NEW TECHNICAL CHALLENGES AND RECENT ADVANCES IN HYDROTREATMENT CATALYSIS - A CRITICAL UPDATING REVIEW

The petroleum industry gets confronted with more stringent requirements with respect to transportation fuels: diminution by a factor of 10, or more, of the sulphur content, and a drastic diminution of the aromatic content. Besides, the quality of the crude oil supply keeps diminishing on an average. For this, the hydrotreating processes (HDS, HDN, HDM, hydrogenation, hydrocracking) will occupy a still increasing place in the refining processes. In a first part, we shall select some of the most important results published recently: use of new modifiers and supports (TiO2, ZrO2, mixed oxides), of metals not yet used in hydrotreating (Ru, Rh, Pd, Pt, possibly Nb, associations RuU, PdU, VU etc.), confirmation of the existence of distinct catalytic sites (hydrogenation and hydrogenolysis of the heteroatom-carbon bonds). Other new results should contribute to clarify the controversies and uncertainties concerning the origin of synergy between different elements and the changes of selectivity as a function of the experimental conditions. For this last topic, reference shall be made to the CoMoS model and the remote control theory. In a second part, we shall summarise the new constraints that the hydrotreating processes will face. It will be necessary to save still more energy. It will also be necessary to achieve a better balance of the various reactions taking place in a given process. The overall selectivity of catalysts and processes will have to be improved. In the third part, we shall try to emphasize directions of research which could help reach the objectives. We shall shortly outline the future contributions of chemical engineering. We shall examine with more details the problems concerning the genesis of adequate catalytic sites (underlining the enormous influence of the activation steps) and the modification of activity by means of the composition of the reacting medium. As the problem of synergy remains crucial for the future developments, we shall also present results with new synergetic systems (WS2 + supported Rh or Pd; MoS2 + supported Pt). The new results give hope that the mechanisms of synergy could get clarified in the near future.