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

2003-04-15

Sample, David (Department: 1755)

Chemistry of inorganic compounds

Zeolite

Organic compound used to form zeolite

C423S708000, C423SDIG003, C208S134000, C208S135000, C585S739000, C585S750000

Reexamination Certificate

active

06548040

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a novel process for preparing zeolites with structure type MTT. More particularly, for example, this process is applicable to synthesising ZSM-23 zeolite. ZSM-23 zeolite generally HAS the following formula in the anhydrous form: 0-20 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, T represents at least one element selected from aluminium, iron, gallium, boron, titanium, vanadium, zirconium, molybdenum, arsenic, antimony, chromium and manganese, and X represents silicon and/or germanium.
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 at least one organic template such as a quaternary diammonium 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=1Angström=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 pyrrolidine (United States patent 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), dodecamethonium 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 an organic 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 novel process for preparing a zeolitic material with structure type MTT in the presence of at least one precursor of an alkylated polymethylene &agr;-&ohgr; diammonium derivative acting as a template selected from monoamines.
IMPORTANCE OF THE INVENTION
The process of the invention can reduce the zeolite crystallisation time after forming the mixture, which reduces the costs. Further, the use of precursors of the template of the invention improves safety when synthesising the zeolite, said precursors being less dangerous than the template itself, and can also reduce the cost of the reactants, said precursors being cheaper than the template itself and than prior art precursors.
Thus, surprisingly, the Applicant has discovered that synthesis of a zeolite characterized by using specific precursors of the template can produce the advantages cited above, i.e., an advantage as regards time, safety and reactant costs.
DESCRIPTION OF THE INVENTION
The invention concerns a process for synthesising a zeolite material with structure type MTT comprising mixing, in an aqueous medium, at least one source of at least one element selected from silicon and germanium and 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, in the presence of at least one precursor of an alkylated polymethylene &agr;-&ohgr; diammonium derivative acting as a template. The mixture is generally maintained at a certain temperature until the zeolite crystallises. The invention is characterized in that at least one precursor of the alkylated polymethylene &agr;-&ohgr; diammonium derivative selected from monoamines is used.
The alkylated polymethylene &agr;-&ohgr; diammonium derivative acting as a template has the following formula:
R
1
R
2
R
3
N
+
(CH
2
)
n
N
+
R
4
R
5
R
6
where n is in the range 3 to 14 and R
1
to R
6
, which may be identical or different, can represent alkyl or hydroxyalkyl radicals containing 1 to 8 carbon atoms; up to five R
1
to R
6
radicals can be hydrogen.
In addition to the precursor(s) of the template selected from monoamines in the process of the present invention, other template group(s) are generally introduced using any suitable precursor to obtain a quaternary ammonium compound. These precursors are of F-R-F′ type where F and F′ are identical or different starting groups such as an alcohol function or a halide. As an example, an additional precursor can be selected which is at least one compound selected from alkanediols and alkane dihalides.
The precursors of the template of the invention and the other precursors can be pre-heated together in the reaction vessel or they can be mixed as they are with the other reactants. The precursors can be introduced at any moment of the zeolite preparation.
Preferably, the template precursors are introduced in solution before adding the other reactants necessary, to synthesise the zeolite.
In one particular implementation, it may be advantageous to add seeds S of at least one zeolite to the reaction medium. Seeds with the MTT zeolite structure type or the structure type of other accessible and cheap zeolites such as zeolites with structure type LTA, FAU, MOR or MFI can be added. These seeds can accelerate crystallisation of the MTT zeolite from the reaction mixture. The seeds can be introduced at any point of the zeolite synthesis. Preferably, in the optional case where the MTT zeolite is synthesised using seeds, said seeds are added after at least partial homogenisation of the mixture containing the other reactants.
In a further particular implementation, independent or otherwise of the preceding implementation, it may be advantageous to add at least one alkali metal or ammonium salt P to the reaction medium. Examples which can be cited are strong acid radicals such as bromide, chloride, iodide, sulphate, phosphate or nitrate, or weak acid radicals such as organic acid radicals, for example citrate or acetate. This salt can accelerate crystallisation of MTT zeolites from the reaction mixture.
The aqueous reaction mixture generally has the following molar composition, expressed in the oxide form:
XO
2
/T
2
O
3
(mol/mol)
at least 10
OH
−
/XO
2
(mol/mol)
0.002 to 2.0
Q/XO
2
(mol/mol)
0.002 to 2.0
Q/(M
+
+ Q) (mol/mol)
0.1 to 1.0
H
2
O/XO
2
(mol/mol)
1 to 500
P/XO
2
(mol/mol)
0 to 5
S/XO
2
(g/g)
0 to 0.1
Preferably, the reaction mixture has the following composition, expressed in the oxide form:
XO
2
/T
2
O
3
(mol/mol)
at least 12
OH
−
/XO
2
(mol/mol)
0.005 to 15
Q/XO
2
(mol/mol)
0.005 to 15
Q/(M
+
+ Q) (mol/mol)
0.1 to 1.0
H
2
O/XO
2
(mol/mol)
3 to 250
P/XO
2
(mol/mol)
0 to 1
S/XO
2
(g/g)
0 to 0.07
and still more preferably, the reaction mixture has the following composition, expressed in the oxide form:
XO
2
/T
2
O
3
(mol/mol)
at least 15
OH
−
/XO
2
(mol/mol)
0.01 to 1
Q/XO
2
(mol/mol)
0.01 to 1

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