Fischer-Tropsch fuel production process

Apart from the oxygenate refining performed by the COD process, the oxygenates in the Fischer-Tropsch aqueous product are refined to alcohols. These alcohols are recovered and may be blended with the transportation fuels or sold as chemicals. 

The production of methanol from synthesis gas is a well-established process (23, 102), and there have been predictions that methanol itself could become the fuel of the future (103). Whether or not this prediction will prove correct is debatable4 meanwhile, Mobil suggests that coupling known methanol production technology with their new process provides an economically attractive alternative to both Fischer-Tropsch fuels and direct utilization of methanol (104). 

The present plants are geared predominantly at the production of gasoline and diesel fuel but a significant fraction of chemicals are also produced in both the coal gasification and in the Fischer-Tropsch (FT) synthesis process. The latter process can be manipulated to increase the production of chemicals, should this be desired. For fuller detail of the production of fuels, the reader is referred to other reviews (1)(2). 

The U.S. currently imports about sixty (60) percent of its oil requirements (7), which is expected to increase to about 70 percent by the year 2025 (7). This reliance on foreign sources of oil has created both national and economic security issues for the U.S. It is desirable to produce liquid transportation fuels from alternative sources. The Fischer-Tropsch (F-T) process can be used to produce liquid fuels from synthesis gas (syngas), a mixture of hydrogen and carbon monoxide. Liquid fuels produced from die F-T process have very low levels of sulfur compared to petroleum products these ultra-clean fuels are environmentally friendly. However, syngas is commonly produced from natural gas, which has become significantly more expensive in recent years (2). Alternative, less expensive feedstocks for syngas production can reduce the costs of liquid fuels produced through the F-T process. 

One of the ways in which natural gas could be converted to liquid products is by Fischer-Tropsch synthesis. In this process, methane is reformed with steam and oxygen to produce a synthesis gas that is a mixture of carbon monoxide and hydrogen. The synthesis gas is then reacted over a catalyst to produce a variety of fuels. However, recently the most emphasis has been on the production of high-cetane, sulfur-free diesel fuel. Fischer-Tropsch fuels can be produced at the equivalent of 14 to 20 a barrel of oil, and plants with capacities of 10 to 100,000 barrels a day have either been built or designed.1... 

Hydrogen is used in a large number of chemical processes, and may be used as a fuel itself or as a reactant in the production of synthetic fuels such as in the Fischer-Tropsch hydrocarbon synthesis process, for example. In applications where hydrogen purification is required, membranes can be used for hydrogen separation. Other hydrogen purification methods include pressure swing adsorption and cryogenic separation. 

Several reviews have appeared on the role of carbon monoxide and metal carbonyl complexes in the commercial production of fuels and chemicals, with emphasis on Fischer-Tropsch-type hydrogenation processes. " ... 

The production of liquid fuels—gasoline and diesel—from coal is not a new process. The first patent was registered in 1913, with the more common Fischer-Tropsch indirect liquefaction process patented in 1925. 

Fischer-Tropsch fuels are those made artificially using the FT process. Basically a fuel such as biomass, or even natural gas, is steam reformed using the methods described in Chapter 8. The product hydrogen and carbon dioxide are then reacted, over catalysts developed by Fischer and Tropsch, to produce liquid fuels such as octane, C9H20, C10H22, etc. 

Zhou, Z, Zhang, Y., Tierney, J.W., Wender, I., 2003. Hybrid zirconia catalysts for conversion of Fischer—Tropsch waxy products to transportation fuels. Fuel Processing Technology 83,... 

Secunda discharges no process water effluents. AU. water streams produced are cleaned and reused in the plant. The methane and light hydrocarbons in the product are reformed with steam to generate synthesis gas for recycle (14). Even at this large scale, the cost of producing fuels and chemicals by the Fischer-Tropsch process is dominated by the cost of synthesis gas production. Sasol has estimated that gas production accounts for 58% of total production costs (39). 

A number of chemical products are derived from Sasol s synthetic fuel operations based on the Fischer-Tropsch synthesis including paraffin waxes from the Arge process and several polar and nonpolar hydrocarbon mixtures from the Synthol process. Products suitable for use as hot melt adhesives, PVC lubricants, cormgated cardboard coating emulsions, and poHshes have been developed from Arge waxes. Wax blends containing medium and hard wax fractions are useful for making candles, and over 20,000 t/yr of wax are sold for this appHcation. 

Natural Gas Upgrading via Fischer-Tropsch. In the United States, as in other countries, scarcities from World War II revived interest in the synthesis of fuel substances. A study of the economics of Fischer synthesis led to the conclusion that the large-scale production of gasoline from natural gas offered hope for commercial utiHty. In the Hydrocol process (Hydrocarbon Research, Inc.) natural gas was treated with high purity oxygen to produce the synthesis gas which was converted in fluidized beds of kon catalysts (42). 

Development of SASOL. Over 70% of South Africa s needs for transportation fuels are being suppHed by iadirect Hquefaction of coal. The medium pressure Fischer-Tropsch process was put iato operation at Sasolburgh, South Africa ia 1955 (47). An overall flow schematic for SASOL I is shown ia Figure 12. The product slate from this faciUty is amazingly complex. Materials ranging from hydrocarbons through oxygenates, alcohols, and acids are all produced. 

Shell Gas B.V. has constructed a 1987 mVd (12,500 bbhd) Fischer-Tropsch plant in Malaysia, start-up occurring in 1994. The Shell Middle Distillate Synthesis (SMDS) process, as it is called, uses natural gas as the feedstock to fixed-bed reactors containing cobalt-based cat- yst. The heavy hydrocarbons from the Fischer-Tropsch reactors are converted to distillate fuels by hydrocracking and hydroisomerization. The quality of the products is very high, the diesel fuel having a cetane number in excess of 75. 

During the late seventies and early eighties, when oil prices rose after the 1973 war, extensive research was done to change coal to liquid hydrocarbons. However, coal-derived hydrocarbons were more expensive than crude oils. Another way to use coal is through gasification to a fuel gas mixture of CO and H2 (medium Btu gas). This gas mixture could be used as a fuel or as a synthesis gas mixture for the production of fuels and chemicals via a Fischer Tropsch synthesis route. This process is... 

The use of a Fischer-Tropsch (FT) process to produce long-chain hydrocarbons is well known in industry, and achieving the desired selectivity from the FT reaction is crucial for the process to make economic sense. It is, however, well known that a one-alpha model does not describe the product spectrum well. From either a chemicals or fuels perspective, hydrocarbon selectivity in the FT process needs to be thoroughly understood in order to manipulate process conditions and allow the optimization of the required product yield to maximize the plant profitability. There are many unanswered questions regarding the selectivity of the iron-based low-temperature Fischer-Tropsch (Fe-LTFT) synthesis. 

Short-chain olefins are not refined and the gaseous LTFT products are employed as fuel gas. Production of this fraction is limited by Co-LTFT synthesis, and with the product being less olefinic than iron-based Fischer-Tropsch syncrude, less benefit would be derived from the inclusion of an olefin oligomerization unit. Furthermore, adding complexity would go against the design objectives of the SMDS process. 

LTFT syncrude is more difficult to refine to on-specification transportation fuels, but has become almost synonymous with distillate production from Fischer-Tropsch-based GTL conversion. In this application the SMDS process has been the trailblazer. However, there are two potential misconceptions that should be pointed out. First, Fischer-Tropsch distillate produced from LTFT syncrude is... 

---