Gas Separation Membranes

1
Gas Separation Membranes

• Properties, Synthesis Applications
• By
• M.Wadah Jawich

2
Gas Separation Membranes

• Types of Membranes
• Isotropic Membranes
• Microporous Membranes
• Nonporous, Dense Membranes
• Electrically Charged Membranes
• Anisotropic Membranes
• Ceramic, Metal and Liquid Membranes

3

• Membrane Processes
• Developed membrane separation industrial
  technologies
• Microfiltration and Ultrafiltration
• Reverse osmosis
• Electrodialysis
• Developing industrial membrane separation
  technologies
• Gas separation
• Pervaporation
• To-be-developed membrane separation technologies
• Carrier facilitated transport
• Membrane contactors
• Piezodialysis membrane

4

• Gas Separation Membrane
• Membrane Materials and Structure
• Metal Membranes
• Polymeric Membranes
• Ceramic and Zeolite Membranes
• Mixed-matrix Membranes
• Applications of Gas Separation Membranes
• Natural Gas Separations
• Dehydration
• H2 Separation

5

• Ceramic Membranes for Gas Separation
• Preparation of Ceramic Membranes
• Slip Casting
• Tape Casting
• Pressing
• Extrusion
• Sol-Gel Process
• Dip Coating
• Chemical Vapor Deposition (CVD)
• Industrial Ceramic Membranes
• Zeolite membranes
• Silica membranes
• Carbon membranes
• Summary and Conclusion

6
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.

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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

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SEM micrograph of a layered ceramic membrane for
oxygen permeation
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??? 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 LoebSourirajan
  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

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• 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

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Types Of Membranes

• A- Isotropic Membranes
• 1- Microporous Membranes
• 2- Nonporous, Dense Membranes
• 3- Electrically Charged Membranes
• B-Anisotropic Membranes
• C- Ceramic, Metal and Liquid Membranes

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• 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.

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• 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.

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• 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.

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• 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.

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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
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• 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

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Membrane 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

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• 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.

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• 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.

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• 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

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• 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 9095 ethanol
  solutions)

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• 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.

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• 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

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Gas Separation Membranes

• Membrane Materials and Structure
• Metal Membranes
• Polymeric Membranes
• Ceramic and Zeolite Membranes
• Mixed-matrix Membranes
• Applications of Gas Separation Membranes
• Natural Gas Separations
• Dehydration
• H2 Separation

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• 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
• gt Gases permeate the membrane by convective
  flow, and no separation occurs.
• If the pores are lt 0.1 µm
• gt The pore diameter is the mean free
  path of the gas molecules
• gt 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.

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• If the pores are extremely small, of the order
  520 A
• gt gases are separated by molecular sieving.
• gt Transport includes both diffusion in the gas
  phase and diffusion of adsorbed
• species on the surface of the
  pores (surface diffusion).

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Membrane Materials and Structure

• 1- Metal Membranes
• - The study of gas permeation through metals
  began with Grahams 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 (gt300 ?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.

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• Hydrogen permeation through a metal membrane is
  believed to follow the multistep process
  illustrated in the figure

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• 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.
• gt 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

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• 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 solgel
  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.

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• 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.

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Applications of Ceramic Membranes

• 1- Natural Gas Separations
• - The major component of raw natural gas is
  methane, typically 7590 of the total. Natural
  gas also contains significant amounts of ethane,
  some propane and butane, and 13 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.

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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
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• 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 56 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

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Dehydration of natural gas is easily performed by
membranes but high cost may limit its scope to
niche applications.
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• 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.

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Ceramic Membranes

• Preparation of Ceramic Membranes
• Slip Casting
• Tape Casting
• Pressing
• Extrusion
• Sol-Gel Process
• Dip Coating
• Chemical Vapor Deposition (CVD)
• Indusrtial Ceramic Membranes
• Zeolite membranes
• Silica membranes
• Carbon membranes

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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.

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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.

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A generalized flow sheet for preparation of
ceramic membranes using various conventional
methods
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• 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.

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• 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.

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• 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.

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• 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.

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• 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 metalorganic
  precursors are mixed with organic solvent to form
  a sol, which is then coated on a membrane
  support, where it forms a polymer gel.

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• 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.
• gt In this case, the membrane can be prepared
  through the polymer sol route using the
  ?-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.
• gt The partial charges of the metal in the
  alkoxides and hydrolyses speed influence the
  hydrolysis behavior

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• 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.

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• 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

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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.

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• 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.

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• 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.

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• 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 473873 K to convert the polymer layer to
  microporous carbon film.
• Another approach is using asymmetric hollow fiber
  membrane precursors.

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Summary and Conclusion
64

• 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
• Developed membrane separation industrial
  technologies (microfiltration and
  ultrafiltration, reverse osmosis , and
  electrodialysis)
• Developing industrial membrane separation
  technologies (Gas separation and pervaporation)
• 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.

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• 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

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• 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

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• Thank you