FIELP OF INVENTION
The present invention generally relates to inorganic porous membranes adapted for
use in filtration, gas separation including a process for the production of the inorganic
porous membranes. The Present invention in particular relates to a method for making
ceramic membranes with tailored pores in the range of 0.6 urn to 50 nm which is a
separation film formed on the inner surface of the channels of the micro porous support
tube. More particularly, the present invention relates to a method of coating membrane
layers for liquid filtration onto a ceramic micro porous support tube of single or multi
channel and forming single or multi layers of porous membrane as a separation film.
The invention further relates to a system for coating a plurality of multi channel micro
porous support tubes for volume production.
BACKGROUND OF THE INVENTION
Filters utilizing a ceramic porous membrane as separation films are more useful as
solid-liquid separation filters when compared to polymer membrane as a separation
film. It has many advantages over the conventional filtration systems with respect to
better efficiency, long term performance, and recyclability, stability to corrosion,
leaching and pH conditions including disposability. In addition to the advantages that

the pore size of the porous ceramic membrane, which determines filtration ability for
micro to ultra filtration range, is precisely controllable. Ceramic ultra-filtration
membrane consists of a micro porous substrate made of ceramic material such as
alumina or zirconia over which layer or layers of ceramic membranes are formed
such that the effective pore size at the membranes are controlled in the range of 50 -
500 nm. The membrane layers are formed by sol-gel process, where a stable
suspension of fine particles of size 20-25 nm are prepared and stabilized in colloidal
suspension called sol. The sol is deposited uniformly over the porous substrate and then
dried without any stresses to avoid development of cracks, followed by annealing so as
to ceramically bond the particles to the substrate. There are many references in
publication to form such sol gel based membrane layer formation including those as
referred in 5-9.
The filter described hereinabove may be manufactured according to conventional
methods by depositing a slurry containing framework particles to form a film, such as a
dipping method or vapour phase method , followed by drying and firing the deposited
film such as described in US Patent 4,929,406. US patent 5,269,926 describes a
method for formation of micro porous ceramic membranes onto a porous support which
includes placing a colloidal suspension of metal or metal oxide particles on one side of
the porous support and exposing the other side of the porous support to a drying
stream of gas or a reactive gas stream so that the particles are deposited on the drying

side of the support as a gel. The gel so deposited can be sintered to form a supported
ceramic membrane. However, these known processes are not versatile for development
of porous membranes having a sharp pore size distribution.
US 6,509,060 discloses a slurry deposition method using a filtration deposition
technique which uses vacuum as well as organic polymer by which film defects such as
pin holes are prevented from being generated,
In the above filtration deposition method, the face of the porous substrate to be
provided with a separation film is isolated to be airtight from the face of the porous
substrate not provided with the separation film in a vacuum chamber, after substituting
air in the fine pores inside of the porous substrate with a liquid. Then, a film deposition
slurry containing ceramic framework particles is allowed to contact the face of the
porous substrate to be provided with the separation film by continuously feeding the
slurry thereon, and a differential filtration pressure is applied between the face of the
porous substrate to be provided with the separation film and the other face, thereby
depositing a slurry film on the desired surface of the porous ceramic substrate,
slurry feed rate determines the film deposition rate.

US 7608298 describes a method of manufacturing a ceramic porous membrane on
inner wall surfaces of through holes of a porous base member. The through holes of
the base member are arranged in a vertical direction, a ceramic sol liquid having a
temperature difference of 50° C. or less between the sol liquid and the base member is
supplied to the inner wall surface of the base member, the liquid supply is stopped
when the sol liquid exceeds an upper end portion of the base member, and then the sol
liquid is extracted from the bottom of the base member. After the sol liquid is
completely extracted, a pressure difference is created so that a pressure on the side of
an outer peripheral surface of the base member becomes lower than that on the side of
the inner wall surface of the base member
The technical problems of the known arts as described hereinabove arise from the fact
that the differential pressure applied on the substrate during deposition of the filtration
film varies depending on the sites on the substrate.
The prior art is delimited to application of a single layer on a micro porous support
tube and does not lend itself for multi layer membrane coatings including nano porous
coating layers . Thus, adapting the multilayer coating for multiplicity of tubes
simultaneously, the vacuum application poses an enormous difficulty.

The present inventors observed that addition of an organic polymer to the film
deposition slurry provides the deposition film layer a filtration resistance. In addition, a
liquid enrichment on the support tube pores including a vacuum on the side of surface
not coated with membrane film facilitates manufacturing of membranes having sharp
pore-size distribution.
The present inventors have further studied various aspects such as slurry sol
optimization, binder and additive optimization, design of coating system, influence of
process parameters and controlling thickness of membrane layers , drying method and
firing including the parameters relating to control of thickness and pores, multi layer
coating and co firing of multi layer membrane coatings . The detailed investigation has
provided a technical solution to the prior art disadvantages in the form of the invention
disclosed herein.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a method for manufacturing a filter having
a uniform film thickness, smooth film surface and sharp micro-pore size distribution
obviating the need for substituting the micro porous support tube with liquid ,
obviating the need of vacuum for creating the differential pressure to form a film on
surface to be coated and also facilitate multi layer coating with same set up sequentially
and also change the flow direction for multilayer coating by simply rotating the fixture
by 180 degrees and proceeding with the coating process. The automation through PLC

allows flexibility to control the process for variety of porous substrates and coating
medium from slurry to sol gels.
According to the method of the present invention, porous membrane of a desired
parameters can be manufactured by appropriately setting the slurry deposition
conditions and slurry compositions. Since the manufacturing method and the system
described is able to form multiple membranes simultaneously with required
characteristics, it is quite useful for easy manufacture.
While the methods according to the present invention will be described in detail in the
examples, the present invention is by no means restricted to these examples.
Thus, there is provided in one aspect a method of coating membrane layers for liquid
filtration onto a ceramic micro porous support tube of single or multi channel and
forming single or multi layers of porous membrane as a separation film, comprising the
steps of: providing an apparatus for coating multiple micro porous support tubes
simultaneously; preparing coating slurry and sols tailored for the coating process;
forming uniform thickness on the inside of the channel for support tubes up to 1.2
meter length; vertically disposing a porous substrate including assembling multiple
support tubes for simultaneously coating by depositing the slurry or sols on inner
surface of the channels of micro porous substrate tubes to obtain a required thickness
including uniform membrane layers.

In another aspect of the invention, there is provided A system for coating a plurality of
multichannel micro porous support tubes, comprising a Perspex covering chamber (4)
having one each top and bottom reservoirs (7,8) on which a plurality of micro porous
support tubes disposed for coating; a main reservoir (1) operably attached to a
peristaltic pump (2) and containing the slurry or sol; a plurality of valves (V1, V2, V3)
based on predetermined timings to allow overflowing of the slurry from the main
reservoir (1) through a tube for coating the support tubes; and the flow of the slurry
including its residual time is adjusted at a receding rate based on the optimized process
parameters.
OBJECTS OF THE INVENTION
Accordingly, it is an object of the present invention to propose a method for
manufacturing a filter having a uniform film thickness, smooth film surface and sharp
micro-pore size distribution with membranes formed on the surface of micro porous
support tubes.
Another object of the present invention to propose a method for manufacturing a filter
having a uniform film thickness, smooth film surface and sharp micro-pore size
distribution with membranes formed on the surface of micro porous support tubes,
which eliminates the need for substituting the micro porous support tube with liquid.

A still another object of the present invention to propose a method for manufacturing a
filter having a uniform film thickness, smooth film surface and sharp micro-pore size
distribution with membranes formed on the surface of micro porous support tubes,
which eliminates the need of vacuum for creating the differential pressure to form a
film on surface to be coated
Yet another object of the present invention to propose a method for manufacturing a
filter having a uniform film thickness, smooth film surface and sharp micro-pore size
distribution with membranes formed on the surface of micro porous support tubes,
which is enabled to modify the slurry or sol to avoid penetration into the micro pores
of the substrate such that the coating is formed during receding levels of the slurry or
sol and ensures an uniform coating film formation by the equilibrium between surface
tension forces including shear and gravity forces of the liquid film.
A further object of the invention is to propose a system for coating ultra porous
membrane layers on micro porous support tubes.
A still further object of the invention is to propose a system for coating ultra porous
membrane layers on micro porous support tubes, which enables an easy change of
direction of the coating if required.

Yet further object of the invention is to propose a system for coating ultra porous
membrane layers on micro porous support tubes , which is enabled to implement the
coating process automatically with flexibility to precisely control the process by simple
parameter settings corresponding to different porous substrates and various coating
medium from slurry to sol gels.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS AND TABLES
FIG. 1 Shows a single membrane coating system used for optimizing membrane
process parameters
Fig 2 : Schematics of a PLC based automated Coating system for coating multiple
membranes according to the invention.
FIG. 3 Graphically exhibits pore size measurements of support and membrane layers
according to the invention.
a. for micro porous support tube,
b. alumina slurry coated first layer membrane
c. Titania sol coated second layer
FIG. 4a SEM micrograph showing a porous membrane formed on a ceramic micro
porous support tube according to an embodiment of the invention.

Fig. 4b is a SEM micrograph showing a porous membrane formed on a ceramic micro
porous support tube according to another embodiment of the invention ( Boehmite+
particle slurry coating and pure Titania sol coating )
Fig.4c is a SEM micrograph showing the porous membrane formed on the ceramic
micro porous support tube according to Example . (Slurry coating & sol-gel titania
coating on slurry coating . H hole region T Top layer (fine coat), I Intermediate layer
(precoat), S Substrate)
Fig.5 Flow characteristics of the coated tubes using pure DI water in a single
membrane test facility
Table 1 : Depicts the coating process conditions and typical characteristics of the
membranes in tabulated form.
Table 2: Exhibits the adhesion strength of membranes on alumina substrate
Table 3 Flow characteristics of the coated tubes using pure DI water in a single
membrane test facility
Table 4 Performance of the tubes in a ceramic filtration module at Effluent treatment
facility

DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, there is provided a process and a system to produce
a porous membrane having uniform film thickness and smooth film surface including a
sharp micro-pore size distribution.
The process for manufacturing a membrane filter according to the present invention is
described in detail hereinafter.
An effective synthesis of a ceramic membrane normally requires control over the
following five major processing steps:
a) selection of a support tube,
b) Slurry /Sol preparation
c) Preparation and slurry /sol, and a coating method including a system for coating
on the support tube,
d) Gelling and drying of the supported membrane, and
e) Firing of the supported membrane.
The details of the important processes are described hereinbelow:
Structure

Ceramic membranes normally have an asymmetrical structure composed of at least two
mostly three, different porosity levels. Micro porous top layer, The macro porous
support ensures the mechanical resistance . Several membrane pore sizes can be
tailored to suit specific filtration needs covering the microfiltration, the ultra filtration,
and nano filtration ranges (from 5 µm down to 1000 Daltons). Ceramic membranes are
formed of plurality types of materials (from alpha alumina to zircon). The most common
membranes are made of Al, Si, Ti or Zr oxides, with Ti and Si being more stable than Al
or Si oxides. Other membranes can be composed of mixed oxides of two of the previous
elements
1. Porous Substrate
Porous substrates are selected for coating membrane layers from various available
types. The micro porous support tube is a multi-channel tube having a ratio of
9:400:1:1 outer diameter, lengths, channel diameter, and average wall thickness. The
micro porous substrate has a narrow range of uniform pore size( measured mercury
infiltration method) around 1.2 µm. The substrate is made of high purity alpha alumina
. Porous membrane having a finer sub micro-pore size may be formed on the porous
body by depositing an alumina or titania, alumina titania slurry or the sol the inner
wall surface of the channels.

The material selection for the substrate is not particularly restricted to alumina so long
as the substrate comprises a porous material, and may include others such as low
temperature firing compositions of alumina, titania, mullite, zirconia, or a mixture
thereof may be advantageously used. The configuration of the substrate according to
the invention, may be one of a single channel, honey comb structure,and plate.
However, the process of the present invention may be particularly advantageous when
the film is formed by deposition of a slurry or sol on the inner wall of a tubular
substrate.
2. Coating Slurry for the first layer of membrane resulting pore sizes in the range of
lower microfiltration.
The most critical step in membrane fabrication is the preparation of a stable colloidal
suspension or sol or slurry which then leads to producing membranes whose properties
are both reproducible and controllable. Many variables must be considered in
synthesizing such sols or slurry . Of great importance is the selection of the starting
materials or chemical precursors. This selection is largely dictated by the desired
physical-chemical properties of the final membrane.
The slurry according to the present invention refers to a solution of alumina sol or
alumina Titania sols with alumina or other ceramic particles in the range of 0.3 to 1mm
dispersed in it, for forming a ceramic porous membrane as a separation film by firing

on the surface of the substrate. The term sol according to present invention refers to
solgels of alumina, titania, zirconia or a mixture of them
Preparation of Boehmite sol
AINO3 9H2O in the range of 100 to 150 gms is dissolved in 1 litre water. The
solution is filtered using a filter paper and a funnel. The filtered solution is
heated to around 90° C. Keeping the temperature constant approximately at 90°
C, an ammonium hydroxide solution is added drop wise. Addition of the ammomium
hydroxide solution was continued till the precipitation is completed at pH
7.5 by maintaining the temperature at about 90° C .The precipitate is filtered
while the solution remains hot. The precipitate is washed with distilled water
till it becomes free from nitrates. The precipitate is aged for about 24
hours, and peptized to a stable sol by addition of around 20% HNO3 at
a pH of 3.5. The results indicates that monomodal distribution of sol particle size
can be obtained which are beneficial in resulting similar distribution on the coated
surface. The average particle size boehmite sol is of the order of ~ 64 nm

-
(a) Preparation of alumina boehmite slurry
A porous membrane having a desired sub micron-pore size can be obtained by
appropriately sizing the particles in the slurry . The framework particles having a
relatively small particles size in a range of 0.1 to 1 urn are used herein since the object
of the present invention is to form a porous membrane having a sub micro-pore size of
0.1 to 0.6 urn. The composition of the particles is not particularly restricted, so long as
the particles comprise a ceramic such as alumina, titania, mullite, , or a mixture
thereof.
Approximately 20g boehmite is dissolved in about 500ml distilled water with constant
stirring followed by addition of 10% HNO3 to control the pH at 3. Then alumina
(average particle size of 0.35 micron) of around 80 gm is added, and the pH maintained
at 3 using 10% nitric acid. This is followed by addition of around 2 wt% poly vinyl
alcohol solution to the mixture.
When the binder comprises ceramic sol particles, the slurry should be maintained in an
acidic solution of pH ~ 3 in order to permit the sol particles to be securely dispersed
and stable. The preferable concentration of the particles alumina in the slurry is usually
adjusted to 10 to20%by weight, although it depends on the desired thickness of the
membrane The pure sol results in a membrane thickness of 1-2 urn while still forming
0.6 urn pores by proper treatment and require multiple coatings to get higher

thicknesses in the range of 10- 40 urn required for the typical 0.2 µm porous
membrane layer. In contrast, by using this slurry, coating thickness up to 50 µm are
easily obtained in a single coating under optimized conditions.
3. Sol gel for forming membrane layer to obtain pores in ultra filtration range
Preparation of Titania sol
Titanyl oxysulphate is used as the precursor for the synthesis of nano
titanium oxide. Titanyl oxysulphate is dissolved in 2 litres of distilled
water (0.2 M ) and hydrolyzed by slow addition of ammonium
hydroxide solution under constant stirring at room temperature, until the
reaction mixture attained a pH of around 8. The precipitate obtained is
separated by filtration and washed free of sulphate ions with distilled
water. The precipitate is further dispersed in 4 litres of hot distilled
water and peptized by addition of 20% HNO3 solution up to a pH
2. The results indicates that monomodal distribution of sol particle size can be obtained
which are beneficial in resulting similar distribution on the coated surface. The average
particle size of the titania sol is ~ 27 nm
The sols are prepared in batches of 2 Itrs initially and upscale for making up to 20 Itrs.
The deposition sol coating according to the present invention contains a ceramic or a
compound that is converted into a ceramic by heat treatment . The second layer or
ultra filtration membrane layer is purely formed with sols with sol particle size in the

range of 20 nm as the objective is to form graded pores up to 10 nm for effective
filtration in the ultra filtration range with high permeability . For the UF, membrane
layer pore size is in the range of 10-20 nm and the thickens in the range of 5 urn is
optimized which limit the pressure drop and reduction in permeation
Selecting and Preparing the support : The support tubes are cleaned in dilute nitric acid,
and the alkaline solution removes any grease dirt etc; Tubes were boiled in distilled
water for about 3 hours and dried in an oven at about 110 deg C and stored in the
oven for coating
4. System for coating and membrane coating Method
During the optimization stage, a single tube coating apparatus is used as shown in
Figure.l. The system consists of a tube (GT) attached to a glass jar GJ) The glass jar
(GJ) containing coating solution, and is enabled to move freely up and down direction
using a motor (M) including a ball screw attachment (BSA) . The jar is slowly moved
to upward direction at a speed of 10-30 cms/min. Then it is kept in rest for 1-5 mins
(dwell time) followed by moving slowly downwards at a speed in the same range. An
adjustable valve (V) is used for controlling the slurry sol rates and for dwelling . The
speed of vertical movements of the jar (GJ) can be adjusted based on a graduated
glass tube (GT) extension beyond the ceramic tube (CT) to be coated. In this process,

the coating solution enters in the ceramic tube (CT) and a thin layer of coating solution
is formed on the inner surface of the ceramic tube (CT). After about 15 minutes time,
this tubes (CT) are placed in a humidity oven (GC) for controlled drying. The typical
parameters established in this invention for alumina slurry coating on micro porous
support tube, is a vertical receding rate of 10-20 cm/min which provides a uniform
coating of ~10-50 urn thickness membrane layer. The method further takes into
consideration the parameters of particle concentration in the range of 10-20 %, and
the binder ratios.
Fig-2 illustrates an automated coating system with PLC-based controls for membrane
coating.
The system shown in fig.-2, can accommodate at least seven tubes for simultaneously
coating membrane layers. All the multi channel or single channel tubes are attached to
the system.
The coating apparatus comprising a Perspex covering chamber (4), a main reservoir
(1), having top and bottom flanges, a peristaltic pump (2),one each bottom and top
auxiliary reservoirs (7,8) is formed as a part of top and bottom flanges of the chamber
(4) in which a plurality of micro porous support tubes to be coated are provided . At
least two neoprene seals( 6) are arranged to ensure no leakage of slurry or sols to the
chamber (4) takes place which interalia ensure that the slurry or sol uniformly flow
through all the channels of all the tubes assembled in the apparatus. After fixing the

tubes in the coating apparatus and with the neoprene sealing (6) between the bottom
and top flanges, the top and bottom reservoir flanges are fixed to the chamber flanges.
The slurry in the main reservoir (1) is continuously pumped using the peristaltic pump
(2), and the slurry flows vertically up in the apparatus. On reaching the top of the
apparatus, the slurry or sol is overflows to the reservoir (1) through the tubing and
through a valve V2. At that time the valve (V3) is open and the drain valve (V1), is
closed. After ensuring a complete flow of the slurry,the PLC timings are programmed to
ensure that the pump (2) and the valves (V1,V2 and V3) remain closed. The slurry or
sol in the column in the channels are held for about 2 minutes. After which the
standing slurry or sol is drained through the valve (V3) which is opened by the PLC.
At that time the pump 2, valves V 2 and V3 are closed. The needle valve (V1) in line
with V3 is adjusted for this typical slurry or sols for a receding rate as per the
optimized process . In the present case it is adjusted typically in the range of 15 cm/
min. On complete removal of the slurry or sol and allowing a status quo about 10-15
minutes, the apparatus is opened up to facilitate removal of coated tubes and
transferred to a humidity drier.
For a typical batch of 7 tubes the process of coating one layer takes about 45 minutes
and the process can continue with a set of new tubes assembled in place. The system is
flexibly interfaced with quick couplers that makes the assembly and disassembly

simpler. The apparatus has a chamber holder which is rotatable by 180 ° so that the
coating can be effected in reverse direction if required and that the slurry or sol flows
vertically upward during filling of the channel whose inside surface has to be coated .
Membrane drying and firing
The slurry or sol coatings has a tendency to form drying cracks . According to the
present invention, an organic polymer poly vinyl pyrolidine or PVA is added to the film
deposition slurry or sol and combined with low pressure peristaltic pumping which
increases the resistance to permeate through substrate during coating process thus
preventing plugging of the micro-pores of the porous membrane or previously coated
membrane layers. The binder that act like a crack preventing agent for preventing
cracks from generating during drying is purposely added which further reduces the
stresses. The drying cracks are avoided by careful humidity drying after the coating
process. The coated tubes are dried at about 50° C and about 59 % RH for 24 hrs and
stored outside for firing. The uniformity of coating and general crack free coatings is
verified using fiber optic probe on a regular basis . On forming ultra porous membrane
coating the tubes are dried in humidity drier as per the earlier procedure. Once fully
dried the coated tubes are stored even for sufficiently long time before being fired to
form a membrane tube .

Ceramic membranes do not have sufficient structural strength when dried for practical
applications. Thus, these membranes are sintered to enable physical interactions to
occur between the particles in the membrane and to allow the support and the
membrane to become a coherent mass. As these materials are heated to higher
temperature, there is a concomitant drop in surface area and a loss of membrane
porosity. Therefore, the necessary measures are be taken to sinter these materials
where both these problems can be minimized.
After the drying, alumina boehmite slurry coating first membrane layer can be obtained
by firing at a rate of 3° per min at 600°C, and 1° per min at 1100°C, with 3 hrs
soaking and final titania coating firing at a rate 1° per min at 800°C at 3 hrs soaking.
The firing of coated tubes is carried out in horizontal manner in a kiln at a maximum
temperature of 1000° C for alumina coating. In the process, a batch of 300 tubes are
fired in a regular production kiln . The coated and fired samples are used for initial
physical inspection followed by characterization by different analytical techniques.
The coating process and system of the invention has been tested and verified. The
table 1 stipulates details of process conditions inclusive of details of support tube and
slurry and sols of the invention.

Hg- Porosimetry Results
Porosity measurements using quanta chrome. The mercury porosimetrv results of the
coated samples and processed under optimum conditions are listed in Table 2. Figs. 3
(a,b ,c) show pore size measurement. It can be seen that in the membrane coatings
a uniform micro-pore size with a sharp micro-pore size mono modal distribution in a
narrow range is present.
Uniformity of the film thickness .
Uniformity of the film thickness has been verified from the mean values of the coating
thicknesses from the photographs generated in a scanning type electron microscope
at different sections of the tube from top, bottom and along the longitudinal direction.
The film having a film thickness variation less than 20 % has been taken as an
yardstick for uniformity.
Films adhesion strength
To validate film adhesive strength, a transparent adhesive tape has been used on the
porous membrane of the filter. After peeling the tape, the adhesive strength is found to
be satisfactory when no porous membrane was peeled off at all. The adhesive strength
is further evaluated and found to be poor when a part of the membrane surface was
peeled off. But it is only qualitative. However to quantify the adhesive strength, the
following technique has been adopted:-.

The porous disks of the same extrusion mass have been fabricated and fired. The disc
is coated using the slurry, slurry and sol, and fired along with multichannel tubes. The
adhesion is tested using a pull tester. The coated disks are attached to a 1" diameter
aluminium dolly by using epoxy . After 24 hrs of curing, the dolly is pulled against the
plate by using the pull tester which is calibrated to give the pull load in kgs. It is
noted that the load bearing capacity of the coating can be estimated using the load and
the proportion of the area where the coating has come out from the coated disk. This
directly gives the adhesion strength . The results confirmed a superior adhesion of
coating onto the substrate which is a prime requirement. The adhesion strength on
porous substrates is in the range of 7 kg/sq.cm which is much higher than 1-2 kg/sq.cm
typically observed for sol coating on glass or smooth substrates. The results of adhesion
strength are tabulated in table 2.
Cut off effectiveness
A solution containing a marker of 100ppm is circulated through a bore of the porous
membrane at a speed of 2.5m/sec and at an inlet pressure of 3kg/cm.sup.2 to analyze
the permeate flux of the membrane thereby to calculate a rejection efficiency of the
marker. As the marker, bovin serum albumin (BSA,66KD, diameter: 11 nm ), gamma.-
globulin (mean molecular weight 156,000), Dextran High MW -2,50,000.have been
selectively used . The molecular cut off results are tabulated in table 3.

Corrosion resistance
The porous membranes are immersed in a solution of HCI (PH=0) at 90.degree. C. and
a solution of NaOH (PH=14) for 168 hours to detect the presence or otherwise of pin
holes and cracks in the thin layers by means of a scanning type electron microscope. If
a drying crack is present, the same is tested using a fiber optic probe. The results show
a good corrosion resistance of the coatings
Microstructure
The micro structural analysis of the coatings is carried out using a scanning electron
microscope. The identification of the coating layer on the substrate, coating thickness,
pore size in the coating and in the substrate are some of the main parameters analysed
using this technique. FIG. 4a is a SEM micrographs showing the porous membrane
formed on the ceramic micro porous support tube according to the 'Example', wherein
the membrane layers are formed using re sol coating and slurry of Boehmite with
alumina particle and pure titania sol on the 19 channel mciro porous support tube. As
is evident from the micro graph,the slurry coated membrane layer is optimized for a
thickness in the range of 20 urn and about 5 urn for second layer titania membrane
layer.

FIG. 4b is a SEM micrograph showing the porous membrane formed on the ceramic
-micro porous support tube according to an Example . The regions are marked as H for
hole region, T for Top layer (fine coat), I for Intermediate layer (precoat),and S for
Substrate)
The photographs of Figure 4 C show that the film thickness of the porous membrane
on the surface of the substrate is uniform in the filter and that the smoothness of the
membrane surface is considerably improved.
Performance Evaluation:
The performance evaluation of the coated tubes is carried out first through a single
tube flux measurement by adapting a known flux testing equipment. The system allows
passing the turbid water through a multi channel single tube, and the filtered water
by a trans-membrane route. The amount of filtered water collected is usually measured
per hour and the flow rate is estimated. Further, the water quality is tested by using
various known analytic techniques like pH, Conductivity, NTU and SDI etc.
Pure water flux
Pure water flux is measured using a single membrane test fixture which has the facility
to vary the flow pressure from 0.5 to 6 kg/sq.cm. The permeate output is collected to
estimate the flux rate of the membranes. The same system is also used to estimate the

flux rates for different types of water. Typical performance of a 19 channel, 1000 mm
long uncoated and coated membranes in a single membrane test fixture is shown in
Figure 5.
Flow characteristics in a 10 Cu.M/hr ceramic membrane filtration system for effluent
treatment is evaluated.
The flux rate of any membrane is largely dependent on the application. Flux rates vary
with the fluid, with the temperature (viscosity affects), solids loading of the fluid,
characteristics of the solids, and operating pressure. Because the operating parameters
have such a large impact upon the flux rates, the standardized flux rates stated at STP
with DI water is only a guiding value.
The flow characteristics of the uncoated and slurry coated tube lots are also carried
out in a 31 element filtration module of a one meter-length ceramic membrane test
system available for processing ETP water. The results of water quality on filtration and
flux rates of effluent water in the 31 element filtration module carried-out in a known
effluent treatment plant are tabulated in table 4.
According to the present invention, a porous membrane with a uniform and smooth film
thickness, as well as a sharp micro-pore size distribution, can be formed. The method
according to the present invention is particularly effective in that the slurry can be

deposited in the through-hole with a uniform film thickness in the long size substrates
and in multi channel substrates. The present invention facilitates the multi layer
membrane coatings and the inventive system facilitates multiple tubes to be coated
simultaneously. It is evident that this process and method makes it suitable for
Industrial Applicability.
REFERENCED PATENTS AND PUBLICATIONS
1. US Patent 4,929,406
2. US patent 5,269,926
3. US Patent: 6,509,060
4. US Patent 7,60,8298
Publications

5. S. Anandkumar. S.G.K. Pillai and K.G.K. Warrier," Colloidal processing of alumina
ceramics" Transactions: Ind. Ceramic society, 58(1) (1999) 9- 15.
6. S. Anandkumar, Vijay Raja and K.G.K. Warrier," Effect of nano particulate
boehmite sol as a dispersant for slurry compaction of alumina ceramics",
Materials Letters, 43 (2000) 174-179.
7. Ceramic Membranes for Separation and Reaction By Kang Li, John Wiley & Sons,
Ltd. Date: 2007-06-30.

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8. G. L Messing, S. Kwon, Constrained densification in boehmite-alumina mixtures
for the
fabrication of porous alumina ceramics, J. Mater. Sci., 33 (1998) 913.
9. R. Helming and H. Frenkel, Using nanoscaled powder as an additive in coarse-
grained
powder, J. Am. Ceram. Soc, 84 (2) (2001) 261.

WE CLAIM:
1. A method of coating membrane layers for liquid filtration onto a ceramic micro
porous support tube of single or multi channel and forming single or multi layers of
porous membrane as a separation film, comprising the steps of: providing an
apparatus for coating multiple micro porous support tubes simultaneously;
preparing coating slurry and sols tailored for the coating process; forming uniform
thickness on the inside of the channel for support tubes up to 1.2 meter length;
vertically disposing a porous substrate including assembling multiple support tubes
for simultaneously coating by depositing the slurry or sols on inner surface of the
channels of micro porous substrate tubes to obtain a required thickness including
uniform membrane layers.
2. The method as claimed in claim 1, wherein a cylindrical porous substrates having a
single or multi channels is formed along a longitudinal direction thereof, and wherein
the substrate is formed with end sealing that facilitates slurry or sol to be available
on the bottom and top reservoirs with no leakage to the area having outer surface
of the ceramic support tubes.

3. The method as claimed in claim 1, comprising feeding the slurry or sol from main
reservoir tank through peristaltic pump with a positive flow without excess pressure
enabling generation of a large trans membrane pressure forcing some slurry or sol
to enrich or fill the micro pores of the substrate resulting in drastically reduced flow
and unpredictable filtration characteristics.
4. The method as claimed in claim 1, wherein the feeding of the slurry or sol from
main reservoir tank through peristaltic pump ensures a smooth laminar positive
flow without any bubbles.
5. The method as claimed in claim 1, wherein the coating process initially reduces the
slurry or sol at a pre determined rate through the channel to be coated upon
verification that the slurry level is above the tube lengths by adapting the peristaltic
pump to cause an overflow of the slurry through the top reservoir, the surface
tension of the receding slurry or sol gel being adjusted to maintain an equilibrium
with gravity forces and shear stresses such that an uniform film is deposited on
said inner surfaces of the single or multi channel through-holes of the porous
substrates.

6. The method as claimed in claim 2 or 5, wherein the surface tension of the receding
slurry or sol gel is adjusted through concentration including addition of binders to
get a uniform film deposition on said inner surfaces of the single or multi channel
through-holes of the porous substrate.
7. The method as claimed in claim 2 or 6, wherein the binder reduces the stress during
drying and inhibiting pin hole or cracks formation.
8. The method as claimed in claim 5, wherein liquid enrichment in the pores of
substrate whose inner surface is to be coated with membrane layers is eliminated.
9. The method as claimed in claim 5, wherein creating a vacuum on the outer surface
side of the support tube is further eliminated.
lO.The method as claimed in claim 5, wherein filtration resistant additive to prevent
the slurry or sol to diffuse in to the pores of the substrate is eliminated.
11.The method as claimed in claim 5, wherein the thickness of the separation film
deposited on said first face of the porous substrate or on the previously coated
membrane layer can be optimized in the range of 1 to 40 urn.

12. The method as claimed in claim 5, wherein the coating slurry or sols are tailored to
yield controlled pore size in the range of 0.6 urn, 0.1 urn in the first layer and in
the range of 20 nm in the second layer.
13. The method as claimed in claim 1, wherein the coating can be formed to higher
thicknesses or in multiple layers with small thicknesses or multi layered membranes
with graded pores.
14.The method as claimed in claim 1, wherein it is possible to form successive coating
layers of same slurry or different slurry or sol systems in a multilayer membrane
coatings without complete drying by humidity drying after every coating and
reassembly.
15.The method as claimed in claim 1 or 14, wherein to effect coating directional
change is enabled to ensure homogenous and uniform coatings in long tubes.
16.The method as claimed in claiml, wherein the method steps are fully automated
and precisely controlled being implementable under a programmable logic controller.

17. The method as claimed in claim 1, wherein the method is enabled to implement a
process for multi layer membrane coatings and multiple tube coatings
simultaneously.
18. The method as claimed in claim 1, which is enabled to further implement a
controlled humidity drying process to ensure crack free membrane film including an
optimized firing cycle to yield ceramic membrane tubes adaptable to liquid filtration
applications.
19. A system for coating a plurality of multichannel micro porous support tubes,
comprising:
- a Perspex covering chamber (4) having one each top and bottom reservoirs (7,8)
on which a plurality of micro porous support tubes disposed for coating;
- a main reservoir (1) operably attached to a peristaltic pump (2) and containing
the slurry or sol;
- a plurality of valves (V1, V2, V3) based on predetermined timings to allow
overflowing of the slurry from the main reservoir (1) through a tube for coating
the support tubes; and
- the flow of the slurry including its residual time is adjusted at a receding rate
based on the optimized process parameters.

20. A method of coating membrane layers for liquid filtration onto a ceramic micro
porous support tube of single or multi channel and forming single or multi layers
of porous membrane as a separation film as substantially described and illustrated
herein with reference to the accompanying drawings.

The present invention describes a process and a system for coating membrane layers
on multiple single or multi channel micro porous ceramic support tubes simultaneously
is provided. The invention comprising the steps preparing various membrane forming
slurry and sols and a process and system for coating multiple single or multi channel
micro porous support tubes simultaneously .