The Pros And Cons Of Ethanol

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Ethanol can be made from many different plant sugars including starch and cellulose. Starch ethanol is the most common biofuel used in the world. It is made from kernels of corn, which is very easy to break down. This means that corn is very easily converted into ethanol. On the other hand, cellulose is not easily broken down into ethanol. Cellulose is found in the cell walls of plants, and resembles plant armor. The cellulose combines with lignin, which makes plants woody. During the process of making ethanol from cellulose, the lignin has to be separated from the cellulose because it is not fermentable. Figure 1 shows the complications of making cellulosic ethanol vs. other biofuels. The question marks indicate where the technology hasn’t …show more content…

The thermochemical process involves breaking down the biomass and building it back up. This poses some benefits over the biochemical process because about one third of the cellulosic biomass, lignin, cannot be

Figure 3: Thermocemical Process of Making Cellulosic Ethanol (Theis, 2007)

converted into ethanol biochemically, but is easy to do thermochemically. The optimal biomasses for thermochemical conversions are trees and mill products. These have a high lignin concentration, so these biomass products respond better to the thermochemical method of ethanol production (Theis, 2007). Figure 3 shows the thermochemical process. The first step is drying the plants. Next the plants are burned into synthesis gas, or syngas. The syngas is made of carbon monoxide (CO) and hydrogen (H2). This is called gasification. The gasification produces tar and sulfur, which is not clean and interferes with the making of ethanol. As a result, the syngas is sent to a tar reformer (Nasr, n.d., Theis, 2007). The tar reformer uses enzymes to convert about 97% of the tar into syngas (Theis, 2007). Then, the syngas is cleaned to get purer CO and H2 gasses. Next, the gas is compressed and mixed with a metal catalyst. The catalyst builds the gas back up into ethanol (Nasr, n.d.). There are some drawbacks to the thermochemical process, however. The catalysts used in the tar reformer are very expensive and the tar remains accumulate. Biorefineries could utilize …show more content…

For cellulosic ethanol to be put in large-scale production, the benefits need to outweigh the concerns. Some of the benefits are that it releases 86% less greenhouse gasses than gasoline, and 52% less than corn ethanol. Also, it lowers the emissions of two cancer causing substances, benzene and 1,3-butadiene. Maybe the most important is that cellulosic biomass is more available than any other source of ethanol. Some of the concerns of cellulosic ethanol involve expenses, low fuel mileage, and not being able to produce enough. Cellulosic ethanol costs more to make than gasoline. This is largely because of the expensive enzymes used to separate the sugars. Also, 100% ethanol is not used as an automotive fuel source. The highest allowed [ethanol] is 15%. This is called E85. E85 produces 25% less miles per gallon than gasoline (Nasr,

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