Ethanol From Carbon Dioxide Is Still A Losing Proposition
Energy Trends Insider, 27 October 2016
If I told you that I had created a process to extract pure gold from seawater, you might deem it an amazing accomplishment. If I issued a press release stating these facts, it very well could go viral. In fact, the oceans do contain an estimated 20 million tons of dissolved gold, worth close to a quadrillion dollars at the current spot market price. But you may have noticed that I have omitted a very important fact.
I haven’t mentioned how much it costs to produce a troy ounce of gold using the process I have designed. That seems like an important detail, so I explain that the production cost is only $50,000 or so per ounce (which today is worth about $1,265), but I am sure that with enough investment dollars — and maybe a few government subsidies — I can get that cost down to something more reasonable. (This is how we subsidize some advanced biofuels where production costs are an order of magnitude above what could be considered economical).
Readers immediately understand the problem. You don’t spend more to produce something than you can sell it for. But change the equation to energy instead of money and people suddenly forget that lesson. Or they fail to recognize that is what is taking place.
That brings me to the point of today’s article, one I’m forced to reiterate often: in the world of energy as in most others, there is no free lunch.
Earlier this month a research paper was published by the Department of Energy’s Oak Ridge National Laboratory (ORNL) called “High-Selectivity Electrochemical Conversion of CO2 to Ethanol using a Copper Nanoparticle/N-Doped Graphene Electrode.” The paper reports on some truly interesting science, and the researchers were measured and cautious in their conclusions.
But something got lost in translation as media outlets sought to portray this as a “holy grail,” “game changer,” “major breakthrough” or “solution to climate change.” The benefits, one story said, were unimaginable. Part of the problem, in my opinion, is that the press release from the Department of Energy was titled Scientists Accidentally Turned CO2 Into Ethanol.
The word “accidental” plays into the misconception people have of how science is done. Many take the romantic view that game-changing, eureka discoveries are merely awaiting the next lucky accident, so when they read this headline the translation becomes something like “New Discovery Solves Climate Change.”
That’s because the public loves its energy miracles. People love the idea of a car that can run on water or the car that gets 400 miles per gallon (which of course GM and Ford suppressed) or the magic pill you can pop in your tank that greatly enhances fuel efficiency. So it isn’t surprising that this kind of story goes viral (in notable contrast to the articles debunking these viral stories.)
In order to understand what’s really going on, let’s consider a fundamental principle of thermodynamics.
If you burn something containing a combination of carbon, hydrogen, and oxygen — e.g., gasoline, ethanol, wood, natural gas — that combustion reaction is going to produce heat, carbon dioxide and water. These are the combustion products.
It is possible to reverse the combustion reaction and convert that water and carbon dioxide back into fuel. But you have to add heat. A lot of heat. How much? More than you can get from burning the fuel in the first place. No new catalyst, and no discovery, accidental or otherwise, can get around that fundamental issue without overturning scientific laws observed and confirmed over 150 years.
Given that, what can we say immediately about this process? Going back to the fundamentals of thermodynamics, we can say, without a doubt, that the process consumes more energy than it produces. In other words, to produce 1 British thermal unit (BTU) of ethanol will require the initial consumption of more than 1 BTU of energy (and generate CO2 emissions.) The resulting 1 BTU of ethanol would ultimately be consumed. The net effect once the ethanol is consumed is more than 2 BTUs’ worth of emissions per BTU of ethanol produced. Or, to be blunt, unless the process can be run on excess renewable or nuclear power (more on that below), converting carbon dioxide into ethanol would actually worsen net carbon dioxide emissions.
Now the researchers involved certainly know this. They actually acknowledged in the paper that the process is unlikely to be economically viable. To my knowledge they haven’t intentionally misled anyone.
But the public has been misled in the retelling of the story. I have heard this research presented as “an efficient way of removing carbon dioxide from the atmosphere.” No, that’s not at all what the researchers claimed. They claimed a Faradaic efficiency in the process of 63%. In other words, 63% of the electricity used in process was utilized in the reaction. They further said that 84% of what was produced was ethanol. That’s the “high-selectivity” part of the title.
But that says nothing at all about the energy consumption required to remove carbon dioxide from the atmosphere so it can participate in this reaction. That is an enormous energy cost because carbon dioxide exists at only 400 parts per million in the atmosphere. Or in the case of passive removal (which is what plants do by means of photosynthesis), the process is very slow.
The high Faradaic efficiency and selectivity also provide little information about the overall energy requirements to turn purified carbon dioxide into purified ethanol, but we already know that it’s more than the energy contained in the ethanol. And it could be a lot more, and that could result in a lot more carbon dioxide emissions.
There is a way that a process like this that is an energy sink could be viable, and that would be if you had cheap, surplus energy that might otherwise be wasted. For example, if a wind farm or nuclear plant produced far more electricity than the grid could handle, you could envision dumping the excess power into such a process. That could in theory reduce carbon dioxide emissions, but there are a lot of caveats that would warrant a longer discussion. Such an intermittent process brings up its own set of issues, and then there’s the question of whether that would really be the best use of the surplus energy.
The bottom line here is if someone presents a scheme for turning air, water, or carbon dioxide into fuel, it is necessarily consumes more energy than it produces. It is an energy sink.
Now, I need to get back to processing ocean water, just as soon as I finish writing this grant proposal for the process.