Fischer-Tropsch (F-T) Fuels

 

Fischer-Tropsch (F-T) diesel is produced by converting synthesis gas (syngas), a mixture of carbon monoxide and hydrogen produced from fossil fuels, such as natural gas and coal, or biomass into liquid diesel.

In 1923, Franz Fischer and Hans Tropsch first studied conversion of coal-derived syngas into useful compounds (diesel is one of many chemicals and fuels that can be derived from syngas), using what was to become known as Fischer-Tropsch synthesis.  Key to the process are catalysts: substances that facilitate a chemical reaction but are not consumed by the reaction.

The benefit of the process lies in converting a relatively inflexible energy source (such as coal or biomass)into a variety of products that meet specific needs.[1]  Because petroleum-based transportation fuels are in high demand worldwide, F-T diesel is a valuable product.

Gas-to-Liquid (GTL)

Gas-to-Liquid (GTL) fuels are created when natural gas is reformed with pure oxygen or air to produce a synthesis gas.  Through the F-T catalysis, the synthesis gas is converted into liquid hydrocarbons.  The resulting waxy synthetic crude is then refined using standard hydrocracking and isomerization process into middle distillate fuels.

GTL diesel has extremely low sulfur (0-5 ppm), aromatics, and toxics.  Preliminary tests using an unmodified diesel engine showed emission reductions of five percent NOx, 30% PM, and 39% CO, relative to standard diesel.[2]  Opportunities may exist to blend GTL fuel with traditional diesel to make a cleaner diesel fuel to comply with the new stringent diesel fuel standards, without compromising fuel-efficiency, increasing capital outlay, or impacting infrastructure or refueling cost.

For GTL diesel to provide an economically feasible alternative, natural gas must be available at a low cost, less than $1 per million BTUs.  Unfortunately, transportation (pipeline) costs for natural gas are typically four times as expensive as traditional oil, which means production facilities will need to be built in close proximity to, often remote, natural gas sources.  Additionally, for the US, given its greater distance from the major locations of stranded gas and the relatively lower importance of diesel in its transport fuel market relative to other regions of the world, it is even more unlikely that GTL will be a significant contributor.[3]

In fact, in the U.S. Energy Information Administration’s (EIA) “Annual Energy Outlook 2010, the high costs of GTL exclude it from the low oil price projection and the reference case projection, and it is only included in the high oil price projection.[4]  Additionally, GTL’s projection in the high oil price case is not a positive one.  GTL is projected to only account for 2.3% of the U.S. liquid fuel supply by 2035.[5]

Since the late 1990s nearly every major oil company including: BP, ChevronTexaco, ExxonMobil, and ConocoPhillips has been working to develop pilot plants to produce synthetic diesel fuel.  By 2004, at least 8 new plants were being planned, with a combined capacity which would have totaled over 500,000 barrels per day.  However, by early 2007, many of these plants had been deferred or cancelled, with many of the projects citing “significant cost overruns” as the primary problem.  For example, in 2007, ExxonMobil and Qatar petroleum announced the cancellation of the proposed 154,000 b/d Palm GTL project, citing severe cost escalation as the main reason.  The plant was originally scheduled to cost about $7 billion, but reports suggested that costs may have risen to around as high as $18 billion.[6]

Currently, there are only two major GTL production facilities.  One is located in South Africa and the other in Indonesia.  However, in June of 2009, Shell and Qatar Petroleum announced plans for the construction of the world's largest gas to liquids (GTL) plant, Pearl GTL in Qatar.  The plant, a joint development by Qatar Petroleum and Shell, will process about three billion barrels-of-oil-equivalent over its lifetime from the world’s largest single non-associated gas field, the North Field, which stretches from Qatar’s coast out into the Gulf.  The North Field contains more than 900 trillion cubic feet of gas, about 15% of worldwide gas resources. Upon completion, the plant is projected to produce 140,000 barrels of GTL diesel per day, more than tripling the current production level of GTL diesel.  Therefore, it suffices to state that the completion of this plant could serve to drastically alter the previously grim future of GTL diesel.[7]

Coal-to-Liquids

Coal-to-liquids is a term describing processes for converting coal into liquid fuels such as gasoline and diesel.  Currently, the major coal-to-liquids production process is the Fischer-Tropsch process, involving conversion of coal into gas and then into liquids.  Several processes that convert coal directly into liquids (direct liquefaction) also exist.  Coal-to-liquids processes have the potential to produce a range of useful fuels and chemicals.  These include transportation fuels such as gasoline, diesel, and methanol.  Producing liquid transportation fuels from coal using the Fischer-Tropsch process has been demonstrated on a large scale.[8]

The following are potential benefits of coal-to-liquids fuels:

·           The location and quantity of U.S. coal reserves are known and mapped.  Therefore, exploration is not necessary.

·           They are compatible with the current petroleum distribution infrastructure and would not require new or modified pipelines, storage tanks, or retail station pumps.

·           Tests indicate coal-to-liquids Fischer-Tropsch (F-T) diesel provides similar or better vehicle performance than conventional diesel.[9]

Biomass-to-Liquids

Biomass to liquids is a term describing processes for converting diverse biomass feedstocks into a range of liquid fuels.  These processes are usually distinguished from enzymatic/fermentation processes and processes that use only part of a biomass feedstock, such as those typically used to produce ethanol, biobutanol, and biodiesel.

Like other biomass-derived fuels, biomass-to-liquids fuels can be produced domestically from a variety of homegrown feedstocks while creating U.S. jobs.  Greenhouse gas emissions are reduced because carbon dioxide captured when the feedstock crops are grown balances carbon dioxide released when the fuels are burned.  Additional potential benefits of biomass-to-liquids fuels include:

·           Biomass-derived gasoline and diesel fuels can be used directly in today's gasoline and diesel powered vehicles.

·           Biomass-derived gasoline and diesel fuels are compatible with the current gasoline and diesel distribution infrastructure and would not require new or modified pipelines, storage tanks, or retail station pumps.

·           Tests indicate gas-to-liquids fuels provide similar or better vehicle performance than their conventional counterparts.

·           Gas-to-liquids fuels have been shown to reduce regulated exhaust emissions from a variety of diesel engines and vehicles, and the near-zero sulfur content of these fuels can enable the use of advanced emission control devices.[10]



[1] U.S. Department of Energy, xLT Fuels, http://www.afdc.energy.gov/fuels/emerging_xtl_fuels.html, (May 23, 2013).

[2] Southwest Research Institute, AIChe, Emissions Performance of Fischer-Tropsch Diesel Fuels, March 1997.  Document Date: (July 5, 2000).

[3] Paul Norton, Keith Vertin, and Brent Bailey (National Renewable Energy Lab), Nigel N. Clark and Donald W. Lyons (West Virginia University), Stephen Goguen and James Eberhardt (US Department of Energy), “Emissions from Trucks using Fischer-Tropsch Diesel Fuel.”  SAE Technical Paper Series (982526).  International Fall Fuels and Lubricants Meeting and Exposition, San Francisco, California, October 19-22, 1998.  www.osti.gov/fcvt/982526.pdf.

[4] The EIA projections are based on previous consumption trends as well as other major indicators such as oil prices.  This is why the EIA makes three projections: low oil price projection, reference oil price projection, and a high oil price projection.  This aallows the EIA to account for unexpected fluctuations in the petroleum market. 

[5] U.S. Energy Information Administration  Annual Energy Outlook 2010, Table 11. Liquid Fuel Supply and Deposition (High World Oil Price).   ( http://www.eia.doe.gov/oiaf/aeo/aeohighprice.html), (May 23, 2013).

[6] National Petroleum Council – Global Oil and Gas Study, Topic Paper #9: Gas to Liquids.  (http://www.npc.org/Study_Topic_Papers/9-STG-Gas-to-Liquids-GTL.pdf, (May 23, 2013).

[8] Höök, M., Aleklett, K., 2009. A review on coal to liquid fuels and its coal consumption, International Journal of Energy Research, (April 17, 2013).

[9] National Mining Association, Liquid Fuels from U.S. Coal, http://www.nma.org/pdf/liquid_coal_fuels_100505.pdf, (May 23, 2013).

[10] Princeton Environmental Institute, Fischer-Tropsch Fuels from Coal and Biomass, http://web.mit.edu/mitei/docs/reports/kreutz-fischer-tropsch.pdf, (May 23, 2013).