HYDROCONVERSION OF HYDROCARBONS

A process for improving the activity and reducing the ageing rate of a catalyst which has become partially deactivated in a process for the hydrocracking of a hydrocarbon charge stock comprises bringing the catalyst into contact under hydrocracking conditions with a hydrocarbon charge stock of reduced polycyclic aromatic content (e.g. containing less than 11% by wt.) as compared with the original charge stock. Suitable hydrocracking catalysts comprise a hydrogenating component such as a Group VIII metal or metal compound, e.g. Ni alone or in conjunction with compounds of molybdenum or tungsten, supported on a cracking component such as Al2O3, MgO, SiO2, or mixtures thereof or a zeolitic alumino-silicate having pore openings of 6-14 rA. Suitable hydrocracking conditions include a temperature of 450-775 DEG F., a pressure of 500-10,000 p.s.i.g. a hydrogen rate of 1000-20,000 SCFB, and a space velocity of liquid charge of 0.1 to 10 vols per vol. of catalyst per hour. When the hydrocarbon charge stock contains more than 20 p.p.m. nitrogen it should be first subjected to a catalytic denitrogenation. If the hydrocracking catalyst is not sensitive to ammonia, the entire effluent from the denitrogenation zone may be sent directly to the hydrocracking zone, but if not, the hydrogen may be subjected to a basic nitrogen removal treatment, e.g. by washing with dilute acid and stripping with an inert gas before being fed to the hydrocracking zone.