In my ebook, I maintain that choosing what to do is in effect choosing between alternative applied theories and in a previous blog, I commented on why I think the fermentation of lignocellulose first to glucose and thence to ethanol to make biofuels is not a good idea, the main reason being the first fermentation is too expensive. What nobody commented on was that that could change if ethanol was not the main product, and it is of interest to view the recent Mascoma IPO, where there is a wide range of other proposed income sources.
There is a broader question: should we pursue ethanol at all? Given sugars, the technology is mature, but what about feedstocks? There are many objections to the use of crops to make ethanol on the basis that with a growing population food is the priority. So, is ethanol a bad biofuel?
"Bad" depends on your "point of view". The farmer wants the best price for his crop, the hungry cannot pay, so who does what? There is a tendency to say, "somebody else should pay", which, in my view, is not helpful. There are also "red herrings" in the analyses, such as "carbon efficiency", "blending efficiency" and "energy efficiency". Carbon efficiency is the worst of these: the argument is that glucose has six carbon atoms, and two disappear off as CO2. That is totally irrelevant: there is no shortage of carbon atoms. Blending efficiency is a red herring because Brazil has shown that provided proper management is undertaken, there are no inherent technical problems. The argument that ethanol has less energy density than hydrocarbons is true but somewhat misleading. The issue is not energy, but useful work, for we have to power a transport fleet. Whether you use more (because of lower energy) is irrelevant if the issue is, can you run your motor? Also, the work on ignition is delta PV, which increases if the pressure is increased. In a spark ignition motor, that requires a higher octane number, and ethanol has a significantly higher octane number than standard fuel, and with blending it is efficient at raising the overall octane. Accordingly we could get more efficiency by raising the motor compression, which raises a question that is seemingly always ignored: what properties will the future transport fuel have? If we do not address that, much of our planning is going to be wrong.
The real question is, how do we power transport once oil becomes scarce? Fermentation of sugars to ethanol has advantages. The first is, it is reasonably efficient on smaller scales. That means it can use wastes, which tend to be produced in smaller local amounts. There is also one other feedstock: synthesis gas. Certain anaerobes, including Clostridium, appear to be able to convert this gas stream to ethanol, and the microbes seem to be tolerant to a wide range of the mix of hydrogen and carbon monoxide. That means in principle we can get fuel from waste streams, such as the gas effluent of steel mills that otherwise have no use.
In my opinion, there appears to be no use other than to make ethanol by fermentation for small amounts of low quality synthesis gas, and no other technology that is convenient for low volumes of sugar waste. Either that ethanol can be used by the chemical industry, or we need to maintain in the long-term spark ignition motors. Long term planning for transport should take that issue into account, however in my opinion, planning for transport fuels appears to be operating on a "market rules" basis. That will have all the aspects of Darwinian evolution, and while the market enthusiasts might argue that evolution guarantees the fittest (actually, it does not – evolution involves survival of the adequate to reproduce) evolution also involves numerous extinctions. Do we wish to nearly extinguish individual transport? If not, some form of planning might seem desirable.
