Hydroisomerization of n-Pentane over Pt/Mordenite Catalyst: Effect of
Feed Composition and Process Conditions
Behrouz Bayati1,2,*, Mahboobeh Ejtemaei1,3, Nazanin Charchi Aghdam1,3, Ali Akbar Babaluo1,3,
Mohammad Haghighi3,4, and Amir Sharafi5
1Nanostructure Materials Research Center (NMRC), Sahand University of Technology, Tabriz, Iran
2Chemical EngineeringDepartment, Ilam University, Ilam, Iran
3Chemical Engineering Department, Sahand University of Technology, Tabriz, Iran
4Reactor and Catalyst Research Center (RCRC), Sahand University of Technology, Tabriz, Iran
5Imam Khomeini Oil Refinery Company of Shazand, Iran
Received: August 25, 2015; revised: January 11, 2016; accepted: March 16, 2016
The hydroisomerization of pure n-pentane over H-mordenite supported Pt-catalyst was investigated in
a fixed bed reactor by changing reaction parameters such as temperature, pressure, and WHSV, as
well as the H2/HC ratio. The maximum yield of isopentane over Pt/mordenite catalyst was achieved at
220 °C and a relatively low reaction pressure. To address the effect of feed composition on the
catalytic performance of the samples, the catalysts were assessed for activity and selectivity in the
isomerization of a mixture consisting of n-pentane (70 wt.%) and isopentane (30 wt.%) at 220 °C. The
effects of pressure, WHSV, and H2/HC ratio on the catalyst performance were also studied using
binary mixtures of the pentane isomers as a feedstock. It was observed that an effect of WHSV and
H2/HC on the catalytic performance was similar to its behavior in pure n-pentane isomerization, while
the conversion of n-pentane in the binary mixture showed a different trend and had a minimum value
at 1.5 bar. It could be due to the presence of isopentane in feed and adsorption phenomenon of binary
mixture on mordenite-supported catalyst.
Keywords: Pentane Isomerization, Pt/Mordenite, Process Conditions, Feed Composition
Due to the increasing demand of isoalkanes the catalytic isomerization of linear alkanes to branched
ones is an industrially important reaction, considered as an efficient alternative for octane boosters
instead of oxygenates and aromatic compounds which are subjected to strict environmental restriction
(Al-Kandari et al., 2009; Kamarudin et al., 2012; Ramos et al., 2005; Villegas et al., 2006). Gasoline
containing high quantity of linear-chain compounds has a low octane number. However, such a
content can be increased when gasoline is subjected to an isomerization process through which linearchain
molecules are converted into ramified molecules (Talebi et al., 2008; Viswanadham et al.;
Yoshioka et al., 2005). The isomerization processes involve acid or bifunctional metal acid catalysts
(Caeiro et al., 2006; Setiabudi et al., 2012b). Chlorinated alumina and zeolites have been developed
for the isomerization of C5-C6 (Essayem et al., 2003). Additional research has been carried out on
* Corresponding Author:
B. Bayati et al./ Hydroisomerization of n-pentane Pentane over Pt/ Mordenite Catalyst … 85
Pt/sulfated ZrO2 and Pt/WOx-ZrO2 catalysts (Chu et al., 1998). Zeolites are strong solid acids, which
are able to initiate the alkane conversion at a relatively low temperature thermodynamically favoring
the branched isomer formation (Valyon et al., 2002). To achieve maximum isomer yields, the
isomerization of C5–C6 paraffins must be carried out at the lowest possible temperatures over highly
efficient catalysts (Essayem et al., 2003).
These catalysts are comprised of a metal component for the dehydrogenation/hydrogenation, which is
provided by a noble metal basically platinum or palladium, and an acid function generated by zeolites
like mordenite, Beta, and ZSM-5 for isomerization/cracking (Kumar et al., 2007; Soualah et al.,
2010). According to the classical isomerization mechanism, paraffins are dehydrogenated on the
catalyst metal sites, and the produced olefins are protonated on the Bronsted acid sites to the
corresponding alkylcarbenium ions. These carbenium ions undergo skeletal rearrangement and β-
scission followed by deprotonation and hydrogenation over metal to the corresponding paraffins
The isomerization of pentane and hexane is successfully carried out using Pt on zeolites catalysts
(Bogdan et al., 2007; Chen et al., 2006; Jiménez et al., 2003; Kusakari et al., 2002; Lenoir et al., 2005;
López et al., 2010; Miyaji et al., 2002; van de Runstraat et al., 1997; Yashima et al., 1996; Zhang et
al., 1995). However, difficulties are encountered with a mixture of linear and branch hydrocarbons;
because of thermodynamic equilibrium restrictions, the linear molecules cannot fully be converted to
the desired branched molecules. On the other hand, the isomerization of the n-pentane and n-hexane
in virgin naphtha appears to be the major gasoline octane improvement process. Light virgin naphtha
consists of linear and branch C5-C6, so a study on the isomerization of C5-C6 isomers mixture is
necessary. Hollo et al. (Holló et al., 2002) studied the kinetic isomerization of n-pentane and n-hexane
mixture using a Pt-HMOR catalyst. Jiménez et al. (Jiménez et al., 2003) examined the
hydroisomerization of a mixture of n-hexane and n-heptane on various catalysts consisting of
platinum supported on different types of zeolite. However, to the best of our knowledge, there are no
data available in the literature correlating to isomerization of pentane or hexane isomer mixtures.
Therefore, a study on this subject is necessary.
The purposes of the present study are (i) further exploring the behavior of Pt/mordenite zeolites as
catalysts for the isomerization of pure n-pentane and (ii) using the results from the first part and
relating the catalyst systems to the isomerization of pentane isomers mixture. To the best our
knowledge, this topic has not previously been described.
2.1. Preparation of the catalysts
Pt/mordenite zeolite catalyst was prepared using a commercially available mordenite zeolite from
Zeolyst. The nominal platinum concentration was 0.5 wt.%. In the impregnation method, 1.00 g of the
mordenite zeolite was impregnated with the minimum amount of H2PtCl6 solution required to wet the
solid and stirred for 24 hrs at ambient temperature. Then, the solvent was removed by evaporation at
100 °C for 12 hrs. Finally, the samples were carefully calcined at a heating rate of 0.5 °C/min to 623
K in a flowing air and maintaining this temperature for 3 hrs.
The XRD patterns of MOR zeolite were determined using a TW3710 Philips X'Pert diffractometer
86 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
using CuKα radiation as a filter (λ=1.54 Å). The data were collected within the 2θ range of 5° and 50°
at a 0.02° 2θ-step and 2 s per step (40 kV and 30 mA). X-ray diffraction (XRD) was performed to
identify the product crystals phase. The morphology and size of zeolite catalysts were investigated
using scanning electron microscopy (SEM, LEO 440I, 3×105, LEO, UK). The BET (Brunauere
Emmette Teller) surface area of the catalysts was determined by N2 physisorption at 77 K using a
Quanta chrome chembet-3000.
2.3. Reactions, reactor system, and product analysis
The reaction network for the alkane isomerization involves many parallel and consecutive
hydrogenation, isomerization, alkylation, and cracking. Main reaction pathway is as follows (Ono,
( ) 5 12 5 10 2 nC H ÛnC H + H on Pt (1)
( ) 5 10 5 11 nC H + H + ®nC H + on solid acid (2)
( ) 5 11 5 11 nC H + Û nC H + on solid acid (3)
( ) 5 11 5 10 isoC H + ÛisoC H + H on solid acid (4)
( ) 5 10 2 5 12 isoC H + H ÛisoC H on Pt (5)
The alkane is dehydrogenated on metallic sites to the corresponding alkene, which is isomerized by
acid sites into a branched alkene. The branched alkene is then hydrogenated into the branched alkane
again on the metallic sites.
Figure 1 shows the schematic drawing of the experimental setup. A stainless-steel flow-type tubular
reactor (internal diameter = 5 mm and length = 4.5 cm) which contains 0.5 g of a catalyst diluted with
inert nonporous silica-glass, possessing the same dimension of the catalyst particles, was used in all
the hydroconversion runs. The reactor was heated in an electrical furnace. Hydrogen gas was used as
a carrier and simultaneously as a reactant in the reactions under study. The organic feed was pumped
into the system by a syringe pump (Fanavaran Nano-Meghyas, model SP. 1000) that allowed slow,
constant flow rates. The gaseous reaction effluent was analyzed using on-line gas chromatograph with
a flame ionization detector (Teif Gostar Co.) and a capillary column (Cat. No. TR-110222, Serial No.:
p2085307, TRB-1, Tecknokroma, l:25 m, ID:0.25).
The experimental data was collected over a wide range of experimental conditions, including pure and
binary mixture of pentane isomers as a feed stock, temperature range of 150–350 °C, pressure range
of 0–2 bar, H2 to hydrocarbon (HC) molar ratio of 7–50, and WHSV range of 0.1–0.8 hr-1.
The total conversion of the n-pentane (Xn-pentane) was calculated according to Equation 6:
tan 100 i n pen e
n pen e
And for the reaction product, or the asset of the products, the selectivity (S) is defined by Equation 7:
B. Bayati et al./ Hydroisomerization of n-pentane Pentane over Pt/ Mordenite Catalyst … 87
i n pen e
A A -
where, Ai is the corrected chromatographic area for a particular compound used to express the
conversion and selectivity as molar percentages (López et al., 2008).
Yield (Yi) to a particular product was calculated according to Equation 8 (Setiabudi et al., 2012a).
n pen e i
Y - ´
Hydrogen Air Helium
NV SP BP
NV Needle Valve
MFC Mass Flow Controller
SP Syringe Pump
SV Selection Valve
MM Membrane Module
TWV Three Way Valve
BP Back pressure Regulator
EF Electrical Furnace
BFM Bubble Flow Metter
A schematic illustration of the experimental setup for the reaction experiments.
3. Results and discussion
Figure 2 shows the SEM micrograph of the Pt/mordenite zeolite catalyst. The image indicates that the
catalyst has a homogeneous morphology. The surface area is a key factor in the catalyst activity. A
high surface area improves the adsorption of reactant. The specific surface area of the catalysts was
measured by the BET method. The surface area of Pt/mordenite zeolite was 296.69 m2/g. The XRD
pattern of Pt/mordenite zeolite (Figure 3) exhibits the most intense diffraction peaks at 2θ = 6–30°,
and it thus confirmed the MOR structure of zeolite as well as its good crystalline nature.
The hydroisomerization of pure n-pentane and n-pentane in a binary mixture of pentane isomers was
performed over the Pt/mordenite catalyst in a wide range of experimental conditions. The
hydroconversion products consist of both isomerization and cracking products. Hence, in the
following subsections, the effects of reaction parameters on the catalytic performance of pure npentane
as the feed are demonstrated by catalytic activity and isomerization selectivity. Then, the
isomerization of n-pentane in the binary mixture is discussed in the last part of this section.
88 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
SEM picture of Pt/MOR zeolite catalyst.
XRD diffractogram of Pt/MOR zeolite catalyst.
5 15 25 35 45
B. Bayati et al./ Hydroisomerization of n-pentane Pentane over Pt/ Mordenite Catalyst … 89
3.1. Isomerization of pure n-pentane
The isomerization experiments were carried out starting with the pure n-pentane as the feed stock
using the Pt/mordenite catalyst.
3.1.1. Effect of reaction temperature
Figure 4 shows the conversion of n-pentane as a function of reaction temperature. The tests were
performed in H2 at temperatures ranging from 150 to 350 °C and atmospheric pressure. It can be
clearly seen that the catalyst showed a high catalytic activity for the isomerization of n-pentane,
particularly in the temperature range of 220-350 °C. Because of the low activity of the catalyst and the
low reactivity of n-pentane, the conversion of n-pentane is negligible for temperatures below 180 °C.
By increasing the temperature from 180 to 220 °C, the conversion of n-pentane increased greatly;
however, a further increase in temperature results in a slow rise in conversion. This can be attributed
to an increase in the number of sites which can be activated for the reaction when the temperature
increases in the range of 180-220 °C; however, the rate of increase in conversion declines because of
thermodynamic restriction at higher temperature. In other words, an increase in temperature always
corresponds to an increase in the reaction rate. Thus, at low temperatures, the actual conversion will
be far below the equilibrium conversion because of low reaction velocity. On the contrary, at higher
temperatures, the equilibrium conversion will be more easily reached due to a high reaction rate.
Consequently as mentioned in the literature (Yasakova et al., 2010), the yield of isoparaffins is limited
by the thermodynamic equilibrium at higher temperatures, while, at lower temperatures, it is limited
by the low reaction rate (kinetic limitation).
Conversion of n-C5 as a function of temperature over Pt/mordenite at atmospheric pressure.
The isomerization selectivity on Pt/mordenite zeolite catalyst was illustrated in Figure 5. Isopentane
selectivity was high and the selectivity was decreased with an increase in reaction temperature. The
100 150 200 250 300 350 400
90 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
cracking reaction was preferred in a high temperature region. Therefore, the selectivity was decreased
dramatically because of the large increase in cracking products.
Cracking at high temperatures over zeolite could be explained on the acidity and pore size within the
structure. In this way, strong acidity and a narrower pore diameter will make the average life time of
the carbocations on the surface longer, and thus the diffusion of the branched product becomes
slower. Both factors will favor the cracking of the tertiary carbocations formed during the
isomerization before they can be desorbed, and the readsorption and cracking of the branched
paraffins before they leave the pores and come into the gas stream (Chica et al., 2001).
Moreover, the influences of H2/n-pentane molar ratio on the catalytic performance of zeolite catalyst
in the hydroisomerization of n-pentane are shown in Figures 4 and 5. With an increase in H2/npentane,
the selectivity toward isomerization increases, while the conversion is observed to decrease
gradually. These results imply that H2 affects the selective formation of isopentane to some extent.
The influence of WHSV on the catalytic behavior of Pt/mordenite zeolite is also presented in Figures
4 and 5. The conversion of n-pentane decreased slowly with an increase in WHSV, whereas the
cracking products increased. At low values of WHSV, the increase in the cracking by raising WHSV
was low, while it rose at high values of WHSV considerably.
Selectivity of isopentane as a function of temperature over Pt/mordenite at atmospheric pressure.
The isomerization yield for n-pentane with Pt/mordenite zeolite catalyst is displayed in Figure 6. It
can be seen that the isomerization yield goes through a maximum at 220 °C while the reaction
temperature increases. This maximum in the isomerization yield is due to the coupling of the
conversion of n-pentane and the isopentane selectivity.
100 150 200 250 300 350 400
B. Bayati et al./ Hydroisomerization of n-pentane Pentane over Pt/ Mordenite Catalyst … 91
Effect of temperature on n-pentane isomerization yield over Pt/mordenite at atmospheric pressure.
The influences of H2/n-pentane molar ratio on the catalytic performance of zeolite catalyst in the
hydroisomerization of n-pentane are shown in Figures 4 and 5. With increasing H2/n-pentane, the
selectivity for isomerization increased, while the conversion was observed to decrease gradually.
These results imply that H2 has a significant effect on the selective formation of isopentane, which is
in accordance with the kinetic models presented in the literature.
3.1.2. Effect of reaction pressure
Figure 7 shows that n-pentane conversion depends on the reaction pressure. At a reaction temperature
of 250 °C, n-pentane conversion and the cracking products show a similar trend, and they are
increased with increasing reaction pressure. Therefore, due to the availability of cracking products at
higher reaction pressures, the selectivity toward iso-pentane was slightly lower than the one at lower
setting pressures (see Figure 8). However, the pressure can suppress the side hydrogenolysis reaction
at pressures higher than 10 bar.
On the other hand, n-pentane conversion slightly decreased as the reaction pressure was increased at a
reaction temperature of 220 °C. The reaction pressure had no significant effect on iso-pentane
selectivity. The reason for such a behavior can be due to negligible cracking reactions at low reaction
temperatures (220 °C) compared to high reaction temperatures, i.e. 250 °C.
From the above results, it can be concluded that that the optimum temperature for pentane
isomerization using this catalyst is 220 °C, resulting in an acceptable conversion and very high
100 150 200 250 300 350 400
92 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
Conversion of n-C5 as a function of pressure over Pt/mordenite at WHSV=0.27 hr-1 and molar ratio of
Selectivity of isopentane and isomerization yield as a function of pressure over Pt/mordenite at WHSV=0.27 hr-1
and molar ratio of H2:HC=4.82.
3.2. Isomerization of n-pentane in pentane isomer mixture
3.2.1. Effect of reaction pressure
To investigate the effect of isopentane in the feed stock on the isomerization process, a binary mixture
0 0.5 1 1.5 2 2.5
Reaction pressure (bar)
0 0.5 1 1.5 2 2.5
Reaction pressure (bar)
B. Bayati et al./ Hydroisomerization of n-pentane Pentane over Pt/ Mordenite Catalyst … 93
(nC5 70% and isopentane 30%) was fed to the isomerization reactor packed with Pt/mordenite zeolite
catalyst. The representative results of n-pentane in binary mixture isomerization over Pt/mordenite are
given as follows.
In Figure 9, the conversion of n-pentane in binary pentane isomers at WHSV=0.3 is plotted as a
function of total reaction pressure. As can be seen, n-pentane conversion decreased with increasing
the reaction pressure for all molar ratios. Normal pentane conversion reached a minimum value at 1.5
bar, and it then increased with increasing the reaction pressure. This behavior was different from the
trend observed in the pure n-pentane isomerization. It can be due to the presence of isopentane in the
feed and the adsorption phenomenon of the binary mixture on the mordenite catalyst. Because of the
limitations of the existing syringe pumps, pressure could not be increased above 2 bar. It is likely that
conversion is much higher at pressures above 2 bar.
Conversion of n-C5 in a binary mixture as a function of pressure over Pt/mordenite at 220 °C and WHSV=0.3
The selectivity toward isopentane as a function of reaction pressure at a temperature of 220 °C for
three molar ratios of H2/HC is shown in Figure 10. It is apparent from Figure 8 that the reaction
pressure had a very little effect on the selectivity to isopentane. At all H2/HC molar ratios, the
selectivity to isopentane varied only 1 or 2 units regardless of the reaction pressure. It can be due to
reaction temperature since cracking reactions do not occur at this temperature. This result is consistent
with the results of pure n-pentane isomerization at 220 °C. Moreover, the variation of the isopentane
yield with reaction pressure for the Pt/mordenite catalyst sample is shown in Figure 11. As can be
seen, isopentane yield showed the same trend in conversion with respect to reaction pressure over the
Pt/mordenite catalyst at a temperature of 220 °C, which is, in accordance with the isopentane
selectivity (100%) at 220 °C and Equation 3..
0 0.5 1 1.5 2 2.5
Reaction pressure (bar)
94 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
Selectivity of isopentane in the hydroisomerization of n-C5 in a binary mixture as a function of pressure over
Pt/mordenite at 220 °C and WHSV=0.3 hr-1.
Yield of hydroisomerization of n-C5 in a binary mixture as a function of pressure over Pt/mordenite at 220 °C
and WHSV=0.3 hr-1.
3.2.2. Effect of contact time
Along with temperature, contact time was the most important process parameter. Contact time was
calculated as the residence time in the reaction space of a unit volume of reactants in the reaction
conditions. At a reaction temperature of 220 °C, a reaction pressure of 1-2 bar, and a constant H2/HC
molar ratio, the effect of WHSV on n-C5 hydroconversion in a binary mixture of pentane isomers was
investigated by proportionally changing the flow rate of H2 and HC mixture. Figures 12-14 present
the influence of WHSV on the catalytic behavior of Pt/mordenite zeolite. As can be seen, the
0 0.5 1 1.5 2 2.5
Reaction pressure (bar)
0 0.5 1 1.5 2 2.5
Reaction pressure (bar)
B. Bayati et al./ Hydroisomerization of n-pentane Pentane over Pt/ Mordenite Catalyst … 95
conversion of n-C5 and the yield of feed isomers decreased with increasing WHSV, while no
significant isomerization selectivity changes were observed. With an increase in WHSV, the contact
time of feed on the catalyst decreased, and thus the decrease in conversion was expectable.
Effect of WHSV on n-C5 conversion in a binary mixture over Pt/mordenite at 220 °C and molar ratio of
Effect of WHSV on selectivity of isopentane in hydroisomerization of n-C5 in a binary mixture over
Pt/mordenite at 220 °C and molar ratio of H2:HC=9.6.
0 0.2 0.4 0.6 0.8
0 0.2 0.4 0.6 0.8
96 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
Effect of WHSV on yield of hydroisomerization of n-C5 in a binary mixture over Pt/mordenite at 220 °C and
molar ratio of H2:HC=9.6.
3.2.3. Effect of H2:HC molar ratio
The influence of H2/HC molar ratio on the hydroconversion of n-pentane in a binary mixture of
pentane isomers was investigated at a constant reaction temperature of 220 °C, reaction pressures of
0.5-1 bar, and WHSV values of 0.2 and 0.3 hr−1 by changing the flow rate of H2. As shown in Figure
15, the conversion of n-C5 decreased with increasing the partial pressure of hydrogen (the H2/HC
mole ratio from 7 to 50), while the isomerization selectivity increased. These reflected the importance
of H2 rule in the isomerization process. The function of H2 could be interpreted as facilitating
isomerization by suppressing cracking reactions and keeping the catalytic activity high by impeding
Effect of H2:HC molar ratio on n-C5 conversion and selectivity of isopentane in hydroisomerization of n-C5 in a
binary mixture over Pt/mordenite at 220 °C; (a) P=0.5 bar and WHSV=0.2 hr-1 and (b) P=1 bar and WHSV=0.3
A comparison between our results and those reported by Chica et al. (2001) is shown in Figure 16.
The trends in conversion and selectivity are similar, but there is a little difference in values, which is
due to the differences in pressure, WHSV, and molar ratio of H2:HC.
0 0.2 0.4 0.6 0.8
0 10 20 30 40 50 60
nC5 conversion and 2MB
H2:HC molar ratio
conv. 0.5 bar
Sel. 0.5 bar
B. Bayati et al./ Hydroisomerization of n-pentane Pentane over Pt/ Mordenite Catalyst … 97
Comparing between results of this work (WHSV=0.15 hr-1, molar ratio of H2:HC=9.6, and atmospheric
pressure) and Chica et al. (WHSV=5.13, molar ratio of H2:HC=15, and pressure=20 bar).
The Pt/mordenite showed a high catalytic activity in the isomerization of n-pentane, particularly in the
temperature range of 220-350 °C. The cracking reactions were preferred in a high temperature region
(>250 °C). With the increase of H2:HC molar ratio, the selectivity toward isomerization increased,
while the conversion was observed to decrease gradually. The conversion of n-pentane decreased
slowly with an increase in WHSV, whereas the cracking products increased. The maximum yield of
isopentane was achieved with the Pt/mordenite catalyst at 220 °C and at relatively low reaction
pressures. The catalysts were assessed for activity and selectivity in the isomerization of n-pentane in
a mixture consisting of n-pentane (70 wt.%) and isopentane (30 wt.%) at 220 °C. Conversion of npentane
changed with the reaction pressure and reached a minimum value at 1.5 bar; this behavior is
different from the trend observed in the pure n-pentane isomerization, which can be due to the
presence of isopentane in feed and the adsorption phenomenon of the binary mixture on Pt/ mordenite
catalyst. The conversion of n-C5 and the yield of feed isomers decreased with increasing WHSV,
while no significant isomerization selectivity changes were observed. With respect to these results, the
investigation of pentane isomerization at a high pressure and the study of the kinetic of pentane
isomerization are suggested for future works.
The authors wish to thank Sahand University of Technology (SUT) for the financial support of this
work. Also, we would like to thank co-workers and technical staff in the Department of Chemical
Engineering, Nanostructure Materials Research Center (NMRC), and Reactor and Catalysis Research
Center (RCRC) of SUT for their help during various stages of this work.
X : n-pentane conversion
A : Corrected chromatographic area
Y : Yield of reaction
S : Selectivity of reaction
0 5 10 15 20 25 30
nC5 conversion and 2MB
H2:HC molar ratio
conv. 1 bar
Sel. 1 bar
98 Iranian Journal of Oil & Gas Science and Technology, Vol. 5 (2016), No. 2
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