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Ethanol from Sugar Beets

written by: •edited by: Lamar Stonecypher•updated: 7/8/2010

Ethanol is an alcohol produced mostly from sugar beets or corn, their sugar or starch being easily extracted for further processing to ethanol. Cellulosic Ethanol has also been produced from the cellulose contained in the stems of grasses, although this is still in the research and development stage

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    Introduction to Ethanol Production from Sugar Beets

    Ethanol can be produced from processing sugar beets, the ethanol alcohol extracted being the same as we use as alcoholic beverages, but used as a gas additive in our cars.

    Many countries also produce ethanol from corn, with the US producing a high percentage of world ethanol production from corn. Ethanol can also be produced from various crops such as grasses and potatoes.

    This is an article on alternative fuels produced from renewable energy sources and in particular the production of ethanol from sugar beets, corn, and grasses.

    We begin by having a look at the production of ethanol from sugar beets, comparing this to ethanol from corn and grass, and examining the energy used to cultivate and process these feedstocks.

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    Production of Ethanol from Sugar Beets

    Because of the bulky nature of sugar beets, transportation can be costly and, added to this, the sugar beets go off high-quality rather rapidly; therefore the processing facility is usually built very close to the cultivation area. After being delivered to the facility, the beets are crushed to extract the glucose which is collected and fed into a vessel where due to microbial fermentation it is slowly converted into ethanol and CO2.

    This ethanol contains water which must be removed, and this is achieved by distillation, which removes about 96% of the water. The remaining 4% or so can be removed through several methods, involving addition of benzene or ternary component and further distillation in columns.

    However, a more efficient method of dehydration is currently being used. Here the ethanol is vaporized and passed through a bed of molecular sieve beads. These beads absorb the water allowing the ethanol to pass on through into a condensing vessel. There are two sets of bead-beds, so whilst one is online, the other is being regenerated to remove the absorbed water. In 2009 world ethanol production for use as fuel topped almost 20 billion gallons, with the US and Brazil being responsible for the vast majority of this, although the US also used corn as feedstock.

    Note:

    The remaining crushed sugar beets fibrous plant stems known as bagasse can be further processed to produce more ethanol or used as fuel in the ethanol process. Molasses is also a by-product of sugar beets processing and can be used as animal fodder supplement.

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    Production of Ethanol from Corn

    The cultivation of corn requires a large amount of ground and, this coupled with the use of only the corn kernels has led to some controversy, replacing food crops with first generation bio-fuel crops, and the clearing of rain forest by the indigenous for corn cultivation. There are two methods used to process the corn known as wet and dry milling, of which dry milling is the current favorite so we will examine this method.

    The kernels are delivered to the ethanol production facility where they are crushed to flour meal and water added to make up a slurry mash, which makes up about 50% of the kernel mass.

    Enzymes (proteins used as catalysts to speed up the chemical reaction) are then added to the mash to convert the starch to sugar. Ammonia is then added and the whole mixture boiled to remove any bacteria, which is then transferred to cooling pots and allowed to ferment.

    Yeast is then added to the mixture in the fermenters and the processing of corn to alcohol commences. Ethanol processing from corn can use up to twice the energy as that from sugar beets due to the extra stage and addition of enzymes.

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    Processing of Switchgrass to Ethanol

    Ethanol processed from switchgrass is known as cellulosic ethanol and is still in the research and development stages. One popular method, acid hydrolysis, is explained below:

    The switchgrass is harvested using conventional baling machinery and delivered to the ethanol processing facility where the bales are broken up and crushed to extract the lignin encased cellulose from the stems and leaves. This mixture is the subjected to pre-treatment which separates the cellulose from the lignin, which is used as a fuel during the entire process.

    Acid hydrolysis technology is used to break down the carbohydrates in the cellulose into sugars, and then microbial fermentation converts this into ethanol and CO2.

    If switchgrass is used to produce ethanol, it would be considered as a second generation biofuel (a crop, or remains of a crop, not used to feed humans).

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    Comparison of Sugar Beets, Corn, and Switchgrass Cultivation and Ethanol Processing

    Comparison of Sugar Beets, Corn, and Switchgrass Cultivation and Ethanol Processing

    Ethanol processed from plants is considered to be CO2 neutral due to the fact that any emissions of CO2 are absorbed by other plants through photosynthesis.

    However, this is not strictly true as other factors should be taken into account as explained below:

    • Cultivation and Transportation of Corn and Sugar Beets Feedstock.

    Nowadays all cultivation is motorized, from the plowing of the land, making drills and sowing, fertilization, harvesting, and transportation. This is all carried out using tractors and attachments which produce CO2 emissions at every stage, plus the release of nitrogen through the extensive use of fertilizers.

    It has been independently calculated that as little as 13% is saved in emissions due to using ethanol as a fuel additive. However this can be increased when corn oil, which is produced as a by-product of the ethanol process, is factored into the equation.

    • Processing of Corn to Ethanol

    Processing ethanol is energy intensive especially when corn is used as the feedstock as distillation is required. To mitigate this to some degree some of the corn crop residues from processing can be used as fuel, and valuable by-products such as corn oil can be obtained during the ethanol processing.

    • Cultivation and Transportation of Switchgrass Feedstock.

    Switchgrass is not like the normal grass in our gardens or that we see in fields. It grows quite tall with spindly stems. However, currently there are many farmers in USA cultivating switchgrass as a means of combating soil erosion and returning nutrients into soil previously over-cultivated to such an extent as to make the soil quite barren.

    Switchgrass can be harvested using conventional cutting/baling machines and as the roots are left in place can produce many crops from the original sowing. As the switchgrass has deep roots it searches for water effectively whilst fertilizing the soil, so little additional fertilizers are required. So, this coupled with easy transportation of harvested bales means that ethanol production from switchgrass can produce about five times the energy expended in cultivation.

    • Processing of Switchgrass to Ethanol

    This is very efficient as the lignin by-product is used as a fuel during processing. The projected costs of the complex procedures used in processing ethanol from the cellulose are still high, but with adequate government subsidies in both research and end product it must be one of the better means of ethanol production.

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    Ethanol Processing Images and Charts

    Ethanol Production ChartSugarbeets Cultivation (http://bioenergy.ornl.gov)Switchgrass Cultivation(http://bioenergy.ornl.gov)





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