Thanks to our inestimable leader, the topic of making fuel from corn and other cellulose sources has received renewed airplay. Unfortunately it suffers from the same problem as every other time this has been discussed: Cellulose is an incredibly long-chain hydrocarbon that looks very little like the alkanes that predominate in fuel oil. For reference, existing gasoline consists of 7-11 carbon hydrocarbons. Because cellulose is almost all sugars, it has to be degraded almost down to nothing, aka ethanol. By the time you get to ethanol, you have not only broken the expensive 1,4 bond between individual sucrose molecules, you’ve also broken the 6 sugar beta-glucose subunits into three pieces. Needless to say, most of the energy in this process has gone to whatever organism or chemical operation you used to break it down that far.
This is why most traditional ethanol producing factories start from the corn kernels from which they can get free, or more cheaply linked, polysachharides. Which is fine, except for the fact that the ears represent a fraction of the mass of the corn plant, and the sugars represent a fraction of the mass of the ear. Additionally, it takes 125 days or so before a corn plant is ready to harvest, so even if you could theoretically get energy from the entire corn plant, you would get 79 * 1015 Btu out of the entire US corn harvest, which would fall short of our current energy demands by over 10 billion Btu/annum.
This problem persists with all macroatomic plants: the bits that are easy to degrade are a small fraction of the plant, and the rest is mostly cellulose.
If you switch to prokaryotes, however, the situation is much better. Take Anabaena, a filamentous bacteria that is incredibly common. In the right conditions, you can get exponential growth that covers the surface of your medium within a month. The bulk of anabaena consists of a polysaccharide mucilage, phospholipids (fat), and peptidoglycan. Peptidoglycan consists of polysaccharides connected with small proteins. We are awash in enzymes that will degrade these molecules; even our tears contain peptidoglycan degrading enzymes.
The phospholipids can be broken down into hydrocarbons (fatty acids) and glycerine fairly easily, using processes similar to those used to make soap. The peptidoglycans can be degraded with the aforementioned enzymes, and the (cheaply linked) polysachharides can be degraded any number of ways.
All this means more of Anabaena can be cheaply utilized to make gasoline-like substances. Even using batch methods, it can be harvested almost 12 times a year and will give you a much larger annual yield than the same acerage devoted to corn. Furthermore, I just picked Anabena because it is very common; there are literally millions of species of bacteria and other microorganisms out there, some of which most certainly are made up of molecules even more amenable to this form of transformation.
Furthermore, breeding bacteria is a process that takes months, not years, so we can selectively breed whatever strains we’re using for more optimal yield.
The general idea that living biomass is the most likely replacement for fossil biomass is dead on: the notion that it will come from plants or other macroorganisms is absurd.