Synthesis of zeolites of faujasite structure

Details Synthesis of zeolites of faujasite structure Synthesis of zeolites of faujasite structure

1990-06-08

1992-03-24

Breneman, R. Bruce

Chemistry of inorganic compounds

Phosphorus or compound thereof

Oxygen containing

423329, 502 79, C01B 3334

Patent

active

050986864

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a process for the synthesis of zeolites belonging to the faujasite structural group. It further relates to the products obtained and to their application in adsorption and catalysis.


DESCRIPTION OF THE RELATED ART

Zeolites are crystalline tectosilicates. The structures consist of assemblies of TO.sub.4 tetrahedra forming a three-dimensional skeleton by sharing oxygen atoms. In zeolites of the aluminosilicate type which are the most common ones, T denotes tetravalent silicon and trivalent aluminium. The abovementioned three-dimensional skeleton exhibits cavities and channels which have molecular dimensions and accommodate cations compensating the charge deficiency linked with the presence of trivalent aluminium in the TO.sub.4 tetrahedra, the said cations being generally exchangeable.
As a general rule, the composition of zeolites may be denoted by the empirical formula (M.sub.2 /.sub.n O; Y.sub.2 O.sub.3 ; x ZO.sub.2) in the dehydrated and calcined state. In this formula Z and Y denote the tetravalent and trivalent elements of the TO.sub.4 tetrahedra respectively, M denotes an electropositive element of valency n, such as an alkali or alkaline-earth metal and constitutes the compensating cation, and x is a number which can vary from 2 to theoretically infinity, in which case the zeolite is a silica.
Each type of zeolite has a distinct microporous structure. The variation in the dimensions and shapes of the micropores from one type to another results in changes in the adsorbent properties. Only molecules which have certain dimensions and shapes are capable of entering the pores of a particular zeolite.
Because of these remarkable characteristics, zeolites are very particularly suitable for the purification or separation of gaseous or liquid mixtures, such as, for example, the separation of hydrocarbons by selective adsorption.
The chemical composition, including in particular the nature of the elements present in the TO.sub.4 tetrahedra and the nature of the exchangeable compensating cations, is also an important factor involved in the selectivity of the adsorption, and above all in the catalytic properties of these products. They are employed as catalysts or catalyst supports in the cracking, reforming and modification of hydrocarbons, and in the conversion of many molecules.
Many zeolites exist in nature; they are aluminosilicates whose availabilities and properties do not always correspond to the requirements of industrial applications. Consequently, the search for products which have new properties has led to the synthesis of a large variety of zeolites, essentially of the aluminosilicate type. Among the many examples of this type there may be mentioned zeolite A (U.S. Pat. No. 2,882,243), zeolite X (U.S. Pat. No. 2,882,244), zeolite Y (U.S. Pat. No. 3,130,007), zeolite L (FR-A-1,224,154), zeolite T (FR-A-1,223,775), zeolite ZSM5 (U.S. Pat. No. 3,702,886), zeolite ZSM 12 (U.S. Pat. No. 3,832,449) and zeolite ZSM 48 (EP-A-0,015,132).
Zeolites of the faujasite structural group are characterized by a three-dimensional framework structure which can be described by means of the assembly of modules called cube-octahedra. Each of these modules consist of 24 tetrahedra containing the elements Si and Al and bridged by oxygen according to the principle described above. In the cube-octahedron the tetrahedra are linked so as to form eight rings containing six tetrahedra and six rings containing four tetrahedra. Each cube-octahedron is joined with tetrahedral coordination, via four rings containing six tetrahedra, to four neighbouring cube-octahedra.
To show the relationships which unite the various members of the structural group it is convenient to consider the structural planes in which the cube-octahedra are arranged at the vertices of a plane network of hexagons. Each cube-octahedron is thus connected to three neighbours in the structural plane.
The fourth connecting direction is directed alternately on each side of the structural plane and enables the cu

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patent: 3306922 (1967-02-01), Barrer et al.
patent: 4377502 (1983-03-01), Klotz
patent: 4714601 (1987-12-01), Vaughan

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