1 of 59

UNIT 2

MEMBRANE PROCESS

2 of 59

THEORY OF MEMBRANE

  • Rate governed separation process
  • Transport of components from higher region concentration to low concentration region using some medium with driving force
  • Chemical potential gradient is the main driving force
  • Energy either absorbed or released by species
  • Free energy available during reaction

3 of 59

THEORY OF MEMBRANE

  • Measured as concentration, pressure, temperature and electrochemical potential gradient

​

4 of 59

THEORY OF MEMBRANE

5 of 59

THEORY OF MEMBRANE

6 of 59

THEORY OF MEMBRANE

  • Feed stream separated into permeate and retentate
  • Separation based on physical and chemical properties of solute in feed stream
  • Phase 1 - Feed / upstream side phase and
  • Phase 2 – permeate / downstream side phase
  • Membrane has ability to transport one component from feed than any other component

​

7 of 59

THEORY OF MEMBRANE

  • Performance of membrane is given by two parameters
      • Selectivity
      • Selectivity expressed by two parameters - retention and separation factor
      • Flow through the membrane – flux
      • Flux – volume passing through membrane per unit time per unit area

8 of 59

THEORY OF MEMBRANE

  • Retention
  • R = (Cf – Cp)/Cf
  • R = 1 – (Cp/Cf)
  • Cf- Solute concentration in in feed side
  • Cp- Solute concentration in permeate side
  • If R=100%, everything retented on surface of membrane
  • If R=0, nothing get retented on surface of membrane

​

9 of 59

THEORY OF MEMBRANE

  • Energy consumption is very low
  • Only the pumping power is considered
  • Hybrid technology is possible

​

​

10 of 59

Membrane

  • Permeable or semi-permeable phase
  • Thin polymeric solid – restrict motion of certain species
  • Barrier between feed stream and one product stream
  • Give one product and a second product- concentrated one

11 of 59

Uses in industry

  • Filtration of micron and sub-micron solid
  • Removal of macromolecules and colloids from liquids
  • Separation of mixtures of miscible liquids
  • Separation of gases & vapors from gas and vapor streams
  • Complete removal of all material, TSS and TDS from water

12 of 59

Reason for selection

  • Low operating cost
  • Higher separation efficiency
  • Faster separation
  • Simplicity in operation
  • Micro and ultra filtration
  • RO/ hyperfiltration
  • No phase change

​

13 of 59

Performance of Membrane

  • Flux
  • Selectivity

14 of 59

Classification of membranes

  • Natural or synthetic
  • Thick or thin
  • Homogeneous or heterogeneous
  • Active or passive transport

15 of 59

Functioning of membrane

  • Depend on structure
      • Symmetric membranes
      • Asymmetric membranes

16 of 59

Symmetric membrane

  • Sintering
  • Casting
  • Etching
  • Extrusion

17 of 59

Asymmetric membrane

  • Phase inversion

18 of 59

Symmetric / isotropic membrane

  • Microporous
  • Non-porous, dense
  • Electrically charged

19 of 59

Asymmetric / anisotropic membrane

  • Loeb sourirajan
  • Thin film composite
  • Liquid membrane

20 of 59

21 of 59

Microporous

  • The simplest form of microporous membrane is a polymer film with cylindrical pores or capillaries
  • Microporous membranes have a more open and random structure, with interconnected pores
  • Very similar in structure and function to conventional filters
  • Pores are extremely small, on the order of 0.01 to 10 micrometer in diameter

22 of 59

Microporous

  • Separation of particles is mainly the function of molecular size and membrane pore size distribution
  • Molecules that differ considerably in size can be effectively separated by microporous membrane

23 of 59

Non-Porous, Dense Membranes

  • Dense film through which permeants are transported by diffusion
  • Driving force - Pressure, Concentration, or electrical potential gradient
  • Separation of various components of a mixture is related directly to their relative transport rates within the membrane
  • Diffusivity and solubility in the membrane material

24 of 59

Non-Porous, Dense Membranes

  • Membranes can separate permeats of similar size if their concentrations in the membrane material (i.e. their solubility) differ significantly.
  • Dense membranes has the disadvantage of low flux unless they can be made extremely thin
  • Most gas separation, pervaporation, and reverse osmosis processes use dense membrane to perform the separation

25 of 59

Electrically-Charged Membranes

  • Also referred to as ion-exchange membranes
  • They can be dense or microporous, but most commonly are very finely microporous
  • pore walls carrying fixed positively or negatively charged ions
  • A membrane fixed with positively-charged ions is called an anion-exchange membrane because it binds anions (negatively charged ions) in the surrounding fluid

26 of 59

Electrically-Charged Membranes

  • Separation is achieved mainly by exclusion of ions of the same charge as the fixed ions on the membrane structure
  • It is affected by the charge and concentration of ions in the solution.
  • This type of membranes is used for processing electrolyte solutions in electrodialysis.

27 of 59

Anisotropic (asymmetric) Membranes

  • Consist of a number of layers, each with different structures and permeabilities
  • Anisotropic membrane has a relatively dense, extremely thin surface layer supported on an open, much thicker porous substructure
  • Separation properties and permeation rates are determined exclusively by the surface layer

28 of 59

Anisotropic (asymmetric) Membranes

  • substructure functions as mechanical support
  • The resistance to mass transfer is determined largely or completely by the thin surface layer
  • The membrane can be made thick enough to withstand the compressive forces used in separation

29 of 59

Anisotropic (asymmetric) Membranes

  • The thin film is always on the high-pressure side of the membrane - feed side,
  • Maximum use of the support layer is made in stabilising the thin film.
  • These membranes had the advantage of higher fluxes, and almost all commercial processes use such membranes.

�

30 of 59

Loeb-Sourirajan Membrane

  • Membranes made by the Loeb-Sourirajan process consist of a single membrane material
  • Porosity and pore size change in different layers of the membrane

31 of 59

Interfacial (Thin-film) Composite Membrane

  • This membrane consists of a thin dense film of highly cross-linked polymer formed on the surface of a thicker microporous support.
  • The dense polymer layer is extremely thin, on the order of 0.1 mm or less, so membrane permeability is high.
  • Because it is highly cross-linked, its selectivity is also high.
  • Interfacial composite membranes are widely used in reverse osmosis and nanofiltration.

​

32 of 59

Liquid Membranes

  • A liquid membrane (LM) is a membrane made of liquid.
  • It consists of a liquid phase (e.g. a thin oil film) existing either in supported or unsupported form that serves as a membrane barrier between two phases of aqueous solutions or gas mixtures.
  • Liquid membranes have become increasingly significant in the context of facilitated transport

​

33 of 59

Liquid Membranes

  • Utilizes "carriers" to selectively transport components such as metal ions at a relatively high rate across the membrane interface.
  • Maintaining and controlling this film and its properties during a mass separation process is difficult
  • The major problem - is stability

​

34 of 59

Liquid Membranes

  • Reinforcement is necessary to avoid break-up of the film
  • Liquid membranes are used on a pilot-plant scale for selective removal of heavy-metal ions and organic solvents from industrial waste streams
  • They have also been used for the separation of oxygen and nitrogen.

​

35 of 59

Liquid Membranes

  • Basic types
  • Emulsion Liquid Membrane (ELM)
  • Immobilized Liquid Membrane (ILM), also called a Supported Liquid Membrane.

36 of 59

Emulsion Liquid Membrane 

37 of 59

Emulsion Liquid Membrane

  • An ELM consisting of a "bubble within a bubble".
  • The inner most bubble is the receiving phase, and the outer bubble is the separation "skin" containing the carriers.
  • Anything outside the bubble is the source phase.

38 of 59

Immobilized Liquid Membrane

  • An ILM is much simpler to visualize.
  • It is made of some kind of rigid polymer membrane, with lots of microscopic pores in it which are filled with organic liquid.
  • The liquid are the carriers that perform the required separation.
  • ILM takes things from one side of the rigid membrane (the source phase) and carries it to the other side (the receiving phase) through this liquid phase.

39 of 59

Immobilized Liquid Membrane

40 of 59

IUPAC Classification

  • Macropores > 50 nm
  • Mesopores 2-50 nm
  • Micropores < 2 nm

41 of 59

Membrane Materials

  • Polymeric
      • Non – polymeric
      • Hybrid matrix
      • Bipolar

42 of 59

Membrane Materials

  • Natural type
  • Wool
  • Rubber
  • Cellulose
  • Synthetic
  • Polyamide
  • Polystyrene
  • Teflon

43 of 59

Membrane Materials

  • Metal
  • Ceramic
  • Carbon
  • Zeolite

44 of 59

Membrane modules

  • Membrane module is the way the membrane is arranged into devices and hardware to separate the feed stream into permeate and retentate streams.
  •  The term module is used to describe a complete unit composed of the membranes, the pressure support structure, the feed inlet, the outlet permeate and retentate streams, and an overall support structure.

45 of 59

46 of 59

47 of 59

Membrane modules

  • Plate and frame
  • Tubular
  • Spiral wound
  • Hollow fiber

48 of 59

Plate-and-Frame Modules�

  • One of the earliest types of membrane system
  • Relatively high cost
  • Largely replaced in most applications by spiral-wound modules and hollow-fiber modules
  • Plate-and-frame modules are now used only in electrodialysis and pervaporation systems
  • Limited number of reverse osmosis and ultrafiltration applications with highly fouling conditions

​

49 of 59

Plate-and-Frame Modules�

50 of 59

Tubular Modules�

  • Limited to ultrafiltration applications
  • For which the benefit of resistance to membrane fouling outweighs the high cost.
  • Tubular membranes contains as many as 5 to 7 smaller tubes, each 0.5 to 1.0 cm in diameter, nested inside a single larger tube.
  • In a typical tubular membrane system, a large number of tubes are manifolded in series.
  • The permeate is removed from each tube and sent to a permeate collection header.

​

51 of 59

Tubular Modules

52 of 59

Spiral-wound modules�

  • Industrial-scale modules contain several membrane envelopes, each with an area of 1 to 2 m2, wrapped around the central collection pipe
  • Multi-envelope designs minimize the pressure drop encountered by the permeate travelling toward the central pipe
  • The standard industrial spiral-wound module is 8-inch in diameter and 40-inch long�

​

53 of 59

Spiral-wound modules�

54 of 59

Spiral-wound modules

  • The module is placed inside a tubular pressure vessel
  • The feed solution passes across the membrane surface, and a portion of the feed permeates into the membrane envelope, where it spirals towards the centre and exits through the collection tube
  • 4 to 6 spiral-wound membrane modules are normally connected in series inside a single pressure vessel. A typical 8-inch diameter tube containing 6 modules has 100 to 200 m2 of membrane area.

​

55 of 59

Hollow-fibre Modules�

  • Hollow-fibre modules are characteristically 4-8 inch (10-20 cm) in diameter and 3-5 (1.0-1.6 m) feet long.
  • Hollow-fibre units are almost always run with the feed stream on the outside of the fibre.
  • Water passes through the membrane into the inside or "lumen" of the fibre.
  • A number of hollow-fibres are collected together and "potted" in an epoxy resin at both ends and installed into an outer shell.

​

56 of 59

Hollow-fibre Modules�

57 of 59

Hollow-fibre Modules

58 of 59

Hollow-fibre Modules�

  • Hollow-fibre membrane modules are formed in 2 basic geometries:

(a) shell-side feed design

(b) bore-side feed design

59 of 59

Hollow-fibre Modules�