Chemistry

Ethanol Production Fermentation



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Ethanol is an alcohol that has the formula C2H5OH. Its' basic constituent is the Ethylene molecule (C2H6), and Ethanol is produced through a process known as hydration synthesis or can be accomplished with fermentation.

ETHANOL PRODUCTION WITH HYDRATION SYNTHESIS:

Ethylene is a relatively common compound. It is the simplest molecule of a group of hydrocarbons known to chemists as the alkyne series. Larger quantities of ethylene are produced around the world every day than any other hydrocarbon, and this compound is the basic hydrocarbon building block for many more complex carbon compounds besides ethanol. The primary source of ethylene is from the cracking of petroleum. By using sulfuric acid as a catalyst to promote the reaction, ethylene can be converted directly into ethanol. This is actually the least expensive and most commercially feasible way to produce ethanol.

ETHANOL BY FERMENTATION OF SUGAR:

Thousands of years ago, humans discovered that fruits and grains stored in sealed containers would produce a liquid which had mysterious properties. What they didn't know was that the liquid was ethyl alcohol or ethanol, and that it was produced by microorganisms call yeast which occurred naturally. Drinking the liquid produced a sense of euphoria, and over time man discovered how he could use this process called fermentation to his advantage.

In modern times, chemists have learned that yeast cells secrete an enzyme called zymase which actually converts monosaccharides such as glucose or fructose (C6H12O6) -simple sugars- or disaccharides like sucrose (C12H22O11) a into ethanol. In all cases, carbon dioxide CO2 is produced as a byproduct. Simple sugars, as well as starches which can be broken down into simple sugars with enzymes, are found in many plants. Many "sugar crops" can therefore be used as feedstocks for the production of ethanol through fermentation.

Once the sugar has been removed from the feedstock, it is diluted in water, to about 16%. This will vary based on the specific yeast organism used and type of sugar. The dilute sugar water and yeast are then placed in a fermentation vat which will allow CO2 to escape, but will not allow outside air to come in contact with the brew. Maintaining a temperature of about 85 degrees F is optimum for the yeast. To much higher or lower and the yeast will not function efficiently or may even die. Maintaining a PH balance is also important, but not as important as temperature.

The fermentation process will take from 30-48 hours, but is basically complete when the percentage of ethanol by volume reaches 12 or 13 percent. This can be measured with a device called a hydrometer. Once the fermentation process is complete, the yeast can be recaptured by straining, and then reused in the next batch. The resulting beer is then heated in a still to vaporize the alcohol and separate it from the water. After several stages of distillation, an alcohol concentration of better than 96% can be achieved.

Concern over increased carbon dioxide levels in the atmosphere in recent years has raised issue with the burning of petroleum based fuels. Using ethanol produced through fermentation solves this problem because the amount of CO2 released during fermentation and combustion of ethanol is equal to that consumed by the plant to produce the sugar in the first place, resulting in zero net increase in atmospheric CO2 levels. As such, ethanol production through fermentation will play an important role as an energy source in future years.

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