Archive for the ‘membrane research’ category

Sen. Ken Salazar DOI Steven Chu DOE

December 18, 2008

In my last post, I mentioned a number of popular ideas to advance alternative energy development. But I didn’t attribute them because nothing had been written of incoming administration officials as yet. A couple of days later several major newspapers mentioned ideas of incoming administration officials which included ideas I talked about. So I inserted these in my last post. If you went to my last post early check back. (Just skim down and check  the writing in block quotes.) This week’s post includes a piece from the Wall St Journal which mentions another popular idea I mentioned in my last post.

How about renewable energy? Dr. Chu already had a taste of Washington power-brokering, in a briefing with current Energy Secretary Samuel Bodman and Treasury Secretary Hank Paulson. He pitched them on the idea of an interstate electricity transmission system to be paid for by ratepayers. That would solve one of the biggest hurdles to wide-spread adoption of clean energy like wind and solar power.

This is interesting because Dr. Chu is the president elect’s choice to lead the DOE.

The president elect’s choice for the Dept of Energy is Dr. Chu. Dr. Chu’s marquee work at the Lawrence Berkeley National Laboratory is the Helios Project. That’s an effort to tackle what Dr. Chu sees as the biggest energy challenge facing the U.S. transportation. That’s because it’s a huge drain on U.S. coffers and an environmental albatross, Dr. Chu says. Helios has focused largely on biofuels—but not the bog-standard kind made from corn and sugar. The Energy Biosciences Institute, a joint effort funded by BP, is looking to make second-generation biofuels more viable. Among the approaches? Researching new ways to break down stubborn cellulosic feedstocks to improve the economics of next-generation biofuels, and finding new kinds of yeast to boost fermentation and make biofuels more plentiful while reducing their environmental impact.

Include algae to fuel in that mix. David Chu does not like coal.

Big Coal won’t be very happy if Dr. Chu gets confirmed as head of the DOE—he’s really, really not a big fan. “Coal is my worst nightmare,” he said repeatedly in a speech earlier this year outlining his lab’s alternative-energy approaches.

Ken Salazar is the president’s pick  to head up the Dept of the Interior. How will he affect water policy? Likely he will be very innovative.

He was raised on a ranch in the San Luis Valley of southern Colorado, and became an attorney with an expertise in water law. “In rural areas,” Salazar said in an interview this summer, “they understand water as their lifeblood.”

How will Salazar be on energy? He’ll be tough on oil  interests.

Earlier this year, Salazar criticized the department for decisions to open Colorado’s picturesque Roan Plateau for drilling. Salazar said the regulations to begin opening land for oil shale development would “sell Colorado short.”

He’s a fan of alternative energy.

The senator campaigned vigorously for Obama in Colorado, a swing state, barnstorming rural areas in a recreational vehicle while preaching alternative-energy development and its potential to revitalize rural economies. After the election, Salazar publicly urged Obama to build his planned economic stimulus package around investments in energy infrastructure.

It might be a good idea to invite Ken Salazar to the national salinity summit. So that he can see some slides that show the best places for solar and wind overlapped with the deepest briny aquifers. He’ll already know Senator Pete Domenici’s saying that you need water to make power and vice versa. He’ll also know that the hoover dam produces both power and water; that too, the hoover dam is the foundation for the economies of the southwest–and its profitable. He may see that the best way to get brackish water desalination plants is to site and budget them with solar and windmill power plants. Then it would be his job to sell the idea to DOE elect Dr. Chu.

“It’s time for a new kind of leadership in Washington that’s committed to using our lands in a responsible way to benefit all our families,” Obama said

Come to think of it, it might be a good idea to invite a bunch of solar wind and desal executives to the National Salinity Conference.

imho Senator Salazar will be interested in accelerated funding for all forms of desalination R&D from Proifera plus a dozen other cutting edge membrane companies to left handed ideas like low temperature cooking water out of gypsum. As well, I would think for experimental reasons both men would be interested in siting at least one solar/desal plant near a coal plant so as to pump the coal plant’s waste CO2 into algae geenhouses. I’ve mentioned this in posts here & here. Texas might be the best place for this because  they have CO2 emitting industrial plants there,sunlight and briny aquifers. There are others.

I think that both Senator Salazar and Dr Chu should be urged to fund research into cheap smart energy efficient water pipelines mentioned here, here and here. I mentioned an initial slant well experiment in the Santa Barbara channel with a Profiera membrane here. Further they should be appraised that the ultimate goal in +-7 years of nanotube and pipeline research are  pipes with one end in the salty pacific through which only fresh water flows inland to points all over the desert southwest. Toward this end, I could easily see several lines of solar power plants in the empty deserts there that point to Arizona. These might double as pumping stations in the future for water pipelines that push water eastward.

Finally it might be helpful to do a little more detailed ranking for best places to site desal/solarwind plants. Ranking might include:

1.)distance from electric AND water grids

2.) ease of getting federal state & local permissions.

3.) time to project ground breaking.

If the DOI was onboard, likely the quickest places to break ground would be BLM lands.
Herbert Hoover as Commerce Secretary signed the initial enabling legislation for the Hoover Dam on November 24, 1922. Ground was not broken on the Hoover Dam until 10 years later in 1932.

That’s a very leisurely pace to ground breaking. Things won’t be nearly so leisurely this time.

Lawrence Summers, the former Treasury Secretary who will head Obama’s National Economic Council, has said a fiscal stimulus will have to be “speedy, substantial and sustained.” Congressional leaders have indicated that spending could even be as large as the $700 billion bailout, but details of how and where the money will be distributed are unknown.

So be forewarned. In the next year or two — guys  will come into your office blue in the face with tension. Help them along their way. Why? Because the very best investment  the government can make is in water and energy. Why? Because water and energy provide the basis for growth in the economy and the government’s future tax base.

said Eric Schmidt, chief executive of Google Inc. and an Obama economic adviser, in an interview. “You would want to invest in something that would not just physically build a bridge, but would help build businesses that would create more wealth.”

That would be water and energy. Why is this important politically? The reason is–this is not a settled issue. The talk is now for +-50 billion to allocate for green projects. But it could be more or less depending on the projects presented –and the vision thing.

Even so, the Obama team remains split over how much money to devote to green and high-tech projects, and how much to focus on traditional infrastructure.

In purely economic terms, a traditional infrastructure building spree might provide the biggest bang, Mr. Zandi said. But, he added, “there’s something to be said for an infrastructure program that captures the imagination, because confidence is just shot.”

The way to settle this in favor of green energy and water desalination projects is to present projects that can be implemented quickly. Oh and one more thing. The size of the investment will depend on the size of the vision.

A National Salinity Summit that can conclude with best sites for solar/wind/desal plants can give solar/wind/desal players legs. Even this is a step behind. Nor is it the big vision I’ve talked about for a couple years.

As it is the big cities already have their make work projects lined up.

LLNL Spinoff Porifera Uses Carbon Nanotube for Desalination

November 9, 2008

Wow. This is downright fun to report. Looks like the first generation (alpha)carbon nanotube membranes will come online within a year or two. Last time I posted a couple weeks back, I mentioned that the NanoTech Institute of the University of Texas at Dallas had learned to produce carbon nanotubes in industrial quantities. Then I opined  — wouldn’t it be nice if someone could adapt that carbon nanotube production method to the carbon nanotube desalination membranes that the LLNL team is working on

Well guess what?

Yep. Yeppers. Yup. Someone did. Now the press release below does not mention the industrial production method that they are using. But it does say that an LLNL spinoff called Porifera is going to be making carbon nanotube membranes for water purification. The first benefit that is touted is the anti fouling aspects of the membrane

The tubes are packed closely together and the water flows through them like it flows through straws. Chirality doesn’t matter, said company representatives I spoke to at the California Clean Tech Open, which held its award gala in San Francisco tonight. The opening of the tubes is so small (a few nanometers wide) that bacteria, biological material and other impurities get cleaned out of the water because they can’t fit where water molecules can. The filter will also likely be useful for desalinating seawater, although purifying waste water will likely be the first application.

Another added bonus: because the impurities get stuck outside of the tubes, membrane fouling is less of a problem. It is difficult to clean traditional membranes because material can be caught inside the membrane. If bacteria or salts accumulate on the outside [of the carbon nanotubes], they can just be swirled away with water.

Curiously the article only mentions the desalination abilities of the membrane as a secondary property. Its not clear why. Consider that  they make this astounding proposition:

Overall, Porifera’s array could cut the cost of desalination by 25 percent or more. In traditional purification and desalination systems, large amounts of energy are required to pressurize water and force it through a membrane. Here, gravity does a lot of the work.

Read that? Gravity does “a lot” of the work. Its not clear here how much “a lot” is. Current membrane technology requires pressures that are the equivalent of about 1700 feet of ocean water. Its too expensive to site desal at those depths. But what would happen to costs if you could site desal membranes in 100 feet of water a couple hundred feet offshore?   Here, look at this animate graphic of an undersea power & water producing unit using wave energy. Notice the desalting unit onshore. Just place the membrane on the ocean floor near the pumps. You let ocean pressures  press the water through the carbon nanotube membranes and let the wave action pumps force the fresh water ashore. (Hmm well some bright desal consultant would have to tease out the relative costs of onshore concentrate disposal/onshore membrane pumps vs offshore installation/offshore maintenance to figure out at what depth/pressure the nanotube membrane becomes more cost effective than onshore desal. Might help if  all the metal parts were coated these new nano scale coating products so as to kill maintenance costs. As well, it would probably be helpful to coat all the underwater machinery with thin layer of  cation-exchange groups. These cause electrostatic repulsion of organic molecules. That said, it might be best to just chuck the whole underwater electrical generation stuff, set the desal membranes offshore and pull the desalinated water onshore with onshore pumps powered by current generation solar cells that  make solar electrical production as cheap as coal.  In the next couple years those solar cell electrical generation costs will drop much further. Do enough solar electrical generation to use the grid as a battery. Another idea would be to have a California water official with seriously good social skills talk to The City of Carpinteria near Santa Barbara negotiating with Venoco over their proposed Paredon Project. The Paredon Project skirts the offshore drilling problem by siting the oil rigs onshore and then drilling down and sideways for a couple miles out into the Santa Barbara straights. California water guys might ask The City of Carpinteria to require of Venoco that they drill and maintain for four years (or the life of the oil wells–which ever is longer) a slant well for water desalination. This would be an experimental project. Whereas the oil wells go out several miles–the slant water well would go down and out only a couple hundred feet/yards. There would be a carbon nanotube membrane on the end of the pipe in the ocean. The state’s costs for the experiment would be to design nanotubes membrane fitting on the end of the well out in the ocean. From the membrane well head –fresh water would flow downhill toward the shore. Seperately, The Paredon Project will create a lot of waste salt water mixed with hydrocarbons and sulfer that needs to be treated. Clean up for this is already built into project costs. I would think If the carbon nanotube membranes can make that water fresh and clean for lower costs–then that might even make up for the costs of the experimental slant water well. )

Sorry about the tangent.

What else?

It would probably be a good idea for someone to mention the problem that evolving membrane technology creates for desal plant designers like Posiden. I mentioned this a couple blogs ago. They’ll need to be able to design new desal plant in such a way that they have has the ability to change over cheaply to future generations of membranes that don’t need pre treatment. For example, if you figure on the outside that these carbon nanotube membranes come out of alpha in 2 years and beta in 5 years…any desal plant coming onstream in the next five years is going to be outdated for much of its productive life.)

Oh and don’t forget to patronize  Porifera

Anyhow here is the article:

Michael Kanellos

Start-Up Cuts Water Purification Costs With Carbon Nanotubes November 6, 2008 at 10:32 PM

Single walled carbon nanotubes are the child prodigy of the material science world.

The tubes-which are spools of carbon atoms that resemble rolls of chicken wire–are stronger than steel and conduct electricity better than metals. They are also incredibly thin, only a few nanometers wide, which gives them an ability to transport other particles with very little energy.

Unfortunately, they also tend to be somewhat tempermental and difficult to control. Manufacturing them in large batches in a uniform manner has proved extremely difficult. The chirality, or how the carbon atoms are arranged in relation to one another in the wall, varies from tube to tube, which changes their properties in many applications. It’s one of the big reason that carbon nanotube semiconductors keep getting pushed further and further into the future. Other applications, such as tennis rackets, can get by with the less spectacular cousin, the multi-walled nanotubes.

Porifera, a spin out of Lawrence Livermore National Labs, has come up with a way to skirt the manufacturing problem and devise a product that leverages the unique thinness of single walled nanotubes. It has made a water filter of single walled carbon nanotubes. The tubes are packed closely together and the water flows through them like it flows through straws. Chirality doesn’t matter, said company representatives I spoke to at the California Clean Tech Open, which held its award gala in San Francisco tonight. The opening of the tubes is so small (a few nanometers wide) that bacteria, biological material and other impurities get cleaned out of the water because they can’t fit where water molecules can. The filter will also likely be useful for desalinating seawater, although purifying wastewater will likely be the first application.

Another added bonus: because the impurities get stuck outside of the tubes, membrane fouling is less of a problem. It is difficult to clean traditional membranes because material can be caught inside the membrane. If bacteria or salts accumulate on the outside, they can just be swirled away with water.

Overall, Porifera’s array could cut the cost of desalination by 25 percent or more. In traditional purification and desalination systems, large amounts of energy are required to pressurize water and force it through a membrane. Here, gravity does a lot of the work.

A nanotube membrane also has the advantage of simplicity. Some companies, such as Denmark’s Aquaporin, are working on molecular filters that rely on a synthetic version of a natural protein called an aquaporin. Although scientists have struggled with making reasonably uniform carbon nanotubes,they are farther along than trying to make synthetic aquaporin. (General Electric, which has been snapping up water companies in the past few years, is working on similar molecular straw membranes.)

Porifera by the way were the runner-up the air, water and waste award at the Clean Tech Open. The winner was Over the Moon Diapers, which is working on environmentally friendly diapers. The prize for Over the Moon came with a $100,000 value and attracts attention from VCs.

Carbon Nanotube Manufacturing, Experiments & Simulations

October 10, 2008

Now we’re cooking with gas. This article in physorg.com entitled Breakthrough for carbon nanotube materials lays out how

NanoTech Institute of the University of Texas at Dallas (UTD) – CSIRO has achieved a major breakthrough in the development of a commercially-viable manufacturing process for a range of materials made from carbon nanotubes.

The article gives their bonafides:

As reported in today’s edition of the prestigious international scientific journal, Science – the UTD/CSIRO team recently demonstrated that synthetically made carbon nanotubes can be commercially manufactured into transparent sheets that are stronger than steel sheets of the same weight.

How is it done? More importantly, what’s their production rate?

Starting from chemically grown, self-assembled structures in which nanotubes are aligned like trees in a forest, the sheets are produced at up to seven meters per minute. Unlike previous sheet fabrication methods – using dispersions of nanotubes in liquids – this dry-state process produces materials made from the ultra-long nanotubes required to optimise their unique set of properties.

How long will it be before this process is available for commercialization?

“Rarely is a processing advance so elegantly simple that rapid commercialisation seems possible, and rarely does such an advance so quickly enable diverse application demonstrations”, says Dr Ray H. Baughman of the NanoTech Institute.

Please someone make sure that funding is available to synch this manufacturing work with the carbon nanotube work being done at LLNL. My wag is that we’re talking about funding $.2 million- $2 million to adapt this process for carbon nanotube membranes. One guy on the ball is all it takes.

A while back I asked a member of the LLNL team what the best investment of dollars would be for research in this field. He said that the best investment currently would be “in coming up with scalable (economical) processes for producing membranes that use nanotubes or other useful nanomaterials for desalination.”

Now that we have the “scalable (economical) processes” –the next job is to adapt it to desalination membranes.
……………..
In what looks like a first for the University of North Carolina at Chapel Hill–a team there has produced some experimental results for the way water behaves inside carbon nanotubes.

The team of scientists, led by Yue Wu, Ph.D., professor of physics in the UNC College of Arts and Sciences, examined carbon nanotubes measuring just 1.4 nanometers in diameter (one nanometer is a billionth of a meter). The seamless cylinders were made from rolled up graphene sheets, the exfoliated layer of graphite.

“Normally, graphene is hydrophobic, or ‘water hating’ – it repels water in the same way that drops of dew will roll off a lotus leaf,” said Wu. “But we found that in the extremely limited space inside these tubes, the structure of water changes, and that it’s possible to change the relationship between the graphene and the liquid to hydrophilic or ‘water-liking’.”

The UNC team did this by making the tubes colder. Using nuclear magnetic resonance – similar to the technology used in advanced medical MRI scanners – they found that at about room temperature (22 degrees centigrade), the interiors of carbon nanotubes take in water only reluctantly.

However, when the tubes were cooled to 8 degrees, water easily went inside. Wu said this shows that it is possible for water in nano-confined regions – either human-made or natural – to take on different structures and properties depending on the size of the confined region and the temperature.

How is this applicable to semipermiable membranes?

In terms of potential practical applications, Wu suggested further research along these lines could impact the design of high-tech devices (for example, nano-fluidic chips that act as microscopic laboratories), microporous sorbent materials such as activated carbon used in water filters, gas masks, and permeable membranes.

“It may be that by exploiting this hydrophobic-hydrophilic transition, it might be possible to use changes in temperature as a kind of ‘on-off’ switch, changing the stickiness of water through nano-channels, and controlling fluid flow.”

I would think too that the next experiment would be in which you varied the pressure on the carbon nanotube. Subsequently, you’d want to build a simulation that modeled for variations of temperature and pressure across a carbon nanotube membrane.
……………

posted on this story back in June about how reseachers at LLNL were working at the 1.6 nanometer level. Their work confirmed simulations that showed salt would be rejected at these levels–and that the primary rejection driver would be charge.

What to do next? Well do a simulation.

This time simulations were done at the 1.0 nanometer level:

Professor N.R. Aluru at the Beckman Institute for Advanced Science and Technology at the University of Illinois at Urbana-Champaign, and Sony Joseph, who defended his Ph.D. thesis recently, have used computer simulations to explore a method by which water transport through smaller carbon nanotubes could be further enhanced.

Why?

“Until now,” Sony Joseph tells PhysOrg.com, “previous simulations had shown that single file water movement in short carbon nanotubes have net transport in both directions. But if you could get the water to orient in one direction, in a long tube, you could have net transport along that direction.

A second press release from the University of Illinois on the subject dated September 16, 2008 elaborates:

“Extraordinarily fast transport of water in carbon nanotubes has generally been attributed to the smoothness of the nanotube walls and their hydrophobic, or water-hating surfaces,” said Narayana R. Aluru, a Willett Faculty Scholar and a professor of mechanical science and engineering at the U. of I.

“We can now show that the fast transport can be enhanced by orienting water molecules in a nanotube,” Aluru said. “Orientation can give rise to a coupling between the water molecules’ rotational and translational motions, resulting in a helical, screw-type motion through the nanotube,” Aluru said.

Using molecular dynamics simulations, Aluru and graduate student Sony Joseph examined the physical mechanism behind orientation-driven rapid transport. For the simulations, the system consisted of water molecules in a 9.83 nanometer long nanotube, connected to a bath at each end. Nanotubes of two diameters (0.78 nanometers and 1.25 nanometers) were used. Aluru and Joseph reported their findings in the journal Physical Review Letters.

For very small nanotubes, water molecules fill the nanotube in single-file fashion, and orient in one direction as a result of confinement effects. This orientation produces water transport in one direction. However, the water molecules can flip their orientations collectively at intervals, reversing the flow and resulting in no net transport.

In bigger nanotubes, water molecules are not oriented in any particular direction, again resulting in no transport.

Water is a polar molecule consisting of two hydrogen atoms and one oxygen atom. Although its net charge is zero, the molecule has a positive side (hydrogen) and a negative side (oxygen). This polarity causes the molecule to orient in a particular direction when in the presence of an electric field.

Creating and maintaining that orientation, either by directly applying an electric field or by attaching chemical functional groups at the ends of the nanotubes, produces rapid transport, the researchers report.

“The molecular mechanism governing the relationship between orientation and flow had not been known,” Aluru said. “The coupling occurs between the rotation of one molecule and the translation of its neighboring molecules. This coupling moves water through the nanotube in a helical, screw-like fashion.”

In addition to explaining recent experimental results obtained by other groups, the researchers’ findings also describe a physical mechanism that could be used to pump water through nanotube membranes in next-generation nanofluidic devices.

I would think that first generation carbon nanotube desalination membranes –in order to keep the flow in one direction–could obtain the charge by “directly applying an electric field”. Then later generation membranes membranes could obtain charge by “attaching chemical functional groups”.

Why is this important?

Joseph and Aluru, are especially interested in using this technology for water purification and nanofiltration. “We are trying to show how this would aid the process of reverse osmosis,” Aluru says.

Joseph and Aluru emphasize that, right now, this work is largely based on computer simulations with theoretical models. Joseph explains that right now water transport through nanotube membranes of two nanometers have been achieved, but that scientists are working toward pumping water through membranes that are less than one nanometer.

“We’ve shown that it is theoretically possible to get this sort of water transport,” Joseph points out. “The next step is getting to the point where this could be tested.”

This looks like it builds on the work of Jason Holt mentioned in my last post on LLNL work.

However, if manufacturers are already able to get commercial production volumes for the longer nanotubes–it may not be so important to do further work with the shorter nanotubes.

Anyhow, the simulation articles are here:

Orienting Flow in Carbon Nanotubes

Simulations help explain fast water transport in nanotubes

Heat Transfer Efficiency For Boiling Water Increased 30 Fold

June 30, 2008

Jeez, here’s still another amazing innovation. Get this. A couple of researchers at Rensselaer Polytechnic Institute have figured out how to make water boil at a 30 fold increase in the number of bubbles created per unit of energy. That means that energy costs to create steam would drop by 30 fold. This process “could translate into considerable efficiency gains and cost savings if incorporated into a wide range of industrial equipment that relies on boiling to create heat or steam.”

Ya think one of them might be desalinaton? Hmm well also there is the Kanzius effect. An efficient heat transfer process there might make the 3000 degree flame net energy for the process. As well you might be able to get more steam for less energy to reduce costs of a kanzius steam reformation process. or efficiently boiled water might be injected into gypsum deposits. imho the salt would play hell on the nanorods that coat the copper sufaces mentioned in the article below. but if you could desalt and heat the water before it hit the nanorod copper plates the steam could be used to drive electrical generation more efficiently to reduce costs of membrane desalination. Finally, a word about pipelines. Maybe an efficient heat transfer material in combination with hydrophobic materials would enable cheaper ways to push water uphill in a pipe. Anyhow check out the article below. Interesting stuff. There’s a Rensselaer Polytechnic Institute Pr

As well as the write up below in PhyOrg.

Anyhow consider the article below.

New nano technique significantly boosts boiling efficiency

 A scanning electron microscope shows copper nanorods deposited on a copper substrate. Air trapped in the forest of nanorods helps to dramatically boost the creation of bubbles and the efficiency of boiling which in turn could lead to new ways of coo ...

A scanning electron microscope shows copper nanorods deposited on a copper substrate. Air trapped in the forest of nanorods helps to dramatically boost the creation of bubbles and the efficiency of boiling, which in turn could lead to new ways of cooling computer chips as well as cost savings for any number of industrial boiling application. Credit: Rensselaer Polytechnic Institute/ Koratkar

Whoever penned the old adage “a watched pot never boils” surely never tried to heat up water in a pot lined with copper nanorods.

A new study from researchers at Rensselaer Polytechnic Institute shows that by adding an invisible layer of the nanomaterials to the bottom of a metal vessel, an order of magnitude less energy is required to bring water to boil. This increase in efficiency could have a big impact on cooling computer chips, improving heat transfer systems, and reducing costs for industrial boiling applications.

“Like so many other nanotechnology and nanomaterials breakthroughs, our discovery was completely unexpected,” said Nikhil A. Koratkar, associate professor in the Department of Mechanical, Aerospace, and Nuclear Engineering at Rensselaer, who led the project. “The increased boiling efficiency seems to be the result of an interesting interplay between the nanoscale and microscale surfaces of the treated metal. The potential applications for this discovery are vast and exciting, and we’re eager to continue our investigations into this phenomenon.”

Bringing water to a boil, and the related phase change that transforms the liquid into vapor, requires an interface between the water and air. In the example of a pot of water, two such interfaces exist: at the top where the water meets air, and at the bottom where the water meets tiny pockets of air trapped in the microscale texture and imperfections on the surface of the pot. Even though most of the water inside of the pot has reached 100 degrees Celsius and is at boiling temperature, it cannot boil because it is surrounded by other water molecules and there is no interface — i.e., no air — present to facilitate a phase change.

Bubbles are typically formed when air is trapped inside a microscale cavity on the metal surface of a vessel, and vapor pressure forces the bubble to the top of the vessel. As this bubble nucleation takes place, water floods the microscale cavity, which in turn prevents any further nucleation from occurring at that specific site.

Koratkar and his team found that by depositing a layer of copper nanorods on the surface of a copper vessel, the nanoscale pockets of air trapped within the forest of nanorods “feed” nanobubbles into the microscale cavities of the vessel surface and help to prevent them from getting flooded with water. This synergistic coupling effect promotes robust boiling and stable bubble nucleation, with large numbers of tiny, frequently occurring bubbles.

“By themselves, the nanoscale and microscale textures are not able to facilitate good boiling, as the nanoscale pockets are simply too small and the microscale cavities are quickly flooded by water and therefore single-use,” Koratkar said. “But working together, the multiscale effect allows for significantly improved boiling. We observed a 30-fold increase in active bubble nucleation site density — a fancy term for the number of bubbles created — on the surface treated with copper nanotubes, over the nontreated surface.”

Boiling is ultimately a vehicle for heat transfer, in that it moves energy from a heat source to the bottom of a vessel and into the contained liquid, which then boils, and turns into vapor that eventually releases the heat into the atmosphere. This new discovery allows this process to become significantly more efficient, which could translate into considerable efficiency gains and cost savings if incorporated into a wide range of industrial equipment that relies on boiling to create heat or steam.

“If you can boil water using 30 times less energy, that’s 30 times less energy you have to pay for,” he said.

The team’s discovery could also revolutionize the process of cooling computer chips. As the physical size of chips has shrunk significantly over the past two decades, it has become increasingly critical to develop ways to cool hot spots and transfer lingering heat away from the chip. This challenge has grown more prevalent in recent years, and threatens to bottleneck the semiconductor industry’s ability to develop smaller and more powerful chips.

Boiling is a potential heat transfer technique that can be used to cool chips, Koratkar said, so depositing copper nanorods onto the copper interconnects of chips could lead to new innovations in heat transfer and dissipation for semiconductors.

“Since computer interconnects are already made of copper, it should be easy and inexpensive to treat those components with a layer of copper nanorods,” Koratkar said, noting that his group plans to further pursue this possibility.

Source: Rensselaer Polytechnic Institute

LLNL Researchers use carbon nanotubes for molecular transport

June 21, 2008

The last time I wrote about the researchers at LLNL was back in December 2006. Their carbon nanotube research is the most promising imho of a half dozen interesting lines of research that I’ve seen. That is, the goal of membrane research is a to have a pipe that ends in in a covered mushroom shape that rises above the ocean floor in 50-100 feet of salt water–someplace where there is a strong coastal current. Fresh water filters through a membrane without extra energy and falls through some kind gas that’s hostile to aerobic and anaerobic bacteria–like maybe chlorine. This research provides a path to that goal.

In the initial discovery, reported in the May 19, 2006 issue of the journal Science, the LLNL team found that water molecules in a carbon nanotube move fast and do not stick to the nanotube’s super smooth surface, much like water moves through biological channels. The water molecules travel in chains – because they interact with each other strongly via hydrogen bonds.

Of course one of the most promising applications for this process is seawater desalination.

These membranes will some day be able to replace conventional membranes and greatly reduce energy use for desalination.

The current study looked at the process in more detail.

In the recent study, the researchers wanted to find out if the membranes with 1.6 nanometer (nm) pores reject ions that make up common salts. In fact, the pores did reject the ions and the team was able to understand the rejection mechanism.

What was the rejection mechanism?

Fast flow through carbon nanotube pores makes nanotube membranes more permeable than other membranes with the same pore sizes. Yet, just like conventional membranes, nanotube membranes exclude ions and other particles due to a combination of small pore size and pore charge effects.

But it was principally charge that did the deed.

“Our study showed that pores with a diameter of 1.6nm on the average, the salts get rejected due to the charge at the ends of the carbon nanotubes,” said Francesco Fornasiero, an LLNL postdoctoral researcher, team member and the study’s first author.

The salinity of the water studied was much lower than brackish water. So work will need to be done to figure out how to increase the charge at the tip of the nanotubes. Might be good to highly charge the filler material. Or put imperfections in the carbon nanotubes to increase their charge. In this blog i mention that charge might be related to something else. Here’s still another take on charge. Might be good work for simulations. Earlier work last fall showed a nice congruence between experimental work and computer models.

Finally Siemans recently announced that they had developed a process that would cut energy use in half. Their method involved removing salt using an electric field. So an interesting way to “artificially” introduce a larger charge for higher salt concentrations would be to create a small electric field along the surface of the carbon nanotube. this of course, costs energy. But it would make an interesting interim step.

As well, its helpful to mention that the study just announced by LLNL was not about how water flowed through the membrane but rather the experiment was designed to more precisely peg the mechanism by which salt rejection took place at the carbon nanotube’s tip. So the animation in the press release is a bit misleading

Some further study of the process by which water flowed through the nanotubes was done by Jason Holt.

He has an experimental project that focuses precisely on the issue of understanding water and ion structure within carbon nanotubes. He has “a paper just published online in Nanoletters that might be of interest (although a little tangential to desalination):”
http://pubs.acs.org/cgi-bin/abstract.cgi/nalefd/asap/abs/nl080569e.html
There is also a review article out that should be accessible to the outside community:
http://www.springerlink.com/content/375433hj6nuj0215/
Here’s a physorg write up of Holt’s work.
Finally, an earlier blog I did on this subject my be helpful.

A while back I asked a member of the LLNL team what the best investment of dollars would be for research in this field. He said that the best investment currently would be “in coming up with scalable (economical) processes for producing membranes that use nanotubes or other useful nanomaterials for desalination.”

Here is a link to the LLNL press release.

More on the LLNL carbon nanotube membranes

December 18, 2006

For several months I have been looking for work that might follow up on the Lawrence Livermore carbon nanotube break through annouced in May that promises in 5-10 years — to enable manufacturers to develop semipermiable membranes that cheaply desalinise water.

A couple weeks ago I posted a piece called Honey I shrunk the carbon nanotubes .

Recently some Japanese researchers figured out how to pack carbon nanotubes together effficiently.

Here are a couple more links to experimental work I’ve posted in the last several months that might follow up on the Livermore work. 1.) 2.) 3.) 4.) 5.) 6.) . This last #7.) discusses how charge could be used for semipermiable membranes.

The reason I mention this, is because according to reports widely published in provincial newspapers from Australia in October it seems that the Livermore team’s solution has already addressed all the problems for which I presented possible solutions. Did their solution come from some exotic process that’s not scaleable? Nope . They said they used “standard microfabrication techniques that in theory can be scaled.” Did the carbon nanotubes successfully filter out salt? Yup. They said current results showed that “nanotube membranes could remove up to 95 per cent of the chloride”–with better results in the offing. Was there any leakage around the sides of the carbon nanotubes? Nope. They said they deposited “a filler material – a matrix material that can fill the tiny gaps between the tubes to allow us to make a stable membrane.” Won’t these little nanotubes clog up quickly? Nope. The carbon nanotube “also showed that they have inherent anti-fouling characteristics.” Here’s the kicker. How come the larger carbon nanotubes were able to reject the smaller sodium ions. Guess. uh huh. Twas charge. “The fact that most of the sodium was not trapped by the experimental membrane pointed to the electrical charge mechanism being the active factor.” (There’s some serious implications here for hydrogen filtration as well.)

So why is this membrane 5-10 years away from a beta mass production model–and not, say, 18 months away?

Question 7How long do you think it will be before the technology you have been discussing becomes, if not everyday, at least usable?

Jason Holt – That’s a good question and one we often get. I think it depends on the kind of investment and partnering that we do with companies. There has been a lot of interest in the States from some of the big water treatment companies like GE and Culligan. They have contacted us and are interested in scale-up and commercialisation of the technology. If we get their involvement, a five-year time line will probably be overly optimistic – it’s more likely to be 10 years.

So it sounds like Mr. Holt is interested in working with smaller production companies that have already mastered the mass production of nanotubes with a a scaled up methodolgy simliar to his own methods for producing carbon nanotubes. Here are two possible candidates that I’ve pulled from back blogs that I’ve posted here and linked to above. One Nanovip.com and the other is NanoH20. There’s likely a couple more mentioned in my blog.

Finally a point should be made as to the real potential cost cutting here. According to the piece.

“The take-home message here is that the combination of fast flow and the small pore size suggests that we could use these membranes to significantly lower the energy cost of nanofiltration or desalination. A 100-fold higher permeability can reduce the energy costs by more than 80 per cent.”

If you just stuck a pipe in the ocean with a carbon nanotube filter on the end– the only enery costs would be pipeline pumping costs. Further, there wouldn’t be a big desal plant that would need to be built. What’s more the carbon nano tube membranes seem to have some anti fouling characteristics. So what the hey. Between collapsed energy, maintenance and capital costs — don’t you think perhaps 10 fold cost reductions can be done in 10 years– and maybe lot less?

Anyhow, this stuff is fun to consider. Here’s link to the brief article. In the meantime I’ve copied and pasted below a detailed article that covers the same event.

[Go to Home page] Australian Academy of Science | Conferences and lectures
Transcripts of lectures and speeches


Forthcoming conferences and lecturesConference proceedingsTranscripts of lectures and speeches PUBLIC LECTURE: Desalinating water cheaply – exploring technologies
Fast water transport through carbon nanotubes and implications for water treatment

The Shine Dome, Canberra, 26 October 2006 Dr Jason K Holt
Chemistry and Materials Science Directorate, Lawrence Livermore National Laboratory, California, USA


Jason HoltIntroduction (Professor Kurt Lambeck)I am pleased to introduce Dr Jason Holt who will speak on something that is very much on everybody’s mind – water! But what will be different from most of the recent water discussions, is that he does not see the solutions in terms of market forces and water trading, beloved by economists. He will be addressing new technologies that promise to produce more of the drinkable form through the use of nanotube membranes and desalination.

Dr Holt is a research scientist at the Lawrence Livermore Laboratory in California with experience in nanomaterials, nanoscale devices and analytical chemistry. His interests are very much in the application of this experience to alternative energies and the environmental sector, including nanotube membranes for water treatments.

Recently his research featured on the cover of Science and this brought his work to our attention. In the press release accompanying the article, he promised that a nanotube membrane on a silicon chip would offer a cheap solution for desalinisation. This is something that our coastal cities are most interested in and this is why Jason will be joining the Academy’s High Flyers Think Tank in Adelaide this coming week.

So without further ado, I invite you Jason to talk about Desalinating water Cheaply.


Jason HoltSlide 1
(Click on image for a larger version) Thank you very much for that introduction and thanks to all of you for coming here this evening. Thanks also to Sophia Dimitriadis for arranging my visit here.Tonight I will tell you about some of our recent work, our recent discovery of enhanced water transport through carbon nanotubes, and what implications that has for water treatment. What I hope to demonstrate today is that this is one of the areas in which nanotechnology can really benefit the environment. I know that there have been some concerns raised about potential environmental or health consequences of nanotechnology. I hope to show you that water treatment is an area where nanotechnology can really lend itself.I want to acknowledge some of my co-workers within our BioNanoSciences Group at the laboratory – in particular, Hyung Gyu Park who is a University of California Berkeley graduate student who has worked with me closely on this project – and also I want to acknowledge our two group leaders, Aleksandr Noy and Olgica Bakajin.Slide 2
(Click on image for a larger version) I will start off with some background information about the water shortage problem and present some relevant facts and figures that most of you will probably be familiar with.I will then introduce available desalination technologies, desalination being one of the technologies that can potentially address the water shortage issue.And then I will discuss our concept of a nanoengineered membrane, based on carbon nanotubes, which I think can address many of the shortcomings that conventional membranes, specifically reverse osmosis (RO) membranes, currently suffer from.

I will present some of our preliminary performance data showing how, in principle, implementing these nanoengineered membranes into an existing RO facility could significantly reduce the costs associated with water treatment.

Then I will wrap up my talk and show you where we are intending to go in the future.

Slide 3
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So what is the problem that we are trying to address? This is nicely summarised by the three quotes on this slide. The general theme here is that to us globally, in the 21st century, water is going to be what oil was in the 20th century: a precious commodity. And the key thing to emphasise here when considering water versus oil is that there are a number of viable alternatives to oil but there really is no substitute for fresh water.

Slide 4
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Our fresh water supplies have always been scarce – as you can see, just a very small fraction of the total amount of water on the planet is fresh water – and these supplies are dwindling. It is estimated that, if current projections hold, there will be a huge increase in the number of people around the world facing water scarcity, reaching as high as 18 per cent of the world’s population in the coming decades.

I also want to emphasise that 70 per cent of water usage is for agricultural purposes, often in very water poor areas – I think this is a global figure but the percentages probably look very similar in Australia. A case in point is China, the northern part of the country has two-thirds of the cropland but only has one-fifth of the water.

I myself am relatively new to the water treatment field and I am astounded by some of these statistics.

Slide 5
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So then where should we go for additional water? You see here a list of the various alternatives, prioritised by relative cost.

One obvious choice is water re-use: recycling water from treatment plants and then potentially injecting that into aquifers for later use, or having a dual distribution where you separate out the non-potable water for use in irrigation and other applications where high purity water is not essential.

Next on the list is the treatment of marginally impaired waters. These are water sources that have maybe one or two species in solution, such as nitrate or arsenic, and none of the other impurities that you would have in, say, sea water. Some of the local water supplies in the Bay Area of San Francisco, where I live, are marginally impaired waters because they have high nitrate levels. Because of this, researchers within our Energy and Environment laboratory are developing so-called ‘smart’ membranes that can selectively remove nitrates from solution.

Finally there is desalination of sea water and brackish water, which has a salinity about one-tenth that of sea water. In the US, desalination of brackish water is more prevalent than desalination of sea water, although the US only uses a very small percentage of the total brackish water reserve.

Sea water desalination has not been widespread. This is because of the energy needed to drive water across the conventional low-permeability, reverse osmosis membranes. In fact, energy use is about 50 per cent of the cost of sea water desalination. If we can significantly reduce that energy figure we can potentially make sea water desalination more widespread.

Slide 8
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We have here a list of the conventional desalination technologies that are available.

In reverse osmosis, a saline solution is pressurised, driven across a membrane – which prevents the sodium and chloride ions from permeating – and fresh water is produced.

Another membrane-based technology is electrodialysis. With this technique cation- and anion-selective membranes, along with electrodes, drive the positive and negative ions to opposite sides, producing demineralised permeate.

Another technique, which is commonly used in arid regions like north Africa and the Middle East, is thermal-based distillation, where heat is used to distil the water. Some of that heat is recaptured from vapour condensation.

Slide 9
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So what do the energy figures look like? This graph shows the salinity, for both reverse osmosis and electrodialysis, plotted against the cost in megajoules per cubic centimetre.

Reverse osmosis, as I have mentioned, involves significant energy costs because of the high pressures needed to push the saline water across the membrane. The natural osmotic pressure has to be overcome, and the water needs to be driven across the membrane at significant flow rates: this is very energy intensive.

Electrodialysis suffers from similar problems. The membranes that are used are not very permeable to the ions; they have high resistivity. And electrodialysis is not very efficient except for brackish water. As you can see from the cost curves, at higher salinities, as represented by sea water, RO is the more cost effective alternative.

The thermal methods require significantly higher energy expenses. Theoretically, the minimum amount of energy required to separate water from the saline solution is about 1000 kW per acre foot. The amount of energy needed to distil saline water is 800 times more than that. This is why thermal distillation isn’t plotted on the curve. It is the most energy intensive of all the techniques and is really only suitable in regions like north Africa and the Middle East.

So, I would argue that of these technologies RO – because it can be used across a range of salinities – is the preferred option if we can improve the existing membrane technologies.

Slide 11
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Listed here are the current problems that we face with reverse osmosis membranes, one of which is low permeability. I will show you later, with our concept of nanotube membranes, where we can have the greatest impact is in developing a high-permeability membrane.

Chemical degradation of conventional RO membranes is also a problem. The membranes are susceptible to fouling, which means that it is essential to pre-treat the water. Polyamide membranes can be degraded by chloride ions, which is a problem given that chloride is one of the major ionic species in sea water. Another type of polymer RO membrane, cellulose acetate, is susceptible to degradation when the pH is outside the target range.

I think nanoengineered membranes offer a potential solution to many of these problems, not just in permeability but also chemical compatibility.

So now I’ll tell you about carbon nanotubes and how we are using carbon nanotube membranes to tackle some of these problems.

Slide 12
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For those of you who are not familiar with carbon nanotubes: nanotubes are atomically-smooth, molecule-sized channels. The tubes that we make are of the order of a nanometre (1 nm) in diameter. To offer a size perspective, 1nm is about 50,000 times thinner than a human hair and just a few water molecules in diameter.

The interesting thing is that water behaves very differently when it is confined within a carbon nanotube. This has been simulated for many years but not measured experimentally until very recently. Researchers predict that water forms unique structures within carbon nanotubes, and under the right conditions, it can actually form a one-dimensional chain of water molecules.

Perhaps because of the water ordering that takes place, it has long been predicted that the water would flow extremely fast through the channels. The best real world analogy we can come up with is that the water flow in these channels is like getting the same flow through a garden hose as you would get through a fire hose or a channel that is ten times larger.

On the bottom right-hand side of this slide you see an enhancement of the flow rate, of several orders of magnitude, through these channels. This is what had been predicted but it had not been measured until very recently.

Slide 13
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How can we make a membrane out of carbon nanotubes? How can we take these interesting properties that the individual nanotubes possess and make a membrane that will allow us to test these predictions?

Our fabrication process is illustrated here schematically. I won’t go into all the details but I am happy to answer questions about the particulars at the end of the lecture.

In brief, we start out with a prepatterned silicon wafer. We deposit a thin bimetallic metal layer on the surface and heat it to a high temperature to form nanoparticle ‘seeds’. These serve as the catalytic seeds to nucleate the growth of carbon nanotubes. And because of the high density of these particles, the tubes that then grow from the nanoparticles are vertically aligned. They have a little bit of ‘squiggle’ in them, as is illustrated in this schematic, but the nanotubes do span from top to bottom.

The next step in the fabrication is to deposit a filler material – a matrix material that can fill the tiny gaps between the tubes to allow us to make a stable membrane. For that purpose we use silicon nitride (Si3N4). We have also demonstrated vapour-phase polymer deposition between the nanotubes, but for the membranes that I will talk about here we have used Si3N4 exclusively.

We coat the nanotubes, use a series of etching processes to open up the channels on either side, and the result is a nanotube membrane where the only pores in the structure are the carbon nanotubes themselves. The 2 x 2 cm square test chip that we made is shown here. I want to emphasise that although thetest chip is extremely small in scale, the techniques that we used are inherently scalable. We are using standard microfabrication techniques that in theory can be scaled up to a size that would be suitable for making a real reverse osmosis membrane.

Slide 14
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I also want to show some microscopy to give you a sense of what the individual nanotubes look like and what the membrane itself looks like. These are transmission electron microscopy (TEM) images of carbon nanotubes. Image A shows bare carbon nanotubes and the inset shows an individual carbon nanotube with an inner channel diameter of less than 2 nm. It was essential to verify the size because the nanotube transport simulations that I mentioned earlier all focused on a regime less than 2 nm in size. Interesting physics happen at that scale and fortunately our TEM expert Yinmin (Morris) Wang went through the images to come up with a size distribution – it turns out that we have an average channel diameter of 1.6 nm.

Image C is a thin slice of the membrane, looking at it down the axis of the nanotubes. We wanted to verify that the only pores in the membrane were the nanotubes themselves and that there were no voids in the Si3N4, because we want to focus on transport through the nanotubes exclusively and ensure that there are no cracks in the structure. The bright spots correspond to holes in the membrane, and all the spots circled in yellow are individual nanotubes which have a channel diameter of less than 2 nm.

Slide 15
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But the question is: how does the membrane perform in real life? What are its filtration characteristics? Can we actually filter out particles that are nominally larger than the 1.6 nm channel that we have measured?

So we carried out a series of filtration experiments where the membrane is mounted in a flow cell and placed in a solution of nanoparticles (the nanoparticles are upstream of the membrane). We apply pressure and collect what comes out.

We started out with a solution containing 5 nm gold particles – these particles are about three or four times larger than the pore size – and we saw no evidence that these particles permeated through the structure. This gave us a good indication that there are no large cracks or voids in the membrane.

We then tried smaller particles, at 2 nm – just nominally larger than the nanotube pore size – and again we saw no evidence for passage of these particles through the membrane.

The only species that we saw permeate through the membrane was a 1.3 nm organometallic dye. Again, this gave us a good indication that the membrane is indeed void-free.

As a control, we also looked at a multiwall carbon nanotube membrane. This has a much larger pore size, about 6 to 7 nm in diameter. It also showed filtration characteristics consistent with the measured pore size; allowing 5 nm particles to permeate but not 10 nm gold metal particles.

Slide 17
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After confirming that the membrane was void-free, we wanted to tackle the physics question: what is the flow rate through an individual carbon nanotube? We needed to answer this so we could compare it to the simulation predictions that had been made several years ago. We also wanted to find out how the nanotube pores compare with those of conventional membranes.

We looked at a series of three carbon nanotube membranes, as well as a polycarbonate membrane – a conventional membrane with a pore size about 10 times larger than our nanotubes and the smallest pore size commercially available. I should emphasise, that to quantify the flow rate per nanotube we need to know how many pores are actually open and expanding the membrane structure and being wetted with water. As you might imagine, this is difficult to pinpoint exactly, but we can come up with an upper limit by using the microscopy images that I showed you earlier.

So, going through and counting the number of pores in several different regions, we come up with an extremely high pore density at 250 billion pores per square centimetre. If we use this pore density as our upper limit, it will allow us to come up with a minimum flow rate per nanotube.

We found that the flow rate per nanotube is orders of magnitude higher than what conventional hydrodynamic theory would suggest. By comparison, the polycarbonate membrane that we measured showed only a very slight enhancement.

Another way of trying to capture this is in terms of what is called slip length – I won’t go into the theory or the equations, but the slip length is an indication of how frictionless the flow is: large values would indicate that the flow through the nanotubes is nearly frictionless. This is something that simulations have long predicted, but it is a matter of being able to measure it experimentally on this scale – less than 2 nm. The flow rates that we measured are comparable with what the simulations have long predicted.

Slide 18
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What does the physics of the flow rates mean in practical terms, particularly for membrane developments and desalination?

I have plotted the permeability for the nanotube membranes and compared it with the permeability for conventional polycarbonate membranes. Permeability is what people in the membrane community care about – that is, the volumetric flow rate per unit area, divided by the pressure drop.

As you might expect from the enhanced flow seen through the tubes and the high packing density, we see a significant enhancement in water permeability when compared to conventional membranes – in fact, about a 100-fold higher water transport rate.

As an aside: we also see enhanced flow of gases. I haven’t discussed this because the application that I am focusing on is water treatment, but if anyone is interested in discussing that afterwards I would be glad to.

The take-home message here is: the combination of fast flow and the small pore size suggests that we could use these membranes to significantly lower the energy cost of filtration – nanofiltration or desalination, in this case.

Slide 21
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So how would this carbon nanotube membrane perform in reverse osmosis applications? We worked with systems modellers to ask the question: what effect would this higher-permeability membrane have on a reverse osmosis facility? The schematic of the model is shown here. We consider the feed stream as well as the permeate stream, and then the brine or concentrated stream.

One thing I should mention is that, unlike a real facility where energy recovery takes place in the high-pressure brine stream, we don’t take this into account in the model. But, in terms of showing how the energy costs scale with permeability, the inclusion of the energy recovery is not really important.

This table shows the impact of enhanced permeability on energy costs. For a typical polymer RO membrane permeability is 10-11 m3/m2-sec-Pa. Our nanotube membranes, as I mentioned, are about 100-fold higher. The cost which is shown here is the energy cost of desalinating, in terms of kilowatt/hours per cubic metre. We include here not only the energy costs of operating the pumps to produce the required pressure but also the energy to pump in the water from the source. You can see that a 100-fold higher permeability can reduce the energy costs by more than 80 per cent. So there is potentially a very significant impact on the energy costs of treating sea water.

In this model we fixed the flow rate, but what if you keep the pressure the same, what effect will higher permeability have on energy cost? Another way of looking at the problem is to ask: if we operate at the same energy or same pressure, what effect would that have? And, as you might imagine, from 100-fold higher permeability at the same pressure we would get 100-fold higher flow rate of water through the membrane. Which way a given plant should operate is perhaps not such a straightforward optimisation problem and may depend on the particular peculiarities of that region. But it shows you that, either way, with the high-permeability membrane we can, in principle, have a large impact.

Slide 22
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What does this mean in dollar terms? A way to look at this is the permeate costs per cubic metre. Here we have included both the cost of the membrane and electricity. On the left hand graph we show permeate costs versus membrane area for three curves in order of increasing permeability and we find a minimum in the permeate cost at about 8000 m2. In the graph on the right hand side, we took that 8000 m2 value and applied it to cost versus permeability and we see a significant reduction in the cost – from about $1 per cubic metre down to 40 cents.

So, in addition to the significant reduction in energy costs, we can reduce the actual dollar cost of treating a given volume of water by about 60 per cent.

Slide 23
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The other question is: what kind of selectivity does this membrane exhibit? It is great to have fast water flow through the tubes, but if we can’t reject salt to any significant level then it is obviously not very useful for desalination.

These are very preliminary data that we obtained just in the last month, but our initial findings are that the membranes show very encouraging salt rejection levels. It is important to note that for these experiments we only do a single pass through the membrane. A conventional RO membrane which you might be familiar with is essentially a spiral-wound membrane around the feed tube, so the water has multiple chances to pass through the membrane structure. In effect, it is like having many membranes in series so in a single pass almost all of the chloride is rejected.

With our membrane, the rejection of sodium is slightly less but, in principle, if we had a number of these membranes in series or, if we formatted it as shown on the right-hand side of this slide, the sodium rejection levels could approach 90 or 95 per cent.

What we don’t know at present is the mechanism: why is the membrane behaving in this fashion? Is there physical size exclusion of these ions from the pores, or is it due to surface charge effects? The initial results suggest surface charge effects dominate, but other experiments that we have performed under slightly different conditions show different rejection characteristics. These results are still very preliminary.

The nanotube membranes have some other properties that I would like to point out. They seem to have inherent antifouling characteristics. They don’t readily clog, and when they do we can regain the original permeability just by briefly washing the membrane with deionised water. There are additional parametric studies we would like to carry out, to see how the rejection characteristics vary with the size of the ion and the effect of pH and ionic strength.

Slide 24
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To conclude: reverse osmosis desalination has long been touted as one of the viable solutions for our water scarcity problem, but there have really been no major developments in membrane technology for decades. I think that is what has made sea water RO economically infeasible. In fact, in the US there is really only one large-scale sea water RO facility that has been built, and it has been tied up in a series of legal and technical problems. In principle, it is supposed to come online later this year. The fact that we only have one such facility in the US highlights that operation of these plants is not economically feasible.

I would offer that the carbon nanotube membranes that we have developed show unprecedented water permeabilities and if they can be scaled up we can significantly reduce energy costs associated with reverse osmosis.

So we are taking a two-pronged approach here. One addresses the issue of scale-up: can we make these membranes on an industrially relevant scale? I think the answer to that is yes because we are using conventional fabrication techniques that are amenable to scale-up.

The other approach is to also tackle some of the science questions. We recently started a project to look at some of these issues, and the main question that we want to tackle is: why are we seeing these transport rate enhancements in nanotubes? Is it a consequence of structural ordering that occurs within the tubes? We don’t know yet, but we will use experimental X-ray based techniques to hopefully answer some of these questions. The science we are doing here is not just for science’s sake but because we think that by answering these questions we can actually design better membranes.

Slide 25
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I would like to acknowledge the intellectual and technical contributions from the people listed here, as well as the three year internal funding we received from our Laboratory Directed Research and Development Fund to get this project to the stage it is at right now.

Thank you for your time, and I would be happy to answer any questions.


Discussion Kurt LambeckThanks very much, Jason, for a very stimulating and informative talk. Question 1Jason, could you go back to your slide entitled ‘What kind of selectivity does a CNT membrane exhibit?’, where you discussed the size of the membrane. You mentioned there that a water molecule was 0.3 nm in diameter. The CNTs were 1.6 nm. That means that the water would go through. But it seems to me that not only the water but also the sodium ions and the chloride ions would go through. The nanotube is much bigger than any of those.Slide 23
(Click on image for a larger version) Jason Holt – Yes, that’s true. If the membrane was working on the basis of size exclusion alone, we would in principle see no preferential rejection of chloride. But that’s why I made mention of surface charge effects. What may be happening is preferential rejection of ions that are the same charge as the surface of the membrane. That is perhaps the reason why we see such a high level of rejection of chloride relative to sodium.Question 1 (cont.)So the sodium ions and the chloride ions remain on the surface of the membrane. Don’t they clog it up? Jason Holt – No. On the figures that I mention here, we frequently see preferential rejection of the chloride – most of it still remains in the feed stream, but we only see a small rejection of sodium. So the sodium actually, by and large, can pass through. But over the course of these experiments we haven’t seen significant clogging of the membrane. It seems reasonable to expect some accumulation of those ions near the surface of the pores but we don’t see any reduction in the flow rate, at least over the duration of these experiments that we have carried out.Another thing to mention here, in terms of practical use of this membrane, is that ordinarily you would decide that there is cross-flow occurring, which would really help to prevent accumulation of ions near the surface. We are doing these experiments on the research scale with just a single pass of the membrane, but in practice you would have cross-flow. There are other engineering designs that you can use to minimise the effect of ion concentration near the surface of the membrane.Question 1 (cont.)The permeate then would have a high sodium ion level?

Jason Holt – Yes. In these initial experiments so far we see high sodium content but a low concentration of chloride.

Question 1 (cont.)Is it possible to remove that sodium concentration?

Jason Holt – Yes. I think one way of doing that is to change the surface charge on the membrane. So, instead of the membrane having the negative charges shown on the slide, there are simple chemical routes to converting those to positively charged groups. So in practice what we might have is a multilayered membrane: one like the electrodialysis membranes that I mentioned before, where you have alternating cation- and anion-selective membranes so you can achieve rejection of both species.

Question 2There has been criticism that the salt by-product will be discharged back into the sea, with environmental effects. Have you had any thought about that process, or is there any way of preventing that salt from being discharged back into the sea?

Jason Holt – As far as I know, the Tampa Bay ecosystem – where the only large-scale sea water RO plant in the US is located – appears to allow for it. But the brine is not being discharged directly. As I understand it, the brine is being diluted by a factor of 50 and then discharged into the Gulf of Mexico. But the environment is something that has to be considered wherever a plant is going to be operated. I am not aware myself of any alternatives to discharge, but I know that is a concern regarding the sea water at really concentrated high-salinity RO facilities.

Question 2 (cont.)I have another question. You opened with the scarcity of fresh water, and how it is disappearing. There is a school of thought that the amount of fresh water we received at the time when the earth was formed is what we always have, and our use of it doesn’t diminish that supply very much. It is a question of that quantity of fresh water being unevenly distributed around the world: we are not getting any here in Australia while someone else is getting our share. But basically the volume of fresh water remains constant.

This is not your area, I suspect, but I am just wondering whether anyone has any comments about that, and whether or not that in fact is proven – or thought – to be the case.

Jason Holt – I don’t have any insights myself. Does the question relate to the distribution of fresh water?

Question 2 (cont.)Well, it is not the question of quantity but the question of distribution that we need to tackle. I don’t know how factual that is.

Kurt LambeckThe total water is more or less conserved but there is no reason why the fresh water should be conserved. Take a case where we just make a mess of all the fresh water we have. I can think of no reason for all of that to be conserved.

Question 3Jason, you made mention of the use of Si3N4 as the filler material in the carbon nanotube forests. I am aware of other people using organic-based materials, rather than the material that you use. Would you care to comment on the pros and cons of Si3N4?

Jason Holt – We started using Si3N4 because that was the deposition process available to us. And it turns out that Si3N4 actually forms a very conformal coating around the nanotubes. I don’t have the SEM image to show this, but it does a nice job of filling the gaps between the tubes, which is really the key to making it a stable membrane. It is true that for making RO membranes we wanted to go the polymer route, and I had done some preliminary work looking at vapour-phase deposition of polyimide and parylene. It turns out parylene might be the best choice. It is very resistant to chemical degradation and you can actually reflow parylene at extremely high temperatures, up to 300 or 350°C. So that might be the route that we take in the future – use the same process but with polymer deposition and, essentially, make a flexible nanotube membrane.

Question 4Do you need the matrix material? Could you pack the tubes together to allow the water to flow around the outside of the tubes?

Jason Holt – It’s a good question. Our feeling is that the flow rate enhancements that we see are unique to the interior of the nanotube: flow through the interior of the nanotube is not necessarily going to be the same as the flow between a bundle of nanotubes. That’s part of the answer.

The other, I think, is an issue with the fragility of the membrane. Even a densely packed bundle of nanotubes with no filler material in between them is extremely fragile. You can easily tear a densely packed bundle of nanotubes. So for practical reasons I think we have to use a matrix material approach.

Question 5Just following on from those last two questions about the membrane: I was wondering, as a consumer of desalinated water, what might happen if I swallowed a bit of your membrane. Would there be a risk from ingesting a nanotube?

Jason Holt – That’s another good question. I think a lot of the health concerns about nanotubes, and other nanoparticles for that matter are about free nanoparticles or nanomaterials in solution – and in the United States there are a number of projects looking into health effects in nanotechnology. With this structure here, in particular the nanotubes are firmly embedded in the membrane; they are not free to move. Unless we are working at extreme pressures where we can actually fracture the membrane – which we are not currently doing and it’s not how we would be operating these membranes in a plant – I think there’s minimal concern with respect to the nanotubes becoming dislodged and getting into the water supply.

Question 6Jason, you’ve got the membrane there; on a single pass you’ve got the negative surface charge, so presumably that would retain the sodium; and then you’d have to have the second pass, which would be positive charge and would repel the chloride ion. How do you put these charges on the membrane? You would have to have some dialysis system, or how do you do that?

Jason Holt – This would be done by changing the surface chemistry. We don’t know this for certain, but most likely the negative surface charge on the membrane is due the presence of acid groups – you have carboxylic groups on there, COO- – and with that kind of surface charge there are easy chemical routes to switch that over to a positively charged group, something like an amine group or a basic group. Although we haven’t done that yet, I don’t think it’s a huge barrier to alter the surface chemistry to make a membrane that will reject cations.

Question 6 (cont.)So you have to have two passes?

Jason Holt – Yes, that’s what I think. I think that in practice, unless you can make a membrane with pores that are so small that you’ll be able to reject both species just on the basis of size, it’s going to be hard to make a membrane that will achieve similar rejection levels for both positive and negative ions. I think that practically speaking it may be easier to adopt a multi-layered approach.

Question 7How long do you think it will be before the technology you have been discussing becomes, if not everyday, at least usable?

Jason Holt – That’s a good question and one we often get. I think it depends on the kind of investment and partnering that we do with companies. There has been a lot of interest in the States from some of the big water treatment companies like GE and Culligan. They have contacted us and are interested in scale-up and commercialisation of the technology. If we get their involvement, a five-year time line will probably be overly optimistic – it’s more likely to be 10 years.

Question 8If I might just briefly get to the gas filtration properties of your membranes: I read in your paper in Science that there was a differential selectivity between carbohydrate and non-carbohydrate gases. I wasn’t exactly sure whether that meant that the carbohydrate gases were preferentially passing through the membrane or whether it was the other way around.

Jason Holt – In addition to higher transport rates for all gases, we also see an enhancement of the overall flow rate, with preferential diffusion of hydrocarbons, if you look at C1 through C5 – methane, ethane, all the way up to pentane. We actually see an enhancement in the transport of those gases, compared to what conventional diffusion theory would predict. And it kind of makes sense, based on what is out there in the simulation literature. One idea is that, because of the similarity in structure between a hydrocarbon molecule and the nanotube surface, it may be that these gases actually adsorb onto the nanotube surface and then can diffuse along the surface, as opposed to simply bouncing off the nanotube walls, so to speak. In addition to the water experiments we are also doing some more detailed measurements to try to better understand the gas transport mechanism, because at this stage it is still speculation as to why you see the enhancement in hydrocarbon diffusion.

Question 8 (cont.)It could also be that it has got more intimate interaction with the carbon nanotube inside. It seems that it is slipping through more easily.

Jason Holt – Yes, that is a possibility.

Question 9 I am just wondering what awareness you have of interest or understanding by water supply authorities or industry in Australia in relation to this technology. What sort of understanding or interest is there in Australia?

Jason Holt – We haven’t been contacted, at least in the past few months, by anyone regarding the technology, although we had a discussion today with Ken Matthews from the National Water Commission and he seemed very interested in the technology.

Question 10Jason, I gather from some of the acronyms in your earlier slides that these are double-wall nanotubes. How tight is the control over that? Are they all double-wall, or do you have some single and some multiwall mixed in?

Jason Holt – I glossed over that subtlety because for the purposes of making the membrane all we really care about is the innermost tube. But in reality, the tubes that we are making are, essentially, concentric single-wall tubes. From what we have seen in TEM – of course, it’s hard to get statistics on these things – we have counted about 500 of these tubes and looked at different regions in the TEM, and they all appear to be double-wall tubes with the size distribution that I showed earlier – about 1.5 nm inner diameter and the size cut-off is at about 2 nm. We don’t see any diameters larger than that.

The way we can control that is by tailoring the thickness of the catalyst layer. We are using, as I mentioned in the paper, an iron and molybdenum catalyst layer supported on aluminum, and by adjusting the thicknesses of these catalyst layers we can in turn affect the size distribution of the nanotubes. In fact, just recently we have been able to make similarly structured single-wall nanotubes – we found a recipe that allows us to make this same kind of membrane but comprising single-wall tubes, also vertically aligned and have a slightly smaller pore size – 1.3 to 1.4 nm instead of 1.6 nm.

Kurt LambeckThank you very much, Jason. This has been a very nice example of how basic science can be put to good practical use. I wish some of our masters were present to hear that. Thank you very much.

Jason Holt – Thank you.


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Engineers develop revolutionary nanotech water desalination membrane

November 10, 2006

The headline news in in desal research this week has been from UCLA Henry Samueli School of Engineering and Applied Science.

engineers develop revolutionary nanotech water desalination membrane

UCLA Engineering’s Eric Hoek holds nanoparticles and a piece of his new RO water desalination membrane. Credit: UCLA Engineering/Don Liebig

Researchers at the UCLA Henry Samueli School of Engineering and Applied Science today announced they have developed a new reverse osmosis (RO) membrane that promises to reduce the cost of seawater desalination and wastewater reclamation.

Guess what? The way the UCLA engineers have done it has been to charge the membrane so as allow the water to pass through and repel salt and waste. Does this sound like something I’ve been talking for the last couple months? No?

The new membrane, developed by civil and environmental engineering assistant professor Eric Hoek and his research team, uses a uniquely cross-linked matrix of polymers and engineered nanoparticles designed to draw in water ions but repel nearly all contaminants. These new membranes are structured at the nanoscale to create molecular tunnels through which water flows more easily than contaminants.

Unlike the current class of commercial RO membranes, which simply filter water through a dense polymer film, Hoek’s membrane contains specially synthesized nanoparticles dispersed throughout the polymer — known as a nanocomposite material.

“The nanoparticles are designed to attract water and are highly porous, soaking up water like a sponge, while repelling dissolved salts and other impurities,” Hoek said. “The water-loving nanoparticles embedded in our membrane also repel organics and bacteria, which tend to clog up conventional membranes over time.”

Well, the only part of this that I could brag about having advocated –is the part about using charge to filter water through a carbon nanotube. It doesn’t look like the membrane described above quite follows on the work of the LLNL scientists in May and the work of University of Kentucky scientists last November that showed super fast flow through rates for water passing through carbon nanotubes.)

With these improvements, less energy is needed to pump water through the membranes. Because they repel particles that might ordinarily stick to the surface, the new membranes foul more slowly than conventional ones. The result is a water purification process that is just as effective as current methods but more energy efficient and potentially much less expensive. Initial tests suggest the new membranes have up to twice the productivity — or consume 50 percent less energy — reducing the total expense of desalinated water by as much as 25 percent.

Earlier this year, the LLNL researchers said that the flow rates they had achieved with carbon nanotubes caused them to expect that they could reduce desalination costs by 75% by allowing purified water to pass through the membranes at room temperture and pressure. Compare this to the UCLA researchers saying the savings realized by their membrane would be 25%. This sounds like they have reduced–but not eliminated — the need for energy intensive & cost expensive pumping & plunging water against the membrane.

Interestingly the UCLA researchers have already partnered with a company called NanoH2O to produce the membranes. However, they don’t expect to go into production for two years.

Hoek is working with NanoH2O, LLP, an early-stage partnership, to develop his patent-pending nanocomposite membrane technology into a new class of low-energy, fouling-resistant membranes for desalination and water reuse. He anticipates the new membranes will be commercially available within the next year or two.

So how do you get these membranes up to production. As I mentioned earlier this week one answer might be Nantero.

Nantero, Inc., a nanotechnology company using carbon nanotubes for the development of next-generation semiconductor devices, has resolved all of the major obstacles that had been preventing carbon nanotubes from being used in mass production in semiconductor fabs.

Semi conductors are not semi permiable membranes but likely a lot of the procedures for creating the one will map over onto the other.

Another place they might go to find a production procedure would be Northwestern. Northwestern University has developed a method for making carbon nanotubes in commercial quantities while solving a quality control problem.

This might be a place where a venture capitalist like Firelake Capital might bring parties like Nantero and NanoH2O into a working alliance. Or if the work is still too early — then a national lab might contribute funds and coordinate efforts at NanoH2O and, say, Northwestern.