Chemistry of inorganic compounds – Zeolite – Organic compound used to form zeolite
Reexamination Certificate
1999-12-23
2003-02-04
Sample, David (Department: 1755)
Chemistry of inorganic compounds
Zeolite
Organic compound used to form zeolite
C423S709000, C423S716000, C423S717000, C423S708000, C502S060000, C502S066000, C502S073000, C502S074000, C585S481000
Reexamination Certificate
active
06514479
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a zeolite with structure type EUO, characterized in that it is in the form of aggregates of zeolite crystals with a specific granulometry. The invention also relates to the use of the zeolite as a catalyst, more particularly as a catalyst for isomerising aromatic compounds containing 8 carbon atoms also known as “C8 aromatic cuts”.
Zeolites with structure type EUO include EU-1, TPZ-3 and ZSM-50 zeolites. Such zeolites generally comprise at least one element X selected from silicon and germanium and at least one element T selected from the group formed by aluminium, iron, gallium, boron, titanium, vanadium, zirconium, molybdenum, arsenic, antimony, chromium and manganese, preferably aluminium, gallium, iron and boron, the overall atomic ratio X/T being 5 or more.
Isomerisation of ethylbenzene to xylenes or of a mixture of xylenes and ethylbenzene requires the presence of an acidic function and a group VIII metal. The main aim of isomerising C8 aromatic cuts is to produce para-xylene. Thus the discovery of novel catalysts which are active in converting a mixture of xylenes and ethylbenzene and which are selective, i.e., for which side reactions are minimised, is important. Such side reactions, which constitute substantial losses for the reaction, result from naphthene ring opening followed or otherwise by cracking or from dismutation and transalkylation reactions of C8 aromatics which lead to the formation of undesirable aromatic compounds.
PRIOR ART
United States patents U.S. Pat. No. 4,723,051 and U.S. Pat. No. 4,665,258 describe optimised formulations based on mordenite zeolites and a group VIII metal which result in catalysts with which side reactions remain non negligible.
French patent applications FR 97/16456 and FR 97/16458 describe a catalyst based on EUO zeolite characterized by good dispersion and good distribution of the group VIII metal and by good mechanical strength and its use in isomerising C8 aromatic compounds. That catalyst leads to a relatively good selectivity, but the activity, in particular for ethylbenzene conversion, is still to be improved.
EU-1 zeolite with structure type EUO, described in European patent EP-B1-0 42 226, has a unidimensional microporous framework, with a pore diameter of 4.1×5.7 Å (1 Å=1 Angström=10
−10
m) (“Atlas of Zeolite Structure Types”, W. M. Meier and D. H. Olson, 4
th
edition, 1996). Further, N. A. Briscoe et al. stated in their article in the review Zeolites (1988, 8, 74) that such unidimensional channels have lateral pockets with a depth of 8.1 Å and a diameter of 6.8×5.8 Å. The crystallite size, also termed EU-1 zeolite crystals, is in the range 1 to 3 microns and the aggregate size is in the range 425 to 1000 microns.
U.S. Pat. No. 4,640,829 concerns a ZSM-50 zeolite which according to the “Atlas of Zeolite Structure Types”, W. M. Meier and D. H. Olson, 4
th
Edition, 1996, has the same EUO structure type as EU-1 zeolite. That patent describes a mode of synthesising ZSM-50 comprising mixing a source of alkali metal ions, dibenzyldimethylammonium ions, silicon oxide, water and aluminium oxide.
EP-A-0 051 318 relates to TPZ-3 zeolite which, according to the “Atlas of Zeolite Structure Types”, W. M. Meier and D. H. Olson, 4
th
edition, 1996, has the same EUO structure type as EU-1 zeolite. That patent describes the use of TPZ-3 zeolite as a catalyst, for example for isomerising C8 aromatic compounds.
SUMMARY OF THE INVENTION
The present invention concerns a zeolite with structure type EUO comprising EUO zeolite crystals with a size of less than 5 &mgr;m, at least a portion of the EUO zeolite crystals being in the form of EUO zeolite aggregates, characterized in that the granulometry of the aggregates is such that Dv,90 is less than or equal to 500 &mgr;m. More particularly, the invention concerns EU-1 zeolite with structure type EUO.
IMPORTANCE OF THE INVENTION
EUO zeolite, for example EU-1 zeolite as defined in the present invention, used as a catalyst in association with at least one binder, at least one metal selected from elements from group VIII of the periodic table, said metal preferably being deposited on the binder, has improved catalytic performances for hydrocarbon transformation in terms of activity, such as isomerisation of C8 aromatic cuts, i.e., of mixtures constituted by xylenes and possibly ethylbenzene.
DESCRIPTION
The crystals and crystal aggregates of the zeolite with structure type EUO of the invention must have specific characteristics in terms of size. The zeolite with structure type EUO of the invention can be EU-1 zeolite, TPZ-3 zeolite or ZSM-50 zeolite. The term “aggregate” as used in the present description means an ensemble formed by at least two crystals of zeolite having at least one contact point between them.
The aggregate size is determined by laser diffraction granulometry. This measurement is carried out on powdered zeolite suspended in water. After a first measurement, the suspension is subjected to ultrasounds for thirty seconds then another measurement is carried out. The ultrasound used is characterized by a power of 50 W and a frequency of 50 kHz. This procedure is repeated until the result no longer changes (to ±5%). The size distribution of the aggregates defined by volume is calculated form the light signals collected by the detectors and using Fraunhofer theory. Dv,X is defined as the diameter of the equivalent sphere such that X% by volume of the aggregates have a diameter less than said diameter, after ultrasound. These characteristics are obtained directly during zeolite synthesis and/or by any method which can reduce the aggregate size, such as post-synthesis grinding or appropriate milling before forming.
The zeolite with structure type EUO of the invention contains at least one element X selected from silicon and germanium and at least one element T selected from the group formed by aluminium, iron, gallium, boron, titanium, vanadium, zirconium, molybdenum, arsenic, antimony, chromium and manganese, preferably aluminium, gallium, iron and boron, the overall atomic ratio X/T being 5 or more. The zeolite is characterized in that the zeolite crystal size must be less than 5 &mgr;m, preferably less than 0.5 &mgr;m and more preferably less than 0.2 &mgr;m, limits included, at least a part of the zeolite crystals being arranged in the form of aggregates, said crystal aggregates having a granulometry such that the value Dv,90 is 500 &mgr;m or less; Dv,90 is preferably 400 &mgr;m or less; more preferably Dv,90 is 200 &mgr;m or less; and still more preferably Dv,90 is 50 &mgr;m or less.
In a first method for preparing the EUO zeolite of the invention, the zeolite crystal and crystal aggregate size can be controlled during synthesis and depend on the crystallisation processes as a whole which are controlled by the synthesis parameters. These parameters include supersaturation (reactant concentration), pH (alkalinity), ionic strength (salt addition), solid seed addition, the temperature profile and the mixing and stirring characteristics.
The zeolite with structure type EUO of the invention is obtained, for example, using a synthesis method comprising reacting an aqueous mixture with at least one source of at least one element X selected from silicon and germanium, at least one source of at least one element T selected from aluminium, iron, gallium, boron, titanium, vanadium, zirconium, molybdenum, arsenic, antimony, chromium and manganese, at least one nitrogen-containing organic compound Q selected from alkylated polymethylene &agr;-&ohgr; diammonium salt derivatives, an amine degradation product of the derivative, precursors of the derivative, a dibenzyldimethylammonium salt and precursors of that salt. The mixture is reacted until the zeolite crystallises. The alkylated polymethylene &agr;-&ohgr; diammonium salt derivative, used in particular for synthesising the EU-1 zeolite, is defined by the formula: R
1
R
2
R
3
N
+
(CH
2
)
n
N
+
R
4
R
5
R
6
, n being in
Alario Fabio
Ferrer Nathalie
Lacombe Sylvie
Magne-Drisch Julia
Martin Olivia
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Sample David
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