Why it would be a good thing if we all learned a little thermodynamics

There is an awful lot of fuss being made of this article in the Independent, about the discovery that if you have enough energy, you can get chemical reactions to happen that would not, in ordinary circumstances, do so.

It’s been a long time since my undergraduate thermodynamics classes, so I’m not going to be able to prove this with calculus, but the idea we are suddenly going to be running significant numbers of cars (or indeed, lawnmowers or anything else) on the end results of this process seem fanciful.

To get a sense of why this is, first let’s understand what’s going on here, using a bit of GSCE-level chemistry. Ironically, the handy way my chemistry teacher taught me to remember this is OIL-RIG – Oxidation Is Loss – Reduction Is Gain (of electrons). By converting CO2 and hydrogen into an alkane, the reactor built by the Air Fuel Synthesis folks has reduced the carbon, stripping joining a number of the carbon atoms together along with a number of hydrogen atoms.  Pushing these atoms together and adding electrons takes energy, which is stored in the chemical bonds of the resulting compound.

Now this is essentially the exact same process that plants perform when photosynthesising – absorbing CO2 and water, and producing a reduced form of carbon (in the case of photosysthesis, the initial product is usually beta-glucose). The ability of the molecular apparatus that exists in every plant to do this is incredible, and is the root (no pun intended) of all life on Earth – without plants to capture the sun’s energy and use it to reduce carbon, no other forms of life would be able to exist.

So what has this got to do with recent events in Stockton-on-Tees? Well, the fossil fuels we’ve been using for the last few hundred years are the accumulated result of many millions of years worth of primary productivity ie, plants using the Sun to reduce carbon, which is then “fixed” in solid form in the plants tissues. These become buried in the Earth’s crust, and transformed over millions of years by heat and pressure into the fuels we use today.  Think about that for a moment – humanity has been able to use millions of years of what amounts to stored sunlight, in a few hundred years.

The amount of energy this represents, in daily consumption of petrol and diesel, fuel oil, aviation fuel, natural gas and coal, is enormous. “But wait a moment”, I hear you cry, “there’s loads of energy around, what about all the wind and waves and sunlight?”. Well, you’re quite right – there is a lot of energy about, but the thing about the wind and the waves is that it is diffuse energy – it is dilute, if you like. It can be harnessed to do useful work, but not in the same way as the tremendously concentrated energy represented by fossil fuels. The best way to do this is to avoid changing the “type” of energy you’re collecting – ie if you want to warm something, use sunlight. If you want to turn something, use moving wind or water. You’ll note this is how our ancestors used energy that was available to them – ships and windmills moved with the wind, grain dried in the sun, and so on.

In order to get from diffuse energy, like wind or waves, or sunlight, to concentrated energy, you have to build large apparatus to collect enough of it, and you have to accept the losses that are incurred when changing energy from one form to another (typically we try to get to high voltage electricity).

Modern civilisation is very dependent on this kind of highly concentrated energy – and we use so much of it, that there’s no way we can replace it with any sort of “renewable” alternative, just as someone born with a multi-billion pound trust fund cannot sustain the same lifestyle by working at an ordinary job.

Now to construct the next step in the argument, we need to consider some thermodynamics, specifically the First Law of Thermodynamics, which tells us that you cannot create or destroy energy. This being the case, the energy contained in the fuel from this new process cannot contain more energy than was put into making it. And because changing energy from one form into another incurs losses, it will almost certainly contain less.

So the amount of fuel you could derive from such a process is limited by the amount of energy you can put into it. As we’ve already discussed, concentrated energy, like high voltage electricity, is only available in any significant quantity by using fossil fuels to generate it.  We could hook up a larger version of the reactor to a wind farm, but we’d be unlikely to generate enough fuel to run more than a handful of vehicles, never mind the millions of cars we have in the UK. And this is assuming we didn’t want to use that electricity for anything else!

So this is not to say that this sort of process could never be useful for anything – there may be circumstances where the ability to generate a small quantity of liquid fuel, given a source of electricity, could be enormously useful. But to pretend that we could generate such fuels in comparable quantities to that in which we use petroleum today, when we have no credible candidate for a source of energy to drive this process, seems to me to be, as they say in Yorkshire, just plain daft.

EDIT 20/10/2012: Minor corrections made to which way the electrons go during reduction :O)