The United States Department of Defense (DoD) has been interested in low-sulfur, environmentally cleaner Fischer-Tropsch (FT) fuels since 2001 because they want to be less dependent upon foreign crude oil and ensure the security of the supply. A three-phase Joint Battlefield-Use Fuel of the Future (BUFF) program was initiated to evaluate, demonstrate, certify, and implement turbine fuels produced from alternative energy resources for use in all of its gas turbine and diesel engine applications. Sasol Synfuels International (Pty) Ltd. and Sasol Chevron Holdings Ltd., among others, were invited to participate in the program with the objective to supply the DoD with a FT BUFF that conforms to Jet Propulsion 8 (JP-8) and JP-5 fuel volatility and lowtemperature fluidity requirements. Although the DoD is more interested in coal-to-liquid (CTL) technology, the product from a gas-to-liquid (GTL) Products Work-Up Demonstration Unit in Sasolburg, South Africa, was used to evaluate (on a bench scale) the possibility of producing a BUFF fraction from the Sasol Slurry Phase Distillate (Sasol SPD) low-temperature FT (LTFT) process and Chevron Isocracking technology. It was concluded from the study that the production of a synthetic FT BUFF is feasible using the Sasol SPD LTFT technology together with the current Chevron isocracking technology. The product yield for a BUFF conforming to JP-8 requirements is 30 vol % of the fractionator feed, whereas the product yield for a BUFF conforming to the JP-5 volatility requirement is slightly less than 22 vol % of the fractionator feed. Also concluded from the study was that the end point of the Sasol SPD LTFT BUFF will be restricted by the freezing point requirement of the DoD and not the maximum viscosity requirement. One would therefore need to optimize the hydrocracking process conditions to increase the Sasol SPD LTFT BUFF product yield.

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Fischer−Tropsch Synthetic Crude is high in olefinicity and needs further hydroprocessing to conform to fuel specifications such as oxidation stability. Different catalysts, that is, sulfided NiMo/Al2O3, CoMo/Al2O3, and unsulfided Ni/Al2O3, have been used, and a kinetic model has been derived for the hydrogenation of Fischer−Tropsch Synthetic Crude. The kinetic model allows for predicting process conditions necessary to meet mandatory fuel specifications and market requirements as well as to compare the catalytic activity of these different hydrogenation catalysts on the basis of the kinetic parameters.

The highly paraffinic related fuel properties such as high H:C ratio, high cetane number, and low density together with the virtually zero-sulfur and very low aromatics content of low-temperature Fischer-Tropsch (LTFT) derived synthetic diesel contribute to its clean combustion performance. The low density and low aromatic content however results in LTFT diesel having a lower volumetric heating value than conventional diesel and elastomer compatibility concerns where the diesel is to be used in a mixed fuel scenario. Blending LTFT diesel with another synthetic derived fuel with similar, good fuel properties, but which contains monoaromatics, such as the coal derived high-temperature Fischer-Tropsch (HTFT) diesel, could unlock potential performance synergies in the fuel properties of such blends. The Fischer-Tropsch (FT) diesel blends have an ultralow sulfur content, high cetane number, and good cold flow properties and are stable under specified storage and oxidizing conditions. With the presence of about 25% mono-aromatics in HTFT diesel, the shrinking nature of swollen elastomer seals typically found in diesel fuel injection systems is less when exposed to the FT blend than when exposed to neat LTFT diesel. The HTFT diesel improves the volumetric heating value and fuel economy of the LTFT diesel in such an FT blend with comparable particular matter and hydrocarbon exhaust emissions. Although the blend with HTFT diesel increases the volumetric heating value, it decreases the specific heating value (mass basis). These alternative diesel fuel blends therefore provide future fuel characteristics that are compatible with current infrastructure and technology.

It has been shown that hydroisomerization of an olefinic feed to an iso-paraffinic product can be performed in a single reactor using a platinum on mordenite (Pt-MOR) zeolite catalyst. This conversion finds application in a Fischer-Tropsch refinery where the syncrude is rich in olefins and conventional hydroisomerization would require hydrogenation of the feed as a feed pretreatment step. In order to demonstrate that the proposed process configuration is viable from a catalysis point of view, the hydroisomerization of 1-pentene over Pt-MOR has been investigated experimentally in the range 200 -270 C, 2 MPa, WHSV 1-3 h À1 , and H 2 :1-pentene molar ratio of 3:1-5:1. The catalyst was stable during one week of continuous operation. The highest iso-pentane yield (69%) was obtained at 250 C. Side reactions (dimerization and cracking) increased with increasing temperature, decreasing H 2 :1-pentene ratio, and increasing space velocity.