The Environmental Impact of Ethanol as an Alternative Fuel
Ethanol, also known as ethyl alcohol, is a clear and colorless liquid that can serve as an alternative fuel to non-renewable energy sources. More than 97% of gasoline in the US contains ethanol, usually in three different mixtures called E10 (10% ethanol and 90% gasoline), E85 (15% gasoline and 85% ethanol), and E15 (15% ethanol and 85% gasoline (‘Ethanol (Ethyl Alcohol)’. Today, about 25% of total greenhouse gas emissions in Europe are from transport emissions. Liquid petroleum is a common fuel used worldwide because it is rich in combustible carbon and thus a good source of energy. However, the combustion of petroleum contributes to increased carbon dioxide emissions and other greenhouse gases. These gases get trapped in the atmosphere, contributing to global warming of the planet (‘How Is Ethanol Produced?’).
Sustainable biofuels are an alternative to this problem, with ethanol being one of them. The first step towards creating ethanol is about growing biomass feedstocks and extracting sugars from them. Usually 6-carbon sugars are withdrawn from these feedstocks as they are ideal for the process of fermentation later on. Glucose (C6H12O6), is a good example of a 6-carbon sugar that is most commonly extracted because all glucose molecules contain six carbon atoms. Examples of sugar-based and starch feedstocks where ethanol derives from include corn, barley, sorghum, sugar beets, and sugar cane. Glucose is the easiest to extract from sugar-based feedstocks as it is simply dissolved in water. Glucose from starch, meanwhile, is extracted through a more complex process called liquefaction and saccharification, where the addition of enzymes (such as amylase) helps break large starch molecules into simpler sugars (‘How is ethanol made?’). Ethanol can also be made from non-food biomass. This includes cellulosic feedstocks, which are crop and wood residues that contain cellulose and hemicellulose (components that are found in plant cell walls), and lignin (a complex polymer which creates the rigidity in plant cell walls). Both cellulose and hemicellulose contain large chains of glucose molecules, however, lingin does not contain any sugars and encloses the cellulose and hemicellulose, which makes the extraction process of glucose more difficult. After the plants are grinded, acid is added by refineries to unravel lingin. Then, acid is further used to produce four component sugars from hemicellulose and free cellulose, where enzymes must further be used to break it into glucose (Nasr, Susan).
Next, sugars extracted from feedstocks are converted into ethanol at a production facility. Here, fermentation is carried out to convert glucose into ethanol with the use of microbes – usually with yeast. The chemical reaction of this process is the following: C6H12O6 (aq) + yeast → 2 C02 (g) + 2 C2H5OH (aq). Yeast is a fungus that contains an enzyme called zymase, which helps accelerate the breakdown of glucose to be used as energy and generate ATP. Waste products are produced along with the metabolization of food, which in this case, are two carbon dioxide and two ethanol molecules (‘Fermentation of Yeast & Sugar – The Sci Guys: Science at Home.’). At this point, a mixture of ethanol, water, and other solids is present. To separate these, the process of distillation is applied. Heat is applied to the mixture, and since ethanol evaporates faster than water, the gas rises up a tube where it is collected and condensed into ethanol, which still contains about 4% water. Therefore, the remaining water is separated by a molecular sieve, which only allows smaller water molecules to pass through, leaving pure ethanol behind (Tabak, John).. After ethanol has been produced, it is transported to a fuel terminal or end-user where it is blended with gasoline to create E85 or E10. It is then further transported to fueling stations, where E15 is created through a blend of E10 and E85 separately (‘Ethanol Fuel Basics.’). When ethanol is used to generate energy, it undergoes the process of combustion. Here, ethanol burns with oxygen, which is found in the air, to produce carbon dioxide, water, and energy. The balanced equation that represents this process is the following: C2H5O8 + 3O2 → 2CO2 + 3H2O. The reaction is exothermic because the bonds of the CO2 and H20 products are stronger than the bonds of the C2H4O8 and O2 reactants, meaning that more energy must be used to form the bonds of the products. The overall net energy change is negative, meaning that heat energy is released, which can further be used for different purposes (‘Ethanol Combustion.’).
The use of ethanol as an alternative fuel can have beneficial environmental impacts. Firstly, less carbon dioxide (CO2) is released through the combustion of ethanol. Although this process releases a greenhouse gas, it is considered carbon neutral because ethanol is composed of biomass. Therefore, as the biomass grows, it absorbs CO2 through the process of photosynthesis, which balances the amount of CO2 released during combustion. In fact, with the use of E10 across Europe, the number of transport emissions resulting from liquid petroleum could be reduced by up to 15 million tonnes with the use of ethanol. Also, when ethanol is added to gasoline, it makes it an oxygenated fuel. With the combustion of fossil fuels, low temperature and oxygen levels can often result in the release of carbon monoxide, a toxic greenhouse gas. Because ethanol molecules contain about 35% oxygen, ethanol helps oxygenate the fuel and decrease the amount of carbon monoxide released (Ciolkosz, Daniel).
Additionally, ethanol is a renewable fuel. Because ethanol comes from plant material, it follows a cycle where carbon dioxide and water are converted into glucose by photosynthesis, which is then fermented to create ethanol. Once ethanol is combusted, carbon dioxide and water are released, where the cycle is further continued. Therefore, while liquid petroleum comes from fossil fuels that must manually be drilled from underneath the ground, ethanol derives from a natural process that is always replenished. Furthermore, ethanol is a biodegradable and nontoxic source. Unlike petrol, which can contaminate groundwater, pose fire hazards, and impact aquatic life when spilled, ethanol would simply break down into harmless substances within a short process of 5 days when spilled because it is composed of biomass (Regoli, Natalie). The use of ethanol can also have a negative impact on the environment.
Although the use of ethanol generally results in less CO2 emissions, the whole process of making ethanol can also have environmental impacts. Firstly, trucks and tractors, which all run on fossil fuels, are widely used to transport crops and other substances for the creation of ethanol. With corn being the most popular crops for the production of ethanol, millions of acres of natural habitat are lost in order to grow corn (Blue, Marie Luise.). Also, many agricultural nutrients and chemicals are used to help with the growing of crops. A large portion of these fertilizers later end up in runoff, which leads into rivers and lakes. Nitrates and phosphorus are both substances found in fertilizer, which significantly increase the growth of algae when they end up in water. This results in decreased levels of oxygen for aquatic life, causing the deaths of many fish and other aquatic flora and fauna (Bhatti, Shalu).
In conclusion, ethanol is a generally effective alternative fuel to liquid petroleum. Produced through the extraction of sugars from feedstocks and the fermentation of glucose, ethanol helps decrease CO2 emissions, and is a renewable and biodegradable source. However, the production of ethanol also results in CO2 emissions and has other negative impacts on the environment.
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