Molecular sieve abstract
A mixed matrix membrane for gas separations is provided with a
nonporous continuous phase of a polymer and a dispersed phase of
molecular sieve particles reacted with a monofunctional organosilicon
compound. The monofunctional organosilicon compound is characterized
by (a) at least one silicon substituent group which reacts or is
compatible with the polymer, and (b) at most one displaceable radical
that can react with the molecular sieve. A process for making a
selectively gas permeable mixed matrix membrane involves reacting
a molecular sieve with the monofunctional organosilicon compound,
uniformly dispersing the reacted sieve with a polymer, and forming
the resulting mixed matrix composition into a membrane structure.
These mixed matrix membranes provide an improved combination of
permeability and selectivity as compared to polymer-only membranes
and mixed matrix membranes in which the molecular sieve is not reacted
with a monofunctional organosilicon compound.
Molecular sieve claims
What is claimed is:
1. A process for separating component gases of a gas mixture comprising
the steps of (A) providing a mixed matrix gas separation membrane
comprising an active layer of a treated molecular sieve dispersed
in a continuous phase of a matrix polymer in which the treated molecular
sieve comprises the reaction product of a (i) molecular sieve through
which at least one component gas in the mixture is preferentially
gas permeable relative to another component gas, with (ii) a monofunctional
organosilicon compound having the formula Si(XYR.sub.1 R.sub.2)
in which X is a displaceable radical, Y is a linking group, and
R.sub.1 and R.sub.2 are each independently any radical other than
a displaceable radical, (B) contacting the gas mixture on one side
of the membrane to cause the component gases to selectively permeate
the membrane, and (C) removing from the opposite side of the membrane
a permeate gas composition enriched in concentration of the at least
one component gas.
2. The process of claim 1 in which the component gas to be separated
from the gas mixture has a kinetic diameter of about 2.0-5.0 .ANG.
(0.2-0.5 nm).
3. The process of claim 2 in which the component gas is oxygen.
4. The process of claim 2 in which the component gas is carbon
dioxide.
5. The process of claim 1 in which the monofunctional organosilicon
compound is a silane selected from the group consisting of 3-aminopropyldimethylethoxy
silane (APDMS), 3-isocyanatopropyl dimethylchlorosilane (ICDMS),
3-aminopropyl diisopropylethoxy silane (APDIPS) and a mixture thereof.
6. The process of claim 5 in which the molecular sieve is selected
from the group consisting of aluminosilicate type SSZ-13 hydrogen-exhanged
aluminosilicate type H-SSZ-13 sodium-exchanged aluminosilicate
type Na-SSZ-13 silicoaluminophosphate type SAPO-34 silicoaluminophosphate
type SAPO-44 aluminosilicate type ZK-5 aluminosilicate type Zeolite
RHO, aluminosilicate type Phillipsite, silicalite and a mixture
thereof.
7. A mixed matrix gas separation membrane comprising particles
of a treated molecular sieve dispersed in a continuous phase consisting
essentially of a matrix polymer, in which the treated molecular
sieve comprises the reaction product of a molecular sieve and a
monofunctional organosilicon compound having the formula Si(XYR.sub.1
R.sub.2) in which X is a displaceable radical, Y is a linking group,
and R.sub.1 and R.sub.2 are each independently any radical other
than a displaceable radical.
8. The mixed matrix membrane of claim 7 in which X is selected
from the group consisting of a halogen atom, a hydroxyl group, an
ester radical having 1-8 carbon atoms an alkoxy group having 1-8
carbon atoms, and a mixture thereof.
9. The mixed matrix membrane of claim 8 in which the monofunctional
organosilicon compound is selected from the group consisting of
3-aminopropyldimethylethoxy silane (APDMS), 3-isocyanatopropyl dimethylchlorosilane
(ICDMS), 3-aminopropyl diisopropylethoxy silane (APDIPS) and a mixture
thereof.
10. The mixed matrix membrane of claim 7 in which Y is selected
from the group consisting of amino radical, amido radical, epoxy
radical, ureido radical, isocyanato radical and a mixture thereof.
11. The mixed matrix membrane of claim 7 in which the molecular
sieve is selected from the group consisting of aluminosilicate molecular
sieve, silicoaluminophosphate molecular sieve, silicalite molecular
sieve, and a mixture thereof.
12. The mixed matrix membrane of claim 11 in which the molecular
sieve is a chabazite type zeolite selected from the group consisting
of aluminosilicate type SSZ-13 hydrogen-exhanged aluminosilicate
type H-SSZ-13 sodium-exchanged aluminosilicate type Na-SSZ-13
silicoaluminophosphate type SAPO-34 silicoaluminophosphate type
SAPO-44 and a mixture thereof.
13. The mixed matrix membrane of claim 12 in which the monofunctional
organosilicon compound is 3-aminopropyldimethylethoxy silane (APDMS).
14. The mixed matrix membrane of claim 11 in which the molecular
sieve is a zeolite selected from the group consisting of aluminosilicate
type ZK-5 aluminosilicate type Zeolite RHO, aluminosilicate type
Phillipsite, and a mixture thereof.
15. The mixed matrix membrane of claim 7 in which the matrix polymer
is selected from the group consisting of polysiloxane, polycarbonate,
silicone-containing polycarbonate, brominated polycarbonate, polysulfone,
polyether sulfone, sulfonated polysulfone, sulfonated polyether
sulfone, polyimide, polyether imide, polyketone, polyether ketone,
polyamide, polyamide/imide, polyolefin, fluorine-containing polyolefin,
polyacetylene, polytrimethysilylpropyne, polyperfluorodioxole and
a mixture thereof.
16. The mixed matrix membrane of claim 7 in which at least one
of R.sub.1 and R.sub.2 is a lining group.
17. A process for making a mixed matrix gas separation membrane
having an active layer of particles of a treated molecular sieve
dispersed in a continuous phase consisting essentially of a matrix
polymer, comprising the steps of, (A) providing a monofunctional
organosilicon compound having the formula Si(XYR.sub.1 R.sub.2)
in which X is a displaceable radical, Y is a linking group, and
R.sub.1 and R.sub.2 are each independently any radical other than
a displaceable radical, (B) reacting a molecular sieve with the
monofunctional organosilicon compound at a temperature and for a
duration effective to bond the molecular sieve to the Si atom of
the monofunctional organosilicon compound by displacing the radical
X, thereby forming the treated molecular sieve, (C) blending the
product of the preceding step with an amount of the matrix polymer
effective to obtain a blend having a proportion of about 5-50 weight
parts molecular sieve per 100 weight parts polymer, and (D) forming
a membrane structure from the blend.
18. The process of claim 17 in which after the reacting step further
comprises the step of sizing the treated molecular sieve with the
polymer comprising reacting a linking group of the treated molecular
sieve to the matrix polymer.
19. The process of claim 18 in which the sizing step occurs after
the forming step.
20. The process of claim 17 in which after the reacting step further
comprises the step of sizing the treated molecular sieve to the
matrix polymer comprising reacting or associating a linking group
with a second polymer to form an adduct capable of reacting or associating
with the matrix polymer.
21. The process of claim 17 in which after the reacting step further
comprises the step of sizing the treated molecular sieve to the
matrix polymer comprising reacting or associating a linking group
with a monomer of the matrix polymer to form an adduct capable of
reacting or associating with the matrix polymer.
22. The process of claim 17 in which the monofunctional organosilicon
compound is a silane selected from the group consisting of 3-aminopropyldimethylethoxy
silane (APDMS), 3-isocyanatopropyl dimethylchlorosilane (ICDMS),
3-aminopropyl diisopropylethoxy silane (APDIPS) and a mixture thereof.
23. The process of claim 22 in which the molecular sieve is selected
from the group consisting of aluminosilicate type SSZ-13 hydrogen-exhanged
aluminosilicate type H-SSZ-13 sodium-exchanged aluminosilicate
type Na-SSZ-13 silicoaluminophosphate type SAPO-34 silicoaluminophosphate
type SAPO-44 silicalite molecular sieve, aluminosilicate molecular
type ZK-5 aluminosilicate molecular sieve type Zeolite RHO, aluminosilicate
molecular sieve type Phillipsite, and a mixture thereof.
Molecular sieve description
FIELD OF THE INVENTION
This invention relates to mixed matrix membranes for gas separation
incorporating a molecular sieve dispersed in a polymeric continuous
phase, and more specifically, to such mixed matrix gas separation
membranes in which the molecular sieve has been treated with a monofunctional
silane compound.
BACKGROUND OF THE INVENTION
The use of selectively gas permeable membranes to separate the
components of gas mixtures is a well developed and commercially
very important art. Such membranes are traditionally composed of
a homogeneous, usually polymeric composition through which the components
to be separated from the mixture are able to travel at different
rates under a given set of driving force conditions, e.g. transmembrane
pressure and concentration gradients.
A relatively recent advance in this field utilizes mixed matrix
membranes. Such membranes are characterized by a heterogeneous,
active gas separation layer comprising a dispersed phase of discrete
particles in a continuous phase of a polymeric material. The dispersed
phase particles are microporous materials that have discriminating
adsorbent properties for certain size molecules. Chemical compounds
of suitable size can selectively migrate through the pores of the
dispersed phase particles. In a gas separation involving a mixed
matrix membrane, the dispersed phase material is selected to provide
separation characteristics which improve the permeability and/or
selectivity performance relative to that of an exclusively continuous
phase polymeric material membrane.
Previous research on mixed matrix membranes with enhanced selectivity
has suggested the use of zeolites for the dispersed phase particles.
Some types of zeolites identified for use in mixed matrix membranes
include: MFI type, such as silicalite, LTA types 4A and 5A, and
FAU types X and Y with various substituted cations. Further understanding
of conventional use of zeolites in mixed matrix membranes may be
understood with reference to the following patents:
U.S. Pat. No. 5127925 (Kulprathipanja et al.) describes a process
for separating a first gas component from a feed gas mixture calling
for contacting the mixture with a mixed matrix membrane of an organic
polymer having an adsorbent incorporated therein. The adsorbent
material is selected from among zeolites such as crystalline aluminosilicates,
silicalite, inorganic oxides, activated carbon or ion exchange resin.
U.S. Pat. No. 4925562 (te Hennepe et al.) discloses a pervaporation
process which employs a membrane comprising an elastomeric polymer
matrix containing zeolite. In a preferred embodiment, the elastomeric
polymer matrix is silicone rubber comprising a polysiloxane. Preferred
zeolites include hydrophobic aluminosilicates with a high Si/Al
ratio. Silicalite is disclosed as a suitable zeolite.
Although this technology has steadily advanced, it is a persistent
general shortcoming of gas separation membranes that usually either
high transmembrane flux or high selectivity can be obtained at sacrifice
of the other. The advent of mixed matrix membranes provided the
ability to better design a membrane to achieve optimum performance
by using two permeable materials with different permeability and
selectivity characteristics. However, the heterogeneous nature of
mixed matrix membranes also introduces certain problems which have
prevented this technology from fully surmounting the aforementioned
shortcoming. In particular, unless there is affinity between the
dispersed phase and continuous phase materials, voids can occur
at the interface during membrane fabrication and use. The migrating
components can travel through the voids and thereby avoid passing
through the selectively permeable materials. This contributes to
poor separation performance.
U.S. Pat. No. 4925459 (Rojey et al.) discloses a gas separation
membrane comprising an active layer including particles of a selective
solid dispersed in a continuous non-porous and non-elastomeric polymer
phase and a porous support. The patent teaches that zeolites are
particularly adapted for use in the dispersed phase. It also states
that the dispersed phase can be pretreated with a binding agent
such as a silane before mixing it with polymer solution. A theory
has now been formulated that certain adhesive agents, including
some silanes, can actually interfere with transport of the selectively
permeating species through the discrete phase particles. For example,
it is suggested that the adhesive can block entry into the pores
or surround the particles with a permeability inhibiting barrier
layer. These or other mechanisms may be responsible for reducing
mixed matrix membrane separation performance. Thus it remains highly
desirable to provide a mixed matrix gas separation membrane having
molecular sieve dispersed in a continuous polymer matrix which can
produce the combination of higher permeability and selectivity than
has heretofore been attainable.
SUMMARY OF THE INVENTION
The present invention now provides a mixed matrix gas separation
membrane comprising particles of a treated molecular sieve dispersed
in a continuous phase consisting essentially of a matrix polymer,
in which the treated molecular sieve comprises the reaction product
of a molecular sieve and a monofunctional organosilicon compound
having the formula Si(XYR.sub.1 R.sub.2) in which X is a displaceable
radical, Y is a linking group, and R.sub.1 and R.sub.2 are each
independently any radical other than a displaceable radical.
There is also provided a process for making a mixed matrix gas
separation membrane having an active layer of particles of a treated
molecular sieve dispersed in a continuous phase consisting essentially
of a matrix polymer, comprising the steps of, (A) providing a monofunctional
organosilicon compound having the formula Si(XYR.sub.1 R.sub.2)
in which X is a displaceable radical, Y is a linking group, and
R.sub.1 and R.sub.2 are each independently any radical other than
a displaceable radical, (B) reacting a molecular sieve with the
monofunctional organosilicon compound at a temperature and for a
duration effective to bond the molecular sieve to the Si atom of
the monofunctional organosilicon compound by displacing the radical
X, thereby forming the treated molecular sieve, (C) blending the
product of the preceding step with an amount of the matrix polymer
effective to obtain a blend having a proportion of about 5-50 weight
parts molecular sieve per 100 weight parts polymer, and (D) forming
a membrane structure from the blend.
In another aspect, this invention provides a process for making
a mixed matrix gas separation membrane as described immediately
above in which after the reacting (B) step further comprises the
step of sizing the treated molecular sieve with the polymer comprising
reacting a linking group of the treated molecular sieve to the matrix
polymer.
There is yet further provided a process for separating component
gases of a gas mixture comprising the steps of (A) providing a mixed
matrix gas separation membrane comprising an active layer of a treated
molecular sieve dispersed in a continuous phase of a matrix polymer
in which the treated molecular sieve comprises the reaction product
of a (i) molecular sieve through which at least one component gas
in the mixture is preferentially gas permeable relative to another
component gas, with (ii) a monofunctional organosilicon compound
having the formula Si(XYR.sub.1 R.sub.2) in which X is a displaceable
radical, Y is a linking group, and R.sub.1 and R.sub.2 are each
independently any radical other than a displaceable radical, (B)
contacting the gas mixture on one side of the membrane to cause
the component gases to selectively permeate the membrane, and (C)
removing from the opposite side of the membrane a permeate gas composition
enriched in concentration of the at least one component gas.
DETAILED DESCRIPTION
This invention pertains to mixed matrix membranes. By "mixed
matrix" is meant that the membrane has a selectively gas permeable
layer which comprises a continuous phase of a polymeric material
and discrete particles of adsorbent material uniformly dispersed
throughout the continuous phase. These particles are collectively
sometimes referred to herein as the "discrete phase" or
the "dispersed phase". Thus the term "mixed matrix"
is used here to designate the composite of discrete phase particles
dispersed within the continuous phase.
The adsorbent material utilized in the present invention is a type
of molecular sieve. Molecular sieves, exist in both natural and
synthetic forms. They are well known in the art to encompass an
extensive variety of species and are described in Atlas of Zeolite
Structure Types W. M. Meier, DH Olson and Ch. Baerlocher, Zeolites
1996 17 (A1-A6), 1-230 (hereinafter "IZA"), in Molecular
Sieves: Principles of Synthesis and Identification, R. Szostak,
Van Nostrand Reinhold, (1989), and in Zeolite Molecular Sieves,
D. Breck, John Wiley and Sons, 1973 (Breck), the complete disclosures
of which are hereby incorporated herein by reference. Molecular
sieves have framework structures which may be characterized by distinctive
wide-angle X-ray diffraction patterns. Zeolites are a subclass of
molecular sieves based on an aluminosilicate composition. Non-zeolitic
molecular sieves are based on other compositions such as aluminophosphates,
silico-aluminophosphates, and silica. Molecular sieves of different
chemical compositions can have the same framework structure.
Zeolites can be further broadly described as molecular sieves in
which complex aluminosilicate molecules assemble to define a three-dimensional
framework structure enclosing cavities occupied by ions and water
molecules which can move with significant freedom within the zeolite
matrix. In commercially useful zeolites, the water molecules can
be removed from or replaced without destroying the framework structure.
Zeolite composition can be represented by the following formula:
M.sub.2/n O.Al.sub.2 O.sub.3.xSiO.sub.2.yH.sub.2 O, wherein M is
a cation of valence n, x is greater than or equal to 2 and y is
a number determined by the porosity and the hydration state of the
zeolites, generally from 0 to 8. In naturally occurring zeolites,
M is principally represented by Na, Ca, K, Mg and Ba in proportions
usually reflecting their approximate geochemical abundance. The
cations M are loosely bound to the structure and can frequently
be completely or partially replaced with other cations or hydrogen
by conventional ion exchange. Acid forms of molecular sieve sorbents
can be prepared by a variety of techniques including ammonium exchange
followed by calcination or by direct exchange of alkali ions for
protons using mineral acids or ion exchangers. For a discussion
of acid sites in zeolites see J. Dwyer, "Zeolite, Structure,
Composition and Catalysis" in Chemistry and Industry, Apr.
2 1984.
The zeolite framework structure has corner-linked tetrahedra with
Al or Si atoms at centers of the tetrahedra and oxygen atoms at
corners. Such tetrahedra are combined in a well-defined repeating
structure comprising various combinations of 4-, 6-, 8-, 10-, and
12-membered rings. The resulting framework structure is one of regular
channels and cages, which has a pore network that is useful for
separation. Pore dimensions are determined by the geometry of the
aluminosilicate tetrahedra forming the zeolite channels or cages,
with nominal openings of 0.26 nm for 6-member rings, 0.40 nm for
8-member rings, 0.55 nm for 10-member rings and 0.74 nm for 12-member
rings (these numbers assume ionic radii for oxygen). Those skilled
in the art will recognize that zeolites with the largest pores being
8-member rings, 10-member rings, and 12-member rings are considered
small, medium, and large pore zeolites, respectively. Pore dimensions
are critical to the performance of these materials in catalytic
and separation applications, since this characteristic determines
whether molecules of certain size can enter and exit the zeolite
framework. In practice, it has been observed that very slight decreases
in ring dimensions can effectively hinder or block movement of particular
molecular species through the zeolite structure.
The effective pore dimensions that control access to the interior
of the zeolites are determined not only by the geometric dimensions
of the tetrahedra forming the pore opening, but also by the presence
or absence of ions in or near the pore. For example, in the case
of zeolite type A, access can be restricted by monovalent ions,
such as Na.sup.+ or K.sup.+, which are situated in or near 8-member
ring openings as well as 6-member ring openings. Access can be enhanced
by divalent ions, such as Ca.sup.2+, which are situated only in
or near 6-member ring openings. Thus, the potassium and sodium salts
of zeolite A exhibit effective pore openings of about 0.3 nm and
0.4 nm respectively, whereas the calcium salt of zeolite A has an
effective pore opening of 0.5 nm. The presence or absence of ions
in or near the pores, channels, and/or cages can also significantly
modify the accessible pore volume of the zeolite for sorbing materials.
Thus the KA zeolite (also known as 3A) allows a constituent whose
molecule has a size less than 3 .ANG. (0.3 nm, 1 .ANG.=1.times.10.sup.-10
m) to be separated from a constituent whose molecule has a size
greater than 3 .ANG. (0.3 nm). For example, KA zeolite therefore
allows separation of water which can enter the pores of the zeolite
from methane which is excluded. Similarly, NaA zeolite (also known
as 4A) allows a constituent whose molecule has a size less than
4 .ANG. (0.4 nm) to be separated from a constituent whose molecule
has a size greater than 4 .ANG., (0.4 nm) and CaA zeolite, (also
known as 5A) allows normal paraffins to be separated from a mixture
of normal paraffins and isoparaffins.
Representative examples of zeolites are small pore zeolites such
as NaA, CaA, Erionite, Rho, ZK-5 and chabazite; medium pore zeolites
such as ZSM-5 ZSM-11 ZSM-22 and ZSM-48 and large pore zeolites
such as zeolite beta, zeolite L, NaX, NaY, and CaY.
The silicon/aluminum atomic ratio of a given zeolite can vary over
a wide range. For example, zeolite X can be synthesized with silicon/aluminum
atomic ratios of from 1 to 1.5; and zeolite Y, from 1.5 to about
3. In some molecular sieves, such as MFI type, the upper limit of
the silicon/aluminum atomic ratio is unbounded. ZSM-5 is one such
example wherein the silicon/aluminum atomic ratio is at least 12.
Low alumina-containing zeolites also can be prepared synthetically
or by modification of high alumina-containing zeolites using methods
well known in the art. These methods include but are not limited
by treatment using SiCl.sub.4 or (NH.sub.4).sub.2 SiF.sub.6 as well
as steaming followed by acid treatment. The SiCl.sub.4 treatment
is described in J. Chem. Ed. 67(6), 519-521 1990. The (NH.sub.4).sub.2
SiF.sub.6 treatment by Breck et al., is described in U.S. Pat. No.
4503023. These treatments are generally very effective at increasing
the Si/Al ratio for zeolites such as zeolites Y and mordenite.
Another class of molecular sieves is characterized by AlO.sub.2
and PO.sub.2 units (AlPO.sub.4 or aluminum phosphates) of which
at least some Al or P constituents optionally may be substituted
by other elements such as Si (called silicoaluminophosphates or
SAPO's), or metals (called metallo-aluminophosphates or MeAPO's)
or combinations thereof (called metalloalumino-phosphosilicates
or MeAPSO's). These AlPO.sub.4 SAPO, MeAPO, and MeAPSO materials
are crystalline and have ordered pore structures which accept certain
molecules while rejecting others.
A type of molecular sieve used in the mixed matrix membrane of
this invention is iso-structural with the mineral zeolite known
as chabazite. That is, they are characterized by the chabazite framework
structure designated as CHA by the IZA reference. This molecular
sieve type derives its name from the structure of a naturally occurring
mineral with the approximate unit cell formula Ca.sub.6 Al.sub.12
Si.sub.24 O.sub.72. The chabazite type (CHA) molecular sieves are
distinguished by channels based on 8-member rings with about 3.8
.ANG..times.3.8 .ANG. (0.38 nm.times.0.38 nm) dimensions.
Identification of chabazite is generally made by X-ray powder diffraction.
A number of synthetic molecular sieves generate the characteristic
diffraction pattern of CHA type and therefore are reported (for
example, in the IZA reference and Szostak cited above) to have the
same CHA framework structure as (or are iso-structural with) the
mineral chabazite.
The integrated intensities of the observed X-ray peaks can be used
as a measure of molecular sieve crystallinity. High intensities
indicate a highly crystalline material. However, as crystallite
size falls below about 50 nm, X-ray diffraction peaks broaden (H.
P. Klug and L. E. Alexander, X-Ray Diffraction Techniques, Wiley-Interscience,
N. Y., 1974). When crystallite size falls below about 2-6 nm, peaks
become so broad that they are difficult to detect by conventional
analog recording spectrometers. Despite a lack of measurable X-ray
peak intensity, such "X-ray amorphous" zeolite crystallites
are capable of shape selective catalysis, as recently reported by
Jacobs et al., J. Chemical Society, Chemical Communications, p.
591 (1981). For such crystallites, molecular sieve crystallinity
is evident from infra-red spectra, sorption measurements, and catalytic
shape selectivity. The CHA molecular sieve materials of the present
invention can be highly crystalline, poorly crystalline, or X-ray
amorphous crystallites. Thus the term "chabazite" herein
is intended to encompass any molecular sieves which exhibit the
characteristic X-ray diffraction pattern of the CHA structure or
can be identified as CHA type by infra-red spectra, sorption measurements
and/or catalytic shape selectivity.
Various synthetic forms of CHA type molecular sieves are known.
Several CHA type zeolites described by Breck are Zeolite "K-G",
a potassium form having a silica: alumina mole ratio of 2.3:1 to
4.15:1 reportedly described in J. Chem Soc., p. 2822 (1956), Barrer
et al; Zeolite D, a sodium-potassium form having a silica:alumina
mole ratio of 4.5:1 to 4.9:1 reportedly described in British Patent
No. 868846 (1961); and Zeolite R, a sodium form which has a silica:alumina
mole ratio of 3.45:1 to 3.65:1 reportedly described in U.S. Pat.
No. 3030181 (1962). A pure SiO2 chabazite type molecular sieve
is described by Cabanas et al. Synthesis and structure of pure SiO2
chabazite, Chem. Commun. 1998 1881-2. Willhendersonite is identified
as a CHA type molecular sieve by Lengauer et al., Dehydration and
structural transformation in the chabazite-type zeolite Willhendersonite,
Eur. J. Miner. 1999 Bh. 1 144. The disclosures of these sources
is hereby incorporated herein by reference.
Additional illustrative examples of CHA type molecular sieves suitable
for use in this invention include SSZ-13 H-SSZ-13 Na-SSZ-13 SAPO-34
and SAPO-44. SSZ-13 is an aluminosilicate molecular sieve material
prepared as disclosed in U.S. Pat. No. 4544538 the entire disclosure
of which is hereby incorporated by reference. Generally, SSZ-13
is a zeolite having a mole ratio of an oxide selected from silicon
oxide, germanium oxide, and mixtures thereof to an oxide selected
from aluminum oxide, gallium oxide, and mixtures thereof greater
than about 5:1 and having the X-ray diffraction lines of Table 1
of U.S. Pat. No. 4544538. The zeolite further has a composition,
as synthesized and in the anhydrous state, in terms of mole ratios
of oxides as follows: (0.5 to 1.4) R.sub.2 O: (0 to 0.50) M.sub.2
O:W.sub.2 O.sub.3 : (greater than 5) YO.sub.2 wherein M is an alkali
metal cation, W is selected from aluminum, gallium, and mixtures
thereof, Y is selected from silicon, germanium and mixtures thereof,
and R is an organic cation. The organic R is removed typically by
calcination at about 280-500.degree. C. SSZ-13 zeolites can have
a YO.sub.2 :W.sub.2 O.sub.3 mole ratio greater than about 5:1. As
prepared, the silica:alumina mole ratio is typically in the range
of 8:1 to about 50:1. Higher mole ratios can be obtained by varying
the relative ratios of reactants. Higher mole ratios can also be
obtained by treating the zeolite with chelating agents or acids
to extract aluminum from the zeolite lattice. The silica:alumina
mole ratio can also be increased by using silicon and carbon halides
and similar compounds. Preferably, SSZ-13 is an aluminosilicate
in which W is aluminum and Y is silicon.
It is sometimes desirable to remove the alkali metal cation from
SSZ-13 and to replace it with hydrogen, ammonium or other desired
metal ion. Ion exchange can occur after the organic moiety R is
removed, usually by calcination. The hydrogen and sodium forms of
SSZ-13 referred to herein respectively as H-SSZ-13 and Na-SSZ-13
are particularly preferred CHA molecular sieves for use in this
invention. H-SSZ-13 is formed from SSZ-13 by hydrogen exchange or
preferably by ammonium exchange followed by heating to about 280-400.degree.
C. A sample of H-SSZ-13 was found to have an Si/Al ratio of about
20-24 and Na/Al ratio of less than about 0.3 by electron spectroscopy
chemical application ("ESCA") analysis or by inductively
coupled plasma ("ICP") analysis.
Description and method of preparation of the silicoaluminophosphate
molecular sieves SAPO-34 and SAPO-44 are found in U.S. Pat. No.
4440871 which is hereby incorporated herein by reference. The
structure of these zeolites is reported by Ashtekar et al., (Journal
of Physical Chemistry, V98 N18 May 5 1994 p. 4878) to be that
of the CHA type. SAPO-34 is also identified as having a CHA type
structure in the Journal of American Chemical Society, 106 p. 6092-93
(1984).
Another type of molecular sieve suitable for use with this invention
is silicalite. Silicalite is a hydrophobic, crystalline silica-based
molecular sieve. Silicalite I can be prepared according to the procedure
described in U.S. Pat. No. 4061724 the disclosure of which is
hereby incorporated herein by reference. Silicalite I is classified
by the IZA reference as having an MFI framework structure based
on ten-member rings with about 5.1 .ANG..times.5.6 .ANG. (0.51 nm.times.0.51
nm) pore dimensions.
The continuous phase of the mixed matrix membrane consists essentially
of polymer. To distinguish from other polymers related to this invention,
the term "matrix" polymer is sometimes used herein to
refer to the polymer of the continuous phase. By "consists
essentially of" is meant that the continuous phase, in addition
to polymeric material, may include non-polymer materials that do
not materially affect the basic and novel properties of this invention.
For example, the continuous phase can include preferably small proportions
of fillers, additives and process aids, such as surfactant residue
used to promote dispersion of the molecular sieve in the polymer
during fabrication of the membrane.
Preferably the polymeric continuous phase is nonporous. By "nonporous"
is meant that the continuous phase is substantially free of dispersed
cavities or pores through which components of the gas mixture could
migrate. Transmembrane flux of the migrating components through
the polymeric continuous phase is thus driven primarily by molecular
solution/diffusion mechanisms. Therefore it is important that this
polymer chosen for the continuous phase is permeable to the components
to be separated from the gas mixture. Preferably the polymer is
selectively gas permeable to the components, meaning that gases
to be separated from each other permeate the membrane at different
rates. That is, a highly permeable gas will travel through the continuous
phase faster than will a less permeable gas. The selectivity of
a gas permeable polymer is the ratio of the permeabilities of the
pure component gases. Hence, the greater the difference between
transmembrane fluxes of individual components, the larger will be
the selectivity of a particular polymer.
Each molecular sieve to be used in the dispersed phase has particular
separation characteristics of permeability and selectivity with
respect to the components of a given gas mixture. These characteristics
are largely determined by such factors as the effective pore size
and framework structure. The molecular sieve separation characteristics
can be chosen to be different from those of the continuous phase
polymer. Usually, the separation characteristics of the molecular
sieve are selected so that overall separation performance through
the mixed matrix membrane is enhanced relative to performance through
a homogenous membrane of the continuous phase material. For example,
a selectively gas permeable polymer might have a high permeability
but low selectivity in relation to a specific mixture of gases.
A molecular sieve having high selectivity for the same gases can
be dispersed in the continuous phase of such polymer to produce
a mixed matrix membrane having a superior combination of selectivity
and permeability.
A diverse variety of polymers can be used for the continuous phase.
Typical polymers suitable for the nonporous polymer of the continuous
phase according to the invention include substituted or unsubstituted
polymers and may be selected from polysiloxane, polycarbonates,
silicone-containing polycarbonates, brominated polycarbonates, polysulfones,
polyether sulfones, sulfonated polysulfones, sulfonated polyether
sulfones, polyimides and aryl polyimides, polyether imides, polyketones,
polyether ketones, polyamides including aryl polyamides, poly(esteramide-diisocyanate),
polyamide/imides, polyolefins such as polyethylene, polypropylene,
polybutylene, poly-4-methyl pentene, polyacetylenes, polytrimethysilylpropyne,
fluorinated polymers such as those formed from tetrafluoroethylene
and perfluorodioxoles, poly(styrenes), including styrene-containing
copolymers such as acrylonitrile-styrene copolymers, styrene-butadiene
copolymers and styrene-vinylbenzylhalide copolymers, cellulosic
polymers, such as cellulose acetate-butyrate, cellulose propionate,
ethyl cellulose, methyl cellulose, cellulose triacetate, and nitrocellulose,
polyethers, poly(arylene oxides) such as poly(phenylene oxide) and
poly(xylene oxide), polyurethanes, polyesters (including polyarylates),
such as poly(ethylene terephthalate), and poly(phenylene terephthalate),
poly(alkyl methacrylates), poly(acrylates), polysulfides, polyvinyls,
e.g., poly(vinyl chloride), poly(vinyl fluoride), poly(vinylidene
chloride), poly(vinylidene fluoride), poly(vinyl alcohol), poly(vinyl
esters) such as poly(vinyl acetate) and poly(vinyl propionate),
poly(vinyl pyridines), poly(vinyl pyrrolidones), poly(vinyl ketones),
poly(vinyl ethers), poly(vinyl aldehydes) such as poly(vinyl formal)
and poly(vinyl butyral), poly(vinyl amides), poly(vinyl amines),
poly(vinyl urethanes), poly(vinyl ureas), poly(vinyl phosphates),
and poly(vinyl sulfates), polyallyls, poly(benzobenzimidazole),
polyhydrazides, polyoxadiazoles, polytriazoles: poly(benzimidazole),
polycarbodiimides, polyphosphazines, and interpolymers, including
block interpolymers containing repeating units from the above such
as terpolymers of acrylonitrile-vinyl bromide-sodium salt of para-sulfophenylmethallyl
ethers, and grafts and blends containing any of the foregoing. The
polymer suitable for use in the continuous phase is intended to
also encompass copolymers of two or more monomers utilized to obtain
any of the homopolymers or copolymers named above. Typical substituents
providing substituted polymers include halogens such as fluorine,
chlorine and bromine, hydroxyl groups, lower alkyl groups, lower
alkoxy groups, monocyclic aryl, lower acyl groups and the like.
Preferred polymers for the continuous phase are polysiloxane, polycarbonates,
silicone-containing polycarbonates, brominated polycarbonates, polysulfones,
polyether sulfones, sulfonated polysulfones, sulfonated polyether
sulfones, polyimides, polyether imides, polyketones, polyether ketones,
polyamides, polyamide/imides, polyolefins such as poly-4-methyl
pentene, polyacetylenes such as polytrimethysilylpropyne, and fluoropolymers
including fluorinated polymers and copolymers of fluorinated monomers
such as fluorinated olefins and fluorodioxoles, and cellulosic polymers,
such as cellulose diacetate and cellulose triacetate.
Any of the above mentioned types of molecular sieve are amenable
to surface treatment with monofunctional organosilicon compound
according to this invention provided that the molecular sieve has
on its surface a sufficient number of silanol or acid groups available
to react with the compound to provide effective compatibility between
the dispersed phase particles and the continuous phase polymer.
One can test a molecular sieve candidate for suitability by directly
determining the surface silanol concentration of the candidate material
and of silicalite. Well known direct measurement techniques include
spectroscopic methods such as Fourier-transform infrared spectroscopy
("FTIR") and nuclear magnetic resonance spectroscopy ("NMR").
See Smith, L. J, et al., A newtonian diffraction and infrared spectroscopy
study of the acid form of the aluminosilicate zeolite, chabazite
(H-SSZ-13) Catalyst Letters (49) 143-146 1997 and Kunkeler, P.
J., et al., Zeolite Beta: The relationship between calcination procedure,
aluminum configuration and Lewis acidity, Journal of Catalysis,
(180), 234-244 (1998). If the surface silanol concentration of the
candidate is about equal to or higher than that of silicalite, it
is likely that the molecular sieve candidate can be adequately treated
to be compatibilized with the continuous phase polymer according
to this invention. Another test for suitability of a molecular sieve
candidate calls for treating the candidate material with a monofunctional
organosilicon compound as will be described in greater detail, below.
The treated candidate is then washed to remove unreacted organosilicon
compound and the concentration of residual compound bound to the
sieve can be determined by measuring the organic portion in the
reaction product; by such well known methods as infrared, NMR and
ESCA For example, for an amino-organosilicon compound, the concentration
of organosilicon compound reacted with the molecular sieve can be
estimated by measuring the amino group response by FTIR, proton-NMR
or ESCA analyses. This amino group concentration response can then
be compared with the corresponding response obtained when silicalite
is treated with the same amino-organosilicon compound. The treatment
should be sufficient if the amino group response is at least about
equal to the response obtained with silicalite. One of ordinary
skill in the art can thus determine whether the silanol content
of a molecular sieve is suitable without undue experimentation.
The molecular sieve particle size should be small enough to provide
a uniform dispersion of the particles in the suspension from which
the mixed matrix membrane will be formed and also to obtain uniform
distribution of the dispersed phase particles in the continuous
phase of the mixed matrix membrane. The median particle size should
be less than about 10 .mu.m, preferably less than 3 .mu.m, and more
preferably less than 1 .mu.m. Large agglomerates should be reduced
to less than about 10 .mu.m and preferably less than about 3 .mu.m.
Very fine molecular sieve particles may be made by various techniques
such as by choosing appropriate synthesis conditions or by physical
size reduction methods well known to those of ordinary skill in
the art, such as ball milling, wet-milliing and ultrasonication.
In some cases, the size reduction process, e.g., ultrasonication
or wet-milling can be advantageously carried out at the same time
as reaction of the molecular sieve with a monofunctional organosilicon
compound in accordance with this invention.
According to this invention the dispersed phase molecular sieve
is made compatible with the continuous phase polymer so that few,
if any, voids form between the sieve and the polymer. Improved compatibility
between the dispersed phase molecular sieve and the continuous phase
polymer also reduces the tendency of the dispersed phase to agglomerate
in the final membrane. As briefly mentioned, voids provide a path
for migrating species to bypass the selectively permeable materials
and therefore can have a negative influence on permeability and/or
selectivity of a mixed matrix membrane. Thus this invention provides
the advantage of enabling production of a reduced-void or void-free
mixed matrix membrane with excellent dispersion of dispersed phase
particles.
Compatibility between sieve and polymer is achieved basically by
treating the sieves with a monofunctional organosilicon compound
in which this compound becomes bonded to the surface of the molecular
sieve. This bonding occurs at only one of the four bond sites of
the silicon atom in the compound. The monofunctional organosilicon
compound also has one or more substituent moieties, occasionally
referred to herein as "linking groups". These are groups
which have affinity for or which chemically react with the polymeric
continuous phase. Hence, attraction between molecular sieve treated
with monofunctional organosilicon compound and the continuous phase
is enhanced. This reduces the formation of voids at the dispersed
phase-continuous phase interface.
The term "monofunctional" emphasizes that the organosilicon
molecule has a single tetravalent silicon atom to which only one
silanol group of the molecular sieve can bond. The single functional
group is sometimes referred to herein as a "displaceable radical".
The monofunctional organosilicon compound can have other substituent
groups which are functional in different ways. For example, the
linking groups can bond or associate with the polymer. This monofunctional
aspect of the organosilicon compound is designed to cause the organosilicon
compound to attach to the surface of the molecular sieve in a mono-molecular
thickness layer and preferably without substantial crosslinking
between neighboring attached organosilicon compound molecules. Without
wishing to be bound by a particular theory, it is contemplated that
the monofunctional organosilicon compound attaches to the sieve
largely without blocking the pores.
Polyfunctional organosilicon compounds can also provide desired
interfacial adhesion. In contrast to the monofunctional compounds,
however, polyfunctional compounds can block the molecular sieve
pores, build up a network over the molecular sieve surface to an
excessive thickness or otherwise interfere with the transport of
the migrating molecules through the membrane. Only with rigorous
control of reaction conditions, e.g., by scrupulously maintaining
an anhydrous system, can polyfunctional organosilicon compounds
form a mono-molecular layer of comparable morphology to that obtained
readily by a monofunctional organosilicon compound.
Mixed matrix membranes having improved gas separation performance
can be produced by using molecular sieve treated with the monofunctional
organosilicon compound which permits the treated sieve particles
to bond or associate with the continuous phase polymer. Broadly
stated, the procedure for using the compound to join the sieve particles
to the polymer includes two major steps. One involves reacting the
monofunctional organosilicon compound at the site of the displaceable
radical with free silanol on the molecular sieve surface. This step,
often called "silanation" of the sieve, typically results
in substitution of the displaceable radical of the compound by the
silanol of the molecular sieve. A molecular sieve having been treated
in this fashion may be said to be "silanated". The monofunctional
organosilicon compound thus becomes chemically bonded via the single
silicon atom bond site formerly occupied by the displaceable radical
prior to silanation.
The other major step relates to uniting the organosilicon compound
affixed to the surface of the molecular sieve particles with the
continuous phase polymer. Two mechanisms for obtaining affinity
between the silanated sieve and the polymer are contemplated. Firstly,
the linking groups can react with the polymer to form direct chemical
bonds therebetween. Alternatively, the linking groups can associate
with the polymer because the chemical compositions of the linking
groups and the polymer are selected to be mutually attractive. For
example, the linking groups and polymer can be populated with moieties
which have mutually attractive polar or dipolar interactions. Affinity
can also be attained by reacting or associating the linking groups
with a monomer of the continuous phase polymer. That is, the linking
groups are caused to react or associate with free monomer so that
the sieve-monomer adduct has enhanced affinity for the polymer by
virtue of the chemical compatibility of the monomer and the polymer.
The step of joining the silanated molecular sieve to the polymer
by either reacting or associating the linking groups with the polymer
or monomer of the polymer is sometimes referred to herein as "sizing".
The term "associate" is used here to mean that the attraction
between the linking groups and polymer is strong but short of a
bond resulting from chemical reaction. A way to determine whether
a linking group is suitable for associating with the polymer calls
for silanating a molecular sieve with an monofunctional organosilicon
compound having the candidate linking group substituted thereon.
The treated sieve is then intimately mixed with the continuous phase
polymer, usually by blending a dispersion of the sieve particles
in a solvent with a solution of the polymer. After removing the
solvent, the mixed matrix material is cross-sectioned by cryo-fracturing
and then gold coated. The section is examined by scanning electron
microscopy ("SEM") at 10000-20000 power magnification.
If no gaps are seen between the continuous phase polymer and the
embedded particles, then the linking group is deemed to acceptably
associate with the polymer for purposes of this invention.
In a preferred embodiment, the monofunctional organosilicon compound
has chemical composition of the formula Si(XYR.sub.1 R.sub.2) which
also may be represented diagramatically by the following structure:
##STR1##
in which X is a displaceable radical, Y is a linking group, and
R.sub.1 and R.sub.2 are each independently any radical other than
a displaceable radical.
"Displaceable radical" means an active functional group
capable of reacting with silanol groups on the molecular sieve such
that X is displaced leaving the molecular sieve bonded to the monofunctional
organosilicon compound at the X--Si bond position. Preferably, the
displaceable radical can be a halogen, a hydroxyl group, or an ester
or alkoxy radical having from 1-8 carbon atoms. Any halogen, i.e.,
fluorine, chlorine, iodine, or bromine atom can be used. A representative
ester is the acetoxy radical. Illustrative examples of alkoxy radicals
of substitutent X include methoxy, ethoxy, n-propoxy and t-butoxy
radicals.
The chemical composition of Y will largely depend upon the composition
of the continuous phase polymer. The linking group is selected for
capability of reacting or associating with the polymer or a monomer
of the polymer. Knowing the latter, one of ordinary skill in the
art can identify functional groups that can react with the polymer
or with a monomer of the polymer. Similarly, the likelihood that
a functional group is able to associate with a particular polymer
or monomer composition can be estimated by one of ordinary skill
in the chemical arts. The usefulness of a particular candidate linking
group to react or associate with the polymer can be verified by
the method described above. Typical examples of Y which can be used
with polymer of suitable co-reactivity include amino radicals, such
as aminopropyl and aminophenyl, amido radicals, such as methacrylamido
and ethacrylamido, ureido radicals, such as ureidopropylepoxy, epoxy
radicals, such as epoxycyclohexyl and glycidoxypropyl, and isocyanoato
radicals, such as cyanoethyl and cyanopropyl. R.sub.1 and R.sub.2
can be non-reactive hydrocarbon radicals including straight chain
and branched alkyls, such as methyl, ethyl, n-propyl, isopropyl,
n-butyl and t-butyl radicals. Optionally, R.sub.1 R.sub.2 or both
can be a linking group. Illustrative of suitable monofunctional
organosilicon compounds include the silanes 3-aminopropyldimethylethoxysilane
(APDMS), 3-isocyanatopropyldimethylchlorosilane (ICDMS), 3-aminopropyldiisopropylethoxysilane
(APDIPS) and mixtures thereof
The silanation step for treating the molecular sieve according
to this invention typically involves a chemical reaction to condense
the monofunctional organosilicon compound onto the molecular sieve
at silanol groups on the molecular sieve surface. Usually this is
carried out in a suspension of the molecular sieves in a liquid
medium of a solvent containing the dissolved compound.
The solvent utilized for the silanation medium is chosen primarily
for its ability to dissolve the monofunctional organosilicon compound.
It is also desirable that the compound and solvent can form a solution
of viscosity which is satisfactory to permit easy mechanical or
ultrasonic dispersion of the compound in the medium at desired solution
concentrations and temperatures. Preferably temperature of the silanation
reaction is about 15-80.degree. C., and more preferably about 25-50.degree.
C. The concentration of the compound in solution is preferably about
0.1 to about 5 wt. % and more preferably about 1-2 wt. %. Representative
solvents which can be used for dissolving monofunctional organosilicon
compound having either alkoxy, hydroxyl or ester displaceable radicals
according to this invention include ethanol, methanol, isopropanol,
water and mixtures thereof. A preferred solvent is 95:5 ethanol:water
solution. For halogen displaceable radicals, anhydrous solvents
should be utilized. Tetrahydrofuran or toluene are representative.
Anhydrous solvents should be used when the monofunctional organosilicon
compound contains hydrolytically unstable linking groups, such as
cyano radicals.
The liquid medium ingredients can be agitated to form a completely
miscible mixture. The organosilicon compound is added in an amount
in excess of the stoichiometric amount required to fully react with
silanol groups on the molecular sieve to be treated. When the homogeneous
liquid medium has been formed, the molecular sieve is added while
maintaining the medium in a state of agitation effective to disperse
the molecular sieve particles uniformly throughout the liquid. Heat
can be applied prior to, during or after addition of the molecular
sieve to attain reaction temperature. These conditions are maintained
for a duration effective to substantially completely condense the
monofunctional organosilicon compound onto the molecular sieve.
For monofunctional organosilicon compounds with alkoxy, hydroxyl
or ester displaceable radicals, preferably the silanation reaction
conditions are continued for about 1 to about 60 minutes. Silanation
with compounds having halogen displaceable radicals may call for
longer reaction time, i.e.., up to about 24 hours, and preferably
at a temperature near the boiling point of the solvent. After reaction
is completed, the temperature of the reaction mass can be lowered
to ambient and the treated molecular sieve particles are then filtered
free of excess reactants and washed, preferably repeatedly, in clean
solvent to remove trace residual reactants.
When an organosilicon compound substituted with reactive linking
groups is used, the linking groups coupled to the molecular sieve
during the silanation step can be further reacted with monomer or
polymer in the subsequent sizing step. Sizing step temperature is
preferably in the range of about 35-200.degree. C., and more preferably
about 120-160.degree. C. The reaction duration is usually about
30 to about 300 minutes. The particles can then be filtered free
of excess reactants, washed, dried and stored for later use. This
provides molecular sieve particles with monomer or polymer bound
to the sieve surface by the organosilicon compound linkage.
In a preferred method of sizing the treated molecular sieves, filtered
and cleaned particles of treated molecular sieve from the silanation
step are suspended in fresh, dilute solution of about 0.2-5%, preferably
about 0.5-1% continuous phase polymer. Representative solvents suitable
for this polymer solution include N-methyl pyrrolidone, dimethyl
acetamide, dioxane and mixtures thereof The treated molecular sieve
particles are added to the dilute solution while maintaining the
solution in a state of agitation effective to disperse the particles
uniformly throughout the solution. Then this suspension is subjected
to sizing step conditions mentioned above. Thereafter, if desired,
the treated particles can be filtered, washed and stored as before.
In another aspect, the sizing step can be bypassed. This is an
option when the monofunctional organosilicon compound contains reactive
linking groups and the continuous phase polymer contains active
sites to react with the linking groups under normal membrane formation
temperature conditions. The sizing step should not be performed
when the compound does not contain reactive linking groups.
Formation of the mixed matrix membrane is completed typically by
dissolving the polymer for the continuous phase in a suitable solvent
and dispersing the silanated or silanated-and-sized molecular sieve
particles in the resulting polymer solution. The particles can be
added to the solution as a powder or as a suspension in a liquid
medium. The order of combining ingredients is not critical. In yet
another optional process variation, if the reactive linking groups
have not yet been reacted with monomer or polymer, the sizing step
can be carried out at this time by raising temperature and holding
while maintaining the particles dispersed in the reaction medium,
as above.
When a uniform dispersion of treated molecular sieves in polymer
solution has been prepared, the membrane structure can be formed
by conventional techniques. For example the suspension can be sprayed
or cast with a doctor knife on a substrate or a substrate can be
dipped into the suspension. The solvent is then removed by such
typical techniques as ventilating the atmosphere above the forming
membrane with a diluent gas, drawing a vacuum or immersing the forming
membrane in a non-solvent for the polymer which is miscible with
the solvent of the polymer solution. Optionally, the atmosphere,
medium and/or the substrate can be heated to facilitate removal
of the solvent. In the case of membranes formed on a substrate material,
when the membrane is substantially free of solvent, it can be detached
from the substrate to form a self-supporting structure or the membrane
can be left in contact with a supportive substrate to form an integral
composite assembly. In such a composite, preferably the substrate
is porous or permeable to gaseous components which the membrane
is intended to separate. Further optional fabrication steps include
washing the membrane in a bath of an appropriate liquid to extract
residual solvent and other foreign matter from the membrane, and
drying the washed membrane to remove residual liquid.
EXAMPLES
This invention is now illustrated by examples of certain representative
embodiments hereof, wherein all parts, proportions and percentages
are by weight unless otherwise indicated. All units of weight and
measure not originally obtained in SI units have been converted
to SI units.
Example Materials SSZ-13 A calcined aluminosilicate (Si/Al ratio
of about 20-24) CHA type molecular sieve characterized by pores
based on 8 member rings with about 3.8.times.3.8 .ANG. (0.38.times.0.38
nm) dimensions which was prepared as disclosed in U.S. Pat. No.
4544538. H-SSZ-13 Na.sup.+ ion form of SSZ-13. The Na/Al ratio
is about 1 measured by ESCA and/or ICP analyses. Silicalite I Hydrophobic
MFI type crystalline silica-based molecular sieve. MFI type molecular
sieves are characterized by pores based on 10 member rings with
about 5.1.times.5.6 .ANG. (0.51.times.0.56 nm) dimensions. APDMS
3-aminopropyldimethylethoxysilane APDIPS 3-aminopropyldiisopropylethoxysilane
APS 3-aminopropyltriethoxysilane APPMS 3-aminopropylmonomethyldiethoxysilane
ICDMS 3-isocyanatopropyldimethychlorosilane DAPI 5x-amino-(4-aminophenyl)-
113 trimethyl indane BTDA 33',44'-benzophenonetetracarboxylicdianhydride
HSMPD 13-diaminobenzene-4-sulfonic acid Ultem.RTM. polyetherimide
of 13-phenylenediamine ("MPD") and bisphenol A dianhydride
("BPADA") from General Electric Co. Matrimid.RTM. polyimide
of DAPI and BTDA from Vantico, Inc. NMP N-methyl-2-pyrrolidone PVAc
polyvinyl acetate
EXAMPLE 1
Molecular sieve H-SSZ-13 (5 g) was dispersed in 100 g of a 2% solution
of APDMS in 95/5 w/w ethanol/water using an ultrasonic horn. The
dispersion was heated to 50.degree. C. and held for 1.5 hours. The
silanated molecular sieve was recovered by filtering through a 0.2
micron polytetrafluoroethylene filter. The filter cake was washed
three times in ethanol and then dried overnight at 110.degree. C.
under vacuum. The cake was then soaked in ethanol for two weeks
with solvent replacement every two days to remove as much free APDMS
as possible. At conclusion of the two-week rinsing period the cake
was dried under vacuum. ESCA analysis of the thoroughly washed cake
showed an increase of carbon and nitrogen compared to the virgin
molecular sieve powder. The increased carbon and nitrogen was consistent
with presence of the aminopropyl moiety and thus demonstrated that
APDMS had condensed onto the sieve particles. The cake can be easily
reslurried for further processing. This example demonstrates silanation
of a molecular sieve with monofunctional organosilicon compound.
EXAMPLE 2
2A: Sizing silanated molecular sieve to polymer in solution:
A polymer solution was prepared by dissolving 0.27 g Ultem.RTM.
1010 polyetherimide in 70 g NMP. To this solution 2 g of silanated
molecular sieve of Example 1 was added and the slurry was well dispersed
by ultrasonication. The dispersion was kept agitated at temperature
in the range of 140-180.degree. C. for 6 hours. After cooling the
excess polymer was removed by filtering through a 0.2 .mu.m polytetrafluoroethylene
("PTFE") filter and the resulting cake was washed three
times with 75 g fresh NMP to complete the sizing process.
The cake was soaked in NMP with replacement of solvent every 2
days for 2 weeks and then vacuum dried. ESCA analysis showed that
carbon and nitrogen had increased in comparison to the silanated
molecular sieve. The nitrogen response was consistent with the presence
of imide group and shows that the polyetherimide had become bound
to the molecular sieve.
The wet cake can be re-slurried in an appropriate medium such as
NMP. The slurry then can be blended into a high concentration polymer
solution, e.g., 10-40% and molecular sieve:polymer weight ratio
in suspension of 0.05-0.50. A mixed matrix membrane can be formed
from the blend.
2B: Sizing silanated molecular sieve to monomer in solution:
APDMS was condensed onto H-SSZ-13 molecular sieve as in Example
1. This silanated molecular sieve was slurried as in Example 2A
except that the solution contained the diamine DAPI and the dianhydride
BTDA dissolved together in NMP. DAPI and BTDA are understood to
be comonomers of commercially available polyimide such as Matrimid.RTM.
polymer. The molecular sieve in contact with the diamine and dianhydride
solution was heat-aged similarly to Example 2A. The molecular sieve
cake after reaction was washed as above and subjected to ESCA. Analytical
results showed that the carbon and nitrogen content of the sized
molecular sieve had increased relative to the silanated molecular
sieve. This confirmed that the monomer units and/or oligomers thereof
had bonded to the silanated molecular sieve.
2C: Sizing silanated molecular sieve to polymer film:
Silanated molecular sieve was prepared as in Example 1 and dispersed
in a solution of polymer as in Example 2. Before reacting the silanated
molecular sieve and polymer however, the dispersion was cast as
a dense film. The film was heated to 140-200.degree. C. overnight
to allow hydrophilic groups on the silanated portion of the molecular
sieve to react with the polymer. The film of mixed matrix polymer
bonded to the molecular sieve was re-dissolved in fresh solvent.
The mixed matrix product was re-cast as a flat membrane.
This example shows various methods of sizing a molecular sieve
that has been treated with a monofunctional organosilicon compound.
EXAMPLE 3
3A: Comparison example, preparation of a continuous phase polymer
solution: A 20% PVAc solution was prepared by diluting a 25% solution
of PVAc in toluene with ethanol.
3B: Comparison example, preparation of polymer solution containing
dispersed untreated molecular sieve: Virgin H-SSZ-13 molecular sieve
was dispersed in ethanol and the resulting suspension was added
to a 25% solution of PVAc in toluene to form a suspension of 15
molecular sieve parts per hundred ("pph") polymer.
3C: Preparation of polymer solution containing dispersed silanated
molecular sieve: H-SSZ-13 molecular sieve was silanated with APDMS
as in Example 1. The APDMS-silanated H-SSZ-13 molecular sieve was
dispersed in ethanol and the resulting suspension was added to a
25% solution of PVAc in toluene to form a suspension of 10 molecular
sieve pph polymer.
Films were separately cast from each of solutions 3A-3C onto a
flat PTFE coated surface with a 0.1 mm gap doctor knife. Residual
solvent was evaporated in a vacuum oven at 100.degree. C. Samples
of each film were tested in a permeation cell with single gases
at 35.degree. C. and 275-410 kPa (40-60 psi) pressure differential.
Film permeability was calculated by the formula
in which P is permeability in units of barrers ("B"),
one barrer=[10.sup.-10 cm.sup.3 (STP).cm/cm.sup.2.sec.cm(Hg)], and
J=rate of gas permeating the sample, cm.sup.3 /sec at standard temperature
and pressure conditions, measured by pressure increase in a constant
evacuated volume. .delta.=membrane thickness, cm, measured by optical
microscopy of film cross section. A=sample area exposed to gas migration,
cm.sup.2 and .DELTA.p=pressure differential, cm (Hg).
Selectivities were calculated as the ratio of permeabilities of
selected gas pairs. Results of these tests are shown in Table I.
Table I shows that untreated mixed matrix molecular sieve 3B increased
nitrogen and oxygen permeability through the membrane compared to
the polymer-only membrane 3A but that the oxygen/nitrogen selectivity
did not improve. This may be due to gas bypassing through voids
at the interface between the molecular sieve and polymer. In comparison
to the polymer-only membrane 3A, Example 3C demonstrates that nitrogen
and oxygen permeability and oxygen/nitrogen selectivity were all
enhanced by silane treatment according to this invention. This enhancement
is more noteworthy in that Example 3C utilized 33% less molecular
sieve than 3B. Carbon dioxide/nitrogen and helium/nitrogen selectivity
also were raised.
EXAMPLE 4
Comparison example of silanation of a molecular sieve with polyfunctional
organosilicon compounds:
H-SSZ-13 molecular sieve was silanated as in Example 1 except that
trifunctional silane APS (Ex. 4A) and that difunctional silane APMMS
(Ex. 4B) were used instead of monofunctional APDMS. The silanated
molecular sieve was formed into films of PVAc as in Example 3C at
a concentration of 15 pph polymer. Permeation test results are shown
in Table I. It is seen that the trifunctional organosilicon compound
treatment had a negligible effect on the oxygen permeability and
oxygen/nitrogen selectivity in comparison to the polymer only membrane
of 3A. Although permeability increased in the samples of Ex. 4B
relative to a polymer only membrane, selectivity did not rise. These
examples demonstrate the importance of utilizing a monofunctional
organosilicon compound.
EXAMPLE 5
Silanation of molecular sieve with monofunctional organosilicon
compound with displaceable chlorine radical:
H-SSZ-13 molecular sieve was silanated with monofunctional chlorosilane
ICDMS in anhydrous toluene. The solution was refluxed for 24 hours
with agitation provided by a Teflon paddle at 150 revolutions per
minute. The silanated molecular sieve was recovered by filtering
through a 0.2 micron polytetrafluoroethylene filter. The filter
cake was rinsed three times with toluene and then dried overnight
at 110.degree. C. under vacuum. A mixed matrix film of 15 parts
of the ICDMS-treated molecular sieve per 100 parts PVAc was formed
as in Example 3. This film was tested for membrane performance as
above. Permeation performance results are also shown in Table I.
The data demonstrate an improvement in both oxygen permeability
and oxygen/nitrogen selectivity over polymer-only membrane (Ex.
3A). Oxygen permeability was equivalent to that of the untreated
molecular sieve mixed matrix (Ex. 3B), however selectivity increased.
EXAMPLE 6
Silanation of silicate molecular sieve with monofunctional organosilicon
compounds: In these examples a MFI type molecular sieve silicalite
I was silanated with monofunctional organosilicon compounds APDIPS
and with APDMS, as in Example 1. Mixed matrix films of 15 molecular
sieve pph PVAc polymer were prepared as described in corresponding
Examples 3B and 3C. Untreated silicalite, APDIPS-treated silicalite
and APDMS-treated silicalite were used in Exs. 6A, 6B and 6C, respectively.
The films were tested for permeation performance as above and results
are reported in Table I.
Comparison of Ex. 6A to 3A shows that untreated silicalite did
not improve the oxygen permeability or the carbon dioxide/nitrogen
selectivity over that of the continuous phase polymer alone. Mixed
matrix membranes of silicalite treated with either APDIPS or APDMS
demonstrated significantly enhanced oxygen permeability and oxygen/nitrogen
and carbon dioxide/nitrogen selectivities.
TABLE I Permeance (Barrers) Selectivity Example N.sub.2 O.sub.2
O.sub.2 /N.sub.2 CO.sub.2 /N.sub.2 He/N.sub.2 3A 0.089 0.53 5.91
34.7 169 3B 0.142 0.81 5.74 0.130 0.77 5.97 average: 0.136 0.80
5.8 3C 0.094 0.67 7.12 0.103 0.73 7.05 6.91 51.1 212 6.94 51.3 212
average 0.099 0.70 7.01 51.2 212 4A 0.55-0.60 5.55-5.96 4B 0.143
0.91 6.37 0.123 0.68 5.52 0.143 0.81 5.70 0.115 0.66 5.71 average
0.75 0.76 5.82 5 0.5-0.8 6.1-6.4 6A average 0.45 6.2 32.3 6B 0.55-0.90
6.2-7.0 average 0.70 6.6 36.9 6C 0.56-0.64 6.5-6.8 42-44 average
0.61 6.7 43.1
EXAMPLES 7-9
Sizing of monofunctional organosilicon compound treated molecular
sieve with various polymers.
7A: A solution of 25% Ultem.RTM. 1000 polyetherimide in NMP was
cast on a glass plate at about 65.degree. C. with a 0.1 mm gap doctor
knife. The film was removed from the plate after 4 hours and was
dried under tension in a vacuum at 150.degree. C. for 7 days.
7B: H-SSZ-13 molecular sieve was initially silanated with APDMS
as in Example 1. The silanated molecular sieve was dispersed by
ultrasonication in a 25% Ultem.RTM. 1000 polyetherimide solution
at 15 parts sieve per 100 parts polymer. A film was cast from this
slurry as in Ex. 7A except that the cast film was stored at 150.degree.
C. overnight. The film was then re-dissolved in an amount of fresh
NMP effective to produce a molecular sieve suspension in 20% polymer
solution. This solution was recast on a glass plate heated to 65.degree.
C. The recast film was removed from the plate after 4 hours and
was dried under tension in vacuum at 150.degree. C. for 7 days.
Films of 7A and 7B were tested for permeation properties as above
and the results are shown in Table II. The treated molecular sieve
mixed matrix membrane exhibited both increased oxygen permeability
and oxygen/nitrogen selectivity relative to the polymer-only membrane.
8: Molecular sieve H-SSZ-13 was silanated with APDMS as in Example
1 and subsequently sized with Ultem.RTM. 1010 polyetherimide according
to the procedure of Example 2A. This silanated and sized sieve was
suspended in NMP by ultrasonication and the suspension was added
to a 20% solution of Ultem.RTM. 1000 in proportion of 15 parts sieve
per 100 parts polymer. The solution was cast onto a 65.degree. C.
glass plate using a 0.1 mm gap doctor knife. The film was removed
from the plate after 4 hours and dried under tension in a vacuum
oven at 150.degree. C. for 7 days. This film was tested for permeation
performance and the results are presented in Table II. The mixed
matrix membrane provided both higher oxygen permeability and oxygen/nitrogen
selectivity than the sieve-free membrane of Example 7A.
9: A solution of about 25% Ultem.RTM. 1000 polyetherimide in chloroform
was spread in a casting ring on a glass plate at ambient temperature
and maintained overnight at room temperature. The resulting film
(Ex. 9A) was placed in a vacuum oven at 80.degree. C. for 7 days.
Molecular sieve H-SSZ-13 was silanated with APDMS as in Example
1 and subsequently sized according to the procedure of Example 2A
with a copolyimide of HSMPD and DAPI in ratio of 3:1 copolymerized
with BPADA. A slurry was made by briefly dispersing with ultrasonication
1.09 g of the copolyimide-sized, silanated molecular sieve in 4.46
g of chloroform. The slurry was hand-mixed in 29.2 g of 25% solution
of Ultem.RTM. 1000 polyetherimide in chloroform to provide approximately
21% polymer concentration in the mixture. The mixture was spread
in a casting ring on a glass plate at ambient temperature and held
overnight and the film thus produced (Ex. 9B) was placed in a vacuum
oven at 80.degree. C. for 7 days.
Films of Exs. 9A and 9B were tested for permeation performance
as above. The results for the polymer-only film were substantially
the same as for polyetherimide film cast from NMP reported for Example
7A. Results for Example 9B are shown in Table II. The mixed matrix
membrane of polyetherimde continuous phase polymer and dispersed
phase of silanated molecular sieve sized with copolyimide demonstrated
both higher oxygen permeability and oxygen/nitrogen selectivity
than the polyetherimide membrane.
Examples 7-9 thus illustrate various schemes for sizing a polymer
to molecular sieve which has been treated with a monofunctional
organosilicon compound. The polymer chosen for sizing can be either
the continuous phase polymer (as in Exs. 7B and 8) or a different
polymer which is compatible with the continuous phase polymer (as
in Ex. 9B).
TABLE II Permeance (Barrers) Selectivity Example O.sub.2 O.sub.2
/N.sub.2 7A 0.40 7.8 7B 0.40-0.53 10.4-10.6 8 .sup. 0.57 10.0 9A
0.40 7.8 9B 0.91-0.95 10.4-10.8
Although specific forms of the invention have been selected for
illustration in the preceding description is drawn in specific terms
for the purpose of describing these forms of the invention fully
and amply for one of average skill in the pertinent art, it should
be understood that various substitutions and modifications which
bring about substantially equivalent or superior results and/or
performance are deemed to be within the scope and spirit of the
following claims. |