U.S. patent application number 10/233496 was filed with the patent office on 2003-04-10 for polymorph-enriched ets-4.
Invention is credited to Jacubinas, Richard M., Kuznicki, Steven M., Langner, Tadeuz W..
Application Number | 20030068270 10/233496 |
Document ID | / |
Family ID | 24567730 |
Filed Date | 2003-04-10 |
United States Patent
Application |
20030068270 |
Kind Code |
A1 |
Kuznicki, Steven M. ; et
al. |
April 10, 2003 |
Polymorph-enriched ETS-4
Abstract
ETS-4 crystalline titanium silicate is produced so as to be
enriched in at least one polymorph thereof which contains channels
which interpenetrate the crystal lattice in both the b- and
c-directions. A process of producing such a polymorph and enriched
ETS-4 titanium silicate comprises the addition of a wetting agent
to the reaction mixture.
Inventors: |
Kuznicki, Steven M.;
(Whitehouse Station, NJ) ; Jacubinas, Richard M.;
(Hillsborough, NJ) ; Langner, Tadeuz W.;
(Maplewood, NJ) |
Correspondence
Address: |
Law Office of Stuart D. Frenkel, P.C.
Suite 330
3975 University Drive
Fairfax
VA
22030
US
|
Family ID: |
24567730 |
Appl. No.: |
10/233496 |
Filed: |
September 4, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10233496 |
Sep 4, 2002 |
|
|
|
09640313 |
Aug 15, 2000 |
|
|
|
6464957 |
|
|
|
|
Current U.S.
Class: |
423/713 ;
423/718; 502/214 |
Current CPC
Class: |
B01J 29/89 20130101;
C01B 39/085 20130101 |
Class at
Publication: |
423/713 ;
423/718; 502/214 |
International
Class: |
C01B 037/00; B01J
029/03 |
Claims
We claim:
1. A synthetic ETS-4 titanium silicate containing greater than 5%
of a polymorph phase characterized as having pores which
interpenetrate the framework of the ETS-4 in the b- and
c-directions.
2. The synthetic ETS-4 titanium silicate of claim 1, wherein said
pores in the c-direction include c-directed channels formed from
12-membered pores.
3. The synthetic ETS-4 titanium silicate of claim 1, wherein said
titanium silicate includes alkaline earth metal cations exchanged
thereon.
4. The synthetic ETS-4 titanium silicate of claim 3, wherein said
alkaline earth metal cations include barium, calcium or
strontium.
5. The synthetic ETS-4 titanium silicate of claim 1, containing at
least 20% of said polymorph.
6. A synthetic ETS-4 titanium silicate, which comprises greater
than 5% of at least one polymorph phase of ETS-4 which contains
non-faulted channels which penetrate the ETS-4 framework in the
c-direction.
7. The synthetic ETS-4 titanium silicate of claim 6, comprising a
mixture of two of said polymorphs, which contain channels which
interpenetrate the framework of ETS-4 in the c-direction.
8. The synthetic ETS-4 titanium silicate of claim 6, which is
exchanged with alkaline earth metal cations.
9. The synthetic ETS-4 titanium silicate of claim 8, wherein said
alkaline earth metal cations include barium, calcium, or
strontium.
10. The synthetic ETS-4 titanium silicate of claim 6 containing at
least 20% of said at least one polymorph phase.
11. A synthetic, crystalline titanium silicate having a composition
in terms of mole ratios of oxides as follows:1.0.+-.0.25
M.sub.2/nO:TiO.sub.2:Y SiO.sub.2:Z H.sub.2Owherein M is at least
one cation having a valence of n, Y is from 1.0 to 100, and Z is
from 0 to 100 and characterized by an X-ray powder diffraction
pattern having the lines and relative intensities set forth in
Table I below:
4 TABLE 1 d-SPACING (ANGS.) I/I.sub.0 11.65 .+-. 0.25 S-VS 6.95
.+-. 0.25 S-VS 5.28 .+-. 0.15 M-S 4.45 .+-. 0.15 W-M 2.98 .+-. 0.05
VS Where, VS = 50-100 S = 30-70 M = 15-50 W = 5-30
wherein said X-ray powder diffraction pattern has an additional
line at a d-spacing greater than 11.65 .ANG. of a relative
intensity I/I.sub.0 of W-M, and the ratio of peak heights of said
additional line to said line at 11.65.+-.0.25 .ANG. is greater than
5%.
12. The synthetic, titanium silicate of claim 11, wherein said
additional line of said X-ray powder diffraction pattern is at a
d-spacing of 12.5.+-.0.25 .ANG..
13. The synthetic, titanium silicate of claim 11, wherein said
additional line of said X-ray powder diffraction pattern is at a
d-spacing of 13.9.+-.0.25 .ANG..
14. The synthetic, titanium silicate of claim 11 wherein the ration
of peak heights of said additional line to said line at
11.65.+-.0.25 .ANG. is greater than 20%
15. The synthetic ETS-4 titanium silicate of claim 1, which has
been heat treated to reduce the pores in the b-direction to less
than 4 .ANG. and the pores in the c-direction to less than 6
.ANG..
16. The synthetic ETS-4 titanium silicate of claim 5, which has
been heat treated to reduce the channels in the c-direction to less
than 6 .ANG. in diameter.
Description
[0001] This application is a continuation in part of U.S. Ser. No.
09/640,313 filed Aug. 15, 2002.
FIELD OF THE INVENTION
[0002] This invention relates to methods for preparing new
crystalline titanium molecular sieve zeolite compositions. More
particularly, the invention is directed to improved variants of
ETS-4, and methods of forming same.
BACKGROUND OF THE INVENTION
[0003] Since the discovery by Milton and coworkers (U.S. Pat. Nos.
2,882,243 and 2,882,244) in the late 1950's that aluminosilicate
systems could be induced to form uniformly porous, internally
charged crystals, analogous to molecular sieve zeolites found in
nature, the properties of synthetic aluminosilicate zeolite
molecular sieves have formed the basis of numerous commercially
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.
[0004] In the publication "Zeolite Molecular Sieves", Chapter 2,
1974, D. W. Breck hypothesized that perhaps 1,000 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. 4,524,055; 4,603,040; and 4,606,899, totally new
aluminosilicate framework structures are being discovered at a
negligible rate.
[0005] With slow progress in the discovery of new 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.
[0006] 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 7.sup.th 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.
[0007] 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.
[0008] 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 7.sup.th International Zeolite Conference, pp. 13-22 (1986)).
While this particular synthesis approach produces materials which,
by definition, totally lack active, charged sites, back
implantation after synthesis would not appear out of the question
although little work appears in the open literature on this
topic.
[0009] 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 68,796 (1983),
Taramasso, et. al.; Proceedings of the 5.sup.th International
Zeolite Conference; pp. 40-48 (1980)); J. W. Ball, et. al.;
Proceedings of the 7.sup.th International Zeolite Conference; pp.
137-144 (1986); U.S. Pat. No. 4,280,305 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.
[0010] In 1967, Young in U.S. Pat. No. 3,329,481 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
dismissed 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 7.sup.th 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
possibly be interpreted as a small pored zeolite, although without
additional supporting evidence, it appears extremely
questionable.
[0011] 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.,
pp. 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), November-December 1979, pp. 686-693.
[0012] 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. 4,410,501 (1983); G. Perego, et. al.; Proceedings of the
7.sup.th International Zeolite Conference; p. 129 (1986)). A
similar claim appeared from researchers in mid-1985 (EPA 132,550
(1985)). The research community reported mixed
aluminosilicate-titanium (IV) (EPA 179,876 (1985); EPA 181,884
(1985) structures which, along with TAPO (EPA 121,232 (1985)
systems, appear to have no possibility of active titanium sites. As
such, their utility, has been limited to catalyzing oxidation.
[0013] In U.S. Pat. No. 4,938,939, issued Jul. 3, 1990, Kuznicki
disclosed a new family of synthetic, stable crystalline
titaniumsilicate molecular sieve zeolites which have a pore size of
approximately 3-4 Angstrom units and a titania/silica mole ratio in
the range of from 1.0 to 10. The entire content of U.S. Pat. No.
4,938,939 is herein incorporated by reference. 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:
1.0.+-.0.25 M.sub.2/nO:TiO.sub.2:YSiO.sub.2:ZH.sub.2O
[0014] wherein M is at least one cation having a valence of n, Y is
from 1.0 to 10.0, 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 2.5 and ranges up to about
5.
[0015] 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-4 in the rare earth-exchanged form have a high
degree of thermal stability of at least 450 C. or higher depending
on cationic form, thus rendering them effective for use in high
temperature catalytic processes. ETS zeolites are highly adsorptive
toward molecules up to approximately 3-5 Angstroms in critical
diameter, e.g. water, ammonia, hydrogen sulfide, SO.sub.2, and
n-hexane and are essentially non-adsorptive toward molecules which
are larger than 5 Angstroms in critical diameter.
1TABLE 1 XRD POWDER PATTERN OF ETS-4 (0-40E 2 theta) SIGNIFICANT
d-SPACING (ANGS.) I/I.sub.0 11.65 .+-. 0.25 S-VS 6.95 .+-. 0.25
S-VS 5.28 .+-. 0.15 M-S 4.45 .+-. 0.15 W-M 2.98 .+-. 0.05 VS In the
above table, VS = 50-100 S = 30-70 M = 15-50 W = 5-30
[0016] The above values were collected using standard techniques on
a Phillips APD3720 diffractometer equipped with a theta
compensator.
[0017] A large pore crystalline titanium molecular sieve
composition having a pore size of about 8 Angstrom units has also
been developed by the present assignee and is disclosed in U.S.
Pat. No. 4,853,202, which patent is herein incorporated by
reference. This crystalline titanium silicate molecular sieve has
been designated ETS-10.
[0018] The new family of microporous titanosilicates developed by
the present assignee, and generically denoted as ETS, are
constructed from fundamentally different building units than
classical aluminosilicate zeolites. Instead of interlocked
tetrahedral metal oxide units as in classical zeolites, the ETS
materials are composed of interlocked octahedral chains and
classical tetrahedral rings. In general, the chains consist of six
oxygen-coordinated titanium octahedra wherein the chains are
connected three dimensionally via tetrahedral silicon oxide units
or bridging titanosilicate units. The inherently different
crystalline titanium silicate structures of these ETS materials
have been shown to produce unusual and unexpected results when
compared with the performance of aluminosilicate zeolite molecular
sieves. For example, the counter-balancing cations of the
crystalline titanium silicates are associated with the charged
titania chains and not the uncharged rings which form the bulk of
the structure. In ETS-10, this association of cations with the
charged titania chains is widely recognized as resulting in the
unusual thermodynamic interactions with a wide variety of sorbates
which have been found. This includes relative weak binding of polar
species such as water and carbon dioxide and relatively stronger
binding of larger species, such as propane and other hydrocarbons.
These thermodynamic interactions form the heart of low temperature
dessication processes as well as evolving Claus gas purification
schemes. The unusual sorbate interactions are derived from the
titanosilicate structure, which places the counter-balancing
cations away from direct contact with the sorbates in the main
ETS-10 channels.
[0019] In recent years, scores of reports on the structure,
adsorption and, more recently, catalytic properties of wide pore,
thermally stable ETS-10 have been made on a worldwide basis. This
worldwide interest has been generated by the fact that ETS-10
represents a large pore thermally stable molecular sieve
constructed from what had previously been thought to be unusable
atomic building blocks.
[0020] Although ETS-4 was the first molecular sieve discovered
which contained the octahedrally coordinated framework atoms and as
such was considered an extremely interesting curiosity of science,
ETS-4 has been virtually ignored by the world research community
because of its small pores and reported low thermal stability.
Recently, however, researchers of the present assignee have
discovered a new phenomenon with respect to ETS-4. In appropriate
cation forms, the pores of ETS-4 can be made to systematically
shrink from slightly larger than 4 .ANG. to less than 3 .ANG.
during calcinations, while maintaining substantial sample
crystallinity. These pores may be "frozen" at any intermediate size
by ceasing thermal treatment at the appropriate point and returning
to ambient temperature. These controlled pore size materials are
referred to as CTS-1 (contracted titanosilicate-1) and are
described in commonly assigned, U.S. Pat. No. 6,068,682, issued May
30, 2000. Thus, ETS-4 may be systematically contracted under
appropriate conditions to CTS-1 with a highly controllable pore
size in the range of 3-4 .ANG.. With this extreme control,
molecules in this range may be separated by size, even if they are
nearly identical. The systematic contraction of ETS-4 to CTS-1 to a
highly controllable pore size has been named the Molecular Gate.TM.
effect. This effect is leading to the development of separation of
molecules differing in size by as little as 0.1 Angstrom, such as
N.sub.2/0.sub.2 (3.6 and 3.5 Angstroms, respectively),
CH.sub.4/N.sub.2 (3.8 and 3.6 Angstroms), or CO/H.sub.2 (3.6 and
2.9 Angstroms). High pressure N.sub.2/CH.sub.4 separation systems
are now being developed. This profound change in adsorptive
behavior is accompanied by systematic structural changes as
evidenced by X-ray diffraction patterns and infrared
spectroscopy.
[0021] As synthesized, ETS-4 has an approximately 4 .ANG. effective
pore diameter. Reference to pore size or "effective pore diameter"
defines the effective diameter of the largest gas molecules
significantly adsorbed by the crystal. This may be significantly
different from, but systematically related to, the crystallographic
framework pore diameter. For ETS-4, the effective pore is defined
by eight-membered rings formed from TiO.sub.6.sup.2- octahedra and
SiO.sub.4 tetrahedra. This pore is analogous to the functional pore
defined by the eight-membered tetrahedral metal oxide rings in
traditional small-pored zeolite molecular sieves. Unlike the
tetrahedrally based molecular sieves, however, the effective pore
size of the eight-membered ring in ETS-4 can be systematically and
permanently contracted with structural dehydration to CTS-1
materials as above described.
[0022] The pores of ETS-4 formed by the eight-membered polyhedral
TiO.sub.6 and SiO.sub.4 units are non-faulted in a singular
direction, the b-direction, of the ETS crystal and, thus, fully
penetrate the crystal, rendering the ETS-4 and the related
contracted version, CTS-1, extremely useful for molecular
separations whether in the liquid, or gaseous state. The crystal
lattice structure of ETS-4, however, is highly faulted along the
other two of the three-dimensional axes. These faulted a- and
c-directions are permeated by various small channel systems which
are not interpenetrating and which contain serious diffusion
blocks. Due to the open channels along the b-direction, and
faulting in the a- and c-directions of the ETS-4 framework, it has
been proposed that ETS-4 can be described as an intergrowth of four
polymorphs. Two of the polymorphs contain non-blocked 12-ring pores
disposed along the c-direction of the unit cell of ETS-4. These
twelve-ring pores of approximately 6 Angstroms in these two
polymorphs are aligned into channels along the c-direction of the
ETS-4 framework structure without faulting. An ETS-4 molecular
sieve formed of, or enriched by either or both of these c-channel
polymorphs would yield intermediate and large pore variants of
ETS-4 and, importantly, provide a superior CTS-type separation
agent, capable of separating molecules having a size range of from
6 down to 4 Angstroms or less. Such polymorph-enriched ETS-4 would
have the ability to participate in a greatly increased number of
adsorptive separations relative to that believed possible with
ETS-4 and contracted versions thereof formed from a random ETS
intergrowth.
SUMMARY OF THE INVENTION
[0023] In accordance with the present invention, an ETS-4 titanium
silicate is formed comprising enriched amounts of polymorphs which
contain channels formed from 12-ring pores, which channels
inter-penetrate the framework of the ETS-4 along the c-direction.
The c-channeled polymorph-enriched ETS-4 also contains the
interconnecting 8-ring pores along the b-direction of the ETS
framework. The interconnecting pores along both the b- and
c-directions can be systematically contracted to CTS-type materials
by thermal dehydration without destroying the crystal structure of
the titanium silicate. The polymorph-enriched ETS-4 and its
contracted versions can separate by adsorption a greater number of
gaseous and liquid molecules from mixtures containing the same than
previously thought using ETS-4. Thus, whereas ETS-4 formed from an
intergrowth of randomly arranged polymorphs can provide separation
of molecules ranging in size from 4 .ANG. to about 2.5 .ANG., the
C-channeled polymorph-enriched ETS-4 is capable of separating
molecules ranging in size from approximately 6 .ANG. to 4
.ANG..
[0024] The C-channeled polymorph-enriched ETS titanium silicate
molecular sieve is formed in accordance with this invention by
heating a reaction mixture containing a titanium source, a source
of silica, a source of alkalinity, water and a wetting agent to a
temperature of from about 100.degree. C. to 300.degree. C. for a
period time ranging from 8 hours to 40 days while controlling the
pH range within the range used for ETS-4 formation. It has been
found that the addition of the wetting agent to the crystalline
titanium silicate-forming mixture results in an ETS-4 molecular
sieve which is enriched in either or both of the polymorphs which
contain interconnecting pores of 3 .ANG. to 4 .ANG. in diameter
along the b-direction of the framework and interconnecting pores of
4 .ANG. to 6 .ANG. along the c-direction of the ETS-4 framework.
What is meant by enriched is that the ETS-4 crystal contains
greater than 5% of the desired polymorph phase. Preferably, the
ETS-4 crystal contains at least 20% of the polymorph phase which
contains interconnecting pores in the b- and c-direction of the
framework.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a skeletal depiction of ETS-4 taken as a section
across the c-direction of the ETS-4 framework.
[0026] FIG. 2 is a skeletal depiction of ETS-4 taken as a section
across the b-direction of the ETS-4 framework.
[0027] FIGS. 3(a)-3(d) are two-dimensional polyhedral depictions of
the four pure polymorphs of ETS-4, respectively, wherein I is a
cross-section across the c-direction of the ETS-4 framework and II
is a section across the a-direction of the ETS-4 framework.
[0028] FIG. 4 is an X-ray diffraction pattern of ETS-4
(0.degree.-15.degree., 2.theta.) of a standard prepared ETS-4.
[0029] FIG. 5 is an X-ray diffraction pattern
(0.degree.-15.degree., 2.theta.) of a polymorph-enriched ETS-4.
[0030] FIG. 6 is an X-ray diffraction pattern
(0.degree.-15.degree., 2.theta.) of a polymorph-enriched ETS-4.
DETAILED DESCRIPTION OF THE INVENTION
[0031] ETS-4 molecular sieve zeolites are prepared in accordance
with aforementioned U.S. Pat. No. 4,938,939 from a reaction mixture
containing a titanium source such as titanium trichloride, a source
of silica, a source of alkalinity such as an alkali metal
hydroxide, water and, optionally, an alkali metal fluoride having a
composition in terms of mole ratios falling within the following
ranges.
2 TABLE 2 Broad Preferred Most Preferred SiO.sub.2/Ti 1-10 1-10 2-3
H.sub.2O/SiO.sub.2 2-100 5-50 10-25 M.sub.n/SiO.sub.2 0.1-10 .5-5
1-3
[0032] wherein M indicates the cations of valence n derived from
the alkali metal hydroxide and potassium fluoride and/or alkali
metal salts used for preparing the titanium silicate according to
the invention. The reaction mixture is heated to a temperature of
from about 100.degree. C. to 300.degree. C. for a period of time
ranging from about 8 hours to 40 days, or more. The hydrothermal
reaction is carried out until crystals are formed and the resulting
crystalline product is thereafter separated from the reaction
mixture by cooling to room temperature filtering and water washed.
The reaction mixture can be stirred although it is not necessary.
It has been found that when using gels, stirring is unnecessary but
can be employed. When using sources of titanium which are solids,
stirring is beneficial. The preferred temperature range is
150.degree. C. to 250.degree. C. for a period of time ranging from
12 hours to 15 days. Crystallization is performed in a continuous
or batchwise manner under autogeneous pressure in an autoclave or
static bomb reactor. Following the water washing step, the
crystalline ETS-4 is dried at temperatures of 100.degree. to
400.degree. F. for periods ranging up to 30 hours.
[0033] The method for preparing ETS-4 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.2O.sub.3.
However, when titanium silicates are prepared from gels, its value
is greatly diminished.
[0034] 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.
[0035] The titanium oxide source includes trivalent or tetravalent
titanium compounds such as titanium trichloride, TiCl.sub.3,
tetrachloride, TiCl.sub.4, titanium sulfate, Ti(SO.sub.4).sub.2,
titanium oxychloride, TiOCl.sub.2, etc. Solid sources of titanium
oxide can also be used including TiO.sub.2 (rutile, anatase or
brookite), and Ti.sub.2O.sub.3.
[0036] 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 10.45 to 11.0.+-.0.1. The alkali metal
hydroxide serves as a source of sodium oxide which can also be
supplied by an aqueous solution of sodium silicate.
[0037] The titanium silicate ETS-4 prepared according to U.S. Pat.
No. 4,938,939 and the improved method (discussed below) of this
invention contains no deliberately added alumina, and may contain
very minor amounts of Al.sub.2O.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.2O.sub.3 will be 0 or higher than 5000 or
more.
[0038] The ETS-4 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, alkyl 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.
[0039] 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 may thereafter be
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.
[0040] Regardless of the synthesized form of the titanium silicate,
ETS-4, 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 1 above.
[0041] FIG. 4 is an X-ray diffraction pattern of a standard
prepared ETS-4 crystal lattice. The two strong--very strong single
peaks shown correspond to the d-spacings of 11.65 .ANG. and 6.95
.ANG. depicted in Table 1 above. As will be discussed later, the
XRD pattern of FIG. 4 which represents an ETS-4 having a random
stacking of the four polymorphs which form ETS-4 is different from
the XRD pattern found with the polymorph-enriched ETS-4 in which
interpenetrating 12-ring pores are located along the c-direction of
the ETS-4 framework. The polymorph-enriched ETS-4 can be considered
as a new titanosilicate species and has been named ETS-6.
[0042] The individual polymorphs, which form the ETS-4 framework
are depicted in FIGS. 3(a) through 3(d) and can be described in
connection with FIGS. 1, 2, and 3(a)-(d). The ETS materials are
composed of chains 10 of six oxygen-coordinated titanium octahedra
12, which are disposed along the b-direction of the ETS framework
and which are connected in the a- and c-directions via tetrahedral
silicon oxide units 14, see FIGS. 1 and 2. The titania chains 10
which run along the b-axis are connected along the a-axis by
12-membered rings 16 formed by two pairs of titania octahedra 12
placed along the b-direction and spaced from each other in the
a-direction, and two pairs of four silica tetrahedra 14 spaced from
each other in the b-direction and which interconnect the two
titania chains 10 in the a-direction. In the c-direction, the
titania chains are connected via a pair of interconnecting silica
tetrahedra 14 as shown in FIG. 2. The structure of ETS-4 is highly
faulted in the a- and c-directions of the framework. Regardless of
the extent of faulting in the a- and c-directions, the ETS-4
crystal lattice contains open channels along the b-direction which
interpenetrate the ETS-4 framework.
[0043] It has been proposed that ETS-4 is an inter-growth of four
pure polymorphs, which are shown in FIGS. 3(a)-3(d). All of the
polymorphs of ETS-4 are faulted (diffusion blocked) in the
a-direction in view of links of silica tetrahedra which cross the
plane of the a-axis of the lattice structure while connecting the
titania chains in the c-direction. These silica tetrahedral links
also form pores which are too small to provide a functional
interpenetrating network of diffusion channels. Two of the
polymorphs are faulted in the c-direction while the other two
polymorphs are non-faulted in the c-direction providing an ETS-4
framework which contains 12-ring pores which interpenetrate the
framework. The two polymorphs of ETS-4 which are faulted in the
c-direction are shown in FIGS. 3(a) and 3(b). Regarding FIGS. 3(a)
and 3(b), the ETS-4 framework as shown includes an arrangement of
12-ring pores which penetrate the framework in the c-direction. As
seen in FIG. 3(a), the open 12-ring pores are arranged in an
alternating ABAB arrangement along the a-direction of the
framework. Thus, every other 12-ring pore placed along the
a-direction is located at the same position on the b-axis of the
framework. In FIG. 3(b), the 12-ring pores are arranged in an ABCD
arrangement in which every fifth 12-ring pore placed along the
a-direction is at the same location on the b-axis of the framework.
The faulting in the c-direction in each of the polymorphs shown in
FIGS. 3(a) and 3(b) is due to the ACAC placement of titanosilicate
bridges 18 across alternating 12-ring pores along the b- and
c-directions. The titanosilicate bridges 18 include a titania
octahedra 12 bridging two pairs of silica tetrahedra 14 forming a
portion of the 12-membered ring pore. The faulting can be seen in
FIGS. 3(a) and 3(b), Section II, where the titanosilicate bridges
18 are present in alternate pores along both the b- and
c-directions of the ETS-4 framework. The 12-ring pores cannot form
interpenetrating channels in the c-direction and are essentially
diffusion blocked.
[0044] The ETS-4 polymorphs, which are non-faulted in the
c-direction are shown in FIGS. 3(c) and 3(d). As in the polymorphs
shown in FIGS. 3(a) and 3(b), the 12-ring pores open along the
c-direction are arranged along the a- and b-directions by an ABAB
arrangement as shown in FIG. 3(c) and an ABCD arrangement as shown
in FIG. 3(d). The 12-ring pores having the equivalent position on
the b-axis are shown by the letter "A" in the respective figures.
Unlike the polymorphs in FIGS. 3(a) and 3(b), however, the
polymorphs shown in FIGS. 3(c) and 3(d) have the titanosilicate
bridges 18 aligned in uniform rows in the b- and c-directions. In
these polymorphs, all of the 12-ring pores spaced along the
c-direction and which are at the same location on the b-axis of the
ETS-4 lattice framework are either constricted with the
titanosilicate bridges 18, or are free of the titanosilicate
bridges 18 leading to formation of 12-ring channels in the
c-direction which interpenetrate the ETS-4 framework. This is shown
in FIGS. 3(c) and 3(d), Section II as channels 20.
[0045] Under the synthesis conditions of ETS-4 as described in U.S.
Pat. No. 4,938,939, the individual polymorphs of ETS-4 shown in
FIGS. 3(a)-3(d) are randomly stacked to form the crystal framework.
Accordingly, the ETS-4 crystal which forms is highly faulted in the
c-direction. The 8-ring pores open in the b-direction remain
unfaulted regardless of how the polymorphs are stacked or
distributed and form b-channels which interpenetrate the ETS-4
framework. The open b-channels provide the useful adsorption and
separation properties of ETS-4 heretofore found. By enriching the
ETS-4 crystal which is formed with the polymorphs ABAB-AA shown in
FIG. 3(c) and/or ABCD-AA shown in FIG. 3(d), the ETS-4 crystal now
includes intermediate sized pores along the c-direction in addition
to the small pores present along the b-direction of the
framework.
[0046] Importantly, the 12-ring pores along the c-direction can
also be contracted by thermal treatment without destruction of the
lattice structure into CTS-type materials. By controlling the
thermal treatment and the shrinkage of the pores, selective
adsorption of one of similar sized molecules can be readily
achieved. Previous to this invention, CTS-1 materials formed by
controlled shrinkage of the b-channels in ETS-4 had pores which
could be controlled in size from about 4 .ANG. to approximately 2.5
.ANG.. By enriching ETS-4 with the polymorphs which are non-faulted
in the c-direction, formation of CTS materials having pores sized
from about 6 .ANG. to 2.5 .ANG. can be obtained. The presence of
the additional intermediate sized interpenetrating pores provides
ETS-4 and contracted versions thereof with the ability to separate
a substantially wider number of molecular mixtures.
[0047] In accordance with this invention, ETS-4 is formed
containing an enriched portion of those polymorphs which have the
interconnecting 12-ring pores in the c-direction of the framework
as shown in FIGS. 3(c) and 3(d). These novel ETS-4 structures are
formed by incorporating within the reaction mixture which contains
a titanium source, a silica source, a source of alkalinity and
water, a wetting agent which is able to reduce the surface tension
of the reaction mixture. The preferred wetting agents are
surfactants which can be anionic, non-ionic, or amphoteric in
nature or mixtures of the various types of surfactants can be
used.
[0048] Anionic surfactants appear to be preferred. Examples of
suitable anionic surfactants are water-soluble salts of the higher
alkyl sulfates, such as sodium lauryl or other suitable alkyl
sulfates having 8 to 18 carbon atoms in the alkyl group,
water-soluble salts of higher fatty acid monoglyceride
monosulfates, such as the sodium salt of the monosulfated
monoglyceride of hydrogenated coconut oil fatty acids, alkyl aryl
sulfonates such as sodium dodecyl benzene sulfonate, higher alkyl
sulfoacetates, higher fatty acid esters of 1,2-dihydroxy propane
sulfonate, and the substantially saturated higher aliphatic acyl
amides of lower aliphatic amino carboxylic acid compounds, such as
those having 12 to 16 carbons in the fatty acid, alkyl or acyl
radicals, and the like. Examples of the last mentioned amides are
N-lauroyl sarcosinate, and the sodium, potassium, and ethanolamine
salts of N-lauroyl, N-myristoly, or N-palmitoyl sarcosinate sold by
W. R. Grace under the tradename "Hamposyl". Also effective are
polycarboxylated ethylene oxide condensates of fatty alcohols
manufactured by Olin under the tradename of "Polytergent CS-1".
[0049] Amphoteric surfactants are a well known class of surfactants
which includes the alkyl beta-aminodipropionates
RN(C.sub.2H.sub.4COOM).sub.2 and the alkyl beta-aminopropionates
RNHCH.sub.4COOM where the alkyl group R contains 8 to 18 carbon
atoms in both formulas and M is a salt-forming cation such as the
sodium ion. Further examples are the long chain imidazole
derivatives, for example, the di-sodium salt of
lauroyl-cycloimidinium-1-ethoxy-ethionic acid-2-ethionic acid, and
the substituted betaines such as alkyl dimethyl amminio acetates
where the alkyl group contains 12 to 18 carbon atoms.
N-alkyl-2-pyrrolidones which are highly polar apiotic solvents, are
also surface active and can be used. "Surfadone LP-100" from
International Specialty Products has been found particularly
useful.
[0050] Suitable non-ionic surfactants include the
polyoxyethylene-polyoxyp- ropylene condensates, which are sold by
BASF under the tradename "Pluronic", polyoxyethylene condensates of
alkyl phenols; polyoxyethylene condensates of aliphatic
alcohols/ethylene oxide condensates having from 1 to 30 moles of
ethylene oxide per mole of coconut alcohol; ethoxylated long chain
alcohols sold by Shell Chemical Co. under the tradename "Neodol",
polyoxyethylene condensates of sorbitan fatty acids, alkanolamides,
such as the monoalkoanolamides, dialkanolamides and the ethoxylated
alkanolamides, for example coconut monoethanolamide, lauric
isopropanolamide and lauric diethanolamide; and amine oxides for
example dodecyldimethylamine oxide.
[0051] The wetting agent will generally be present in amounts of
from about 0.05 to about 20.0% by weight based on the content of
the reaction mixture, preferably from about 0.5 to about 10.0% by
weight based on the total weight of the reaction mixture. The
wetting agent is simply mixed with all the reactants and the
mixture heated as described in U.S. Pat. No. 4,938,939.
[0052] 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. For use as adsorbents, membranes of ETS-4 may be
useful.
[0053] The novel polymorph-enriched ETS-4 materials of this
invention are useful as adsorbents to separate gaseous and liquid
mixtures and as catalysts. When particularly used as a catalyst, it
is desired to incorporate the new crystalline titanium silicate
with another material resistant 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 slectivity of the catalyst in certain organic conversion
processes such as the cracking of n-hexane. 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 the crush strength of the catalyst under
commercial 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.
[0054] Naturally occurring clays that can be composited with the
crystalline titanium silicate described herein include the
montmorillonite and kaolin family, which families include the
sub-bentonites and the kaolins known commonly as Dixie, McNamee,
Georgia 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 calcinations, acid treatment or chemical modification.
[0055] In addition to the foregoing materials, the crystalline
titanium silicate may be composited with a porous matrix material
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%
by weight and more usually in the range of about 2% to about 50% by
weight of the composite.
[0056] 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.
[0057] 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.
EXAMPLE I
[0058] In this Example, the preparation of a polymorph-enriched
ETS-4 is set forth.
[0059] The following ingredients were mixed in a beaker.
3 Component Amount H.sub.2O 4.0 grams NaOH(s) 2.0 grams
Sodiumsilicate.sup.1 5.3 grams Titanium oxide 0.369 grams ETS-4
0.041 grams Sodium lauryl sulfate.sup.2 0.50 grams .sup.1N-Brand
.RTM. .sup.2Ivory Snow .RTM.
[0060] The mixed reactants were poured into a Teflon-lined
autoclave, which was sealed. The autoclave was heated to
225.degree. C. and maintained at temperature for seventeen hours.
The product was filtered and washed with hot water and dried at
100.degree. C.
[0061] FIG. 5 is an X-ray diffraction pattern of the product formed
as above-described. The XRD pattern was formed on a Philips
APD37320 diffractometer equipped with a theta compensator. The
theta compensator maintains a constant area of illumination on the
sample, so X-ray intensities obtained from a theta compensated unit
are not directly comparable to those of a non-compensated unit.
Thus, all values mentioned in the specification and claims with
regard to the novel ETS-4 materials of this invention were
determined by the theta compensated X-ray equipment. The radiation
was the K-alpha doublet of copper, and a scintillation counter
spectrometer was used. The peak heights, I, and the positions as a
function of 2 times theta, where theta is the Bragg angle were read
from the spectrometer chart. From these, the relative intensities,
100 I/I.sub.0, where I.sub.0 is the intensity of the strongest line
or peak, and d, the interplanar spacing in angstroms, corresponding
to the recorded lines, were calculated.
[0062] A comparison of FIG. 5 with FIG. 4, which is an XRD pattern
of ETS-4 prepared by the standard method without wetting agent
reveals that both materials contain the strong peaks corresponding
to d-values of 11.65 .ANG. and 6.95 .ANG.. What is unique in the
XRD pattern of the polymorph-enriched ETS-4 of this invention is
the significant peak corresponding to a d-value of greater than
11.65 which is not seen in the ETS-4 material formed by the
standard method. The peak shown indicated by reference numeral 30
is at a d-spacing of 12.5.+-.0.25 .ANG.. The ETS-4 of FIG. 5
contains at least 20% of the desired polymorph phase.
EXAMPLE II
[0063] A polymorph-enriched ETS-4 was produced by the procedure of
Example I. Exceptions included a reduced level of titanium dioxide
(0.1575 grams versus 0.369 grams) and an increased level of ETS-4
seed (0.0525 grams versus 0.041 grams). The reactants were mixed
and heated as set forth in Example I above.
[0064] FIG. 6 is the XRD pattern for the material, which was
formed. As in FIGS. 4 and 5, the XRD pattern in FIG. 6 includes the
strong peaks, which correspond to d-spacings of 11.65 .ANG. and
6.95 .ANG.. Further, similar to FIG. 5, the XRD pattern shows a
distinct peak indicated by reference numeral 32 corresponding to a
d-spacing of greater than 11.65 .ANG. which peak is absent from the
XRD pattern of ETS-4 formed by the standard procedure. The new peak
32 corresponds to a d-spacing of 13.9.+-.0.25 .ANG. and corresponds
to an ETS-4 containing over 5% of the desired polymorph phase.
DISCUSSION
[0065] The XRD patterns set forth in FIGS. 5 and 6 correspond
almost perfectly with computer simulated XRD patterns developed
from proposed polymorphs ABAB-AA and ABCD-AA as set forth in FIGS.
3(c) and 3(d). The proposed polymorphs and computer XRD simulation
assumed zero faulting in the c-direction. The substantially perfect
match between the computer simulated XRD pattern and those found
with the formed materials shows that the material produced includes
at least a portion of the ETS-4 polymorphs which are non-faulted in
the c-direction of the crystal framework. The ETS-4 materials which
are enriched in the polymorphs, which are non-faulted in the
c-direction can be considered a different species of
titanosilicate. Accordingly, these polymorphs of ETS-4, which
contain the 12-ring channels interpenetrating the lattice framework
in the c-direction have been given the name ETS-6.
[0066] Once given the above disclosure, many other features,
modifications, and improvements will become apparent to the skilled
artisan. Such other features, modifications, and improvements are,
therefore, considered to be a part of this invention, the scope of
which is to be determined by the following claims.
* * * * *