Hydrogenation without simultaneous cracking is used for saturating olefins or for converting aromatics to naphthenes. Under atmospheric pressure, olefins can be hydrogenated up to about 500 1C, but beyond this temperature hydrogenation commences. It has become the most common process in modern petroleum refineries. Bio-crude may also be processed by a conventional refinery and potentially augmented with petroleum crude. The oxygen in bio-oils can be removed via hydrotreating. The catalysts commonly used for hydrotreating are sulphide CoMo/Al2O3,NiMo/Al2O3 systems