Chemistry of inorganic compounds – Zeolite
Reexamination Certificate
1999-11-10
2001-06-05
Sample, David R (Department: 1755)
Chemistry of inorganic compounds
Zeolite
C423S705000, C423S706000, C423S716000, C423S305000, C423S306000, C423S326000, C423S328200, C423SDIG002, C423SDIG002, C423SDIG003, C502S060000, C502S064000, C502S077000, C502S208000, C502S214000
Reexamination Certificate
active
06241960
ABSTRACT:
The present invention is directed to the preparation and isolation of small zeotype crystals.
In particular, the invention concerns a novel method by which it is possible to achieve well defined sizes of zeotype crystals for example useful in the preparation of catalysts.
Zeotype is defined as the collective name of zeolites and related compounds, where Si is partly or completely substituted by Al and/or P and/or metals. Zeolites are zeotypes with a low degree of Si substitution.
Small zeotype crystals are interesting for a variety of catalytic reactions and many attempts to minimize the crystal size have been reported.
Castagnola et al. use low-temperature ageing in the presence of sucrose in order to synthesize 2500 Å aggregates of individual 130 Å crystals of zeolite X (N. B. Castagnola, P. K. Dutta, J. Phys. Chem. B, 1998, 102, 1696-1702). By decreasing the Si/Al ratio and increasing the OH/Si ratio Yamamura et al. synthesise 300-500 Å ZSM-5 consisting of individual 130-200 Å crystals (M. Yamamura, K. Chaki, T. Wakatsuki, H. Okado, K. Fujimoto, Zeolites, 1994, 14, 643-649.).
Zeolite Beta was synthesised with a crystal size down to 100 Å by decreasing the Si/Al ratio in the absence of alkali metal cations are described by M. A. Camblor, A. Corma, A. Mifsud, J. Pérez-Pariente, S. Valencia, Progress in Zeolite and Microsporous Materials, Studies in Surface Science and Catalysis, 1997, 105, 341-348.
Varying the ratios of Si/Al, H
2
O/Al and K/Al Meng and co-workers prepare 300 Å crystals of zeolite L [X. Meng, Y. Zhang, C. Meng, W. Pang, The proceedings of the 9
th
international zeolite conference, Montreal 1992, Eds. R. von Ballmoos et al., 297-304].
The advantages of small zeotype crystal sizes are in particular,
(1) a reduction of the diffusion resistance in the zeotype (K. Beschmann, L. Riekert, J. Catal., 1993, 141, 548-565), (N. Y. Chen, W. E. Garwood, J. Catal., 1978, 52, 453-458), (S. B. Pu, T. Inui, Zeolites, 1996, 17, 334-39);
(2) a reduction of the deactivation rate of the zeotype caused by coke deposition at the external surface (M. Yamamura, K. Chaki, T. Wakatsuki, H. Okado, K. Fujimoto, Zeolites, 1994, 14, 643-649), (H. van Bekkum, E. M. Flanigen, J. C. Jansen (editors), Elsevier, Amsterdam, Vol. 58, 1991, 619).
It has now been found that by crystallizing the zeotype inside a porous support material with pores smaller than 1000 Å, the size of the zeotype crystals can be controlled. The porous support material is preferably removable in order to isolate the pure zeotype or useful as component of a desired catalyst. Examples of typical porous support materials are carbon and magnesium oxide representing the group of removable porous support materials and silica alumina, which may be a desirable constituent of the catalyst. But any other suitable material having pores smaller than 1000 Å may be applied as a support material.
The parameters, which control the zeotype crystal sizes, are the pore size of the porous support material, the concentration of the zeotype precursors in the pores of the porous support material, and the detailed conditions of crystallization.
The pore size distributions in the porous support material can be determined by the BET method and Hg intrusion. The zeotype crystal sizes can be determined by broadening of X-ray powder diffraction lines (XRPD) using the Debye-Scherrer approach and by transmission electron microscopy (TEM).
In accordance with the above finding, this invention provides a novel method for the preparation and isolation of small zeotype crystals with controlled sizes.
An advantage of the invention is that the maximum size of the zeotype crystals obtained is given by the pore diameter of the porous support material.
A further advantage of the method of the present invention is that it is applicable for the preparation of any type of zeotypes.
Still, an advantage is that the extent of agglomeration of the individual zeotype crystals is strongly reduced, when the crystallization is proceeding within the porous support material. This is useful in applications, where the porous support material is not removed from the zeotype in that the zeotype crystals are thereby excellently dispersed throughout the pore system of the porous support material.
As further an advantage, when applying removable support materials such as carbon or MgO, which are removed by pyrolysis and acid hydrolysis respectively, the removal of the porous support material secures a secondary pore system in between the zeotype crystals, which facilitates the diffusion of reactants into the zeotype and reaction products out of the resulting zeotype crystals.
Thus, the prepared zeotype crystals are useful as catalyst in a number of chemical reactions, including hydrocracking and other known refinery processes.
Examples of specific embodiments of the present invention are described below.
DETAILED DESCRIPTION OF THE INVENTION
In all the examples described below, distilled water was used as the source of water. Additionally, all the synthesis gel compositions presented below are given in mole ratios of the individual components.
Generally, zeotypes are prepared by use of a primary Si/Al/P-source (precursor source), which is hydrolyzed under synthesis conditions, and a template mixture, which is depending on the zeotype to be formed, contains an organic or inorganic (alkali) template promoting the formation of the desired zeotype from the corresponding synthesis gel (hydrolyzed precursor source and template mixture). The template mixture may in addition to the zeotype promoters (template) contain compounds providing for desired elements of the resulting zeotype (secondary precursor sources), which are insoluble in the primary precursor source thus added along with the template in the template mixture. The obtained synthesis gel may contain hydrolyzed oxide compounds of Si, Al, P and metals together with the template. Zeotype crystals are obtained from the synthesis gel by heating or autoclaving the synthesis gel according to known methods. Volatile organic templates are removed from the resulting zeotype during activation.
The chemical sources used in the synthesis must be soluble in either water or an organic volatile solvent. Below are given examples of typical sources of Si, Al and P. However, any source complying with the solubility criterion may be used.
Suitable silicium sources are M
2
SiO
3
, M=Na, K or Si(OR)
4
, where R=alkyl.
Suitable aluminium sources are Al(NO
3
)
3
, Al
2
(SO
4
)
3
, NaAlO
2
, KAlO
2
and Al(OR)
3
, where R=alkyl.
Suitable phosphor sources are H
3
PO
x
, where x=2,3,4.
Useful organic templates are alkyl amines or tetraalkyl ammonium salts, tetra-alkyl ammonium bromides or hydroxides and inorganic templates are alkali metals.
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patent: 4557858 (1985-12-01), Galloway
patent: 4567152 (1986-01-01), Pine
patent: 4681864 (1987-07-01), Edwards et al.
patent: 4977122 (1990-12-01), Eberly
patent: 6004527 (1999-12-01), Murrell et al.
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Castagnola et al., “Nanometer-Sized Zeolite X Crystals: Use as Photochemical Hosts,” J. Phys. Chem. B, vol. 102, No. 10, pp. 1696-1702, 1998.*
M. Yamamura et al., “Synthesis of ZSM-5 Zeolite with Small Crystal Size and its Catalytic Performance for Ethylene Oligomerization”,Zeolites, vol. 14, Nov./Dec. 1994, pp. 643-649.
M.A. Camblor et al., “Synthesis of Nanocrystalline Zeolite Beta in the Absence of Alkali Metal Cations”,Studies in Surface Science and Catalysis, vol. 15, 1997, pp. 341-348 (No Month).
K. Beschmann et al., “Isomerization of Xylene and Methylation of Toluene on Zeolite H-ZSM-5, Compound Kinetics and Selectivity”,Journal of Catalysis, 1993, pp. 548-565 (No Month).
N.Y. Chen et al., “Some Catalytic Properties of ZSM-5, A New Shape Selective Zeolite”,Journal of Catalysis, 1978, pp. 453-458 (No Month).
S. Pu and T. Inui, “Influence of Crystallite Size on Catalytic Performance of HZSM-5 Prepared by Different Methods in 2,7-dimethyl
Brorson Michael
Jacobsen Claus J. H.
Madsen Claus
Schmidt Iver
Topsøe Haldor F. A.
Haldor Topsoe A/S
Ostrolenk Faber Gerb & Soffen, LLP
Sample David R
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