transported in pipelines used for petroleum transport, as discussed earlier in this chapter, it is currently transported by rail or barge. But if cellulosic biomass were dedicated to thermochemical conversion by FT or MTG, the resultant fuels would be chemically equivalent to conventional gasoline and diesel. They could thus be transported via existing pipelines, and the infrastructural challenge associated with ethanol would be minimized.
The committee’s analyses provide a snapshot of the potential costs of liquid fuels—from biomass by biochemical or thermochemical conversion, and from combined biomass and coal by thermochemical conversion. But the costs of fuels are dynamic, fluctuating as a result of externalities such as the costs of feedstocks, labor, and construction; the economic environment; and government policies. With the wide variation in most commodity prices, especially for oil, investors will need to have confidence that policies—including carbon caps, carbon price, mandated greenhouse gas reductions, or tariffs on imported oil—will ensure that alternative liquid transportation fuels can compete with fuels refined from crude oil. The price of carbon emissions, or the existence of fuel standards that require specified reductions in fuels’ life-cycle greenhouse gas emissions, will affect the relative economic choices.
Biodiesel refers to diesel fuel made by transesterifying oil from biological sources. A potential biodiesel feedstock that is not a commodity crop is algae, such as algal glycerolipids, which can be transesterified to produce fatty acid methyl (or ethyl) esters. Cellular lipids can also be converted via a catalytic hydrocracking process into a mixture of alkanes suitable for use as a jet fuel or gasoline ingredient; certain algae, such as Botryococcus, produce long-chain hydrocarbons that are potentially usable as a fuel after hydrocracking to reduce the chain length of the molecules. In most production schemes, the algal oil is extracted from the harvested algae.
Recent reevaluation suggests that current costs are well over $4/gal and that much more progress is needed if this technology is to have an impact in the