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Energy & Fuels 2009, 23, 38–45
Hydroprocessing Euro 4-Type Diesel from High-Temperature Fischer-Tropsch Vacuum Gas Oils Dieter Leckel* Fischer-Tropsch Refinery Catalysis, Sasol Technology Research and DeVelopment, Post Office Box 1, Sasolburg 1947, South Africa ReceiVed July 30, 2008. ReVised Manuscript ReceiVed October 1, 2008
Various configurations were studied to hydroprocess high-temperature Fischer-Tropsch (HTFT) vacuum gas oils to diesel fuel in compliance with EN590/Euro 4 fuel specifications. Conventional hydroprocessing generates a distillate not conforming to the fuel specifications; however, addition of an isomerization function and extra hydrotreating capacity markedly improved density and cold-flow properties. Hydrocracking the heavy part of the HTFT vacuum gas oil proved to be a viable alternative to generate a HTFT diesel with higher density and good cold-flow properties. Complementary blending studies confirmed that Euro 4 diesel fuel specifications are achievable by blending isomerized hydrotreated HTFT light distillate with HTFT heavy distillates and coal-pyrolysis-derived distillate fractions.
Introduction There are two main classes of commercial Fischer-Tropsch technology, namely, low-temperature Fischer-Trospch (LTFT) and high-temperature Fischer-Tropsch (HTFT). The HTFT process operates at temperatures of 310-340 °C and is used primarily for the production of liquid fuels, such as petrol and diesel.1 Olefins are extracted as major byproducts. The ironbased HTFT synthesis is conducted industrially in Sasol Synthol and Sasol Advanced Synthol reactors and produces a SchulzFlory carbon number distribution with high selectivity toward lighter hydrocarbon material. The HTFT syncrude typically consists of 60% material, not exceeding a boiling point of 150 °C and with only ca. 5.0% of residual material boiling above 360 °C. The distillate (C10-C22) and the residue fractions make up about 10% of the total products from Fischer-Tropsch synthesis. The products are mainly linear, with 40% being present as isoalkanes.2 The HTFT syncrude is highly olefinic (predominantly R-olefins) and rich in oxygenates, such as alcohols, aldehydes, ketones, and acids.3 Aromatics are present in percentage levels (about 15%) consisting typically of monoaromatics, such as alkylated benzenes, tetralin, and indan. Because all sulfur compounds are removed upstream of the FT reactors, the FT primary synthesis products are essentially sulfurfree. Nitrogen is only present at negligible parts per million levels. A HTFT synfuels refinery just like a crude oil refinery has to meet the challenge of today’s fuel specifications.4-6The main diesel specification drivers are sulfur, cetane, polynuclear aromatics (PNAs), density and boiling point reduction, in particular, the 95% distillation American Society for Testing and Materials (ASTM) D86 recovery (T95). This often requires * To whom correspondence should be addressed. Telephone: +27-16960-3830. Fax: +27-11-522-3975. E-mail:
[email protected]. (1) Jager, B. Natural gas conversion studies IV. Stud. Surf. Sci. Catal. 1997, 107, 219. (2) Dry, M. E.; Hoogendoorn, J. C. Catal. ReV.sSci. Eng. 1981, 23 (1 and 2), 265–278. (3) Dry, M. E. In Applied Industrial Catalysis; Leech, B. E., Ed.; Academic Press: New York, 1983; Vol. 2, pp 167-213.
Table 1. Comparison of HTFT Syncrude and Crude Oil Composition10 component
HTFT syncrude
crude oil
paraffins naphthenes olefins aromatics oxygenates sulfur nitrogen organometallics water
>10%
