18th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 16-17, 2008
Hydrocracking on Nanoporous Zeolite Catalysts
Koji Sakashita, Sachio Asaoka
Graduate School of Environmental Engineering,
The University of Kitakyushu, Kitakyushu 808-0135, Japan
e-mail asaoka@env.kitakyu-u.ac.jp, fax +81-93-695-3382
ABSTRACT
Hydrocracking of heavier fractions to lighter clean fuels noted recently as
environmentally-conscience refining was studied on zeolite catalysts consisting of
nano-components. The catalysts were composed of nano-porous alumina or silica, and
nano-size zeolite. The composites held different pore distributions at nano-pore region
(pore diameter: 1.5~15 nm) due to two kinds of physical interface. The composites
prepared of different nano-oxides and/or different nano-zeolites showed different
catalytic activities due to two kinds of chemical interface. The acid sites were generated
at the nano-interface by the combination work of the nano-oxide and the nano-zeolite as
desirable or undesirable active sites. The catalytic sites at the nano-zeolite surface were
modified with the nano-oxide and the Al removal. The novel catalysis at the
nano-interface between the nano-oxide and the nano-zeolite has been revealed for
hydrocracking.
1. INTRODUCTION
Recently, the hydrocracking (HC) is enumerated as a catalytic process to which it
pays attention by concern with the environments in the oil refinery. Recent progress of
zeolite catalysts is also targeted at the hydrocracking as one of the most important
applications.
Now, the sharp rise of the oil price which leads even to a price boost of not only
the products made from oil as raw materials but also agricultural products is
frightfulness and is having big influence on the world economy or social life.
Meanwhile, the supply-demand gap, accompanying shifts of heavier crude oil supply
and lighter product demand, actualizes. The supply and demand trend of residual oil is
shown in Fig.1. Development of the process and catalyst which utilize heavy crude oil
efficiently is required from this prospect of oil product consumption.
"Hydrocracking" serves as an effective method with which the subject of efficient
processing is solved for this heavy crude oil. This report is concerned to the
investigation state of the zeolite catalyst in this field.
18th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 16-17, 2008
Million b/d
80
Others
Gasoline
Middle Distillate
Residual Fuel
25
20
Million b/d
100
60
40
20
Residual Fuel Demand
15
50% :Surplus
10
5
0
VR Production
Lighter
Oils
50% :Consumption
0
1996
2001
Year
2006
1990 1995 2000 2005 2010 2015
Year
Fig.1: Supply and demand trend of residual oil.
2. HYDROCRACKING CATALYST
In the hydrocracking, residual oil and vacuum gas oil can be used as raw materials.
The catalysts used for the hydrocracking are roughly grouped into two types, an
amorphous type (non-crystal) and a zeolite type (crystal). Amorphous type catalysts are
composite oxide matrices made of amorphous substances such as silica-alumina,
alumina, silica-titania, in which exhibiting solid acidity and pore structure are controlled.
The mild hydrocracking activity is given by containing non-zeolitic promoter such as
boron and supporting metals such as Ni-Mo. On the other hand, zeolite type catalysts
contain zeolite whose is crystalline aluminosilicate for a catalytic component. Their
cracking function is strengthened since they contain much amounts of acidity and the
quality is stronger in comparison with that of amorphous types. [1] ~ [4]
There were few cases where the zeolite type catalysts were used for the
hydrocracking of residual oils by the reason why their cracking function tended to
receive poisoned highly. Therefore, Co-Mo / alumina catalysts with mild cracking
activity were usually applied for residual oils. However, after the hydrocracking process
using the zeolite type catalyst supporting Ni-W or Ni-Mo was developed, selection of
the catalyst and process which are united with a user's needs from viewpoints such as
feedstock oil, cracking activity, middle fraction selectivity, the purpose product, and a
catalyst life, is performed at present, taken advantage of each feature.
On the other hand, the history of the zeolite type catalyst in hydrocracking of
vacuum gas oil was old and Y zeolite had been used for the 1970s. In recent years,
ultra-stable Y zeolite (USY) in which the stability over steam or heat was increased is
frequently applied. The strengthening of the stability is made by dealumination of Y
zeolite with steaming at high temperature and acid treating. [5] ~ [7]
The reaction scheme of hydrocracking can be expressed as follows:
Heavy oils Æ Middle fractions (Gas Oil, Kerosene, Gasoline) Æ Light Naphtha, LPG.
In general, although the cracking conversion of an amorphous catalyst is slightly
low, the selectivity of middle fractions is high. Also, as mentioned above, a zeolite type
18th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 16-17, 2008
catalyst is suitable for production increase of gasoline or jet fuel because of the high
cracking activity. However, since middle fractions are partly decomposed more into
light naphtha and LPG, the selectivity to middle fractions becomes a little lower. The
amorphous type catalyst having high selectivity to middle fractions has been used for
the hydrocracking process aiming at middle fractions. However, the middle fraction
selectivity can be raised now by use of USY zeolite which characteristic research has
been progressed in recent years. USY is raised in the silica/alumina ratio of a zeolite
framework by dealumination, reduced in the ratio of the octahedral type aluminum
outside the framework and acquired with nano-pores (nanometer-size of pore mouth
diameter). The zeolite which possesses nano-pores is equivalent to nano-zeolite
(nanometer-size crystalline). Nowadays, some processes are developed as a
hydrocracking process of vacuum gas oil using the USY zeolite type catalyst. [8]
3. HYDROCRACKING OF RESIDUAL OIL
As shown in Fig. 2, residual oils are obtained, as atmospheric residue (AR) by
atmospheric distillation (AD), as vacuum gas oil (VGO) and vacuum residue (VR) by
vacuum distillation (VD), as deasphalting oil (DAO) from AR or VR (ARDAO or
VRDAO) by solvent deasphalting (SDA), rejected asphaltenes (AS). In this paper I will
discuss about typical three residual oils and model compound, VRDAO, VGO,
HT-VGO and heavier paraffin.
HTVGO
HT
AD
VGO
HC
HC
AR
VRDAO
VD
VR
HT
HC
HT
SDA
AS
Fig. 2:
Residual Oils for Hydrocracking.
In the hydrocracking of the residue, the specifically-modified zeolite such as
Ti-USY, Ti-treated Al2O3, B2O3-SiO2-Al2O3 is used as an acidic support. Generally,
Ni-Mo and Ni-W faction's hydrocracking activities are higher as metallic species, and
the Co-Mo has mild cracking activity.
As for the zeolite, the strong acid site that originates in zeolite-structure Al and
becomes an excessive cracking site can be controlled by zeolite species and
18th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 16-17, 2008
dealumination, as shown in Fig. 3. Moreover, the dispersion state of the metal is
controlled by the kind, the composition ratio, and the method of preparing, of the mixed
oxide support.
Hydrogenation of the aromatic ring is enumerated as a feature reaction mechanism
in the hydrocracking. The acidity of the catalyst support assists the hydrogenation on the
metal. The aromatic compounds do not directly adsorb on the metals but on the acid
sites due to the basicity of the aromatic ring. The adsorbed aromatic compounds easily
move to Ni sites to be hydrogenated.
2
CR Reduction
Relative Activities (-)
1.5
HC
H-Saturation
1
(Ni-W)/(ZSM5-Matrix)
(Ni-W)/(USY-Matrix)
0.5
0
ZSM-5
Y
USY
-0.5
-1
-1.5
Zeolite in (Ni-W)/(Zeolite-Matrix) Catalyst
Fig. 3: VR DAO HC Catalysts and Reaction Products.
Moreover, the cracking progresses without excessive increase of aromaticity only
after the hydrogenation of the aromatic rings. This reaction scheme is different from the
catalytic cracking. The side-reaction of the hydrocracking is the reverse-reaction, that is,
the ring formation, the dehydrogenation, and the polymerization, followed by tar and
coke formation to cause the catalyst degradation. This side-reaction can be suppressed
by controlling the acidity of the catalyst.
Beforehand to demonstrate the hydrocracking performance to its maximum that
originates in the characters of the hydrocracking catalyst, especially an acidity, it is
necessary to remove the basic compounds in the feed oil, the nitrogen compounds, and
the multi-ring aromatics etc. that become poisons. For instance, Ni-Mo of an amorphous
catalyst with the pore structure controlled to have high activity for hydrogenation of
aromatics and denitrification is known as a pretreating catalyst for the hydrocracking.
4. HYDROCRACKING OF VACUUM GAS OIL (VGO)
In the hydrocracking, the vacuum gas oil is converted to diesel, kerosene, naphtha
(gasoline fraction), etc. at high temperature (360 to 420 oC) under high pressure (10 to
20 MPa). As the hydrocracking catalyst is equipped with the ultra-deep
hydrodesulfurization activity for kerosene and diesel and operated in the conditions, the
18th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 16-17, 2008
Hydrogenation, Ring-opening and Isomerization
obtained products substantially become sulfur-free (sulfur content is several ppm or
less). Therefore, clean light fuel oil can be manufactured by making the best use of the
hydrocracking.
As shown in Fig. 4, there are two directions as a reaction component in the
hydrocracking reactions which decide the product selectivity:
1) ring-opening and isomerization according to hydrogenation that at the low
temperature is advantageous in reaction equilibrium,
2) cracking reaction (cracking of C-C bond) that is advantageous at high
temperature and finally up to gas (LPG).
The hydrocracking intermediate products to aim at these two abilities by
combining the active species and the operating condition of the catalyst are obtained.
Kerosene, Diesel
Heavy Oil
Gasoline
LPG
n-C16H34 Conversion
to Gasoline
(Model Reaction of HC)
Cracking
Fig. 4:
Role of HC Reactions for Light Oils Produced from Heavy Oils.
The catalyst for the HC is roughly divided to two types of amorphous and
zeolite-containing when the distillate, especially the vacuum gas oil is used as a
feedstock. Typical examples are shown in Fig. 5. [9]
H
Mo
Ni-Mo
HDS/HC Product Molecules
M
BTiO
2O3 2 -modified
Unimodal Porous
Al2O3
Mo
Mo
Mo
Ni-Mo
Mo
Ni-Mo
Ni-Mo
M
BTiO
2O3 2 -modified
Unimodal Porous
Al2O3
Mo
Mo
Ni-Mo
Ni-Mo
Ni-Mo
Mo
TiO2-modified
Unimodal Porous
Al2O3
Mo
Mo
Mo
Ni-Mo
Nano-porous
Al2O3
Mo
Mo
Ni-Mo
Cracked Product (C=)
Amorphous Catalyst :
(Ni-Mo)/(Al2O3-B2O3)
Fig. 5:
USY Zeolite
Binder for Catalyst
Strength
Zeolite Catalyst :
[(Ni-Mo)/( TiO2- Al2O3)]-nanoAl2O3 –USY
VGO HC Catalyst Examples.
18th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 16-17, 2008
The typical example of the zeolite catalyst shown in Fig. 5 possessed newly
generated acids as novel active sites formed concertedly at an interface of nano-oxide
and nano-zeolite. The newly generated acid sites are confirmed by NH3 TPD and IR
measurement [10]. The acid amount of (Ni-Mo)/(γ-Al2O3)-npAl2O3-USY catalyst is
larger than that of (Ni-Mo)/(γ-Al2O3)-USY or that of (Ni-Mo)/(γAl2O3)- np-SiO2-USY
as shown in Fig. 6. This result means that the existence of the npAl2O3 generates the
new acid sites in medium and strong acid strength. The new acid generation is not
observed either when the np-SiO2 is used instead of the np- Al2O3 or when the npAl2O3
or the USY component is impregnated by metal species before catalyst calcination.
Therefore, both of Al-OH in the npAl2O3 and Si-OH in the USY have inevitable roles
for the new acid generation in (Ni-Mo)/(γ-Al2O3)-npAl2O3-USY catalyst. It is
considered that these novel active sites (moderate and strong acids) are formed as
shown in Fig. 6. Si-OH in the nano-pores of USY resulted from dealumination catches
Al-OH in the npAl2O3 to form Si-O-Al-O-Al-O-Si instead of Si-O-Al-O-Si-O-Si.
1.8
with npSiO2 with npAl2O3
Acid Amount (USY base)
1.6
w/o np Oxides
1.4
1.2
We ak
1
Me adium
Strong
0.8
Total
0.6
0.4
0.2
0
1
2
3
4
5
6
Catalysts and Compone nts
Fig. 6: Acidity Measured by NH3-TPD Method.
Sample 1: (Ni-Mo)/(γ-Al2O3), 2: USY, 3: (Ni-Mo)/(γ-Al2O3) + USY,
4: (Ni-Mo)/(γ-Al2O3)-USY, 5: (Ni-Mo)/(γ-Al2O3)- npSiO2-USY,
6: (Ni-Mo)/(γ-Al2O3)- npAl2O3-USY[Concerted Catalyst]
5. HYDROCRACKING OF HYDROTREATED OIL
The VGO HC reactivity can be increased by hydrotreating (HT) before the HC,
because the HC reactivity remarkably depends on N content of feedstock, as shown in
Fig. 7. Though the pretreating is usually unnecessary for the amorphous catalyst used
for mild hydrocracking (MHC) that raises the selectivity for middle distillates, it
becomes necessary according to the required severity of reaction. The pretreating of the
feedstock is inevitable to draw out high activity of the zeolite catalyst. The combination
18th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 16-17, 2008
of the pretreating catalyst and the hydrocracking catalyst is optimized aiming at the
production increase for gasoline or middle distillates at a high cracking conversion.
7
7
R e la tiv e R e a c tiv ity (-)
6
Relative Reactivity (-)
HC
HDS
5
4
3
2
HTVGO
6
HC
5
HDS
4
3
VGO
2
VRDAO
1
1
0
0
HT-VGO
VGO
0
VRDAO
500
1000
1500
2000
2500
3000
N Content of HC Feedstock (ppm)
HC Feedstock
Fig. 7: Feedstock Reactivity and N Content.
6. HYDROCRACKING ON NANOPOROUS ZEOLITE CATALYST
Differential Intrusion (µl/g-npAl2O3/nm
Nano-pore structure of nano-oxide was changed by depending on the concerted
component as shown in Fig. 8. The nano-oxide bound to the zeolite has smaller pores
relative to the sole nano-oxide. The nano-oxide bound to the fractal 11nm pores has
larger pores relative to the sole nano-oxide. [11]
2.5
npAl2O3(sole)
npAl2O3-γAl2O3
npAl2O3-Zeolite
2
1.5
1
0.5
0
2
Fig. 8:
3
4
5
6
7
8
9
10
Pore Size Diameter (nm)
Nano-Pore Structures Depending on Concerted Components.
○: nano-oxide bound to the zeolite, △: nano-oxide bound to the fractal 11 nm pores
The design and the preparation for the hydrocracking catalyst were studied, based
18th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 16-17, 2008
on a new concept of the metal-acid corporation through the nano-pore combinations.
Three orders of nano-pores combined with metal sites and acids can be served to
prepare concertedly-nanoporous catalyst. The pores at 11 nanometers are effective to
disperse the active metal species. The selection of the reactants and the products in the
zeolitic pores with acids at the order of sub-nanometer by means of the molecular
structures is advantageous for the hydrocracking. The nano-oxide with the pores at the
order of nanometer not only gives the path from the pores of tens nanometer to the
zeolitic pores, but also connects unexpectedly with the pores at 11 nanometers or the
zeolitic pores to newly generate acids. Therefore, it is possible that designing and
preparing the catalyst with the concerted pore-structure lead to not only providing the
preferable reaction circumstance and loop at the nano-orders but also controlling
chemical properties of the catalyst at the order of nanometers.
Typical result of concerted effect from novel active system on tri-modally
nano-porous catalyst composed of zeolite and nano-porous oxides is obtained on
(Ni-Mo)/(γ-Al2O3)-npAl2O3-BEA zeolite. The conversions on the tri-composite catalyst
(filled circle) are higher than the theoretically additive value without concerted effect
(unfilled circle) at higher temperature as shown in Fig. 9.
100
100
(Ni-Mo)/(γ-Al2O3)-npAl2O3-β
Cracking Selectivity (%)
(Ni-Mo)/(γ-Al2O3)+(npAl2O3-β)
npAl2O3-β
80
Conversion (%)
(Ni-Mo)/(γ-Al2O3)
60
40
20
0
200
250
300
350
80
60
40
NiMo/γAl2O3
npAl2O3-BEA
NiMo/γAl2O3-npAl2O3-BEA
20
0
0
20
40
Temperature (℃ )
NiMo/γ -Al2O3-npAl2O3-BEA
40
50
Selectivity (%
)
Selectivity(%
)
50
30
20
20
0
0
2
3
4
5
6
7
8
9
10 11
C- number
Fig. 9:
12 13 14
15 16
50
30
10
60
NiMo/γ -Al2O3
40
10
1
80
100
Conversion (%)
60
Selectivity(%
)
60
60
npAl2O3-BEA
40
30
20
10
0
1 2 3 4 5 6 7 8 9 10 11 1213 14 1516
Carbon Number
1 2 3 4 5 6 7 8 9 10111213141516
Carbon Number
Hexadecane Conversion Depending on catalyst.
NiMo/(γ-Al2O3)-np Al2O3-BEA zeolite, npAl2O3-BEA zeolite, NiMo/(γ-Al2O3).
Though the carbon numbers of the product on (Ni-Mo)/(γ-Al2O3)-npAl2O3-BEA
zeolite are similar to that on npAl2O3-BEA zeolite, the conversion is higher and the
product selectivity of iso-hydrocarbon is improved on the concerted catalyst composed
18th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 16-17, 2008
of (Ni-Mo)/(γ-Al2O3) catalyst due to isomerization as shown in Fig. 9.
In the concerted effect newly generated acid sites maybe have a major role for
isomerization and cracking. It was also considered that the catalytic property of
(Ni-Mo)/(γ-Al2O3)-npAl2O3-BEA zeolite catalyst is due to novel sites (moderate and
strong acids) formed as less active for isomerization and cracking of higher n-paraffins
but active for cracking of higher iso-paraffins and isomerization of lower n-paraffins.
Similar results of the effect enhancing npAl2O3-zeolite with (Ni-Mo)/(γ-Al2O3)
are also confirmed on USY and H-MFI composite catalyst. There are similar concerted
effects from novel active system on tri-modally nano- porous catalyst composed of
zeolite and nano- porous oxides.
Since either the nano-oxide or the nano-zeolite is important for the
hydro-isomerization /cracking reaction, the interface between the nano-oxide and the
nano-zeolite is considered to be further examined.
30
Selectivity(%
)
100
80
a)
npAl2O3-β
20
10
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Selectivity(%
)
b) npAl2O3-deAlβ
60
20
10
0
1
2
3
4
5
6
7
8
9
10 11 12
13 14 15
16
40
npAl
zeolite
np
Al2O3/
β ゼオライト
2O3/BEA
npAl
BEA ゼオライト
zeolite
np
Al2O3/
酸処理β
2O3/deAl
20
Selectivity(%
)
30
250
275
300
Temperat ure(℃）
325
10
1
npSiO
BEAゼオライト
zeolite
np
SiO2/
酸処理β
2/deAl
225
20
npSiO2-β
2
3
4
5
6
7
8
9
10
11 12
13 14
15 16
30
0
200
c)
0
npSiO
zeolite
2/BEA
np
SiO2/
β ゼオライト
350
iso
Selectivity(%
)
Co n ve r sio n ( %)
30
d)
normal
npS iO2-deAlβ
20
10
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Carbon Number
Fig. 10: Conversion and Product Distribution on Tri-component Catalyst
Consisting of NiMo/ (γ-Al2O3), np Oxide and BEA Zeolites.
The n-hexadecane conversions were clearly changed when the component of
nano-oxide was replaced from npAl2O3 to npSiO2, or when the component of nano-BEA
zeolite was dealuminated at the surface. Typical results at various reaction temperatures
are shown in Fig. 10. The conversion changed in each different way. The conversions
on the catalyst composed of npSiO2 and BEA zeolite, or npAl2O3 and dealuminated
BEA zeolite were obviously improved relative to npAl2O3 and BEA zeolite. On the
other hand the conversions on the catalyst composed of npSiO2 and dealuminated BEA
zeolite was similar to npAl2O3 and BEA zeolite. The product selectivities were different
each other and the product on the catalyst composed of npSiO2 and BEA zeolite is more
cracked than that on npAl2O3 and dealuminated BEA zeolite.
In the hybrid catalyst consisting of nano-oxide and nano-zeolite, the nano-porous
acid restructuring occurs as shown in Fig. 11. The unstable Al on nano-zeolite surface
18th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 16-17, 2008
reacted with OH of nano-oxide precursor.
H
O
O
H
H
O
O
Al
Al
H
O
O
Al
O
O
O
Si
Al
Al
Al
Si
Si
Si
H
O
O
H
Si
H
O
O
O
Si
Al
O
Si
H
H
O
O
Si
O
Si
Si
H
O
Si
H
O
Si
Si
O
O
H
Al
Al
H
O
O
O
H
H
O
O
Si
Si
H
H
H
O
O
O
Al
Al
O
Si
Si
O
O
Si
Si
Si
Fig. 11: Model of the Interface between Nano-oxide and BEA Zeolite
As shown in Fig. 11, the dealuminated zeolite has nests of Si-OH. Nano-particles
of pseudo-boehmite easily access into the Si-OH nests of the dealuminated zeolite.
Al-OH of the pseudo-boehmite reacts with Si-OH of the dealuminated zeolite and forms
Si-O-Al. The Si-O-Al gives moderate acidity different from the zeolite network. The
acidity is improved only with coupling of Al-OH and Si-OH. There is no improvement
of acidity in the couple of Si-OH and Si-OH of dealuminated zeolite. The proposed
mechanism of nano-porous acid generation is also supported by NH3 TPD. The acidity
is improved only with coupling of bare nano-oxide and bare zeolite.
5. CONCLUSIONS
Hydrocracking of heavier fractions to lighter clean fuels noted recently as
environmentally-conscience refining was studied on zeolitic catalysts consisting of
nano-components.
Especially, the conversion of heavier n-paraffin to lighter iso-paraffin as the
primitive hydrocracking reaction was also studied on the catalysts consisting of
nano-components. The composite catalysts of three components, Ni-Mo on unimodal
alumina with 11 nm diameter pores, nano-porous alumina or silica, and nano-size
H-BEA zeolite, were selected. The composites held different pore distributions at
nano-pore region due to the two kinds of physical interface effect. The composites
prepared of different nano-oxides and/or different nano-zeolites held different catalytic
activities due to the two kinds of chemical interface effect. The acid sites were
generated on nano-interface by the combination work of nano-oxide and nano-zeolite as
undesirable or desirable active sites. The catalytic site on nano-zeolite surface was
modified with the nano-oxide and the Al removal. The novel catalysis on nano-interface
between nano-oxide and nano-zeolite has revealed.
18th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 16-17, 2008
Acknowledgments: Financial support from JCCP, Japan Cooperation Center,
Petroleum, to this symposium is greatly acknowledged. Financial support from CREST,
Japan Science and Technology Agency to the work related to this paper is also greatly
acknowledged. A part of basic analyses for the work were performed at the
Instrumentation Center of the University of Kitakyushu. Dr. Ashlaf M. Ali of King Fahd
University of Petroleum & Minerals (KFUPM) and Dr. Hisham S. Bamufleh of King
Abdulaziz University are also acknowledged for their works related to this review paper.
We thank our co-workers, S. Minohara, K. Ito and S. Sudo for their research and
technical assistance.
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