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What are biofuels?
Biofuels are fuels produced by biological means, normally by processing plant matter. Technically the term 'biofuel' would include fuels such as wood chips but is more associated with liquid fuels that can be burned in internal combustion engines. There are two established biofuels of significance. Bioethanol which is produced from any crops that have a reasonable sugar content such as wheat and sugar cane. These are fermented with yeast in exactly the same way as in wine making, but distilled to a higher concentration (typically 95 percent plus by volume). And Biodiesel which is esterified vegetable oil. Although vegetable oil can be used directly in diesel engines, it can lead to starting problems. The esterification process solves this by making the oil chemically similar to regular diesel oil. Biofuels are said to be 'carbon neutral' because the carbon dioxide released when the fuel is burned is primarily that taken in during plant growth. Up to a point carbon neutrality is undermined as significant quantities of biofuels are produced by processes that involve energy inputs that often come from non carbon neutral sources. Nonetheless, the opportunity to make carbon neutral biofuels is there and in any event, the fuels lack the sulfur content of their oil derived equivalents.
The Brazilian Ethanol Program
Production of ethanol from sugar cane was pioneered by the Brazilians in the 1970's as a solution to an oil import bill they could ill afford. The project was by far the most ambitious alternative energy undertaking to date and it has been in many respects very successful. Virtually all cars on Brazil's roads today can run on ethanol, gasoline or various mixtures of the two. Ethanol is an important part of the energy mix, replacing billions of liters of oil each year and saving tens of millions of tons of CO2 emissions.
The ethanol program worked for Brazil because they had plenty of land available for growing sugar cane and at the time, plenty of cheap labor with which to harvest it. Today this economic benefit is increasingly questionable. Brazil's economy has moved forward in leaps and bounds and its labor and its land is not as cheap as it was. And oil, which Brazil now has, is currently cheap and not particularly likely to return to the recent $100 per barrel level anytime soon if ever. Ethanol is struggling to compete and as Brazil's economy develops further, will likely struggle more.
More importantly, while the program provides jobs and saves CO2 emissions it has other detrimental environmental and social impacts. Most notably, Ethanol directly competes with us for foodstuffs - as the Americans have found out with their own corn based ethanol programs. Much of this was common sense ignored for political posturing over emissions. As any schoolchild knows, a key component in economic development is farm mechanization in which cheap energy does the digging for us! The ethanol program runs counter to this notion and so does the production of bio- deisel. The simple truth is the world does not have enough land to produce anywhere near the quantity of ethanol or biodiesel we would need to make any dent in our oil consumption.
Gasification and Fuel Synthesis
The idea that biofuels can wholly or even significantly replace oil depends on a quantum leap in efficiency. The plants matter used should either be that wasted in normal food production (e.g. stalks), or where crops are grown specifically for fuel, the whole plant should be used. This way the yield per hectare is significantly increased. The way to do this is gasification.
Gasification and fuel synthesis on any scale was first used in Germany during WW2 and later by the apartheid regime in South Africa. Both programs converted plentiful coal into scarce petroleum products such as diesel and gasoline. Casting the dubious politics aside, the science of it offers a way forward for biofuels as plant matter can also easily be gasified and the resulting syngas (a mixture of hydrogen and carbon monoxide) turned into the same range of liquid fuels.
Gasification is about turning material containing carbon into syn-gas, a mixture of hydrogen and carbon monoxide, by reacting it with water. For pure carbon the reaction is C + H2O -> CO + H2 while for methane it would be CH4 + H2O -> CO + 3H2. Different input materials produce different proportions of CO and H2 but the CO can be further reacted with steam to produce more hydrogen by the following reaction CO + H2O -> CO2 + H2. While coal and methane are the most commonly used inputs for this process today it doesn't have to be that way. Plant matter also contains carbon and can be gasified. And it does not have to be the stuff we eat, it can be the stalks. The reactions are endothermic meaning heat has to be supplied and commonly this has been supplied by burning some of the input carbon or methane. But again it doesn't have to be like this. The heat can be from solar concentration. You can literally put grass and stalks in a solar furnace and pipe off syn-gas - and do so in quantities that equate to per hectare yields way beyond what Brazil and America are achieving with their current ethanol programs.
And from syngas you can make a very wide range of fuels including all the ones currently derived from oil. This provides a lot of opportunity to cut CO2 emissions but comes with a very clear moral hazard - the synthetic hydrocarbons will always be in competition with oil. And the price of oil is the key determinant in its perceived availability as well as its use. When reserves are stated this is not a measure of how much oil is in a given field but a measure of how much oil can be extracted economically. At $100 per barrel the term 'peak oil' applies to the demand and not the supply! There are still significant oil fields (many millions of barrels per day) that can be operated at a profit at less than $10 per barrel and these are not going to run low anytime soon. Improvements in biofuel production are very unlikely to ever force oil out of the market and so only government intervention can meaningfully cut CO2 emissions associated with hydrocarbon use.