Biofuels and Renewable Energy: What Is a Biofuel Anyway?
Biofuels are a leading source of renewable energy, particularly as transportation fuels that would replace oil-derived gasoline and diesel. But when you think about it, oil deposits are derived from biomass that has decomposed and been compressed underneath the surface of the earth for millennia.Aï¿½ Given that the origin of petroleum is biological, why isn’t oil considered a biofuel? What is the distinction between petroleum and, for example, ethanol or biodiesel? And just what exactly is a biofuel anyway?
These are fair questions worth answering, and I will try to provide some answers here.
First of all, biofuels are essentially defined as being derived from recently dead biomass, as opposed to long dead biomass that gives rise to petroleum. This distinction is not an arbitrary one. In fact, there is sound reasoning behind making a distinction between plants that were harvested (and thus made “dead” a few months ago) and biomass that “died” millions of years ago.
One of the main purposes of replacing oil-derived fuels and products with bio-based fuels and chemicals is to reduce the net carbon emissions. (Having an alternate fuels source that would keep a lid on the cost of oil supplied by an unfriendly, price-fixing cartel would be another useful purpose of biofuels.) In the case of biofuels produced from sugar cane, corn or plant waste, the biomass replacement occurs in less than a year as a new crop comes in. The new biomass is roughly equivalent to the carbon emitted when that biofuel is burned. Thus, the net carbon emission is near zero from that cycle, and that carbon cycle is complete within a year.
Contrast the situation with corn or sugar-derived biofuels with that of oil. The production of the petroleum requires millions of years. Thus, the replacement cycle time for petroleum that is burned is thousands of millennia rather than the length of a single crop cycle. In other words, it will require millions of years for the carbon emitted by burning oil to be reconstituted into petroleum for creating a second cycle of use as a fuel. It will only take a year or less for the carbon dioxide emitted from burning bio-ethanol to be reconstituted as sugar cane or corn for conversion into a new cycle of biofuel.
Therefore, it is the difference in the length of the carbon cycle that creates the distinction between petroleum, which is derived from long-dead biomass, not being a biofuel while a similar combustible liquid (ethanol or biodiesel) produced from recently dead biomass is a biofuel.