Raytheon says it is testing a leak-proof method of keeping sequestered carbon dioxide buried deep in the ground — using some of the same technology it developed to increase production of oil from shale.

The latest sequestration method involves encasing the gas in gel, pumping it underground, and then heating it with microwaves until the gel solidifies. The extraction technology, for its part, involves heating the shale with microwaves before pumping liquid carbon dioxide into the formations to separate kerogen, an organic precursor of oil, from the rock.

In both instances, Raytheon partnered with CF Technologies of Hyde Park, Mass. CF Technologies specializes in so-called supercritical fluids, substances that share properties of both liquids and gases when subjected to high pressure and temperature. Carbon dioxide is commonly used as a supercritical fluid.

It is possible that we will eventually be able to sequester the CO2 from burning coal, other fossil fuels, or biomass and do so using less energy than the power plants would produce. There is, however, enough doubt about the viability of carbon capture and storage to make it unwise to depend on it emerging quickly and inexpensively.

As such, we should be transitioning away from coal as a power source, especially in richer states that can easily afford alternatives.

Liquified Co2 doesn’t really have any stability across geological time, not if water gets anywhere near it. Isolating liquid CO2 from water on a geological scale means storing it with the same kind of care as we store nuclear waste.

The key similarities between coal and what we would ideally want to bury are high carbon content and stability across geological time. Whatever we bury will also have embedded energy in it: either chemical energy in a form that some reaction could release or energy embedded in its production and processing, such as separating CO2 from the waste gas stream of a facility and liquifying it.

In any case, the point is that we would probably be wiser to leave existing coal in the ground.

I agree. A thing is its potency – if it weren’t for the potency of coal to become carbon dioxide and release heat, it wouldn’t be coal – it would be something else, and we wouldn’t mine it. So in a certain sense, a coal mountain is the possibility of turning a coal mountain into a lot of Co2 for a (proportionally) small amount of energy.

This is definitely wrong. Of course it’s possible to turn C02 into coal, but that would use – under theoretical ideal conditions – exactly as much energy as we got out of burning it (the C-O2 bond, the creation of which released energy, would have to be broken). What we in fact will be burying is liquid Co2, which is extremely nasty stuff because of what happens if it happens to react with water.

For accuracy, it makes sense to see coal as a densely packed form of carbon (with varying levels of other elements), not carbon dioxide. I’m not trying to be pedantic but I think it’s worthwhile to make the distinction, especially because the formerly living organisms that became the coal would have released substantial quantities of oxygen to the atmosphere. It’s important for people to know the whole cycle.