Experimental study on two-stage catalytic hydroprocessing
of middle-temperature coal tar to clean liquid fuels
Tao Kan, Hongyan Wang, Hongxing He, Chunshan Li
⇑
, Suojiang Zhang
⇑
State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, PR China
article info
Article history:
Received 25 March 2011
Received in revised form 7 June 2011
Accepted 12 June 2011
Available online 22 June 2011
Keywords:
Middle-temperature coal tar
Hydroprocessing
Oil
Two-stage
Catalyst
abstract
Special Mo–Co/
c
-Al
2
O
3
and W–Ni/
c
-Al
2
O
3
catalysts with different metal loadings were prepared applying
new synthesis technologies that combine ultrasonic-assisted impregnation and temperature-program-
ming methods. Clean liquid oil was obtained from middle-temperature coal tar via hydrogenation in
two-stage fixed beds filled with the laboratory made catalysts. The Mo–Co/
c
-Al
2
O
3
catalyst with
12.59 wt.% Mo and 3.37 wt.% Co loadings, and the W–Ni/
c
-Al
2
O
3
catalyst with 15.75 wt.% W and
2.47 wt.% Ni loadings were selected. The effects of pressure and liquid hourly space velocity on hydroge-
nation performance were investigated while other experimental conditions remained constant. Gasoline
(6180 °C) and diesel (180–360 °C) fractions were separated from the oil product and analyzed. The two-
stage reacting system was capable of removing nitrogen and sulfur from 1.69 and 0.98 wt.% in the feed to
less than 10 ppm and 100 ppm, respectively in the products. The results indicated that the raw coal tar
could be considerably upgraded through catalytic hydroprocessing and high-quality fuels were obtained.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
In view of growing concerns about the petroleum depletion cri-
sis and rising fuel price, major efforts are being dedicated to the
development of various usable energy sources to ensure energy
security. China is one of the largest coal producers in the world
and extensive studies have been focused on the fuel production
from coal [1–4]. Abundant coal tar has been produced every year
during coal carbonization and gasification [5]. The coal tar can be
used as an alternative source for producing conventional liquid
fuels (e.g., gasoline and diesel) through its hydrogenation. On the
other hand, liquid fuel production is currently subject to strict
environmental standards for transport liquid fuels and refractory
feeds for refiners [6]. Environmental and economic benefits are
inevitably linked to the hydroprocessing of coal tar to produce
clean transport fuels with ultra-low heteroatom content.
Coal tar is a complex mixture consisting of aliphatic, aromatic,
alicyclic, and heterocyclic compounds. The complexity of coal tar
has driven researches that focused on a pure model compound,
such as naphthalene [7–10], phenanthrene [10], anthracene [11],
and quinoline [12], rather than on a real fraction. Extensive inves-
tigations on thermodynamics and kinetics have been performed
[13–16]. Detailed reviews of studies on the reaction networks have
been provided by Girgis and Gates [17]. The kinetics of the removal
of sulfur compounds and other impurities has a critical effect on
the optimization of process variables and the selection of catalyst
for hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and
hydrodeoxygenation (HDO) processes [6]. Although studies de-
scribed above are helpful in understanding the behavior of certain
compounds under hydroprocessing conditions, an overall picture
of coal tar hydrogenation was not provided. At the temperature
and pressure required for hydrotreatment, many undesirable reac-
tions including dehydrogenation, polymerization, isomerization,
and condensation would occur [18].
The performance of hydroprocessing units is greatly influenced
by the catalyst, type of reactor, process flow, and operating param-
eters. Physical properties such as the density, porosity, size, and
shape of a catalyst are crucial parameters in hydroprocessing heavy
feeds [19]. These parameters are feed dependent [20], implying that
for certain coal tar feedstock, catalysts with special properties (usu-
ally high BET surface and large pore volume) are required. Mo–Co
supported on alumina has long life, and under suitable conditions,
enables the removal of a high degree of sulfur with little more than
theoretical hydrogen consumption [21]. Also, in the study by Raje
et al., the hydrotreatment of coal-derived naphtha was evaluated
over unsupported transition metal sulfide catalysts of Group VIII
in the Periodic Table, and ruthenium sulfide (RuS
2
) was found to
be the most active catalyst for the heteroatom removal [22]. Fur-
thermore, a low loading Ru/zeolite catalyst was believed to exceed
the commercial Mo–Co and Mo–Ni catalysts in HDN activity per
weight of metal and price [23]. But it showed a much lower HDS
activity. Tungsten sulfide has been claimed as an effective catalyst
0016-2361/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.fuel.2011.06.012
⇑
Corresponding authors. Tel./fax: +86 10 82547800 (C. Li), +86 10 82627080
(S. Zhang).
E-mail addresses: csli@home.ipe.ac.cn (C. Li), sjzhang@home.ipe.ac.cn (S. Zhang).
Fuel 90 (2011) 3404–3409
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