Technical field

The present invention is in the field of piezodialysis (pressure dialysis) but without using mosaic ion exchange membrane. And by replacing mosaic IXM with two nanoporous oppositely charged filters arranged close to each other to form the concentrate brine in this space room between them where the two other rooms from both sides are desalinated water rooms and are fused to form the desalination rooms .

Background technology

Piezodialysis PD is a process which is used for separation of electrolytes from nonelectrolytes or for desalination by using mosaic ion exchange membrane which contain both cation exchange domain and anion exchange domain in the same membrane each one is penetrating and connecting the two sides of the membrane so cation and anion from the electrolyte can pass the membrane on the same time, each from the correct domain under the driving force which is the hydraulic pressure to increase the chemical potential of ions to overcome the concentration potential

Disadvantages of using mosaic IXM:-

From more than 40 years from the first appear of the idea there is no success for commercially manufacture mosaic IXM with perfect efficacy as the following defects is present:-

A- manufactory problems in construction the two IXM domains penetrating the two sides of the membrane perfectly

B- improperly adhesion between the two domains allowing water and neutral molecules to pass as a leakage specially with higher pressure

C- larger granules size of the two domains increasing the electrical resistance between the two centers of each adjacent pair of IXM domains

2- The mosaic IXM may suffer from self polarization as the anionic groups and the cationic groups however they are in the same backbone polymers or from two adjacent polymers may rotate to meet each other so decreasing the charge capacity of IXM .

3- Disadvantages of IXM itself for

Building mosaic IXM membrane

A- for higher perm selectivity we need higher charge capacity so IXM should be of higher thickness which will increase the resistance and increase the required pressure .

B- if we increasing the cationic and anionic groups number which is (EIC) in the membrane to increase the charge capacity then higher hydration and swelling will occur which will again decrease the charge capacity and decrease the membrane resistance for pressure in the case of mosaic IXM and to overcome this problem by increasing the crosslinking of polymer chains which again will lower the charge capacity (I EC)

The higher permeability of the IXM to the counter-ion and nearly no permeability to water molecules means that The flow pattern is non continuum this is considered as the number of the solution molecules in a TS of the nanochannel in this case may fall below 10 molecules considering the hydrated ion as one molecule and also the mechanism behind the flow in IXM nanochannel is different from the pressure driving flow of solution inside nanochannel in case of non charged nanochannel of constant width according to navier-stockes equations in that the counter-ion and the water molecules did not pass as unit or current but when a counter-ion of highly kinetic energy which is coming from one side is collide with counter-ion inside the nanochannels the later will repel the adjacent counter-ion and at the end the last counter-ion leave the nanochannel towards the other end of the nanochannel So the liquid solution inside the nanochannel may be considered static as a whole where the ions may pass through it from one time to other so the friction between the ions with the solution is at the maximum comparing with case if the total solution inside the nanochannel is flowing according to the continuum pattern which is not happen in the IXM for many reasons like the long length of the nanochannels And non equal width of the nanochannels And other factors

And also this point has another important effect as when the counter-ion pass the nanochannel and it's concentration in the other side increase then concentration gradient will resist the pressure gradient and we should increase the pressure difference every time for increasing the concentration and this exactly like the case of RO where the membrane is permeable only to the solvent so suffer from osmotic pressure which is increased during the process and need greater pressure to overcome where in the case of piezodialysis the membrane is permeable only to the salt but if we imagine the membrane is permeable to both salt and solvent in the level where each species can transport the collision energy to the other side even though one species is moving in the vicinity of wall only and the other is freely transported this effect will disappear and there is no more pressure is required The counter-ions when passing the nanochannels is jumping between the oppositely charged ionic groups of IXM it loss it's activated kinetic energy which were acquired by the pressure difference easily

The nanochannels don't have constant width but it ranged from 1 nano to 6 nano with narrow nodes and wider ones which mean irregular movement or flow of the counter-ion, and the nanochannels network is not distinct and every moment one branche appear and other one disappear the phenomena is like wink

Due to the higher elasticity of IXM when this membrane is subjected to higher pressure this cause the nanochannels to narrow in both the core of membrane and the other side of the membrane which again increase the resistance of movement of the ions or water inside it

-IXM membrane suffer from fouling with divalent and multivalent cations

-IXM suffer from fouling with organic matter and overgrowth of bacteria and molds

Capacitive deionization :-

This technic depend on passing saline between two charged plates of very high surface area with voltage below the decomposition voltage and when saturation of adsorbed ions is reached the capacitor is discharged to allow the concentrated solution between the plates to discharged and the remaining solution become desalted fresh water Disadvantages of GDI :- 1 -its need high electric charge capacity and energy which is near the Faradaic charge in that concentration so in case of sea water it's consume more energy which approach heating methods if there is no energy recovery

2- it's need to charge /discharge the plates many times in the cycles for sorption/desorption and every time the solution between the plates is discharged and even may recycled which means time consuming and again more energy consumption for moving the solution and recycling it

3- it's required plates of very high surface area like activated carbon which suffer from high contact resistance between carbon particles which lead to increasing energy lose in each cycle or even using porous carbon electrode or the expensive carbon nanotube with very large amount

4- it's require complicated system for the energy recovery of the charging /discharging the capacitors

WO/2019/120461

Electric double layer filtration for water desalting.

Is a method for desalination with main embodiment of two adjacent electrically charged nano porous filters with low distance between each others from nano to micrometers the saline water is entered to this narrow room and EDL overlapping occur inside the pores of the porous filter so the co-ions can't enter the filters and counter- ions can enter but can't pass the filters and water only can pass each filters to the right and left rooms which become the desalinated water rooms while the middle room become the brine or concentrate room

Disadvantages of this method

The EDL overlapping in the case of seawater occur in narrow window make the diffuse layer between 1 to 3 nm and this distance is also occupied with hydrated counter-ions of diffuse layer besides the water molecules so this hydrated ions decrease the actual space for water molecules and effective width of nanochannel in the same time where only water molecules can pass the channels where hydrated ions are suspended in that space and moves in brownian motion but can't leave the pore.

This method remove the major from the minor like RO method

Brief description of the invention and its ability to solve these problems

When two porous oppositely charged filters are arranged close to each others where the separated distance from 0.1 Micrometer to 1 mm this room in between the two filters is the brine room

The two other rooms on the right and left side of the filters are connected together or fused together to form the desalinated freshwater rooms .

The diameter of the nanoporous is designed to allow EDL overlapping in the nanopore or nanochannels under the condition of the feed salinity and the nanochannels wall charge density or voltage .

The nanochannel's shape may be cylindrical or conical where it's wide Base in the diluted solution and the lower size Base in the brine side. Where the conical design is preferred as its ability to concentrate the feed and resist the concentration gradient is higher as it acts like a light convex lens but here collecting the collision energy from the wide Base side to the low Base side .

The diffuse layer in the nanochannels contain higher absolute concentration of the counter-ion than the core concentration of the counter-ion in the bulk solution in both the middle concentrated room and the right or left diluted solutions rooms

The feed enters from right and left rooms under higher hydraulic pressure so each type of ions is concentrated in the nanochannels by the effect of the wall charge to form EDL overlapping while the ions of the diffuse layer can move easily in the nanochannels which themselves have thin thickness .

The pressure push the counter-ions and the water in the form of current toward the middle room where counter-ions from the left side and right side meet each other and neutralize each others preventing the forming of the streaming potential inside any filter nanochannels While the remaining Co-ions from each side meet each other as the two rooms are fused away from the position of the filters.

There are two main division :-

1 -First division where the porous filters is made of electrically conductive materials like metals as gold or silver or steel ... .etc

Or from perforated graphite sheets or from specific design of VACNT membrane to allow the CNT to connect electric current or from perforated nanoporous conductive polymer And this filters is connected to a DC voltage below the decomposition voltage which is 1 .2 to 1 .4 volt this volt is constant all the time no charge discharge occur so no any lose of electrical energy and the energy is consumed only from the pump which is applying the hydraulic pressure

2- The second division where the filters is made of non conductive porous filters and the charges is come from static charge of ionizable chemical groups of materials lining the pores like polyelectrolyte where the remaining width of the pores is designed to allow EDL overlapping under the concentration of the feed

Effect of this design to solve the prior art problems

Mosaic IXM

One important goal of the mosaic IXM design is to make the domains size of cations and anions of very small size to decrease electrical resistance between the passed cations and anions to meet each others in brine side

This goal is achieved here by arranging the two filters close to each others from 0.1 urn to 1000 urn in this case the electrical resistance is minimized so in our design this goal is perfectly achieved and avoiding mosaic IXM problems as

-It's easy to design and construct and maintain the membrane without any limits and with any size Without defects or leakage or polarization or losing part of the charge capacity of the neighboring domains .

And avoiding the problem of IXM itself as In both divisions we can get very thin membranes with maximum surface charge capacity inside the pores without swelling or membrane rupture or dilution of the charge concentration or decrease of charge capacity .

All the solution inside the nanochannels which is consist of counter-ions together with the water molecules which pass the nanochannels in the form of one unite or current in the continuum flow pattern so we get two advantages the first is Low friction resistance And the second is the concentrated brine cannot resist the process and the flow back of the counter- ion to the diluted sides under any concentration difference as all the species have the ability to transfer the collision energy from one side to the other so they can respond to the pressure difference and we can extensively concentrate the brine without more energy requirements and increasing the desalination efficacy .

The nanochannels has distinct dimensions and characters so less flow resistance and less flow turbulence

Less bacterial and biological fouling

The DC charged division is not subjected to fouling with divalent or multivalent cations

When comparing with CDI

While the filters in the first division is electrically charged with DC below the decomposition voltage like the CDI but there is no charge/discharge there is no two phase or cycles of adsorption /desorption as the adsorption phase is present all the time as the diffuse layer of EDL overlapping can move under hydraulic pressure and spontaneously regenerated from the water current .

So no any electrical energy is consumed from the battery and the energy is consumed only from the pump applying the hydraulic pressure so lower energy consumption comparing with CDI

- no needs for electrode of ultra high surface area and many materials are suspected to be used as an electrode or filters

- lower time for separation as there is no relation between the equivalent faradaic charge of a said concentration and the separation process in this design

Solving the problem of (WO/2019/120461)

The present invention use all the actual size of the diameter where diffuse layer is occupying (counter-ions and water molecules ) to pass as a unite or current so we have already larger diameter for the flow so greatly lower flow resistance This invention extract the minor (concentrated salt) from the major ( brackish or seawater) so lower energy required There is no problem from co-ion leakage into the nanochannels in lower concentration so there is no need for the special consideration to prevent co-ions from passing the nanochannels as the perm selectivity is not important here but the required is only to concentrate the ions in the EDL overlapping region with the majority of the counter-ions The principal behind the invention:- Introduction when a charged nanochannel is immersed in saline the Co-ions will move away from the nanochannels due to repulsion and the counter-ions is enriched near the walls and are arranged in two layers

The first is The stern layer where the electric attraction force is greater than the the kinetic energy of the conuter- ion so the ions is arranged close to the wall and from layers of non mobile counter- ions (stern layer)

The second is The diffuse layer where the kinetic energy of the counter-ions is slightly larger than or in the same range of the electric attraction force to the walls, so the ions can move in certain range near the wall in a manner like the brownian motion and it's concentration in the midline is many times greater than the bulk solution concentration

When applying pressure from one side of a nanochannel the counter-ions of the diffuse layer will move to the other side to a certain limit as the streaming potential formed will resist the pressure and later will decrease the rate of transferring the counter-ions to the other side . The length of the nanochannels is very important as the longer one is not only increase the flow resistance by friction with walls according to flow in continuum assumption but it's also resist the flow by other mechanism as the diffuse layer is partially attracted to the wall so if increasing the length of the nanochannel this increase the pressure drop by integrating force of each TS layer of diffuse layer attraction to the wall in all the length of the nanochannel.

So if we use shorter nanochannel we will decrease the energy required and also may increasing the efficacy of concentrating power of the nanochannels as the pressure may detach few layer of the ions of stern layer near the diffuse layer level or simply we can consider that the hydraulic pressure may increase the zeta potential and decrease the thickness of the stern layer increasing the concentration efficacy in ultrathin nanochannels

Details description:-

The backbone concept and aspects of the invention :-

When two oppositely charged nanoporous filters is arranged close to each others forming three rooms

The left and right rooms are fused together away from the position of the filters this rooms will receive the feed of saline under high hydraulic pressure

The saline water is concentrated in the nanoporous filters each ions enriched in one filters inside it's nanochannels as EDL overlapping is present at the feed salinity

And the hydraulic pressure is pushing the diffuse layer and part of the stern layer towards the middle room and as the middle room width is small from 0.1 Micrometer to 1 mm the counter-ions from the two filters will meet each others and neutralize each others in this middle room which become the brine room

So no streaming potential formed in the nanochannels so the ions will continue to pass the filters without limit or resistance related to this effect.

The remaining co-ions to each filter from both rooms are met together in the regions of fusions or connections of the two rooms to neutralize each others and this connections region should be of short width to decrease the distance the co-ions have to cut There are multiple connections which connect the same type of rooms at constant distances to prevent concentration polarization .

Finally the middle room become the brine room and the two sided fused rooms become the fresh water room

However this design may be reversed in certain embodiments as the feed saline is enter the middle room under pressure and the two left and right fused rooms become the brine water where the middle room at the end of process become the fresh water room This design is more suitable for highly diluted feed to decrease the electrical resistance of the Co-ions as we can increase the salinity of two sided rooms to lower the electrical resistance.

The thickness of the filters should be too small to lower the pressure drop from the flow resistance and from integrating the attraction force of the counter-ion in the diffuse layer so increasing the efficacy of the system to concentrate the feed with low energy

The role of the wall charge is to concentrate one kind of feed charge inside the nanochannel at the same time where these concentrated ions can move when applying suitable hydraulic pressure from one side to the other side without the need for discharging the wall charge .

So no need to charge I discharge like GDI

The counter-ions can move while no discharging of the plate charge by the effect of EDL overlapping in the diffuse layer level or due to the low thickness allow detach some ions of the stern layer under high pressure .

The speed of the feed and feed pressure should be suitable with certain limit as :-

If it is too fast then there is no suitable time of wall charge to concentrate the feed and collect the feed counter-ion charge inside the nanochannels

If it's too low then the pressure is not enough to overcome the attraction force of the diffuse layer with the nanochannels wall charge or it's not sufficient to overcome the concentration gradient .

As all the counter-ion solution of the diffuse layer (ions and water molecules ) can move as a current or a unite so the concentration gradient can't resist desalination process as the pressure from the diluted solution is larger than concentration solution side so the total collision from the diluted side is greater than the total collisions from concentrated side as both the counter-ion and water molecules can pass the nanochannels So the salt from the concentrated side have no chance to enter the nanochannel under higher concentration gradient as the extra counter-ions kinetic energy from the brine side is suppressed by the extra water molecules kinetic energy from the diluent side.

The actual system is consisting of a plurality of alternatively arranged positively charged filter and negatively charged filters arranged close to each other to form a circle of filters where the distance between any two filters even the first and last one become too small from 0.1 micrometer to 1 mm to decrease the electrical resistance of any solution specially the diluted rooms

The diluent rooms is more narrow than the concentration rooms

And all the diluted room are joined together to form a diluent network

And all the concentrate rooms are joined together to form the concentrate network The diluent network and the concentrate network are separated from each others the feed enter from the marginal feed entry of the circle to the diluent network then enter the diluent rooms where it is become desalinated at the end of the path near the center of the circle and exit from the center of the circle at the desalination exit

The different ions pass through the charged filters where it's become concentrated and then meet each others in the concentrate rooms then pass to the concentrate network and exit from the concentrate exit which is present near the margin of the circle

In this design completely overcome the problem of the co-ions to each filter which should travel certain distance in low concentration to meet each other as in this design there in no co-ion remained or co-ion polarization because the co-ion to each filter which remain after the counter-ions left the room are already close to each other in the diluent room so they don't need to travel to each others and later they can considered counter-ions to the other filters on the other side and pass the filters as counter-ions

This design also lower the electrical resistance of the diluent from other aspect as the feed enter from the marginal of the circle where the wide of diluent room is large and exit from the center of the circle where the wide of the diluent room become too small at the moment where this feed become desalinated water so the electrical resistance is largely lowered as the two filters become closer to each others

In conclusion this design lowers the electrical resistance to the minimum limit so lower the required pressure and energy consumption and increases the rate of desalination.

And this design is easy to construct and maintain with perfect efficacy with the larger surface area of the membrane used with compact design

The way of charging the filters is dividing the embodiment into two main division:- A-the first division when using DC voltage under decomposition voltage where the filters is made of

1- conductive porous metal like gold/silver /steel/ copper / alloy/ semiconductor. ..etc

2- 2D flat perforated sheet of graphene

3- VACNT membrane where the interstitial filler between the carbon nanotube is conductive material like conductive liquid or ultrafine carbon powder fused or metal or conductive polymer etc .

4- porous perforated conductive polymer supported by porous non conductive material or polymer

The DC charging divisions may be further subdivided according the voltage used into :- 1- low voltage just below decomposition voltage where no insulated material is used

2- high voltage DC when using insulated material in this case the stern layer is thick multilayer and the diffuse layer thickness is small area in the midline of the pore .the goal of this design is we can use nano pore of higher diameter than EDL overlapping to occur and we can fill this diameter with multilayer stern layer by increasing the voltage to reach EDL overlap in case of not availability of the low pore diameter filters or we can use ultrathin layer of filter and the pressure will be able to move even some layers of the stern layer beside the diffused layer. The insulating material should be of ultra thin thickness according to its dielectric strength to be suitable with voltage used and with higher dielectric constant B- the second division where the charge is electrostatic charge from ionization of chemical groups or adsorption of certain ionic species where deposition the ionic material to coat and line the interior of the nanochannels with suitable material which can ionize when become in contact with the solution as one filter will be designed to become positively charged and the other become negatively charged

This material like polyelectrolyte or monomer of IXM and later polymerization or any other suitable material can be used.

The finial diameter of the nanochannels is reached to be the exact diameter to allow EDL overlapping under the feed concentration

The nanoporous fram filters is made from any suitable material with well arranged nanochannels which embedded through it with high density and regular shape and wide with narrow nanochannel diameter variations like

1- AAO (Anodic Aluminum Oxide )

2- VACANT where the CNT membrane used

3- track-etching high density polyethylene or polycarbonate or polyurethane. Etc

Detail description of the two divisions according to source of charge:-

First division DC electrically conductive electrode

Where the voltage used below the decomposition voltage which is practically between 1.4 to 1.2 volt or lower according to the required voltage manipulation to allow EDL overlap under the feed concentration the pore size which is required for the sea water is between 1 to 5 nanometer as the dybe length is referring to the diffuse part of EDL so actual diffuse layer of the overlapped EDL is between 1 to 2 nano meter

While for brackish and highly diluted water It is may reached to 10 nano or even more So the final effective pore diameter is carefully designed

1- Porous filter where the filter is made from non toxic stable metal sheet like gold /silver/steel /alloy or semiconductor etc

The sheet thickness is below micrometer and the sheet is supported on meso porous layer followed by macroporous layer of non conductive supporting porous material like polyvinyl or ceramic etc

A-The pore is made in the metal sheets by any methods known in the art like track -etching B- The second method for designing the metal porous electrode is using a frame or molds like AAO porous material then coating the pores with all the mold by layer of metals by spattering or atomic layer deposition or by electroless plating with silver or gold or any metal

2- the second electrode material in the conductive materials is graphene sheet which is perforated to contain pores of the required diameters and then the sheet is supported by porous non conductive supporting material and every graphene sheet is connected to a DC voltage as described in the main designs while the thickness of the supporting material here is too small or even stand alone graphene sheet as the graphene sheets have good strength to bear the high pressure itself . This design allow to get 2D planer filter where the thickness is just one layer of carbon so ultra low pressure drop and the highest ability to concentrate the feed passing from the pores even though the diffuse layer small or even the diffuse is disappeared at all and only there is thick stern layer which fill all the space of the pore when using maximum EDL overlap by choosing the pore too small to allow EDL overlapping on deep level in the level of stern layer or just near it while the voltage is at the max level just below the decomposition voltage

Where the electrical attraction of the counter-ion to the wall of the nanochannels is greater than the brownian kinetic energy in all the diameter in the nanopore so all the pore is fully occupied by only stern layer but when applying greater pressure to level where the force applied on the counter-ion is greater than the electrical attraction force to the wall then the pressure will overcome the electrical force and displace the counter-ions from the pore easily as it's thickness is one layer only so lower pressure is required to displace the stern layer ions comparing to the usual circumstances in the usual nanochannel in other material where the pore is long .

The speed of the feed should be carefully adjusted to allow forming of the EDL and renewing it continually as the too fast speed will pass only diluted feed as no time to renew the EDL which has displaced and on the other hand too low speed will not be able to overcome the electrical attraction between EDL ions and wall charge and also overcome the concentration gradient as previously described

The only disadvantage of the graphene sheet design is the manufactory complications to build larger area sheet

While there are many methods for its Building which is well known in the art like deposition single layer graphene by chemical vapor deposition on micro porous layer of teflon or ceramic or sintered glass polycarbonate, polytetrafluoroethylene .nitrocellulose plastic or metallic grids etc then by irradiation by heavy ions or electron beams for the graphene flake to form the nano pores and may then subjected to chemical etching to widen the pore to the required radius

Another known method is by dissemination of the graphene flakes from graphite by surfactant -assist exfoliating by (sharifi et Al ) and allowed to be deposited on the porous substrate like teflon and using silica cement to fill the interstitial space between partially overlapped flakes of graphene and the 2D graphene layer is irradiated by heavy ions or electron beam or laser printing to form the nano pores of the required diameters or by cu-assisted etching or chemical etching

3- The third design on conductive electrode is the VACNT (vertically aligned carbon nanotube ) array membrane

The usual methods for preparing VACNT forest is by chemical vapor deposition CVD or laser ablation or arc discharge Then CNT is subjected to condensation to decrease the interstitial distance between the nanotubes to increase and improve the rate of flow then the interstitial space is filled for short length like 1 Micrometer or more or less with electrically conductive material this material may be metal like copper or silver or aluminum or gold or tin the method of deposition such materials may be electroplating to fill all the interstitial space in the required length of the array or any other well known method like using CVD to deposit low melting metals specially tin in this space or atomic layer deposition ALD

Or we can carbonize the interstitial space with the methods will known in the art by filling the interstitial space with conductive carbon powder or layer for example by filling the required space with polymer and then burning the polymer or using concentrated sulfuric acid to dehydrate the polymer to carbon

Or we can fill the interstitial space with conductive polymer by the usual methods of injection the monomer in the interstitial space and then induce polymerization

After we get thin layer of conductive material we will fill the remaining length of the forest with non conductive polymer as usual like Si3N4 or epoxy or polyurethane to get VACNT membrane with a leakage free and can withstand the the expected operation pressure for the desalination

Then detaching of the array from the substrate and etching for removal of the fullerene cap and catalyst with the chemical or mechanical routes for opening the CNT

At the end the membranes is arranged in the invention designs and is connected to the DC current as detailed description above

The length of the array which is the thickness of the membrane should be low enough to decrease the pressure drop but in the same time can withstand the required pressure for desalination however we can use fillers of porous non conductive material between membranes which allow using thinner membrane and withstand higher pressure and also decrease the cost of the membrane

The fast molecular transport in CNT is expected to be lower than expected when this membrane is used because the development of EDL inside the CNT will decrease the hydrophobic character of it to a certain limit. While the ultra smooth character of the CNT wall will not changed

This membranes has very low flow resistance and the pores diameter can easily tailored we can get pores diameter from 1 to 5 nanometer for seawater desalination and from 3 to 10 nanometer or even more for brackish water desalination

The membrane is inert and has great antibacterial and antifouling natural properties

4-The fourth material under DC charge

Is using conductive polymer where we use conjugated polymer doped with bromine or iodine of polyaniline , polypyrrole , polythiophene ,poly para phenylene , poly phenylene nylon and polyfuran

The conductive polymer is prepared to be thin sheet and then the nano pores is formed by the usual methods like track-etching or laser printing and then the this sheet is compressed over porous material as a support to withstand the pressure

The conjugated doped polymer has high conductivity and low price and easy to manufacture and corrosion resistance and flexibility

The second division of the membrane according to source of charge is the Functionalization of the interior walls of the nano channels like

1- Functionalization of the CNT with ionizable functional groups

By lining the walls of VACNT(where the interstitial voids is filled by inert occlusive material like Si3 N4 ) and the inner wall of the CNT is lined with conjugated polymer or conjugated polyelectrolyte where the backbone of the polymer is attracted to the CNT wall only with strong pi-pi pond and there is no covalent ponds in the same time where the side chain of the polymer has either positively charged groups or negatively charged groups to form positively or negatively charged membrane filter ,a good example is using the poly (phenylene ethynylene) as conjugated backbone which is either Functionalization with alkyl imidazolium side group or any other suitable cationic side group In case of positively charged filter or acetate or sulfate or phthalate for example as side group In case of negatively charged side group and in case of IXM we can use suitable ionic ion exchange polymer to from the membrane with cationic or anionic membrane .

There is one important special difference between this Functionalization the CNT in this embodiment and the earlier methods used for desalination where here all the length of the CNT should be lined with the polyelectrolyte or conjugated polymer and the Functionalization of the CNT in the previous art is used to limit the entrance of certain ions by Functionalization of either one or the two ends of the CNT with negatively or positively charge groups

As the ability to concentrate the feed of nanochannels is increased by increasing the length of the charged part of the nanochannel and with decreasing the diameter of the nanochannels

So the MWCNT lined length with the polyelectrolyte and the diameter is carefully selected according to the concentration of the feed as the thickness of the polyelectrolyte layer from 1 to 3 nano so MWCNT of diameter at least is 5 to 6 nano as the remaining free path space to be from 1 to 2 nano in case of sea water or from 2 to 10 nano for brackish water desalination The polyelectrolyte or the conjugated polymer is preferred to have conjugated backbone like poly (phenylene ethynylene) as this backbone is attracted to the inner wall of carbon nanotube by the pi-pi bond while the branched groups is either cationic group like acetate or salufonate or phthalate or phosphonate etc

While the anionic groups like amomium primary or secondary or tertiary or imidazole side group for example

In case of polyelectrolyte it's dissolved in non aqueous solvent and the solution is passed in the membrane of VACNT and allow the liquid to be evaporated to allow the polyelectrolyte to preceptated into the nano channel

In case of conjugated polymer it's introduced in the nanochannels either in the form of solution of the polymer or the solution of monomer and allow heat or light or electrical polymerization

When the sea water solution is allowed to pass then there are two forces which attach the ployer in its place the first is pi -pi bond between the polymer backbone and the inner nanochannel wall of carbon and the second is the repulsion force between the two faced ionized groups which carry the same charge of the faced polyelectrolyte chains which are lining the interior nanochannels walls .

2- the second membrane in the second division is a technique which is well known in the art where The micro porous material filled with ion exchange polymers

The pores diameter range from 0.01 to 2 micrometer of the porous substrate and with thin thickness and is filled by either cationic exchange resin or anionic exchange resin

The ion exchange resin is either introduced by solvent and later evaporation or by monomer solution and later polymerization this technique allow using High ion exchange capacity (IEC) without water swelling or dissolution of the resin as the porous substrate prevent swelling and provide mechanical stability

While the disadvantage of this technique is:-

1- there is mixture of pore size range no distinct pore size so the EDL overlapping is not occur in all the region of porous substrate equally and there is regions of high EDL overlapping and regions of low EDL overlapping

2- when using pores between 10 and 20 nano the arrangement of the ion exchange polymers will be two layer one is on the inner wall lining it and the other is central cylindrical micelle of polymer by aggregation of the hydrophobic backbones of the polymer together in the midline allowing narrow cylindrical region of saline between this micelle and the polymer on the wall

This decrease the diameter of the nanochannels without increasing the capacity of equivalent charged groups

And later this micelle will be washed with continuously using the membrane leaving only the polymer in the wall and wide space of non overlapping EDL

This technique is well known in the art As a type of IXM for different uses and can be used as a membrane according to our designs in the invention while we introduce new technique by using track-etching method to from nanochannel with diameter less than 10 nanometer and when filled by ion exchange polymer

The substrate material for pore forming may be any polymer material like polycarbonate or poly phthalate or high density polyethylene or any other suitable polymeric material

Where when using such low diameter below 10 namo There are no ion exchange polymer in the midline of the nano channel and it's present only on the wall of channel which give good crystalline structure and great ion conductivity as soon as there is overlapping between the EDL inside the nanochannels

Both types of the well known art and low diameter pore types can be used in this patent .