Preparation of a porous composite material based on EU-1 zeolite and its implementation in the isomerization of C8 aromatics

#The present invention relates to the field of the preparation of a porous composite material comprising EU-1 zeolite crystals on its external surface and the application of said material for the isomerization of C8 aromatic compounds. More precisely, the preparation of said material according to the invention uses the conversion to EU-1 zeolite of an amorphous and porous structure composed of one or more inorganic oxide(s). This conversion is carried out during a hydrothermal treatment carried out in the presence of a determined quantity of an external aqueous phase.

#The EU-1 zeolite, of EUO structural type, is described in the prior art (W. M. Meier and D. H. Olson, “Atlas of Zeolite Structure types”, 5th Edition, 2001) and has a mono-dimensional microporous network, the diameter of the pores of which is 4.1×5.4 Å (1 Å=1 Angström=1×10−10 m). N. A. Briscoe et al have taught that these mono-dimensional channels have side pockets with a depth of 8.1 Å and a diameter of 6.8×5.8 Å (Zeolites, 8, 74, 1988).

#European patent application EP-A-0,042,226 describes the EU-1 zeolite with the following formula: at least 10 XO2:Y2O3:0.5-1.5R2/nO:0-100H2O where R represents a cation of valency n, X represents silicon and/or germanium, Y represents at least one element chosen from aluminium, iron, gallium, boron. It also describes the process for the preparation of said EU-1 zeolite, which comprises the mixing in aqueous medium of at least one source of an element X, at least one source of an element Y and a nitrogen-containing organic compound that acts as a structuring agent Q, which is either the alkylated derivative of a α-ω diammonium polymethylene, or a degradation product of said derivative, or also precursors of said derivative. The reaction mixture is then placed under autogenous pressure, at a temperature comprised between 85 and 250° C., until zeolite crystals form. The product obtained is recovered by filtration, washed, dried, calcined in order to remove the organic structuring agent and optionally subjected to ion exchanges in order to obtain the acid form of the EU-1 zeolite. It is known to use the acid form of the EU-1 zeolite prepared in this way in a process for the isomerization of C8 aromatic compounds. The EU-1 zeolite, prepared by the standard process described in European patent application EP-A-0,042,226, is obtained in the form of a powder and requires forming with a binder before being used as a catalyst. A hydrogenating metal is then deposited on the zeolite or/and on the binder. For example, U.S. Pat. No. 6,057,486 describes a catalyst for the isomerization of C8 aromatic compounds and having 1 to 90% by weight of EU-1 zeolite mixed in a homogeneous manner with an inorganic binder, for example alumina, and having 0.01 to 20% by weight of at least one element of group VIII of the periodic table of the elements.

#A subject of the present invention is a process for the preparation of a porous composite material formed from an amorphous core based on at least one silicon oxide on which EU-1 zeolite crystals are dispersed, said process comprising at least the following stages: 1) impregnation of a solid comprising at least one silicon oxide and at least one aluminium oxide with at least one aqueous solution comprising at least one quaternary diammonium cation of formula [R1R2R3—N—(CH2)n—N—R4R5R6]2+, n being comprised between 3 and 12, R1 to R6, equal or different, are alkyl or hydroxyalkyl groups with 1 to 8 carbon atoms, and up to 5 of the R1 to R6 groups can be hydrogen atoms, 2) the hydrothermal treatment, implemented in an autoclave of volume V (ml) under steam and at a temperature T comprised between 120 and 220° C., of said solid from stage 1), the quantity of water introduced beforehand into said autoclave being strictly greater than a volumetric quantity equal to V*[23.48*10−10*T3−48*10−8*T2+5*10−5*T−0.002] and less than or equal to 0.25*V, and is such that said solid is not in direct contact with it, 3) the drying then calcination of the solid from stage 2) so as to obtain said porous composite material.

#In accordance with the invention, the material prepared by the process of the invention is a porous composite material formed from an amorphous core based on at least one silicon oxide on which EU-1 zeolite crystals are dispersed. Said material thus obtained is in the main macroporous. It has wider pores and a pore volume at least 30% less than the pore volume of the solid comprising at least one silicon oxide and at least one aluminium oxide used for the implementation of said stage 1) of the process of the invention. The amorphous core of said material is formed from silicon oxide or from a mixture of silicon oxide and aluminium oxide, preferably, it is entirely constituted by silicon oxide. Crystals and agglomerates of crystals of EU-1 zeolite are dispersed on the external surface of said core without a continuous and crystallized layer of EU-1 zeolite entirely covering said surface. Said material is characterized by transmission electron microscopy (TEM) and by scanning electron microscopy (SEM). Said porous composite material prepared according to the process of the invention can be in different macroscopic forms, for example in the form of extrudates or beads, preferably in the form of extrudates. In accordance with the invention, said porous composite material is in the same macroscopic form as that of the solid comprising at least one silicon oxide and at least one aluminium oxide used for the implementation of said stage 1) of the process of the invention.

#The solid comprising at least one silicon oxide and at least one aluminium oxide used for the implementation of stage 1) of the process for the preparation of the material according to the invention is for example an amorphous silica-alumina having an overall SiO2/Al2O3 molar ratio of at least 10 and preferably comprised between 10 and 150. Said silica-alumina can be in different macroscopic forms, for example extrudates, beads or any other form known to a person skilled in the art. The average size of said silica-alumina can vary between 0.1 and 5 mm and preferably between 0.5 and 3 mm. It has an ordered or random porous system, comprising meso- and/or macropores, i.e. with an average pore diameter greater than 2 nm and a pore volume comprised between 0.01 and 2 ml·g−1 and preferably between 0.1 and 1.5 ml·g−1. In accordance with the invention, said porous composite material is in the same macroscopic form as that of the silica-alumina.