Process for the conversion of hydrocarbons to olefins
A method for converting hydrocarbons in a hydrocarbon stream includes contacting the hydrocarbon stream with steam and a catalyst system under steam enhanced catalytic cracking conditions to produce an effluent comprising olefins. The catalyst system includes a framework-substituted pentasil zeolite. The framework-substituted pentasil zeolite has a modified pentasil framework. The modified pentasil framework includes a pentasil aluminosilicate framework in which a portion of framework aluminum atoms of the pentasil aluminosilicate framework are substituted with Ce atoms and Fe atoms. At least a portion of the Fe atoms are monomeric.
1 . A method for converting hydrocarbons in a hydrocarbon stream, the method comprising contacting the hydrocarbon stream with steam and a catalyst system under steam enhanced catalytic cracking conditions to produce an effluent comprising olefins, where:
the catalyst system comprises a framework-substituted pentasil zeolite comprising from 0.2 to 1.0 wt. % Ce atoms and from 0.2 to 0.5 wt. % Fe atoms, as calculated on an oxide basis, based on the total mass of the framework-substituted pentasil zeolite;
the framework-substituted pentasil zeolite has a modified pentasil framework, the modified pentasil framework comprising a pentasil aluminosilicate framework in which a portion of framework aluminum atoms of the pentasil aluminosilicate framework are substituted with Ce atoms and Fe atoms using solid state ion exchange;
at least 80 mol. % of the Fe atoms are monomeric; and
the steam enhanced catalytic cracking conditions comprise:
a steam to hydrocarbon ratio of from 0.2 to 0.8;
a reaction temperature from 450° C. to 750° C.;
a reaction pressure from 1 bar to 5 bar; and
a residence time from 0.5 seconds to 1000 seconds.
2 . The method of claim 1 , where at least a portion of the Ce atoms are monomeric.
3 . The method of claim 1 , where a ratio of Ce atoms to Fe atoms is from 1:5 to 3:5.
4 . The method of claim 1 , where the framework-substituted pentasil zeolite has:
(a) a specific surface area of 200 m 2 /g to 600 m 2 /g;
(b) a molar ratio of SiO 2 to Al 2 0 3 from 10 to 200; and
(c) a pore volume from 0.1 cm 3 /g to 0.6 cm 3 /g.
5 . The method of claim 1 , where at least 80 mol. % of the Ce atoms are monomeric.
6 . The method of claim 5 , where at least 99 mol. % of the Ce atoms are monomeric.
7 . The method of claim 1 , where at least 99 mol. % of the Fe atoms are monomeric.
8 . The method of claim 1 , where the framework aluminum atoms are simultaneously substituted for Ce and Fe atoms using solid state ion exchange.
9 . The method of claim 1 , where the catalyst system comprises particles with a particle size of from 150 m to 200 m.
10 . The method of claim 1 , where the hydrocarbon stream comprises crude oil.
11 . The method of claim 1 , where the framework-substituted pentasil zeolite is prepared by a method comprising:
combining a pentasil aluminosilicate framework with an iron precursor and a cerium precursor, thereby forming a first mixture; and
calcining the first mixture, thereby forming the framework-substituted pentasil zeolite.
12 . The method of claim 11 , where calcining the first mixture comprises exposing the first mixture to air at a temperature of at least 500 for at least 1 hr.
13 . The method of claim 11 , where the first mixture is a dry mixture.
14 . The method of claim 1 , where the effluent comprises at least 46 wt. % of light olefins.
15 . The method of claim 1 , wherein the framework-substitution atoms of the pentasil zeolite consist of Fe atoms and Ce atoms.