Note: Descriptions are shown in the official language in which they were submitted.
68~
MEMBRANEOUS SYNT~1~TIC ZEOLITE AN~ PQOCESS
FOR PRODUCING THE SAME
BAC~GROUND OF T~1E INV~NTION
1. ~ield of the Invention
This invention relates to a separation membrane for use
in separating materials. More particularly, th;s invention
relates to a membraneous æeolite for use as a separation
memebrane and to a process for producing the same.
2. Description of the Prior Art
Heretofore, material separation by a separation membrane
has attracted notice and has actually found wide acceptance
because of its good efficiency. However, separation membranes
put into actual use are mostly organic materials typified by
polymers, SG that there have been drawbacks that they are
not satisfactory in respect of thermal stability and
durability, that the selectivity in material separation
and energy loss during operation are not satisfactory, and
that the condition of its use must be limited.
Therefore, when the heat resistance and durability are
taken into consideration, inor~anic separation membranes
such as porous membranes and metallic membranes are
advantageous. However, these inorganic separation membranes
have a drawback that they generally have a low separation
ef~iciency, and especially when metallic membranes are used,
these are subject to corrosion and have markedly limited use.
Therefore, no inorganic separation membranes have been
actually put into widespread use.
On the other hand, it is known that crystalline
aluminosilicates, generally called æeolites, consist
of a three-dimensional structure formed in such a way
that regular tetrahedra of, chiefly, SiO4 are bonded to
common oxygen atoms, and according to the manner of this
~ ~ ~ S~ 8 ~
bonding, these SiO4 tetrahedra constitute basic un;ts by
forming 4-, 5-, 6-, $-, 10- or 12-membered ring formed hy
interconnecting 4, 5, 6, 8, 10. or 12 regular tetrahe~ra
chiefly consisting of ~i~4, and double rings formed by
superposing each of these 4-, 5-, 6-, 8-, 10- or 12-membered
rings, and these basic units are interconnected to determine
the framework of a crystalline aluminosilicate.
Special cavities are present in this framework
determined by the manner of bonding, and the entrance of the
cavity structure forms an opening consisting of 6-, 8-, 10-
or 12-membered rings. The cavities thus formed have uniform
diameters, and lie in a state in which the molecules of a
special sizes or below can be adsorbed but the molecules of
larger si~es can not get into the cavities. Thus, the
crystalline aluminosilicates are known as molecular sieves
for the sake of their action, and by virtue of the above-
mentioned properties, they are used in industry as adsorbents
in a variety of chemical processes.
~urther, in the crystalline aluminosilicates, the
2~ aluminum atom in the framework constitutes a tetrahedral
structure and produces a charge (A ~ 0 4 ~~ . In this
case, in order to counterbalance this charge, a variety of
ca tions, such as sodium ions, are introduced.
Because these cations have ion exchange ability, it is
possible to produce solid acid points in the vicinity of the
aluminum atoms and to impart catalytic ability to the
crystalline aluminosilicate by exchanging the cations with a
variety of cations such as metal cations or ammonium ions.
Namely, the molecular sieve adsorptive action is thought to
arise from the two mechanisms :
(~) special substances are adsorbed by cavities determined
by the framework according to their molecular shapes and
si~es, and (2) substances having dipoles, quadrupoles, or
unsaturated bonds and those having high polarity are
adsorbed by the action of the cations present in the crystal
~3~i6~
structure, but it is generally believed that the cations are
present where no molecular sieve action is exhibited.
Therefore scarcely any discussion of adsorptive separation
have dealt with cationic species, their e%change ratio or
the like except in such special cases where the radii of
cations differ greatly as in the case of a combination of
potassium and sodium, and where there is a difference in
quantity due to the difference in the number of charges of
cations as in the case of a combination of sodium and
calcium. However, when a species to be adsorbed, which
interacts with cationic species, is present, for example,
when water is present, interruption of adsorption due to
strong adsorption becomes a very serious problem. For
adsorptive separation of such a water-containing system~ a
silica-based membrane having hydrophobicity is thought to be
suited and, in fact, it is effective in separating alcohols
from water.
~ rom these conventional knowledges it is expected that
if zeolite can be formed into membrane, the conventional
?0 drawbacks can be solved and a novel good inorganic membrane
for material separation can be obtained.
As a result of extensive studies made under these
circumstances, the inventors of this invention have found
that it is possible to obtain membraneous zeolite having a
~5 molecular sieve adsorptive action.
SUMMARY OF THE IN~ENTION
Therefore, it is a primary object of this invention to
provide an inorganic membrane excellent in selectivity in
material separation, durability, and thermal stability.
It is a secondary object of this invention to provide a
synthetic zeolite membrane which, in itself, has an excellent
function of adsorptive separation.
Furtherl it is a third object of this invention to
35~8~
~ 4 --
provide a process for producing a synthetic zeoli-te membrane
which retains a crystal s-tructure which is capable of
showing a molecular sieve adsorptive action.
In meeting these and other objeets, this invention
provides a filter for substance separation, comprising a
substrate made of a porous glass and a zeolite-based film
formed direetly on the porous glass, the zeolite-based film
having a thiekness of 1 ~Im to 500 ~m.
The invention also provides a process for
produeing a filter for substanee separation eomprising:
(a) using as a starting material a glass compound
having the following composition:
X230.3 ~ 30% by weight
YO250 ~ 99% by weight
2~ 20~ by weight
ignition loss0 ~ 10% by weight
at 900 C, 1 hour
wherein X is a member selected from the group consisting of
aluminum, gallium and boron, or a mixture of at least two of
them, and Y is a member selected from the group consisting
of silicon and germanium, or a mixture thereof;
(b) adding an alkali and water to the glass
eompound to form a mixture having the following composition
in molar ratio:
Na2O/H2O ~ 0.01
~R~ /H2O 0.0002 ~ 0.02
H2O ~YO2 1 ~ 200
wherein, CR~ is at least one organie nitrogen-eontaining
eation and/or at least one organie nitrogen-containing
eation souree whieh can be arbitrarily selected, and Y is a
member seleeted from the group eonsisting of silicon and
germanium, or a mixture thereof; and
(e) heating and maintaining this reaction mixture
at a crystallization temperature in a reaction vessel until
~23~6~4
- 4a -
a zeolite crystal layer is formed on a glass surface.
Since the material separation membrane obtained in
this invention comprises a zeolite as an inorganic
material, it has high thermal resistance and can be used for
material
~ ~ 3 ~
separation under temperature conditions which can not be
adopted up to this time. This not only widens the scope
of application of material separation but also can reduce
energy loss in the process for material separation, and
therefore the significance of this invention is great. ~he
durability as a separation membrane is also improved in
connection with the above.
DESCRIPTION OF TIIE PREFERRED EMB0DIMENTS
Crystalline aluminosilicates can be generally produced
by using SiOz as a source of silicon and AQ 2 O 3 as a
source of aluminum in a ratio falling within a definite range,
forming an aqueous reaction mixture by adding a suitable
source of an alkali and water into above sources in a ratio
falling within a definite range, and heating and maintaining
the aqueous reaction mixture at a crystallization temperature
until crystals are fo~med. This production condition can be
reali~ed, for example, by maintaining the mixture at about
12~ to about 230C and an autogeneous pressure for about l0
hours to about l0 days.
Examples of the silicon sources for this case include
sodium silicate, silica gel, silicic acid, aqueous colloidal
silica gel, fused silica, powdery silica, and amorphous
silica, among which sodium silicate, water glass, and
colloidal silica are particularly preferred.
Examples of the aluminum sources include active alumina,
r -alumina, alumina trihydrate, and aluminum salts such as
nitrates and sulfates, among which sodium aluminate and
aluminum sulfate are particularly preferred.
In this invention, although it is possible to mix
separately prepared respective starting materials, with each
other, it is preferred to use a glass compound containing
an oxide of a Group m b element of the Periodic Table,
represented by the general formula X2 O 3 , SiOz , and/or
~3S68~
Ge O 2 and, if necessary, Naz 0, more particularly the above-
mentioned glass compound having an ignition loss (at 900c,
1 hour) of 0 to 10 % by weight.
Although the glass compound ~ A ) being used in this
S invention is amorphous, it contains silicon and/or germanium
atoms in the form of Y02 , and takes the form of an oxide
in which the tetrahedra are connected to each other by bonding
to common oxygen atoms. Preferable X's which may be contained
in this glass compound are boron, aluminum, and gsllium. ~s
these elements can take the form of the tetrahedral structure
like the above silicon or germanium, these can form ~eolite.
Therefore, when a hydrothermal reaction is effected by
using the aboYe glass compound ( A ) as a starting material,
and an alkali is added during this hydrothermal reaction,
the solid phase in the reaction mixture is first dissolved
and forms zeolite nuclei, which grow into crystals and form
a zeolite membrane.
In this case, when a gel is present in the reaction
mixture, it forms a solid-phase amorphous phase which directly
~0 transforms into a crystalline phase and forms zeolite, and
therefore it is impossible to obtain membraneous zeolite
though it is possible to obtain lump- or powder-form zeolite.
Therefore, it is necessary to exclude any gel from the
reaction mixture.
~5 In order to facilitate the deposition of ~eolite crystals
in the hydrothermal reaction of this invention, it is
necessary that the composition of the material glass compound
falls within a definite range. Namely, the total content of
X 2 O 3 in the glass compound ( A ~ used in this invention
is 0 to 50 % by weight, preferably 0.5 to 30 % by weight,
the total content of Y02 is ~0 ~ 99 % by weight, preferably
50 to 99 % by weight. ~urther, the preferable amount of
Na2 0 is Q to 20 % by weight. ~xamples of these glass
compound materials include borosilicate glass, soda lime
glass, aluminosilicate glass and silica glass,
1~3568~
The alka]is which are added during the hydrothermal
reaction in this invention may be those which are usually
used, but because it is important to control the alkali
concentration in order to form a zeolite membrane by growing
crystals from the liquid phase, it is preferred to use a
mixture ~A ) having the composition (in terms of a molar
ratio) :
N a ~ O / H ~ O 0~ 0.01
~R ) / H 2 O 0.0002 ~ 0.02
l~ H 2 O / Y O 2 1 ~ 200
wherein ~R ~ is at least one organic nitrogen-containing
cation and~or at least one organic nitrogen-containing cation
source which may be arbitrarilY selected, and N a 2
includes free Na2 0 and Na2 0 contained in the glass compound
~ A) , which can be controlled by adding sulfuric acid,
hydrochloric acid, or nitric acid.
The organic nitrogen-containing cation source to be used
in this invention may increase the pH value under a condition
of the hydrothermal reaction, and thereby increases oligomers
such as dimer and trimer, of silicate ions, and provides an
environment faborable for the deposition of crystals from the
solution. The organic nitrogen-containing cation source,
which may be used for this purpose, may be one kind alone or
an arbitrary combination of at least two of them.
~5 Examples of these organic nitrogen-containing cation
sources include quaternary ammonium salts such as tetra-
methylammonium, tetraethlammonlum, tetrabutylammonium,
diethylammonium, triethylammonium, dibenzylammonium,
dibenzyldimethylammonium, dibenzyldiethylammonium, benzyl-
triethylammonium, and choline salts; alkylamines such as
trimethylamine, triethylamine, tripropylamine, ethylenediamine,
propanediamine, butanediamine, pentanediamine, hexanediamine,
methylamine, ethylamine~ propylamine, butylamine, dimethylamine,
diethylamine, and dipropylamine; aromatic amines such as
benzylamine and aniline; and cyclic amines such as pyridine,
~L~3S~84
piperidine and Pyrrolidine, among which tetrapropylammonium
salts, propylamine, and derivatives thereof are particularly
preferable.
Since the alkali concentration thus greatly influences
the growth of zeolite crystals in this invention, the thick-
ness of a zeolite membrane formed can easily be controlled
by adjusting the alkali concentration.
In this invention, it is necessary to use a base on which
2eolite crystals can be deposited in the form of a membrane.
1~ Examples of these bases include glass, mullite and cordierite
ceramics, alumina, silica, and a base (e.g., metal~ coated
with an inorganic substance, among which glass, especially
silicate glass, is preferred, because it facilitates the
deposition of zeolite crystals and can form excellent membrane.
Examples of the silicate glass include quartz glass based on
Si O 2 , alkali silicate glass based on Na2 O-siO2 , soda lime
81ass based on Na2 O-CaO-Si O 2 , potash lime glass based on
K2 O-CaO-Si O 2 , lead ~alkali) glass based on K2 O-PbO-Si O 2 ,
barium glass based on BaO-Si O 2 -B2 O 3 , and borosilicate
~0 glass based on Na2 O-B2 O 3 -SiO2 . Among these, the one
which is substantially the same as the glass compound ~ A ~
is preferable. The glass layer having the surface thus coated
with membraneous zeolite in this invention (referred to as an
intermediate layer~ is prone to increase the Na2 O content
as compared with the initial composition ratio, but still
remains amorphous and can perform well as a support for the
zeolite membrane.
In the hydrothermal reaction according to this invention,
it is possible to add a mineralizer in performing crystal-
lization. This mineralizer is one which can accelerate theformation of zeolite and includes, for example, neutral sal~s
of an alkali metal or alkaline earth metal such as NaC e,
Na2 CO3 , Na2 SO4, Na2 Se O 4, KC e, KBr, KF, eac e 2 , an~
BaBr2 . Among these mineralizers, Nac e is particularly
perferred. The zeolite formed on the glass surface in the
?~Z356B4
g
synthetic process of a zeolite membrane is removed from the
reaction vessel, then washed with pure water, and dried at
room temperature to 120 C for 1 to 16 hours. When this
membrane is observed by means of a secondary electron
microscope (SEM), large crystal grains having a particle
size of several ~um to several hundreds um appear to be
united with each other according to some bonding form.
Therefore, the X-ray diffraction pattern of the membraneous
zeolite is similar to that of a single crystal, and many
peaks appear additionally among the six main peaks which
appear also in a single crystal, as shown in Table 1.
TABLE 1
Interplanar spacings d(~) Relative intensity (I/Io)
11.2 + 0.2 Strong
10.1 + 0.2 Strong
3.86 + 0.05 Very Strong
3.76 + 0.05 Strong
3.72 + 0.05 Strong
3.64 + O.OS Strong
Further, at least two diffraction peaks are observed
between, 3.76 R and at least one diffraction peak is
observed between 3.72 ~ and 3.64 ~.
These values were determined by standard
techniques with an X-ray diffractometer (Geigerflex* RAD,
model rA, manufactured by Rigaku Denki Co., Ltd.).
The radiation was K-~ doublet of copper, and a
scintillation counter with a strip chart pen recorder was
used. The peak heights and the positionsas a function of 2
O (where ~ is the Bragg angle) were read from the char-t.
* (trade mark)
~3~689~
- 9a -
From these data, the relative intensities and the
interplanar spacings (d) R, in terms of Angstroms,
corresponding to the recorded lines were determined.
;~356~
The composition ~in terms of a molar ratio of oxides)
of thus-prepared zeolite of this invention was as fol]ows:
0 ~ l.0 Na2 0 0.1 ~l.0 ~ RR'0 X ~ O 3
l0~ l0.000 Y0z 0 ~~0 H2
wherein R and R'in the RR'0 represent an organic nitrogen-
containing cation which may be different from each other, and
~ RR'0 for a case where at least two organic nitrogen-
containing cations are mixed and used in the hydrothermal
reaction of this invention means the sum of all RR'0 forrned
by combining R and R' present in the reaction system.
Since the membraneous synthetic zeolite obtained in this
invention is, in its essence, a zeolite having a function of
separating molecules by selective adsorption, its performance
of material separation is expected to be extremely high.
Further, as mentioned earlier, the electronic balance in
the tetrahedron containing the aluminum of the crystalline
sodium aluminosilicate according to this invention is
maintained by holding cations such as sodium ions within the
crystal. These cations are replaced by ion exchange by a
variety of methods to form a hydrogen-form or metal ion-
exchanged type zeolite, which can function as a solid acid
catalyst.
The metal cations originally present at the time of the
~eolite synthesis can be replaced, at least in part, by ion
exchange, etc. This ion exchange can be performed with a
Group Il throu~h ~III metal of the Periodic Table, with
ammonium ions, or with hydronium ions. This can be applied
also to the membraneous synthetic zeolite of this invention,
and permits material separation by using the membrane in
various forms.
EXAMPLES
The following examples are provided to illustrate
present invention, but are not to be construed as limiting
present invention in any way.
~Z3S684L
11
~xample 1
A 2Q0-cc autoclave was charged with ~.5 ~ of l.U5 mm-thick
boronsilicate ~lass (95.3 ~ by weight of SiO2 , 2.87 ~ by
weight of B2 O 3 , 0.26 % by weight of Al2 O 3 , and 0.02 %
by weight of Na2 O) together with a solution prepared by
dissolving 0.6 ~ of NaOH and l.9 g of tetrapropylammonium
bromide in 131 g of pure water, and then sealed. The
reaction mixture was heated to 190C under agitation, and
maintained at this temperature for 64 hours. After the
completion of the reaction, the borosilicate glass was
withdrawn from the autoclave, washed with pure water,
and dried at 100C for about 16 hours.
A translucent zeolite layer was formed on the surface
of the transparent glass, The powder X-ray diffraction
analysis of the formed zeolite revealed that this zeolite
was one having the X-ray diffraction pattern shown in Table
~, and had a ]ayer thickness of about 5 ~ m. The reaction
conditions and the experimental results are as shown in
Table 2.
Example 2
This experiment was carried out in the same way as in
Example 1 except that the amount of NaOH added was varied
as shown in Table 2.
A translucent layer was formed on the transparent surface
of glass, and the thickness of the translucent layer was
about 113 ~ m. An analysis of the product by powder X-ray
diffractometry revealed that it was zeolite showing an X-
ray diffraction pattern which was substantially the same as
that in Example 1.
Example 3
This experiment was carried out by the same way as in
Example 1, except that the amount of NaOH was varied as shown
in Table 2.
~Z~35684
.
12
A translucent layer was formed on the transparent surface
layer of glass, and the thickness of the translucent layer was
about 170 ~m. An analysis of the product by powder X-ray
diffractometry revealed that it was a zeolite showing sub-
stantially the same X-ray diffract;on pattern as that in
Example 1.
Example ~
A 200-cc autoclave was charged with 2.5 g of 1~15 mm-
thick porous borosilicate glass Isurface area of 165.1 ~/g,88.7 % by weight of Si O 2 , 2.67 % by weight of B 2 3 ~
0.24 % by wei~ht of A12 O 3 , and 0.02 % by weight of Na2 )
together with a solution formed by dissolving 0.5 g of NaOH,
1.06 g of tetrapropylammonium bromide and 5.1 g of NaC~ in
73.4 g of pure water, and then selaed. The reaction mixture
was heated to 1~3 C under agitation and maintained at this
temperature for 63 hours. After the completion of the
reaction, the reaction product was discharged from the
autoclave, washed with pure water, and dried at 10~ C
~0 for about 16 hours.
The surface layer of the product was covered with a trans-
lucent layer, and the thickness of this layer was about 325
~ m, An analysis of the product by powder X-ray diffractometry
reveled that it was a ~eolite having an X-ray diffraction
pattern which was essentially the same as that in Example 1.
The experimental results are shown in Table 2.
Comparative Example
This experiment was carried out in the same way as in
Example ~, except that, as shown in table 2, no tetrapropy1-
ammonium bromide was used,
No translucent layer was formed on the surface layer of
the product. An analysis of the product by powder X-ray
dif~ractometry revealed that it was amorphous.
~5~:i89
Examples S to 9
The experiments were carried out in the same way as in
Example 4, except that the Na2 O/Si O 2 molar ratio was
different. As the experimental results in table 3 show,
membraneous synthetic zeolites could be obtained in all cases.
These results illustrate that reaction conditions of present
invention are suitable to form membraneous zeolite provided
by this invention.
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