Microsoft Word - TOC_R.doc

HUNGARIAN JOURNAL
OF INDUSTRIAL CHEMISTRY

VESZPRÉM
Vol. 37(2) pp. 69-75 (2009)

INVESTIGATION OF HYDROGENATION OF AROMATIC HYDROCARBONS
ON Pt/Pd/USY CATALYST

G. NAGY1, Z. VARGA1, D. KALLÓ2, J. HANCSÓK1

1University of Pannonia, Institute of Chemical and Process Engineering
Department of MOL Hydrocarbon and Coal Processing, Veszprém, P.O.Box.: 158. H-8201, HUNGARY

E-mail: hancsokj@almos.uni-pannon.hu
2Hungarian Academia of Sciences, Chemical Research Centre, Budapest, P.O. Box 17, H-1525, HUNGARY

In this paper the aromatic reduction of gas oils and the conversion of several hydrocarbon groups in the conditions of
hydrodearomatization were investigated on Pt/Pd/USY catalyst. It was concluded that in case of hydrodearomatization of
gas oils cycloparaffin hydrocarbons (naphthenes) were key components, i.e. the practical process parameters of
hydrodearomatization in case of a defined catalytic system (catalyst, feed, etc.) is that where the concentration of naphthenes
have a maximum value. In case of this the deep hydrodearomatization and further deep heteroatom reduction can be carried
out with maximum yield of gas oil. It was additionally determined that in the condition of hydrodearomatization mainly
isoparaffins are formed via ring opening of naphthenes, the rate of increase of n-paraffin concentration is slower, i.e. the
decadence of cold flow properties of reduced aromatic containing products are less beside the high cetane number. Therefore
the gas oil products can be applied as winter quality diesel fuel blending components.

Keywords: aromatic reduction, noble metal catalyst, gas oil, cetane number.

Introduction

In the last couple of years the demand for diesel fuel has
increased due to the increasing number of diesel fuelled
passenger cars and heavy duty vehicles [1]. Additionally
the decreasing emission level of these vehicles results
the continuously tightening specifications of diesel fuels
[2] (Table 1). Since 1st January, 2009 the maximum
sulphur content of diesel fuels has been 10 mg/kg, the
maximum allowable polycyclic aromatic content has
decreased from 11% to 8% (in the future 2–4%) and the
maximum level of total aromatic content might be
specified (about 15–20%) [3].

The importance of deep heteroatom and aromatic
reductions technologies, which is one of the key
technologies of the production of modern diesel fuel
blending components, has increased beside the quality
specifications and demand. In the first step of these
technologies the deep heteroatom reduction and partial
hydrodearomatization takes place on supported transition
metal catalysts (e.g. CoMo/Al2O3, NiMo/Al2O3) [4, 5].
In the second step deep hydrodearomatization and
further deep heteroatom reduction occurs on supported
noble metal catalysts.

Nowadays the increasing of heteroatom resistance
and hydrodearomatization activity of the above
mentioned supported noble metal catalysts is in the
focus of research and development activities [6, 7, 8].

The particular reactions of hydrodearomatization are
studied in these catalysts as well [9].

The main focus of our research activity was the
investigation of hydrodearomatization of aromatic
hydrocarbons and the conversion of main hydrocarbon
groups in the condition of hydrodearomatization in real
gas oil matrix.

Experimental

The hydrodearomatization experiment was carried out
in a high pressure reactor system with 100 cm3 efficient
volume tube reactor. It contains equipment and devices
applied in the reactor system of hydrotreating plants.

The range of the applied process parameters – based
on the results of preliminary experiments – was the
following: T: 260–340 °C, P: 35–60 bar, liquid hourly
space velocity (LHSV): 1.0–4.0 h-1, H2/hydrocarbon
volume ratio (in further: H2/HC) = 600 Nm

3/m3.
Prehydrogenated gas oil fraction derived from

Russian crude was used for the hydrodearomatization
experiments. Its important properties are summarized in
Table 2.

The hydrodearomatization experiments were carried
out on PtPd/USY zeolite (SiO2/Al2O3 molar ratio: 33.6,
total and mesoporous surface area: 650 m2/g and 51 m2/g,
total noble metal content: 0.9%, Pd/Pt atomic ratio: 3.7:1,
metal dispersion: 55%, acidity: 0.20 mmol NH3/g)
catalyst in continuous flow operation.

Table 1: The change of diesel fuel specifications

Hungary Hungary (EU)

Properties MSZ
1627

(1973)

MSZ
1627

(1974)

MSZ
1627

(1986)

MSZ
1627

(1993)

MSZ
1627

(1997)

MSZ EN
590

(1999)

MSZ EN
590

(2000)

MSZ
EN 590
(2004)

MSZ EN
590

(2009)
Cetane number, minimum 48/45 48/45 42 48 48 49 51 51 51
Density (kg/m3) 815-860 815-860 815-860 820-860 820-860 820-860 820-845 820-845 820-845

Total aromatic content (%) - - - - - - - -
-

15-20*

Polycyclic aromatic content (%) - - - - - - 11.0 11.0
8.0

(2.0-4.0***)

Sulphur content (mg/kg)
10000
/5000/
2000

10000
/5000/
2000

5000/
2000

2000/
500/
100

500/
100 500 350

50/
10** 10

The MSZ 1627 diesel fuel standard was overruled in 1999 and the MSZ EN 590 standard became operative. i.e. the Hungarian
and EU standards of diesel fuels have been the same since 1999.
* It might be introduced in the near future, - No specifications
** The 10 mg/kg maximum sulphur containing diesel fuels have to be available in a regionally balanced manner
*** It might be introduced in the near future

Table 2: Main specifications of feed

Properties Value
Density at 15.6°C (g/cm3) 0.8374
Sulphur content (mg/kg) 6
Nitrogen content (mg/kg) <1
Aromatic content (%)

total 25.5
mono 23.1
di- and poly 3.4

Cetane number 50
Distillation range (°C) 184–350

The properties of the feed and products were

determined and calculated by standard test methods
(Table 3). The hydrodearomatization activity of the
catalysts was calculated by equation 1.

HAD (%) = 100(Af-Ap)/Af (1)

where: HDA: hydrodearomatization activity (%),
Af: aromatic content of feed (%),

Ap: aromatic content of product (%).

Table 3: Standard test methods

Properties Methods
Density EN ISO 3675
Sulphur content EN ISO 20846
Nitrogen content ASTM D 6366
Aromatic content EN 12916
Distillation range EN ISO 3405
Cetane number EN ISO 5165

The rate of conversion of individual hydrocarbon

groups in the condition of hydrodearomatization was
determined by the diagram of logarithmic conversion
vs. contact time (equation 2).

LHSV
k

tk
C
C

ln ff
A

0A == (2)

where: cA0 – total aromatic content of feed,
cA – total aromatic content of product,
kf – pseudo reaction rate of hydrodearomatization,
LHSV – liquid-hourly-space-velocity.

The pseudo reaction rate constant of hydrode-

aromatization is calculated by the gradient of this curve.
The determination of the composition of feeds and

products was carried out by the results of GCxGC
method. The equipment was a Thermo Trace 2DGC
instrument containing a FID detector. The conditions
were the following:

• columns: 0.25 μm Rtx (118 m x 0.25 mmid) and
0.1 μm BPX50 (140 cm x 0.1 mmid),

• carrier gas: 6.0 purity helium with 0,1 cm3/min
flow rate,

• temperature programme: 40 °C → 280 °C 4 °C/min
heating rate.

The liquid products were separated to lighter (<200 °C

boiling range) and to gas oil (>200 °C boiling range)
fractions and the change of the yield and quality of the
products was examined as a function of the process
parameters.

Results and discussion

The yield of the gas oil changed according to the
projection; it decreased with increasing temperature and
total pressure and decreasing LHSV; i.e. the rate of
hydrocracking reactions, which produce the lighter
hydrocarbons, increased (Fig. 1, 2). Temperature has the
highest effect on the yield of the gas oil. For example it
increased from 85% to 94% with decreasing temperature
at 45 bar and LHSV = 1.0 h-1 in the investigated
temperature range. The gas oil yield changed between
84% and 98% in the overall range of process parameters,
therefore the lowest yield of gas oil occurred at the
strictest process parameter (T = 340 °C, LHSV = 1.0 h-1,
P = 60 bar, H2/HC = 600 Nm

3/m3).

100

250 270 290 310 330 350 370

Temperature (°C)

Y
ie

ld
o

f g
as

o
il

(%
)

35 bar 45 bar 60 bar

Figure 1: The effect of temperature and pressure on the
yield of gas oil (LHSV = 1.0 h-1, H2/HC = 600 Nm

3/m3)

100

0.5 1.5 2.5 3.5 4.5

LHSV (h-1)

Y
ie

ld
o

f g
as

o
il

(%
)

260°C 280°C 300°C

320°C 340°C 360°C

Figure 2: The effect of LHSV and temperature on the

yield of gas oil (P = 45 bar, H2/HC = 600 Nm
3/m3)

The hydrodearomatization activity of the investigated

catalyst as a function of process parameters is presented
in Fig. 3, 4 and 5. The rate of hydrodearomatization
increased in the lower temperature range from 240 to
320 °C. After the optimal temperature (320 °C) it
decreased, i.e. the optimal temperature of hydro-
dearomatization of the investigated catalyst was 320 °C.
The reason of this was the exothermic reaction profile
of aromatic hydrogenation. The change of hydro-
dearomatization as a function of LHSV and total pressure
was according to the projection, i.e. it increased with
decreasing LHSV and increasing total pressure. It was
concluded that the hydrodearomatization efficiency of
the investigated catalysts was relatively high, because
the polycyclic aromatic content of the products changed
in the reproducibility range of the applied test method
(it was maximum 0.1%). Consequently the products did
not contain polycyclic aromatic hydrocarbons. Therefore
the hydrodearomatization efficiency was calculated by
the monoaromatic content, which was practically the
same as the total aromatic content. The hydride-
aromatization efficiency was between 12% and 88% in
the range of the investigated process parameters. The
lowest aromatic containing product was produced (~3%,
hydrodearomatization efficiency: 88%) at 320 °C,
60 bar and LHSV = 1.0 h-1.

240 280 320 360
Temperature (°C)

H
D

A
(%

)

35 bar 45 bar 60 bar

Figure 3: The change of hydrodearomatization
efficiency as a function of temperature and total

pressure (LHSV = 2.0 h-1, H2/HC = 600 Nm
3/m3)

100

240 280 320 360
Temperature (°C)

H
D

A
(%

)

LHSV=1,0 LHSV=2,0 LHSV=3,0 LHSV=4,0

Figure 4: The change of hydrodearomatization

efficiency as a function of temperature and LHSV
(P = 45 bar, H2/HC = 600 Nm

3/m3)

100

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

LHSV (h-1)

H
D

A
(%

)

P=35 bar P=45 bar P=60 bar

Figure 5: The change of hydrodearomatization

efficiency as a function of total pressure and LHSV
(T = 320 °C, H2/HC = 600 Nm

3/m3)

The rate of abatement of hydrodearomatization

efficiency after the optimal temperature of aromatic
hydrogenation (cause of thermodynamic properties)
changed as a function of total pressure. The decrease of
hydrodearomatization efficiency was high in case of
low total pressure (e.g. 35 bar) and it was significantly
lower at 60 bar. The reason of this phenomenon was the
fact that in case of higher total pressure the rate of ring
opening reactions of naphthenes increased. Therefore
paraffines formed from naphthenes, which were

produced from aromatic hydrocarbons. Consequently the
equilibrium reaction system of polycyclic aromatic
monoaromatic naphthene changed to naphthenes,
because the ring opening reactions are irreversible. It
can be seen in the change of hydrocarbon composition
(Fig. 6, 7).

240 280 320 360
Temperature (°C)

R
at

io
(%

)

Cp% Ca% Cn%

Figure 6: The change of hydrocarbon composition of

the products as a function of temperature (rate of carbon
atoms in CP: paraffinic-, CA: aromatic- and

CN: naphthenic, P = 45 bar, LHSV = 1.0 h
-1,

H2/HC = 600 Nm
3/m3)

30 35 40 45 50 55 60 65 70
Pressure (bar)

R
at

io
(%

) Cp% Ca% Cn%

Figure 7: The change of hydrocarbon composition of

the products as a function of total pressure (rate of
carbon atoms in CP: paraffinic-, CA: aromatic- and

CN: naphthenic, T = 320 °C, LHSV = 1.0 h
-1,

H2/HC = 600 Nm
3/m3)

It can be seen that the rate of ring opening and/or

hydrocracking reactions increased with temperature (CP
was increased). The rate of the increase of carbon atoms
in paraffinic bond increased with total pressure. The
increase (about 1–2%) of carbon atoms in paraffinic
bond was low in the lower temperature range (260 °C →
320 °C), but at higher temperature it was significantly
higher (about 10%). I can be seen that the carbon atoms
in naphthenic bond changed as a maximum curve.

It was concluded based on the yield and hydrocarbon
composition of the gas oils that the yield of the gas oil
significantly decreased with increasing paraffin content,
i.e. in hydrodearomatization conditions the paraffinic
hydrocarbons are cracked with the production of lower

boiling range hydrocarbons. Based on the above mentioned
phenomenon the following inference was drawn: the
hydrogenation of aromatic hydrocarbons should be done
in a range of process parameters where the concentration
of naphthenic hydrocarbons has a maximum value
(Tmax = 320–330 °C). In this situation deep hydro-
dearomatization can be carried out with high gas oil
yield. Therefore the naphthenic hydrocarbons become
key components in case of hydrodearomatization.

The investigation of hydrogenation of individual
hydrocarbon groups was carried out with model
compounds and their mixtures in the literature. Therefore
there is just a little information about the experimental
results with real gas oil matrix. The reason of this is that
the mono-, di- and polycyclic aromatic hydrocarbons
and naphthenic molecules transform via numerous
reactions to each other and to paraffines on the catalyst
surface. These reactions take place in serial and parallel
succession, therefore in the real gas oil matrix only the
transformation of individual hydrocarbon groups can be
investigated (e.g. monoaromatics, diaromatics, normal
and isoparaffines).

Therefore the second objective of our experiments
was to study the conversion of individual hydrocarbon
groups on the condition of aromatic hydrogenation on
the investigated catalyst.

The change of the concentration of alkyl-diaromatic
hydrocarbons as a function of temperature is shown in
Fig. 8. It can be seen that the optimal temperature of
hydrogenation of alkyl-diaromatic compounds was
between 280–290 °C.

0.0

0.5

1.0

1.5

2.0

240 260 280 300 320 340 360
Temperature (°C)

A
lk

yl
-d

ia
ro

m
at

ic
s

(%
)...

1,0 2,0 3,0 4,0LHSV, h-1

Figure 8: Change of the concentration of alkyl-

diaromatic compounds as a function of temperature
(P = 35 bar, H2/HC = 600 Nm

3/m3)

The optimal temperature of hydrogenation of

cycloalkyl-aromatics was 300 °C (Fig. 9), but the
highest optimal hydrogenation temperature was that of
the alkyl-benzenes (320 °C) (Fig. 10).

Based on the results it was concluded that the
hydrogenation rate of the different aromatic compounds
from the slower to the fastest changed in the following
order: alkyl-naphthalenes (condensate alkyl-diaromatics) <
cycloalkyl-aromatics (decalin containing different carbon
number alkyl-groupa) < alkyl-monoaromatics (alkyl-
benzenes) (Fig. 11).

240 260 280 300 320 340 360
Temperature (°C)

C
yc

lo
al

ky
l-b

en
ze

ne
s

(%
)

1,0 2,0 3,0 4,0LHSV, h-1

Figure 9: The change of the concentration of

cycloalkyl-benzenes as a function of temperature
(P = 35 bar, H2/HC = 600 Nm

3/m3)

240 260 280 300 320 340 360
Temperature (°C)

A
lk

yl
-b

en
ze

ne
s

(%
)

1,0 2,0 3,0 4,0LHSV, h-1

Figure 10: The change of the concentration of alkyl-

benzenes as a function of temperature
(P = 35 bar, H2/HC = 600 Nm

3/m3)

R2 = 0.9943

R2 = 0.9956

R2 = 0.9822

0.0

0.5

1.0

1.5

2.0

2.5

0.0 0.2 0.4 0.6 0.8 1.0 1.2
1/LHSV (h)

ln
(c

A
0/

c A
)

Alkyl-diaromatics
Cycloalkyl-benzenes
Alkyl-benzenes

Figure 11: The hydrogenation rate of different one- and

two-ring akly(cyclioalkyl)-aromatic hydrocarbons
(T = 300 °C, P = 35 bar, H2/HC = 600 Nm

3/m3)

Therefore the hydrogenation rate of the first ring of

aromatic compounds increases with the increasing
number of rings in the molecules. The reason of this
might be the fact that the aromatic electron system of
condensate diaromatic is distortional.

The change of the concentration of formed one- and
two-ring naphthenes produced by hydrogenation of

aromatics as a function of temperature is shown in
Fig. 12 and 13. It can be seen that the concentration of
alkyl-dicycliparaffines decreased with increasing
temperature. This means that these compounds are
transformed to alkyl-monocycloparaffines via ring opening
even in case of the mildest process conditions.

240 260 280 300 320 340 360
Temperature (°C)

A
lk

yl
-d

ec
al

in
es

(%
)...

1,0 2,0 3,0 4,0LHSV, h
-1

Figure 12: The change of the concentration of alkyl-

dicycloparaffines as a function of temperature (P = 35
bar, H2/HC = 600 Nm

3/m3)

240 260 280 300 320 340 360
Temperature (°C)

A
lk

yl
-c

yc
lo

pa
ra

ff
in

es
(%

)...
.

1,0 2,0 3,0 4,0LHSV, h-1

Figure 13: The change of the concentration of alkyl-

cycloparaffines as a function of temperature
(P = 35 bar, H2/HC = 600 Nm

3/m3)

The concentration of alkyl-cycloparaffines changed

as a maximum curve, i.e. it first increased with
temperature (alkyl-cycloparaffines are formed in the
low temperature range via ring opening from alkyl-
dicycloparaffines and via hydrogenation from alkyl-
benzenes). After the maximum point (300 °C) it
decreased with increasing temperature (the reaction rate
of ring opening of alky-cycloparaffines increased,
therefore the ring opening of alkyl-dicycloparaffines
and hydrogenation of alkyl-benzenes could not
compensate the quantity of alkyl-cycloparaffines, which
were transformed to paraffines via ring opening).

The ring opening of alkyl-cycloparaffines can be seen
in the increasing concentration of paraffin hydrocarbons
with the temperature in the investigated temperature
range (Fig. 14, 15).

240 260 280 300 320 340 360
Temperature (°C)

i-p
ar

af
fin

es
(%

)..
.

1.0 2.0 3.0 4.0LHSV, h
-1

Figure 14: The change of the concentration of

i-paraffines as a function of temperature
(P = 35 bar, H2/HC = 600 Nm

3/m3)

It can be further concluded from the change of the

concentration of n- and i-paraffines that i-paraffines are
formed via ring opening. The concentration of n-
paraffines increased with temperature by only a few
degrees in the lower temperature range (260–300 °C).
After this range it set to a constant value, i.e. the curve
became saturation. It means that the reaction rate of ring
opening to n-paraffines was low. It was caused by the
following two facts. On the one hand the shrinking of
the 6-member ring to a 5-member ring branched with
one alkyl-group takes place on the strong acidic
catalyst. On the other hand the rate of ring opening is
lower in the substituted carbon atom [15-18], due to the
steric hindrance and the fact that the alkyl-groups have
electron-donor properties, which lead to the increasing
electron-density of the orto- and para-located carbon
atoms. Therefore the ring opening reactions take place
in these atoms.

240 260 280 300 320 340 360
Temperature (°C)

n-
pa

ra
ff

in
es

(%
)..

1,0 2,0 3,0 4,0LHSV, h
-1

Figure 15: The change of the concentration of n-

paraffines as a function of temperature
(P = 35 bar, H2/HC = 600 Nm

3/m3)

The main advantage of the formation of a large

amount of isoparaffins in case of the hydrodearomatization
is the better cold flow properties of the products than in
the case of n-paraffines. Therefore these products can be
applied as blending components of winter quality diesel
fuels.

Conclusions

The objective of our research and development work
was to study the hydrogenation of aromatic compounds
on PtPd/USY catalysts in case of real gas oil matrix as
feedstock, and the determination of conversion of
individual hydrocarbon groups in the condition of
aromatic hydrogenation, respectively.

It was concluded that the cycloparaffines are key
components in hydrodearomatization, i.e. the aromatic
hydrogenation in extant catalytic system (feed, catalyst)
should be done at process parameters where they have a
maximum concentration. In case of this the hydro-
dearomatization can be carried out with maximum yield
of gas oils, and the hydrogen consumption can also be
decreased. The reason of the latter is the fact that it does
not need extra hydrogen consumption without ring
opening to produce saturated hydrocarbons.

On the investigated catalysts modern diesel fuel
blending components can be produced, which satisfy the
future requirements (<10 mg/kg sulphur-, <1mg/kg
nitrogen content, <15-20% total- and <2.0–4.0 polycyclic
aromatics, at T = 320°C, P = 45 bar, LHSV = 1.0–2.0 h-1,
H2/HC: 600 Nm

3/m3 process parameters with high yield
(about 90%).

It was further concluded that in case of hydrode-
aromatization condition mainly isoparaffines are formed
via ring opening of naphthenes on the investigated
catalyst, the increase of the concentration of n-paraffins
was lower. Therefore the hydrodearomatization can be
done with high gas oil yield with the use of appropriate
process parameters, and the decadence of cold flow
properties of partially aromatic saturated products is
lower.

REFERENCES

1. LARIVÉ J. F.: “Concawe Review”, 15 (2006) 2.
2. Worldwide Fuel Charter, Sept. 2006.
3. SZALKOWSKA U.: Proceedings of the 7th International

Colloquium on Fuels, edited by.: Bartz, W. J., 2009,
59–62 (ISBN: 3-924813-67-1).

4. ABU I. I., SMITH K. J.: Applied Catalysis A., 328
(2007) 58-67.

5. OLIVAS A., GALVÁN, D. H., ALONSO, G., FUENTES,
S.: Applied Catalysis A., 352 (2009), 10–16.

6. VARGA Z., HANCSÓK J., NAGY G., KALLÓ D.: Stud.
Surf. Sci. Catal., 158 (2005), 1891–1898.

7. YOSHIMURA Y., TOBA M., MATSUI T.: Applied
Catalysis A., 322 (2007), 152–171.

8. YOSHIMURA Y., TOBA M., FARAG H., SAKANISHI K.:
Catalysis Surveys from Asia, 8(1) (2004), 47–60.

9. YASUDA H., KAMEOKA T., SATO T., KIJIMA N.,
YOSHIMURA Y.: Applied Catalysis A., 185 (1999),
199–201.

10. WILSON M. F., KRIZ J. F.: Fuel, 63 (1984), 190.
11. FUJIKAWA T., IDEI K., OHKI K., MIZUGUCHI H.,

USUI K.: Applied Catalysis A, 205 (2001), 71–77.
12. YUI S. M., SANFORD E. C.: Proc.-Refining

Department, Petroleum Institute, 64 (1985), 290–
297.

13. CORMA A., MARTINEZ A., MARTINEZ-SORIA V.:
Journal of Catalysis, 169 (1997), 480–489.

14. CORMA A., MARTINEZ A., MARTINEZ-SORIA V.:
Journal of Catalysis, 200 (2001), 259–269.

15. SANTANA R. C., DO P. T., SANTIKUNAPORN M.,
ALVAREZ W. E., TAYLOR J. D., SUGHRUE E. L.,
RESASCO D. E.: Fuel, 85 (2006), 643–656.

16. MCVICKER G., DAAGE M., TOUVELLE M., HUDSON
C., KLEIN D., BAIRD W.: Journal of Catalysis,
210(1) (2002), 137–148.

17. KUBICKA D., KUMAR N., MAKI-ARVELA P., TIITTA
M., NIEMI V., KARHU H., SALMI T., MURZIN D. Y.:
Journal of Catalysis, 227 (2004), 313–327.

18. SANTIKUNAPORN M., HERERA J. E., JONGPATIWUT
S., RESASCO D. E., ALVAREZ W. E., SUGHURE E. L.:
Journal of Catalysis, 228 (2004), 100–113.