Converting Sunlight Into Liquid Fuel With a Bionic Leaf

hypnosec writes: Artificial leaf techology made waves the moment it was announced by Daniel Nocera back in 2011. His latest research, published in PNAS, involves gathering hydrogen from this artificial leaf, carbon dioxide from another source, and feeding it to Ralstonia eutropha bacteria to create liquid fuel. Once the materials are fed to the bacteria, "An enzyme takes the hydrogen back to protons and electrons, then combines them with carbon dioxide to replicate—making more cells. Next, ... new pathways in the bacterium are metabolically engineered to make isopropanol." Researchers say the same process could be used to make vitamins.

Comments

Animal, not plant

[MrLogic17]

The headline implies that we have a machine replicating the process of a plant. The summary indicates that what they have is a vat of bacteria that are making alcohol. Not nearly as attention grabbing, considering mankind has been using yeast & bacteria to make alcohols of various forms since the dawn of time.

If they have a more efficient process with simpler (cheaper) inputs, kudos to them. But this ain't no artificial leaf.

Re:Animal, not plant

[itzly]

mankind has been using yeast & bacteria to make alcohols of various forms since the dawn of time

Not from hydrogen and carbon dioxide, though.

Re:Animal, not plant

[gstoddart]

The summary indicates that what they have is a vat of bacteria that are making alcohol

Hmmmm ... are you sure?

Their work integrates an "artificial leaf," which uses a catalyst to make sunlight split water into hydrogen and oxygen, with a bacterium engineered to convert carbon dioxide plus hydrogen into the liquid fuel isopropanol.

So, they're clearly doing more than just making alcohol with yeast.

"This is a proof of concept that you can have a way of harvesting solar energy and storing it in the form of a liquid fuel

In fact, I'd say it sounds quite different.

Re:Animal, not plant

[jdschulteis]

If it is so good, why not just store the hydrogen for fuel? Wouldn't it be cheaper/easier to skip the last steps?

Hydrogen is difficult to store in a lightweight, compact system. One good way to store hydrogen is to chemically combine it with carbon and oxygen and put the resulting liquid in tanks at ordinary temperatures and pressures.

energy balance doesn't work out

[Noah Haders]

The energy balance doesn't work out here. Max solar intensity is 1 kw / m^2, or 1 kj per square meter every second, or 3.6 MJ per square meter per hour. A gallon of gasoline is 120 MJ. So assuming 100% efficiency and 100% peak sunlight, it would take 30 hours to make a gallon of gas from one square meter of artificial leaf. Considering the average solar intensity is about 10% the max, and any process involving the sun is max 20% efficient, it starts to take a very long time to make one gallon of gas. Not even including the energy requirements of the leaf / enzyme process.

Re:energy balance doesn't work out

[gstoddart]

Hmmmm .... 100 square kms ... producing flammable alcohol.

Have you seriously thought about this?

The first guy to realize he can light a match and have hilarity ensue will probably create something visible from orbit, and get himself a Darwin award.

Actually, scratch that ... bring it on! That would be funny.

Re:energy balance doesn't work out

[smithmc]

I don't know, except that the energy density of propanol is roughly similar to that of gasoline.

Re:energy balance doesn't work out

[Noah Haders]

134 billion gallons. based on your math, it's 140,000 km^2 of bionic leaf to make the gasoline for USA.

134 billion gallons / (266,666 gallons per day per 100 square km (calculated above) * 365)

What else is 140,000 square km? new York state. so is north Carolina. so is iowa. it's a lot of room.

another perspective: it took millions of years of sunshine to grow plants to feed dinosaurs to be melted into oil and used today. it's really hard to replace that with a solution that runs in steady state, as in we produce enough for our annual consumption in one year. Maybe we need a dyson sphere...

Re:That's nothing

[davester666]

And it dries faster when you spread it out everywhere.

No, it's chemistry.

[Ungrounded Lightning]

An enzyme takes the hydrogen back to protons and electrons...
Isn't that nuclear fission?

No, it's chemistry. Specificially, ionization.

Monatomic hydrogen has a single proton (and very occasionally one or two neutrons) for its nucleus, "orbited" by a single electron. Molecular hydrogen has two atoms of hydrogen - two protons bound together into a molecule by sharing their associated electrons in a chemical bond.

Separating the individual nuclei from their chemical bonds (typically dragging along all but one or all but a few of their electrons) is a chemical process, producing a dissolved positive ion. Because hydrogen has a single proton and electon per atom, a positive ion of (non-heavy) hydrogen, missing one electron, is a bare proton.

Now if you wanted to change the number of protons and/or neutrons in the nucleus, change a proton to a neutron or vice-versa, or rearrange a multi-nucleon atom into or out of an excited state (say by adding or releasing a gamma ray), you WOULD be talking nuclear processes. If it cosisted of separating the nucleons of a single nucleus into two groups it would be nuclear fission. But separating the nuclei of different atoms from a molecular bond and/or removing electrons from them, is just chemistry. Energies per operation are measured in single-digit electron volts, rather than kilovolts or higher.