Catalytic activation of methane using n-pentane as co-reactant over
Zn/H-ZSM-11 zeolite
Oscar A. Anunziata
*
,Griselda V. Gonza
´
lez Mercado,and Liliana B. Pierella
Grupo Fisicoquı
´
mica de Nuevos Materiales, Centro de Investigacio
´
n y Tecnologı
´
a Quı
´
mica (CITeQ), Facultad Co
´
rdoba,
Universidad Tecnolo
´
gica Nacional, CC36 -Suc16(5016)- Co
´
rdoba, Argentina
Received 14 November 2002; accepted 3 February 2003
The catalytic conversion of methane (C1) into higher hydrocarbons using n-pentane (n-C5) as co-reactant over Zn/H-ZSM-11 zeolite
material was studied. The aromatics yield was very high,achieving values of over 40 mol% at 500 8Candw/f ¼ 30 g h mol
ÿ1
with a
C1=(C1 þ C5) molar fraction (XC1) ¼ 0.30. Contact time and time-on-stream effects on the product distribution were analyzed in detail
in order to obtain information about the evolution of different species. The C1 conversion was as high as 30 mol% without CO
x
reaction
products.
KEY WORDS: methane conversion; co-reactant; n-pentane; higher hydrocarbons; Zn zeolites.
1. Introduction
Chemical utilization of short-chain alkanes (less than
6 carbon atoms) is one of the dominant scientific
challenges in the field of petrochemistry. These com-
pounds are present in natural gasoline (constituted
by ethane (C
2
) ¼ 2.4,butane (C
4
) ¼ 1.3,pentane
(C
5
) ¼ 67.1,hexane (C
6
) ¼ 22.0,heptane (C
7
) ¼ 5.7,and
octane (C8) ¼ 1.5% w/w) [1],liquefied petroleum gas
(LPG) (C3 ¼ 38.7,iC4 ¼ 36.3,and C4 ¼ 25.0 mol%) [2],
and natural gas (constituted by methane (C1) ¼ 82.8,
C2 ¼ 16.1,and C3–C4 ¼ 1.1% w/w) [3]. Furthermore,
refinery processes such as fluid catalytic cracking
(FCC) and hydrotreating operations produce large
amounts of saturated compounds. Thus,our target is
the direct transformation of lower alkanes for applica-
tion as aromatics,for instance in blending to enhance
the octane number of gasoline (despite strong environ-
mental restrictions for the legal content of benzene in
gasoline [4]),to produce more valuable raw chemical
products in the petrochemistry industry,and to get
liquids transportable by existing petroleum pipelines,
especially for remote regions.
ZSM-5 and ZSM-11 zeolites have been extensively
studied as catalysts for aromatization of light paraffins
[5–7]. Modified ZSM zeolite materials with Zn or Ga
have been successfully used for this purpose [8],and
Inui [9] described the effect of these in paraffin conversion.
Anunziata et al. have reported that Zn-ZSM-11 shows
excellent aromatization behavior for ethane (C2),propane
(C3),LPG,and light gasoline (n-C5, n-C6, n-C7) [10–12].
Methane (C1),the main component of natural gas (up to
90% w/w depending on the source [13]),is the lowest
paraffin and the hardest to activate because of its high
stability–low reactivity. Wang et al. [14] and Pierella
et al. [15] reported C1 aromatization in the presence of
small amounts of light hydrocarbons under non-oxidizing
conditions on transition metal ions supported on H-
zeolite. In previous papers,aromatization of C1 using
different light paraffins as co-reactants was reported
using Zn-ZSM-11 catalyst [2,3,15,16]. Now, we progress
to the functionalization of C1 using n-C5 as a co-reactant.
Thus,this work deals with the activation of C1 with
n-pentane,the main product present in natural gasoline.
2. Experimental
Catalytic reactions were carried out in a fixed-bed
continuous flow quartz reactor,with a 10 mm diameter,
at 1 atm total pressure. This reactor was operated on-
line with a gas chromatograph equipped with FID-TC
detectors. Products were withdrawn periodically from
reactor outlet,and analyzed using a 2.2 m Porapak
column. The delivery tubes were all heated to 250 8Cat
the exit of the reactor to avoid liquid condensation in
the pipework. Feedstocks used in this study were high-
purity methane (>99.97% w/w) supplied by AGA and
n-pentane (99.5% w/w) supplied by Ciccarelli. The
reactions were carried out first using N
2
þ n-C5 as feed
at different molar fractions of N
2
,with the objective to
study the effect of the partial pressure of n-C5 on its
conversion in the presence of an inert gas. Then,methane
was used instead of N
2
under the following reaction
conditions: methane XC1 ( ¼ C1/(C1 þ n-C5)) from
Catalysis Letters Vol. 87, Nos. 3–4, April 2003 (# 2003) 167
1011-372X/03/0400-0167/0 # 2003 Plenum Publishing Corporation
*
To whom correspondence should be addressed.
E-mail: oanunziata@scdt.frc.utn.edu.ar