マスクとDAC

12月のマスクのツイートで反応が大きかったものの一つが以下のもので、これ以上の詳細を語っていないのですが、Direct Air Capturing(DAC)の技術を使うのではと噂されています。

マスクのツイート

SpaceX is starting a program to take CO2 out of atmosphere & turn it into rocket fuel. Please join if interested.

SpaceX is planning to take CO2 from atmosphere to use as rocket fuel, says Elon Musk

By Luke Hurst  •  Updated: 15/12/2021

Direct Air Capturing(DAC)の技術に関しては、マスクがこの技術開発で有望なものに今年1月に1億ドルの賞金を出すとして話題になっていました。Timeの記事では議論の大きいものの一つとしてのトンデモ系の扱いです。。。

Man of the Yearの記事から

Some of Musk’s initiatives have generated more controversy. His effort to produce and sell solar roof tiles has stumbled. The Boring Co., which Musk started in 2016, put forward a plan to alleviate urban congestion by building miles of underground tunnels to whisk cars along at more than 100 m.p.h., but critics say plain old subways would be more efficient and equitable. Musk’s move to accept Bitcoin as payment for Teslas this spring prompted accusations of hypocrisy; the cryptocurrency’s computational “mining” operations are a climate disaster, drawing gargantuan amounts of electricity to process transactions. Musk subsequently shelved the plan.

Musk’s January announcement of a $100 million climate prize rankled some environmentalists because of its inclusion of proposals for direct-air carbon capture—giant machines to suck carbon dioxide out of the atmosphere. While some experts say researching that technology is necessary, others see it as a costly distraction. “Direct-air capture is a boondoggle,” says Mark Jacobson, director of Stanford’s Atmosphere/Energy program. “We can’t waste our time and money on things that just don’t work very well.”

Direct Air Capturing(DAC)は今ではまだ高価なだけで小規模なもののようですが、現実に稼働し始めているようです。9月にはアイスランドでこれまでで最大規模のプラントが立ち上がったそうです。

この動画はDACの動向がコンパクトにまとまっています。英語表現的には僅かのCO2しか捕集できていない現在のDACをa drop in in the bucketと表現しています。

What's behind me is a drop in in the bucket. this plant removes about 900 tonnes of co2 per year to put it in perspective globally we emit 40 billion tons 

But the bucket is getting bigger quickly as new companies like climb works as well as governments seek to monumentally expand what is called direct carbon capture

（ジーニアス）

a dróp in the búcket ［｟英｠ócean］

（必要な量に比べて）少なすぎる量； 【聖】 大海の一滴, 焼け石に水.

（オックスフォード）

a ˌdrop in the ˈocean British English 

North American English a ˌdrop in the ˈbucket 

an amount of something that is too small or unimportant to make any real difference to a situation

The amount of money raised was a drop in the ocean compared to what we needed.

余談ですが、物書堂で 英英辞典ではa drop in in the bucketだと成句で出てきませんでした。イギリスの辞書なので a drop in in the oceanで見出しにしていました。物書堂さんにはこのようにNorth American Englishのところも検索に引っ掛かるようにしてもらえるとさらに良くなるので余裕がある時にでもお願いします。

この技術の現状について調査記事を書いた記者にインタビューしたものがこちら。コスト面からまだまだ本格実用化は先になりそうなようです。

The Controversial Plan to Vacuum Carbon Out of the Atmosphere

BY LIZZIE O’LEARY DEC 20, 20219:00 AM

On a practical level, even saying there was the global will for this, it seems like there are three big structural hurdles: cost, transportation and storage. How much does it cost to do this?

The estimate that I most often heard is that right now the cheapest they can do is about $500 per ton of CO2. Everyone who looks at this field basically says that that is way too much. That is way too expensive to be able to do what we need to do. Because the IPCC was talking about removing 10 gigatons a year, which is billions of tons. So at 500 per ton, you’re talking about trillions and trillions of dollars.

So, what price does it need to get to? No one really knows. But if it were around $100 per ton, then there starts to be a more of a market for this stuff. If you got it down to $50 or $10 a ton, then you’re really talking.

*****

You’re not really selling direct air capture to me here.

Let me make it a little bit worse by pointing out that traditionally pipelines get run through Indigenous lands. So yeah, am I selling it? No. My goal with this story was to paint a very realistic picture of the enormous opportunity but the enormous challenge here. I’m not saying it would be impossible to do that, and if it became like “we have no other option,” then I guess we would bite the bullet and figure it out. But it’s something you’d want to really think hard and plan for if you’re going to do it, which is a good reason to think about the problems now.

こちらが調査記事ですが、DACの技術がどのように航空機燃料に結びつくのかを説明しています。

Is Sucking Carbon Out of the Air the Solution to Our Climate Crisis?

Or just another Big Oil boondoggle?

Clive Thompson November+December 2021 Issue

5. A vision of synthetic fuels

And so, as the DAC boosters argue, our best bet is to work within the existing oil-and-gas infrastructure. You would use DAC to suck up tons of CO2 and use solar or wind energy to convert it into carbon monoxide and oxygen. Separately, using electrolysis, you’d split water into hydrogen and oxygen. Combining the hydrogen with the carbon monoxide under the right conditions yields fuels that can be used, with minor engine modifications, to power ships, trucks, and planes. Burning the synfuels emits CO2, but if you go the catch-and-release route, you create, in Oldham’s words, a “closed loop.”

C02を排出抑制するのではなく、大気中のC02を除去する技術をネガティブエミッションと言うようでDACはその一つのようです。こういうのは日本語記事を読んでからではないと英語の記事が入ってきません。

「ネガティブエミッション技術」を3分解説！

ネガティブエミッション技術とは、大気中のCO2を減らす技術

全体像をきっちりまとめてくれていたのが、雑誌Economist。COP26の時に出た号でネガティブエミッション技術全体を最新情報も絡めながら報じてくれていました。Michael MannのThe New Climate Warと言う本ではgeo-engineeringに懐疑的で植林の方がマシだという常識的に共感できそうな主張だったのですが、Economistは植林は植林の問題があることを指摘してくれています（まあ、Economistはgeo-engineering賛成派なので少し間引いてみる必要もあるかもしれません）

以下がその記事で丁寧に読まないと全体像が掴めなかったのですが、引用しているのはDACを扱っていた部分でC02吸収をメインにするのはまだ難しいので、吸収したC02を活用することで打開しようとしている部分です。

Why the world needs negative emissions

If negative emissions are to play a role in policy much more needs to be done to make them practically achievable

Special report　Oct 30th 2021 edition

Neither company focuses on offsetting as a core business. Carbon Engineering, which is partnered with Occidental Petroleum, an oil firm, plans to pump the CO2 it isolates in Texas into oilfields to squeeze out oil that is otherwise reluctant to flow. Because the CO2 stays underground, the oil will count as a low-carbon fuel which can be sold at a premium, thanks to regulations in California. It is also looking at combining the CO2 it captures with hydrogen to make synthetic fuels—a business Climeworks is keen on. A startup called Prometheus Fuels claims to be able to do this profitably with a cheaper form of DAC, but has yet to provide details.

Such fuels may help with decarbonisation in some of the places electricity cannot reach, such as aircraft flying over oceans. But the greatest potential for DAC lies in changing the overall carbon budget. If applied on a scale close to that of today’s natural-gas industry it could in principle create space in the atmosphere for hundreds of billions of tonnes of further emissions as the world weans itself off fossil fuels and in the decades after it does so.

CO2を使って地中の石油を取り出す方法と飛行機などの燃料にする方法が紹介されています。調査記事ではもっと詳しく説明してくれているので興味がある方はそちらもご確認ください。Economistのこの記事では、他のネガティブエミッション技術も説明してくれていて全体像が掴めます。