Chemisty and Industry Article

1. Catalysis
Liquid fuel revival
Catalytic synthesis of liquid fuel from solids or
gases is making a comeback both on decentralised
small-scale and big refinery-sized plants.
Michael Gross reports
In the 20th century, synthetic fuel has often been
SunDiesel
the last resort used by countries cut off from
global oil supplies for one reason or another.
While gasoline was never quite expensive enough
to make the synthetic alternative attractive in the
global marketplace, isolated countries ranging from
Germany to South Africa used synthesis on a massive
scale.
As soon as the Nazis seized power in Germany in
1933, they made the development of large-scale fuel
synthesis from coal a national priority. It was a typical
example of dual use science. Officially, the fuel was
for the rapidly growing number of cars on the new
Autobahn, which helped to pull the economy out of
the crisis, but without it, Hitler’s wars would not have
been possible either.
To turn the country’s abundant coal into liquid
fuel, there were two methods to choose from:
•Catalytic hydration of coal at high pressure was
based on the work of Friedrich Bergius, who won the
Nobel prize for chemistry for his high pressure work
in 1931.
•The conversion of the coal feedstock into synthesis
gas (CO + H2), which is then turned into liquid fuel
at atmospheric or moderate pressure using a cobalt
catalyst or at intermediate high pressures using an
iron catalyst. This method, which can also start from
gas feedstocks, was invented by Franz Fischer and
Hans Tropsch in 1925.
IG Farben boss Carl Bosch, having witnessed the
spread of gasoline-fuelled cars in the US, was keen to
In Brief
• Germany and South Africa were among
the first countries to promote the use of
Fischer-Tropsch synthesis to make fuel
from coal
• Today, companies have revived the
process mainly because of its use of
renewable feedstocks such as biomass
• Fischer-Tropsch fuel production
currently amounts to 500,000bbl/day,
just under 1% of crude oil production
• Its versatility for carbon feedstocks
including biomass means that it is likely
to play a bigger role in the future Feedstock flexibility: new opportunities for Fischer-Tropsch synthesis from biomass
Chemistry & Industry 23 November 2009 21

2. Catalysis
make synthetic fuel his company’s next blockbuster
product after the success of the nitrogen fertilisers
from the Haber-Bosch process. From April 1927,
IG’s plant at Leuna in Germany started producing
fuel using the Bergius process. Shortly after that,
however, the discovery of the Oklahoma oil fields
eliminated all hopes of ever making the so called
‘Leunabenzin’ competitive in the market, and Leuna
remained the only plant producing it.
In December 1933, the Nazis, keen to make
Germany independent of oil imports, made a contract
or Benzin-Vertrag with IG Farben, guaranteeing the
company a fixed price in exchange for a minimal
production of 200t/year of fuel. Although a small
amount today, this was 10% of Germany’s total fuel
consumption at that time.
This was just the first step. The following year,
the government forced the companies mining
lignite – brown coal – to invest in coal hydration
plants, strategically located deep in the middle of
the country. Three hydration plants and one Fischer-
Tropsch plant took up production in 1936. By 1939,
there were half a dozen of them.
In 1943, in the middle of the war, Germany
produced nearly 6.2m t of oil, half of it by catalytic
hydration. Another 368,000t was produced using
the Fischer-Tropsch synthesis. Only in May 1944 did
the Allies start bombing these factories.
After the war, the German Democratic Republic
(GDR) continued to turn its abundant lignite supplies
into fuel, using both the Bergius and the Fischer-
Tropsch processes. In South Africa, the company Sasol
used Fischer-Tropsch catalysis to convert both coal
and gas into various petroleum products, opening its
first coal-to-liquid plant in 1955. It became a global
Harvesting coppice: feedstock for Choren's Beta plant at Freiberg, Germany
‘The FT microchannel petrochemical company after successfully expanding 1m t of dry wood matter annually, will be sourced
reactor provides a its operations to Qatar, Iran, and Nigeria. from recycled and forest wood, and increasingly
from woody crops.
new way to make the Green revival
Today, several companies have revived the Fischer-
Another company adapting the Fischer-Tropsch
technology is Oxford Catalysts, a spin-out from the
production of next Tropsch process for entirely different reasons, mainly chemistry department at Oxford University. It has
generation biofuels at to do with using new, climate-friendly feedstocks,
such as biomass and ‘stranded’ gas. Choren Industries
developed a new way of producing metal catalysts,
the organic matrix combustion (OMX) method,
a local scale workable – the name implies it uses C, H, O from RENewable
sources – has built on engineering expertise from
which ensures a narrower particle size range than
conventional methods. This method is applicable
and economically GDR times to adapt the Fischer-Tropsch method to to the production of metal catalysts for a range of
the use of biomass as feedstock. Fuel expert Bodo different processes, including cobalt catalysts for
feasible, while Wolf founded the company in 1990, building on Fischer-Tropsch synthesis.
avoiding the need experience gained in the GDR’s research programme
aimed at converting the abundant lignite into fuel.
In the OMX method, the metal salt forms a
complex with an organic component that serves
to transport waste Shell helped to develop the process used to convert
the synthesis gas into diesel fuel, by a variant of the
to stabilise the metal. On rapid combustion, as the
metal cores are separate from each other and don’t
to large centralised established Fischer-Tropsch procedure using cobalt have time to sinter, nanocrystallites are produced
production facilities catalysts.
Currently, Choren is beginning production of
with a tightly controlled size range and a terraced
surface, both highly desirable features for catalysis.
and reducing the synthesis gas at its Beta plant at Freiberg, Saxony,
Germany. Fuel production, with an annual capacity
The young company champions a decentralised
approach with a larger number of facilities operating
amount of waste of 15,000t of biomass-to-liquid (BTL), is scheduled on a much smaller scale. Its Fischer-Tropsch catalysts
going to landfill’ to start in early 2010. Provided the necessary
industrial policy legislation is in place, the Choren
are to be used in special microchannel reactors
developed by its subsidiary Velocys.
Group is planning to build a large industrial-scale Microchannel reactors are made up of individual
Derek Atkinson,
BTL production plant in Schwedt in the state of modules, each just 0.6 x 0.6 x 0.6m in size and
Oxford Catalysts
Brandenburg. The feedstock for this plant, around capable of producing more than 25 barrels/day of
22 Chemistry & Industry 23 November 2009

3. Catalysis
Choren
Choren
Control room: overseeing plant operations at Choren's Beta plant
Emirate of Qatar, which hosts 14% of the world’s a way of regenerating their catalyst, bringing it
known natural gas reserves, and a growing number back to almost 100% of its original activity. At a
of Fischer-Tropsch plants. recent conference on catalyst deactivation in Delft,
Sasol, which has been using Fischer-Tropsch to Netherlands, says Niemantsverdriet, ‘the stability
convert coal to diesel fuel in South Africa since 1955, of Fischer-Tropsch catalysts was discussed in great
set up a 34,000 bbl/day gas-to-liquid (GTL) plant at detail. It is a hot topic.’
Ras Laffan, Qatar, in 2007. Other multinational oil So far, Fischer-Tropsch production accounts for
companies, including Shell, Exxon, and Syntroleum, 500,000bbl/day of fuel, less than 1% of the 80m bbl/
have also started to invest in Fischer-Tropsch plants day fuels generated from crude oil. But considering
in Qatar. its potential to be adapted to all kinds of carbon
The Sasol plant uses a catalyst consisting of sources, including biomass, it is likely to play a much
cobalt nanocrystals supported on an Al2O3 matrix larger role in the future. It appears that, 85 years
liquid fuel. In the modules the key process steps take and activated by traces of platinum. ‘The intrinsic after its invention, the ‘ersatz’ fuel of yesteryear could
place in parallel arrays of microchannels, each with problem with the cobalt catalyst used in these plants become the fuel of choice for a more sustainable
diameters ranging from 0.1 to 5mm. Plant size can is its limited stability,’ explains Hans Niemantsverdriet future.
be increased by simply adding additional modules, from the Schuit Institute of Catalysis at the
which greatly reduces both capital and operating Technical University of Eindhoven, Netherlands. Michael Gross is a science writer based in
costs. In collaboration with Sasol, Niemantsverdriet has Oxford, UK.
Derek Atkinson, business development director studied spent catalyst material from the Qatar plant
at Oxford Catalysts explains: ‘The FT microchannel to work out what the problem was.
Choren
reactor provides a new way to make the production A popular hypothesis was that water – the
of next generation biofuels at a local scale workable main by-product of the Fischer-Tropsch process,
and economically feasible, while avoiding the need and thus not avoidable – oxidised the cobalt. At
to transport waste to large centralised production the high temperatures of 230oC and moderate
facilities and reducing the amount of waste going to pressures of 20 bar typical of the process, water
landfill.’ With this approach, the large scale flaring of partial pressures reach 4 to 6 bar, which might
‘stranded’ natural gas, for example, at oil production conceivably corrode the metal. However, detailed
sites, could also be abolished, as gas could be turned research of Niemantsverdriet’s group using materials
into transportable liquids. from the Sasol plant showed that oxidation was not
Oxford Catalysts plans to deploy a number of the problem, and that it could be easily avoided by
commercial-scale demonstration units during 2009 choosing a suitable cobalt crystal size and adjusting
and 2010, in preparation for full commercialisation the partial pressures of hydrogen and water.
planned for 2011. Recently, the group identified an unexpected
reaction that appears to play an important role in
Scaling up catalyst deterioration, namely the accumulation of
In recent years, the Fischer-Tropsch process has carbon species. Niemantsverdriet summarises the
also experienced a renaissance on a large industrial results: ‘The catalyst deactivates due to a number
scale, especially in places where supplies of natural of factors: sintering, poisons, and inactive carbon
gas from oil fields exceeds local demand and cannot formation at a very slow rate.’ Quality counts: analysing fuel quality
be transported economically. This is the case for the At the same time, researchers at Sasol discovered
Chemistry & Industry 23 November 2009 23