[louprado]

"It's time to invest and avidly pursue a new wave of technological solutions to this problem - including those that are risky, unproven, even unlikely to work".

I had a recent crackpot idea that falls into the "unlikely to work" category since my background is not chemistry.

Given that a modern automobile's tailpipe emissions are mostly C02 + H20, those molecules can be converted into ethylene (C2H2) using known efficient electro-catalytic processes. The conversion of ethylene gas to a polyethylene (plastic) is well known and has the added benefit of being exothermic.

The end goal is for my car to output a lump of plastic I can drop into the recycling bin instead of CO2.

But my gut tells me that:

1) There is no way to speed up the reactions to keep up with the 80 liters per second of tailpipe exhaust (~40rps * 2.0 liter engine) without this system being impractically large and/or requiring energy intensive compressors.

2) No one, including me, wants to drive around with a tank of hydrogen and a tank of ethylene gas.

But still, it might be fun to hack on something like this assuming I can do it safely. If anyone has any feedback, or has experience making polyethylene, I would be grateful for feedback even if it is negative. Thanks.

[thereisnospork]

The short answer is that while that reaction works in a beaker, it is too slow, inefficient and fragile. Plus there's also the thermodynamic perpetual motion machine in using the energy from a combustion reaction to reverse that combustion reaction.

Basically you'd need a second car worth of engine to generate the electricity to convert 1/3ish of the co2 from the first engine to ethylene (the rest winds up as methane, ethane, and CO.). Plus storage, maintenance and misc.

There are a few reviews by Hori that are more or less the gold standard on the chemistry if you want to read more. Unfortunately the literature is full of fud though.

[philipkglass]

There's an even worse third constraint:

3) The energy content of the hydrogen tank needs to be greater than the energy content of the fuel tank.

And if you were going to add such a huge hydrogen tank to the car, and keep it filled, it would be simpler to use the hydrogen itself as fuel. Many people have indeed proposed hydrogen powered cars. Hydrogen powered cars in turn don't look like they have a very bright future because battery electric vehicles are reaching mass production first, and because batteries are more energetically efficient than storing/transforming energy via hydrogen.

[ageofwant]

That is interesting. Perhaps more applicable to large industrial CO2 emitters like fossil fuel power plants.