Introduction to water desalination techniques and the use of CNT in Desalination.

1. Water
Desalination
and Use of
CNT

2. Water
• Seawater constitutes about 96.5% of the Earth’s water
• 1.7% of water is trapped in ice caps
• 1% water is classified as Brackish, i.e. having moderate
concentration of salt but not as much as that in seawater.
• Only 0.8% of Earth’s water share is fresh water suitable for
usage

3. • Reverse Osmosis and Multi-Stage Flash are the two
dominating technologies
Desalination

4. • Electrical Not Thermal Energy Source.
• The sea water is pressured against a semipermeable
membrane
• With increased salinity, High pressure is required due to
increased Osmotic Pressure.
Reverse Osmosis

5. Multi-Stage Flash
• Thermal Source of Energy.
• The sea water is Pressured and Heated up to 110 degrees then passed to
another chamber with lower pressure.
• The water flashs as steam and condense on the heat exchange surface.
• The saline drops are collected in a tray underneath.
• The water Flash goes through Further Flashing process (4-40 times)

6. Aquaporin AQP
• It’s a protein in cell membrane that serve as water channel.
• They occur in kidneys with large amounts
• The channels smallest point are just 0.28 Nanometers wide, H2O size is 0.275
Nanometer
• they pass only water molecules and not even Protons bonded to H2O
molecules nor smaller Cations.

7. Drawbacks of using Nanomaterials in Water
Desalination
• Thermal instability
• Requirement of high pressure
• Fouling
• Pollutant precipitation and pore blocking
• Low influx
• Slow reaction,
• Formation of toxic intermediates and freshly
synthesized ion particles that aggregate on storage.
• Low chances of reusability
• Unknown risks to eco-systems.

8. CNT Features
• CNT-membranes provide near friction-less water flow through them with the retention of a broad spectrum
of water pollutants.
• The inner hollow cavity of CNTs provides a great possibility for desalinating water.
• The high aspect ratios, smooth hydrophobic walls and inner pore diameter of CNTs allow ultra efficient
transport of water molecules
• excellent adsorptive properties against both chemical and biological contaminants

9. CNTs in Water
Desalination
• CNTs as Artificial Water Channels
• CNTs based Membranes
• CNTs based Electrodes

10. CNT Functionalization;
• Pre Functionalization is a must as CNT tend to aggregate which decreases water flux
• Functionalized CNT membranes show good water permeability, mechanical and thermal stability, fouling
resistance, pollutant degradation and self-cleaning functions
• Functionalization decreases energy consumption through increased permeability and physical adjustability
• CNT membranes can also be decorated with various nanoparticles for water treatment.

11. Water Behavior inside
CNTs
• CNTs are considered Nano Fluidic Device, where
neither Newtonian flow nor simple diffusion laws
apply.
• When the tube diameter range between 1.25-1.39 nm
,the water undergoes a transition from bulk phase
water into Solid-like Organized water.
• If the tube diameter is lower than 0.9nm , the water
adopts a single file structure similar to AQP.

12. Artificial Water Channels (AWC)
Aquaporins are hard to use in artificial filtration systems
They are pretty fragile and hard to reproduce, also expensive and require
complex operation conditions.
So they are replaced with synthetic channels known as Artificial Water
Channels (AWC) .
CNTs are embedded in bilayer lipid membranes which resembles the

13. CNT as AWC
CNTs were fabricated with diameter of 0.8 nanometers, and just
like aquaporins, they channel water molecules in a single line,
filtering water six times faster than aquaporins.
Carbon Nanotube Porins
(CNTPs);
~10-nm-long CNT segments
(Yellow) that spontaneously
insert into a lipid membrane
(Blue)
The 0.8-nm-diameter CNTPs,
force water into a (1D) wire
configuration

14. CNTs Membranes;
1.Freestanding CNT
i. Bucky Paper
Random arrangements of CNTs in a large porous 3D structure.
Low Water Flux, Easy synthesis

15. ii. Vertically Aligned CNTs
CNTs are aligned as cylindrical pores that forces the fluid to pass only
through the hollow CNT or between the CNTs bundles.
High Water Flux yet it’s a complex fabrication process.

16. 2.Mixed CNT (Nano Composite)
Analogous structure to Reverse and Forward Osmosis Membranes (usually
CNT with Polymer)
incorporation of CNTs into the membrane matrix made it possible to
manipulate membrane properties;
• improvement in surface hydrophilicity and permeability
• Increased solute rejection
• Reduced fouling tendency
• Enhanced tensile strength and electrical conductivity
• Controlled pore size, surface chemistry, and polymer crystallinity

18. 3.CNT Self Heating Membranes
Reach boiling point using less energy

19. CNT Handling
No material is against fouling, and Nanomaterials are
no exception.
Sooner or later they will stop functioning as desired,
and they might leak to water or out to the environment.
The life spam of CNT and their reaction with living
organisms and environmental impact is not
completely understood, so guidelines in using CNTs
and other Nanomaterials needs to be further assessed
and developed, specially in sectors that directly
influence Humans.

20. Facts
• Brine production is around 142 million m³/day globally
• Brine production in Saudi Arabia, UAE, Kuwait, and Qatar yields
55% of the total global share ( double the volume of desalinated
water produced)
• Brine back in sea results in increased density and decreased the
amount of dissolved O2
• Brine can be treated for mineral recovery
These include sodium, magnesium, calcium, potassium, bromine,
boron, strontium, lithium, rubidium, and uranium.
• There have been a variety of interesting options of using brine
such as for aquaculture and irrigation of saline crops