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Energy & Fuels 2004, 18, 682-684
Thermally Stable Blends of Fischer Tropsch and LCO Diesel Fuel Components Dennis J. O’Rear,* John D. Bacha,† and Andrea N. Tiedemann ChevronTexaco Energy Research and Technology Company, 100 Chevron Way, Richmond, California 94802-0627 Received October 14, 2003. Revised Manuscript Received February 19, 2004
Due to their excellent cetane numbers and low sulfur content, Fischer Tropsch derived diesel fuels will likely be blended with poorer quality stocks in order to incorporate them into specification fuels. However, the blending of Fischer Tropsch diesel fuels with highly aromatic stocks, such as LCO, can create unstable products. This paper explores the magnitude of this problem and identifies several solutions.
Introduction While several aspects of fuel stability are potentially important (long-term storage, peroxide formation,1 etc.), the formation of insoluble particulate matter during high temperature use with limited air exposure is potentially the greatest concern with blends of Fischer Tropsch diesel fuels. This aspect of thermal stability can be readily evaluated by ASTM D6468. ASTM D6468 describes the test procedure, but does not set limits. In setting limits, it is important to consider the entire path from producer to consumer. The fuel must not form deposits in the diesel engine, in the service station, in the regional storage tanks, or during transfer.2 From commercial practice, a fuel should have a reflectance value of at least 65% as measured by ASTM D6468 where the test is conducted at 150 °C for 90 min when measured at the refinery gate. Higher reflectance values are of course preferred, and a high reflectance value at 180 min is also preferred. Tests at 180 min are felt to be more reflective of the real environment encountered by diesel fuel. The formation of insoluble particulate matter appears to be related to three factors: the concentration of species that are readily oxidizable,3 the ability of the blend to keep oxidized products dissolved, and the conditions of the oxidation, such as, temperature, time, moisture, and the presence of oxidation promoters or inhibitors.4 Blends of Fischer Tropsch and LCO diesel fuel components represent an extreme situation not hitherto encountered with conventional fuels, but one likely to be encountered soon when these fuels become more commonplace. * Corresponding author. E-mail:
[email protected]. † Deceased August 20, 2001. (1) Vardi et al. Peroxide Formation in Low Sulfur Automotive Diesel Fuels, SAE Paper 920826, International Congress & Exposition, Detroit, MI, February 24-28, 1992. (2) Bacha, J. D.; Tiedemann, A. N. DIESEL FUEL AND INSTABILITY: A SIMPLE CONCEPTUAL MODEL, IASH 2000, the 7th International Conference on Stability and Handling of Liquid Fuels, Graz, Austria, September 24-29, 2000; pp 1-7. (3) Pedley et al. Storage Stability of Petroleum-Derived Diesel Fuel. Fuel 1989, 68, 27-31. (4) Technical Review Diesel Fuels, Chevron Products Company, Copyright 1998; pp 29-30. Available at http://www.chevron.com/ prodserv/fuels/bulletin/diesel/.
Table 1. Properties of Fuel Blend Components description sulfur, ppm group types by mass spec, LV% paraffins cycloparaffins aromatics and sulfur types thermal stability, ASTM D6468 at 150 °C @ 90 min @ 180 min
Fischer Tropsch
LAD
LCO
