Method and process for converting the ethylene present in the overhead effluent from a FCC in a manner such as to increase the propylene production

A process for fractionating a gaseous fraction discharged from the head of a fractionation column of a catalytic cracking unit, the gaseous fraction containing liquefied petroleum gas (LPG), gasoline, and a residual gas termed “fuel gas” which itself contains a certain quantity of ethylene, comprising the following steps:

• separating the gaseous fraction into a fuel gas (15) and a liquid fraction containing gasoline and LPG (10) in a first absorption section (6),
• separating said liquid fraction (10) into gasoline and LPG in a first debutanizer section (11),
• introducing said fuel gas (15) into a catalytic conversion unit (22) containing a zeolite catalyst, wherein ethylene contained in said fuel gas (15) is converted into propylene and aromatics, in the presence of said zeolite catalyst,
• removing effluents from the catalytic conversion unit (22) and, after recompression, introducing said effluents into a first absorption section (31) wherein propylene, butene and gasoline fractions contained in said effluents are recovered in said first absorption section (31) by using an absorbent, wherein said absorbent is gasoline obtained from said first debutanization section (11),
• introducing a gas stream (33) obtained from said first absorption section (31) into a second absorption section (16), and
• introducing propylene, butene and gasoline fractions (34) recovered in said first absorption section (31) into a second debutanizer section (35) wherein a stabilized gasoline (36) and an LPG fraction (37) are produced.