Hydrotreatment of Oil Fractions For The Production of Low-Sulfur Diesel

Abstract

Abstract In Europe there is a continuous increase in the demand for diesel fuel. Also, regulations to reduce tail pipe emissions to the atmosphere impose new and more stringent specifications; for diesel transportation fuel, main pressure being on the reduction of sulphur and polyaromatic concentration, reduction of density and decrease of final boiling point. For example, maximum sulphur level allowed now is 350 ppm, with reductions to levels of around 50 ppm foreseen in the short term. Further reductions (even to less than 10 ppm) are also on the horizon. Hydrotreatment (HDT), as a variety of processes, is the main tool available to the refinery industry to improve diesel quality. This paper deals with the reach of hydrotreatment (HDT) technologies to adapt diesel fuel to the new regulations. The discussion is centred on three aspects: feed processability, process conditions and catalysts employed. Feed processability is studied in terms of how some feed properties such as sulphur content and specific gravity have an effect on the HDS conversion. Correlations are shown that explain the effect of such variables. Main process conditions such as space velocity and hydrogen partial pressure are studied, and their effect on the product sulphur level is shown. Typical CoMo and NiMo hydrotreatment catalysts are compared upon on the perspective of actual and future specifications. Changes in product properties occurring during hydrotreatment (aromatic content, cetane index and specific gravity) are also shown. This comprehensive study of the HDT process allows us to estimate hydrotreatment requirements to adapt our refineries to future specifications of the diesel fuel.