Chemistry of inorganic compounds – Zeolite – Organic compound used to form zeolite
Reexamination Certificate
2001-07-13
2003-09-09
Sample, David (Department: 1755)
Chemistry of inorganic compounds
Zeolite
Organic compound used to form zeolite
C423SDIG002, C423SDIG002
Reexamination Certificate
active
06616911
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for preparing medium pore size zeolites using pyrrolidinium cations as structure directing agents (SDA's).
2. State of the Art
It has now been found that zeolites can be prepared using pyrrolidinium cations as structure directing agents.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a process for preparing a medium pore size zeolite which comprises:
(a) preparing an aqueous solution from (1) sources of an alkali metal oxide, alkaline earth metal oxide or mixtures thereof, (2) sources of an oxide selected from oxides of silicon, germanium or mixtures thereof; (3) sources of an oxide selected from the oxides of aluminum, boron, iron, gallium, indium, titanium, vanadium or mixtures thereof; and (4) at least one pyrrolidinium cation capable of forming the zeolite having the formula
where R
1
is C
1
-C
4
alkyl or benzyl, and R
2
is C
5
-C
8
cycloalkyl, or alkylated C
5
-C
8
cycloalkyl;
(b) maintaining the aqueous solution under conditions sufficient to form crystals of the zeolite; and
(c) recovering the crystals of the zeolite.
The present invention also provides this process further comprising replacing alkali and/or alkaline earth metal cations of the recovered zeolite, at least in part, by ion exchange with a cation or mixture of cations selected from the group consisting of hydrogen and hydrogen precursors, rare earth metals, and metals from Groups IIA, IIIA, IVA, IB, IIB, IIIB, IVB, VIB, and VIII of the Periodic Table of Elements.
The present invention also provides a zeolite composition, as-synthesized and in the anhydrous state, whose general composition, in terms of mole ratios, is as follows:
YO
2
/W
c
O
d
≧20
Q/YO
2
0.02-0.10
M
2
/YO
2
0.01-0.10
wherein Y is silicon, germanium or a mixture thereof; W is aluminum, boron, gallium, indium, iron, titanium, vanadium or mixtures thereof; c is 1 or 2; d is 2 when c is 1 (i.e., W is tetravalent) or d is 3 or 5 when c is 2 (i.e., d is 3 when W is trivalent or 5 when W is pentavalent); Q is at least one pyrrolidinium cation capable of forming the zeolite and having formula (I) above; M is an alkali metal cation, alkaline earth metal cation or mixtures thereof; and n is the valence of M (i.e., 1 or 2).
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention comprises:
(a) preparing an aqueous solution from sources of oxides capable of forming a zeolite and at least one pyrrolidinium cation capable of forming the zeolite and having formula (I) above;
(b) maintaining the aqueous solution under conditions sufficient to form crystals of the zeolite; and
(c) recovering the crystals of the zeolite.
While not wishing to be bound or limited by any theory, it is believed that the pyrrolidinium cations of this invention act as a structure directing agent or templating agent in the reaction which forms the zeolite.
The process of the present invention comprises forming a reaction mixture from sources of alkali and/or alkaline earth metal (M) cations with valences n (i.e., 1 or 2); sources of an oxide of aluminum, boron, iron, gallium, indium, titanium, vanadium or mixtures thereof (W); sources of an oxide of silicon, germanium or mixtures thereof (Y); at least one pyrrolidinium cation of this invention (Q); and water, said reaction mixture having a composition in terms of mole ratios within the following ranges:
Reactants
General
Preferred
YO
2
/W
a
O
b
20-∞
25-90
OH
−
/YO
2
0.10-0.50
0.15-0.30
Q/YO
2
0.05-0.50
0.10-0.30
M
2
/YO
2
0.02-0.40
0.01-0.30
H
2
O/YO
2
10-100
25-50
Where Y, W, Q, M and n are as defined above, and a is 1 or 2, and b is 2 when a is 1 (i.e., W is tetravalent) and b is 3 when a is 2 (i.e., W is trivalent).
Typical sources of aluminum oxide for the reaction mixture include aluminates, alumina, hydrated aluminum hydroxides, and aluminum compounds such as AlCl
3
and Al
2
(SO
4
)
3
. Typical sources of silicon oxide include silica hydrogel, silicic acid, colloidal silica, tetraalkyl orthosilicates, silica hydroxides, and fumed silicas. Gallium, iron, boron, indium, titanium, vanadium and germanium can be added in forms corresponding to their aluminum and silicon counterparts. Trivalent elements stabilized on silica colloids are also useful reagents.
The pyrrolidinium cations useful in the practice of this invention are those which are capable of forming a zeolite. The pyrrolidinium cations of this invention are represented by the following formula:
where R
1
is C
1
-C
4
alkyl (e.g., methyl, ethyl, propyl, butyl or isobutyl) or benzyl, and R
2
is C
5
-C
8
cycloalkyl (e.g., cyclopentyl, cyclohexyl, or cyclooctyl), or alkylated C
5
-C
8
cycloalkyl (e.g., 2,4,4-trimethylcyclopentyl or 3,3,5-trimethylcyclohexyl).
In preparing the zeolites in accordance with the present invention, the reactants and the pyrrolidinium cation are dissolved in water and the resulting reaction mixture is maintained at an elevated temperature until crystals are formed. The hydrothermal crystallization is usually conducted under autogenous pressure, at a temperature between 100° C. and 200° C., preferably between 135° C. and 160° C. The crystallization period is typically greater than 1 day and preferably from about 3 days to about 20 days.
The hydrothermal crystallization is usually conducted under pressure and usually in an autoclave so that the reaction mixture is subject to autogenous pressure. The reaction mixture should be stirred during crystallization.
Once the crystals have formed, the solid product is separated from the reaction mixture by standard mechanical separation techniques, such as filtration. The crystals are water-washed and then dried, e.g., at 90° C. to 150° C. for from 8 to 24 hours, to obtain the as-synthesized zeolite crystals. The drying step can be performed at atmospheric or subatmospheric pressures.
During the hydrothermal crystallization step, the crystals can be allowed to nucleate spontaneously from the reaction mixture. The reaction mixture can also be seeded with crystals of the desired zeolite both to direct, and accelerate the crystallization, as well as to minimize the formation of any undesired crystalline phases. When seed crystals are used, typically about 0.5% to about 5.0% by weight (based on the weight of silica used in the reaction mixture) of the seed crystals are added.
Due to the unpredictability of the factors which control nucleation and crystallization in the art of crystalline oxide synthesis, not every combination of reagents, reactant ratios, and reaction conditions will result in crystalline products. Selecting crystallization conditions which are effective for producing crystals may require routine modifications to the reaction mixture or to the reaction conditions, such as temperature, and/or crystallization time. Making these modifications are well within the capabilities of one skilled in the art.
The zeolite product made by the process of this invention has an as-synthesized composition comprising, in terms of mole ratios in the anhydrous state, the following:
YO
2
/W
c
O
d
≧20
Q/YO
2
0.02-0.10
M
2
/YO
2
0.01-0.10
wherein Y, W, c, d, Q, M and n are as defined above. Preferably, Y is silicon, W is aluminum, and M is sodium.
The zeolite products made in accordance with this invention were identified by their X-ray diffraction (XRD) pattern. The X-ray powder diffraction patterns were determined by standard techniques. The radiation was the K-alpha/doublet of copper. In the X-ray data shown below, the peak heights I and the positions, as a function of 2 theta where theta is the Bragg angle, were read from the relative intensities, 100×I/I
o
where I
o
is the intensity of the strongest line or peak, and d, the interplanar spacing in Angstroms corresponding to the recorded lines, can be calculated.
The pyrrolidinium SDA's of this invention can be used to prepare a variety of medium pore zeolites, including beta zeolite, ZSM-11, ZSM-12, SSZ-37, SSZ-55, SSZ-57, SSZ-58, and SSZ-60. Table A
Chevron U.S.A. Inc.
Sample David
Sheridan Richard J.
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