Fischer-Tropsch process

The Fischer-Tropsch process is a catalyzed chemical reaction in which carbon monoxide and hydrogen are converted into liquid hydrocarbons of various forms. Typical catalysts used are based on iron and cobalt. The principal purpose of this process is to produce a synthetic petroleum substitute, typically from coal or natural gas, for use as synthetic lubrication oil or as synthetic fuel.

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Original process

The original Fischer-Tropsch process is described by the following chemical equation (where 'n' is a positive integer):

(2n+1)H₂ + nCO → C_nH_(2n+2) + nH₂O

The initial reactants in the above reaction (i.e. CO and H₂) can be produced by other reactions such as the partial combustion of a hydrocarbon:

C_nH_(2n+2) + ½ nO₂ → (n+1)H₂ + nCO

for example (when n=1), methane (in the case of gas to liquids applications):

2CH₄ + O₂ → 4H₂ + 2CO

or by the gasification of coal or biomass:

C + H₂O → H₂ + CO

The energy needed for this endothermic reaction of coal or biomass and steam is usually provided by (exothermic) combustion with air or oxygen. This leads to the following reaction:

2C + O₂ → 2CO

The mixture of carbon monoxide and hydrogen is called synthesis gas or syngas. The resulting hydrocarbon products are refined to produce the desired synthetic fuel.

The carbon dioxide and carbon monoxide is generated by partial oxidation of coal and wood-based fuels. The utility of the process is primarily in its role in producing fluid hydrocarbons from a solid feedstock, such as coal or solid carbon-containing wastes of various types. Non-oxidative pyrolysis of the solid material produces syngas which can be used directly as a fuel without being taken through Fischer-Tropsch transformations. If liquid petroleum-like fuel, lubricant, or wax is required, the Fischer-Tropsch process can be applied.

History

Since the invention of the original process by the German researchers Franz Fischer and Hans Tropsch, working at the Kaiser Wilhelm Institute in the 1920s, many refinements and adjustments have been made, and the term "Fischer-Tropsch" now applies to a wide variety of similar processes (Fischer-Tropsch synthesis or Fischer-Tropsch chemistry)

The process was invented in petroleum-poor but coal-rich Germany in the 1920s, to produce liquid fuels. It was used by Germany and Japan during World War II to produce ersatz fuels. Germany's annual synthetic fuel production reached more than 124,000 barrels per day from 25 plants ~ 6.5 million tons in 1944.^[1]

After the war, captured German scientists recruited in Operation Paperclip continued to work on synthetic fuels in the United States in a United States Bureau of Mines program initiated by the Synthetic Liquid Fuels Act.

Utilization

    Currently, only a handful of companies have commercialised their FT technology.

1. Shell in Bintulu, Malaysia, uses natural gas as a feedstock, and produces primarily low-sulfur diesel fuels and food-grade wax.
2. Sasol in South Africa uses coal and natural gas as a feedstock, and produces a variety of synthetic petroleum products. Sasol produces most of the country's diesel fuel.

The process was used in South Africa to meet its energy needs during its isolation under Apartheid. This process has received renewed attention in the quest to produce low-sulfur diesel fuel in order to minimize the environmental impact from the use of diesel engines.

A small US-based company, Rentech, is currently focusing on converting nitrogen-fertiliser plants from using a natural gas feedstock to using coal or coke, and producing liquid hydrocarbons as a by-product.

Also Choren Industries has built a FT plant in Germany. ^[2][3]

The FT process is an established technology and already applied on a large scale, although its popularity is hampered by high capital costs, high operation and maintenance costs, and the uncertain and volatile price of crude oil. In particular, the use of natural gas as a feedstock only becomes practical when using "stranded gas", i.e. sources of natural gas far from major cities which are impractical to exploit with conventional gas pipelines and LNG technology; otherwise, the direct sale of natural gas to consumers would become much more profitable. There are several companies developing the process to enable practical exploitation of so-called stranded gas reserves. It is expected by geologists that supplies of natural gas will peak 5-15 years after oil does, although such predictions are difficult to make and often highly uncertain.

There are large coal reserves which may increasingly be used as a fuel source during oil depletion. Since there are large coal reserves in the world, this technology could be used as an interim transportation fuel if conventional oil were to become more expensive. Combination of biomass gasification (BG) and Fischer-Tropsch (FT) synthesis is a very promising route to produce renewable or ‘green’ transportation fuels.

In Sept. 2005, Pennsylvania governor Edward Rendell announced a venture with Waste Management and Processors Inc. - using technology licensed from Shell and Sasol - to build an FT plant that will convert so-called waste coal (leftovers from the mining process) into low-sulfur diesel fuel at a site outside of Mahanoy City, northwest of Philadelphia.^[4] The state of Pennsylvania has committed to buy a significant percentage of the plant's output and, together with the U.S. Dept. of Energy, has offered over $140 million in tax incentives. Other coal-producing states are exploring similar plans. Governor Brian Schweitzer of Montana has proposed developing a plant that would use the FT process to turn his state's coal reserves into fuel in order to help alleviate the United States' dependence on foreign oil. ^[5]

In Oct. 2006, Finnish paper and pulp manufacturer UPM announced its plans to produce biodiesel by Fischer-Tropsch process alongside the manufacturing processes at its European paper and pulp plants, using waste biomass resulted by paper and pulp manufacturing processes as source material. ^[6]

In August 2007, Louisiana State University announced they had received funding from the US Department of Energy and Conoco Phillips for development of new nanotechnologies for catalysis of coal syngas to ethanol conversion.^[7]

U.S. Air Force certification

Syntroleum, a publicly traded US company (Nasdaq: SYNM) has produced over 400,000 gallons of diesel and jet fuel from the Fischer-Tropsch process at its demonstration plant near Tulsa, Oklahoma. Syntroleum is working to commercialize its proprietary Fischer-Tropsch technology via coal-to-liquid plants in the US, China, and Germany, as well as gas-to-liquid plants internationally. Using natural gas as a feedstock, the ultra-clean, low sulfur fuel has been tested extensively by the US Department of Energy, the Department of Transportation, and most recently, Syntroleum has been working with the U. S. Air Force to develop a synthetic jet fuel blend that will help the Air Force to reduce its dependence on imported petroleum. The Air Force, which is the U.S. military's largest user of fuel, began exploring alternative fuel sources in 1999. On December 15, 2006, a B-52 took off from Edwards AFB, CA for the first time powered solely by a 50-50 blend of JP-8 and Syntroleum's FT fuel. The seven-hour flight test was considered a success. The goal of the flight test program is to qualify the fuel blend for fleet use on the service's B-52s, and then flight test and qualification on other aircraft.^[8]

On August 8 2007, Air Force Secretary Michael Wynne certified the B-52H as fully approved to use the FT blend, marking the formal conclusion of the test program.^[9]

This program is part of the Department of Defense Assured Fuel Initiative, an effort to develop secure domestic sources for the military energy needs. The Pentagon hopes to reduce its use of crude oil from foreign producers and obtain about half of its aviation fuel from alternative sources by 2016.^[8] With the B-52 now approved to use the FT blend, the USAF will use the test protocols developed during the program to certify the C-17 Globemaster III and then the B-1B to use the fuel. The Air Force intends to test and certify every airframe in its inventory to use the fuel by 2011.^[9]

C-17 Fischer-Tropsch fuel demonstration testing was completed on October 22 2007 at Edwards AFB. Testing consisted of a ground test and two flights which demonstrated engine performance throughout the C-17 flight envelope and during some operationally representative maneuvers. Test data is still being reviewed by the 418th FLTS to validate the subjective results of the test. On December 17, 2007, A C-17 Globemaster III using the synthetic fuel blend lifted off shortly before dawn at McChord Air Force Base, Wash., and arrived in the early afternoon at McGuire AFB, N.J., where it was greeted by Secretary of the Air Force Michael W. Wynne, New Jersey Rep. Jim Saxton, and a number of officials from both the airline and energy industries. Based on the two successful tests, the Air Force hopes to certify all of its C-17 fleet for the synthetic fuel mixture.^{[citation needed]}

Environmental concerns

One issue that has yet to be addressed in the emerging discussion about large-scale development of synthetic fuels is the increase in primary energy use and carbon emissions inherent in conversion of gaseous and solid carbon sources to a usable liquid form, assuming the energy used to drive the process comes from burning coal or hydrocarbon fuels. Recent work by the National Renewable Energy Laboratory indicates that full fuel cycle greenhouse gas emissions for coal-based synfuels are nearly twice as high as their petroleum-based equivalent. Emissions of other pollutants are vastly increased as well, although many of these emissions can be captured during production. Emerging Carbon sequestration technologies have been suggested as a future mitigation strategy for greenhouse gas emissions.

However, biomass gasification technology may offer a less carbon-intensive alternative. Biomass-powered synthetic fuel plants may become technologically and economically-convincing energy possibilities for a carbon-neutral economy^[10] in the future, although there are currently problems in scaling up the process to commercial volumes^[11]

Hybrid hydrogen-carbon processes have also been proposed recently^[12] as another closed-carbon cycle alternative, combining 'clean' electricity, recycled CO, H₂ and captured CO₂ with biomass as inputs as a way of reducing the biomass needed.

See also

• Abiogenic petroleum origin
• Bergius process
• Biomass to liquid
• Future energy development
• Hubbert peak
• Karrick process
• Non-conventional oil
• Synthetic Liquid Fuels Program
• Thomas Gold
• Wood gas

References