Ceramic Membranes by mikesanye

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									Properties, Synthesis & Applications
                 By:
            M.Wadah Jawich
  Gas Separation Membranes
1. Types of Membranes
  A.          Isotropic Membranes
       I.       Microporous Membranes
       II.      Nonporous, Dense Membranes
       III.     Electrically Charged Membranes

  B.          Anisotropic Membranes

  C.          Ceramic, Metal and Liquid Membranes
2. Membrane Processes
  A.          Developed membrane separation industrial technologies
       I.       Microfiltration and Ultrafiltration
       II.      Reverse osmosis
       III.     Electrodialysis

  B.          Developing industrial membrane separation technologies
       I.       Gas separation
       II.      Pervaporation


  C.          To-be-developed membrane separation technologies
       I.       Carrier facilitated transport
       II.      Membrane contactors
       III.     Piezodialysis membrane
3.    Gas Separation Membrane
     Membrane Materials and Structure
       I.     Metal Membranes
       II.    Polymeric Membranes
       III.   Ceramic and Zeolite Membranes
       IV.    Mixed-matrix Membranes


     Applications of Gas Separation Membranes
       I.     Natural Gas Separations
       II.    Dehydration
       III.   H2 Separation
4. Ceramic Membranes for Gas Separation
   Preparation of Ceramic Membranes
     I.     Slip Casting
     II.    Tape Casting
     III.   Pressing
     IV.    Extrusion
     V.     Sol-Gel Process
     VI.    Dip Coating
     VII.   Chemical Vapor Deposition (CVD)
   Industrial Ceramic Membranes
     A.     Zeolite membranes
     B.     Silica membranes
     C.     Carbon membranes

5. Summary and Conclusion
Introduction
 In general, a membrane can be described as a permselective barrier or a fine sieve.

 Permeability and separation factor of a ceramic membrane are the two most
  important performance indicators .

 For a porous ceramic membrane, they are typically governed by :

     Thickness
     Pore size
     Surface porosity of the membrane.
What Does A Ceramic Membrane Consist Of?
 Ceramic membranes are usually composite ones consisting of several layers of one or
  more different ceramic materials.

 They generally have:
      A macroporous support
      One or two mesoporous intermediate layers
      And a microporous (or a dense) top layer.


 The bottom layer provides mechanical support, while the middle layers bridge the
  pore size differences between the support layer and the top layer where the actual
  separation takes place.

   Commonly used materials for ceramic membranes are Al2O3, TiO2, ZrO2, SiO2 etc. or a
    combination of these materials   .
 Most commercial ceramic membranes are in disc, plate or tubular configuration in
  order to increase the surface area to volume ratio , which gives more separation area
  per unit volume of membrane element
SEM micrograph of a layered ceramic membrane for oxygen permeation
A Brief Overview On The Development of Artificial Membranes

 Systematic studies of membrane phenomena can be traced to the
  eighteenth century philosopher scientists.

 Through the nineteenth and early twentieth centuries, membranes had
  no industrial or commercial uses, but were used as laboratory tools to
  develop physical/chemical theories.

 The period from 1960 to 1980 produced a significant change in the status of
  membrane technology.
          Building on the original Loeb–Sourirajan technique. Other membrane
          formation processes, including interfacial polymerization and multilayer
          composite casting and coating, were developed for making high performance
          membranes with selective layers as thin as 0.1 μm or less .

         Methods of packaging membranes into large-membrane-area spiral-wound,
          hollow-fine-fiber, capillary, and plate-and-frame modules were also developed
 By 1980, microfiltration, ultrafiltration, reverse osmosis and electrodialysis
  were all established processes with large plants installed worldwide.

 The principal development in the 1980s was the emergence of industrial
  membrane gas separation processes. The first major development was the
  Monsanto Prism membrane for hydrogen separation, introduced in 1980.

 Within a few years, Dow was producing systems to separate nitrogen from
  air, and Cynara and Separex were producing systems to separate carbon
  dioxide from natural gas.

 The final development of the 1980s was the introduction by GFT, a small
  German engineering company, of the first commercial pervaporation systems
  for dehydration of alcohol.

 Gas separation technology is evolving and expanding rapidly; further
  substantial growth will be seen in the coming years
A- Isotropic Membranes
  1- Microporous Membranes
  2- Nonporous, Dense Membranes
  3- Electrically Charged Membranes

B-Anisotropic Membranes

C- Ceramic, Metal and Liquid Membranes
A. Isotropic Membranes.
 1- Microporous Membranes

      A microporous membrane is very similar in structure and function to a
   conventional filter. It has a rigid, highly voided structure with randomly
   distributed, interconnected pores.


      However, these pores differ from those in a conventional filter by being
   extremely small, on the order of 0.01 to 10 μm in diameter.


      All particles larger than the largest pores are completely rejected by
   the membrane. Separation of solutes by microporous membranes is mainly
   a function of molecular size and pore size distribution.
2- Nonporous, Dense Membranes.

       Nonporous, dense membranes consist of a dense film through which
  permeants are    transported by diffusion under the driving force of a
  pressure, concentration, or electrical potential gradient.



       The separation of various components of a mixture is related directly to
  their relative transport rate within the membrane, which is determined
  by their diffusivity and solubility in the membrane material.
3- Electrically Charged Membranes.

        Electrically charged membranes can be dense or microporous, but are
  most commonly very finely microporous, with the pore walls carrying fixed
  positively or negatively charged ions.

        A membrane with fixed positively charged ions is referred to as an anion-
  exchange membrane because it binds anions in the surrounding fluid.
  Similarly, a membrane containing fixed negatively charged ions is called a
  cation-exchange membrane.

        Separation with charged membranes is achieved mainly by exclusion of
  ions of the same charge as the fixed ions of the membrane structure, and to a
  much lesser extent by the pore size.

        The separation is affected by the charge and concentration of the ions
  in solution.
B. Anisotropic Membranes

      The transport rate of a species through a membrane is inversely
   proportional to the membrane thickness. High transport rates are
   desirable in membrane separation processes for economic reasons; therefore,
   the membrane should be as thin as possible.


      The advantages of the anisotropic membranes is higher fluxes. The
   separation properties and permeation rates of the membrane are determined
   exclusively by the surface layer; the substructure functions as a mechanical
   support.
Anisotropic membranes consist of an extremely thin surface layer supported on a
much thicker, porous substructure. The surface layer and its substructure may
be formed in a single operation or separately
C. Ceramic, Metal and Liquid Membranes

      Ceramic membranes, a special class of microporous membranes, are
   being used in ultrafiltration and microfiltration applications for which
   solvent resistance and thermal stability are required .


      Dense metal membranes, particularly palladium membranes, are being
   considered for the separation of hydrogen from gas mixtures, and
   supported liquid films are being developed for carrier-facilitated transport
   processes
A- Developed membrane separation industrial technologies
  1- Microfiltration and Ultrafiltration
  2- Reverse osmosis
  3- Electrodialysis

B- Developing industrial membrane separation technologies
  1- Gas separation
  2- Pervaporation


C- To-be-developed membrane separation technologies
    1- Carrier facilitated transport
    2-Membrane contactors
    3-Piezodialysis membrane
A- Developed Membrane Separation Industrial Technologies
       1- Microfiltration and Ultrafiltration
            In ultrafiltration and microfiltration the mode of          separation is
       molecular sieving through increasingly fine pores.
       - Microfiltration membranes filter colloidal particles and bacteria

       -Ultrafiltration membranes can filter dissolved macromolecules, such   as
       proteins, from solutions


       2- Reverse osmosis.
            In osmosis membranes the membrane pores are so small and are within
       the range of thermal motion of the polymer chains that form the membrane.

            The accepted mechanism of transport through these membranes is called
       the solution-diffusion model.
3- Electrodialysis
    A charged membranes are used to separate ions from aqueous solutions
under the driving force of an electrical potential difference.

    The process utilizes an electrodialysis stack, built on the filter-press principle
and containing several hundred individual cells, each formed by a pair of anion
and cation exchange membranes.
B- Developing Membrane Separation Industrial Technologies
  1- Gas separation
    In gas separation, a gas mixture at an elevated

  pressure is passed across the surface of a membr-

  ane that is selectively permeable to one com-

  ponent of the feed mixture; the membrane permeate is enriched in this
  species.

     Major current applications of gas separation membranes are the separation
  of hydrogen from nitrogen, argon and methane in ammonia plants; the
  production of nitrogen from air; and the separation of carbon dioxide from
  methane in natural gas operations
2- Pervaporation
      In pervaporation, a liquid mixture contacts
one side of a membrane, and the permeate is
removed as a vapor from the other. The driving
force for the process is the low vapor pressure on
the permeate side of the membrane generated by
cooling and condensing the permeate vapor.

      Pervaporation offers the possibility of
separating   closely     boiling   mixtures     or
azeotropes that are difficult to separate by
distillation or other means (the dehydration of 90–
95% ethanol solutions)
C- To-Be- Developed Membrane Separation Technologies
  1- Carrier Facilitated Transport
           It employs liquid membranes containing a complexing or carrier
  agent. The carrier agent reacts with one component of a mixture on the feed
  side of the membrane and then diffuses across the membrane to release the
  permeant on the product side of the membrane.

 2- Membrane Contactors
           Membrane contactors are devices that allow a gaseous phase and a liquid
  phase to come into direct contact with each other, for the purpose of mass
  transfer between the phases, without dispersing one phase into the other.

           A typical use for these devices is the removal or dissolution of gases in
  water.
3- Piezodialysis Membrane


      If fixed-ions of both anion and cation species are attach to a polymeric
membrane, pressure can be used as the driving force to transport both ions of a
salt across a single membrane, leaving a diluted aqueous stream on the
pressurized side.

      A zeolite-based piezodialysis membranes are being developed for
desalination processes and some medical applications in urology and
cardiology
Membrane Materials and Structure
 I.     Metal Membranes
 II.    Polymeric Membranes
 III.   Ceramic and Zeolite Membranes
 IV.    Mixed-matrix Membranes


Applications of Gas Separation Membranes
 I.     Natural Gas Separations
 II.    Dehydration
 III.   H2 Separation
Theoretical Background

Both porous and dense membranes can be used as selective gas separation barriers; Three types
   of porous membranes, differing in pore size, are shown in the figure below.

     If the pores size = 0.1 to 10 μm :

        => Gases permeate the membrane by convective flow, and no separation occurs.


     If the pores are < 0.1 μm:

          => The pore diameter is ≤ the mean free path of the gas molecules :
          => Diffusion through such pores is governed by Knudsen diffusion, and the
              transport rate of any gas is inversely proportional to the square root of its

               molecular weight.
 If the pores are extremely small, of the order 5–20 A˚

     => gases are separated by molecular sieving.

     => Transport includes both diffusion in the gas phase and diffusion of adsorbed

        species on the surface of the pores (surface diffusion).
Membrane Materials and Structure

1- Metal Membranes
 *- The study of gas permeation through metals began with Graham’s
 observation of hydrogen permeation through palladium.

 *- Hydrogen permeates a number of metals including palladium, tantalum,
 niobium, vanadium, nickel, iron, copper, cobalt and platinum.

 *- In most cases, the metal membrane must be operated at high temperatures
 (>300 ◦C) to obtain useful permeation rates and to prevent embrittlement and
 cracking of the metal by adsorbed hydrogen.

 *-Hydrogen-permeable metal membranes are extraordinarily selective,
 being extremely permeable to hydrogen but essentially impermeable to all
 other gases.
Hydrogen permeation through a metal membrane is believed to follow the
multistep process illustrated in the figure
2- Polymeric Membranes
 *- Early gas separation membranes were adapted from the cellulose acetate
 membranes produced for reverse osmosis.

 *- These membranes are produced by precipitation in water; the water must be
 removed before the membranes can be used to separate gases.
       => The capillary forces generated as the liquid evaporates cause collapse
       of the finely microporous substrate of the cellulose acetate
       membrane, destroying its usefulness.

 *- This problem has been overcome by a solvent exchange process in which
 the water is first exchanged for an alcohol, then for hexane.

 *- Experience has shown that gas separation membranes are far more
 sensitive to minor defects, such as pinholes in the selective membrane layer,
 than membranes used in reverse osmosis or ultrafiltration
3- Ceramic and Zeolite Membranes
 *- These microporous membranes are made from aluminum, titanium or
 silica oxides.

 *- Ceramic membranes have the advantages of being chemically inert and
 stable at high temperatures, conditions under which polymer membranes
 fail.
 *-This stability makes ceramic microfiltration/ultrafiltration membranes
 particularly suitable for food, biotechnology and pharmaceutical
 applications.

 *- These membranes are all multilayer composite structures formed by coating
 a thin selective ceramic or zeolite layer onto a microporous ceramic
 support.
       - Ceramic membranes are prepared by the sol–gel process
       - Zeolite membranes are prepared by direct crystallization, in
       which the thin zeolite layer is crystallized at high pressure and
       temperature directly onto the microporous support.
4- Mixed-Matrix Membranes
 *- The ceramic and zeolite membranes have exceptional selectivities for a
 number of important separations. However, the membranes are not easy to
 make and expensive for many separations.

 *- One solution to this problem is to prepare membranes from materials
 consisting of zeolite particles dispersed in a polymer matrix.

 *- These membranes are expected to combine the selectivity of zeolite
 membranes with the low cost and ease of manufacture of polymer
 membranes. Such membranes are called mixed-matrix membranes.
          Applications of Ceramic Membranes
1- Natural Gas Separations
 *- The major component of raw natural gas is methane, typically 75–90% of the
 total. Natural gas also contains significant amounts of ethane, some propane and
 butane, and 1–3% of other higher hydrocarbons. In addition, the gas contains
 undesirable impurities: water, carbon dioxide, nitrogen and hydrogen sulfide.

 *- To minimize recompression costs at gas processing plants, impurities must be
 removed from the gas, leaving the methane, ethane, and other hydrocarbons in the
 high-pressure residue gas.

 *-Carbon dioxide is best separated by glassy membranes (utilizing size
 selectivity)

 *- Hydrogen sulfide, which is larger and more condensable than carbon dioxide, is
 best separated by rubbery membranes (utilizing sorption selectivity).

 *- Propane and other hydrocarbons, because of their condensability, are best
 separated from methane with rubbery sorption-selective membranes.
The relative size and condensability (boiling point) of the principal components of
 natural gas. Glassy membranes generally separate by differences in size; rubbery
               membranes separate by differences in condensability
2- Dehydration
 *- All natural gas must be dried before entering the national distribution
 pipeline to control corrosion of the pipeline and to prevent formation of solid
 hydrocarbon/water hydrates that can choke valves.

 *- Currently glycol dehydrators are widely used. However, glycol dehydrators
 are not well suited for use on small gas streams or on offshore platforms,
 increasingly common sources of natural gas

 *- Membrane processes offer an alternative approach to natural gas
 dehydration. Two possible process designs are available.

   In the first design, a small one-stage system removes 90% of the water in the feed
   gas, producing a low-pressure permeate gas representing 5–6% of the initial gas
   flow. This gas contains the removed water

   In the second design, the wet, low-pressure permeate gas is recompressed and
   cooled, so the water vapor condenses and is removed as liquid water. The natural
   gas that permeates the membrane is then recovered, but the capital cost of the
   system approximately doubles
Dehydration of natural gas is easily performed by membranes
   but high cost may limit its scope to niche applications.
3- H2 Separation
 *-It is desirable to develop inorganic zeolite membranes that are capable of highly
 selective H2 separation from other light gases (CO2, CH4, CO).

 *-Currently used zeolite membranes have not been successful for H2 separation,
 because they either have zeolite pores too big for separating H2 from other light
 gases or have many non-zeolite pores bigger than the zeolite pores, so called
 defects.

 *-To selectively separate H2 from other light gases (CO, CO2, CH4), the zeolite
 membrane will have to discriminate between molecules that are approximately
 0.3-0.4 nm in size and 0.1 nm or less in size difference.

 *-To accomplish this sieving we need to:

        A- Synthesize zeolite membranes with small pore in this size range

       B- Post-treat existing zeolite membranes to systematically reduce the
          pore size and/or the number of defects.
Preparation of Ceramic Membranes
     I.     Slip Casting
     II.    Tape Casting
     III.   Pressing
     IV.    Extrusion
     V.     Sol-Gel Process
     VI.    Dip Coating
     VII.   Chemical Vapor Deposition (CVD)


Indusrtial Ceramic Membranes
     A.     Zeolite membranes
     B.     Silica membranes
     C.     Carbon membranes
Ceramic Membranes For Gas Separation
 There are two types of ceramic membranes suitable for gas separations: (1) dense
  and (2) porous, especially microporous, membranes.


      Dense Ceramic Membranes are made from crystalline ceramic materials
       such as fluorites, which allow permeation of only oxygen or hydrogen
       through the crystal lattice. Therefore, they are mostly impermeable to all
       other gases, giving extremely high selectivity towards oxygen or hydrogen.

    Microporous Ceramic Membranes with pore sizes less than 2 nm.
         *- They are mainly composed of amorphous silica or zeolites.
         *- They are usually prepared as a thin film supported on a macroporous
         ceramic support, which provides mechanical strength, but offers minimal
         gas transfer resistances.
         *- In most cases, some intermediate layers are required between the
         macroporous support and the top separation layer to bridge the gap
         between the large pores of the support and the small pores of the top
         separation layer.
Preparation of Ceramic Membranes
 In general, preparation of ceramic membranes involves several steps:

  (1) Formation of particle suspensions.

  (2) Packing of the particles in the suspensions into a membrane precursor
  with a certain shape such as flat sheet, monolith or tube

  (3) Consolidation of the membrane precursor by a heat treatment at high
  temperatures.
A generalized flow sheet for preparation of ceramic membranes
             using various conventional methods
1- Slip Casting
   *- When a well mixed powder suspension (slurry) is poured into a porous mould,
  solvent of suspension is extracted into the pores of the mould via the capillary
  driving force or capillary suction. The slip particles are, therefore, consolidated on
  the surface of the mould to form a layer of particles or a gel layer.
2- Tape Casting

  *- The process consists of a stationary casting knife, a reservoir for powder
 suspensions, a moving carrier and a drying zone. In preparing flat sheet ceramic
 membranes, the powder suspension is poured into a reservoir behind the casting
 knife, and the carrier to be cast upon is set in motion.

 *-The casting knife gap between the knife blade and carrier determines the
 thickness of the cast layer. Other variables which are important include reservoir
 depth, speed of carrier and viscosity of the powder suspension.

 *-The wet cast layer passes into a drying chamber, and the solvent is evaporated
 from surface, leaving a dry membrane precursor on the carrier surface.
3- Pressing

  *- The particle consolidation into a dense layer occurs by an applied force. This
 easily handled pressure press method has been frequently employed in screening
 new ionic and mixed conducting materials for development of oxygen or hydrogen
 permeable ceramic membranes.

 *- A special press machine is used to apply more than 100 MPa pressure to press
 powders into a compacted disc. The diameter of the disc is usually a few of cm, the
 thickness is often around 0.5 mm and the disc is dense after firing.
4- Extrusion

 *- The extrusion process is similar to fibre spinning processes, but there are a few
 differences between extrusion and spinning.

   In extrusion: a stiff paste is compacted and shaped by forcing it through a
    nozzle. A requirement is that the precursor should exhibit plastic behavior, that
    is at lower stresses behave like a rigid solid and deform only when the stress
    reaches a certain value called the yield stress.

   In spinning: a viscous solution or suspension is transformed into a stable shape
    in a coagulation bath through a spinneret.

   In addition, the precursor made by extrusion possesses a homogeneous
    structure over the cross section, while it shows an asymmetric structure if
    prepared through the spinning process.
5- Sol-Gel Process

  *- The advantage of the sol-gel technique is that the pore size of the membrane
 can be desirably controlled, especially for small pores.

 *- There are two main routes through which the sol-gel membrane is prepared:

       (1) The colloidal route, in which a metal salt is mixed with water to form a
       sol. The sol is coated on a membrane support, where it forms a colloidal
       gel.

       (2) The polymer route, in which metal–organic precursors are mixed with
       organic solvent to form a sol, which is then coated on a membrane support,
       where it forms a polymer gel.
5- Sol-Gel Process

 *- The Colloidal sols are the colloidal solutions of dense oxide particles such as
 Al2O3, SiO2, TiO2 or ZrO2.

 *- For gas separation based on molecular sieving effects, ceramic membranes with
 pore sizes less than 1 nm must be employed.
        => In this case, the membrane can be prepared through the polymer sol
        route using the γ-alumina membrane as a support.

 *- It should be noted that in the polymer sol route, the pore size of the membrane
 prepared is determined by the degree of branching of the inorganic polymer.

 *- Sols of very small particles are prepared through hydrolysis and condensation
 of their corresponding alkoxides.
        => The partial charges of the metal in the alkoxides and hydrolyses speed
        influence the hydrolysis behavior
6- Dip Coating

  *- The critical factors in dip coating are the viscosity of the particle suspension and
 the coating speed or time.

 *- The drying process starts simultaneously with the dip coating, when the substrate
 is in contact with a atmosphere that has a relative humidity below 100 %.

 *- In a multiple step process, after calcinations of the first layer, the complete cycle
 of dipping, drying and calcination is repeated.
7- Chemical Vapor Deposition (CVD)

  *- Chemical vapor deposition is a technique which modifies the properties of
 membrane surfaces by depositing a layer of the same or a different compound
 through chemical reactions in a gaseous medium surrounding the component at an
 elevated temperature.

 *- CVD system which includes a system of metering a mixture of reactive and carrier
 gases, a heated reaction chamber, and a system for the treatment and disposal of
 exhaust gases.

 *- The gas mixture (which typically consists of hydrogen, nitrogen or argon, and
 reactive gases such as metal halides and hydrocarbons) is carried into a reaction
 chamber that is heated to the desired temperature.

 *- The deposition of coatings by CVD can be achieved in a number of ways such as
 thermal decomposition, oxidation and hydrolysis
Industrial Ceramic Membranes
 In According to the IUPAC definition:
“Microporous membranes are referred to as those with a
          pore diameter smaller than 2 nm”

 There are two main types of microporous membranes used in gas
 separations, namely crystalline zeolite membranes and XRD
 amorphous membranes such as silica, carbon, etc.

  The practically useful crystalline microporous membranes have
 polycrystalline structures, consisting of many crystallites packed
 together without any crystallite (grain) boundary gap in the ideal
 case.
1- Zeolite Membranes
*- Zeolites are crystalline microporous aluminosilicate materials with a regular three
  dimensional pore structure, which is relatively stable at high temperatures.
*- They are currently used as catalysts or catalyst supports for a number of high
   temperature reactions.

*- The unique properties of zeolite membranes are:
   (1) their size and shape selective separation behavior.

   (2) their thermal and chemical stabilities, which are also the general   advantages
      of ceramic membranes.

*- Due to their ‘molecular sieve’ function, zeolite membranes can principally
   discriminate the components of gaseous or liquid mixtures dependent on their
   molecular size.

*- In order to perform the molecular sieving function, the membranes must have
   negligible amounts of defects and pinholes of larger than 2 nm.
2- Silica Membranes
 *- Microporous silica (SiO2) membranes are prominent representatives of
 amorphous membranes.

 *- The first successful silica membranes for gas permeation/separation with good
 quality and high flux were prepared in 1989 using a sol-gel method where SiO2
 polymer sols were firstly prepared by acid catalysed hydrolysis of tetraethoxysilane
 (TEOS) in alcoholic solution.

 *- The acid catalyst reduces hydrolysis but enhances polycondenstion rates during
 the sol preparation process resulting in a polymeric sol containing silica particles of
 fractal structure.

 *- Chemical vapor deposition (CVD) is another method used in preparation of
 microporous silica membranes.
3- Carbon Membranes
 *- Carbon membranes are inexpensive, highly selective due to their pores of
 molecular dimensions.

 *- They are prepared basically by carbonizing organic polymers as starting materials
 at high temperatures under controlled conditions. It is expected that carbonized
 materials are stable at high temperatures and resist chemical attack.

 *-The challenge for carbon membranes is how to increase the gas permeation rate.

        One approach is to make the membranes on mesoporous substrates.
            For example, carbon membranes were prepared by ultrasonic deposition of
             polyfurfuryl alcohol on a porous inorganic support, followed by pyrolysis at
             473–873 K to convert the polymer layer to microporous carbon film.


        Another approach is using asymmetric hollow fiber membrane
         precursors.
 In general, a membrane can be described as a permselective barrier or a fine sieve.


 There are several fields on which membrane technologies are used:

    A. Developed membrane separation industrial technologies (microfiltration and
       ultrafiltration, reverse osmosis , and electrodialysis)

    B. Developing industrial membrane separation technologies (Gas separation and
       pervaporation)

    C. To-be-developed   membrane separation technologies (Carrier facilitated
       transport , membrane contactors, and piezodialysis membrane)

   There are a lot of applications of gas separation membranes ( natural gas
    separations, dehydration, and H2 separation)

   Membrane materials include metal membranes, polymeric membranes, ceramic
    and zeolite membranes , and mixed-matrix membrane.
 Gas separation has become a major industrial application of membrane technology
  only during the past 20 years. Gas separation technology is evolving and expanding
  rapidly; further substantial growth will be seen in the coming years.

 Ceramic membranes, a special class of microporous membranes, are being used in
  ultrafiltration and microfiltration applications for which solvent resistance and
  thermal stability are required.

 Ceramic membranes are usually composite ones consisting of several layers of one
  or more different ceramic materials.

 There are two types of ceramic membranes suitable for gas separations: (1) dense
  and (2) porous, especially microporous, membranes.

    Dense ceramic membranes are made from crystalline ceramic materials
    Microporous ceramic membranes are mainly composed of amorphous silica or
      zeolites
 Dense metal membranes, particularly palladium membranes, are being considered
  for the separation of hydrogen from gas mixtures, and supported liquid films are
  being developed for carrier-facilitated transport processes.

 On the industrial level: There are two main types of microporous membranes used
  in gas separations, namely crystalline zeolite membranes and XRD amorphous
  membranes such as silica, carbon, etc

 Zeolite membrane synthesis is an important new field for development of ceramic
  membrane, the specifications that zeolite have makes it a promising material for
  investigation.

 Several researches are being held for the manufacturing of ceramic membranes for
  gas separation out of zeolite, and there are several other medical and military
  applications that will find its way to the market in the coming years
Thank you

								
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