Note: Descriptions are shown in the official language in which they were submitted.
CA 02248060 1998-09-01
WO 97132815 PCT/GB97/00635
Mesoporous Material
The present invention relates to porous amorphous structures and methods of
making them, in particular it relates to compositions with large pore sizes which
can contain metal ions and can be used as adsorbents and catalysts.
US Patent 5,108,725 discloses synthetic compositions of large pore materials
and methods of making these compositions. This US Patent gives a detailed
description of known and disclosed porous materials and prior art references
which are incorporated herein by reference.
This US Patent discloses a method of forming porous compounds by reacting
certain alumino-silicates with an organic directing agent which is a quaternary
ammonium compound under specified conditions to precipitate the compound.
It is known from an article by S Gontier and A Tuel in 'Zeolites' 15:601-610,
1995 to form tit~ni~lm containing mesoporous silicas by reacting a solution of
tetraethyl orthosilicate with a solution of tetraisopropyl orthotitanate and adding
this reaction mixture to a long chain alkylamine as a templating agent to obtain a
Ti-cont~ining mesoporous silica with enlarged pore structure.
Silica materials are known which are amorphous in the sense that they have no
long range order and are characterised with a pore size distribution over a widerange of sizes and have no X-ray diffraction pattern. Their porosity arises forrn
the voids between dense particles of silica.
Paracrystalline materials are known such as the transitional ~ min~ which have
broad X-ray peaks. The microstructure of these materials consists of tiny
crystalline regions of conden~ed ~lumin~ phases and the porosity of these
materials results from irregular voids between these regions. As there is no
controlling lon8 range order, the pore size variability is typically very wide in
these materials.
CA 02248060 1998-09-01
WO 97132815 PCT/GB97100635
Zeolite membranes are known with a narrow defined pore size range and are
commonly referred to as molecular sieves, however these have a pore size below
15 Angstroms and are I ere" ed to in detail in US Patent 5,108,725 these
materials are described as having a microporous structure.
However hitherto it has not been possible to obtain a silica material with a
narrow pore size distribution which is above the microporous range.
We have invented a new silica cont~-ning material of enlarged pore size and a
method of making it.
According to the invention there is provided a silica composition of pore size of
above 15 Angstroms and preferably of pore size 15 to 500
Angstroms.
The pore size can be measured by using the techniqlle of bubble point pressure
as defined in ISO4003 or by nitrogen adsorbtion using the Polimore Head
method. The composition should have a regular pore size with a narrow pore
size distribution, e.g. the second and third quartile are within the specified range,
the pore size distribution may be measured by a Coulter Porometer (Trademark).
The structure of the material can be in the form of a chain of molecules linked
together in a linear fashion to form what is subst~nti~lly a chain or it can be in the
forrn of a subst~nti~lly planar structure of molecules linked together subst~nti~lly
in one plane or it can be in the form of a three dimensional structure with
molecules linked together accoldi.,gly.
In each of the structures the size will depend on the conditions and treatment and
each structure will only approach an ideal uniform structure.
The materials of the invention preferably have a benzene adsorption capacity of
greater than 10 grams benzene/100 grams at 50 torr and 25 degrees C as
measured in US Patent 5,108,725.
CA 02248060 1998-09-01
WO 97/32815 PCT/GB97/00635
The materials of the present invention essenti~lly comprise a series of polysilicic
acid units linked together, each unit co,~.p.isi~g a polysilicic acid molecule as
described in GB Patent Application 9316350.9 and comprising a plurality of
three dimensional species linked together with each species either having silicon
atom bridges with an oxygen atom between each silicon atom or hydroxyl groups
on the silicon atoms. The linking together of these units forms the structure ofthe compounds of the invention.
The compositions of the present invention can be formed by the conden~tion of
a polysilicic acid from solution in the presence of a surfactant. The polysilicic
acid preferably has a weight average molecular weight of 700 to 2000. This acid
is preferably dissolved in an alcohol such as ethanol or butanol to form the
solution. The surfactant is thought to act to hold the individual units in a suitable
orientation and separation to form the mesoporous compounds of the invention
when they are joined together.
The surfactant is preferably a compound which is at least partially miscible with
silicic acid solution and can be in the form of a suspension or solution, e.g. in an
alcohol.
The surfactant can be a cationic, anionic or non-ionic.
Examples of suitable surfAct~nts include amines, quaternary ammonium
compounds and siloxanes. Suitable amines include long chain alkyl amines, e.g.
cont~inin~ 6-25 carbon atoms.
Suitable quaternary ammonium compounds include tetra-alkyl ammonium
compounds.
The composition of the present invention can be formed by adding a solution of
the silicic acid to a solution or suspension of the surfactant to form the
composltlon.
CA 02248060 1998-09-01
WO 97/32815 PCT/GB97/00635
Optionally, other silicon co..~ g compounds can be incorporated in the silicic
acid solution to modify the structure of the composition obtained. Suitable
compounds include silanes, siloxanes, and functionalised silanes and siloxanes,
etc.
To form the structures of the present invention, the polysilicic acid solution is
mixed with the surfactant solution, preferably with vigorous stirring and the
product filtered and dried.
The material is preferably calcined, e.g. above 350 degrees C.
The composition of the present invention can incorporate metals in addition to or
in place of the silicon atoms to modify the pore structure of the material.
Suitable metals include titanium, zirconium and any metal which can form, e.g.
an oxide, hydroxide, alkoxide, acetonate or acetyl acetonate and any other
functionality which can undergo a conden~tion reaction and which can form a
solution or gel and which can conden~e to form a polymeric type structure.
This can be carried out by mixing a solution or suspension of a metal oxide or
hydroxide with the polysilicic acid solution before mixing with the surfactant.
The pore size of the composition formed by the process of the invention will
depend on the conditions and the presence of other metals.
The compositions of the present invention can be used in filtration, the pore size
being larger than in conventional zeolite ~n~;...b,~nes enables them to be used as
filter media for separations which are not possible using zeolite membranes.
Their robustness and te~ ure resist~nce compared with polymeric
membranes enables them to be used in separations which are not possible using
polymers.
CA 02248060 1998-09-01
WO 97/32815 PCT/GB97/00635 ~-
They can also be used as catalyst supports e.g. for preparing polymers such as
polyolefins e.g. polyethylene, polypropylene etc. as well as other polymers for
example as supports for metallic catalysts such as titanium based catalysts where
their pore size enables specific control of the polymer formed to be achieved and
in other catalytic processes.
The invention will now be described with reference to the following examples:-
Fx~m~rle 1
Solntion A Silicic Acid
31.956grm. of a polysilicic acid weight average molecular weight 800 wasdissolved in n-butanol and ethanol to form a solution.
Sol-l~ion R 1-h~x~ ryl~min~
I-hexadecylamine (0.027 mol.) was added to a solution of 3.6 mol of distilled
water and 0.02 mol hydrochloric acid and the reslllting mixture vigorously stirred
for 30 minlltec. and a white creamy mixture formed.
MPc- poronc Silica
Solution A was added slowly to solution B under vigorous stirring conditions forabout 15 mins. A white solid was precipitated which was washed several times
with dictilled water and dried in a fume cupboard for 24 hours. The solid was
calcined at 650~C for six hours. The X ray diffraction pattern of the HMS
product was taken and was compared with that of HMS fabricated from T~OS
as in the S Gontier and A Tuel article referred to above and was found to be
identical with a single peak at 3.2~- D- Spacing.
T~ .;cs;on electron micrographs were taken at di~lenl magnifications and the
results shown in the accompanying micrographs, with fig. I being at a
m~gnifi~.~tion of 100 and at 80 KV and fig. 2 being at a magnification of 63 at 80
KV. As can be seen the compounds have a large pore structure.
,
CA 02248060 1998-09-01
W O 97132815 PCT/GB97/00635
F.x~mple ~
~ixtllre A hex~ yl~mine
(a) A first solution (mixture A) was prepared by adding hexadecylamine (0.027
mol) into a beaker cont~ininv distilled water (3.6 mol) and hydrochloric acid
(0.002 mol). After the mixture was stirred vigorously for 30 minutes at room
temperature, a thick creamy white acidic surfactant mixture was formed.
~ixtllre P~ Si~i~ic Acid
(b) A second solution mixture B was prepared by adding silicic acid/n-butanol
solution (cont~ininSg 0.1 mol Si) to absolute ethanol (0.65 mol). The silicic
acid/n-butanol solution was prepared by adding 2 gram of sodium silicate
powder into 8.35 gram of distilled water with constant stirring for 15 minutes
The sodium silicate solution was added slowly into lOOml of cold 3M
hydrochloric acid with constant stirring. The mixture was stirred vigorously for 2
hours and the silicic acid extracted with n-butanol to form the si}icic
acid/n-butanol solution.
Mesoporous Silica
(c) Mixture B was added slowly to mixture A under vigorous stirring. The
stirring was m~int~ined for approximately 15 minlltes. White solids were formed
in~lA~-IAI-eously on mixing the two mixtures. The product was recovered by
filtration, washed with an excess amount of distilled water, and allowed to dry at
room temperature. The organic materials were removed by calcination of the
as-synthesiseci solids in air at 650~C for 6 hours. The as-synthesised and calcined
product consisted of a very fine white powder.
The adsorption isotherm for this material is shown in figure 3. The inflection is at
p/pO ~0.35, the pore ~ meter was 30 Angstroms and the surface area was
1 161m3/g.
CA 02248060 1998-09-01
WO 97132815 PCT/GB97100635
F.x~n~le 3
Cetyltrimethyl~mmonillmhrorni-le (CTl~ARr)
Silicic Acid
(a) A silicic acid solution was pl~paled as in Example 2 except that the
polymeric silicic acid solution formed was not extracted with butanol but was
used immediately.
CTMA~r
(b) The surfactant mixture was prepared by dissolving I gram CTMABr in 10.3
gram distilled water.
Mesoporous ~ilica
(c) The silicic acid solution of (a) was added to the surfactant mixture. The
resulting mixture was transferred into a sealed plastic bottle and placed in an
oven at 80~C. The resulting mixture was left for 24 hours. The product was
recovered by filtration, washed with an excess amount of distilled water and
allowed to dry at room tenlpel~lure. The organic materials were removed by
calcination of the as-synthe~ised solids in air at 650~C for 6 hours. The
as-synthesised and caJcined product consisted of a very fine white powder. This
was shown to be to be hexagonal mesoporous silica, the diffraction pattern is
shown in figure 4. The pore size was 30 Angstroms.
