U.S. patent application number 09/820940 was filed with the patent office on 2001-11-22 for porous solid for gas adsorption separation and gas adsorption separation process employing it.
This patent application is currently assigned to KABUSHIKI KAISHA TOYOTA CHUO KENKYUSHO. Invention is credited to Inagaki, Shinji, Miyazawa, Kohji.
Application Number | 20010042440 09/820940 |
Document ID | / |
Family ID | 18613903 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010042440 |
Kind Code |
A1 |
Miyazawa, Kohji ; et
al. |
November 22, 2001 |
Porous solid for gas adsorption separation and gas adsorption
separation process employing it
Abstract
A gas adsorption separation process characterized by adsorption
separation of components in a gas by contacting the gas with a
porous solid which is a porous solid having an X-ray diffraction
pattern with at least one peak at a diffraction angle corresponding
to a d value of 1 nm or greater; and having a nitrogen adsorption
isotherm measured at liquid nitrogen temperature with at least one
section where the change in nitrogen adsorption in terms of the
volume of nitrogen under standard conditions is 50 ml/g or greater
with a relative vapor pressure change of 0.1 in a relative vapor
pressure range of 0.2-0.8; wherein the porous solid possesses
mesopores with a median pore size of 2-50 nm in the pore size
distribution curve and pore walls that are porous.
Inventors: |
Miyazawa, Kohji; (Aichi-gun,
JP) ; Inagaki, Shinji; (Aichi-gun, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
KABUSHIKI KAISHA TOYOTA CHUO
KENKYUSHO
41-1, Aza Yokomichi, Oaza Nagakute Nagakute-cho
Aichi-gun
JP
480-1192
|
Family ID: |
18613903 |
Appl. No.: |
09/820940 |
Filed: |
March 30, 2001 |
Current U.S.
Class: |
95/139 ; 502/402;
96/108 |
Current CPC
Class: |
B01J 20/28088 20130101;
B01D 53/02 20130101; B01J 20/28083 20130101; B01J 20/2808 20130101;
B01J 20/28069 20130101; B01J 20/28078 20130101; B01J 20/28042
20130101 |
Class at
Publication: |
95/139 ; 96/108;
502/402 |
International
Class: |
B01D 053/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2000 |
JP |
2000-099564 |
Claims
What is claimed is:
1. A porous solid for gas adsorption separation; having an X-ray
diffraction pattern with at least one peak at a diffraction angle
corresponding to a d value of 1 nm or greater; and having a
nitrogen adsorption isotherm measured at liquid nitrogen
temperature with at least one section where a change in nitrogen
adsorption in terms of the volume of nitrogen under a standard
condition is 50 ml/g or greater with a relative vapor pressure
change of 0.1 in a relative vapor pressure range of 0.2-0.8;
wherein said porous solid possesses mesopores with a median pore
size of 2-50 nm in a pore size distribution curve and pore walls
that are porous.
2. The porous solid for gas adsorption separation according to
claim 1, wherein said pore walls have micropores with a mean pore
size of less than 2 nm.
3. The porous solid for gas adsorption separation according to
claim 2, wherein the total volume of said micropores is 0.05 ml/g
or greater.
4. The porous solid for gas adsorption separation according to
claim 2, wherein at least 60% of the total pore volume excluding
said micropores is in a range of .+-.40% of said median pore
size.
5. The porous solid for gas adsorption separation according to
claim 2, wherein the mean size of said micropores is at least 0.2
nm and less than 2 nm.
6. The porous solid for gas adsorption separation according to
claim 2, wherein the median pore size of said mesopores is from 3
nm to 30 nm.
7. The porous solid for gas adsorption separation according to
claim 2, wherein the total volume of said micropores is at least
10% of the total pore volume.
8. The porous solid for gas adsorption separation according to
claim 1, wherein the thickness of said pore walls is 2 nm or
greater.
9. The porous solid for gas adsorption separation according to
claim 1, wherein said porous solid comprises an organic/inorganic
hybrid-based framework.
10. A gas adsorption separation process whereby adsorption
separation of components in a gas is accomplished by contacting the
gas with a porous solid having an X-ray diffraction pattern with at
least one peak at a diffraction angle corresponding to a d value of
1 nm or greater; and having a nitrogen adsorption isotherm measured
at liquid nitrogen temperature with at least one section where the
change in nitrogen adsorption in terms of the volume of nitrogen
under standard conditions is 50 ml/g or greater with a relative
vapor pressure change of 0.1 in a relative vapor pressure range of
0.2-0.8; wherein said porous solid possesses mesopores with a
median pore size of 2-50 nm in the pore size distribution curve and
pore walls that are porous.
11. The gas adsorption separation process according to claim 10,
wherein said pore walls have micropores with a mean pore size of
less than 2 nm.
12. The gas adsorption separation process according to claim 11,
wherein the total volume of said micropores is 0.05 ml/g or
greater.
13. The gas adsorption separation process according to claim 11,
wherein at least 60% of the total pore volume excluding said
micropores is in a range of .+-.40% of said median pore size.
14. The gas adsorption separation process according to claim 11,
wherein the mean size of said micropores is at least 0.2 nm and
less than 2 nm.
15. The gas adsorption separation process according to claim 11,
wherein the median pore size of said mesopores is from 3 nm to 30
nm.
16. The gas adsorption separation process according to claim 11,
wherein the total volume of said micropores is at least 10% of the
total pore volume.
17. The gas adsorption separation process according to 10, wherein
the thickness of said pore walls is 2 nm or greater.
18. The gas adsorption separation process according to claim 10,
wherein said components in the gas include one or more components
selected from the group consisting of carbon dioxide and
hydrocarbons.
19. The gas adsorption separation process according to claim 10,
wherein said porous solid comprises an organic/inorganic
hybrid-based framework.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a porous solid for
adsorption separation of components in gases, and to an adsorption
separation process employing it for components in gases.
[0003] 2. Related Background Art
[0004] Zeolite, mesoporous substances, silica gel, alumina and the
like are among the porous substances of the prior art utilizable
for adsorption and separation of components in gases, and each has
their unique features, which are described below.
[0005] Zeolite-based crystalline porous solids are utilized in a
wide range of industrial fields as catalysts and ion-exchangers
because of the physical and chemical surface properties of the
porous solids. Since zeolite-based crystalline porous solids have
an extremely fine uniform structure with a pore size of 0.3-1.3 nm,
they exhibit an excellent function in terms of highly selective
catalytic reactivity for low molecular weight compounds, etc. and
excellent adsorption properties.
[0006] The crystalline mesoporous substance (mesoporous solid) with
pores in the meso range of 2-50 nm described in Japanese Unexamined
Patent Publication HEI No. 8-67578 and elsewhere has a high surface
to volume ratio and excellent homogeneity of the porous structure,
and it can therefore be used as a selective catalyst or adsorbent
for high molecular weight compounds, i.e. compounds with a
molecular size approximately equivalent to the pore size, while the
molecular diffusion rate is also excellent due to the sizes of the
pores.
[0007] Amorphous porous solids of silica gel or alumina are usually
prepared by sol-gel methods, and structural control can be easily
accomplished by using various organic substances as templates.
Because such amorphous porous solids have a wide pore size
distribution from micropores to mesopores to macropores, the
presence of the macropores allows their greatly extended function
as an adsorption carrier, while their wide pore size distribution
allows their use as adsorption carriers and reaction catalysts for
an extremely wide range of organic compounds, from low molecular
weight to high molecular weight. Japanese Unexamined Patent
Publication HEI No. 9-295811 discloses an amorphous porous solid
produced by such a sol-gel method and having micropores, mesopores
and macropores distributed according to a fractal rule, and it is
stated that the amorphous porous solid can be used as an adsorption
carrier or as a packing material for chromatography.
SUMMARY OF THE INVENTION
[0008] However, while the extremely fine and uniform microstructure
of the aforementioned conventional zeolite-based crystalline porous
solids provides high selectivity and adsorption properties for low
molecular weight compounds, the fine microstructure also limits
their use as catalysts and adsorbents for compounds with bulky
molecular structures or high molecular weight compounds, and their
low molecular diffusion rate has also presented a problem from the
standpoint of efficiency.
[0009] On the other hand, while the aforementioned conventional
crystalline mesoporous substances can be utilized as excellent
selective catalysts or adsorbents for high molecular weight
compounds and their large pore sizes give a high molecular
diffusion rate, the relatively large pore sizes and amorphous pore
walls also constitute a problem hampering the expression of the
specific catalyst and adsorption properties of zeolite and similar
materials as molecular sieves.
[0010] The aforementioned amorphous porous solids have pores in the
full range from micropores to mesopores and even macropores, and
can therefore be used as adsorption carriers and catalysts for a
wide range of compounds from low molecular weight to high molecular
weight, but their drawback is particularly low specific and
selective catalytic reactivity and adsorption separation properties
for specific compounds.
[0011] Thus, none of the conventional porous substances are yet
adequate in terms of performance as adsorbents for adsorption
separation of specific compounds, and it has been particularly
difficult to accomplish adsorption separation of harmful
hydrocarbons and global warming-implicated CO.sub.2 in exhaust gas
in a selective and efficient manner using conventional porous
substances as the adsorbents.
[0012] It is an object of the present invention, which has been
accomplished in light of the aforementioned problems of the prior
art, to provide a porous solid for gas adsorption separation, and a
gas adsorption separation process employing it, which allow
selective and efficient adsorption separation of specific
components in gases, such as hydrocarbons and CO.sub.2.
[0013] As a result of diligent research directed toward achieving
this object, the present inventors have discovered that by
distributing pore sections (of micropores) in the pore walls
themselves separating the pores of crystalline mesoporous
substances (mesoporous solids), it is possible to notably improve
the adsorption separation performance for specific components in
gases, and especially for low molecular weight compounds, thereby
accomplishing selective and efficient adsorption separation of the
specific components in gases, and the present invention has thus
been completed.
[0014] The porous solid for gas adsorption separation according to
the invention is a porous solid having an X-ray diffraction pattern
with at least one peak at a diffraction angle corresponding to a d
value of 1 nm or greater; and
[0015] having a nitrogen adsorption isotherm measured at liquid
nitrogen temperature with at least one section where the change in
nitrogen adsorption in terms of the volume of nitrogen under
standard conditions is 50 ml/g or greater with a relative vapor
pressure change of 0.1 in a relative vapor pressure range of
0.2-0.8;
[0016] wherein the porous solid possesses mesopores with a median
pore size of 2-50 nm in the pore size distribution curve and pore
walls that are porous.
[0017] The gas adsorption separation process of the invention is
characterized by adsorption separation of components in a gas by
contacting the gas with a porous solid having an X-ray diffraction
pattern with at least one peak at a diffraction angle corresponding
to a d value of 1 nm or greater; and
[0018] having a nitrogen adsorption isotherm measured at liquid
nitrogen temperature with at least one section where the change in
nitrogen adsorption in terms of the volume of nitrogen under
standard conditions is 50 ml/g or greater with a relative vapor
pressure change of 0.1 in a relative vapor pressure range of
0.2-0.8;
[0019] wherein the porous solid possesses mesopores with a median
pore size of 2-50 nm in the pore size distribution curve and pore
walls that are porous.
[0020] The reason for the notably improved adsorption separation
performance by the porous solid of the invention has not been
established, but the present inventors believe it to be as follows.
Specifically, in the porous solid of the invention, the gas
molecules diffuse rapidly through the relatively large mesopores
into the interior of the pores. Subsequently, the gas molecules are
adsorbed and separated by micropores which are formed on the
surface of the mesopores (pore walls) and have a pore size
corresponding to the molecular size. As this occurs, the gas
molecules are selectively adsorbed and separated (filtered)
depending on the gas molecule size and the chemical properties of
the porous solid surface. The present inventors believe that it is
this rapid diffusion and filtering of the gas molecules
simultaneously accomplished in the porous solid of the invention
that accounts for the selective and efficient adsorption separation
of specific components in the gas (such as carbon dioxide or
hydrocarbons) from the other components.
[0021] The pore walls of the porous solid of the invention are
porous with micropores of a mean size of less than 2 nm, and the
total volume of these micropores is preferably at least 0.05 ml/g.
The total volume of micropores in the porous solid of the invention
is preferably at least 10% of the total pore volume. A porous solid
with such a large micropore volume tends to exhibit even further
improved adsorption separation performance.
[0022] In the porous solid of the invention, at least 60% of the
total pore volume excluding the micropores is preferably in a range
of .+-.40% of the median pore size. A mesopore structure with this
degree of homogeneity tends to further improve the selectivity for
components in gases.
[0023] It is preferred for the median pore size of the mesopores in
the porous solid of the invention to be from 3 nm to 30 nm, for the
mean size of the micropores to be at least 0.2 nm and less than 2
nm, and for the thickness of the pore walls to be at least 2 nm. A
porous solid of this type will tend to exhibit even more
satisfactory adsorption separation properties.
[0024] The gas adsorption separation process of the invention
allows selective and efficient adsorption separation of
hydrocarbons, CO.sub.2 and the like, as mentioned above, and
therefore the target component in the gas is preferably at least
one selected from the group consisting of carbon dioxide and
hydrocarbons.
[0025] The present invention will be more fully understood from the
detailed description given hereinbelow and the accompanying
drawings, which are given by way of illustration only and are not
to be considered as limiting the present invention.
[0026] Further scope of applicability of the present invention will
become apparent from the detailed description given hereinafter.
However, it should be understood that the detailed description and
specific examples, while indicating preferred embodiments of the
invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the
invention will be apparent to those skilled in the art from this
detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a graph showing slopes for each t value block, on
a plot of pore volume (V) against thickness (t).
[0028] FIG. 2 is a graph showing a distribution curve of micropores
drawn based on FIG. 1.
[0029] FIG. 3 is a graph showing an XRD pattern for Sample 1.
[0030] FIG. 4A is a graph showing a nitrogen adsorption isotherm,
FIG. 4B is a graph showing a pore size distribution curve
determined by BJH.
[0031] FIG. 5 is a table of data for a standard isotherm.
[0032] FIGS. 6A to 6D are graphs showing approximate curves
obtained based on the respective standard isotherms.
[0033] FIG. 7 is a t-plot graph of a nitrogen adsorption isotherm
for Sample 1.
[0034] FIG. 8 is a graph of a nitrogen adsorption isotherm for
Sample 2.
[0035] FIG. 9 is a graph of a nitrogen adsorption isotherm for
Sample 3.
[0036] FIG. 10 is a graph of a nitrogen adsorption isotherm for
Sample 4.
[0037] FIG. 11 is a graph of a nitrogen adsorption isotherm for a
comparison sample.
[0038] FIG. 12 is a t-plot graph of a nitrogen adsorption isotherm
for a comparison sample.
[0039] FIG. 13 is a graph showing an XRD pattern for Samples a, b
and c.
[0040] FIG. 14 is a graph showing nitrogen adsorption isotherms for
Samples a, b and c.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0041] Preferred embodiments of the invention will now be explained
in detail.
[0042] [Porous solid for gas adsorption separation of the
invention]
[0043] A porous solid for gas adsorption separation according to
the invention will be explained first.
[0044] (X-ray diffraction pattern)
[0045] The porous solid for gas adsorption separation of the
invention has an X-ray diffraction pattern with at least one peak
at a diffraction angle corresponding to a d value of 1 nm or
greater. The regular pore structure exhibits adequately effective
adsorption separation properties as a mesoporous solid, while the
porous pore walls which are described below impart selective
adsorption separation properties.
[0046] An X-ray diffraction peak means that the sample has a
periodic structure with a d value corresponding to that peak angle.
The X-ray diffraction pattern reflects a structure of pores
regularly arranged at a spacing of 1 nm or greater. That is, a
mesoporous solid with such a diffraction pattern has a uniform pore
structure and pore size due to the regularity of the structure
represented by that diffraction pattern. More preferably, it has at
least one peak at a diffraction angle corresponding to a d value of
5 nm or greater.
[0047] (Median pore size, nitrogen adsorption and pore size
distribution)
[0048] The porous solid for gas adsorption separation of the
invention has mesopores with a median pore size of 2-50 nm,
preferably 2-30 nm, more preferably 5-30 nm and even more
preferably 5-15 nm, in the pore size distribution curve. When such
mesopores are present, functional organic compounds of large
molecular size can easily enter into the pores so that molecular
diffusion can be rapidly accomplished in the pores for efficient
adsorption separation.
[0049] The above-mentioned pore size distribution curve may be
determined in the following manner. Specifically, the pore size
distribution curve is a curve representing the derivative of the
pore volume (V) with respect to the pore size (D) (dV/dD), plotted
against the pore size (D), for example, and the median pore size is
the pore size for which the value of dV/dD of the pore size
distribution curve is greatest (the maximum peak is exhibited).
[0050] This pore size distribution curve is derived from the
adsorption isotherm obtained by measurement of the adsorption of
nitrogen gas, for example, according to several equations. An
example of an adsorption isotherm measurement method is explained
below. Nitrogen is the gas most often used for this method.
[0051] First, the mesoporous solid is cooled to liquid nitrogen
temperature (-196.degree. C.), nitrogen gas is introduced, and the
adsorption is determined by fixed displacement or gravimetry. The
pressure of the introduced nitrogen gas is gradually increased, and
the adsorption of nitrogen gas at each equilibrium pressure is
plotted to produce an adsorption isotherm.
[0052] The pore size distribution curve can be derived from this
adsorption isotherm according to the equation for the
Cranston-Inklay method, Dollimore-Heal method, BJH method, etc. For
example, if the maximum peak for the pore size distribution curve
is at 3.00 nm, the median pore size is 3.00 nm.
[0053] The porous solid for gas adsorption separation according to
the invention is a porous solid having at least one section wherein
the change in nitrogen adsorption (nitrogen adsorption in terms of
the volume of nitrogen under standard conditions) is 50 ml/g or
greater with a relative vapor pressure change of 0.1 in a relative
vapor pressure range of 0.2-0.8 for the nitrogen adsorption
isotherm measured at liquid nitrogen temperature. A mesoporous
solid satisfying this condition has mesopores of a substantially
uniform pore size, and this uniform pore structure of the mesopores
notably improves the selectivity for components in gases.
[0054] In the porous solid for gas adsorption separation of the
invention, at least 60% of the total pore volume excluding the
micropores is preferably in a range of .+-.40% of the median pore
size. This condition also indicates that the mesoporous solid has
mesopores of a substantially uniform pore size, and a mesopore
structure with this degree of homogeneity tends to further improve
the selectivity for components in gases.
[0055] For example, if the median pore size in the pore size
distribution curve is 3.00 nm and at least 60% of the total pore
volume excluding the micropores is in a pore size range of .+-.40%
thereof, then the total volume of pores with a pore size in the
range of 1.80-4.20 will constitute at least 60% of the total pore
volume excluding the micropores (the total volume of pores with a
size of no greater than 50 nm as the maximum that can be measured
by gas adsorption and at least 2 nm as the minimum for mesopores).
Specifically, this means that the value of the integral of the pore
volume of pores with a size of 1.80-4.20 nm in the pore size
distribution curve is at least 60% of the total value of the
integral of the pore volume of pores with a size of 2-50 nm in the
pore size distribution curve.
[0056] (Pore structure)
[0057] The shapes of the pores in the porous solid for gas
adsorption separation of the invention may be one-dimensionally
extending tunnel shapes, or three-dimensional box shapes or
spherical shapes wherein the pores are connected. The pore
structure of the porous material of the invention may be a
two-dimensional hexagonal structure (p6mm), a three-dimensional
hexagonal structure (P6.sub.3/mmc), a cubic structure (Ia3.sup.-d,
Pm3.sup.-n), lamellar, or an irregular structure, but the preferred
pore structure is one with mesopores wherein the pores are
three-dimensionally connected. With mesopores extending as tunnel
shapes, the gas components can enter into the pores more easily and
diffuse more rapidly in the pores, thus tending to allow greater
efficiency for adsorption separation.
[0058] (Framework composition of pore walls)
[0059] The porous solid with such mesopores has pore walls of an
inorganic-based framework or pore walls of an inorganic/organic
hybrid-based framework. That is, the pore walls of the porous solid
for gas adsorption separation of the invention have an
inorganic-based framework or an inorganic/organic hybrid-based
framework.
[0060] An inorganic-based framework comprises a polymer main chain
of an inorganic oxide such as a silicate. As atoms to replace
silicon in a basic silicate framework, or as atoms to be added to
the silicate framework, there may be mentioned aluminum, titanium,
magnesium, zirconium, tantalum, niobium, molybdenum, cobalt,
nickel, gallium, beryllium, yttrium, lanthanum, hafnium, tin, lead,
vanadium, boron and the like.
[0061] As other inorganic-based frameworks there may be mentioned
non-Si-based inorganic oxides such as zirconia, titania, niobium
oxide, tantalum oxide, tungsten oxide, tin oxide, hafnium oxide and
alumina, or compound oxides wherein these inorganic oxides
incorporate atoms into the aforementioned silicate framework as the
basic framework.
[0062] Various organic groups and the like may be added as side
chains on such inorganic basic frameworks. As such side chains
there may be mentioned thiol and thiol-containing organic groups,
lower alkyl groups such as methyl and ethyl, as well as phenyl,
carboxyl, amino, vinyl and the like.
[0063] An inorganic/organic-based hybrid framework has an organic
group containing one, two or more carbon atoms bonded to the metal
atom-containing polymer main chain, either directly from the carbon
atoms to the metal atoms of the main chain or via oxygen atoms. The
bonding between the organic group and the polymer main chain may
occur at one, two or more points. The main chain form is not
particularly restricted and may be linear, reticular, branched or
any of other various forms.
[0064] The metal atom in the main chain is not particularly
restricted, and there may be mentioned silicon, aluminum,
zirconium, tantalum, niobium, tin, hafnium, magnesium, molybdenum,
cobalt, nickel, gallium, beryllium, yttrium, lanthanum, lead,
vanadium, titanium and the like. Silicon, titanium, zirconium and
aluminum are preferred, and silicon is most preferred among these.
According to the invention, any one or combination of two or more
different metal atoms may be used.
[0065] In the main chain, carbon is included in the form of an
organic group of one, two or more carbon atoms. The one or more
carbon atoms in the organic group are bonded at one, two or more
points on the metal atom of the main chain. The bonding site with
the metal atom may be the end of the organic group or any other
site other than the end.
[0066] There are no particular restrictions on the organic group.
It may be any of several hydrocarbon groups, such as alkyl chains,
alkenyl chains, vinyl chains, alkynyl chains, cycloalkyl chains,
benzene rings or benzene ring-containing hydrocarbons, as well as
organic functional groups such as hydroxyl, amino, carboxyl and
thiol groups, and organic groups derived from compounds with one or
more carbon atoms. The organic group may be one type or two or more
types in combination.
[0067] As organic groups to bond at two points onto the polymer
main chain there are preferred hydrocarbon groups derived from
alkyl chains, and more preferably hydrocarbon groups derived from
linear alkyl chains of 1-5 carbons. Specifically there may be
mentioned alkylene chains such as methylene (--CH.sub.2CH.sub.2--).
As a preferred organic group there may be mentioned phenylene-group
(--C.sub.6H.sub.4--).
[0068] The atoms of the inorganic/organic hybrid-based main chain
may include metal atoms and carbon atoms, as well as other atoms.
The "other atoms" are not particularly restricted, but are
preferably oxygen atoms positioned between the metal atoms and
metal atoms. Specifically there may be mentioned bonds such as
Si--O, Al--O, Ti--O, Nb--O, Sn--O and Zr--O. These bonds correspond
to bonds between metal atoms and oxygen atoms in polymetalloxanes
of transition metals, such as polysiloxanes and polyalloxanes. The
bonds may be of one type of combinations of two or more types.
Atoms such as nitrogen, sulfur or various halogens may also be
included.
[0069] In the inorganic/organic hybrid-based main chain structure
explained above, the side chain portion bonded to the atom of the
main chain may also have an added metal atom, organic functional
group or inorganic functional group. Preferred examples are thiol
groups, carboxyl groups, lower alkyl groups such as methyl and
ethyl, phenyl groups, amino groups, vinyl groups and the like.
[0070] (Pore wall structure)
[0071] The porous solid for gas adsorption separation of the
invention has porous pore walls possessing the framework described
above.
[0072] That the pore walls are porous means that the pore walls
have numerous cavities. These cavities in the pore walls will
hereunder be referred to as micropores. The size (mean size) of the
micropores is preferably less than 2 nm, more preferably at least
0.2 nm and less than 2.0 nm, and even more preferably at least 0.5
nm and no greater than 1.5 nm. The size of the micropores is also
preferably smaller than the median pore size of the mesopores of
the porous solid. Thus, the micropores preferably have a size of at
least 0.2 nm and less than 2 nm compared to at least 3 nm and less
than 30 nm for the median pore size, and more preferably the
micropores have a size of at least 0.5 nm and less than 1.5 nm
compared to at least 5 nm and less than 30 nm for the median pore
size. A porous solid with this structure will tend to exhibit even
better adsorption separation properties with the micropores.
[0073] The t-plot method may be used to detect the presence of the
micropores in the mesoporous solid, and to determine their volume
and size distribution. The t-plot is a curve of the adsorption (v)
plotted against the mean film thickness (t) of the adsorption film
(where the x-axis is the mean film thickness and the y-axis is the
adsorption). A t-plot can be derived from the adsorption isotherm
of the mesoporous solid (the adsorption plotted against the
relative pressure of adsorption gas).
[0074] For detection of the presence of micropores, an adsorption
isotherm for the mesoporous solid is obtained first. An approximate
curve is then drawn from an appropriate standard isotherm to
convert the relative pressure (P/P.sub.0) into the adsorption layer
film thickness (t), and this approximate curve is used to convert
the relative pressure into the adsorption layer film thickness, for
the adsorption isotherm of the mesoporous solid.
[0075] The standard isotherm used here is preferably an isotherm
for a material with the same C value as the mesoporous solid, based
on the BET equation. Specifically, a nonporous material with a
similar composition is used. For example, if the mesoporous solid
sample is a silica material, the standard isotherm is one drawn
using nonporous silica. The t-plot method is described in M. R.
Bhambhani et al., J. Colloid and Interface Sci., 38, 109(1972).
[0076] When no micropores are present in the mesoporous solid, the
t-plot of the mesoporous solid is a straight line traversing the
origin. When micropores are present, however, the straight line of
the t-plot does not traverse the origin, and the point of
intersection with the vertical axis (y-axis), i.e. the y-intercept,
is positive. The value of the y-intercept indicates the volume of
the micropores.
[0077] The micropore size can be determined by the MP method (R.
SH. Mikhail et al., J. Colloid and Interface Sci., 26,
45(1968)).
[0078] In this t-plot, the 1st, 2nd, 3rd . . . nth linear slopes
are drawn for each t value block from the origin to 4 .ANG., 4-4.5
.ANG., 4.5-5 .ANG. . . . An example is shown in FIG. 1. For this
linear slope, the average film thickness (t) of the adsorption
layer is obtained by the following equation.
t(.ANG.)=10.sup.4.times.(adsorption (V)/surface area (BET))
[0079] The surface area for each linear slope can be determined
from this equation. For example, the pore surface area with a
thickness in the range of 4-4.5 .ANG. is the difference between the
surface area value determined from the first slope and the surface
area value determined from the 2nd slope.
[0080] The micropore volume V is calculated according to the
following equation until the value of the linear slope no longer
decreases (until a state with all of the micropores filled is
reached).
Micropore volume V
(mg/g)=10.sup.-4.times.(S.sub.1-S.sub.2)(t.sub.1+t.sub.- 2)/2
[0081] For each t value block, the result of dividing the
difference in the pore volume, .DELTA.V=V.sub.n-V.sub.n-1, by the
difference in the mean pore size r (=t.sub.n+t.sub.n-1), .DELTA.r
(=r.sub.n-r.sub.n-1), is plotted against the mean pore size r, to
give the micropore distribution. An example is shown in FIG. 2.
[0082] In the porous solid for gas adsorption separation of the
invention, the micropore volume is preferably 0.05 ml/g or greater,
more preferably from 0.05 ml/g to 0.3 ml/g, and even more
preferably from 0.1 ml/g to 0.3 ml/g. If the micropore volume
satisfies these conditions, the selective adsorption separation
performance of the micropores will tend to be improved.
[0083] The micropore volume is preferably at least 10% and more
preferably from 20% to 50% of the total pore volume. Such a pore
volume relationship will facilitate expression of the adsorption
separation properties due to the presence of the micropores.
[0084] (Thickness of pore walls)
[0085] The porous solid for gas adsorption separation of the
invention preferably has pore walls with a thickness of at least 2
nm, more preferably at least 3 nm, even more preferably at least 4
nm and most preferably at least 5 nm. This is to ensure the
strength, heat resistance and hot water resistance of the pore
walls, and also to ensure the micropore volume. A certain degree of
strength and micropore volume will tend to more satisfactorily
exhibit the adsorption separation properties of the micropores. The
pore wall thickness can be determined by subtracting the median
pore size from the lattice constant a.sub.0
(a.sub.0=d.sub.100.times.2/1.732) determined by X-ray
diffraction.
[0086] The porous solid for gas adsorption separation of the
invention may be in the form of a powder, granules, support film,
self-supporting film, transparent film, oriented film, spheres,
fibers, or clear particles of micrometer size burned onto a
substrate. The preferred form is a powder.
[0087] (Porous solid production method)
[0088] The porous solid for gas adsorption separation according to
the invention is preferably obtained by the following production
method.
[0089] Specifically, the porous solid for gas adsorption separation
of the invention is basically obtained by condensation
polymerization of the framework component of the mesoporous solid
using a surfactant as the template to obtain a porous structure,
and then removing the surfactant.
[0090] (Framework component)
[0091] Alkoxysilanes, sodium silicate or silica may be used as
inorganic-based framework components to form the inorganic-based
polymer main chain by condensation polymerization. As alkoxysilanes
there may be used tetramethoxysilane, tetraethoxysilane and
tetrapropoxysilane. These framework components form silicate
frameworks.
[0092] There may also be used alkylalkoxysilanes with lower alkyl
groups, such as methyltrimethoxysilane and ethyltrimethoxysilane,
as well as alkoxysilanes with other organic groups and functional
groups. Phenyl-group may be mentioned as an organic group. Amino,
carboxyl and thiol groups may be mentioned as functional groups.
Alkoxysilanes containing such organic groups or functional groups
may be used to introduce those organic groups or functional groups
into the basic silicate framework. Any of these alkoxysilanes, etc.
may be used alone or in combinations of two or more.
[0093] Compounds or inorganic-based framework components containing
other elements may also be used instead of sodium silicate, silica
or alkoxysilanes. For example, pseudo-boehmite, sodium aluminate,
aluminum sulfate or a dialkoxyaluminotrialkoxysilane can be added
as an Al source to synthesize a mesoporous solid with a basic
framework composed of SiO.sub.2--Al.sub.2O.sub.3. Alternatively, an
oxide compound with Si replaced with a metal such as Ti, Zr, Ta,
Nb, Sn or Hf may be used. This can yield a metallosilicate-based
mesoporous solid (SiO.sub.2--MO.sub.n/2) with various metals
(M.sup.n+, where n is the charge of the metal) included in a
silicate framework. For example, addition of a titanate compound
such as Ti(OC.sub.2H.sub.5).sub.4, vanadyl sulfate (VOSO.sub.4),
boric acid (H.sub.3BO.sub.3) or manganese chloride (MnCl.sub.2) to
an alkoxysilane co-condensation reaction can yield a
metallosilicate-based mesoporous solid with Ti, V, B or Mn
introduced therein, respectively.
[0094] Any of the organometallic compounds listed below may be used
as the inorganic/organic hybrid-based framework component forming
the inorganic/organic hybrid-based framework by condensation
polymerization. The organic group in the organometallic compound
may be an organic group introduced into the basic framework of the
mesoporous solid. This metal compound is an organometallic compound
having an organic group bonded to two or more metal atoms, and
having one or more alkoxyl groups or halogen groups with each of
the two or more metal atoms bonded to the organic group. That is,
the organic group in the organometallic compound has one, two or
more carbon atoms, and the carbon atoms are bonded to two or more
metal atoms.
[0095] There are no particular restrictions on the metal atoms, and
there may be mentioned silicon, aluminum, zirconium, tantalum,
niobium, tin, hafnium, magnesium, molybdenum, cobalt, nickel,
gallium, beryllium, yttrium, lanthanum, lead, vanadium, and the
like. The organometallic compounds used for the invention may have
one of these metal atoms, or a combination of two or more
thereof.
[0096] The organic group in the organometallic compound has one,
two or more carbon atoms and two or more bonding sites with the
metal atoms among these carbon atoms. One of the carbon atoms in
the organic group may have two or more bonding sites with the metal
atoms, or two or more different carbon atoms will sometimes have
separate bonding sites with the metal atoms.
[0097] The organic group is not particularly restricted other than
being bonded to two or more metal atoms. It may be any of several
hydrocarbon groups, such as alkyl chains, alkenyl chains, vinyl
chains, alkynyl chains, cycloalkyl chains, benzene rings or benzene
ring-containing hydrocarbons, as well as organic functional groups
such as hydroxyl, carboxyl and thiol groups, and organic groups
derived from compounds with one, two or more carbon atoms.
Specifically there may be mentioned alkylene chains such as
methylene (--CH.sub.2CH.sub.2--), and phenylene
(--C.sub.6H.sub.4--).
[0098] The organometallic compound of the invention has one or more
alkoxyl groups or halogens on each metal atom to which the organic
group is bonded. The hydrocarbon group in the alkoxyl group is a
linear, cyclic or alicyclic hydrocarbon group. It is preferably an
alkyl group, and more preferably a linear alkyl group of 1-5
carbons. As halogens there may be used any of the common halogens
such as chlorine, bromine, fluorine or iodine. One or more alkoxyl
groups or halogens may be present on each metal atom to which the
organic group is bonded, and other alkoxyl groups or halogens may
also be present.
[0099] As such organometallic compounds there may be mentioned,
specifically, organometallic compounds with metallic alkoxy groups
or metallic halogen groups on both ends of the organic groups. An
example is
(CH.sub.3O).sub.3Si--CH.sub.2--CH.sub.2--Si(OCH.sub.3).sub.3. There
may also be used
(CH.sub.3O).sub.3Si--C.sub.6H.sub.4--Si(OCH.sub.3).sub.3, wherein
the --CH.sub.2--CH.sub.2-- portion is replaced with another organic
group such as --C.sub.6H.sub.4--. Compounds wherein Si is replaced
with another metal such as Al, Ti, Zr, Ta, Nb, Sn or Hf may also be
used. A compound wherein the methoxyl group is replaced with a
halogen may also be used. The alkoxyl group or halogen is a
hydrolyzable group in the condensation polymerization reaction.
[0100] The organometallic compound may also include other atoms or
organic or inorganic functional groups in addition to the metal
atom and organic group. There are no particular restrictions on
other atoms or functional groups, and atoms such as nitrogen,
sulfur or halogens, or functional groups containing these atoms,
may be included.
[0101] Thus, a combination of various of the aforementioned organic
groups and metal atoms may be obtained as the organometallic
compound. The organometallic compound may be used as a single type
or a combination of two or more types. The organometallic compound
may also be used alone as the framework component, or the
organometallic compound may be used as the framework component
together with another framework component such as an
alkoxysilane.
[0102] (Template)
[0103] A non-ionic surfactant may be used as the surfactant to
serve as the template. There are no particular restrictions so long
as it is a non-ionic surfactant, and for example, there may be used
a polyethylene oxide-based non-ionic surfactant having a
hydrocarbon chain as the hydrophobic portion and polyethylene oxide
as the hydrophilic portion. As such surfactants there may be
mentioned C.sub.16H.sub.33(OCH.sub.2CH.sub.- 2)OH (This structure
will hereunder be abbreviated to C.sub.16EO.sub.2.),
C.sub.12EO.sub.4, C.sub.16EO.sub.10, C.sub.16EO.sub.20,
C.sub.18EO.sub.10, C.sub.16EO.sub.20, C.sub.18H.sub.35EO.sub.10,
C.sub.12EO.sub.23 and C.sub.16EO.sub.10.
[0104] The hydrophobic portion may be any of various sorbitan fatty
acids esters with fatty acids such as oleic acid, lauric acid,
stearic acid, palmitic acid and the like. Specific ones include
CH.sub.3C(CH.sub.3)CH.s-
ub.2C(CH.sub.3).sub.2C.sub.6H.sub.4(OCH.sub.2CH.sub.2).sub.xOH
(where x is an average of 10), TritonX-100 (Aldrich),
polyethyleneoxide (20) sorbitan monolaurylate (Tween 20, Aldrich),
polyethyleneoxide (20) sorbitan monopalmitate (Tween 40),
polyethyleneoxide (20) sorbitan monostearate, polyethyleneoxide
(20) sorbitan monooleate (Tween 60) and sorbitan monopalmitate
(Span 40). One type of polyethylene oxide-based non-ionic
surfactant may be used, or two or more types may be used in
combination.
[0105] Triblock copolymers with three polyalkylene oxide chains may
also be used. Particularly preferred is the use of a polyethylene
oxide chain-polypropylene oxide chain-polyethylene oxide chain
triblock copolymer. This surfactant has a structure with a
polypropylene oxide chain in the center and polyethylene oxide
chains at both ends, and hydroxyl groups at both ends. The basic
structure of this triblock copolymer is represented as
(EO).sub.x(PO).sub.y(EO).sub.x. There are no particular
restrictions on x and y. For example, the triblock copolymer may
have a structure with the following ranges: x=5-110, y=15-70. A
triblock copolymer with x=15-20, y=50-60 is preferred. Preferred
triblock copolymers have the formula (EO).sub.x(PO).sub.y(EO).sub.x
obtained with a combination of any x value selected from 15, 16,
18, 19 and 20, with a y value which is an integer included in
y=50-60.
[0106] There may likewise be used a polypropylene oxide
chain-polyethylene oxide chain-polypropylene oxide chain triblock
copolymer, with the reverse sequence of blocks
((PO).sub.x(EO).sub.y(PO).sub.x). There are also no particular
restrictions on x and y in this copolymer, but the following
ranges: x=5-110, y=15-70 are preferred, and a triblock copolymer
wherein x=15-20 and y=50-60 is more preferred.
[0107] Specific triblock copolymers that may be used include
EO.sub.5PO.sub.70EO.sub.5, EO.sub.13PO.sub.30EO.sub.13,
EO.sub.20PO.sub.30EO.sub.20, EO.sub.26PO.sub.39EO.sub.26,
EO.sub.17PO.sub.56EO.sub.17, EO.sub.17PO.sub.58EO.sub.17,
EO.sub.20PO.sub.70EO.sub.20, EO.sub.80PO.sub.30EO.sub.80,
EO.sub.106PO.sub.70EO.sub.106, EO.sub.100PO.sub.39EO.sub.100,
EO.sub.19PO.sub.33EO.sub.19 and EO.sub.26PO.sub.39EO.sub.26, with
EO.sub.17PO.sub.56EO.sub.17 and EO.sub.17PO.sub.58EO.sub.17 being
preferred. These triblock copolymers are industrially available
from BASF Corp. and elsewhere, and triblock copolymers with desired
x and y values are obtainable on a small-scale production level.
One type of triblock copolymer may be used, or two or more types
may be used in combination.
[0108] There may also be used a star diblock copolymer having two
polyethylene oxide chain-polypropylene oxide chain segments linked
to each of the two nitrogen atoms in ethylenediamine. As examples
there may be mentioned
(EO.sub.113PO.sub.22).sub.2NCH.sub.2CH.sub.2N(PO.sub.22EO.su-
b.113).sub.2,
(EO.sub.3PO.sub.18).sub.2NCH.sub.2CH.sub.2N(PO.sub.18EO.sub.-
3).sub.2 and
(PO.sub.19EO.sub.16).sub.2NCH.sub.2CH.sub.2N(EO.sub.16PO.sub.-
19).sub.2. One type of star diblock copolymer may be used, or two
or more types may be used in combination.
[0109] A primary alkylamine or the like may also be used as the
non-ionic surfactant. The resulting pore size can be controlled by
the type of surfactant used, and particularly by the length of the
hydrophobic portion, such as an alkyl chain, in the surfactant.
[0110] (Condensation polymerization)
[0111] A porous solid for gas adsorption separation is then
obtained from the reaction system (liquid) containing the framework
component and the surfactant. The solvent used for the condensation
polymerization reaction may be water, an organic solvent, a mixture
of water and an organic solvent, etc., but water is preferred.
[0112] The reaction system for the condensation polymerization
reaction is not limited to being alkali, neutral or acidic, but it
is preferably acidic. Specifically, the pH is preferably no higher
than 1. For example, hydrochloric acid, boric acid, hydrobromic
acid, hydrofluoric acid, hydroiodic acid, nitric acid, sulfuric
acid, phosphoric acid or the like may be used. According to the
invention, the acid may be of one type or a combination of two or
more. The acid used for the invention is preferably hydrochloric
acid or sulfuric acid. It is particularly preferred to use
hydrochloric acid to adjust the pH to no higher than 0.5.
[0113] The surfactant is preferably used at low concentration to
obtain a porous solid according to the invention. It is preferably
in a range of less than 29.67 g/l with respect to the total volume
of the solvent used in the reaction system. This is because
micropores will not form if the concentration is 29.67 g/l or
higher. It is also preferably at least 7 g/l, because micelle
formation is inhibited if it is less than 7 g/l. The upper limit
for the concentration is preferably 29 g/l, more preferably 25 g/l
and even more preferably 20 g/l. The lower limit is preferably 10
g/l and preferably 12 g/l. The most preferred concentration is
approximately 15 g/l.
[0114] The framework component is preferably present at 0.012 mole
or greater with respect to 1 g of the surfactant.
[0115] There are no particular restrictions on the method of mixing
the reaction system components, but it is preferred to mix the
surfactant with the solvent and simultaneously or subsequently add
the acid for the preferred acidic environment, and then add the
framework component. The temperature of the mixture system to which
the surfactant, acid, etc. are added, and the duration of the
addition, may be sufficient to give a solution which uniformly
dissolves the surfactant and is otherwise not restricted, but a
temperature of 0.degree. C. to 100.degree. C. is preferred.
[0116] The condensation polymerization reaction will start so long
as the surfactant and framework component are in a state allowing
condensation polymerization, such as in the presence of an acidic
environment. The framework component may be added at once, or
gradually added while stirring. The temperature for addition of the
framework component is not particularly restricted, but is
preferably from 35.degree. C. to 80.degree. C., and more preferably
from 40.degree. C. to 45.degree. C. There are also no particular
restrictions on the duration of the addition, but it is preferably
one minute or longer.
[0117] The molar ratio of each constituent component, i.e. the
molar ratio for the framework component:surfactant:hydrochloric
acid:solvent in the reaction system, is preferably
0.042-0.175:0.00073-0.0030:1:27.79. In this case, the solvent is
preferably water. The molar ratio for the framework
component:surfactant (framework component/surfactant) is preferably
60 or greater, more preferably 90 or greater and even more
preferably 120 or greater. An increasing molar ratio will give a
smaller pore size and thicker pore walls. It will also allow a
smaller pore volume.
[0118] A greater molar ratio (thicker pore walls) can also increase
the micropore volume. Increasing the molar ratio reduces the pore
volume to increase the micropore volume, thereby increasing the
ratio (%) of the micropore volume with respect to the pore
volume.
[0119] A large molar ratio is achieved by reducing the amount of
surfactant used and/or increasing the amount of framework component
used. If the surfactant is limited to a fixed concentration, and
specifically less than 29.67 g/l or more preferably no greater than
15 g/l, using a greater amount of framework component can provide
the effect of successfully increasing the micropore size. The
framework component is preferably used in an amount of at least
0.012 mole with respect to 1 g of the surfactant.
[0120] The condensation polymerization reaction temperature will
differ depending on the type and concentration of the surfactant
and framework component used, but the reaction will usually be
conducted in a temperature range from 0.degree. C. to 100.degree.
C., and more preferably from 35.degree. C. to 80.degree. C. When a
triblock copolymer is used as the surfactant, this range is
preferably from 40.degree. C. to 45.degree. C. A lower temperature
will tend to give higher regularity to the structure of the
product. A lower temperature will also tend to give a smaller pore
size and thicker pore walls.
[0121] The duration of the condensation polymerization will differ
depending on the constituent components in the reaction system, but
will generally be from 8 hours to 24 hours. The reaction may be
carried out in a static state, an agitated state, or a combination
of agitated and static states. The temperature conditions may also
be changed depending on the reaction state.
[0122] The pore size of the porous solid of the invention may be
controlled by adding a hydrophobic compound such as
trimethylbenzene or triisopropylbenzene to the surfactant.
[0123] (Hot water treatment)
[0124] If necessary, hot water treatment is carried out after the
condensation polymerization reaction. Specifically, the following
hot water treatment may be carried out before the treatment to
remove the surfactant from the porous solid precursor (that is, the
product with the surfactant filling the pores).
[0125] The porous solid precursor is dispersed in an aqueous
solution containing the same surfactant used for the condensation
polymerization reaction (typically with a surfactant concentration
equal to or lower than that of the condensation polymerization
reaction), and the precursor is subjected to hot water treatment in
a temperature range from 50.degree. C. to 200.degree. C. More
specifically, the reaction solution is heated either directly or
after dilution. The heating temperature is preferably from
60.degree. C. to 100.degree. C., and more preferably from
70.degree. C. to 80.degree. C. Here, the pH may be slightly
alkaline, and is preferably from 8 to 8.5. It may be appropriately
adjusted with hydrochloric acid or sodium hydroxide. The treatment
time is not particularly restricted, but is preferably at least an
hour, and more preferably from 3 to 8 hours. It may be continued
for even a longer time, but no notable difference in effect will be
seen even if the treatment time is extended for a longer time. The
hot water solution is preferably agitated during the treatment.
After the hot water treatment, the precursor is filtered and dried,
and the excess treatment solution is eliminated. Agitation
treatment may also be carried out at room temperature after
dispersion of the precursor in the aforementioned aqueous solution
and before the hot water treatment. This can increase the effect of
the hot water treatment.
[0126] As a result of this hot water treatment, it is possible to
enhance the strength and structural regularity of the porous solid
after removal of the surfactant. It is thereby possible to provide
a mesoporous solid with more excellent pore stability and
structural regularity, i.e. uniform pore distribution, than a
porous solid that has not undergone such hot water treatment. For
example, if a porous solid precursor with a hexagonal structure is
subjected to such hot water treatment, the pore size of the
mesoporous solid (the final product) can be easily rendered uniform
to an extent wherein at least 60% of the total pore volume is in a
range of .+-.40% of the pore size exhibiting the maximum peak in
the pore size distribution curve.
[0127] (Surfactant removal)
[0128] After the condensation polymerization reaction, or after the
hot water treatment, the produced precipitate or gel is filtered,
and if necessary is washed with water and then dried to yield a
solid product. The surfactant is then removed from the solid
product. The removal of the surfactant from the solidified product
may be accomplished by a firing method or by a method of treatment
with a solvent such as water or alcohol.
[0129] A firing method involves heating in a range from 300.degree.
C. to 1000.degree. C., and preferably in a range from 400.degree.
C. to 700.degree. C. The heating time may be 30 minutes or longer,
but is preferably at least an hour to completely remove the organic
components. The atmosphere may be an air stream, and because of the
large volume of firing gas that is generated, it may be a stream of
an inert gas such as nitrogen at the start of firing.
[0130] A method of treatment with a solvent or the like involves
dispersion of the solid product in a solvent with a high solubility
for the surfactant, followed by agitation and then recovery of the
solid. The solvent used is one with a high solubility for the
surfactant, such as water, ethanol, methanol or acetone. Treatment
with water is preferably carried out in a range from 25.degree. C.
to 80.degree. C. A small amount of a cationic component may also be
added for adequate solubility. Cationic component-containing
substances that may be added include hydrochloric acid, acetic
acid, sodium chloride, potassium chloride and the like. The cation
addition concentration is preferably 0.1-10 moles/l. The solid
product is preferably dispersed in an ethanol solvent with the
solid product at 0.5 to 50 g with respect to 100 cc of the ethanol
solvent. The dispersion is preferably agitated in a temperature
range from 25.degree. C. to 100.degree. C. In the case of a
non-ionic surfactant, extraction will sometimes be carried out with
the solvent alone. The extraction of the surfactant will sometimes
be facilitated by using water or hydrochloric acid-added water as
the solvent. Pulverization, sifting, shaping, etc. may be carried
out either before or after removal of the surfactant.
[0131] As a preferred condensation polymerization method, a lower
tetraalkoxysilane of 1-5 carbons such as tetramethoxysilane or
tetraethoxysilane, or
(CH.sub.3O).sub.3Si--CH.sub.2--CH.sub.2--Si(OCH.sub- .3).sub.3,
(CH.sub.3O).sub.3Si--C.sub.6H.sub.4--Si(OCH.sub.3).sub.3 or the
like is used as the framework component, a triblock copolymer
represented as (EO).sub.x(PO).sub.y(EO).sub.x (where x=5-110,
y=15-70, and preferably x=15-20, y=50-60) is used at a
concentration of no greater than 29.67 g/l and preferably no
greater than 15 g/l as the surfactant and water is used as the
solvent, and the condensation polymerization is conducted under
hydrochloric acid acidity.
[0132] This type of reaction system can consistently yield a porous
solid having an X-ray diffraction pattern with at least one peak at
a diffraction angle corresponding to a d value of 1 nm or greater
and having at least one section wherein the change in nitrogen
adsorption (nitrogen adsorption in terms of the volume of nitrogen
under standard conditions) is 50 ml/g or greater with a relative
vapor pressure change of 0.1 in a relative vapor pressure range of
0.2-0.8 for a nitrogen adsorption isotherm measured at liquid
nitrogen temperature, which porous solid possesses mesopores with a
median pore size of 2-50 nm in the pore size distribution curve and
has pore walls that are porous.
[0133] [Gas adsorption separation process of the invention]
[0134] The gas adsorption separation process of the invention will
now be explained.
[0135] The gas adsorption separation process of the invention
involves using the porous solid for gas adsorption separation of
the invention for contact of gas with the porous solid, whereby
specific components in the gas are adsorbed onto the porous solid
and then separated based on their subsequent retention times. There
are no particular restrictions on the method of contacting the gas
with the porous solid, and for example, a gas chromatography method
may be employed wherein the porous solid is packed into a column
and vapor containing the gas components to be treated is
continuously or intermittently contacted therewith. When the
specific components in the gas are separated by mere adsorption
onto the porous solid, the porous solid and the vapor containing
the gas components to be treated may be contacted in a batch
system.
[0136] As gas components for targets of treatment there may be
mentioned hydrocarbons (for example, methane, ethane, ethylene,
propane, propylene, n-butane, i-butane, hexane, octane, benzene,
cyclohexane, toluene), CO.sub.2, CO, NO.sub.x, HC, SO.sub.x,
H.sub.2S, methanol, ethanol, etc. in exhaust gas, plant gas,
reformed gas and air, and preferably at least one gas component
selected from the group consisting of CO.sub.2 and hydrocarbons.
The conditions for contacting the gas with the porous solid of the
invention are not particularly restricted, and the temperature
range may be appropriately selected to allow efficient adsorption
separation depending on the combination of the porous solid used
and the gas components to be treated.
EXAMPLES
[0137] The present invention will now be explained in greater
detail by way of examples and comparative examples, with the
understanding that the invention is in no way restricted by these
examples.
Example 1
[0138] A triblock copolymer represented by the compositional
formula (EO).sub.17(PO).sub.58(EO).sub.17 (hereunder referred to as
P104. Product of BASF Corp.) was used as a non-ionic surfactant,
and tetraethyl silicate (TEOS) was used as the framework component.
The TEOS was hydrolyzed using hydrochloric acid as the catalyst in
the presence of the P104, for condensation polymerization.
[0139] Specifically, after dissolving 1.76 g (0.00035 mole) of P104
in 105 ml of ion-exchange water, 20 ml (0.24 mole) of 12 N
hydrochloric acid was added to the surfactant solution (total
water: 6.67 moles, surfactant concentration: 14.67 g/l). After then
adding 4.73 g (0.021 mole) of TEOS at once to this mixture in a
water bath at 45.degree. C., it was agitated for 8 hours. It was
then stationed for 8 hours in a hot water bath at 80.degree. C. The
white precipitate produced was collected by reduced pressure
filtration and thoroughly washed with an abundant amount of
ion-exchange water, and then allowed to stand overnight in a dryer
at 45.degree. C. The surfactant was removed by raising the
temperature from room temperature to 550.degree. C. over a period
of 2 hours under an air stream (flow rate: 0.5 ml/min), and firing
at 550.degree. C. for 6 hours. This yielded a porous solid (powder)
as Sample 1.
[0140] The XRD pattern of Sample 1 in the low-angle region was
measured, giving the results shown in FIG. 3. Sample 1 exhibited a
strong peak at d=1.96 and a weak peak at the high-angle end. The
diffraction pattern corresponded to the (100), (110) and (120)
diffraction planes from the low-angle end, thus confirming that
Sample 1 has a hexagonal structure.
[0141] The nitrogen adsorption isotherm and pore distribution curve
(BJH method) for Sample 1 were determined, giving the results shown
in FIGS. 4A and 4B. The mesopore median pore size, area to weight
ratio and total pore volume (with relative pressure P/P.sub.0=0.98)
for Sample 1 were determined from the pore distribution curve, and
the pore wall thickness was determined from the difference between
the lattice constant a.sub.0 (a.sub.0=d.sub.100.times.2/1.732)
determined by powder X-ray diffraction and the pore size determined
by nitrogen adsorption measurement. The results are shown in Table
1.
[0142] Also, the nitrogen adsorption isotherm for Sample 1 was
t-plotted using the nitrogen adsorption isotherm for nonporous
silica with an area to weight ratio of 38.7 m.sup.2/g as the
standard isotherm, to calculate the micropore volume. The data for
the standard isotherm are shown in FIG. 5, and the approximate
curves applying to each relative pressure range with t-plot
conversion are shown in FIGS. 6A to 6D.
[0143] These approximate curves were used for a t-plot of the
nitrogen adsorption isotherm for Sample 1, giving the graph shown
in FIG. 7. Sample 1 was shown to possess micropores, with a total
micropore volume of 0.072 ml/g.
[0144] This t-plot was used to derive a micropore distribution
curve by the MP method, and the micropore size (mean size) obtained
from this distribution curve is shown in Table 1.
[0145] These analytical data were used to determine the volume
ratio of micropores with respect to the pores, the total pore
volume, the total pore volume excluding the micropores, the pore
volume in a range of .+-.40% of the median pore size (mesopore
volume) and the mesopore volume with respect to the total pore
volume excluding the micropores, and the results are shown in
Tables 1 and 2. The nitrogen adsorption isotherm shown in FIG. 4A
was used to determine the maximum value for the change in nitrogen
adsorption (nitrogen adsorption in terms of the volume of nitrogen
under standard conditions) with a relative vapor pressure change of
0.1 in a relative vapor pressure range of 0.2-0.8, and the results
are shown in Table 3.
Examples 2-4
[0146] Porous solids (powders) for Samples 2, 3 and 4 were obtained
in the same manner as Example 1, except that TEOS was used in an
amount of 6.56 g (0.0315 mole, Example 2), 8.75 g (0.042 mole,
Example 3) and 11.04 g (0.053 mole, Example 4). The nitrogen
adsorption isotherms determined for Samples 2, 3 and 4 are shown in
FIGS. 8 to 10, respectively. The analytical data for Samples 2, 3
and 4 were obtained as in Example 1, and the results are shown in
Tables 1 to 3.
Examples 5-6
[0147] Porous solids (powders) for Samples 5 and 6 were obtained in
the same manner as Example 1, except that the stationed
temperatures of the mixture after agitating at 45.degree. C. for 8
hours were 90.degree. C. (Example 5) and 100.degree. C. (Example
6), and the TEOS/P104 was 120. The analytical data for Samples 5
and 6 were obtained according to the procedure as shown in Example
1, and the results are shown in Tables 1 to 3.
1 TABLE 1 Molar Ratio (%) of ratio Synthesis Mesopores micropore
Surfactant (framework tempera- Pore wall Micropores volume with
concentration component/ ture BET Size Volume* thickness Size
Volume respect to (g/l) P104) (.degree. C.) (m.sup.2/g) (nm) (ml/g)
(nm) (nm) (ml/g) mesopores Sample 1 14.67 60 80 886.2 5.75 0.392
4.14 <1.0 0.072 18.38 Sample 2 14.67 90 80 723.1 5.39 0.374 5.34
<1.0 0.096 25.67 Sample 3 14.67 120 80 873.6 4.65 0.333 6.18
<1.0 0.154 46.25 Sample 4 14.67 150 80 810.7 4.86 0.250 6.46
<1.0 0.192 76.80 Comparison sample 1 29.67 60 80 850.0 8.90 --
3.10 n.d. n.d. n.d. Sample 5 14.67 120 90 734.1 5.01 0.553 4.98
<1.0 0.127 18.68 Sample 6 14.67 120 100 618.5 5.76 0.560 4.64
<1.0 0.080 12.50 Comparison sample 2 14.67 60 100 646.0 6.42
0.580 3.98 n.d. n.d. n.d. *: Volume within .+-.40% of median pore
size.
[0148]
2 TABLE 2 Total pore volume Ratio (%) of mesopore Total excluding
Mesopore volume with respect to pore micropores volume* total pore
volume volume (ml/g) (ml/g) excluding micropores (ml/g) Sample 1
0.511 0.392 76.71 0.638 Sample 2 0.418 0.374 89.47 0.514 Sample 3
0.355 0.333 93.80 0.509 Sample 4 0.261 0.250 95.79 0.453 Sample 5
0.553 0.450 81.37 0.680 Sample 6 0.560 0.430 76.79 0.640 *Volume
within .+-.40% of median pore size.
[0149]
3 TABLE 3 Maximum value for change in nitrogen adsorption*.sup.2
with relative vapor pressure change*.sup.1 of 0.1*.sup.3 [ml/g]
Sample 1 110 Sample 2 105 Sample 3 100 Sample 4 55 Sample 5 90
Sample 6 80 *.sup.1For nitrogen adsorption isotherm at liquid
nitrogen temperature. *.sup.2Value in terms of nitrogen volume
under standard conditions. *.sup.3Maximum in relative vapor
pressure range of 0.2-0.8.
[0150] As seen from the results in Tables 1 to 3, it was confirmed
that all of the porous solids obtained in Examples 1 to 6 (Samples
1 to 6) satisfied all of the following conditions.
[0151] (1) Having an X-ray diffraction pattern with at least one
peak at a diffraction angle corresponding to a d value of 1 nm or
greater;
[0152] (2) Having a nitrogen adsorption isotherm measured at liquid
nitrogen temperature with at least one section where the change in
nitrogen adsorption (nitrogen adsorption in terms of the volume of
nitrogen under standard conditions) is 50 ml/g or greater with a
relative vapor pressure change of 0.1 in a relative vapor pressure
range of 0.2-0.8;
[0153] (3) Possessing mesopores with a median pore size of 2-50 nm
in the pore size distribution curve;
[0154] (4) Having pore walls that are porous with a mean pore size
of less than 2 nm;
[0155] (5) Having a total micropore volume of 0.05 ml/g or greater;
and
[0156] (6) Having at least 60% of the total pore volume excluding
the micropores in a range of .+-.40% of the median pore size.
[0157] The results in Tables 1 to 3 confirmed that when the
surfactant concentration is limited to a certain level, increasing
the molar ratio of the framework component/surfactant allows
control of the micropore volume, pore size and pore volume.
Comparative Example 1
[0158] A porous solid (powder) was obtained as a comparative sample
1 in the same manner as Example 1 except for using 3.56 g of P104
(surfactant concentration: 29.67 g/l), in order to confirm that the
micropore formation is closely related to the surfactant
concentration. This sample had a hexagonal structure based on
powder X-ray diffraction, and the nitrogen adsorption isotherm was
as shown in FIG. 11. The adsorption isotherm for the comparative
sample 1 matched the standard curve shown in FIG. 12, and no
micropores were found.
Comparative Example 2
[0159] A Porous solid (powder) was obtained as a comparative sample
2 in the same manner as Example 1, except that the stationed
temperature of the mixture after agitating at 45.degree. C. for 8
hours was 100.degree. C., and the TEOS/P104 was 60. No micropores
were found for the comparative sample 2.
Examples 7-8
[0160] Porous solids for samples a and b were obtained in the same
manner as Example 1, except that the following amounts of starting
materials were used.
4 (Example 7) P104 17.2 g Ion-exchange water 1060 mL 12 N
hydrochloric acid aqueous solution 200 mL TEOS 87.8 g (Example 8)
P104 34.4 g Ion-exchange water 1060 mL 12 N hydrochloric acid
aqueous solution 200 mL TEOS 87.8 g
[0161] Next, 30 g of the mesoporous solids of samples a and b was
dispersed in 100 mL of an aqueous methanol solution diluted to 10%
(v/v), and after stirring for one minute, the precipitate was
collected by filtration under reduced pressure. The collected
precipitate was dried in a dryer at 45.degree. C. and compressed at
a pressure of 500 kgf/cm.sup.2, and the surfactant template was
removed by firing at 550.degree. C. for 6 hours under an oxygen
atmosphere. Each of the fired samples was crushed with a mortar,
and the powder particles were adjusted to between 150 .mu.m and 300
.mu.m with a sieve to prepare a gas molecule separating column
packing material.
Comparative Example 3
[0162] FSM-16 was used as a comparison mesoporous solid with no
micropores in the pore walls. The FSM-16 was synthesized according
to an outside publication. The procedure was as follows.
[0163] After dispersing 50.0 g of sodium disilicate
(.--Na.sub.2Si.sub.2O.sub.5) in 500 mL of ion-exchange water and
stirring at room temperature for 3 hours, the precipitate was
collected by filtration under reduced pressure. The precipitate was
dispersed in an aqueous solution of 32.0 g of
hexadecyltrimethylammonium chloride dissolved in 1 liter of
ion-exchange water, and after stirring for 3 hours in a hot water
bath at 70.degree. C., a 2 N hydrochloric acid aqueous solution was
used to adjust the pH to 8.5. An additional 3 hours of stirring in
a hot water bath at 70.degree. C. yielded a white precipitate. The
white precipitate produced was collected by reduced pressure
filtration and thoroughly washed with an abundant amount of
ion-exchange water, and then allowed to stand overnight in a dryer
at 45.degree. C. for drying to obtain a porous solid as Sample
c.
[0164] After then compressing Sample c (FSM-16) at a pressure of
500 kgf/cm.sup.2, the surfactant template was removed by firing at
550.degree. C. for 6 hours under an oxygen atmosphere. The fired
sample was crushed with a mortar, and the powder particles were
adjusted to between 150 .mu.m and 300 .mu.m with a sieve to prepare
a gas molecule separating column packing material.
[0165] [Analysis of physical properties, etc.]
[0166] The powder X-ray diffraction (XRD) patterns and adsorption
isotherms for samples (packing materials) a, b and c obtained in
Examples 7-8 and Comparative Example 3 were determined in the same
manner as Example 1, and their powder X-ray diffraction (XRD)
patterns and adsorption isotherms are shown in FIGS. 13 and 14,
respectively. The analytical data for Samples a, b and c were
obtained as in Example 1, and the results are shown in Tables 4 to
6.
[0167] As indicated by the results of the powder X-ray diffraction
(XRD) pattern shown in FIG. 13, samples a, b and c each exhibited a
strong peak near 1.degree. and several weak peaks at the wide-angle
end, thus confirming formation of a regular mesostructure. The
observed XRD patterns also indicated that Samples a, b and c each
formed two-dimensional hexagonal framework structures, and the
peaks matched the diffraction peaks for (100), (110) and (200) from
the low-angle end.
[0168] As clearly seen from the adsorption isotherms shown in FIG.
14 and the data shown in Tables 4 to 6, the micropore volume of
Sample a was 0.110 ml/g and that of Sample b was 0.051 ml/g, but no
micropores were present in Sample c. Moreover, it was confirmed
that both of the porous solids (Samples a and b) obtained in
Examples 7 and 8 satisfied all of the conditions listed above as
(1) to (6).
5 TABLE 4 Micropore Pore size BET volume Sample (nm) (m.sup.2/g)
(cc/g) a 5.73 729.9 0.110 b 4.73 617.9 0.051 c 2.57 865.5 0
[0169]
6TABLE 5 Ratio (%) of mesopore volume with respect to Total pore
Mesopore total pore volume Total pore volume excluding volume*
excluding volume Sample micropores (ml/g) (ml/g) micropores (ml/g)
a 0.546 0.456 83.52 0.728 b 0.497 0.406 82.69 0.591 c 0.896 0.570
63.62 0.896 *Volume within .+-.40% of median pore size.
[0170]
7 TABLE 6 Maximum value for change in nitrogen adsorption*.sup.2
with relative vapor pressure change*.sup.1 of 0.1*.sup.3 Sample
[ml/g] a 130 b 100 c 105 *.sup.1For nitrogen adsorption isotherm at
liquid nitrogen temperature. *.sup.2Value in terms of nitrogen
volume under standard conditions. *.sup.3Maximum in relative vapor
pressure range of 0.2-0.8.
[0171] [Gas component adsorption separation test]
[0172] Samples (gas separation column packing materials) a, b and c
obtained in Examples 7-8 and Comparative Example 3 were used for
measurement of the retention times of different gas molecules by
gas chromatography (GC) under the conditions shown below, and the
adsorption separation properties for the gas molecules were
evaluated. As pretreatment of the packing materials before
measurement, they were exposed to a helium carrier gas for 6 hours
at a flow rate of 40 mL/min at 150.degree. C., and then the packing
materials were dried. The GC measurement conditions were as
follows.
8 Column Glass column (2 m) Carrier gas Helium (40 mL/min) INJ
temperature 50.degree. C. TCD temperature 80.degree. C. Column
temperature 50.degree. C.
[0173] These samples (gas separation column packing materials) a, b
and c were used for gas molecule adsorption separation evaluation
(retention time measurement), giving the results shown in Table 7.
The gas molecules used were hydrogen (H.sub.2), carbon monoxide
(CO), nitrogen (N.sub.2), oxygen (O.sub.2), nitrogen monoxide (NO)
and carbon dioxide (CO.sub.2) as acidic gases, and methane
(CH.sub.4), ethane (C.sub.2H.sub.6), propane (C.sub.3H.sub.8),
n-butane (n-C.sub.4H.sub.10), i-butane (i-C.sub.4H.sub.10),
ethylene (CH.sub.2.dbd.CH.sub.2) and propylene
(C.sub.2.dbd.CHCH.sub.3) as hydrocarbon gases.
9 TABLE 7 Gas Retention time (min) component Sample a Sample b
Sample c H.sub.2 1.1 0.9 0.8 CO 1.8 1.6 1.3 N.sub.2 1.6 1.4 1.2
O.sub.2 1.6 1.4 1.2 NO 1.6 1.4 1.2 CO.sub.2 10.1 7.5 4.7 CH.sub.4
2.1 1.8 1.3 C.sub.2H.sub.6 6.9 -- 3.3 C.sub.3H.sub.8 27.5 -- 11.2
n-C.sub.4H.sub.10 134.4 -- 40.0 i-C.sub.4H.sub.10 108.0 -- 33.5
CH.sub.2.dbd.CH.sub.2 11.5 -- 4.2 CH.sub.2.dbd.CHCH.sub.3 104.4
77.9 16.9
[0174] As seen by the results shown in Table 7, Samples (gas
component column packing materials) a and b obtained in Examples 7
and 8 had much longer retention times for the specific gas
components than Sample c obtained in Comparative Example 3, which
possessed no micropores, thus confirming their ability to
efficiently and selectively accomplish adsorption separation
particularly of hydrocarbon gases such as CO, CO.sub.2 and
propylene from other gases. The tendency for a longer retention
time for the specific gas components was demonstrated to increase
proportionally with the volume of micropores present in the pore
walls.
Comparative Examples 4-5
[0175] For comparison, MS-3A Zeolite (Comparative Example 4) and
USY Zeolite (Comparative Example 5) were used for measurement of
the retention times for nitrogen monoxide (NO), carbon dioxide
(CO.sub.2) and propylene (C.sub.3H.sub.6) in the same manner as the
above-mentioned gas component adsorption separation test. The
results are shown in Table 8.
10 TABLE 8 Retention time (min.) Gas Type MS-3A USY NO 0.73 1.73
CO.sub.2 1.25 5.18 C.sub.3H.sub.6 0.99 44.13 MS-3A Zeolite Pore
size: 0.3 nm, Pore volume: 0.23 cc/g, Specific surface area: 643.9
m.sup.2/g USY Zeolite Pore size: 0.9 nm, Pore volume: 0.30 cc/g,
Specific surface area: 840.0 m.sup.2/g
[0176] As seen by the results shown in Tables 7 and 8, Samples a
and b of Examples 7-8 according to the present invention were
confirmed to have retention times for carbon dioxide (CO.sub.2) and
propylene (C.sub.3H.sub.6) that were approximately twice those of
conventional zeolite products.
[0177] As explained above, the porous solid for gas adsorption
separation according to the present invention and the gas
adsorption separation process of the invention which employs it
allow selective and efficient adsorption separation of specific
components in gases, such as hydrocarbons and CO.sub.2.
[0178] The porous solid for gas adsorption separation of the
invention is therefore highly effective as an adsorbent for
temporary adsorption of hydrocarbons in exhaust gas during engine
starting (cold starting) and then release of the hydrocarbons when
the catalyst warms to an activation temperature, as an adsorbent
for removing impurities such as CO and CO.sub.2 in hydrogen
produced by reforming hydrocarbons, as an adsorbent in apparatuses
for separation and recovery of CO.sub.2 in fuel exhaust gas or
chemical plant processing gas by pressure swing absorption (PSA),
or as an adsorbent for solvent recovery apparatuses.
* * * * *