FIELD OF THE INVENTION
The present invention relates to a porous titania membrane with defined,
uniform and unimodal pores for solid-liquid separation devices. The invention
further relates to a method of manufacturing a titania membrane for solid-liquid
separation device.
BACKGROUND OF THE INVENTION
In comparison with the existing polymeric membranes, a ceramic filter in which a
porous membrane having pores of a smaller diameter is formed on the surface of
a ceramic porous substrate, is useful as a filter, for a solid-liquid separation in
view of a high reliability due to its excellent physical properties and durability, in
view of a very small deterioration even after cleaning by acids or alkalis due to
its high corrosion resistance and, further, in view of being capable of precisely
controlling a pore diameter upon which filtering ability-depends.
In general, a ceramic porous membrane can be obtained by a process in which
a slurry comprising ceramic particles is deposited on the surface of a substrate,
and then fired at a high temperature of not less than 1300 DEG C to thereby
solid-phase sinter the ceramic particles with each other. This generally results in
a membrane of pore size in microns to sub microns and pore size can be
controlled by the particle size of the ceramic particles in the slurry. To obtain
membranes of much smaller in size ie below 500 nm, a sol of the ceramic
precursor is coated and heat treated to get a thin film. The firing temperature is
generally lower than 1300°C.
There are many methods of forming ceramic membranes mainly Alumina, ZrO2
and SiC which are variants of the general methods discussed above.
EP 0850680 discloses a method of manufacturing a ceramic porous membrane
where in 1 to 30% by weight ceramic sol is added to the ceramic particles and
depositing or molding the resulting mixture, and heat treating the resulting film
or molded product at lower than 700 DEG C.
RU2190461 discloses a ceramic membrane filter of asymmetrical structure
includes layer of porous carrier and one or several microporous layers of particles
of inorganic powder. Each layer consists of particles of similar size and has
spherical shape; average sizes of particles in layer of carrier and microporous
layers are related as 6:1.
CN 1899680 describes an asymmetric porous ceramic ultra-filtering membrane
with high permeability, prepared with nanometer metal oxide fiber to replace
conventionally used metal oxide grain as the transition layer and separation layer
film material, and porous alpha-alumina ceramic substrate. Compared with
available ceramic ultra-filtering membrane prepared with micron metal oxide
grains this showed a two times higher pure water permeability.
JP 2002253915 describes a method in which pulverized organic polymer gel is
added to the slurry for manufacturing a filter with a ceramic porous membrane.
WO 2007051643 discloses a method for preparing a ceramic microporous
membrane made of ZrO2 and/or TiO2 on a support membrane, using a polymeric
solution comprising polymeric ZrO2 particles, TiO2 particles and mixtures thereof,
an alcohol amine and a solvent and firing the support membrane applied with
the polymeric solution, thereby forming the microporous membrane on the
support membrane.
US 2001001453 describes an inorganic nanofiltration membrane with a
detachment threshold between 100 and 200 daltons. The membrane comprising:
a multichannel ceramic monolith support consisting of a mixture of AI203 and of
TiO2, a microfiltration membrane separating layer, and ultrafiltration membrane
separating layer, preferably consisting of ZrO2, a, nanofiltration membrane
separating layer, preferably consisting of ZrO2, and obtained by a sol-gel type
method. This inorganic nanofiltration membrane is designed for use in the sugar
industry.
US 2008092502 describes a method for making a microporous ceramic material
using a metal silicon powder and including a reaction sintering process of the
silicon. JP 2007131528 & JP 2004083354 provide methods for manufacturing a
non-oxide porous ceramic material suitable for being used as a substrate for a
ceramic separation membrane:
EP 0585152 discloses a porous ceramic monolithic support for an inorganic
membrane made from Alumina grains partially coated with TiO2 grains, used for
a monolithic support with micro and ultrafiltration membranes. Here TiO2 is
coated on AI203 grains and the pore size of the filter is 1 to 20 microns.
According to JP 62149309, liquid dispersion of ceramic particles is filtered by a
cross flow by using an organic filter membrane such as cellulose which is burnt
during baking to obtain a dense and thin membrane. JP 61174918 discloses a
production process of multi-layered filter by casting one kind of ceramic powder
slurry different in the average grain size into a mold. Both of these methods
limited to make disk type membranes.
JP 2003230823 discloses a ceramic filter which has a titania separation layer
having an average pore diameter of 0.08 to 1 microns and a membrane
thickness of 5 to 20 microns to provide a ceramic filter which is excellent in both
fouling resistance and bacteria-removing property and is suitable for water
purification treatment.
CN 101053781 discloses a method for preparing TiO2 ceramics micro-filter film
on the porous stainless steel matrix. Titanic acid four dinbutyl phthalate is
hydrolyzed to get TiO2 sol. The TiO2 ceramics micro-filter film with an aperture
of 0.3-0.8 mum can be prepared on the porous stainless steel matrix with an
aperture of 1 micron.
CN 1401417 discloses a reverse-osmosis separating membrane with high
resistance to scale deposit is prepared through hydrolyzing Ti compound in acidic
aqueous solution to generate TiO2 nanoparticles, dispersing them in anaqueous
solution (pH=l-6 or 9-13), and dipping the reverse-osmosis separating
membrane in it for fixing said TiO2 nanoparticles on it.
WO 2008050812/ US 2010193438/EP 2258465 discloses a ceramic filter provided
with a ceramic porous membrane/filter includes : a porous substrate which is a
microfiltration membrane, a titania UF membrane formed on the porous
substrate and has an average pore size of 2 to 20 nm and an average thickness
of 0.1 to 1.0 microns, and a silica membrane which is formed on the titania UF
membrane. Here, TiO2 membrane is prepared by using TiO2 sol over which SiO2
membrane is formed.
US 2008105613 describes a ceramic filter formed by different multi-layers
membranes with final layer of Carbon TiO2 layer is formed using TiO2 sol.
US 7,655,277 describes a titania composite membrane for separating
water/alcohol mixtures and TiO2 membrane is prepared by using TiO2 sol. US
7,717,272 disclosed a ceramic porous membrane formed in which TiO2
membrane is prepared by using TiO2 sol over which SiO2 membrane is formed.
JP 2002012422 discloses a manufacturing process which uses polyol and a 4-
valence titanate and/or a 4-valence titanium compound expressed by the general
formula Ti(OR)4, wherein R represents an alkyl and/or an aryl for forming a
titania membrane. WO 2007051643 also uses very expensive polymeric sol of Ti.
CN 101306358 discloses a method of forming Titanium dioxide nanometer film
on the aluminum matrix by using mixture containing ethanol, Polyethylene glycol
is added into complex crystal nanosize titanium dioxide powder. CN 101187021
provided is a process for preparing titanium dioxide membrane on the Ti metal
by acid & thermal treatment.
US 5342521 describes a reverse osmosis or nanofiltration membrane and to its
production process. Mesoporous TiO2 (<10nm) coated first followed by polymer
membrane coating.
JP 10235172 & EP 0850681 respectively describes production processes in which
upto 30% sol is added to the slurry and coated and fired at low temp of 700
DEG C. But not for TiO2 sol.
Most of the above referred prior-patents disclose the preparation of ceramic
membranes of Alumina, ZrO2 or silicon carbide. However, the prior art is silent on
TiO2 membrane, which possesses excellent properties such as thermal stability,
mechanical strength and good permeability of water due to the hydrophilic
property of the titania surface layer. TiO2 can also be used as support as well as
final separating layer. TiO2 support or membrane can be prepared at much lower
temperature compared Alumina support or membranes. There are few
disclosures related to TiO2 based membrane.
Nevertheless, in many of the prior art methods, costly Ti sol is used to make
TiO2 membranes of pore size in nm range and when TiO2 particles are used they
results in pores of above 100nm, moreover separate firing process is required. It
is advantageous as observed by the inventors to use a precursor which are not
costly chemicals but a commercial raw materials of TiO2 which gives membrane
of pore size below 100nm and also the sintering temperature is synchronized
with that of support or intermediate coating to reduce the firing steps.
OBJECTS OF THE INVENTION
It is therefore, an object of the invention to propose a porous titania membrane
with defined, uniform and unimodal pores for solid-liquid separation devices.
Another object of the present invention is to propose the invention further
relates to a method of manufacturing a titania membrane for solid-liquid
separation device, which produces the membrane on a porous support at a low
temperature by using inexpensive titania precursor.
A still another object of the present invention is to propose the invention further
relates to a method of manufacturing a titania membrane for solid-liquid
separation device, in which the source of Titania is an intermediate product of
Titania production such as hydrated titania or meta titanic acid.
SUMMARY OF THE INVENTION
In one aspect of the present invention, there is provided a method of
manufacturing a titania porous membrane, which comprises the steps of mixing
of ceramic bonding material to titania precursor powder and preparing a slurry
with a solvent including organic binder, depositing the resulting slurry on to a
support body and firing at low temperature of below 1250°C The porous
membrane is prepared using raw materials which is an intermediate product of
Titania production from minerals. The preferred source is meta titanic acid or
hydrated titania which is an intermediate product of titania or rutile production
from lliminite like minerals.
In another aspect of the invention, there is provided a porous ceramic membrane
on a porous body comprising a thin layer of titania having uniform pore size
between 20 to 50 nm, the porous body having pore size of 0.5 to 2 microns
which constitutes an intermediate layer formed on a base support supporting
the porous body and having a pore size of 2 to 30 microns.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
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.
The preferred embodiment of the invention will now be described with reference
to the accompanying drawing in which
Figure 1 : Shows a SEM photograph of membrane coating on ceramic support
showing different membrane layers and the corresponding pore distribution of
membrane pores according to the invention.
TABLE 1 : Shows characteristics of Titania membranes according to the
invention.
EXAMPLE 1:
42g of PVB (Ploy vinyl Butyral) is added to 2000 mL of Ethanol while stirring the
solution for 2 hrs. 45.3 gms of ceramic bond and 230 gms of hydrated TiO2 are
mixed thoroughly and added to the above solution 200 ml of PVP solution is
added and stirred vigorously for another 2Hrs.
The silicon carbide tubes of 30 mm diameter and 500 mm long with 19 channels
having pore size of 8 microns is used as supports which are coated with SiC
membranes. They are boiled in water and dried, on a vertical stand. Then the
slurry is pumped for 4 minutes continuously though the tubes using peristaltic
pump at 160rpm. After draining they are dried and fired at temperature of 1230
°C for 2 hr.
The obtained membrane has uniform thickness of about 35- to 50 microns and
unimodal pores of 50 nm as shown Fig. 1 and the characteristics as given in
Table l.
EXAMPLE 2
The silicon carbide supports and membrane used are unfired. The coating of
TiO2 membrane is prepared as per above Example 1. The coated tubes are dried
at 100°C and then sintered at a temperature of 1230°C.
The obtained membrane has uniform thickness of about 30 microns and
unimodal pores of 50 nm and the characteristics are matching. The water flux is
4000 Lit/M2/H and Slit density Index (SDI) of <3 when used for Effluent
Treatment Plant.
DETAIL DESCRIPTION OF THE INVENTION
According to the present invention, fine powders of titania raw material is mixed
with ceramic bond, organic binders and a solvent to form a slurry, depositing the
slurry onto a support by one of a known methods, and firing the support body at
a low temperature the base support and the porous body for coating the
membrane being a porous ceramics with uniform porosity and pore size
distribution. According to one embodiment, the base support is porous Silicon
carbide with porosity of 40% and uniform pores of 8 microns, on which a porous
layer of silicon carbide membrane is formed having a pore size preferably 0.5 to
2 microns. This ensures very good flux through the support. The supports can be
in the form of discs, tubes, one end closed candles, hollow fibres, multi channel
tubes or multi channel honeycombs.
In the present invention, ceramic bond is formed by using a mixture of powder
which is prepared by grinding mineral sources for Si, Al and alkaline/alkaline
earth fluxes preferably Si and Al source is clay which is more than 50% of the
total weight of the mixture and total flux preferably consists of more than 2
mineral sources and its weight ratio is not more than 30% of the total weight of
the mixture. The step of depositing the slurry can be implemented by one of the
known techniques such as dipping, spraying, and coating. The solvent used for
preparing the slurry is preferably an alcohol. The porous ceramics is selected
from a group consisting of alumina, mullite, TiO2, Silicon Carbide (SiC) , and
clay. The temperature for low-temperature filing of the supports is between 1200
to 1250°C.
The ceramic bond in this invention is preferably 10 to 25% by wt of the Titania
raw material and used such that the same bond is used for the bonding of
ceramic grains in the raw support, fine ceramic grains in the porous intermediate
layer coating as well as TiO2 particles in the membrane layer such that the
membrane layers are cured in a single firing at temperature of below 1250 DEG
C.
The Titania membrane prepared by this invention can be used a filter or
membrane for prefiltration of water or particulate removal from liquid or gas,
The TiO2 membrane prepared by this invention can also used as a support for
forming nano porous or mesoporous membranes such as Alumina, TiO2, SiO2,
ZrO2 for ultra or nano filtration of liquids or micro porous materials such as
Zeolites for gas separation applications. In one such application membrane based
on Titania (TiO2) with 50 nm pore size is prepared on SiC support of 8 microns
having an intermediate layer of SiC membrane of 2 microns pore size. Such
membranes are prepared on SiC supports of 25 mm diameter and 0.5 to 1m long
tubes having 19 channels. Such membrane showed water flux rate of above
4000 Lit/M2/H and Slit density Index (SDl) of below1 3 when used for Effluent
Treatment Plant.
WE CLAIM :
1. A method of manufacturing a titania membrane for solid-liquid
separation devices, comprising the steps of:
- mixing a raw material in the form of fine powders of titania with ceramic
bond, organic binders, and a solvent to form a slurry;
- preparing a porous support having a base support;
- depositing the slurry onto the support body by a known deposition
technique; and
- firing the deposited supports at a low temperature for a predetermined
period.
2. The method as claimed in claim 1, wherein the organic binder and the
solvent can be selected as Polyvinyl. Butyral (PVB) and ethanol
respectively and stirred for about 2-hrs under environmental conditions
to form a solution, wherein the ceramic bond and the raw material for
Titania can be respectively selected as mixture of powder which is
prepared by grinding mineral sources for Si, Al and alkaline/alkaline
earth fluxes and meta titanic acid or hydrated TiO2, and wherein the
solution is added to the ceramic bond and the raw material and Stirred
for another 2 hrs.
3. The method as claimed in claim 1 or 2, wherein the solution is
prepared by adding around 40 gms of PVB and 2000 ml of ethanol
wherein ceramic bond about 45 gms and hydrated TiO2 are mixed, and
wherein 200 ml of the solution is added to the mixture of ceramic bond
and hydrated TiO2.
4. The method as claimed in claim 1, wherein the supports are formed by
coating with SiC, a multi-channel silicon carbide tube having pore size
of about 8 microns.
5. The method as claimed in any of the proceeding claims, wherein the
coated tubes are dried at about a temperature of 100°C and sintered
at a low temperature of 1200°C to 1250°C.
6. The method as claimed in claim 1, wherein the supports are optionally
boiled in water and dried on a vertical stand, followed by depositing of
slurry, draining-out the slurry, drying, and heating the coated supports
at said low temperature.
7. A porous titania membrane with defined, uniform, and unimodal pores
for solid-liquid separation devices, comprising :
- a porous body having pore size between 0.5 to 2.0 microns;
- a base body supporting the porous body having pore size between 2 to 30
microns; and
- a membrane comprising a thin layer of titania and applicable to the
porous body having pore size between 20 to 50 nm.
8. A method of manufacturing a titania membrane for solid-liquid
separation devices as substantially described and illustrated herein
with reference to the accompanying drawings.

The invention relates to a method of manufacturing a titania membrane for solid-
liquid separation devices, comprising the steps of mixing a raw material in the
form of fine powders of titania with ceramic bond, organic binders, and a solvent
to form a slurry; preparing a porous support having a base support; depositing
the slurry onto the support body by a known deposition technique; and firing the
deposited supports at a low temperature for a predetermined period.