Back in Lesson 2, I included a chemistry tutorial on some of the basic constituents of fuels. In Lesson 7, we will be discussing the production of ethanol (CH3-CH2-OH) and butanol (CH3-CH2-CH2-CH2-OH) from starch and sugar. Ethanol, or ethyl alcohol, is a chemical that is volatile, colorless, and flammable. It can be produced from petroleum via chemical transformation of ethylene, but it can also be produced by fermentation of glucose, using yeast or other microorganisms; current fuel ethanol plants make ethanol via fermentation.
The basic formula for making ethanol from sugar glucose is as follows:
For fermentation, yeast is needed (other enzymes are used but yeast is most common), a sugar such as glucose is the carbon source, and anaerobic conditions (without oxygen) must be present. If you have aerobic (with oxygen) conditions, the sugar will be completely converted into CO2 with little ethanol produced. Other nutrients include water, a nitrogen source, and micronutrients.
Here in the US, the current common method of ethanol fuel production comes from starches, such as corn, wheat, and potatoes. The starch is hydrolyzed into glucose before proceeding with the rest of the process. In Brazil, sucrose, or sugar in sugarcane is the most common feedstock. And in Europe, the most common feed is sugar beets. Cellulose is being used in developing methods, which includes wood, grasses, and crop residues. It is considered developing, because converting the cellulose into glucose is more challenging than in starches and sugars.
As stated above, the primary feedstock for ethanol in the US and worldwide has been coarse grains (i.e., corn), however, the production of ethanol from these feeds is expected to plateau in 2015. The increase in ethanol production in the next 10 years is expected to be from sugar-based ethanol (cane, beets). It is expected that 2nd generation biofuel production (from cellulosic feeds) will increase after 2015. Figure 7.1 shows graphically how the feedstocks compare.
World production of ethanol based by country is shown in Figure 7.2. The US produces the most ethanol worldwide (~57%), primarily from corn. Brazil is the next largest producer with 27%, primarily from sugarcane. Other countries, including Australia, Columbia, India, Peru, Cuba, Ethiopia, Vietnam, and Zimbabwe, are also beginning to produce ethanol from sugarcane.
Figure 7.3a shows the growth of sugarcane in the world, in tropical or temperate regions. Sugar beet production in Europe is the other source of sugar for ethanol. It is grown in more northern regions than sugarcane, primarily in Europe and a small amount in the US. Figure 7.3b shows the growth of sugar beets in the world.