Synthetic Or Reformulated Fuels: a Challenge for Catalysis
Oil & Gas Science and Technology Ð Rev. IFP, Vol.
Synthetic or Reformulated Fuels: a Challenge for Catalysis*
Ph. Courty 0
P. Chaumette 0
C. Raimbault 0
0 Institut français du pétrole , 1 et 4, avenue de Bois-Préau, 92852 Rueil-Malmaison Cedex - France
Ñ Synthetic or Reformulated Fuels: a Challenge for Catalysis Ñ Despite comparative figures for wordwide crude oil and natural gas proven reserves, present time contribution of syngas chemistry to motorfuels remains marginal when the refining industry is faced to main constraints: market demand evolution, stringent specifications and environmental issues. Actually natural gas upgrading via syngas chemistry yields key products (e.g. methanol) among which clean motorfuels (ethers, FT products) should develop despite the huge investments required, mostly for syngas production. Main challenges and corresponding issues for catalysts and related technologies are identified for Fischer-Tropsch synthesis and motorfuels long-term reformulation. Among other, mastering the chain-growth (FT synthesis) improving the FCC products: gasoline, and LCO for Diesel pool. All these issues need
significant progresses in catalyst and technology to be solved. Lastly, our economical study, focused on
Diesel-fuel production, shows up that clean diesel (from SR-LCO mixtures) and FT Diesel reach similar
production costs when cheap NG is available.
In the future FT middle distillates should amount to a few percent (5-150 Mt) of the 1700-2000 Mt of
transport middle distillates expected from oil refining. However they should more and more be a
compulsory part of diesel pool if the level of investment for an FT process continues to decrease significantly.
Keywords: crude oil, natural gas, syngas chemistry, Fischer-Trospch synthesis, mortorfuels reformulation, Diesel pool, catalyst,
technology, middle distillates, oil refining, economics.
Natural gas proven resources are still increasing and reached
133 Gtep which amounted to 98% of oil resources in 1995
]. Most of these resources are located in Eastern Europe
(CEI) and Middle Eastern countries (Iran, Qatar, Abu Dhabi,
In the mean time, the refining industry is facing three
Ð market demand evolution towards more and more clean
Ð more stringent specifications on sulfur, aromatics, cetane
and octane indexes;
Ð environmental issues: pollution control on gaseous
emissions (including CO2) as well as on liquid and solid
In view of the fact that the present-time contribution of
syngas chemistry to motorfuels remains marginal, to what
extent a competition might occur beetween clean and
1 THE CHEMICAL CONVERSION OF NATURAL GAS
Syngas can easily be synthesized from natural gas and can be
transformed to motorfuels through many different pathways
(Fig. 1). Gasoline as well as ethers can be prepared from
methanol, and dimethyl ether has recently been suggested as
a substitute to standard Diesel-fuel by Amoco and Topsoe [
Fischer-Tropsch synthesis dates back to 1923, with the
discovery of an efficient catalyst to convert synthesis gas into
hydrocarbons mixtures. After coal-based synthetic fuels
production during the second world war in Germany, and
later in South Africa (Sasol), the energy crisis of the 1970Õs
and 1980Õs renewed the interest towards the conversion of the
increasing remote natural gas reserves to liquid fuels [
Between 1984 and 1988, IFP and Idemitsu Kosan
demonstrated their modified Fischer-Tropsch process for
alcohols production in Japan, under Rapad subsidy [
1993, two pioneering gas conversion plants started their
operations: one by Shell in Malaysia, another one in South
Africa (Mossgas). Other companies, such as Exxon, Statoil,
(H2, CO, CO2)
Gasoline Acetic Acid
Fischer Tropsch synthesis
Gas oil pool
Chemical conversion of natural gas; contribution of syngas chemistry to motorfuels.
Sasol, Syntroleum and IFP are involved in the development
of a new generation of natural gas based Fischer-Tropsch
A high quality Diesel-fuel or kerosene, free from sulfur,
aromatics or heavy metals can be synthesized through the
Fischer-Tropsch process and hydroisomerization of the
paraffins obtained. The Diesel oil prepared through
FischerTropsch presents a very high cetane number (over 75) and
the kerosene a smoke point over 50.
The integrated Fischer-Tropsch process includes three
steps (Fig. 2). The first one allows to transform natural gas
into syngas, and is followed by the Fischer-Tropsch synthesis
itself. The heavy paraffins obtained in the second step are
transformed into diesel oil, kerosene and lube oils in the last
The existing Fischer-Tropsch plant in Bintulu (Malaysia)
built by Shell [
] needed an investment of around
$55 000/bpd of capacity. Technological improvements and
larger overall plant capacities allows to decrease this level of
investment to about $35 000/bpd capacity. Since 55% of total
investments are linked to the syngas production section,
whereas the Fischer-Tropsch synthesis and the
hydroisomerization only represent 30% and 15% respectively,
there are at present strong incentives to develop new
technologies for syngas generation.
Partial oxidation alone, or in combination with steam
reforming, seems to be the best choice at present [
the POX process needs pure oxygen. Savings could be
achieved through oxygen separation from air with dense
membranes inside a POX reactor. Cryogenic separation of
oxygen, an efficient but expensive technology, would then
be avoided. This challenging oxygen separation with
membranes is actively studied through a joint venture
between Amoco, BP, Praxair, Sasol and Statoil (ceramic
membranes) and by Air Products under a DOE contract
(ionic membranes). Cuts on investments as high as 25% are
Adaptation to the Fischer-Tropsch process of the
autothermal reforming process used for methanol (ATR, [
and in which partial oxidation (POX) and steam-reforming
(SR) are integrated in a single reactor, could be another way
to cut down investments.
Although the Fischer-Tropsch step only represents 30% of
total investments, improvements of this old technology are
still needed (Table 1). The Fischer-Tropsch synthesis is
catalyzed by cobalt or iron based catalyst, cobalt being more
suitable for kerosene and Diesel-fuel production. This
reaction is highly exothermic and leads to a wide linear
paraffin distribution, due to a Schulz-Flory type chain growth
mechanism. The catalyst performances strongly depend on
operating conditions, catalyst and reactor technology.
New cobalt based catalysts allow to reach higher wax
productivities in the Fischer-Tropsch section, thanks to the
use of promoters such as ruthenium. Silica and alumina
supports, sometimes doped by zirconia or titania, help to
maintain a good cobalt dispersion, and to obtain the right
paraffin distribution to be sent to the hydroisomerization
Cobalt being far less active than iron in the water gas shift
reaction, water is the main by product obtained and CO2
100 000 Nm3/h
Partial oxydation +
H2/CO = 1.5-3
Catalyst: Co, Fe
FT synthesis; the integrated gas to liquid process.
formation remains very low. This small amount of CO can
eventually be recycled to the syngas production section.
Despite the progress accomplished, there is still a need for
a further increase of activity, together with a mastering of the
heat produced. The use of slurry reactors, rather than
multitubular fixed bed ones, should help in this respect.
However, this technology has only been proven at a scale of
around 2400 bpd at Sasol I, in the case of the
There would also be an interest in performing the
FischerTropsch and the hydroisomerization reaction in a single step.
There have been attempts to do so by using cobalt/zeolites
catalysts, but the shape selectivity of zeolites does not operate
on long chain paraffins and leads to the transformation of
olefinic intermediates into aromatics, which are not desired in
the final fuels. Thus, a separate hydroisomerization step
cannot be avoided for the time being.
The gasoline pool is made of the following bases:
Ð liquid petroleum gases (LPG); mostly C4;
Ð isomerate (C4-C6 paraffins);
Ð reformate (C5-C12 hydrocarbons); mainly aromatics;
Ð hydrocracking gasoline (C5-C12 hydrocarbons), mainly
paraffins and naphthenes;
Ð gasoline from thermal conversion (C5-C12 hydrocarbons),
mainly paraffins and naphthenes;
Ð alkylate (C5-C12 paraffins);
Ð polymerisation gasoline (C5-C12 olefins);
Ð ethers (C5-C6-C7).
In view of their MON and RON figures, a limited number:
alkylate, reforming, ethers, exceed the target. Isomerates
meet the target when FCC gasoline, hydrocracking (HCK)
gasoline and SR naphtha are far below.
Figure 3 plots octane vs aromatics content. Apart from
isomerate and alkylate, very rich in double-branched
paraffins with high octane ratings, best MON figures of other
bases correspond to aromatic-rich cuts. This situation makes
it difficult to meet the main gasoline constraints of the years
2005 and over: limited amount of olefins (6-14%) aromatics
(25-35%) and sulfur (30-50 ppm). These constraints imply a
drastic evolution with reference to conventional gasoline
formulation, as seen in Table 2. Main changes deal with a
severe decrease of aromatics (reforming and FCC gasoline)
olefins (FCC and poly gasoline) sulfur (FCC gasoline) when
a limited increase of oxygen content will possibly favor
alcohols at the expense of ethers [
SRL naphtha FCC
in Table 4. A good example of Diesel pool improvement is
that of pure LCO using the two step IFP hydrotreating
]. In a first stage (Table 5) a very deep
hydropurification lowers sulfur and nitrogen far below 0.005%
under moderate pressure followed in a second stage by a
deep aromatics hydrogenation on a sulfur-resistant noble
metal catalyst. A significant cetane increase is noticed and
(di+triaromatics) content becomes practically nil. Medium
term issues will be to further improve the cetane number via
advanced selective opening of naphthene rings into slightly
branched paraffins of same carbon number.
Issues for gasoline pool reformulation will arise from
catalysts and technology progresses as seen in Table 3.
Indeed the ideal environmentally friendly gasoline would
be made of isoparaffins and posibly of alcohol or ethers
(10-15%), which strongly pushes forward the alkylate
demand. However, more iC4 (C4 isomerisation) C4= and
C5= olefins (dehydrogenation, improved steam cracking,
dedicated FCC) would be needed, when the main demand
concerns a new solid acid alkylation catalyst sought after
together with a competing technology and attractive
3 DIESEL OIL
For the Diesel pool, the main challenges (Fig. 4) deal with
cetane indexes (> 50) and sulfur content (less than 0.045%).
Apart from gas oil cut from HCK and in the future FT gas
oil, none of the other bases meet the specifications since they
show a low cetane and high di- and polyaromatics and sulfur
contents. In fact, Diesel oil bases have very different
properties. Diesel cuts from conversion processes have high
aromatic and sulfur contents, with low cetane indexes, when
diesel cuts from HCK contain no aromatics, have a very high
cetane (³ 70) and a very low sulfur content (< 0.01%). Key
challenges concern LCO from FCC and gas oil from thermal
conversion units: a very deep desulfurization is needed
with polyaromatics hydrogenation to monoalkylaromatics,
monoalkylnaphthenes and slightly branched paraffins. This
should lead to a significant cetane improvement, however
required at a competitive cost.
Actually, main Diesel oil constraints of 2005 years will be
difficult to meet: high cetane number (> 53), low sulfur
content (< 0.005%), possible limitations of di- and
polyaromatics content (1-6%), density and heaviest ends. As
for premium gasoline, issues for diesel pool improvement
will arise from catalyst and technology progresses as seen
FCC gas oil < 25
Coking gas oil
Visbreaker gas oil < 30 50
Straight-run gas oil
Dimethyl ether is also a possible candidate as a Òclean
fuelÓ for DI Diesel engines: its synthesis from methanol was
already proven in the methanol-to-gasoline industrial
achievements of Mobil. In addition its direct synthesis from
syngas is now developed [
] based on a dual catalyst system
which process economics are comparable to that of methanol
synthesis. Fleet test results show very low NOx and particle
emissions (cetane number > 70). In the future DME could be
a possible ÒLPG equivalentÓ for dedicated direct injection
4 ECONOMICS AND VIEW ON FUTURE
Our economical study is focused on Diesel-fuel production
with the objective to compare costs of production of FT
diesel with that of clean diesel processed from todays
SR/LCO Diesel pool and, lastly, to compare these figures
with production costs of methanol and DME.
This study is based on the following data:
Ð production capacity: 30 000-50 000 bpd;
Ð natural gas available at $0.6/MBtu;
Ð capital depreciation: 10 years;
Ð 80/20 SR/LCO Diesel oil available at $19/bbl.
Clean Diesel issues from the two-steps IFP's
hydrotreating technology of Table 5 (operating pressure lower
than 1500 psig) and DME costs are evaluated from a two
step synthesis (methanol then DME).
Diesel fuel properties sought after for both FT product
and clean Diesel from SR/LCO HDT are described in
Our results are summarised in Table 7 which details the
lowest investments and production costs based on available
It appears that FT Diesel oil and clean gas oil have
equivalent costs of production. Methanol is much cheaper.
The direct synthesis is expected to lower the production cost
of dimethyl ether since its lower heating value hampers DME
with reference to conventional fuels.
In view of investments the syngas route implies the higher
figures. Should a return on investment be needed, FT product
prices would increase more rapidly than for clean gas oil.
Hence, even in the case of reduced costs for FT synthesis the
challenge remains open considering that refining industry
usually generate low margins which makes difficult to make
high investment projects profitable.
Lastly, it seems worthwhile to compare the expected
changes in world oil refining, transport fuel and middle
distillate figures to those of today's methanol and tomorrow's
Fischer Tropsch middle distillates possible production
Indeed the growth of oil refining will continue and an
increased fraction will be dedicated to transport fuels. Hence,
a demand of 2.7 Gt of transport fuels is predicted for year
In the same time the growth of methanol production
should be limited as recent MTBE's ban in the United States
do not constitute incentives. FT growth should not start
before years 2000-2010 provided that oil prices recover.
In the years 2010 to 2020, FT middle distillates
production could contribute to the increase in demand for clean
middle distillates. A scenario where very clean Diesel fuels
have to be produced could lead to a potential FT Diesel oil
use of more than 100 Mt/y. At that time, FT Diesel could
issue as a very attractive cetane booster, drastically reducing
impurities of the diesel pool and improving its overall
More and more Fischer-Tropsch technology will develop
since its diesel cut might be the best available Diesel
fuel improver in the market (cetane number and purity)
provided that significant savings occur on syngas and FT
The authors wish to thank J.F. Gruson for his kind
contribution in this paper.
1 Chaumette, P. ( 1996 ) Revue de lÕInstitut franais du ptrole , 51 , 711, septembre-octobre 1996 .
2 Sorenson, S.C. and Mikkelsen , S.E. ( 1995 ) SAE technical paper series , No. 950064. International SAE Congress, Detroit, February 27-March 2 , 1995 .
3 Sanfilippo, D. ( 1998 ) Preprints of 13th Gas convention PDVSA Quimica - AVPG Valencia, May 6- 8 , 1998 .
4 Courty, Ph., Chaumette , P. , Raimbault , C. and Travers , Ph. ( 1990 ) Revue de lÕInstitut franais du ptrole , 45 , 561 .
5 Van Wechem , V.M.H. and Senden , M.M.G. ( 1994 ) Studies in Surface Science and Catalysis, 81 , 43 - 71 .
6 Christensen, T.S. and Primdhal , I.I. ( 1994 ) Hydrocarbon Processing, 39 , March 1994 .
7 Koseoglu, R. , Due, D.D. and Billon , A. ( 1997 ) In Upgrading Heavy Ends with IFP , IFP ed, 75 - 82 .
8 Sigault, B. ( 1998 ) European Oil Refining Conference and Exhibition, Prague, June 25-26, 1998 .