I’n now seeing articles about “fourth generation” biofuels, like the one below from Biopact, while I was still in the second generation.
For those who are maybe as confused as I am, this is how I understand it it.
First Generation – these are the ones we all know and the industry is busy making money out of, turning carbohydrates and oils into ethanol and biodiesel. These are generally economic to do so long as their is some kind of subsidy where the efficiencies are poor eg ethanol from wheat in Europe.
The actual overall energy and environmental benefit of these is under discussion with competing analyses, but is anyway rather marginal. However, the largest negative that is coming through is the fact that in a world with starving people and rising food prices biofuels don’t make a lot of sense.
Second Generation – these are the ones that are doable but are still much too expensive for commercial implementation. They look at using waste products rather than food as their carbon source eg ethanol from maize stalks and biodiesel from flue gas.
Lignin and cellulose are basically the cell wall material of plants and are the most the basis for most of these kinds of processes and are the most plentiful organic compounds in nature eg grass, trees, timber wastes and food crop wastes all rich in lignocelluloses and offer the opportunity to provide biofuels without impacting on food availability.
Third Generation – these are based on the genetic manipulation of plants to produce dedicated energy crops that vastly improve the economics of second generation type conversions eg maize with its own enzymes to convert cellulose and wood with reduced lignin which would be a more efficient producer of ethanol.
These three generations of biofuels are seen to be “carbon neutral” in that they do not add to greenhouse gasses because the CO2 they release on combustion will be extracted from the atmosphere by the plants that are grown to produce the biofuel.
Fourth Generation – these technologies are based on new plants that would be able to absorb more CO2 than would be released on combustion by the biofuels produced from them. They would therefore actively reduce the amount of CO2 in the atmosphere.