U.S. patent application number 11/403682 was filed with the patent office on 2006-11-09 for molecular sieve layers and processes for their manufacture.
Invention is credited to Antonie Jan Bons, Anthonie Jan Burggraaf, Edward William JR. Corcoran, Lothar Ruediger Czarnetzki, Harry William Deckman, Allan Joseph Jacobson, Klaas Keizer, Frank Wenyih Lai, James Alexander McHenry, Wilfred Jozef Mortier, Jannetje Maatje van den Berge, Johannes Petrus Verduijn, Zeger Alexander Eduard Pieter Vroon.
Application Number | 20060252631 11/403682 |
Document ID | / |
Family ID | 8214389 |
Filed Date | 2006-11-09 |
United States Patent
Application |
20060252631 |
Kind Code |
A1 |
Deckman; Harry William ; et
al. |
November 9, 2006 |
Molecular sieve layers and processes for their manufacture
Abstract
Layers comprising a molecular sieve layer on a porous or
non-porous support, having uniform properties and allowing high
flux are prepared from colloidal solutions of zeolite or other
molecular sieve precursors (particle size less than 100 nm), by
deposition, e.g., by spin or dip-coating, or by in situ
crystallization.
Inventors: |
Deckman; Harry William;
(Clinton, NJ) ; van den Berge; Jannetje Maatje;
(Oostvoorne, NL) ; Jacobson; Allan Joseph;
(Houston, TX) ; McHenry; James Alexander;
(Washington, NJ) ; Keizer; Klaas; (Hoogeveen,
NL) ; Vroon; Zeger Alexander Eduard Pieter;
(Eindhoven, NL) ; Czarnetzki; Lothar Ruediger;
(Karlsruhe, DE) ; Lai; Frank Wenyih; (Bridgewater,
NJ) ; Bons; Antonie Jan; (Kessel-Lo, BE) ;
Burggraaf; Anthonie Jan; (Enschede, NL) ; Verduijn;
Johannes Petrus; (Leefdaal, BE) ; Corcoran; Edward
William JR.; (Easton, PA) ; Mortier; Wilfred
Jozef; (Kessel-Lo, BE) |
Correspondence
Address: |
EXXONMOBIL RESEARCH AND ENGINEERING COMPANY
P.O. BOX 900
1545 ROUTE 22 EAST
ANNANDALE
NJ
08801-0900
US
|
Family ID: |
8214389 |
Appl. No.: |
11/403682 |
Filed: |
April 13, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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08545707 |
Sep 28, 1998 |
7049259 |
|
|
PCT/EP94/01301 |
Apr 25, 1994 |
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11403682 |
Apr 13, 2006 |
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Current U.S.
Class: |
502/60 |
Current CPC
Class: |
B01J 35/1057 20130101;
B01D 2323/08 20130101; B01J 2229/42 20130101; B01J 35/10 20130101;
B01J 37/0246 20130101; B01D 67/0046 20130101; B01J 20/183 20130101;
B01D 71/028 20130101; B01D 2325/02 20130101; B01J 29/40 20130101;
B01J 35/065 20130101; B01D 69/141 20130101; B01J 2229/64 20130101;
B01J 29/06 20130101; B01J 35/1061 20130101; B01J 29/035 20130101;
B01D 2325/04 20130101; B01D 67/0051 20130101 |
Class at
Publication: |
502/060 |
International
Class: |
B01J 29/04 20060101
B01J029/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 23, 1993 |
EP |
93303187.4 |
Claims
1. A process for catalyzing a chemical reaction which comprises
contacting a feedstock with a supported inorganic layer which is in
active catalytic form, comprising contiguous particles of a
crystalline molecular sieve, the particles having a mean particle
size within the range of from 20 nm to 1 .mu.m, and wherein the
layer primarily contains nanopores having a size of between 1 and
10 nm, under catalytic conversion conditions and recovering a
composition comprising at least one conversion product.
2. The process of claim 2, wherein the supported inorganic layer
primarily contains micropores having a size of between 0.2 and 1
nm.
3. The process of claim 1, wherein the particle size distribution
of the supported inorganic layer is such that at least 95% of the
particles have a size within .+-.33% of the mean.
4. The process of claim 1, wherein the support is selected from the
group consisting of glass, fused quartz, silica, silicon, clay,
metal, porous glass, sintered porous metal, titania, and
cordierite.
5. The process of claim 4, wherein the supported inorganic layer
primarily contains micropores having a size of between 0.2 and 1
nm.
6. The process of claim 5, wherein the particle size distribution
of the supported inorganic layer is such that at least 95% of the
particles have a size within .+-.33% of the mean.
7. A process for catalyzing a chemical reaction which comprises
contacting a feedstock with one face of an supported inorganic
layer which is in the form of a membrane and is in active catalytic
form, comprising contiguous particles of a crystalline molecular
sieve, the particles having a mean particle size within the range
of from 20 nm to 1 .mu.m, and wherein the layer primarily contains
nanopores having a size of between 1 and 10 nm, under catalytic
conversion conditions and recovering from an opposite face of the
layer at least one conversion product.
8. The process of claim 7, wherein the supported inorganic layer
primarily contains micropores having a size of between 0.2 and 1
nm.
9. The process of claim 7, wherein the particle size distribution
of the supported inorganic layer is such that at least 95% of the
particles have a size within .+-.33% of the mean.
10. The process of claim 7, wherein the support is selected from
the group consisting of glass, fused quartz, silica, silicon, clay,
metal, porous glass, sintered porous metal, titania, and
cordierite.
11. The process of claim 10, wherein the supported inorganic layer
primarily contains micropores having a size of between 0.2 and 1
nm.
12. The process of claim 11, wherein the particle size distribution
of the supported inorganic layer is such that at least 95% of the
particles have a size within .+-.33% of the mean.
13. The process of claim 7, wherein the concentration of at least
one of the conversion products recovered from the opposite face of
the layer is different than the equilibrium concentration of the
conversion product in the reaction mixture.
14. The process of claim 10, wherein the concentration of at least
one of the conversion products recovered from the opposite face of
the layer is different than the equilibrium concentration of the
conversion product in the reaction mixture.
15. The process of claim 12, wherein the concentration of at least
one of the conversion products recovered from the opposite face of
the layer is different than the equilibrium concentration of the
conversion product in the reaction mixture.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 08/545,707, which is the National Stage of International
Application Number PCT/EP94/01301 filed Apr. 25, 1994, which claims
the benefit of European Application Number 93303187.4, filed Apr.
23, 1993.
BACKGROUND OF THE INVENTION
[0002] This invention relates to molecular sieves, more especially
to crystalline molecular sieves, and to layers containing them.
More especially, the invention relates to a layer, especially a
supported layer, containing particles of a crystalline molecular
sieve.
[0003] Molecular sieves find many uses in physical,
physicochemical, and chemical processes, most notably as selective
sorbents, effecting separation of components in mixtures, and as
catalysts. In these applications, the crystallographically-defined
pore structure within the molecular sieve material is normally
required to be open, and it is then a prerequisite that any
structure-directing agent, or template, that has been employed in
the manufacture of the molecular sieve be removed, usually by
calcination.
[0004] Numerous materials are known to act as molecular sieves,
among which zeolites form a well-known class. Examples of zeolites
and other materials suitable for use in the invention will be given
below.
[0005] When molecular sieves are used as sorbents or catalysts they
are often in granular form. Such granules may be composed entirely
of the molecular sieve or be a composite of a binder or support and
the molecular sieve, with the latter distributed throughout the
entire volume of the granule. In any event, the granule usually
contains a non-molecular sieve pore structure which improves mass
transfer through the granule.
[0006] The support may be continuous, e.g., in the form of a plate,
or it may be discontinuous, e.g., in the form of granules. The
molecular sieve crystals may be of such a size that, although the
pores of the support are occupied by the crystals, the pores remain
open. Alternatively, the molecular sieve may occupy the pores to an
extent that the pores are effectively closed; in this case, when
the support is continuous a molecular sieve membrane may
result.
[0007] Thus, depending on the arrangement chosen and the nature and
size of the material to be contacted by the molecular sieve,
material may pass through the bulk of the molecular sieve material
entirely through the pores of the molecular sieve material, or
entirely through interstices between individual particles of the
molecular sieve material, or partly through the pores and partly
through the interstices.
[0008] Molecular sieve layers having the permeation path entirely
through the molecular sieve crystals have been proposed for a
variety of size and shape selective separations. Membranes
containing molecular sieve crystals have also been proposed as
catalysts having the advantage that they may perform catalysis and
separation simultaneously if desired.
[0009] In EP-A-135069, there is disclosed a composite membrane
comprising a porous support, which may be a metal, e.g., sintered
stainless steel, an inorganic material, or a polymer, one surface
of which is combined with an ultra thin (less than 25 nm) film of a
zeolite. In the corresponding U.S. Pat. No. 4,699,892, it is
specifically stated that the zeolite is non-granular. In
EP-A-180200, a composite membrane is disclosed, employing a zeolite
that has been subjected to microfiltration to remove all particles
of 7.5 nm and above. The membrane is made by impregnation of a
porous support by the ultrafiltered zeolite solution, resulting in
a distribution of the zeolite crystals within the pore
structure.
[0010] In EP-A-481660, which contains an extensive discussion of
earlier references to membranes, there is disclosed a zeolite
membrane on a porous support, in which the zeolite crystals are
stated to form an essentially continuous layer over and be directly
bonded to the support. The membrane is formed by immersing the
support in a synthesis gel, multiple immersions being employed to
ensure that any pinholes are occluded by the zeolite crystals being
formed within the pores.
[0011] Zeolites with a small particle size and narrow size
distribution are disclosed for use in composite
polydimethylsiloxane membranes in J. Mem. Sci. 73 (1992) p 119 to
128, by Meng-Dong Jia et al; however, the crystal size, though
uniform, is within the range of 200 to 500 nm. Bein et al, in
Zeolites, Facts, Figures, Future, Elsevier, 1989, pp 887 to 896,
disclose the manufacture of zeolite Y crystals of a size of about
250 nm and embedding them in a glassy silica matrix. Even smaller
sizes such as 2 to 10 nm are envisaged in WO 92/19574.
[0012] In Zeolites, 1992, Vol. 12, p 126, Tsikoyiannis and Haag
describe the formation of membranes from zeolite synthesis gels on
both porous and non-porous supports; when the support is
non-porous, e.g., poly-tetrafluorethylene or silver, the membrane
is separable from the support. When the support is porous, e.g., a
Vycor (a trademark) porous glass disk, the membrane is strongly
bonded to the surface, zeolite crystallization within the pores
being prevented by presoaking the disk in water.
[0013] Numerous other techniques for forming membranes have been
proposed. In EP-A-397216, methods of making crack- and pinhole-free
alumina films of a thickness within the range of from 0.01 to 2
.mu.m on a porous support layer are described, the methods
including brush, spray, dip, spin coating, electrophoretic and
thermophoretic techniques. The membranes may be pretreated.
[0014] Despite the proposals in these literature and patent
references, there still remains a need for a supported inorganic
molecular sieve layer having a controllable thickness that may, if
desired, be of a thickness of the order of only a few microns.
There accordingly also remains a need for a process of
manufacturing such a layer whereby the uniformity of the layer
thickness may be controlled, even when the layer is thin.
[0015] Such a layer and a process for its manufacture make possible
the production of a number of useful products, including membranes,
which because of their uniformity and thinness will have
predictable properties, and will permit a high flux.
SUMMARY OF THE INVENTION
[0016] It has now been found that such a supported layer is
obtainable using as starting material a crystalline molecular sieve
of very small particle size, preferably of a size that a true
colloidal dispersion of the particles may be obtained, and
preferably also of a narrow particle size distribution.
[0017] In a first aspect of the invention, there is provided a
layer comprising a supported inorganic layer comprising contiguous
particles of a crystalline molecular sieve, the particles having a
mean particle size within the range of from 20 nm to 1 .mu.m.
[0018] Advantageously, in the first aspect of the invention, the
mean particle size is within the range of from 20 to 500 nm,
preferably it is within the range of from 20 to 300 nm and most
preferably within the range of from 20 to 200 nm. Alternatively,
the mean particle size is advantageously such that at least 5% of
the unit cells of the crystal are at the crystal surface.
[0019] In a second aspect of the invention, there is provided a
supported inorganic layer comprising particles of a crystalline
molecular sieve, the particles having a mean particle size within
the range of from 20 to 200 nm.
[0020] In both the first and second aspects of the invention, the
layer comprises molecular sieve particles optionally coated with
skin of a different material; these are identifiable as individual
particles (although they may be intergrown as indicated below) by
electron microscopy. The layer, at least after activation, is
mechanically cohesive and rigid. Within the interstices between the
particles in this rigid layer, there may exist a plethora of
non-molecular sieve pores, which may be open, or partially open, to
permit passage of material through or within the layer, or may be
completely sealed, permitting passage through the layer only
through the pores in the particles.
[0021] Advantageously, the particle size distribution is such that
95% of the particles have a size within .+-.33% of the mean,
preferably 95% are within .+-.15% of the mean, preferably .+-.10%
of the mean and most preferably 95% are within .+-.7.5% of the
mean.
[0022] It will be understood that the particle size of the
molecular sieve material forming the layer may vary continuously or
stepwise with distance from the support. In such a case, the
requirement for uniformity is met if the particle size distribution
is within the defined limit at one given distance from the support,
although advantageously the particle size distribution will be
within the defined limit at each given distance from the
support.
[0023] The use of molecular sieve crystals of small particle size
and preferably of homogeneous size distribution facilitates the
manufacture of a three-dimensional structure which may if desired
be thin but which is still of controlled thickness.
BRIEF DESCRIPTION OF THE FIGURES
[0024] FIG. 1 is a Scanning Electron Microscopy ("SEM") image of
the cross-section of a silica/zeolite layer manufactured on a
porous alpha-alumina support by spin-coating in conjunction with
the use of a temporary barrier layer.
[0025] FIG. 2 is an SEM image of the cross-section of a
silica/zeolite layer manufactured on a porous alpha-alumina support
by spin-coating in conjunction without the use of a temporary
barrier layer.
[0026] FIG. 3 is an SEM image of the cross-section of a
silica/zeolite layer manufactured on an alpha-alumina support by
spin-coating in conjunction with the use of a permanent barrier
layer.
[0027] FIG. 4 is an SEM image of the top-view of a silica/zeolite
layer manufactured on an alpha-alumina support by spin-coating in
conjunction with the use of a permanent barrier layer.
[0028] FIG. 5 is a data plot illustrating the separation properties
of a silica/zeolite layer manufactured on a alpha-alumina support
by spin-coating in conjunction with the use of a permanent barrier
layer as shown in FIGS. 3 and 4. The data plot shows of a relative
molar concentrations of the permeate obtained from subjecting the
structure to an equimolar mixture of toluene, m-xylene, n-octane,
and i-octane.
[0029] FIG. 6 is an SEM image of the cross-section of a
silica/zeolite layer manufactured on a porous alpha-alumina support
by spin-coating in conjunction with the use of a temporary barrier
layer and hydrothermal crystallization techniques.
[0030] FIG. 7 is an SEM image of the top-view of a silica/zeolite
layer manufactured on alpha-alumina support by dipping the support
into a silica/zeolite mixture in conjunction with the use of an
aging solution and heat treatment.
[0031] FIG. 8 is an SEM image of the cross-section of a
silica/zeolite layer manufactured on alpha-alumina support by
dipping the support into a silica/zeolite mixture in conjunction
with the use of an aging solution and heat treatment.
[0032] FIG. 9 is an SEM image of an alpha-alumina support surface
prior to in-situ formation of zeolite crystals on the support.
[0033] FIG. 10 is an SEM image of an alpha-alumina support surface
following in-situ formation of zeolite crystals on the support at
150.degree. C. followed by calcining.
[0034] FIG. 11 is an SEM image of an alpha-alumina support surface
following in-situ formation of zeolite crystals on the support at
98.degree. C. followed by calcining.
[0035] FIG. 12 is an SEM image (at 156.times. magnification) of a
alpha-alumina support surface following in-situ formation of
zeolite crystals on the support at 120.degree. C. followed by
calcining.
[0036] FIG. 13 is an SEM image (at 10,000.times. magnification) of
the same alpha-alumina support surface as FIGS. 12 and 14.
[0037] FIG. 14 is an SEM image (at 80,000.times. magnification) of
the same alpha-alumina support surface as FIGS. 12 and 13.
[0038] FIG. 15 is an SEM image of a cross-section of a
alpha-alumina support surface following in-situ formation of
zeolite crystals on the support at 120.degree. C. followed by
calcining as shown in FIGS. 12-14.
DETAILED DESCRIPTION OF THE INVENTION
[0039] In the first aspect of the invention, the particles are
contiguous, i.e., substantially every particle is in contact with
one or more of its neighbours, as evidenced by electron microscopy
preferably high resolution microscopy although not necessarily in
contact with all its closest neighbours. Such contact may be such
in some embodiments that neighbouring crystal particles are
intergrown, provided they retain their identity as individual
crystalline particles. Advantageously, the resulting three
dimensional structure is grain-supported, rather than
matrix-supported, in the embodiments where the layer does not
consist essentially of the crystalline molecular sieve particles.
In a preferred embodiment, the particles in the layer are closely
packed.
[0040] In the second aspect of the invention, the particles may be
contiguous, but need not be.
[0041] A layer in accordance with either the first or the second
aspect of the invention may be constructed to contain passageways
between the particles that provide a non-molecular sieve pore
structure through or into the layer. Such a layer may consist
essentially of the particles or may contain another component,
which may be loosely termed a matrix which, while surrounding the
particles, does not so completely or closely do so that all
pathways round the particles are closed. Alternatively, the layer
may be constructed so that a matrix present completely closes such
pathways, with the result that the only path through or into the
layer is through the particles themselves.
[0042] It will be understood that references herein to the support
of a layer include both continuous and discontinuous supports.
[0043] References to particle size are throughout this
specification to the longest dimension of the particle and particle
sizes are as measured by direct imaging with electron microscopy.
Particle size distribution may be determined by inspection of
scanning or transmission electron micrograph images preferably on
lattice images, and analysing an appropriately sized population of
particles for particle size.
[0044] As molecular sieve, there may be mentioned a silicate,
metallosilicate, an aluminosilicate, an aluminophosphate, a
silicoaluminophosphate, a metalloaluminophosphate, or a
metalloaluminophosphosilicate, or a gallosilicate.
[0045] The preferred molecular sieve will depend on the chosen
application, for example, separation, catalytic applications, and
combined reaction separation. There are many known ways to tailor
the properties of the molecular sieves, for example, structure
type, chemical composition, ion-exchange, and activation
procedures.
[0046] Representative examples are molecular sieves/zeolites of the
structure types AFI, AEL, BEA, CHA, EUO, FAU, FER, KFI, LTA, LTL,
MAZ, MOR, MFI, MEL, MTW, OFF and TON.
[0047] Some of the above materials while not being true zeolites
are frequently referred to in the literature as such, and this term
will be used broadly in the specification below.
[0048] A supported layer according to the invention may be
manufactured in a number of different ways. In one embodiment the
invention provides a process of making a layer by deposition on a
support from a colloidal zeolite suspension obtainable by preparing
an aqueous synthesis mixture comprising a source of silica and an
organic structure directing agent in a proportion sufficient to
effect substantially complete dissolution of the silica source in
the mixture at the boiling temperature of the mixture, and
crystallization from the synthesis mixture. The synthesis mixture
will contain, in addition, a source of the other component or
components, if any, in the zeolite.
[0049] The particle size of the crystals formed may be controlled
by the crystallization temperature, or any other process capable of
giving crystals of highly uniform particle size, in a size such
that a stable colloidal suspension may be obtained. A stable
colloidal suspension is one in which no visible separation occurs
on standing for a prolonged period, e.g., one month. Details of the
procedure for preparing the colloidal suspension mentioned above
are given in our co-pending Application No. PCT/EP92/02386, the
entire disclosure of which is incorporated by reference herein.
[0050] The invention also provides a supported layer made by the
above process.
[0051] In accordance with preferred processes according to the
invention, the silica is advantageously introduced into the
synthesis mixture as silicic acid powder.
[0052] The organic structure directing agent is advantageously
introduced into the synthesis mixture in the form of a base,
specifically in the form of a hydroxide, but a salt, e.g., a
halide, especially a bromide, may be employed.
[0053] The structure directing agent may be, for example, the
hydroxide or salt of tetramethylammonium (TMA), tetraethylammonium
(TEA), triethylmethylammonium (TEMA), tetrapropylammonium (TPA),
tetrabutylammonium (TBA), tetrabutylphosphonium (TBP),
trimethylbenzylammonium (TMBA), trimethylcetylammonium (TMCA),
trimethylneo-pentylammonium (TMNA), triphenylbenzylphosphonium
(TPBP), bispyrrolidinium (BP), ethylpyridinium (EP),
diethylpiperidinium (DEPP) or a substituted azoniabicyclooctane,
e.g. methyl or ethyl substituted quinuclidine or
1,4-diazoniabicyclo-(2,2,2)octane. Preferred structure directing
agents are the hydroxides of TMA, TEA, TPA and TBA.
[0054] Further processes for the manufacture of layers according to
the invention, including specific methods of depositing the
molecular sieve on the support and post-treatment of the resulting
layer, will be given below.
[0055] The thickness of the molecular sieve layer is advantageously
within the range of 0.1 to 20 .mu.m, preferably 0.1 to 15 .mu.m,
more preferably from 0.1 to 2 .mu.m. Advantageously, the thickness
of the layer and the particle size of the molecular sieve are such
that the layer thickness is at least twice the particle size,
resulting in a layer several particles thick rather than a
monolayer of particles.
[0056] Advantageously, the layer is substantially free of pinholes,
i.e., substantially free from apertures of greatest dimension
greater than 0.1 .mu.m. Advantageously, at most 0.1% and preferably
at most 0.0001% of the surface area is occupied by such
apertures.
[0057] Depending on the intended end use of the layer, a greater or
smaller proportion of the area of the layer may be occupied by
macropores, apertures having a greatest dimension less than 0.1
.mu.m but greater than 1 nm. These macropores may be formed by the
interstices between the crystals of the molecular sieve, if the
layer consists essentially of the molecular sieve, and elsewhere,
if the layer comprises the molecular sieve and other components.
Such layers may be used, inter alia, for ultrafiltration, catalytic
conversion, and separations based on differences in molecular mass
(Knudsen diffusion), and indeed for any processes in which a high
surface area is important.
[0058] The layer advantageously has a large proportion of its area
occupied by crystalline-bounded micropores, i.e., pores of a size
between 0.2 and 1 nm, depending on the particular molecular sieve
being employed. Pores of size within the micropore range result,
for example, when the layer contains a component in addition to one
derived from colloidal molecular sieve particles. In another
embodiment especially suitable for ultrafiltration, the layer
contains nanopores, i.e., pores of a size between 1 and 10 nm.
[0059] The layer support may be either non-porous or, preferably,
porous, and may be continuous or particulate. As examples of
non-porous supports there may be mentioned glass, fused quartz, and
silica, silicon, dense ceramic, for example, clay, and metals. As
examples of porous supports, there may be mentioned porous glass,
sintered porous metals, e.g., steel or nickel (which have pore
sizes typically within the range of 0.2 to 15 .mu.m), and,
especially, an inorganic oxide, e.g., alpha-alumina, titania, an
alumina/zirconia mixture, or Cordierite.
[0060] At the surface in contact with the layer, the support may
have pores of dimensions up to 50 times the layer thickness, but
preferably the pore dimensions are comparable to the layer
thickness.
[0061] Advantageously, the support is porous alpha-alumina with a
surface pore size within the range of from 0.08 to 10 .mu.m,
preferably from 0.08 to 1 .mu.m, most preferably from 0.08 to 0.16
.mu.m, and advantageously with a narrow pore size distribution. The
support may be multilayered; for example, to improve the mass
transfer characteristics of the layer, only the surface region of
the support in contact with the layer may have small diameter
pores, while the bulk of the support, toward the surface remote
from the layer, may have large diameter pores. An example of such a
multilayer support is an alpha-alumina disk having pores of about 1
.mu.m diameter coated with a layer of alpha-alumina with pore size
about 0.08 .mu.m.
[0062] The invention also provides a structure in which the
support, especially a continuous porous support, has a molecular
sieve layer on each side of the support, the layers on the two
sides being the same or different.
[0063] The layer may, and for many uses advantageously does,
consist essentially of the molecular sieve material, or it may be a
composite of the molecular sieve material and intercalating
material which is also inorganic. The intercalating material may be
the material of the support. If the layer is a composite it may, as
indicated above, contain macropores and/or micropores, bounded by
molecular sieve portions, by portions of intercalating material, or
by both molecular sieve and intercalating material. The material
may be applied to the support simultaneously with or after
deposition of the molecular sieve, and may be applied, for example,
by a sol-gel process followed by thermal curing. Suitable materials
include, for example, inorganic oxides, e.g., silica, alumina, and
titania.
[0064] The intercalating material is advantageously present in
sufficiently low a proportion of the total material of the layer
that the molecular sieve crystals remain contiguous.
[0065] The invention further provides additional preferred
processes for manufacturing a layer.
[0066] The present invention accordingly also provides a process
for the manufacture of a layer comprising a crystalline molecular
sieve on a porous support, which comprises pre-treating the porous
support to form at a surface thereof a barrier layer, and applying
to the support a reaction mixture comprising a colloidal suspension
of molecular sieve crystals, having a mean particle size of at most
100 nm and advantageously a particle size distribution such that at
least 95% of the particles have a size within .+-.15%, preferably
.+-.10%, more preferably within .+-.7.5%, of the mean, colloidal
silica and optionally an organic structure directing agent, to form
a supported molecular sieve layer, and if desired or required
activating the resulting layer.
[0067] Activation removes the template and can be achieved by
calcination, ozone treatment, plasma treatment or chemical
extraction such as acid extraction.
[0068] The invention also provides a supported layer formed by the
process.
[0069] The barrier layer functions to prevent the water in the
aqueous reaction mixture from preferentially entering the pores of
the support to an extent such that the silica and zeolite particles
form a thick gel layer on the support.
[0070] The barrier layer may be temporary or permanent. As a
temporary layer, there may be mentioned an impregnating fluid that
is capable of being retained in the pores during application of the
reaction mixture, and readily removed after such application and
any subsequent treatment.
[0071] As indicated below, spin coating is an advantageous
technique for applying the reaction mixture to the support
according to this and other aspects of the invention. The
impregnating fluid should accordingly be one that will be retained
in the pores during spinning if that technique is used; accordingly
the rate of rotation, pore size, and physical properties of the
fluid need to be taken into account in choosing the fluid.
[0072] The fluid should also be compatible with the reaction
mixture, for example if the reaction mixture is polar, the barrier
fluid should also be polar. As the reaction mixture is
advantageously an aqueous reaction mixture, water is advantageously
used as the barrier layer.
[0073] To improve penetration, the fluid barrier may be applied at
reduced pressure or elevated temperature. If spin-coating is used,
the support treated with the barrier fluid is advantageously spun
for a time and at a rate that will remove excess surface fluid, but
not remove fluid from the pores. Premature evaporation of fluid
from the outermost pores during treatment may be prevented by
providing an atmosphere saturated with the liquid vapour.
[0074] As a temporary barrier layer suitable, for example, for an
alpha-alumina support there may be especially mentioned water or
glycol. As a permanent barrier suitable for an alpha-alumina
support there may be mentioned titania, gamma-alumina or an
alpha-alumina coating of smaller pore size.
[0075] The colloidal suspension of molecular sieve crystals is
advantageously prepared by the process indicated above, i.e., that
described in PCT Application EP/92/02386. The colloidal silica may
be prepared by methods known in the art; see for example Brinker
and Scherer, Sol-Gel Science, Academic Press, 1990. A preferred
method is by the acid hydrolysis of tetraethyl orthosilicate. The
organic structure directing agent, if used, is advantageously one
of those mentioned above.
[0076] As indicated above, the reaction mixture is advantageously
applied to the support by spin-coating, the viscosity of the
mixture and the spin rate controlling coating thickness. The
mixture is advantageously first contacted with the stationary
support, then after a short contact time the support is spun at the
desired rate. After spinning, the silica is advantageously aged by
retaining the supported layer in a high humidity environment, and
subsequently dried, advantageously first at room temperature and
then in an oven.
[0077] In a further embodiment of the invention, there is provided
a process for the manufacture of a layer comprising a crystalline
molecular sieve on a porous support which comprises applying to the
support by dip-coating a colloidal suspension of molecular sieve
crystals, having a mean particle size of at most 100 nm and
advantageously a particle size distribution such that at least 95%
of the particles have a size within .+-.15%, preferably .+-.10%,
more preferably .+-.7.5%, of the mean, drying the resulting gel on
the support and if desired or required calcining the resulting
layer.
[0078] The invention also provides a layer made by the process. In
this embodiment of the invention, the pH of the suspension is an
important factor. For example, at a pH above 12, colloidal
silicalite crystals tend to dissolve in the medium. Adhesion of the
layer to the support improves as pH is reduced, with acceptable
adhesion being obtained between pH 7 and 11, good adhesion between
pH 4.0 and 7, and very good adhesion below pH 4.0, although
agglomeration of particles may occur at too low a pH.
[0079] Adhesion of the layer to its support may be enhanced by the
inclusion in the suspension of an organic binder or surfactant, the
presence of an appropriate proportion of which may also reduce the
incidence of cracks in the final layer. Among binders there may be
mentioned polyvinyl alcohol (PVA), advantageously with a molecular
weight of from 1000 to 100000, preferably from 2000 to 10000, most
preferably in the region of 3000, and hydroxyalkyl cellulose,
especially hydroxypropyl cellulose (HPC), advantageously with a
molecular weight of from 50000 to 150000, and preferably in the
region of 100000.
[0080] An appropriate proportion of crystals in the suspension may
readily be determined by routine experiment; if the proportion is
too low a continuous layer will not be reliably formed while if it
is too high the layer will tend to contain cracks after
calcination. For silicalite, advantageous lower and upper limits
are 0.5% (preferably 0.75%) and 1.5% respectively.
[0081] The time spent by the support immersed in the suspension
also affects the thickness of the layer and its quality.
Advantageously the dip-time is at most 15 seconds with a solution
containing 1.1% by weight silicalite crystals; an immersion of from
1 to 10 seconds gives a crack-free layer of thickness 0.7 to 3
.mu.m.
[0082] In our co-pending Application No. PCT/EP92/02330, the entire
disclosure of which is incorporated by reference herein, there is
disclosed the formation of an aqueous synthesis mixture comprising
a source of particulate silica in which the particles
advantageously have a mean diameter of at most 1 .mu.m, seeds of an
MFI zeolite having a mean particle size of at most 100 nm in the
form of a colloidal suspension, an organic structure directing
agent, and a source of fluorine or of an alkali metal, the
synthesis mixture having an alkalinity, expressed as a molar ratio
of OH.sup.-:SiO.sub.2 of at most 0.1. Crystallization of this
synthesis mixture produces very uniform, small, zeolite crystals.
The proportion of seed, based on the weight of the mixture, is
given as from 0.05 to 1700 wppm. The synthesis mixture will
additionally contain a source of any other zeolite component.
[0083] In a further embodiment of the present invention, a seeding
technique may be used. In this embodiment, the invention provides a
process for the manufacture of a layer comprising a crystalline
molecular sieve on a porous support, which comprises applying to or
forming on the support a layer comprising amorphous silica
containing seeds of a zeolite having a mean particle size of at
most 100 nm, and advantageously having a particle size distribution
such that at least 95% of the particle have a size within .+-.15%,
preferably .+-.10%, more preferably within .+-.7.5%, of the mean,
subjecting the layer to hydrothermal crystallization, and if
desired or required calcining the crystallized layer.
[0084] Again, other components useful in forming the zeolite layer
may be present. Such components may include, for example, an
organic structure directing agent, which may be in salt form.
[0085] The invention also provides a supported layer made by the
process. The layer is advantageously applied to or formed on the
support by dipcoating or spincoating, advantageously substantially
as described above.
[0086] If dipcoating is used, the support is advantageously dipped
into a solution containing the amorphous silica in colloidal form,
advantageously with a particle size at most 0.1 .mu.m; the solution
may if desired contain other components useful in forming the final
zeolite layer. If spincoating is used, the silica may be of larger
particle size but is advantageously colloidal.
[0087] The layer thickness at this stage, after dipcoating or
spincoating, is advantageously within the range of from 0.1 to 20
.mu.m.
[0088] Hydrothermal crystallization to form the zeolite layer is
advantageously carried out by immersing the layer in a solution
described below, and heating for a time and at the temperature
necessary to effect crystallization.
[0089] The solution advantageously contains either all the
components necessary to form a zeolite or only those components
necessary but which are not already present in the layer on the
support. In the latter case, crystals do not form in the solution,
which remains clear and may be re-used.
[0090] After crystallization, the supported layer may be washed,
dried, and calcined in the normal way.
[0091] By this embodiment of the invention, a dense, homogeneous,
and crack-free supported layer may be obtained. A 1 .mu.m thick
zeolite layer may readily be obtained, with a grain size of 100 to
300 nm.
[0092] In a further embodiment of the invention, molecular sieve
crystals are synthesized in situ on the support. According to this
embodiment, the invention provides a process for the manufacture of
a layer comprising a crystalline molecular sieve on a porous
support, which comprises preparing a synthesis mixture comprising a
source of silica and an organic structure directing agent
preferably in the form of a hydroxide in a proportion sufficient to
effect substantially complete dissolution of the silica source in
the mixture at the boiling temperature of the mixture, immersing
the support in the synthesis mixture, crystallizing zeolite from
the synthesis mixture onto the support, and if desired or required
calcining the crystallized layer.
[0093] The invention also provides a supported layer made by the
process. The synthesis mixture will also contain a source of other
components, if any, in the zeolite.
[0094] Advantageously, to obtain colloidal material,
crystallization is effected at a temperature less than 120.degree.
C. As indicated in PCT/EP92/02386, the lower the crystallization
temperature the smaller the resulting particle size of the
crystals. For zeolites made in the presence of an alumina source,
the particle size may also be varied by varying the alumina
content. The effect of varying the alumina content is, however, not
the same for all zeolites; for example, for zeolite beta, the
particle size varies inversely with alumina content while for an
MFI-structured zeolite the relationship is direct.
[0095] The substrate used in accordance with this aspect of the
invention may be any one of those described above in connexion with
other processes; an alpha-alumina support is advantageously used;
the pore size may vary with the intended use of the layer; a pore
size within the range 100 nm to 1.5 .mu.m may conveniently be used.
Care should be taken to avoid undue weakening of the support by,
for example, controlling prolonged exposure to high temperature and
alkalinity.
[0096] Although the various processes of the invention described
above yield a supported layer of good quality, the resulting layer
may still contain apertures of greater size than desired for the
intended use of the product. For example, apertures greater than
those through the molecular sieve itself are undesirable if the
supported layer is to be used for certain types of separation
process since they result in a flux greater than desired and
impaired separation. If this is the case, the supported layer may
be subjected to a reparation procedure. In this procedure, the
supported layer may be subjected to one of the various reparation
techniques known to those skilled in the art.
[0097] It is therefore in accordance with the invention to
manufacture a supported layer by first carrying out one of the
layer-forming processes according to the invention and described
above and following it by reparation of the layer by a method known
per se.
[0098] Preferably, however, the reparation is carried out by again
subjecting the supported layer to a manufacturing process of the
invention.
[0099] The invention accordingly also provides a process for the
manufacture of a supported layer in which one of the layer-forming
processes above is carried out two or more times, or in which one
of the processes above carried out one or more times is followed by
another of the processes above, carried out one or more times, or
in which one of the processes above is carried out two or more
times with another or others of the processes above, carried out
one or more times, intervening. The invention also provides a
supported layer, especially a membrane, made by such a process.
[0100] The layers according to the invention and produced in
accordance with the processes of the invention may be treated in
manners known per se to adjust their properties, e.g., by steaming
or ion exchange to introduce different cations or anions, by
chemical modification, e.g., deposition of organic compounds into
the pores of the molecular sieve, or by introduction of a
metal.
[0101] The layers may be used in the form of a membrane, used
herein to describe a barrier having separation properties, for
separation of fluid (gaseous, liquid, or mixed) mixtures, for
example, separation of a feed for a reaction from a feedstock
mixture, or in catalytic applications, which may if desired combine
catalysed conversion of a reactant or reactants and separation of
reaction products.
[0102] Separations which may be carried out using a membrane
comprising a layer in accordance with the invention include, for
example, separation of normal alkanes from co-boiling hydrocarbons,
for example normal alkanes from isoalkanes such as C.sub.4 to
C.sub.6 mixtures and n-C.sub.10 to C.sub.16 alkanes from kerosene;
separation of aromatic compounds from one another, especially
separation of C.sub.8 aromatic isomers from each other, more
especially para-xylene from a mixture of xylenes and, optionally,
ethylbenzene, and separation of aromatics of different carbon
numbers, for example, mixtures of benzene, toluene, and mixed
C.sub.8 aromatics; separation of aromatic compounds from aliphatic
compounds, especially aromatic molecules with from 6 to 8 carbon
atoms from C.sub.5 to C.sub.10 (naphtha range) aliphatics;
separation of olefinic compounds from saturated compounds,
especially light alkenes from alkane/alkene mixtures, more
especially ethene from ethane and propene from propane; removing
hydrogen from hydrogen-containing streams, especially from light
refinery and petrochemical gas streams, more especially from
C.sub.2 and lighter components; and alcohols from aqueous
streams.
[0103] Separation of heteroatomic compounds from hydrocarbons such
as alcohols and sulphur containing materials such as H.sub.2S and
mercaptans.
[0104] The supported layer of the invention may be employed as a
membrane in such separations without the problem of being damaged
by contact with the materials to be separated. Furthermore, many of
these separations are carried out at elevated temperatures, as high
as 500.degree. C., and it is an advantage of the supported layer of
the present invention that it may be used at such elevated
temperatures.
[0105] The present invention accordingly also provides a process
for the separation of a fluid mixture which comprises contacting
the mixture with one face of a layer according to the invention in
the form of a membrane under conditions such that at least one
component of the mixture has a different steady state permeability
through the layer from that of another component and recovering a
component or mixture of components from the other face of the
layer.
[0106] Some specific reaction systems where these membranes would
be advantageous for selective separation either in the reactor or
on reactor effluent include: selective removal of a para-Xylene
rich mixture from the reactor, reactor product, reactor feed or
other locations in a Xylenes isomerization process; selective
separation of aromatics fractions or specific aromatics molecule
rich streams from catalytic reforming or other aromatics generation
processes such as light alkane and alkene dehydrocyclization
processes (e.g. C.sub.3-C.sub.7 paraffins to aromatics from
processes such as Cyclar), methanol to gasoline and catalytic
cracking processes; selective separation of benzene rich fractions
from refinery and chemicals plant streams and processes, selective
separations of olefins or specific olefin fractions from refinery
and chemicals processing units including catalytic and thermal
cracking, olefins isomerization processes, methanol to olefins
processes, naphtha to olefins conversion processes, alkane
dehydrogenation processes such as propane dehydrogenation to
propylene; selective removal of hydrogen from refinery and
chemicals streams and processes such as catalytic reforming, alkane
dehydrogenation, catalytic cracking, thermal cracking, light
alkane/alkene dehydrocyclization, ethylbenzene dehydrogenation,
paraffin dehydrogenation; selective separation of molecular isomers
in processes such as butane isomerization, butylene isomerization,
paraffin isomerization, olefin isomerization; selective separation
of alcohols from aqueous streams and/or other hydrocarbons;
selective separation of products of bimolecular reactions where
equilibrium limits conversion to the desired products, e.g. MTBE
production from methanol and isobutylene, ethylbenzene from
ethylene and benzene, and cumene from propylene and benzene;
selective removal of 2,6 dimethyl naphthalene from mixtures of
alkane substituted naphthalenes during alkylation and/or
isomerization.
[0107] The invention further provides a process for catalysing a
chemical reaction which comprises contacting a feedstock with a
layer according to the invention which is in active catalytic form
under catalytic conversion conditions and recovering a composition
comprising at least one conversion product.
[0108] The invention further provides a process for catalysing a
chemical reaction which comprises contacting a feedstock with one
face of a layer according to the invention, that is in the form of
a membrane and in active catalytic form, under catalytic conversion
conditions, and recovering from an opposite face of the layer at
least one conversion product, advantageously in a concentration
differing from its equilibrium concentration in the reaction
mixture.
[0109] The following examples illustrate the invention:
EXAMPLES
Example 1
[0110] This example illustrates manufacture of a layer by
spin-coating with a temporary barrier layer.
[0111] A porous alpha-alumina disk, diameter 25 mm, thickness 3 mm,
pore size 80 nm, is soaked in demineralized water for 3 days. The
soaked disk is placed in the specimen chuck of a CONVAC Model MTS-4
Spinner, and hot water is placed in the process cup to increase the
humidity of the atmosphere. The disk is spun at 4000 rpm for 30
seconds. The disk is then immediately covered with a slurry
comprising 25% by weight of Ludox (a trademark) AS-40 colloidal
silica and 75% by weight of an aqueous dispersion containing 6.5%
by weight colloidal silicalite (MFI) zeolite, mean particle size 50
nm. 10 seconds after contact between the slurry and the disk, the
disk is spun at 4000 rpm for 30 seconds. The disk and the resulting
silica-zeolite layer are kept in a closed vessel at relative
humidity close to 100% for 3 hours to age the silica, air dried at
room temperature for 2 hours and subsequently in an oven at
110.degree. C. for 2 hours.
[0112] Under an optical microscope, the resulting silica-zeolite
layer appeared smooth, crack-free, and homogeneous. Scanning
Electron Microscopy (SEM) of a cross-section through the supported
layer shows a layer about 1 .mu.m thick containing uniformly sized
zeolite particles--see FIG. 1. The homogeneity and continuity of
the layer, coupled with its thinness, confirm that the resulting
structure after calcining will form a layer according to the
invention.
[0113] In a comparison experiment, instead of soaking the disk, it
was dried at 150.degree. C. in air for 12 hours, other process
steps remaining the same. As can be seen from the SEM cross section
shown in FIG. 2, the resulting layer is about 40 .mu.m thick. It is
also cracked, and not firmly attached to the substrate, making it
unsuitable for use as a layer.
Example 2
[0114] This example illustrates manufacture of a layer by
spin-coating using a permanent barrier layer.
[0115] The support comprised an alpha-alumina base with a barrier
layer of gamma-alumina, and was prepared as follows:
[0116] A slurry was prepared by ball milling 800 g Al.sub.2O.sub.3
in 500 ml distilled water containing 4.3 ml hydrochloric acid for
16 hours to give alumina particles of mean diameter 0.5 .mu.m. The
slurry was degassed, poured into moulds and allowed to dry at
ambient temperature for 3 days. The cast pieces were heated at
5.degree. C./min to 1200.degree. C., then fired at 1200.degree. C.
for 2 hours. The fired pieces were then polished front and back to
a thickness of about 3 mm. A gamma-alumina coating was applied by
dipping the alpha-alumina piece once into a colloidal suspension of
Boehmite, prepared by hydrolysis of alumina sec-butoxide in 600 ml
water and 0.76 ml nitric acid. The Boehmite layer was converted to
gamma-alumina by heating to 400.degree. C. at a rate of 10.degree.
C./hour and holding for 24 hours. The coated product provides a
support.
[0117] A silica sol was prepared from tetraethylorthosilicate,
water, and hydrochloric acid and aged at 50.degree. C. for 90
minutes.
[0118] A suspension of silicalite 1, mean particle size 55 nm,
particle size range 40 to 70 nm, containing 8.7% by weight
colloidal crystals in aqueous TPAOH, pH 10.3, was prepared and a
coating slurry formed by mixing equal weights of the suspension and
the sol. The resulting slurry was spin-coated onto the support at
4000 rpm.
[0119] The resulting structure was then heated to 600.degree. C. at
a heating rate of 20.degree. C./hour. The final layer structure is
shown edge on and from the top surface in FIGS. 3 and 4. The edge
on view demonstrates that the layer thickness is about 0.2 .mu.m
and the top view shows the organization of the crystals in the
layer, and that the crystals are incorporated into the layer with
little or no change in crystal size and shape.
Example 3
[0120] This example illustrates the use of a layer according to the
invention in the separation of a hydrocarbon mixture.
[0121] The layer of Example 2 was used to separate an equimolar
mixture of toluene, m-xylene, n-octane and iso-octane. The mixture
was applied to the layer side of the layer structure in a
continuous flow. A gas sweep (Argon 40-500 ml/min) was applied to
the support side of the layer structure, and sampled by a gas
chromatograph operating with a 10'.times.1/8'' (about 3 m.times.3
mm) stainless steel, GP5% SP1200/5% Bentone 34 on 100/120
Supelcoport column. The total pressure drop across the layer was
1000 kPa. Analysis of the gc data shows that the layer permeate had
an enhanced aromatics content relative to feed content.
Representative data at a temperature of 180.degree. C. are shown in
FIG. 5. The plot shows the relative concentrations of toluene,
m-xylene, n-octane and iso-octane as a function of elapsed time.
The largest separation factor is observed for toluene/iso-octane
with a value of 10. The total flux of hydrocarbon through the layer
corresponds to 100 kg/m.sup.2/day at the start and after 16 hours
to an average of 40 kg/m.sup.2/day.
Examples 4 to 26
[0122] These examples illustrate manufacture of a layer by
dip-coating.
[0123] In each of the following Examples, a colloidal MFI zeolite
crystal suspension having a mean particle size of 70 nm was
employed, together with a gamma-alumina-surfaced alpha-alumina
support as described in Example 2. After dipping, the supported
layer was dried at 40.degree. C. for 3 hours, at a relative
humidity of 60%. Each layer was heated at 10.degree. C./hour to
550.degree. C., maintained at that temperature for 3 hours to
effect calcination, and cooled to room temperature at 20.degree.
C./hour.
Examples 4 to 9
[0124] These examples were conducted at a dip time of 5 seconds, a
concentration of zeolite of 1.1%, and 1.6 g/l of hydroxypropyl
cellulose, varying the pH by adding small amounts of a one molar
HNO.sub.3 solution, the effect of pH on adhesion being shown.
TABLE-US-00001 Example No. pH Adhesion 4 3.6 very good 5 5.2 good 6
7.6 acceptable 7 9.1 acceptable 8 10.6 acceptable 9 11.7 poor
[0125] Observation of adhesion standard was subjective; the zeolite
layer thickness varied between 1.5 and 2 .mu.m, as determined by
S.E.M.
Examples 10 to 14
[0126] These examples were conducted at a dip time of 5 seconds, a
zeolite concentration of 1.1%, a pH of 3.5, and with different
binders/surfactants. TABLE-US-00002 Conc. Observation Example No.
Additive g/l Ad; Conty 10 PVA, M = 72000 20 very bad; cracks 11
PVA, M = 3000 20 acceptable; cont. 12 HPC, M = 100000 1.6 very
good; cont. 13 PVA, M = 3000 20} good; cont. HPC, M = 100000 1.6}
14 None Ad = adherence Conty = continuity of layer Cont =
continuous
Example 15 to 20
[0127] In these examples, the effects on the properties of the
layer resulting from varying the zeolite concentration were
studied; the dip time was 5 seconds, pH was 3.5, additive HPC, 1.6
g/litre. TABLE-US-00003 Zeolite Conc. Layer Example No. g/l
Thickness .mu.m Observation 15 0.1 -- not continuous 16 0.5 -- not
continuous 17 0.8 1.0 continuous, few cracks 18 1.1 2.5 continuous,
few cracks 19 1.6 5.0 continuous, cracks 20 2.1 6.5 continuous,
cracks
Examples 21 to 26
[0128] In these Examples, the effect of the dipping time was
studied; pH was 3.0, additive was HPC at 1.6 g/litre, zeolite
content 1.1%. TABLE-US-00004 Dipping Time Layer Example No. seconds
Thickness .mu.m Observation 21 1 0.7 to 1.1 no cracks 22 3 1.5 to 2
no cracks 23 6 2 no cracks 24 10 2 to 3 no cracks 25 20 3.5 cracks
26 60 6.5 to 7 cracks
[0129] The experiments show that dipcoating can give good
continuous layers of low thickness; reparation to remove cracks may
be effected by multiple applications.
Example 27
[0130] This and the following example illustrate manufacture of a
layer using hydrothermal crystallization techniques. In this
example, the ageing solution contained all the zeolite-forming
ingredients.
[0131] A synthesis mixture was prepared from the following
components, in parts by weight: TABLE-US-00005 Colloidal ZSM-5
suspension, 50 nm mean 18.79 particle size, 6.5% by weight ZSM-5
Tetrapropylammonium bromide (TPABr) 1.55 Ludox AS-40 colloidal
silica 6.25
[0132] Using the barrier-forming and spin-coating procedure of
Example 1 a water-soaked alpha-alumina disk with 80 nm diameter
pores is spincoated with part of the synthesis mixture. The coated
disk is transferred to an autoclave and covered with the remainder
of the synthesis mixture. The autoclave was transferred to an oven,
heated to 160.degree. C. over the course of 2 hours, maintained at
that temperature for 120 hours, and cooled to room temperature. The
cooled coated disk was washed in flowing tap water for 4 hours,
washed twice in demineralized water and then twice more at
80.degree. C. The disk was dried by heating in an oven at
10.degree. C./hour to 110.degree. C., maintained at 110.degree. C.
for 5 hours, and allowed to cool at room temperature. Calcining was
effected by heating at 10.degree. C./hour to 550.degree. C.,
maintaining at that temperature for 16 hours, and cooling at
60.degree. C. per hour to room temperature.
[0133] From optical and SEM observations--see FIG. 6--the resultant
layer is about 1 .mu.m thick and crack-free, with a final grain
size of from 100 to 300 nm.
Example 28
[0134] In this example, the ageing solution contained only those
ingredients not already in the layer.
[0135] A synthesis mixture was prepared from the following
components, in parts by weight: TABLE-US-00006 Colloidal silicalite
1 suspension, 20 to 30 nm 20.00 particle size distribution, 7.2% by
weight solids, including template present in the zeolite Ludox
AS-40 colloidal silica 20.00 Demineralized water 22.50
[0136] An alpha-alumina disk was dipped into the solution for 5
seconds, and immediately placed in an autoclave and covered with an
ageing solution, pH 11.5 with a molar composition of
6.36(NH.sub.4).sub.2O/1TPABr/130H.sub.2O/0.96HNO.sub.3. The
autoclave was put in an oven at 152.degree. C. and maintained there
for 7 days. After removal from the autoclave, the disk was
repeatedly washed with demineralized water at 70.degree. C. until
the conductivity of the last wash--water was 10 microSiemens per
centimetre. The disk was then dried at 40.degree. C., relative
humidity 60%, for several hours, followed by drying for 1 hour at
105.degree. C.
[0137] Visual inspection showed the disk to be very homogeneous and
smooth, with no visual terracing or scaling. By SEM it was seen
that the layer had the crystal habit of silicalite--see FIG.
7--with a mean diameter of 100 nm; the cross-section--FIG.
8--indicating a layer thickness of about 10 .mu.m.
Example 29
[0138] This example illustrates in situ formation of zeolite
crystals on a support.
[0139] A synthesis solution was prepared from the following
components, the parts being given by weight: TABLE-US-00007 TPAOH
(20% by weight in water) 41.02 NaOH, pellets 0.58 SiO.sub.2 powder
(10% of water) 8.94
[0140] The sodium hydroxide was dissolved in the TPAOH solution at
room temperature, the silica added, and the mixture heated to
boiling with vigorous stirring until a clear solution was obtained.
The solution was cooled, weight loss compensated with demineralized
water, and the solution filtered through a 0.45 .mu.m filter. The
molar composition of the synthesis mixture was:
0.52Na.sub.2O/1.50(TPA).sub.2O/10SiO.sub.2/142H.sub.2O
[0141] A quarter of an alpha-alumina disk, pore size 1 .mu.m,
diameter 47 mm, was air dried for 2 hours at 150.degree. C., and
weighed. 25.05 g of synthesis solution was poured onto the disk in
a 150 ml stainless steel autoclave. The autoclave was placed in an
oven, heated up to 150.degree. C. in the course of 1 hour and
maintained at that temperature for 24 hours.
[0142] After cooling the autoclave the support was removed,
repeatedly washed with deionized water and air dried at 150.degree.
C. for 2 hours. A disk weight increase of 6.9% was noted.
[0143] The dried disk was then heated at 2.degree. C./min to a
temperature of 475.degree. C. and heated in air at that temperature
for 6 hours. Comparison of SEMs of the original alpha-alumina
surface--FIG. 9--and of the calcined layer--FIG. 10--shows that the
surface of the disk is homogeneously coated with intergrown
spherical crystals of about 0.4 .mu.m size, which show the typical
crystal habit of silicalite.
Example 30
[0144] Example 29 was repeated except that crystallization took
place at 98.degree. C. for 19 hours. An SEM--FIG. 11--again shows a
homogeneous coating of the disk surface, but the crystal size is
now smaller, between 0.2 and 0.3 .mu.m.
Example 31
[0145] A synthesis solution was prepared as described in Example
29. The support was an alpha-alumina substrate with a pore size of
160 nm; this was dried at 185.degree. C., placed on the bottom of a
300 ml stainless steel autoclave, covered with 220.4 g of synthesis
solution, and the autoclave maintained at 120.degree. C. for 24
hours. After washing, drying and calcining at 475.degree. C. for 12
hours in air, the supported layer was examined by SEM. The
photographs--FIGS. 12 to 14 show the surface, FIG. 15 shows a
cross-section--indicate a uniform coating of 0.3 .mu.m intergrown
silicalite crystals and a layer thickness of about 0.5 .mu.m.
Example 32
[0146] This example illustrates the manufacture of a zeolite layer
by two in-situ crystallization steps at 120.degree. C.
[0147] The support comprises a porous alpha-alumina disk, having an
average pore diameter of 160 nm, and polished on at least one side.
After polishing the support is stored submerged in demineralised
water until a day before the preparation of the zeolite layer. Then
the support is placed in an oven, heated up at a rate of 1.degree.
C./minute to 400.degree. C., kept at 400.degree. C. for 4 hours,
and cooled down.
[0148] For the first crystallization step, a synthesis mixture is
prepared by mixing silica (Baker, >99.75 pure SiO.sub.2),
Tetrapropyl-ammoniun-hydroxide (TPAOH, Fluka practical grade, 20%
in water), NaOH (Merck, 99.99 pure) and demineralised water to get
100 ml of mixture with the following molar composition;
[0149] 10Si0.sub.2/1.5(TPA)20/0.53Na.sub.20/142H.sub.2O. The
mixture is boiled on a hotplate for 5 minutes while stirring
vigorously. Then the mixture is taken from the hotplate and left to
cool down, after which H.sub.2O is added to compensate for
evaporation losses during boiling. The dry support disk is taken
out of the oven and placed on the bottom of a stainless steel
autoclave with the polished side facing up. The synthesis mixture
is poured in the autoclave next to the disk, which is eventually
submerged in the mixture. The autoclage is closed and placed in an
oven at 120.degree. C. for 72 hours. After removal from the
autoclave the disk is washed 5 to 10 times in demineralised water
of 70.degree. C.
[0150] For the second crystallization step, a fresh synthesis
mixture, identical to the mixture described for the first step, is
prepared. The disk is placed in a clean autoclave while still wet,
in the same orientation as in the first step, and the fresh
synthesis mixture is poured in the autoclave so that the disk is
completely submerged. The autoclave is closed and put in an oven at
120.degree. C. for 72 hours. After removal from the autoclave the
disk is washed 5 to 10 times in demineralised water of 70.degree.
C. After washing the disk is dried in air at 30.degree. C. for 1.5
days. Then the disk is heated up in air at a rate of 10.degree.
C./hour to 550.degree. C., kept at that temperature for 16 hours,
and cooled down to room temperature at a rate of 20.degree.
C./hour.
[0151] X-ray Diffraction (XRD) analysis shows that MFI-type zeolite
crystals have formed on both the top and the bottom surfaces of the
disk, the intensity of the XRD-peaks suggesting a zeolite layer
thickness of a few microns. Scanning Electron Microscope (SEM)
micrographs show that a dense layer, 3 to 5 micrometer in
thickness, has formed at the top surface of the disk, and also at
the bottom surface of the disk.
Examples 33, 34, 35 and 36
[0152] These examples illustrate the increase in the amount of
zeolite formed on the support with increasing number of
crystallization steps. The preparation is identical to that of
Example 32, the number of crystallization steps varies from one to
four.
[0153] XRD patterns have been obtained from these disks after
drying but before the thermal treatment at 550.degree. C.
Comparison of the XRD-patterns shows that with each step the height
of the MFI-zeolite peaks increases while the height of the
alpha-alumina peaks decreases, as shown in the following table,
where the intensity ratio refers to the ratio between the intensity
of the MFI (501) (051) (431) peak and the alpha-alumina (012) peak:
TABLE-US-00008 Example Number of Steps Ratio 33 1 0.37 34 2 0.71 35
3 1.41 36 4 2.78
[0154] This indicates that the amount of zeolite on the disk
increases with each crystallization step.
Example 37
[0155] This example describes the Helium permeation characteristics
of disks prepared using one or two crystallization steps similar to
Example 32, the first crystallization step done at 120.degree. C.
and the second crystallization step done at 90.degree. C.
[0156] Helium permeation through the disk has been measured at
total pressures in the range of 1 to 3 bar. Disks prepared using a
single crystallization step at 120.degree. C. show He-permeations
of several hundreds mmol/sm2bar, increasing with pressure. However,
disks prepared using two crystallization steps (120.degree. C. and
90.degree. C.) show He-permeations of a few tens of mmol/sm2 bar
that are constant over the pressure range of 1-3 bar.
Example 38
[0157] A membrane fabricated according to the process of example 32
was mounted into a holder and a `Wicke-Kallenbach` experiment was
carried out. A gas mixture of 49.9% n-butane, 49.9% methane and
0.2% i-butane was passed over one side of the membrane, the other
side being continuously purged with a dry helium stream. Both sides
of the membrane were kept at atmospheric pressure. The analyses of
both gas streams by an on-line gas chromatograph were evaluated and
transformed to the corresponding fluxes through the membrane.
Selectivities are given by:
[0158] S=(C1(perm)/CL(ret))/(C2(perm)/C2(ret)), where C1 and C2 are
concentrations of components 1 and 2, and permeate and retentate
streams are indicated by perm and ret, respectively. The calculated
fluxes and selectivities are given in the following table:
TABLE-US-00009 Methane flux n-Butane flux S (n- T [C.]
[mol/m.sup.2s] * 10.sup.4 [mol/m.sup.2s] * 10.sup.3 butane/methane)
25 1.35 2.44 18.07 50 2.15 2.67 12.42 75 2.78 2.81 10.11 100 4.94
3.14 6.36 125 8.75 3.36 3.84 150 13.1 3.40 2.60 175 17.1 3.24 1.89
200 21.3 3.07 1.44 (Reference: E. Wicke and R. Kallenbach, Surface
diffusion of carbon dioxide in activated charcoals, Kolloid Z., 97
(1941), 135).
Example 39
[0159] A membrane fabricated according to the process of example 32
was used for a test similar to that in example 38. A gas mixture of
48.3% methane and 51.7% i-butane was used as feed stream. The
calculated fluxes and selectivities are given in the following
table: TABLE-US-00010 Methane flux n-Butane flux S (methane/i- T
[C.] [mol/m.sup.2s] * 10.sup.4 [mol/m.sup.2s] * 10.sup.5 butane) 25
1.29 7.18 1.92 50 2.38 7.29 3.49 75 3.76 7.41 5.43 100 4.90 9.38
5.59 125 6.29 13.2 5.10 150 8.42 17.7 5.09 175 12.2 22.3 5.86 200
17.8 25.7 7.41
Example 40
[0160] A membrane fabricated according to the process described in
example 32 was used for test similar to that in example 38. A gas
mixture of 50.0% n-butane and 50.0% i-butane was used as feed
stream. The calculated fluxes and selectivities are given in the
following table: TABLE-US-00011 n-Butane flux i-Butane flux S
(n-butane/i- T [C.] [mol/m.sup.2s] * 10.sup.3 [mol/m.sup.2s] *
10.sup.4 butane) 25 1.33 0.26 51.95 50 1.66 0.71 23.55 75 1.99 0.82
24.21 100 2.29 1.21 18.93 125 2.24 1.60 14.00 150 2.45 1.85 13.24
175 2.28 1.89 12.06 200 2.26 2.06 10.97
Example 41
[0161] A membrane fabricated according to the description in
example 32 was used for a test similar to that in example 38. A gas
mixture containing 0.31% p-xyklene, 0.26% o-xylene and methane as
balance was used as feed stream. The calculated fluxes and
selectivities are given in the following table: TABLE-US-00012
p-Xylene flux o-Xylene flux S (p-xylene/o- T [C.] [mol/m.sup.2s] *
10.sup.6 [mol/m.sup.2s] * 10.sup.7 xylene) 100 3.54 0.49 60.10 150
3.43 0.66 43.46 175 3.33 0.92 30.49 200 3.02 1.22 20.76
Example 42
[0162] A membrane fabricated according to the description in
example 32 was used for a test similar to that in example 38. A gas
mixture containing 5.5% benzene, 5.5% cyclohexane and methane as
balance was used as feed stream. The calculated fluxes and
selectivities are given in the following table: TABLE-US-00013
Benzene flux Cyclohexane flux S (benzene/ T [C.] [mol/m2s] * 107
[mol/m.sup.2s] * 10.sup.7 cyclohexane) 25 2.64 0.53 5.01 50 3.03
0.66 4.60 75 4.61 0.92 4.99 100 5.67 1.98 2.86 125 9.23 3.20 2.88
150 9.49 4.48 2.12 175 10.9 3.30 3.30 200 17.8 4.48 3.97
Example 43
[0163] A membrane fabricated according to the description in
example 32 was used for a test similar to that in example 38. A gas
mixture containing 7.6% n-hexane, 15.4% 2,2-dimethylbutane and
methane as balance was used as feed stream. The calculated fluxes
and selectivities are given in the following table: TABLE-US-00014
n-Hexane flux 2,2-Dimethylbutane S (benzene/ T [C.] [mol/m.sup.2s]
* 10.sup.4 flux [mol/m.sup.2s] * 10.sup.7 cyclohexane) 20 1.2 1.9
600 50 1.5 2.3 340 100 3.1 2.7 1150 150 3.0 1.9 1560 200 2.4 1.2
2090
Example 44
[0164] This example illustrates the growth of zeolite layers by
multiple crystallizations, without refreshing the synthesis mixture
as in example 32, but by increasing the crystallization temperature
stepwise.
[0165] A porous alpha-alumina disk with a pore diameter of 160 nm
and polished on one side was cut into four equal-sized parts. The
parts were weighed and placed, polished side up, on Teflon rings
resting on the bottom of a stainless steel autoclave. In the
autoclave was poured 70.22 g of a synthesis solution with a molar
composition of
10SiO.sub.2/1.56(TPA)20/0.275Na.sub.2O/147H.sub.2O
[0166] The open autoclave was placed in an exsiccator, which was
then evacuated during 0.5 hours to increase the penetration of
synthesis solution into the disks. Then the autoclave was taken out
of the exsiccator, closed, and placed in an oven at room
temperature. The oven was heated up to 90.degree. C. in a few
minutes and kept at that temperature for 48 hours. The autoclave
was then cooled to room temperature, opened and one of the support
pieces was removed. The autoclave was closed again and placed in an
oven at room temperature. The oven was heated up to 110.degree. C.
in a few minutes and kept at that temperature for 24 hours. The
autoclave was cooled down again and the second piece was removed.
The temperature cycle was repeated two more times, first for 24
hours at 130.degree. C. and then for 24 hours at 150.degree. C. The
four pieces of the disk were all washed with demineralised water of
70.degree. C. until the washing water had a conductivity of about 6
micro Siemens/cm, dried at 105.degree. C. and cooled to room
temperature in an exsiccator. It was observed that with each aging
step the weight of the disk pieces increased, as shown in the
following table. TABLE-US-00015 Disk Piece # Temperature History
.degree. C. Weight increase % 1 90 0.88 2 90 + 110 2.04 3 90 + 110
+ 130 3.50 4 90 + 110 + 130 + 150 5.63
[0167] XRD analysis showed that with each aging step the intensity
of the zeolite peaks increased with respect to the intensity of the
alpha-alumina peaks, as shown in the following table:
TABLE-US-00016 Peak Intensity ratio: Peak at d = 0.385 nm (MFI)/
Disk Piece # Peak at d = 0.348 nm (A1.sub.20.sub.3) 1 0.190 2 0.217
3 0.236 4 0.332
These results indicate that with each aging step at a higher
temperature new zeolite crystals are deposited on the
supported.
* * * * *