Title: Supported composite membranes for gas separation and method of making
the same.
FIELD OF INVENTION:
The invention relates to a supported composite gas separation membrane
wherein the membrane layer is composed of a polymer matrix with mesoporous
silica dispersed in the matrix.
This invention also relates to a process of the manufacture of mesoporous silica
filled polymer membranes for gas separation such as CO2 from natural gas or
flue gas or exhaust or coal gas or similar applications.
BACKGROUND OF INVENTION:
The discernable warming of the global climate may be tied to the anthropogenic
production of carbon dioxide; thus CO2 separation and sequestration are of
paramount importance. C02 removal from power plant exhaust or from coal gas
in IGCC using membrane is being considered as a potential among many
technologies available for reducing the green house effect. The digestive gas
from the anaerobic treatment of biomass contains CH4 and CO2. Natural gas from
wells often contains fairly high amounts of CO2. Both applications require the
removal of CO2 to utilize enriched CH4 or natural gas as a fuel. Membrane
separation is becoming more economical and appropriate method of gas
separation. Mainly inorganic membranes and polymer membranes are being
explored for these gas separation applications. Inorganic membranes such as
zeolites have permselectivities that are five times to ten times higher than
traditional polymeric materials and moreover are more stable in
aggressive feeds and high

temperatures, they are not economically feasible for large-scale applications. An
advantage of polymeric materials is that they can be processed into any shapes
such as fibers, which offer high separation productivity due to the inherently high
surface area to volume ratio. Thus, most commercially available gas separating
membranes are still made from polymers despite the limited membrane
performace. To obtain the best of the both materials, composite membranes
consisting of polymer matrix and inorganic materials as filler are prepared.
There have been a number of attempts to incorporate zeolite into polymer
matrices in order to improve membrane separation (D. Jia, K.V.Peinemann, R.D.
Behling "Preparation and characterization of thin-film zeolite-PDMS composite
membranes' J. Membr.Sci.73(1992) and T.M.Gur, Permselectivity of zeolite filled
polysulfone gas separation membranes, J. Membrane Sci. 93 (1994)). The
addition of zeolite into a continuous polymer phase induces a microporous cavity
and channeling system of a defined size in the zeolite-polymer composite
membrane. Significant differences in measured permeability and calculated
selectivity values demonstrate the importance of the type and percentage of
zeolite. Permeabilities and selectivities are enhanced at high zeolite loadings in
the polymer matrix with zeolites 13X and 4A for H2/N2 and CO2/N2 gas
separations (M.G.Suer et al, Gas permeation characteristics of polymer-zeolite
mixed matrix membranes, J. Membrane Sci.91, (1994)), but there is no
performance increase for H2/CO2. One problem associated with zeolite-glassy-
polymer composite membranes is the formation of voids around the zeolite
particles due to poor adhesion of the polymer to the external zeolite surface.
The incorporation of particular molecular sieves into polymeric membranes is
also disclosed in many patents:
U.S. Patent 4,740,219 discloses the method of using silicalite zeolite and other

additives with various polymers for gas separation but separation factor obtained
is very low. A family of innovative composite zeolite materials and methods for
making the same are disclosed in US Patent 6248682. Zeolites 3A and 13X have
been incorporated into hybrid polysiloxane polymers to form composite materials
which are useful as membranes for separating a variety of gaseous and liquid
materials. U.S.Pat.No. 4,340,428 discloses a semi-permeable asymmetrical
membrane which is useful for the desalination of water utilizing a reverse
osmosis process. The membrane which is used for this purpose comprises a
cellulose acetate polymer which has incorporated therein a swelling medium
consisting of an organophilic bentonite. However, the reference does not
maintain that a change in salt rejection is accomplished by the presence of the
bentonite.
Some more recent patents on mixed matrix composites with zeolite
are:U.S.Pat.No.6,605,140 for "composite gas separation membranes.", U.S.
Pat.No. 6726744 for Mixed matrix membrane for separation of gases; U.S. Pat.
Application No. 2005/0043167 for Mixed matrix membrane with super water
washed silica containing molecular sieves and methods for making and using the
same. U.S. Pat. No. 6881364 for Hydrophilic mixed matrix materials having
reversible water absorbing properties. U.S. Pat. Application no. 2006/0107830 for
Mixed matrix membrane with mesoporous particles and methods for making and
using the same.
All the above patents and papers discloses the advantages of incorporation of
zeolites which are of pores in the range of 0.3 to 0.7 nm, still the separation
factor of CO2 from other gases are poor.
The invention of molecular sieves with pores above lnm of the types MCM41 has
provided the option of another good fillers because of its very high surface area

and bigger pore size. USPTO Application No 20070022877 discloses a method of
making Mixed matrix membrane with addition of mesoporous silica such as
MCM41 but CO2/N2 and CO2/CH4 separation factor is not more than 29.
For the practical gas separation application membranes need to be formed on
porous support for long term durability with enhances permeability. Hence new
method of forming filled polymer membrane on ceramic support is required. This
membrane layer should have high separation factor for CO2/N2 and CO2/CH4
which is not practically obtained by either only zeolite membrane or by polymer
membrane.
OBJECTS OF THE INVENTION:
An object of the present invention is to propose a process for the manufacture of
membranes on porous supports;
A further object of the present invention is to propose a process for the
manufacture of supported membranes whereby the membrane layer consists of
mesoporous silica dispersed in a polymer matrix.
Another object of the present invention is to propose a process for the
manufacture of supported polymer membrane filled with aluminum containing
mesoporous silica which has greater separation of CO2 from Natural gas and flue
gas streams;
Still another object of the present invention is to propose a process for the
manufacture of mesoporous filled polymer membrane layer on Porous ceramic
supports and manufacture of membrane modules for gas separation of CO2/N2
and CO2/CH4;

Further objects and advantages of this invention will be more apparent from the
ensuing description.
At the outset of the description which follows, it is to be understood that the
ensuing description only illustrates a particular form of this invention. However,
such a particular form is only an exemplary embodiment and the teaching of the
invention is not intended to be taken restrictively.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The preferred embodiment of the invention will now be described with reference
to the accompanying drawing in which
Figure 1: shows the SEM photograph of membrane coating on ceramic support
showing uniform membrane layer of about 45 microns (A) Surface (B) Cross
sectional view of the membrane;
Figure 2: XRD pattern of membrane layer AI-MCM41.
Figure 3: CO2 selectivity from CO2/N2 gas mixtures at various feed pressures (in
Kg/cm2) for samples with different quantities of AI-MCM41;
Figure 4: CO2/CH4 selectivity for samples with different quantities ofAI-MCM41 at
various feed pressure (3, 5 & 8 kg/cm2).
BRIEF DESCRIPTION OF THE INVENTION:
According to this invention there is provided a supported composite gas
separation membrane for separation of CO2 from natural gases or flue gases
comprising a membrane layer composed of a polymer matrix with mesoporous
silica dispersed in the said matrix.

In accordance with this invention there is also provided a process for preparing a
composite separation membrane comprising;
preparing an homogeneous solution of a polymer;
dispersing silica particles in the said homogeneous solution;
subjecting the mixture to the step of stirring to obtain a homogeneous solution;
coating a support with the said solution to form a thin layer and subjecting the
said layer to the step of drying resulting in a membranes.
DETAILED DESCRIPTION OF THE INVENTION:
This invention relates to a process for the manufacture of ceramic supported
composite membrane comprising of preparing a solution containing a polymer
such as hydroxyethylcellulose (HEC) thin membrane layer incorporated with
Alumina containing Mobile Composition Matter-41 (A1-MCM41) and coating the
composite solution onto the SiC disc to form a composite membrane when
prepared by the dip-coating technique. The composite membrane coated onto
ceramic disc support was used as a barrier membrane to achieve the selective
separation of CO2 from CO2+N2 and CO2+CH4 gas mixtures. The invention also
reports the permeation results on CO2/N2 and CO2/CH4 gas mixtures under
different experimental conditions such as varying pressures and varying mixture
compositions as well as varying the concentration of AI-MCM41 particles in
polymer HEC solution. The present invention also reports the very high (>50)
separation factor of CO2/N2 using this novel composite membrane:
Materials:
Polymers such as cellulose derivatives such as Hydroxyethylcellulose (HEC),
Hydroxy prophyl methyl cellulose (HPMC), Hydroxy prophyl cellulose (HPC),
Methyl cellulose (MC).

Mesoporous silica: This is a class of molecular sieves with long range ordering as
revealed by a XRD peak at low angle. Al-containing mesoporous silica viz., Al-
MCM41 is synthesized by the hydrothermal treatment of aluminosilicate
precursor with required Si/AI ratio using a surfactant cetyltrimethylammonium
bromide as templates as per method disclosed elsewhere. The powder X-ray
diffraction technique confirmed the formation of a mesoporous structure. The
mesoporous powder was characterized by nitrogen adsorption-desorption
isotherm to study the porous properties (BET surface area, pore volume and
pore size). The BET surface area is more than 1000m2/g and pore size is 2.6 nm.
Supports preferably Ceramics such as Alumina, mullite, Silicon carbide (SiC), clay
etc., with uniform porosity and pore size distribution. One such preferred support
is porous Silicon carbide with porosity of 40% and uniform pores of 6 microns.
This ensures very good flux through the support. The supports can be in the
form of discs, tubes, multi channel tubes or multi channel honeycombs.
Membrane preparation:
The process of membrane preparation involves preparation of aqueous solution
of cellulose of known concentration preferably 2 to 10% and incorporating Al-
MCM41 powder of known quantity after proper dispersion by sonication and
vigorous mixing and thus obtaining well dispersed homogeneous solution of
cellulose. The concentration of cellulose is controlled to maintain the viscosity of
the solution of coating process. The preferred concentration of high viscous
cellulose is 2 to 10%, more preferably 3 to 5%. The quantity of AI-MCM41
powder is preferably 2 to 20% more preferably 5 to 10%. Higher quantity of Al-
MCM41 powder leads to the higher viscosity of the solution and poor dispersion
of powder in the polymer matrix and hence not preferred.

The solution is coated on the cleaned support by the any one of the known
process Viz: dipping, brushing, spraying, pumping etc to form a uniform thin
layer of membrane on the support. The coated support is dried in room
temperature for 1 day followed by 1 day at 50 C.
The prepared membranes are characterized by SEM, XRD, pore size distribution,
BET, etc. The membranes are tested for single gas permeability of CO2, N2/ CH4
and separation factors of CO2/N2 and CO2/CH4 are evaluated.
The membrane module is fabricated by using Ceramic tubes of 60 mm OD,
40mm ID and 200 mm long. These tubes were coated with composite
membranes and assembled in a membrane modules. The separation of CO2 was
measure by passing CO2 containing gas mixture and analyzing for CO2 in the
feed and permeate.
SEM micrographs of membranes on ceramic support and the cross section were
taken see to observe the distribution of A1-MCM41 particles in the polymer
matrix and the thickness of membrane. The thickness is in the range of 45 to 60
microns.
The separation factors of CO2/N2 at various AI-MCM41 loading is shown in Table
1. The separation factors of CO2/CH4 at various AI-MCM14 loading tested for two
different feed gas concentrations are shown in Table 2 & Table 3.

EXAMPLES:
Example 1: 3 gms of Hydroxyethylcellulose (HEC) was stirred vigorously in 80 mL
of water until the solution became homogenous. Known weight of dry AI-MCM41
particles (i.e., 3, 6 and 10 wt. % with respect to weight of HEC) were dispersed
in 20 mL of water, sonicated for 120 min and added to the above prepared HEC
solution. The whole mixture was stirred for about 24 h to obtain the
homogeneous solution, which was used to coat on SiC discs. SiC discs are of
50mm dia and 2 mm thick. The thin film composite membrane were prepared by
dip coating technique by using SiC discs. The prepared membranes were kept at
ambient temperature for drying; the dried membranes were evaluated to
separate gaseous mixture. The hybrid composite membranes are designated as
HEC/AI-MCM41 (1 wt.%), HEC/AI-MCM41 (5 wt. %) and HEC/AI-MCM41 (10 wt.
%), respectively which contained 1, 5 and lOwt. % of AI-MCM41.
It was found that the AI-MCM41 loading had a significant influence on the
uniformity of the membranes. Thin film hybrid composite membranes formed
were homogeneous at 1, 5 and 10 wt. % loadings of the filler, but non-uniform
and brittle membranes were obtained at higher loadings.
The separation factor of CO2/N2 and CO2/CH4 at various AI-MCM41 loading is
shown in Table 1, Table 2 & Table 3.
Example 2: In this case, the precursor solution used was same as in example 1,
but substrates used was SiC tubes of 60mm OD and 40 mm ID and 200 mm
long. The solution of HEC was prepared with 10% of AI-MCM41 added to it.
Coating is repeated 2 times to get thicker and uniform coating. The coating is
done preferably on the inside surface.

Example 3: In this case, the precursor solution used was same as in example 1,
but substrates used is multi channel tubes of SiC tubes of 25 mm OD with 19
channels of 3mm dia. The solution of HEC was prepared with 10% of AI-MCM41
added to it. Coating is repeated 2 times to get thicker and uniform coating.

WE CLAIM:
1. A supported composite gas separation membrane for separation of CO2
from natural gases or flue gases or coal gas comprising a membrane layer
composed of a polymer matrix with mesoporous silica dispersed in the
said matrix.
2. The gas membrane as claimed in claim 1, wherein the polymer is selected
from Hydroxyethylcellulose, Hydroxy propheyl methyl cellulose, Hydroxy
propheyl cellulose & Methyl cellulose.
3. The gas separation membrane as claimed in claim 1 wherein the said
mesoporous silica has uniform mesopores such as MCM41 which is further
characterized by very high BET surface area in excess of 1000m2/g.
4. A process for preparing a composite separation membrane comprising;
preparing an homogeneous solution of a polymer;
dispersing mesoporous silica particles in the said homogeneous solution;
subjecting the mixture to the step of stirring to obtain a homogeneous
solution;
coating a support with the said solution to form a thin layer and
subjecting the said layer to the step of drying resulting in a membranes.
5. The process as claimed in claim 4, wherein the said support is preferably
porous ceramics selected from Cordierite, Mullite, Alumina, Magnesia,
Zirconia, Spinel, Silicon carbide, Clays or Metakaolin or combination of
these.

6. The method as claimed in claim 4, wherein the said polymer is preferably
Hydroxyethylcellulose.
7. The method as claimed in claim 4, wherein said mesoporous silica particle
is preferably AI-MCM41.
8. The method as claimed in claim 4, wherein said mesoporous silica
optionally contains Alumina, preferably Si/AI ratio of 20 to 100.
9. The method as claimed in claim 4, wherein the preferred concentration of
cellulose is 2 to 10%, more preferably 3 to 5%.
10.The method as claimed in claim 4, wherein AI-MCM41 powder is
preferably 2 to 20% more preferably 5 to 10%.

A novel supported composite membrane for gas separation is disclosed. The gas separation membrane is formed on a porous ceramic support. The membrane layer is composed of a polymer matrix with mesoporous silica dispersed in the matrix. The alumina containing mesoporous material of the MCM41 family is uniformly dispersed in Hydroxyethylcellulose membrane
layer. This increased the selective permeation of CO2 through this composite membranes. The membrane layer formed on silicon carbide supports showed CO2/N2 selectivity of 50 and CO2/CH4 selectivity of 46.