Fluidized-bed catalytic cracking process for a hydrocarbon feedstock, particularly a feedstock with a high content of basic nitrogen compounds

DETAILED DESCRIPTION The present invention overcomes the drawbacks of the prior art by the surprisingly simple expedient of using a downflow FCC process with a cracking catalyst that is resistant to basic nitrogen compounds.
A purpose of said process is to make possible the cracking of hydrocarbon feedstocks containing more than 350 ppm by weight of basic nitrogen under favorable conditions.
The nitrogen content may even be as high as 1300 ppm by weight or higher.
Another purpose of the invention is to suppress or limit the reactor wall effects in such a process and the back-mixing of catalyst particles.
Applicants have discovered that such an advantageous result can be attained by the conjoint use of a reactor wherein the feedstock to be treated and the fluidized catalyst bed move co-currently from the top to the bottom of the reactor in a manner which in itself is known; particles of a catalyst which under equilibrium conditions at 150.
degree.
C.
and at a pressure of 5 mbar adsorbs less than 250 micromols of pyridine/g and preferably less than 50 micromols of pyridine/g and whose pyridine retention does not exceed 20% after heating at 350.
degree.
C.
under vacuum.
Thus, the invention has as a preferred embodiment a fluidized-bed catalytic cracking process for a hydrocarbon feedstock, particularly a feedstock with a high content of basic nitrogen compounds, in a tubular reaction zone, said process comprising: a step of feeding at least partly regenerated catalyst particles from the top of the reaction zone; a step of introducing and atomizing the feedstock to be treated at the top of the reaction zone, below the catalyst feeding zone; a step of circulating the catalyst and the feedstock to be treated in mutual contact in the reaction zone under suitable conditions to cause cracking of the feedstock; a step of separating the deactivated catalyst from the products of the cracking reaction at the bottom of the reaction zone; a step of stripping the deactivated catalyst; a step of regenerating at least part of the stripped, deactivated catalyst in a regeneration zone; a step of recycling the regenerated catalyst to the top of the reaction zone, and a step of transferring the products of the hydrocarbon feedstock cracking toward a separation zone for said products, said process being characterized by the fact that the feedstock and the catalyst circulate co-currently from the top to the bottom of the tubular zone and that under equilibrium conditions at 150