Kombinert fremgangsmate for forbedret hydrogenbehandling av dieseldrivstoffer

Described herein is a combined process for improved hydrotreating of diesel fuels, in which the feed to be hydrotreated is pretreated with a selective adsorbent prior to the hydrotreating step to remove polar materials, especially nitrogen containing compounds (N-compounds). By removing the N-compounds in this way, it is possible to achieve extremely high conversions of refractory sulphur compounds in the diesel fuel at moderate hydroprocessing conditions. If the diesel fuel is hydrotreated without prior removal of N-compounds, excessive amounts of hydrotreating catalysts must be used and high temperatures and pressures must be employed. This is particularly true when sulphur levels of below 500 ppm are desired. The selective adsorption process can employ either liquid or solid adsorbents, and may be operated in a variety of modes, including stirred tanks, hydroclones, moving beds, fixed beds, ebulated beds or fluidized beds. In operations, where the adsorbent and diesel fuel are both moving through the reaction adsorption zone, the flows can be either cocurrent or countercurrent. After contact of the adsorbent with the diesel fuel feed, the adsorbent containing undesired polar compounds is separated from the diesel fuel and the inhibitor free fuel is processed in conventional equipment. The separated adsorbent is then subjected to a two step procedure for regeneration. First any physically adsorbed inhibitor free fuel is recovered. For example, if a solid adsorbent is employed, the solid containing physically adsorbed diesel fuel is contacted with a stripper gas such as steam to strip off the inhibitor free fuel, while leaving the polar compounds strongly adsorbed on the solid adsorbent. The polar compounds may then be removed either by an oxygenative or hydrogenative process. A schematic representation of this combined process is shown in Fig. 1.