Feb 16 2010
This week on the SGU I discussed a company, Carbon Sciences, Inc., who plans to make gasoline from atmospheric carbon dioxide (CO2). I focused on the particular application discussed in the news report, but the story raised many more questions than I answered, and so I would like to delve into this potential new technology in more depth.
These kinds of applications always fascinate me – it’s the game of follow the energy, the rules of which are the laws of thermodynamics. For quick review, essentially the first law of thermodynamics is that energy cannot be created or destroyed, it can only change forms. In other words, in any isolated system, the total energy will remain constant.
The second law of thermodynamics states that in any process of converting energy from one form to another, entropy must increase. Therefore, heat will flow from a relatively warmer system to a connected cooler system, not the other way around. Your coffee tends to cool down to room temperature – it does not spontaneously heat up, taking energy from the cooler surrounding air. The second law also means that any time you convert energy from one form to another, some of that energy is lost to entropy – it’s still there, it has just dissipated as heat or some other form and is no longer in a stored usable form.
With that as background, we can begin to think about the energy systems off of which we run our civilization, and also evaluate proposed new “green” energy systems to see if they make sense. Do biofuels, for example, make sense? Can we run our society off of hydrogen?
The next basic principle we have to consider is whether or not any energy medium is being used as a source of energy or as a way to store and transport energy. To give a simple example, when I charge a battery, the battery is not a source of energy, it is solely a way of storing energy in a usable form. Gasoline (and fossil fuels generally) is both a source and a convenient way to store energy.
An finally, we can evaluate energy systems based upon their environmental impact, and here I will focus on their effect on CO2 in the atmosphere.
Let’s take a quick look at the coming (heh) hydrogen economy. It seems this has hit a few technical snags, but that aside – can we even theoretically run our world on hydrogen? The answer is no – hydrogen is not a source of energy, because there is no free hydrogen on the earth. We must therefore obtain our hydrogen from other sources. If we split hydrogen from water that requires energy, and the second law tells us it requires more energy than we will get back from burning the hydrogen. We will need an actual source of energy to split off the hydrogen in the first place. If we obtain hydrogen from natural gas, then we are essentially using the fossil fuel as a source of energy.
So either way – hydrogen is not a source of energy. It is purely a storage medium. It may turn out to be a convenient storage medium, but then we still have the problem of where our energy is coming from. Creating and burning hydrogen may itself be carbon neutral, but you have to consider the carbon footprint of the energy production.
Biofuels are a bit more complex, because they can be both a source and way of storing usable energy. They are not as energy dense as gasoline, but close enough to be suitable for the internal combustion engine. They also have desirable properties in terms of stability vs combustibility, and temperature tolerance. So they are a reasonable storage medium.
The question of biofuels is – are they a net source of energy. The answer depends on how they are produced. Ethanol from corn, the way it is currently grown (which often involves fossil fuel-based fertilizer) is close to being energy neutral. If you consider growing, fertilizing, harvesting, and processing the plant material in order to make ethanol, biofuels are not energy efficient. There is also the separate factor of displacing farm land from food production.
Biofuels by themselves are carbon neutral – but they are only really carbon neutral to the extent that they give back more energy than they take to create. If I burn a gallon of gas to produce an equivalent energy of ethanol, I still burned the gas.
But biofuels are a potential source of energy, because part of their energy comes from the sun – plants trap solar energy through photosynthesis, and then we can harvest the chemicals they produce which store some of that energy – usually cellulose. We just need to find a plant that efficiently uses land and is sufficiently energy dense. Then we need to find a process that is energy efficient enough that at the end of the day we end up with more energy in ethanol (or some similar storage medium) than went into the entire process (not including the sunlight, which is the true ultimate source of the energy). There are labs and companies who claim to be able to do this, but the process needs to be scaled up to industrial mass production. We’ll see.
What about the question at hand – making gasoline from atmospheric CO2? Carbon Sciences claimed a year ago that they had a process for taking carbon from the air and making it into a stable solid form, which can then be used to make paper, plastics, and similar products. This is just using carbon as a raw material, and does not have to be energy efficient to make sense – as long as it’s competitive to other manufacturing processes. There is the added bonus of taking carbon out of the atmosphere, so we would need to consider what that is worth also.
But now the company is claiming they can use their process to make commercial grade gasoline or even jet fuel.
The company announced last week that it has developed a “breakthrough technology” that converts atmospheric carbon dioxide into commercial-grade gasoline, diesel fuel and jet fuel. Founded in 2006, Carbon Sciences had previously converted CO-2 into low-grade methanol using an enzyme-based technology. Now, it said, it has combined chemical and biological engineering in a bio-catalytic process that transforms carbon emissions into “a cost-efficient” energy resource.
I find this hard to believe. But I note the term “energy resource” is a bit vague – do they mean energy source, or just energy storage medium? Let us first consider this technology as an energy source. The proposed plan is to take the exhaust of coal-burning power plants (where carbon will be dense), take the carbon and use their process to make gasoline. Thermodynamics tells us that this process must take a considerable input of energy – more energy than you can possibly get out of burning the resulting gasoline. So it is trivial to conclude that this process cannot be a source of energy.
One proposal is to dedicate a nuclear power plant to providing the energy to make the gasoline. This seems absurd to me. Essentially this process will use nuclear energy to make electricity, while simultaneously burning coal to make electricity for the grid. The nuclear electricity will be used to take carbon from the coal-burning process and make it into gasoline, which can then be burned in cars. That is a lot of energy conversions – very thermodynamically inefficient.
You would be better off simply hooking the nuclear power plant into the grid and never burning the coal in the first place – that’s just one energy conversion. Or, we would be better off developing electric cars and using electrical energy to run them, charged off the nuclear power-plant supplied grid, then burning gasoline from this process.
From a carbon perspective this accomplishes nothing – because you eventually burn the gasoline you make . That carbon which was sequestered for millions of years in the coal still winds up in the atmosphere. From a carbon perspective, you are better off using this process to make solid material that will sequester the carbon for a long time.
So really the net effect of this process is to turn nuclear power into gasoline. This process itself is carbon neutral. But you are still burning coal to generate electricity, and that carbon is still winding up in the atmosphere.
If we consider this process as a way of storing energy, however, it can make sense. When you think about it – all energy production must generate usable energy, and preferably store it in a stable medium. Power generation generally does not store or buffer much energy – they simply supply what is needed moment to moment. As we explore sustainable power generation – solar, wind, geothermal, tidal, and hydroelectric – one of the challenges is that many of these energy sources are variable over time, and so to be really useful we need to store energy for when it is needed. Batteries are not a great option – they are expensive, inefficient, and usually involve a great deal of raw materials, some of which are toxic.
One option being explored is compressing gas in a large underground cavern. This is an interesting idea, but just in the theoretical stage.
Making gasoline or something similar (like ethanol) is actually a reasonable idea. If we could convert solar or wind power into gasoline, using exhaust or atmospheric carbon as raw material – we would have a carbon neutral method for storing that energy. We already have a gasoline-based infrastructure as well.
However, I don’t think this is a good idea in the short term. It is more efficient to use that electricity directly than to convert it into another form (thermodynamics again). It would probably be far better to use electricity from renewable sources to displace coal-burning power plants.
It may be a good idea in the future – it depends. Right now it is difficult to compete with the cost-efficiency of burning fossil fuels – the energy is there in a convenient form. And what carbon neutral or sustainable energy we can produce is probably best used on the grid. (The other factor that needs to be considered here is the efficiency of the grid itself – how much energy is lost in transport. I acknowledge that using electricity locally to make gasoline may be more efficient than transporting that electricity a long distance before being used. That calculation needs to be done. And, of course, the other solution, which is being talked about, is both upgrading the grid, and distributing energy production so it is more local.)
If over the next 20 years we shift our automobile fleet into one that is mostly electric, then this process of turning CO2 into gasoline may never become useful. If, however, we are burning gas indefinitely and one of two things happen, then this technology may see its day. If we begin to run out of oil, then finding alternative sources of gasoline will become crucial. Some technologies, like jets and industrial vehicles, may remain dependent on energy-dense fuel. We may have no choice, therefore, than to make jet fuel out of an energy inefficient process because we need the energy stored in that form.
Also – if we develop sustainable energy sources that more than meet the needs of the power grid (let’s say fusion power becomes feasible, or solar power comes into its own) so that in essence we have excess power generation capacity, we can store that excess power as gasoline made from CO2.
This does raise another point – current power companies do have excess power generation capacity – off peak. This is a source of inefficiency, as power plants needs to be able to make energy for immediate use during peak hours, and this extra capacity sits idle during off peak hours. This is because there is no way to efficiently store all that energy – it has to be used immediately. Extra capacity is therefore wasted. So another idea to explore is using off-peak wasted power generation capacity to store energy in this kind of process. If this would make power plants more efficient – because they have a way of leveling off their power generation (any unused power being shunted into making gasoline) that might be feasible.
This topic is a good example of the relative strengths and weaknesses of podcasts vs blogs for the discussion of various topics. The podcast is more entertaining and personal, and people like the convenience of listening while doing other things. Reading blogs requires a bit more of a commitment.
But writing a blog allows for getting into more depth and detail than the spoken (especially unscripted) format.
When I discussed this topic on the SGU I focused on the core claim of using a nuclear power plant to make gasoline from the exhaust of a coal-burning power plant. This makes no sense, for the reasons I discussed above. However it seemed as if I was dismissing this technology in all its possible applications. This blog post is therefore a nice companion piece to the podcast discussion, because I have the time to explore more of the nuances of this story.
In the end, I do not know if this technology will ever see the light of day. It is still a laboratory phenomenon, not ready for industrial use. The company, I suspect, is either looking for investors or to pump up its stock price. At the moment this technology seems to be mainly industry hype.
If the technology itself pans out, then we will need to think carefully about how best to apply it – which includes thinking through every step of energy production and use, and how these might compare to the alternatives. In the end, we are slaves to the laws of thermodynamics and we ignore them at our peril.
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