10.3: Liquid Biofuels

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Of all sectors of American economy, the two that are the largest emitters of CO₂ are the electric power sector (29%), and transportation (27%). The figures may be different for individual states. The pie chart in Figure 10.4 show how much CO₂ is emitted by each sector of US economy, and Fig. 10.5 how much fuel of different kinds is consumed by the US transportation.

As can be seen in the graph, an overwhelming part (over 90%) of the US transportation is powered by liquid fuels: gasoline, diesel fuel, and jet fuel. In other states the percents may be somewhat different. But the overall picture for the entire country is essentially the same – nearly all American transportation is powered by these three kinds of fuels, and they all are derived from crude petroleum oil.

The good news is that currently there exist technologies of producing biofuels that can replace the currently used petroleum products. For diesel engines the conversion to biofuel is pretty simple – just fill the tank with biodiesel, and that’s it. There exist technologies of making bio-aviation fuel equivalent to petroleum jet fuel. And replacing gasoline with its “number one” bio-substitute – namely, bioethanol – may require some modification of the fuel injection system in the engine, but not replacing the entire engine.

CO2 emissions by sector: Transport 30%, Electricity 28%, Industry 22% Agriculture 9%, Commercial 7%, Homes 5% — Figure $\PageIndex{1}$: CO₂ emission of the US economy by sector (source: US EPA).

transportation fuels: Gasoline 56%, diesel 22%, jet fuel 11%, natural gas 3 $=%, biofuels 5%, other 3%. — Figure $\PageIndex{2}$: : The consumption of different kinds of fuels by the US transportation sector (Source: US Energy Information Administration, 2015).

A serious interest in biofuels for cars and trucks has erupted for the first time after the “oil crisis of 1970-s”. Since then, the interest keeps alternating – it increases at times when oil and gasoline prices are surging, and dwindles when the prices fall. The prices since 1929 exhibit many maxima – the most recent price surge happened around the year 2007, mostly because the crude oil prices grew to the level well over $100 per barrel, and after a short break they stayed at a level close to $100/barrel until 2014. Over that period, there was much interest in biofuels in the US. Then the oil and natural gas prices dropped considerably, due to the application of novel “fracking” drilling techniques that have brought the US close to the state of “energy independence”. In the 2007-14 period the prices of biofuels were still higher that those of the petroleum products, but there was much hope that eventually the bio- prices might become competitive with the petroprices. But after 2014 those hopes disappeared, and, understandably, the interest of researchers and industrialists in biofuels markedly dwindled.

Nonetheless, no matter how “uncompetitive” the biofuel prices are, nothing can change the fact that their “emission intensity” will always be lower that of petroleum fuels. And if one day the emission intensity of a fuel be- comes more important than its price, then research on biofuels may be put on the “fast track” again.