Abstract.

Diesel engine emissions are sensitive to fuel quality. Characteristics such as sulfur and aromatic content, density and cetane number are known to be the most important parameters.

Catalytic hydrotreatment allows the refiner to adjust these characteristics to variable levels. The hydrotreatment feed stocks consist of various middle-distillates differing by crude origin, distillation curve, initial processing (SR, LCO, coking.. .). Knowledge of their reactivity and the development of new high performance catalysts make possible the selection of optimal operating conditions to reach the required quality in attractive economical conditions.

Examples of hydrotreatment of some diesel cuts leading to sulfur reduction (100 to 500 ppm) as well as aromatic reduction (5 to 15%) are shown.

The resulting products were tested in a light-duty diesel engine under various operating conditions (steadystate and transient). The relationship between emissions and fuel quality is complex and also depends on the engine operating conditions. However, we show the hydrotreatment severity to exert a beneficial influence on CO, HC, particulate and PAH emissions.

Diesel engine emissions are sensitive to fuel properties. Characteristics such as sulfur and aromatic content, density and cetane number are known to be the most important parameters. For the sulfur, the limitation to a 500 ppm level will be the nearly worldwide rule in the near future. For the aromatics, extensive studies are in progress in order to define the future regulations; at the present time, aromatic content specification is in the range 5–25 vol% and concerns only limited areas.

The catalytic hydrotreatment process allows the refiner to adjust these characteristics to variable levels. It is relatively easy to desulfurize the diesel cuts up to very low level; the aromatic content is not much affected. But it is much more difficult to reduce the aromatic content, particularly for highly aromatic feedstocks; the corresponding sulfur content of the products is very low. In both cases, knowledge of the reactivity of various feedstocks to hydrotreatment and the availability of high performance catalysts are required to make these challenges industrially feasible.

The hydrotreating unit feedstocks consist of various middle-distillates which can be differentiated by their crude origin, their initial processing (straight run, LCO, coking.. .) and their distillation curve.

Knowledge of their reactivity is mainly obtained thanks to an extensive hydrotreatment pilot test program with various feedstocks, catalysts, and operating conditions. The obtained correlations allow a determination of the main operating conditions of the industrial unit (catalyst volume, hyd

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