Environment & Energy

Consider polyethylene, which is the most common plastic in the world, with an annual production rate of roughly 100 million tons per year.

It is definitely accessible by the hydrogenation of CO₂ to methanol, followed by the well known "MTO" - methanol to olefins - process. Polyethylene is just shy of 90% carbon, slightly lower, but let's use that number as a first approximation, meaning about 90 million tons. The ratio between the molecular weight of CO₂ to carbon is roughly 3.66, meaning 100 million tons of PE containing 90 million tons of carbon would involve the reduction of 90X10⁶ * 3.66 = 330 million tons of carbon dioxide. This is less than 1% of the amount of carbon dioxide emitted each year, roughly 35 billion tons, while we all wait for the "renewable energy" nirvana that didn't come, isn't here and won't come.

Moreover, the polyethylene will be overwhelmingly discarded after a single use. If - this is a good idea - we reform municipal waste with nuclear generated steam or supercritical water, this carbon would be continuously recycled. If recycling were a hundred percent efficient - it won't come close - it is unlikely, at least theoretically, that much new carbon would be required. Where polyethylene is not recycled - only a very tiny amount actually is - it is becoming a huge environmental problem.

A better case can be made for some permanent, long term use plastics, for instance methacrylate, and related hard permanent plastics used as structural materials, furniture, certain types of tough glass and similar uses. There are carbon fibers of course, which if they can be made less expensive would also sequester carbon, and certainly carbides like the refractory silicon carbide, and metallic carbides. The electrochemical reduction of CO₂ is well known, but as electricity is thermodynamically degraded, exploiting a Boudouard type system involving disproportionation of CO also offers some application, possibly thermodynamically superior, where industrial carbon is required.

Concrete is another possibility, depending on the source of lime. Right now concrete is a net contributor to extreme global heating; in theory it might be a sink.

The point is though that the solution is not easy. It is difficult because of scale. I do think we need to consider carbon based structural materials as permanent sequestration tools, but it might take centuries to undo the damage already done, even in an ideal nuclear powered world.

Thanks for your comment.