Monday, September 7, 2020

Solar & wind into petrol


I expect we've all seen those ads inviting us to send $50 for the secret of how to run your car on water instead of petrol (gasoline).  Well here's something far more convincing. [From Science Mag]

SAN FRANCISCO, CALIFORNIA—On a warm March day here, you could almost mistake Rob McGinnis for a huckster newly arrived in a frontier town as he delivers a rapid-fire pitch to an audience of thousands of would-be investors. McGinnis, a chemical engineer and entrepreneur, isn't hawking snake oil, however: His elixir is gasoline. Nearly everyone in the developed world is hopelessly addicted to it. Collectively, we use nearly 3 trillion liters every year.

At the pitch fair, McGinnis wears the Silicon Valley entrepreneur uniform of jeans, a black T-shirt, and black leather biker boots. On a theater-size stage, he delivers his spiel, sandwiched between 3-minute presentations for an online personalized clothing store and an outfit that would rent scooters by the month. "We make gasoline from air, water, and electricity," McGinnis announces. "Today, gasoline sells for $3.50 a gallon in California. Next year, we will be selling it for $3 per gallon." Other startups peddling ideas at the fair foresee markets in the billions, but McGinnis aims higher. "We're talking about a $2 trillion [per year] gasoline market," he says.

If all that sounds too good to be true, it might be. "I hope they're right," says Olgica Bakajin, CEO of Porifera Inc., a San Leandro, California, company that has also worked on systems like those at the heart of McGinnis's fuelmaker. But she notes that McGinnis "is a good talker who sells things well."

Synthesizing gasoline, instead of refining it from oil, isn't a new idea. German chemists in the 1920s discovered they could turn coal into carbon monoxide (CO) and hydrogen—a combination known as synthesis gas. Catalysts, along with heat and pressure, could then transform synthesis gas into gasoline and other liquid hydrocarbons.

But McGinnis's setup requires no heat, pressure, or coal. It uses only air, water, and electricity, which can come from the sun or wind. And with those renewable resources becoming ever cheaper, he's betting he can deliver gasoline more economically—and far more cleanly—than companies that must find oil, drill for it, ship it, and refine it.

Several other startups and academic labs are pursuing the same dream. "There has been a lot of progress in the last few years" in turning CO2 into more-complex compounds, says Peidong Yang, a pioneer in the field at the University of California, Berkeley.

Yet many of those efforts have stumbled over the expensive, energy-intensive steps needed to separate the hydrocarbons from the water they are produced in. Prometheus relies instead on a proprietary carbon nanotube membrane sieve that it says readily parts the hydrocarbons from water. "If they indeed have a low-energy separation process, that solves a big problem," Yang says.

Synthesizing the fuel is the easy part. Peidong Yang's team and groups at Oak Ridge National Laboratory (ORNL) in Tennessee and the University of Illinois in Urbana have published papers in the past 3 years showing that electricity and nanosize copper catalysts can turn CO2 and water into a mix of alcohols. And startups including a New Orleans, Louisiana, company called ReactWell are pursuing related approaches.

Thus far, the ORNL team has reported the highest efficiency, turning 23% of the electrical energy into fuel. [For comparison, Tesla says its lithium-ion batteries are ~90% efficient] But all the groups using the approach to make alcohols face the challenge of separating the fuel from the water. McGinnis says his membranes are the answer. They are "the new piece in the puzzle no one else has."

In the air-to-fuel machine he hoped to demonstrate at Y Combinator, the membranes filter a liquid that flows from a meter-wide chamber containing two electrodes dunked in water. When air blows through the chamber, the CO2 it contains reacts with water, producing carbonic acid—the same molecule acidifying the oceans. That acid, in turn, reacts on a copper catalyst coating the negative electrode, or cathode, to create CO. The cathode also strips protons off water molecules, leaving behind negatively charged hydroxide ions. Those ions travel to a positively charged electrode, or anode, where they react to form water and oxygen gas. Meanwhile, at the cathode, multiple CO molecules and protons are transformed into ethanol and other alcohols.

The result is the alcohol and water mixture that goes through the nanotube fibers. Prometheus has repaired its machine since the pitch fair, and it produces "a pretty steady drip" of fuel, McGinnis says: 10 milliliters per hour of alcohol that trickles out a red valve in the back. Over the next month, McGinnis and his colleagues plan to increase the size of their electrodes and catalysts to raise the production rate to 50 to 100 milliliters per hour.

Ultimately, McGinnis plans to add a second catalytic step using commercially available catalysts called zeolites, which would convert the mix of alcohols to the larger hydrocarbon molecules found in gasoline. "All of the pieces of this process have been proved to work. But no one has put them all together," he says. "Until now." He expects the device, when optimized, to produce 20 liters of gasoline per week.

[It's a long article, and worth reading.  You can read the rest here]

The article is a little doubtful that the process will work.  But BMW seems to believe it'll work.  It's invested $12.5 million into McGinnis's company.

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