Catalytic cracking of metal contaminated mineral oil fractions

In a process for catalytic cracking of a metal-containing hydrocarbon charge by contacting the charge at cracking temperature with a particle form solid cracking catalyst whereby components of the charge are converted to lower boiling hydrocarbons with concurrent deposition on the catalyst of metals from the charge and of an inactivating carbonaceous contaminant, regenerating catalytic cracking activity of the contaminated catalyst by burning carbonaceous deposit therefrom while retaining metals deposited on the catalyst, and contacting catalyst so regenerated with additional such charge, whereby the catalyst accumulates metal to detriment of the cracking reaction and declines in regenerated activity over repeated cycles of charge contact and regeneration;

• the average activity and metals content of the catalyst inventory being maintained at substantially constant equilibrium values by replacing a portion of the catalyst inventory with fresh catalyst of activity above and metals content below said equilibrium values;
• the improvement whereby said equilibrium values of activity and metals content are decoupled which comprises replacing a portion of said catalyst as aforesaid by adding part of such replacement as catalyst of activity above and metals content below said equilibrium values and the remainder as inert porous solid particles of metals content below said equilibrium value and physical characteristics like that of said catalyst and varying the ratio between fresh catalyst and inert particles for separate control of said equilibrium value.