Chemistry of hydrocarbon compounds – Aromatic compound synthesis – By ring formation from nonring moiety – e.g. – aromatization,...
Reexamination Certificate
2000-01-12
2001-07-10
Sample, David R (Department: 1755)
Chemistry of hydrocarbon compounds
Aromatic compound synthesis
By ring formation from nonring moiety, e.g., aromatization,...
C585S734000, C585S739000, C423S713000, C423S716000, C423SDIG002, C502S061000
Reexamination Certificate
active
06258991
ABSTRACT:
This invention relates to zeolites of structure type LTL, to processes for the manufacture of such zeolites, and to the use of the zeolites as catalysts and catalyst bases. The zeolites have a 12 membered ring structure with pore dimensions of 0.55 to 0.72 nm.
BACKGROUND OF THE INVENTION
An example of a zeolite of LTL structure type is zeolite L, and processes for the manufacture of zeolite L are described in U.S. Pat. No. 3,216,789, EP-A-219354, and EP-A-595465, the disclosures of all of which are incorporated by reference herein. The two European patent applications, which have extensive prior art discussions to which the reader is referred for more background, and the U.S. Patent list the significant X-ray diffraction data for crystalline zeolite L and give its formula in terms of moles of oxides as
0.9 to 1.3 M
2
O:Al
2
O
3
:5.2 to 6.9 SiO
2
:yH
2
O,
where M represents an exchangeable cation of valence n, and y represents a value within the range of from 0 to about 9. In Proceedings of the 9th International Zeolite Conference, Ed. von Ballmoos et al, 1993, p. 297, Xianping Meng et al describe the effect of varying crystallization conditions and reactant ratios on a process for the manufacture of ultrafine (particle size about 30 nm) zeolite L.
Products of such a small particle size have advantages over larger particle size products, such as those produced by the procedure of U.S. Pat. No. 3,216,789, when used as a catalyst, or catalyst base, for reactions involving hydrocarbon conversions because of their enhanced ratio of surface area to mass, high diffusion rates and reactivities, and resistance to deactivation by pore plugging and surface contamination. For similar reasons they have advantages in hydrocarbon separations, and are also valuable as starting materials in the manufacture of supported zeolite layers, especially membranes, as described in WO 94/25151, the disclosure of which is also incorporated herein by reference. For the latter purpose, a zeolite having a particle size, whether in the form of agglomerates or single crystals, of at most 100 nm, and advantageously at most 75 nm, is normally required since the zeolite layer is formed by deposition from a colloidal suspension onto a support; if for any reason the suspension is not stable it is unsuitable for the purpose. Although EP-A-595465 describes the product of the inventive process, in which ammonia is used as a co-solvent to water in the zeolite synthesis mixture, as being in mono-crystalline form, and refers to carrying out the hydrothermal treatment at a temperature in the range of 70 to 160° C. to yield a product having crystallites of diameter less than about 30 nm, it appears from the description and micrograph in the Application that the product consists of larger agglomerates of the nanocrystals incapable of forming a colloidal suspension. The same is true of the product of EP-A-323893, the small crystallites of which agglomerate into readily recoverable particles (page 2, lines 31 to 33).
It has now surprisingly been found that if a synthesis mixture as described in U.S. Pat. No. 3,216,789 is subjected to heat treatment at a temperature below 100° C. a colloidal suspension of zeolite results.
DESCRIPTION OF THE INVENTION
The present invention accordingly provides a process for the manufacture of a colloidal suspension of an LTL zeolite, wherein a synthesis mixture having a composition, given in terms of molar proportions with the solid components being calculated in terms of their oxides, in the ranges:
K
2
OX:(K
2
O+Na
2
O) from 0.33 to 1:1
(K
2
O+Na
2
O)X:SiO
2
from 0.35 to 0.5:1
SiO
2
X:Al
2
O
3
from 10 to 40:1
solvent X:(K
2
O+Na
2
O) from 15 to 25:1
is subjected to thermal treatment at a temperature below 100° C. for a time sufficient to form a colloidal suspension of an LTL zeolite for the solvent.
Advantageously, the SiO
2
/Al
2
O
3
ratio is at least 12:1, and advantageously the ratio is at most 28:1.
Advantageously, the solvent is water, but the presence of a co-solvent, e.g., ammonia, is not excluded, in which case its molar proportion is included in the specified range.
The invention further provides a process for the manufacture of an LTL zeolite of particle size at most 100 nm, wherein the colloidal suspension prepared as described above is washed with water to a pH within the range of 9 to 12, advantageously 10 to 11, and if desired cation exchanged, dried and, if desired, calcined.
Advantageously, the resulting zeolite is one having a composition of Formula I
0.9 to 1.3 M
2
O:Al
2
O
3
:5.2 to 6.9 SiO
2
(I)
wherein M is an exchangeable cation of valence n.
The process of the invention provides either individual crystals or agglomerates which form a colloidal suspension, i.e., the suspension produced directly, or by washing, is a stable one.
A stable suspension is one in which settlement does not take place, or one in which any settlement that takes place does so so slowly as to be insignificant over the relevant timescale. Such a suspension is referred to herein as colloidal.
As described above, the zeolites of the invention are primarily aluminosilicates, and will be described herein as such. It is, however, within the scope of the invention to replace aluminium, wholly or partly, with gallium, and partly with boron, iron or other trivalent elements, and silicon may similarly be replaced by germanium or phosphorus. It is also within the scope of the invention to include cations other than potassium and sodium in the synthesis mixture.
The sources of the various elements required in the final product may be any of those in commercial use or described in the literature, as may the preparation of the synthesis mixture.
For example, the source of silicon may be a silicate, e.g., an alkali metal silicate, or a tetraalkyl orthosilicate, but there is preferably used an aqueous colloidal suspension of silica, for example one sold by E. I. du Pont de Nemours under the trade name Ludox. Ludox HS-40 is a sodium-containing product, while AS-40 contains very little sodium.
The source of aluminium is preferably Al
2
O
3
.3H
2
O, dissolved in alkali. Other aluminium sources include, for example, a water-soluble aluminium salt, e.g., aluminium sulphate, or an alkoxide, e.g., aluminium isopropoxide.
The potassium source is advantageously potassium hydroxide and the sodium source, if present, is advantageously also the hydroxide.
The synthesis mixture is conveniently prepared by mixing two solutions, one containing the potassium and aluminium sources, and the other the silica source, each containing water in a quantity such that, on mixing, the required molar proportions result.
Crystallization is effected, either under static conditions or with moderate stirring, and, if desired, under reflux.
Thermal treatment (also known as ageing at elevated temperature) at a temperature in the range of from 40 to 97° C. is convenient; advantageously from 40 to 95° C. and preferably from 40 to 85° C. Although crystallization times are normally described in the prior art as being longer at lower temperatures, it has been surprisingly found that, while times from 48 to 500 hours may be used, even at temperatures at the lower end of the present range, times up to 84 hours may suffice. A lower temperature in general gives a smaller particle size zeolite, if other conditions remain constant. By appropriate choice of temperature, agglomerates of greatest dimensions in the range of 25 nm to 100 nm may be obtained, with good uniformity of particle sizes.
The synthesis mixture may, if desired, be aged at a temperature below that at which crystallization takes place, i.e., at a temperature less than 40° C., for example for up to 2 days. Including this low temperature ageing generally results in a smaller crystallite size, compared with an otherwise similar procedure omitting it.
The colloidal suspension, or the crystals obtainable from the suspension, produced by the processes described above may be used in a number of applications including the manufacture of thin films on substra
Anthonis Marc H
Mertens Machteld M
Verduijn Johannes Petrus
ExxonMobil Chemical Patents Inc.
Sample David R
Sherer Edward F.
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