Variation in Biofuel Quality
Many biofuel crops are used to make biodiesel. The oil in their seeds is pressed out, filtered and converted to fuel using a chemical process. But while different crops can become biodiesel through the same process, the resulting fuel can vary greatly in its ability to produce power. In other words, not all biofuel crops are created equal.
First, there's the issue of yield. The amount of vegetable oil available in an acre of crops can vary widely, from 18 gallons per acre for corn to 635 gallons for oil palm [source: Journey to Forever]. And again, not every climate region is suitable for a high-yield crop that could produce economically viable biodiesel [source: Burpee].
Second, the oil these plants produce is not equal. Think about the oils in your kitchen: While the olive oil in the cupboard is easy to pour, the lard and vegetable shortening have a paste-like consistency. These differences in state at a given temperature come from the oils' molecular makeup. The molecular bonds in oils low in saturated fats, which stay liquid at lower temperatures, vary from those high in saturated fats, which often form solids in average temperature ranges.
This difference has an effect on the oils' viability as fuel. One obvious consideration is the gel, or clouding, point: A fuel that turns solid well above water's freezing point would not be very useful in a cold location. Consequently, it makes sense to look for an unsaturated oil as a biofuel source.
But there's another complication that arises with this selection. Many unsaturated oils have undesirable burn characteristics: They'll leave gummy residue in an engine when used as fuel. Hydrogenating, or treating the oil with hydrogen, can mitigate this problem, but increased processing means increased cost [source: Journey to Forever].