Process for preparing a zeolite with structure type MTT...

Details Process for preparing a zeolite with structure type MTT... Process for preparing a zeolite with structure type MTT...

2000-09-29

2002-11-05

Sample, David (Department: 1755)

Chemistry of inorganic compounds

Zeolite

Organic compound used to form zeolite

C423S709000, C423SDIG003, C585S654000

Reexamination Certificate

active

06475464

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a novel process for preparing zeolites with structure type MTT. This zeolite generally has the following formula in the anhydrous form: 0 to 20 R
2
O: 0-10 T
2
O
3
: 100XO
2
where R represents a monovalent cation or 1
of a cation with valency n, X represents silicon and/or germanium, T represents at least one element selected from aluminium, iron, gallium, boron, titanium, vanadium, zirconium, molybdenum, arsenic, antimony, chromium and manganese.
Zeolites with structure type MTT such as ZSM-23 zeolite are generally synthesised by mixing, in an aqueous medium, at least one source of silica and/or germanium and at least one source of at least one element selected from aluminium, iron, gallium, boron, titanium, vanadium, zirconium, molybdenum, arsenic, antimony, chromium and manganese in the presence of an organic nitrogen-containing compound acting as a template, or precursors of the organic compound. The mixture is generally maintained at a certain temperature until the zeolite crystallises.
PRIOR ART
ZSM-23 zeolite with structure type MTT, which has already been described in the prior art, has a unidimensional microporous framework, with a pore diameter of 4.5×5.2 Å (1 Å=1 Angström=1×10
−10
m) (“Atlas of Zeolite Structure Types”, W. M. Meier and D. H. Olson, 4
th
edition, 1996). Further, A. C. Rohmann et al (Zeolites, 5, 352, 1985), J. L. Schenker et al (private communication, 1992) and B. Marler et al (J. Appl. Cryst. 26; 636, 1993) have stated that the crystalline lattice has orthorhombic symmetry (Pmn2
1
, a=21.5 Å, b=11.1 Å, c=5.0 Å) with channels parallel to axis c, delimited by rings of 10 tetrahedra. The synthesis mode and physico-chemical characteristics of ZSM-23 zeolite have been described in a variety of patents which differ in the nature of the organic template used. That zeolite can be synthesised using at least one organic template selected from pyrrolidine (U.S. Pat. No. 4,076,842), diisopropanolamine (British patent GB-A-2 190 910), quaternary ammonium compounds such as heptamethonium bromide (U.S. Pat. No. 4,490,342), octamethonium bromide (GB-A-2 202 838), dodecamethonium bromide (U.S. Pat. No. 5,405,596) and quaternary triammonium compounds (U.S. Pat. No. 5,332,566). The mode of synthesis comprises mixing an oxide, generally a silicon oxide, and an oxide, generally an aluminium oxide, in the presence of the template.
Other zeolites have structure type MTT and differ from ZSM-23 zeolite in the mode of preparation, in particular in the organic template used. These are EU-13 zeolite (European patent EP-A-0 108 486), using a quaternary methylated ammonium or phosphonium salt, ISI-4 zeolite (EP-A-0 102 497) using ethylene glycol or a monoethanolamine, SSZ-32 zeolite (U.S. Pat. No. 4,483,835) using imidazole derivatives or KZ-1 zeolite using a variety of amines (L. M. Parker et al., Zeolites, 3, 8, 1988).
SUMMARY OF THE INVENTION
The present invention concerns a process for preparing a zeolite with structure type MTT comprising at least one element X selected from silicon and germanium and at least one element T selected from iron, aluminium, gallium, boron, titanium, vanadium, zirconium, molybdenum, arsenic, antimony, chromium and manganese, characterized in that seeds of at least one zeolitic material comprising at least one element X′ selected from silicon and germanium and at least one element T′ selected from iron, aluminium, gallium, boron, titanium, vanadium, zirconium, molybdenum, arsenic, antimony, chromium and manganese is used, said seeds being different from the zeolite with structure type MTT which is prepared.
IMPORTANCE OF THE INVENTION
The process of the invention can reduce the crystallisation time of the MTT zeolite after forming the mixture, to achieve a maximum yield of pure product, which reduces the costs. The reaction medium composition can have a wider range, which increases flexibility.
Thus, the Applicant has discovered that synthesis of a zeolite with structure type MTT characterized by using seeds of at least one zeolitic material different from the material to be synthesised can achieve the advantages cited above, i.e., an advantage as regards time, pure product yield and flexibility in reaction mixture composition.
DESCRIPTION OF THE INVENTION
The invention concerns a process for preparing a zeolitic material with structure type MTT comprising at least one element X selected from silicon and germanium and at least one element T selected from iron, aluminium, gallium, boron, titanium, vanadium, zirconium, molybdenum, arsenic, antimony, chromium and manganese, characterized in that seeds of at least one zeolitic material comprising at least one element X′ selected from silicon and germanium and at least one element T′ selected from iron, aluminium, gallium, boron, titanium, vanadium, zirconium, molybdenum, arsenic, antimony, chromium and manganese is used, said seeds being different from the zeolite with structure type MTT which is prepared.
The difference between the zeolite with structure type MTT which is to be synthesised and the zeolitic material introduced as seeds lies either in the difference in structure type, or in the difference in chemical composition of the crystalline framework, or in the difference in structure type and the difference in chemical composition of the crystalline framework.
The preparation process of the invention comprises mixing, in an aqueous medium, 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 derivatives, precursors corresponding to said organic compound Q, and seeds S of a zeolitic material. The invention is characterized in that the seeds used comprise at least one zeolitic material different from the MTT zeolite which is to be prepared. Reaction of the mixture is maintained until the zeolite crystallises.
The alkylated polymethylene &agr;-&ohgr; diammonium derivative acting as a template, used more particularly for the synthesis of ZSM-23 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 the range 3 to 14 and R
1
to R
6
, which may be identical or different, representing alkyl or hydroxyalkyl radicals containing 1 to 8 carbon atoms; up to five R
1
to R
6
radicals can be hydrogen.
Thus it is possible to use seeds of at least one solid with structure type LTA such as A zeolite, with structure type LTL, structure type FAU such as X and Y zeolites, structure type MOR, structure type MAZ, structure type OFF, structure type FER, structure type ERI, structure type BEA, structure type MFI such as ZSM-5 and silicalite, structure type MTW, structure type EUO, structure type LEV, structure type TON, structure type NES such as NU-87 zeolite, or a NU-85, NU-86, NU-88 or IM-5 zeolite or a zeolite with structure type MTT with a chemical composition of the crystalline framework which is different from the chemical composition of the crystalline framework of the MTT zeolite to be prepared, in particular with different X′/T′ ratios. Preferably, the seeds for synthesising a zeolite with structure type MTT are constituted by seeds of zeolites with structure type LTA, FAU, MOR, MFI, MTT, the seeds with structure type MTT having an X′/T′ ratio which is different from that of the zeolite which is synthesised.
The zeolitic materials acting as seeds can be introduced at any point in the preparation of the zeolite which is to be synthesised. The seeds can be introduced at the same time as the sources of the elements X and T, or as organic template Q, or the seeds can be introduced first into the aqueous mixture, or the seeds can be introduced after introducing the

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