Ethanol, or ethyl alcohol is the same alcohol found in liquor and other spirits. Apart from beverages, ethanol’s main use is as a gasoline additive used to reduce harmful vehicle emissions. It is most widely used in Brazil and the United States. In fact, these countries were responsible for 88% of the entire globe’s ethanol production in 2010.
Surprisingly, ethanol – an additive used in petroleum fuels to reduce emissions – can in fact be produced from petroleum. In 2003, about 5% of the world’s ethanol was derived from petroleum. This synthetically produced ethanol product is indistinguishable from biological ethanol and works exactly the same. It is made by catalytic hydration of ethylene using sulfuric acid as a catalyst. The ethylene and acetylene used in synthetic ethanol can be derived from calcium carbide, coal, oil gas, and other petroleum products.
Organic ethanol is derived primarily from carbon based feedstock. Because the only energy needed to produce them comes from the sun and all minerals and nutrients are returned to the soil after harvest, agricultural feedstocks are considered to be renewable resources.
Ethanol can be produced from a wide variety of biological feedstock sources including:
- Sugar cane
- Sugar beet
- Sweet potatoes
- Cellulose waste and harvestings
Ethanol Production Process
Large scale ethanol production requires several steps to go from sugar cane in the field or petroleum products to pure ethanol or synthetic ethanol. The basic steps in this production process are:
- Cellulolysis of cellulose and starch into sugar
- Microbial sugar fermentation
During the fermentation process, yeast is used to ferment sugars producing ethanol. Currently, this fermentation only works with sugars. Starch and cellulose – principally composed of sugars – can be converted to sugar for fermentation, but cannot be directly fermented.
Recently, however, a large amount of research has been directed to the area of cellulosic ethanol. A process whereby the cellulose found in plant matter is broken down into sugar and subsequently converted to ethanol.
In order to be used as fuel, the water found in ethanol must be removed. Water is removed through the distillation process. Due to the formation of a low-boiling water-ethanol azeotrope purity can only be taken to 95 – 96%. When used as a stand-alone fuel, the 4 – 5% water content is acceptable, but to be used as a gasoline additive, the ethanol must be further treated to remove all moisture.
There are several different dehydration methods of removing the moisture from an azeotropic ethanol/water mix.
- Azeotropic Distillation – Used in early ethanol production facilities, azeotropic distillation is a process whereby benzene or cyclohexane are added to the ethanol. This produces a vapor-liquid-liquid equilibrium. When distilled the pure ethanol can be extracted from the bottom column of this mixture.
- Extractive Distillation – This early method of dehydration uses a ternary component which, when added to ethanol, increases its relative volatility. When distilled, this mixture produces ethanol on the column’s top stream.
- Molecular Sieves – This distillation-free method of dehydration used molecular sieves to remove water from ethanol. Ethanol vapor is passed through molecular sieve bead beds under pressure. The beads absorb water and exclude ethanol.
Denaturing is the process of adding a chemical to ethanol to render it unfit for human consumption. This allows companies using ethanol for fuel to bypass liquor and other alcoholic beverage taxes.