Molecular sieve abstract
New crystalline titanium molecular sieve zeolite compositions having
a pore size of about 8 Angstrom Units are disclosed together with
methods for preparing the same and organic compound conversions.
Molecular sieve claims
What is claimed is:
1. A crystalline titaniumsilicate molecular sieve zeolite having
a pore size of approximately 8 Angstrom units and a composition
in terms of mole ratios of oxides as follows:
wherein M is at least one cation having a valence of n, y is from
2.5 to 25 and z is from 0 to 100 said zeolite being characterized
by an X-ray powder diffraction pattern having the lines and relative
intensities set forth in Table I of the specification.
2. The zeolite of claim 1 wherein y is 3.5 to 10.
3. The zeolite of claim 1 wherein M is a mixture of sodium and
potassium.
4. The zeolite of claim 1 wherein at least a portion of M is hydrogen.
5. The zeolite of claim 1 wherein at least a portion of M is rare
earth.
Molecular sieve description
BACKGROUND OF THE INVENTION 1. Field of the Invention
This invention relates to new crystalline titanium molecular sieve
zeolite compositions, methods for preparing the same and to organic
compound conversions therewith, especially hydrocarbon conversions.
2. Background of the Invention and Prior Art
Since the discovery by Milton and coworkers (U.S. Pat. No. 2882243
and U.S. Pat. No. 2882244) in the late 1950's that aluminosilicate
systems could be induced to form uniformly porous, internally charged
crystals, analogous to molecular sieves zeolites found in nature,
the properties of synthetic aluminosilicate zeolite molecular sieves
have formed the basis of numerous commerically important catalytic,
adsorptive and ion-exchange applications. This high degree of utility
is the result of a unique combination of high surface area and uniform
porosity dictated by the "framework" structure of the
zeolite crystals coupled with the electrostatically charged sites
induced by tetrahedrally coordinated Al.sup.+3. Thus, a large number
of "active" charged sites are readily accessible to molecules
of the proper size and geometry for adsorptive or catalytic interactions.
Further, since charge compensating cations are electrostatically
and not covalently bound to the aluminosilicate framework, they
are generally base exchangeable for other cations with different
inherent properties. This offers wide latitude for modification
of active sites whereby specific adsorbents and catalysts can be
tailormade for a given utility.
In the publication "Zeolite Molecular Sieves", Chapter
2 1974 D.W. Breck hypothesized that perhaps 1000 aluminosilicate
zeolite framework structures are theoretically possible, but to
date only approximately 150 have been identified. While compositional
nuances have been described in publications such as U.S. Pat. Nos.
4524055 4603040 and 4606899 totally new aluminosilicate
framework structures are being discovered at a negligible rate.
Of particular importance to fundamental progress in the catalysis
of relatively large hydrocarbon molecules, especially fluid cracking
operations, is the fact that it has been a generation since the
discovery of any new large pored aluminosilicate zeolite.
With slow progress in the discovery of new wide pored aluminosilicate
based molecular sieves, researchers have taken various approaches
to replace aluminum or silicon in zeolite synthesis in the hope
of generating either new zeolite-like framework structures or inducing
the formation of qualitatively different active sites than are available
in analogous aluminosilicate based materials. While progress of
academic interest has been made from different approaches, little
or no success has been achieved in discovering new wide pore molecular
sieve zeolites.
It has been believed for a generation that phosphorus could be
incorporated, to varying degrees, in a zeolite type aluminosilicate
framework. In the more recent past (JACS 104 pp. 1146 (1982); Proceedings
of the 7th International Zeolite Conference, pp. 103-112 1986)
E. M. Flanigan and coworkers have demonstrated the preparation of
pure aluminophosphate based molecular sieves of a wide variety of
structures. However, the site inducing Al.sup.+3 is essentially
neutralized by the p.sup.+5 imparting a +1 charge to the framework.
Thus, while a new class of "molecular sieves" was created,
they are not zeolites in the fundamental sense since they lack "active"
charged sites.
Realizing this inherent utility limiting deficiency, for the past
few years the research community has emphasized the synthesis of
mixed aluminosilicate-metal oxide and mixed aluminophosphate-metal
oxide framework systems. While this approach to overcoming the slow
progress in aluminosilicate zeolite synthesis has generated approximately
200 new compositions, all of them suffer either from the site removing
effect of incorporated p.sup.+5 or the site diluting effect of incorporating
effectively neutral tetrahedral +4 metal into an aluminosilicate
framework. As a result, extensive research in the research community
has failed to demonstrate significant utility for any of these materials.
A series of zeolite-like "framework" silicates have been
synthesized, some of which have larger uniform pores than are observed
for aluminosilicate zeolites. (W. M. Meier, Proceedings of the 7th
International Zeolite Conference, pp. 13-22 (1986).) While this
particular synthesis approach produces materials which, by definition,
totally lack active, charged sites, back implementation after synthesis
would not appear out of the question although little work appears
in the open literature on this topic.
Another and most straightforward means of potentially generating
new structures or qualitatively different sites than those induced
by aluminum would be the direct substitution of some charge inducing
species for aluminum in a zeolite-like structure. To date the most
notably successful example of this approach appears to be boron
in the case of ZSM-5 analogs, although iron has also been claimed
in similar materials. (EPA 68796 (1983), Taramasso et al; Proceedings
of the 5th International Zeolite Conference; pp. 40-48 (1980));
J. W. Ball et al; Proceedings of the 7th International Zeolite Conference;
pp. 137-144 (1986); U.S. Pat. No. 4280305 to Kouenhowen et al.
Unfortunately, the low levels of incorporation of the species substituting
for aluminum usually leaves doubt if the species are occluded or
framework incorporated.
In 1967 Young in U.S. Pat. No. 3329481 reported that the synthesis
of charge bearing (exchangeable) titaniumsilicates under conditions
similar to aluminosilicate zeolite formation was possible if the
titanium was present as a "critical reagent" +III peroxo
species. While these materials were called "titanium zeolites"
no evidence was presented beyond some questionable X-ray diffraction
(XRD) patterns and his claim has generally been dismmised by the
zeolite research community. (D. W. Breck, Zeolite Molecular Sieves,
p. 322 (1974); R. M. Barrer, Hydrothermal Chemistry of Zeolites,
p. 293 (1982); G. Perego et al, Proceedings of 7th International
Zeolite Conference, p. 129 (1986).) For all but one end member of
this series of materials (denoted TS materials), the presented XRD
patterns indicate phases too dense to be molecular sieves. In the
case of the one questionable end member (denoted TS-26), the XRD
pattern might possible be interpreted as a small pored zeolite,
although without additional supporting evidence, it appears extremely
questionable.
A naturally occurring alkaline titanosilicate identified as "Zorite"
was discovered in trace quantities on the Siberian Tundra in 1972
(A. N. Mer'kov et al; Zapiski Vses Mineralog. Obshch., pages 54-62
(1973)). The published XRD pattern was challenged and a proposed
structure reported in a later article entitled "The OD Structure
of Zorite", Sandomirskii et al, Sov. Phys. Crystallogr. 24
(6), Nov-Dec 1979 pages 686-693.
No further reports on "titanium zeolites" appeared in
the open literature until 1983 when trace levels of tetrahedral
Ti(IV) were reported in a ZSM-5 analog. (M. Taramasso et al; U.S.
Pat. No. 4410501 (1983); G. Perego et al., Proceedings of the
7th International Zeolite Conference; p. 129 (1986).) A similar
claim appeared from researchers in mid-1985 (EPA 132550 (1985).)
More recently, the reserach community reported mixed aluminosilicate-titanium(IV)
(EPA 179876 (1985); EPA 181884 (1985) structures which, along
with TAPO (EPA 121232 (1985) systems, appear to have no possibility
of active titanium sites. As such, their utility is highly questionable.
That charge bearing, exchangeable titanium silicates are possible
is inferred not only from the existence of exchangeable alkali titanates
and the early work disclosed in U.S. Pat. No. 3329481 on ill defined
titaniumsilicates but also from the observation (S. M. Kuznicki
et al; J. Phys. Chem.; 84; pp. 535-537 (1980)) of TiO.sub.4 - units
in some modified zeolites.
SUMMARY OF THE INVENTION
The present invention relates to a new family of stable, large
pore crystalline titaniumsilicate molecular sieve zeolites, hereinafter
designated ETS, their method of preparation and the use of such
compositions as adsorbents and catalysts for the conversion of a
wide variety of organic compounds, e.g., hydrocarbon compounds and
oxygenates such as methanol.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a new family of stable crystalline
titaniumsilicate molecular sieve zeolites which have a pore size
of approximately 8.degree. Angstrom units and a titania/silica mole
ratio in the range of from 2.5 to 25. These titanium silicates have
a definite X-ray diffraction pattern unlike other molecular sieve
zeolites and can be identified in terms of mole ratios of oxides
as follows:
wherein M is at least one cation having a valence of n, y is from
2.5 to 25 and z is from 0 to 100. In a preferred embodiment, M
is a mixture of alkali metal cations, particularly sodium and potassium,
and y is at least 3.5 and ranges up to about 10.
The original cations M can be replaced at least in part with other
cations by well known exchange techniques. Preferred replacing cations
include hydrogen, ammonium rare earth, and mixtures thereof. Members
of the family of molecular sieve zeolites designated ETS in the
rare earth-exchanged form have a high degree of thermal stability
of at least 450.degree. C. or higher, thus rendering them effective
for use in high temperature catalytic processes. ETS zeolites are
highly adsorptive toward molecules up to approximately 8 Angstroms
in critical diameter, e.g., triethylamine, and are essentially non-adsorptive
toward molecules such as 135-trimethylbenzene, which is at least
8 Angstroms in minimum dimension. In the sodium form, ETS is completely
reversibly dehydratable with a water capacity of approximately 20
weight percent.
The method of preparing ETS compositions comprises the preparation
of a reaction mixture constituted by sources of silica, sources
of titanium, sources of alkalinity such as sodium and/or potassium
oxide and water having a reagent molar ratio composition as set
forth in Table 2. Optionally, sources of fluoride such as potassium
fluoride can be used, particularly to assist in solubilizing a solid
titanium source such as Ti.sub.2 O.sub.3. However, when titanium
silicates are prepared from gels, its value is greatly diminished.
The silica source includes most any reactive source of silicon
such as silica, silica hydrosol, silica gel, silicic acid, alkoxides
of silicon, alkali metal silicates, preferably sodium or potassium,
or mixtures of the foregoing.
The titanium oxide source is a trivalent compound such as titanium
trichloride, TiCl.sub.3.
The source of alkalinity is preferably an aqueous solution of an
alkali metal hydroxide, such as sodium hydroxide, which provides
a source of alkali metal ions for maintaining electrovalent neutrality
and controlling the pH of the reaction mixture within the range
of 9.9 to 10.3.+-.0.1. As shown in the examples hereinafter, pH
is critical for the production of ETS. The alkali metal hydroxide
serves as a source of sodium oxide which can also be supplied by
an aqueous solution of sodium silicate.
It is to be noted that at the higher end of the pH range, a mixture
of titanium zeolites tends to form while at the lower end of the
pH range, quartz appears as an impurity.
The titanium silicate molecular sieve zeolites prepared according
to the invention contain no deliberately added alumina, and may
contain very minor amounts of Al.sub.2 O.sub.3 due to the presence
of impurity levels in the reagents employed, e.g., sodium silicate,
and in the reaction equipment, The molar ratio of SiO.sub.2 /Al.sub.2
O.sub.3 will be 0 or higher than 500 or more.
The crystalline titanium silicate as synthesized can have the original
components thereof replaced by a wide variety of others according
to techniques well known in the art. Typical replacing components
would include hydrogen, ammonium, alkyal ammonium and aryl ammonium
and metals, including mixtures of the same. The hydrogen form may
be prepared, for example, by substitution of original sodium with
ammonium, The composition is then calcined at a temperature of,
say, 1000.degree. F. causing evolution of ammonia and retention
of hydrogen in the composition, i.e., hydrogen and/or decationized
form. Of the replacing metals, preference is accorded to metals
of Groups II, IV and VIII of the Periodic Table, preferably the
rare earth metals.
It has been found that a special calcination procedure must be
used to convert the ammonium form to the hydrogen form and maintain
its stability. The calcination can be described as a "shock"
calcination because the NH.sub.3 exchanged zeolite is rapidly heated
to temperatures in excess of about 400.degree. C. Temperature profiles
of at least about 20.degree. C./min are satisfactory.
Another method comprises depositing the ammonium form on a pre-heated
silica tray in an oven at 500.degree. C. for about 30 minutes.
The crystalline titanium silicates are then preferably washed with
water and dried at a temperature ranging from 150.degree. F. to
about 600.degree. F. and thereafter calcined in air or other inert
gas at temperatures ranging from 500.degree. F. to 1500.degree.
F. for periods of time ranging from 1 to 48 hours or more.
Regardless of the synthesized form of the titanium silicate the
spatial arrangement of atoms which form the basic crystal lattices
remain essentially unchanged by the replacement or sodium or other
alkali metal or by the presence in the initial reaction mixture
of metals in addition to sodium, as determined by an X-ray powder
diffraction pattern of the resulting titanium silicate. The X-ray
diffraction patterns of such products are essentially the same as
those set forth in Table I above.
The crystalline titanium silicates prepared in accordance with
the invention are formed in a wide variety of particular sizes.
Generally, the particles can be in the form of powder, a granule,
or a molded product such as an extrudate having a particle size
sufficient to pass through a 2 mesh (Tyler) screen and be maintained
on a 400 mesh (Tyler) screen in cases where the catalyst is molded
such as by extrusion. The titanium silicate can be extruded before
drying or dried or partially dried and then extruded.
When used as a catalyst, it is desired to incorporate the new crystalline
titanium silicate with another material resitant to the temperatures
and other conditions employed in organic processes. Such materials
include active and inactive materials and synthetic and naturally
occurring zeolites as well as inorganic materials such as clays,
silica and/or metal oxides. The latter may be either naturally occurring
or in the form of gelatinous precipitates or gels including mixtures
of silica and metal oxides. Use of a material in conjunction with
the new crystalline titanium silicate, i.e., combined therewith
which is active, tends to improve the conversion and/or selectivity
of the catalyst in certain organic conversion processes. Inactive
materials suitably serve as diluents to control the amount of conversion
in a given process so that products can be obtained economically
and in an orderly manner without employing other means for controlling
the rate of reaction. Normally, crystalline materials have been
incorporated into naturally occurring clays, e.g., bentonite and
kaolin to improve th crush strength of the catalyst under commerical
operating conditions. These materials, i.e., clays, oxides, etc.,
function as binders for the catalyst. It is desirable to provide
a catalyst having good crush strength because in a petroleum refinery
the catalyst is often subjected to rough handling which tends to
break the catalyst down into powder-like materials which cause problems
in processing. These clay binders have been employed for the purpose
of improving the crush strength of the catalyst.
Naturally occurring clays that can be composited with the crystalline
titanium silicate described herein include the smectite and kaoline
families, which families include the montmorillonites such as sub-bentonites
and the kaolins known commonly as Dixie, McNamee, Ga. and Florida
or others in which the main constituent is halloysite, kaolinite,
dickite, nacrite or anauxite. Such clays can be used in the raw
state as originally mined or initially subjected to calcination,
acid treatment or chemical modification.
In addition to the foregoing materials, the crystalline titanium
silicate may be composited with matrix materials such as silica-alumina,
silica-magnesia, silica-zirconia, silica-thoria, silica-berylia,
silica-titania as well as ternary compositions such as silica-alumina-thoria,
silica-alumina-zirconia, silica-alumina-magnesia and silica-magnesia-zirconia.
The matrix can be in the form of a cogel. The relative proportions
of finally divided crystalline metal organosilicate and inorganic
oxide gel matrix can vary widely with the crystalline organosilicate
content ranging from about 1 to 90 percent by weight and more usually
in the range of about 2 to to about 50 percent by weight of the
composite.
As is known in the art, it is desirable to limit the alkali metal
content of materials used for acid catalyzed reactions. This is
usually accomplished by ion exchange with hydrogen ions or precursors
thereof such as ammonium and/or metal cations such as rare earth.
Employing the catalyst of this invention, containing a hydrogenation
component, heavy petroleum residual stocks, cycle stocks, and other
hydrocrackable charge stocks can be hydrocracked at temperatures
between 400.degree. F. and 825.degree. F. using molar ratios of
hydrogen to hydrocarbon charge in the range between 2 and 80. The
pressure employed will vary between 10 and 2500 psig and the liquid
hourly space velocity between 0.1 and 10.
Employing the catalyst of this invention for catalytic cracking,
hydrocarbon cracking stocks can be cracked at a liquid hourly space
velocity between about 0.5 and 50 a temperature between about 550.degree.
F. and 1100.degree. F., a pressure between about subatmospheric
and several hundred atmospheres.
Employing a catalytically active form of a member of the family
of zeolites of this invention containing a hydrogenation component,
reforming stocks can be reformed employing a temperature between
700.degree. F. and 1000.degree. F. The pressure can be between 100
and 1000 psig, but is preferably between 200 to 700 psig. The liquid
hourly space velocity is generally between 0.1 and 10 preferably
between 0.5 and 4 and the hydrogen to hydrocarbon mole ratio is
generally between 1 and 20 preferably between 4 and 12.
The catalyst can also be used for hydroisomerization of normal
paraffins when provided with a hydrogenation component, e.g., platinum.
Hydroisomerization is carried out at a temperature between 200.degree.
and 700.degree. F., preferably 300.degree. F. to 550.degree. F.,
with a liquid hourly space velocity between 0.01 and 2 preferably
between 0.25 and 0.50 employing hydrogen such that the hydrogen
to hydrocarbon mole ratio is between 1:1 and 5:1. Additionally,
the catalyst can be used for olefin isomerization employing temperatures
between 30.degree. F. and 500.degree. F.
In order to more fully illustrate the nature of the invention and
a manner of practicing the same, the following examples illustrate
the best mode now contemplated. |