Can Fischer−Tropsch Syncrude Be Refined to On-Specification Diesel Fuel?

Abstract

The interchangeable colloquial use of the terms “distillate” (boiling range) and “diesel fuel” (distillate meeting legislated fuel specifications), led to misleading perceptions about the suitability of Fischer−Tropsch syncrude for diesel fuel production. Two questions are addressed: Can Fischer−Tropsch syncrude be refined to diesel fuel, and which Fischer−Tropsch technology is best for maximizing distillate and ultimately diesel fuel production? The distillate yield that can be obtained from Fischer−Tropsch syncrude in an uncomplicated refinery employing only hydrocracking and/or oligomerization follows the order: Fe-LTFT > Co-LTFT > Fe-HTFT. Conversely, producing diesel fuel (not distillate) from Fe-HTFT syncrude is easier. On a molecular level, Fischer−Tropsch syncrude was found to be unsuitable for the production of EN 590:2004 diesel fuel in high yield. There is a trade-off between distillate density, cetane number, and yield, which is called the Fischer−Tropsch density−cetane−yield triangle. It is possible to meet any two of these three requirements without too much refining effort, but meeting all three with Fischer−Tropsch syncrude as feed material, is difficult. Strategies have been suggested to overcome the Fischer−Tropsch density−cetane−yield triangle and to improve the yield of on-specification diesel fuel. Some industrial implications for the standalone Fischer−Tropsch-based production of diesel fuel are discussed. High-temperature Fischer−Tropsch (HTFT) and low-temperature Fischer−Tropsch (LTFT) fuels refinery designs based on current refining technology to maximize EN 590:2004 diesel fuel are provided.