First Generation Biofuels
Agricultural products that are specifically grown for their use as biofuels include corn, soybeans, flaxseed, rapeseed/canola, sugar cane, palm oil, cassava and jatropha. Because biofuels can be created from any type of organic matter that ferments, vegetable oil, animal fats, and other types of €˜rubbish' are used as well. These materials are converted into two main types of fuels: Ethanol and Biodiesel. Biofuels have a huge advantage over fossil fuels: The source plants absorb carbon dioxide from the atmosphere as they grow, and the carbon dioxide released when biofuels are burned does not provide a net addition to the greenhouse gases in the atmosphere.
Ethanol is a type of biofuel made from starches (corn, grains, potatoes), sugars (sugar cane or sugar beet), or other biomass. By 2008, 65.7 billion liters were produced, and it is primarily used in conjunction with petrol to create a transport fuel. There are two key reactions that occur in order for biomass to become ethanol:
1. Hydrolysis – this chemical reaction converts complex polysaccharides in the raw feedstock (starches, sugars, etc.) into simple sugars. Acids and enzymes are used to catalyze this reaction.
2. Fermentation – a series of chemical reactions that convert sugars into ethanols. The fermentation reaction is caused by yeast or bacteria, which feed on the simple sugars created during hydrolysis. Ethanol and carbon dioxide are produced as the sugar is consumed. Two types of fermentation occur: glucose fermentation and pentose fermentation.
After these two reactions take place, the last step is ethanol recovery, which includes distillation and drying. The product of glucose and pentose fermentation is called ethanol broth. In this process, the ethanol is separated from the other components in the broth. Then the final step of dehydration takes place, where any remaining water is removed from the ethanol.
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Biodiesel is a non-toxic, biodegradable fuel, and by 2005 3.8 billion liters had already been produced. It is used as a replacement for diesel fuel or is used in a blend with traditional diesel fuel, and is primarily used as a transport fuel. Soybean oil, recycled cooking oil, vegetable oils, and animals fats comprise the feedstock that are used to make biodiesel. There are four steps that are part of the biodiesel production process:
1. Acid Esterification – oil feedstock that contain more than 4% free fatty acids go through this process to increase its yields. After the feedstocks are filtered and preprocessed, sulfuric acid is dissolved in methanol and then mixed with the oils. The mixture is heated and stirred, and the free fatty acids are converted to biodiesel. Then water is removed and the product is introduced into the next process.
2. Transesterification – feedstocks that contain less than 4% free fatty acids are filtered and preprocessed, then are combined with the products of acid esterification. Potassium hydroxide is dissolved into methanol and then mixed with the preheated oil. If acid esterification is used, then another catalyst must be added to neutralize the acid added in that step. After the reaction is complete, the major co-products, biodiesel and glycerin, are separated into two layers.
3. Methanol Recovery – The methanol is removed after the biodiesel and glycerin have been separated to prevent the reaction from reversing itself. The methanol is cleaned and reused to begin the process all over again.
4. Biodiesel refining – After the biodiesel is separated from the glycerin, it undergoes a clean-up process that remove excess alcohol, residual catalysts and soaps. One or more washings with clean water occur and then it is then dried and sent to storage.