Fluid coking with the addition of polymetaphosphoric acid catalysts

In a fluid coking process comprising the steps of:

• contacting a carbonaceous chargestock with hot fluidized solids in a fluidized bed contained in a coking zone maintained in a fluidized state by the introduction of a fluidizing gas and operated at coking conditions, to produce a vapor phase product and a solid carbonaceous material which deposits on said fluidized solids, the improvement which comprises the presence, in said coking zone, of an effective amount of a phosphorus-containing component selected from the group consisting of polymetaphosphoric acids, salts of polymetaphosphoric acids, precursors of said acids and of said salts, and mixtures thereof.