modification of existing membranes and properties enhancements

8/10/2019 Modification of Existing Membranes and Properties Enhancements

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Modification of Existing

Membranes and Proper

EnhancementHafiz Imran Akhter Muhammad Nade

2013-MS-PE-1 2013-MS-PE-15


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Introduction

Membrane TechnologyMembrane technology has become an emerging separation tethe past few decades.

Use

We use the membranes in industrial applications for many advaphase changes or chemical additives needed. A modular is simoperation and it is easy to scale up, and relatively low energy co


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Cont..

Material of Construction

Primary material used forinorganic membranes are:

aluminum oxide, zirconium oxide,

Organic materials are:

polysulfone, poly(ether sulfone), polyacrylonitrile, polyamide, popoly(vinylidenefluoride) and polytetrafluoroethylene.


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Driving force

The driving force is pressure difference, concentration gradient, variation and electrical force across the membrane for the permmolecules through a membrane barrier.


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Membrane surface

Surface characteristics are important in membrane separatiomolecules from the feed stream will first contact with the memsurface.

Two common surface features of membrane are

1. hydrophobicity

2. hydrophilicity.

The hydrophobic property is water repellent and prohibiting twettability. Hydrophobic surface resist to spread water and recontact with the surface


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Membranes Modification

Fouling and wetting will reduce the membrane efficiency and dperformance, consequently increasing the operation cost and efailure

Modification of membranes with hydroxyl and ethylene-glycogroups can reduce membrane fouling.


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Cont..

Fouling can be effected by

Increased hydraulic resistance

Changes in colloid surface properties due to organic adsorpt

Membrane fouling depends upon:

i. pH,

ii. ionic composition,

iii. ionic strength and type and

iv. concentration of foulants in the feed water.


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Feed water pretreatment

Pretreatment can reduce fouling potential, increase membramaintain performance level by altering the physical, chemicbiological properties of the feed water

Most frequently processes are used for feed water pretreatm

Coagulation

The role of coagulants is to effectively neutralize same charges asuspended solids to group together in flocs


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Activated carbon adsorption

Adsorption is an important way to remove soluble non-polar orgin water, natural organic matter as well as emerging pollutants sendocrine disrupting compounds.

Activated carbon adsorption, either in granular or powder form,

considered as a feasible mean for reducing membrane fouling, in combination with other pretreatment processes.

Filtration


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Chemical agent addition

Acid addition

Antiscalant addition

Disinfectant addition

Disinfection is a necessary and effective way to kill bacterial celachieved through addition of a strong oxidant, such as chlorine hypochlorite (NaClO), monochloramie (NH2Cl), chlorine dioxide (O3), or UV irradiation


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Membranes Modification Techn

Generally membranes modification techniques

1. surface coating

2. surface grafting

3. incorporation with hydrophilic monomers

4. Incorporation with inorganic particles

5. zwitterionic modification

6. low temperature plazma


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Surface Coating

The modified membrane revealed more hydrophilic, smootheanti-bacterial property than unmodified one.

It can be seen that the materials used for surface coating arehydrophilic polymers containing hydroxyl, carboxyl, amino grenzyme. The presence of coating layer could significantly enhydrophilicity and reduce surface charge and roughness of mrendering a better anti-fouling property

Surface coatings are relatively simple to apply and selective of the membrane is not likely to be affected by the adsorbedHowever, coating layer tended to offer an additional resistanpermeation and render flux decline.


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Cont..

One of the major concerns is that anti-fouling property of themay be gradually deteriorated, because the coating layer aattached to the membrane surface by van der Waals attrachydrogen bond, or/and electrostatic interaction, which may washing away of the coating layer in the chemical cleaning long term operation process.

Commercial TFC aromatic polyamide RO membrane is modi

coating a layer of natural polymer sericin that contains hydroamino, and amide groups to improve anti-fouling property. Bmodification membrane show improved surface hydrophilicitsurface negative charge, and smooth surface morphology apure water permeability.


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Surface grafting

Surface grafting has been widely used because of its simpliciand breadth field of applications.

Free radical-, photochemical-, radiation-, redox-, plasma-indand chemical crosslinking are currently used to covalently athydrophilic monomers onto the surface of NF/RO membrane

Short wavelength (254 nm) possessing high energy may dammembrane support resulting in polymer degradation due to t

scission of polymer backbone and poor chemical selectivity imodification reactions. In generally, UV-system with 350 nm wwas used to prevent damaging TFC RO membrane. Thereforechallenge to modify the TFC polyamide membranes for bothfouling resistance and enhanced separation performance, i.epermeation flux and salt rejection


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Cont..

The activation of carboxylic acid groups by coupling reagenethy-3-(3-dimethyl amidopropyl) carbodiimide (EDC) has beechemical grafting to enhance anti-fouling ability of NF/RO m

The modified membranes were more resistant to fouling in prcationic surfactant feed water compared to unmodified me

Nanoparticles can also be grafted to the surface of polyamidmembrane to reduce biofouling through covalent bonding.

Membrane surface modification by grafting hydrophilic or aningredients on membrane top layer has been reported to haeffect on anti-fouling, but it has uncontrollable grafting densioperation step, and may damage the membrane pore struca decline performance


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Incorporation with hydrophilic mono

Incorporation of hydrophilic monomers into membrane selecconsidered to be a convenience and effective strategy to emembrane anti-fouling capacity.

Incorporation with hydrophilic monomers could improve the ability of the NF/RO membranes, the thermal stability,mechanicalproperties, dimensional stability, anti-swelling perthe ductility of these membranes.


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Incorporation with inorganic par

For inorganic nanoparticles, which have a higher specific arenegatively charged hydroxyl groups existing on the surface, inew good properties such as thermostability, anti-fouling, andproperties for the composite materials.

Several types of inorganic materials have been used as addipolymers in NF/RO membrane preparation process, which incdioxide (TiO2), silicon dioxide (SiO2), zeolite, carbon nanotube

nanosilver (nAg).


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Modification with zwitterionic ma

Zwitterionic materials possess both negative and positive chacan create stronger and more stable electrostatic bonds withhydrophilic materials, resulting in excellent biocompatibility aproperty.

zwitterionic polyelectrolytes can improve the anti-fouling of tmembranes to a great extent with changing other membranperformances slightly. However, the synthesis process of the z

polyelectrolyte is complicated and the consumption of chemabundant.


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Low temperature plazma

Low-temperature plasma is a potential technique becausesurface hydrophilicity of polymer membrane without alteriproperties and unfavorable thermal effects; i.e., the favorattributes can be maintained .


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Advantages and DisadvantageModification Methods

M/Modification Methods Advantages Disadvantages

Surface coating Process simplicityNo damage to selective layerstructure

Permeability dPoor Stability

Surface grafting More stable than surface coating Uncontrollable Cost for extra oMay damage mstructureMay cause per

Incorporation with hydrophilicmonomers

Without permeability decline May cause themechanical prstability, anti-swdecline

Incorporation with inorganic particles Without permeability decline Nanoparticle leBiotoxicity

Modification with zwitterionicmaterials

With performance altering slightly Process compleConsumption aagents


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Thank you

For your great patience and valuable time

modification of existing membranes and properties enhancements

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