Galactic Tech Empire

Chapter 154 Desalination
7 month 1 day.

Huang Haojie and a group of researchers from the Seawater Desalination Research Institute are discussing some issues about seawater desalination technology.

Theoretical calculations prove that graphene can be applied to seawater desalination, and the single-layer nanoporous two-dimensional film made has ultra-high selective separation efficiency compared with traditional seawater desalination membranes.

However, the grain boundaries existing inside large-area graphene will reduce the mechanical properties of graphene, and the process of introducing nanopores will further reduce the mechanical properties, resulting in the easy local rupture of the separation film, which greatly reduces the separation efficiency and separation selectivity.

Of course, this problem is nothing to Galaxy Technology, and atomic manipulation technology can perfectly solve this problem.

Current graphene desalination membranes fall into two categories.

One type is the single-atom-thick nanoporous film researched by the team of MIT professor Rohit Karnik.

However, the mechanical strength of single-atom-thick graphene is weak, so the graphene used in the experimental research is supported by polymer membranes.

Moreover, subnanopores are directly introduced into graphene by high-energy electron beam bombardment or oxygen plasma etching, and the pore size distribution is wide, which greatly reduces the separation efficiency, so it cannot be applied in practice.

The other is the graphene oxide film studied by the team of Andre Geim, the winner of the Explosives Physics Prize and a professor at the University of Manchester.

Graphene oxide is easy to mass-produce, but after the graphene oxide film is soaked in the solution, the graphene oxide sheets will absorb water to expand the interlayer distance, which reduces the efficiency of seawater desalination. Therefore, the existing research work mainly focuses on how to control the graphite oxide Interlayer spacing between ene sheets.

In addition, there are related research results in China.

That is the binary structure graphene film that combines graphene nanosieves and carbon nanotubes, which has both the selective separation efficiency of the former and the strength advantage of the latter.

Nanoporous two-dimensional materials with a single atomic layer thickness have the smallest water transport resistance and the largest water permeation flux, and are ideal materials for constructing ultrathin and efficient seawater desalination membranes.

However, the application of ultrathin two-dimensional materials to practical seawater desalination faces two major challenges.

The first is how to prepare large-area crack-free nanoporous [-]D films with excellent mechanical strength and flexibility.

The second is how to introduce sub-nanometer pores with high density and uniform pore size distribution inside the film to achieve efficient and selective passage of water molecules and effective interception of salt ions/organic molecules.

For the first difficulty, carbon nanotubes have excellent mechanical properties and are similar in structure to graphene, and the two can interact through π-π bonds and van der Waals forces.

The carbon nanotube film formed by overlapping carbon nanotubes is a film with a porous network structure (average pore size of 300 nanometers), which not only perfectly matches the structure of graphene, but also does not affect the water permeability.

Therefore, domestic research institutions thought of combining nanoporous graphene with carbon nanotubes to make up for the defects of the former.

They first grew a layer of single-layer graphene on the copper foil, and then covered some areas above with a network of interconnected carbon nanotubes. After the copper foil was dissolved away, a graphene film supported by carbon nanotubes was obtained.

In order to obtain subnanopores with high density and uniform pore size distribution, they grew a layer of mesoporous silicon oxide (average pore size 2 nm) on the surface of graphene as a mask, and etched away the mesoporous silicon oxide with oxygen plasma Graphene inside the pores.

The longer the oxygen plasma etching time, the more graphene is etched away, and the pore size of graphene is also larger.

In this way, the pore size of the graphene nanosieve can be adjusted by adjusting the time of oxygen plasma etching.When the etching time is controlled at 10 seconds, the pore diameter is 0.63 nanometers, which can effectively allow water molecules with a diameter of 0.32 nanometers to pass through and block salt ions with a diameter of 0.7 nanometers.

The film can be suspended, bent, and stretched without a polymer support without significant cracks.

The test and calculation results show that the new film can withstand a stress of 380.6MPa, and the Young's modulus reaches 9.7GPa, which is 3 times that of the carbon nanotube film, equivalent to 2.4 times the tensile stiffness and 10000 times the bending of the nanoporous graphene film. stiffness.

So, they made a large and strong graphene mesoporous film.

So what about its filtering performance?

Within 10 seconds, the permeability of the etched graphene nanosieve/carbon nanotube film can reach 20.6 liters per square meter per hour per atmosphere.

After 24 hours of permeation, the salt ion rejection rate is greater than 97%.

Compared with the commercial cellulose triacetate desalination membrane, the water permeability of the new graphene nanosieve/carbon nanotube membrane is 100 times higher, and the anti-pollution ability is stronger.

And because it is not restricted by the internal concentration polarization effect, the membrane can still maintain a high water permeability in a high-concentration salt environment.

The new graphene nanosieve/carbon nanotube film made by domestic research institutes is durable without polymer support, and has multiple permeation efficiency advantages.

Of course, this seawater desalination technology is not without problems, that is, it is difficult to mass produce, and if the mass production problem is solved, it can be applied on a large scale.

When Huang Haojie was eyeing graphene seawater desalination technology, he recruited this domestic research team.

"Dr. Yuan, is there any problem with your desalination membrane?"

Hearing Huang Haojie's words, Yuan Quan replied with a smile:

"There is no big problem. The composite film of graphene and carbon nanotubes, with the help of atomic manipulation technology, has achieved preliminary mass production, and our film quality is very strong."

She really admires Huang Haojie, the atomic manipulation technology is definitely a revolutionary technology.

If the graphene carbon nanotube composite film developed by her previous team has a seawater desalination efficiency of 1 per square meter; then the graphene carbon nanofilm made using atomic manipulation technology has a seawater desalination efficiency of 10 per square meter.

The reason for such a large gap is that the graphene carbon nanotube composite film made by atom manipulation technology has no defects.

Although this new type of film is also a graphene-carbon nanotube composite film, its strength is nearly ten times stronger. The increase in strength can increase the pressure to force desalination of seawater faster.

At present, one square meter of film can produce 80 cubic meters of fresh water in one hour, and 70 cubic meters of fresh water in one year.

In other words, if the annual production of 400 billion cubic meters of fresh water is to be achieved, only 5.7 square meters of membranes are needed.

Of course, the service life of this film is about 4100 hours, which is equivalent to needing to be replaced every six months.

The production cost of this seawater desalination film is about 1500 Chinese yuan per square meter.

Calculated in this way, a factory with an annual output of 400 billion cubic meters of fresh water needs to purchase 1.71 million yuan of seawater desalination membranes every year.

Of course, Huang Haojie will not sell it to a seawater desalination plant at cost price. After all, this enterprise is dominated by the national team, and the ex-factory price of the film has at least five times.

Including other electricity bills, the annual operating cost of a factory with an annual output of 400 billion cubic meters of fresh water is about 12 billion Chinese yuan.

The operating cost is equivalent to 0.03 Huayuan per cubic meter, plus the shared equipment, infrastructure, and transportation costs, the cost per cubic meter of fresh water can be reduced to about 0.17 Huayuan.

At present, the water charges of various industries are: residential water: 2.80 yuan/cubic meter; administrative water: 3.90 yuan/cubic meter; industrial and commercial water: 4.10 yuan/cubic meter;
Water for hotels, restaurants, catering, etc.: 4.60 yuan/m60; bathing industry: 40 yuan/m0.60; car washing, pure water: [-] yuan/m[-]; agricultural water: [-] yuan/m[-].

Even agricultural water still has a 400% profit margin.

Of course, due to the nature of this enterprise, except for agricultural water, the remaining water is wholesaled to various cities for use, and the wholesale price is 0.5 Huayuan per cubic meter.

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(End of this chapter)