAꢀ15
Fig.5 shows the XRD patterns of the solid catalysts after activation. When the
Ni2P/SBAꢀ15 catalyst was activated at 200 °C, almost no characteristic peak was found.
Combined with TGꢀDTA curves shown in Fig.3, it can be seen that nickel
hypophosphite begins to decompose, but nickel hypophosphite still occupied most of
nickel compounds. The peaks at 40.6 o, 44.5 o, 47.2 o, and 54.0o are well matched with
the characteristic peaks of Ni2P (JCPDS No. 74ꢀ1385). However, this does not indicate
that the TGꢀDTA curves cannot match with XRD patterns. The reason can be attributed
to the amount of material generating is very little or no other stable crystalline can be
detected.

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Ni P(JPCDS No.74ꢀ1385)
♦
2
♦
♦
♦
♦
600 oC
500 oC
400 oC
300 oC
200 oC
20
40
60
80
2θ /degree
Fig.5 XRD patterns for the Ni2P/SBAꢀ15 catalysts with different activation temperature
XPS in the Ni 2p and P 2p regions for Ni2P/SBAꢀ15 catalysts with different
activation temperature are shown in Fig.6 and Fig.7. The corresponding binding
energies and relative concentrations are summarized in Table 1. C 1s was selected as a
reference with value at 284.8 eV, due to the errors in catalyst charge correction. The
binding energy of Ni 2p3/2 from 852.24 to 852.62 eV are assigned to Niδ+ specie and
from 855.52 to 855.90 eV are assigned to Ni2+ specie, respectively. The binding
energies are fitting with Ni2P/SiO2 (857.2 eV for Ni2+ and 853.5 eV for Niδ+) and
unsupported Ni2P (857.1 eV for Ni2+ and 853.1 eV for Niδ+). The binding energy of P
2p from 128.53 to 128.78 eV are assigned to P1+ specie of Ni(H2PO2)2, from 129.14 to
1229.66 eV are assigned to Pδꢀ specie of Ni2P and Ni5P4 and from 130.03 to 130.06 eV
are assigned to P5+ specie, respectively. Thus, when the activate temperature was 300
oC, the ratio of Pδꢀ/Ptotal reached the highest, namely the content of Ni2P and Ni5P4
reached the highest.

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600
500
℃
℃
400
300
200
℃
℃
℃
880
875
870
865
860
855
850
845
840
Binding energy /eV
Fig.6 Xꢀray photoelectron spectra in the Ni 2p regions for Ni2P/SBAꢀ15 catalysts with different
activation temperature
600
℃
500
400
℃
℃
300
200
℃
℃
135
133
131
129
127
125
Binding energy /eV
Fig.7 Xꢀray photoelectron spectra in the P 2p regions for Ni2P/SBAꢀ15 catalysts with different
activation temperature

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Tab.1 XPS binding energies (BE,eV) and relative concentrations of Ni2P/SBAꢀ15 catalysts with different activation temperatures
Activation
Ni 2p3/2
Ni satellite
Ni 2p1/2
Ni satellite
P 2p
Ni/P
temperature
/
°C
200
300
400
500
600
852.24
855.96
855.52
855.71
855.53
855.90
859.05
858.97
859.04
859.03
859.29
870.14
873.81
874.22
874.15
874.29
874.18
876.83
877.48
877.25
877.25
877.26
128.53
0.25
0.17
0.21
0.22
0.24
852.30
852.47
852.49
852.62
870.23
870.33
870.52
870.54
128.78
129.14
129.25
129.19
129.66
130.06
130.05
130.03

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TEM analysis of Ni2P/SBAꢀ15 at different magnifications are shown in Fig.8.
The results reveal he active constituents evenly distributed on the carrier. The
morphology of SBAꢀ15 is regularly porous and hexagonalꢀlike material. It can be
seen from Fig.8a that supported catalyst has ordered hexagonal pore structures and the
active ingredient were uniformly dispersed on this carrier. Fig.8b shows that the
active components present the same structure as that of the carrier.
a
b
Fig.8 Transmission electron micrographs of Ni2P/SBAꢀ15 at different magnifications
3.2 The selection of IL
The effect of different anions and cations of the IL on Nꢀremoval efficiency were
investigated using solid catalyst and imidazole ILs, and the results were shown in Tab.2.
For the imidazole ILs with different anion structures, the extraction efficiency increases
with the electronegativity, and the order is: [Bmim]Cl > [Bmim]Br > [Bmim]BF4.
However, when using ILs coupling with solid catalyst, it did not follow this order.
[Bmim]BF4 coupled with solid catalyst shows a best performance among the ILs with
different anion structures. The HDN efficiency, only using [Bmim]Cl (or [Bmim]Br), is
lower than corresponding extraction 39.01% (or 29.30%) or that only use solid catalyst
(27.09%). This phenomenon can be attributed to the decomposition temperature of
[Bmim]Cl or [Bmim]Br is very near to the reaction temperature. For different cations,
[Bmim]BF4 shows better performance than [Emim]BF4 both in extraction and HDN
reaction. DFT calculation using Gaussian 09 was carried out to explain the
intermolecular forces of hydrogenꢀnꢀhexane and hydrogenꢀ[Bmim]BF4. The
geometrics were optimized at the B3LYP/6ꢀ311+g(d, p) level. The binding energies
between
hydrogen
and
ILs
(hydrogenꢀ[Bmim]BF4,
2.5405
kJ/mol;

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hydrogenꢀ[Emim]BF4, 2.5552 kJ/mol; hydrogenꢀ[Bmim]Cl, 3.7577 kJ/mol;
hydrogenꢀ[Bmim]Br, 2.6304 kJ/mol) are higher than the energy between hydrogen
and nꢀhexane (0.0029 kJ/mol). The results are shown in Fig.12. The calculation can
prove that ILs have better hydrogen solubility than nꢀhexane, which is another
important factor in HDN reaction. In all, considering the effects of extraction, stability
of ILs and capacity of hydrogen, [Bmim]BF4 was chosen as a reference.
Tab.2 Effect of different ILs on the Nꢀremoval efficiency
Nꢀremoval efficiency /%
Types
ILs
[Bmim]BF4
[Bmim]Cl
[Bmim]Br
[Emim]BF4
Extraction
HDN reaction
16.27
39.01
29.30
13.39
73.48
21.97
6.28
45.26
(IL+ Ni2P/SBAꢀ15)
Conditions: hydrogen pressure, 3 MPa; reaction temperature, 150 OC; reaction time, 3 h; model oil,
50 g; catalyst, 0.2 g; ILs, 5 g.
Fig.9 Structure of hydrogenꢀnꢀhexane (a) and hydrogenꢀILs: (b) [Bmim]BF4; (c)
[Emim]BF4; (d) [Bmim]Cl; (e) [Bmim]Br
3.3 The optimization of reaction conditions
3.3.1 Effect of IL dosage on HDN reaction

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Fig.10 shows the effect of IL dosage on HDN reaction by the coupling of
[Bmim]BF4 with Ni2P/SBAꢀ15 under the same reaction condition. In the amount of 5 g
[Bmim]BF4, the Nꢀremoval efficiency achieves the best result. Initially, the Nꢀremoval
efficiency enhances with the increasing dosage of [Bmim]BF4. With the continued
increase in the amount of [Bmim]BF4, the Nꢀremoval efficiency has emerged a
downward trend, from 73.48% to 33.45%. It shows that the amount of [Bmim]BF4 also
has significant effect on handling the same amount of model oil. Meanwhile, the above
data also indicates that when the dosage of [Bmim]BF4 is less than 5 g, the solid
catalyst Ni2P/SBAꢀ15 will play a main role in the reaction. [Bmim]BF4 captured
hydrogen and then hydrogen transferred the surface of solid catalyst. However, due to
the high viscosity of [Bmim]BF4, hydrogen and pyridine cannot quickly transfer to
the catalyst surface in a certain time when the amount of [Bmim]BF4 was increased.
Therefore, the catalytic process would be concealed or suppressed by the insufficient or
excess [Bmim]BF4.
80
70
60
50
40
30
1
3
5
7
10
The amout of IL/g
Fig.10 Effect of IL dosage on Nꢀremoval eddiciency
Conditions: hydrogen pressure, 3 MPa; reaction temperature, 150 OC; reaction time, 3 h; model oil,
50 g; catalyst, 0.2 g.

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3.3.2 Effect of reaction temperature on HDN reaction
Fig.11 shows the effect of reaction temperature on HDN reaction catalyzed by
Ni2P/SBAꢀ15 coupling with [Bmim]BF4. The temperature range was investigated from
o
o
90 C to 210 C. Under the constant conditions (hydrogen pressure, 3 MPa; reaction
time, 3 h; model oil, 50 g; catalyst, 0.2 g; [Bmim]BF4, 5 g), with the increase of reaction
temperature, the HDN efficiency rises to the maximum at 150 oC and then decreases.
o
When the reaction temperature is lower than 150 C, the HDN process is
controlled by the reaction rate, and the conversion increases with enhanced temperature.
The IL covered around the surface of solid catalyst could capture the hydrogen atom
and serve for the HDN process. And this coupling system could not only promote the
diffusion of hydrogen atom, but also accelerate the hydrogenation process. However,
the higher temperature would lead to the decomposition of [Bmim]BF4 which had been
already proved in research results of Dai [36]
.
75
70
65
60
55
50
45
40
90
120
150
180
210
o
Reaction temperature / C
Fig.11 Effect of reaction temperature on Nꢀremoval eddiciency
Conditions: hydrogen pressure, 3 MPa; reaction time, 3 h; model oil, 50 g; catalyst, 0.2 g;
[Bmim]BF4, 5 g.
3.3.3 Effect of hydrogen pressure on HDN reaction

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Fig.12 shows the trend of the Nꢀremoval efficiency under different hydrogen
pressure. While maintaining other reaction conditions constant (reaction temperature,
150 oC; reaction time, 3 h; nꢀhexane, 50 g; catalyst, 0.2 g; [Bmim]BF4, 5 g), hydrogen
pressure has a significant impact on Nꢀremoval efficiency. Nitrogen removal efficiency
presents the optimal one at 3MPa. Higher hydrogen pressure can promote the
hydrogenation reaction and the production of nitrogenꢀcontaining gas compounds.
These gases will have an inhibition effect on the chemical reaction equilibrium. It has
been proved by Mohan who studied the competitive effect of nitrogen and sulfur
content on activity of hydrotreating CoMo/Al2O3 catalysts in a batch reactor [38]
.
75
70
65
60
55
50
45
40
1
3
5
7
Hydrogen pressure /MPa
Fig.12 Effect of hydrogen pressure on Nꢀremoval eddiciency
Conditions: reaction temperature, 150 OC; reaction time, 3 h; model oil, 50 g; catalyst, 0.2 g;
[Bmim]BF4, 5 g.
3.4 Process and mechanism of HDN by solid catalyst coupling with IL
Traditional studies suggest that hydrogenation process is controlled by the
diffusion of hydrogen on the catalyst. Hydrogen involved in the reaction, passed
through the surface of the oil phase to penetrate the interior of the oil, then diffused to
the film between the surface of solid catalyst and oil phase, and finally spread to the
catalyst surface. Hydrogen atom is absorbed and activated by the active center of the

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solid catalyst and the activated hydrogen atom reacts with pyridine on the surface of
solid catalyst. Solubility of hydrogen in the liquid phase will directly affect the rate of
hydrogenation and the efficiency of hydrogenation [39]. Compared with the model oil,
IL has greater hydrogen solubility and it is conducive to the diffusion of hydrogen to
the surface of the solid catalyst. Hydrogen is activated on the surface of the solid
catalyst, and then reacts with adsorbed nitrogenꢀcontaining compounds. The process
is shown in Fig. 13.
Fig.13 HDN process by solid catalyst coupling with IL
The products of the HDN reaction using Ni2P/SBAꢀ15 coupling with [Bmim]BF4
were analyzed by GCꢀMS. The main products detected by GCꢀMS were methane,
2ꢀbutene, butane, pentane and tetrahydropyridine. The mechanism of pyridine
hydrogenation reaction can be proposed based on the analysis of the products using
Ni2P/SBAꢀ15 coupling with [Bmim]BF4.

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NH3
CH4
NH
N
N
N
NH3
N
H
N
H
NH3
CH4
NH2
Fig.14 The mechanism of the HDN by solid catalyst Ni2P/SBAꢀ15 coupling with [Bmim]BF4
3.5 The regeneration of ILs
For the standpoints of environmental protection and technical application, the
regeneration and recycling of ILs is very important. The regeneration of ILs has several
ways. Distillation is the most simple and practical option, as ILs has no vapor pressure
and they will keep in liquid phase. Vacuum distillation was chosen to remove debris in
IL.
From Tab.3, it can be seen that when using fresh [Bmim]BF4, Nꢀremoval
efficiency is 73.48%. In subsequent regeneration and cycles, Nꢀremoval efficiency has
a slight downward trend from 73.48% to 70.32%. FTꢀIR was also used to qualitative
analysis the recycled BmimBF4. The spectra of the fresh and recycled [Bmim]BF4 are
shown in Fig.15. From the FTꢀIR spectra, the conclusion can be drawn that the recycled
substance is [Bmim]BF4.
Tab.3 The regeneration of ILs
Recycling times
Nꢀremoval efficiency
/%
Fresh
73.48
72.16
71.25
70.32
Recycle 2
Recycle 3
Recycle 4
Conditions: hydrogen pressure, 3 MPa; reaction temperature, 150 OC; reaction time, 3 h; model oil,

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50 g; catalyst, 0.2 g; [Bmim]BF4, 5 g.
Standard [Bmim]BF
4
Recycled [Bmim]BF
4
3500
3000
2500
2000
1500
1000
500
-1
Wavennumber /cm
Fig.15 FTꢀIR spectra of [Bmim]BF4 before and after use
4. Conclusion
In this study, deep HDN reaction of model oil was carried out using solid
catalyst coupling with IL under mild conditions in a batch reactor. Ni2P/SBAꢀ15 was
found to exhibit high Nꢀremoval efficiency when coupled with IL. The comparative
experiments were conducted to demonstrate that solid catalyst coupling with IL have
better performance on HDN reaction than that only catalyzed by solid catalyst under
mild conditions. A series of ILs ([Bmim]BF4, [Bmim]Cl, [Bmim]Br, and [Emim]BF4)
were selected and used to promote the Nꢀremoval efficiency of model oil coupling
with Ni2P/SBAꢀ15. [Bmim]BF4 coupled with Ni2P/SBAꢀ15 presents the highest
catalytic activity with Nꢀremoval efficiency up to 73.48 %. Moreover, the effects of
reaction temperature, hydrogen pressure and the amount of IL were also investigated.
As determined, optimum parameters for HDN of model oil using [Bmim]BF4
o
coupling with Ni2P/SBAꢀ15 were as follows: reaction temperature 150 C, hydrogen
pressure 3 MP, IL 5 g and reaction time 3 h. In addition, after recycled three times,

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the [Bmim]BF4 have no significant change on reactivity. This research provides a new
method for deep HDN reaction of fuels at mild reaction conditions.
Acknowledgement
The authors wish to acknowledge the National Science Fund for Excellent
Young Scholars (21422607), National Natural Science Foundation of China
(21576261), CAS/SAFEA International Partnership Program for Creative Research
Teams.
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