Another dead end rabbit hole? Whenever the phrase global warming, carbon capture or greenhouse gas comes up I am immediately skeptical of what I’m being told.
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Probably not as efficient as plants turning CO2 into wood. The perfect energy storage is already invented.
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It is entirely possible. The energy input is most likely greater then any energy output. simplified: Now you have the energy used to split co2 and hydrogen, then you have the fischer-tropsch reaction to create the alkanes. Not impossible or improbable. Just really energy intensive unless they found some super special catalyst and then it is still energy intensive.
CO2 → CO +H2 → alkanes.
However most of it is electric power, so if you had a bunch of excess solar, it could be a way to long term store it. Where as if you just stopped at hydrogen, it is much harder to store because of the pressure required.
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Direct air capture into hydrocarbons… The US Navy would adopt this tech on carriers at an effective cost of $20+ per gallon diesel/JP1 for fueling aircraft secondarily for non-nuclear escort ships. That they haven’t is proof the tech is not ready for prime time.
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Just for grins, their 10 kg of CO2 per day would be: 1.8 kg/m3 CO2 at STP, so call it 5 m3. Assume 400 ppm CO2 in the atmosphere, so multiply by 2500, so about 12,500 m3 per day. Almost 9 m3/min, or around 300 cfm. Seems like a lot of air to process.
If they start with water and CO2 from air, as Sean said, all the energy is gone, so all the energy you get out you have to put in. You might as well charge batteries for your EV. I’m going to say JO is right 
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I wouldn’t be quite so sure. Trees are 1-2% efficient at converting sunlight to energy according to what google AI pulled up. Then you have to add all the energy used to cut, transport and process it. Solar panels are at 20+% efficiency. There is quite a bit of energy to waste and still end up more efficient.
What is true wood is absolutely wins the startup cost battle. 
They are bubbling air through potassium hydroxide to capture the CO2, then combining it with hydrogen from electrolysis to make methanol, then using the methanol to create the alkanes.
This is not what I expected. I think there are more efficient and faster ways to do this.
There is a possibly that even with lower efficiency for the conversion, the tree still wins overall efficiency.
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I am totally in favor of trees. I think there are huge tracts of our planet that burn off periodically. Example: the Rocky Mountains. We have what we call pine beetle kill up here. Billions of tons of standing dead wood. FIRE HAZZARD. And yes, there is an outfit called BioCharNow in Berthod, CO that is converting about about 100K tons per year to BioChar, God bless them. But it’s not enough. More darnit, more!!!
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The irony is a lot of the rocky mountain trees require the heat from fire to get the seeds out of the cones. So they have adapted to the forest burning down on a fairly regular basis.
I have to get to making biochar again this summer, but I don’t make a 100k tons.
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The contrast in approaches: a man-made chemical factory footprint versus a trees growing forest makes cherry-picking out efficiency numbers ridiculous.
An actually growing forest as J.O., JanA., Tone and others work from, is a diverse environment benefiting many. Not just a mono-crop of rows in line tree plantation.
Ha! Satellite view the whole region of the State that I live in and it is an 80% land covered with 35-50 years cycling, regenerating forest. Managed for only 1/35 a year harvested. Sucks in a lot of atmospheric and rain water carbon dioxide annually. Nurtures hundreds of interdependent species. Numbering in 10’s and 100’s of thousands in each species.
And I’ve said; and will say again our commercial forests here at harvest, only remove ~1/3 of the grown bio-mass. The rest left to soils condition and enrich for the next grown crop.
What we Pragmatic Practical’ist here now fight is those who prove well they hate themselves; hate their own species; hate their own futures. Insisting that all must worship their new declared god Gaia.
Not just yet. Ain’t dead yet. Ain’t brain dead yet. Ain’t willing to give up logic, reason, and direct eyes on observations for a life of emotional deep-dives immersion.
“Trees are the Answer.” An early 1990’s bumper sticker.
Steve Unruh
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Jean Pain figured out that chopping up all that underbrush and created a huge compost heap, he could make hot water for his home. In the center of the heap he put a tank to make methane to run his car…
I do believe this is well worth considering.
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What I would love to see is someone hybridize the technologies. The output of a composting pile would be Methane and carbon dioxide. Both would make great feedstocks for the gasoline mini unit. Of course you could feed the co2 into a charcoal gasifier and use the methane directly… We don’t have a lack of solutions we have a lack of desire to implement them.
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Yep, we have a shortage of time, and chose the most likely path to a solution.
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We usually take the easiest path to a solution because of shortage of time and money. The methane produced can run a car for a short period of time. It might work for Tom, who only goes to town once every couple of weeks. But he is also 20 miles from town, so hauling that much uncompressed gas is a lot of gas to run a car. The better option would be to convert it to electric and charge the electric vehicle for the trip to town, even though it sounds a lot more convoluted. Then you are only replacing 15c/kwh of electric. So running a 5kwh generator is only going to save you 75c/hr. And it is both time and work plus equipment costs to save that 75c. You can skip most of the work by just installing solar panels.
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