But each would-be jet biofuel–maker faces other challenges as well. Solazyme can make lots of oil from its stressed algae grown in the dark and fed industrial-grade sugar, but the source of that sugar makes the ultimate fuels less sustainable. Sapphire wants to grow its algae in ponds, which will make it more sustainable but also much more costly to produce. AltAir does better by sourcing its bio–jet fuel from oil seed–bearing plants, like camelina, but that limits the amount that can be planted in rotation with food crops like wheat given constraints on the amount of land available for the latter.
SG Biofuels gets high marks in all respects from the Carbon War Room and relies on jatropha grown in Guatemala and other parts of Central and South America. This hardy plant seems ideal, given that it can resist droughts and grow on marginal lands, producing oily seeds. But the biofuel crop has already come in for criticism both because it is displacing cereals in other places where it is grown, such as Kenya and Tanzania, as well as requiring fertilizers to get good oil yields.
That leaves Lanzatech, which has a technology to turn synthesis gas derived from almost anything composed of hydrogen and carbon into fuels and chemicals. But, of course, that technology doesn't have to use sustainably grown plants as a starting point. They can just as easily use other alternatives, like alcohol or coal. In fact, that is exactly what Lanzatech is attempting with Chinese coal mining company, the Yankuang Group.
Turning coal to motive fuel is something that South Africa's SASOL has been doing for a long time. For years SASOL has been making jet fuel (and diesel for trucks and buses) out of coal. It is actually chemically the same fuel as that which is made from plants—synthetic paraffinic kerosene. Unfortunately, jet fuel derived from coal results in even more CO2 emissions, which makes it no alternative at all if the goal is to combat climate change.