Process for fluid catalytic cracking of hydrocarbon feedstocks with high levels of basic nitrogen

Abstract

A process is described for fluid catalytic cracking of hydrocarbons with high levels of basic nitrogen, where hydrocarbon feedstocks A and B with different levels of basic nitrogen are injected in a segregated fashion, into different risers of a multiple riser FCCU that possesses at least two risers. The injection of the feedstocks is made in such a way that feedstock A, to be injected in the riser with greater volume—main riser 7—possessing a level of basic nitrogen at least 200 ppm lower than the level of feedstock B to be injected into the riser with lower volume—secondary riser (8).

Description

[0001] This application is a continuation of U.S. application Ser. No. 10 / 689,662, filed Oct. 22, 2003, the entire content of which is incorporated by reference in this application.FIELD OF THE INVENTION [0002] The present invention relates to a process for fluid catalytic cracking (FCC) of hydrocarbon feedstocks with high levels of basic nitrogen in FCC units (FCCU) provided with multiple conversion zones (risers). More specifically, the invention relates to a process for fluid catalytic cracking of hydrocarbon feedstocks with different levels of basic nitrogen, which uses a segregating route of said hydrocarbon feedstocks that are fed into different risers in the multiple risers FCCU. BACKGROUND OF THE INVENTION [0003] There have been ever increasing oil discoveries in Brazil that contain high concentrations of basic nitrogenous compounds, be they aromatic or polyaromatic, that may or may not be branched, with predominantly heterocyclic chemical structures, that are concentrated i...

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Benefits of technology

[0052] d) recover cracked reaction products with an increase in bottom conversion, a greater proportion of gasoline and LPG, at the same time reducing the proportion of coke and combustible gas.

[0053] Therefore, the invention provides the possibility of processing, simultaneously, in different risers in the same FCCU with multiple risers, segregated feedstocks of hydrocarbons, with different levels of basic nitrogen.

[0054] The invention still provides for the catalytic cracking processing of segregated feedstocks of hydrocarbons with different levels of basic nitrogen, which affords an optimization in the conversion selectivity rates of cracking.

[0055] The invention still provides for the catalytic cracking processing of segregated feedstocks of hydrocarbons with different levels of basic nitrogen where the production of coke and combustible gas is minimized, while the production of gasoline and LPG is maximized, resulting in a better economy of the FCC process.

[0056] The invention also provides for a process that will allow for more operational flexibility, once the reaction temperature may be altered in each riser and the thermal balance modified, increasing the CTO in both risers.

Problems solved by technology

Basic nitrogenous compounds, when present in fluid catalytic cracking processing, feedstocks tend to promote deactivation of the catalyst acid sites and to increase the level of coke deposits on the catalyst, with the subsequent loss of product conversion and selectivity in the process.

A lower production of these last two products, besides expediting an increase in the production of gasoline and LPG, by increasing the process selectivity towards these derivatives, provides as a result the additional benefit of lower air blower and wet gas compressor use (machines with a high deadweight and large power consumption), which in turn usually cause a limitation of the FCCU capacity.

If this rapid vaporization is not achieved, thermal cracking will result of the feedstock's liquid fractions.

It is well known that thermal cracking leads to the formation of by-products such as coke and combustible gas, mainly in residual feedstock cracking.

Coke, in addition to its low commercial value, obstructs the pores of the catalyst.

Therefore, thermal cracking in the bed of the riser competes in an undesirable fashion with catalytic cracking, which is the purpose of the process.

However, the lower catalyst circulation rate demanded by the great difference in temperature between the regenerator and the reactor, which results in a decrease in the catalyst / oil ratio, which in turn lowers the conversion.

However, (for the indicated reasons), very elevated temperatures are undesirable in the regeneration operation.

However, fluidized bed reactors with an elevated L / D ratio are expensive, difficult to build and maintain because they must have very large and heavy separating tanks in the top, containing, in their interior, equally heavy equipment, that are targeted at capturing and controlling the catalyst flow and the products in the reactor.

The increase in participation of domestic petroleum, originating from the oil fields of Campos Basin, on the coast of the State of Rio de Janeiro, presents some technical problems regarding the refining of hydrocarbon feedstocks derived from these oils, especially when the presence of basic organic nitrogenous compounds compromises the performance of the catalysts used in the fluid catalytic cracking (FCC) process, the major supplier of gasoline, diesel and liquefied petroleum gas (LPG) for domestic consumption.

In summary, all this represents a loss of capacity in the catalytic cracking unit with consequent great financial damage to the refinery.

However, when basic nitrogenous compounds are made up of aromatic or polyaromatic compounds that are of a higher molecular weight, as is the case with the basic nitrogenous compounds present, for example, in CGOs, the deposit of the molecules of these basic nitrogenous compounds onto the surface of the catalyst particles is irreversible because it neutralizes the acid centers and reduces the specific area of the catalyst, that loses activity and selectivity.

This is not, therefore, a good solution for fluid catalytic cracking units that process heavy feedstocks of hydrocarbons with these basic nitrogen characteristics.

It should be emphasized that, industrially speaking, this procedure is an extremely complicated job, due to the fact that the patent description suggests alternating feeds in intervals or cycles of between 20 seconds and 2 minutes to achieve an increase in conversion.

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