Fuel ethanol generally refers to ethanol with the volumetric concentration which is higher than 99.5%. Nowadays, fuel ethanol refers to ethanol obtained from biological substances through biological fermentation and other means that can be used as fuel. Fuel ethanol is a clean high-octane fuel that is a renewable energy source. Ethanol is not only a good fuel, but also an excellent fuel additive. Its excellent properties manifest as follows : Ethanol is an oxygenator for gasoline, increasing the internal oxygen content of gasoline and promoting complete combustion to achieve the goals of energy saving and environmental protection; Ethanol can also economically and effectively reduce the content of aromatic hydrocarbons and olefins, i.e., reduce the refinery retrofitting costs and meet the new gasoline standard.
The main fuel ethanol production technologies include the first and second generations. The first generation fuel ethanol technology uses sugar and starch crops as raw materials to produce ethanol. The process generally consists of five stages: liquefaction, saccharification, fermentation, distillation,and dehydration. The second generation fuel ethanol technology uses woody fiber as raw material to produce ethanol. Compared with the first generation technology, the second generation fuel ethanol technology firstly needs to undergo pretreatment, i.e., remove lignin to increase the looseness of the raw material to enhance the contact between enzymes and cellulose and improve enzyme efficiency. After the raw material is decomposed into fermentable sugars, it enters the fermentation, distillation, and dehydration stages.
The main raw materials for fuel ethanol in China are aged grain and cassava, sweet sorghum, and other starch or sugar non-grain crops. In the future, the research and development focus will mainly be on second-generation fuel ethanol technology using woody fiber as raw material. The National Development and Reform Commission of China has approved non-food pilot projects such as cassava fuel ethanol in Guangxi province, sweet sorghum fuel ethanol in Inner Mongolia and wood sugar residue fuel ethanol in Shandong province, and the technology of producing ethanol fuel from lignocellulosic raw materials such as agricultural and forestry waste has entered the pilot stage with an annual output scale which is about ten of thousands tons.
01 As an additive for gasoline, it can improve the octane value of gasoline
The octane value of automotive gasoline is generally required to be 90 or 93, and the octane value of ethanol can reach 111. Therefore, adding fuel ethanol to gasoline can greatly improve the octane value of gasoline, and ethanol's octane-boosting effect on aliphatic gasoline components (alkylate oil, light gas oil) is better than that of olefinic gasoline components (catalytic cracking gasoline) and aromatic gasoline components (catalytic reforming gasoline). Adding ethanol can also effectively improve the gasoline's anti-detonating property.
02 Renewable energy
If sweet sorghum, wheat, corn, rice hulls, potatoes, sugarcane, molasses, etc. are fermented into ethanol using biomass, the CO2 emitted during combustion and the CO2 consumed by the biological sources used as raw materials are approximately equal in quantity, which is of great significance in reducing atmospheric pollution and mitigating the greenhouse effect.
03 It is an oxygenator
Fuel ethanol is an excellent quality improver for oil products, or an oxygenator. It plays the same role as MTBE, which was developed by China's petroleum industry in the late 1990s to improve oil quality. The oxygenating effect of ethanol is twice that of MTBE.
01 Dehydration Method
Dehydration technology is one of the key technologies in the production of fuel ethanol. The highest quality concentration of ethanol that can be obtained from the normal distillation section is only 95%, and further concentration cannot be achieved by using the normal distillation method. This is because at this time, alcohol and water form the constant boiling mixture (the corresponding constant boiling temperature is 78.15℃), and it is difficult to separate them using the normal distillation method. In order to improve the ethanol concentration and remove excess water, special dehydration methods need to be used. The main methods for preparing fuel ethanol include chemical reaction dehydration method, azeotropic distillation, extraction distillation, adsorption, membrane separation, vacuum distillation method, ion exchange resin method, etc.
02 Fermentation Method
The fermentation method uses various sugar-containing (disaccharide), starch (polysaccharide), cellulose (polyhexose) agricultural products, agro-forestry by-products and wild plants as raw materials, through hydrolysis (i.e. saccharification), fermentation to convert disaccharides and polysaccharides into monosaccharides and further converted into ethanol. Under the action of microorganisms, starch is hydrolyzed to glucose, and then further fermented to produce ethanol. The process of fermentation alcohol production includes raw material pretreatment, stewing, saccharification, fermentation, distillation, waste mash treatment and so on. In addition to ethanol and a large amount of water, there are solid substances and many impurities in the mature fermentation mash. The ethanol in the fermentation mash needs to be distilled to get high concentration of ethanol, and the by-product is fusel oil and a large amount of distillers' grains.
At present, China's annual production capacity of biofuel ethanol reaches about 2.3 million tons, and the annual production and consumption rank third place in the world after the United States and Brazil. Since 2000, China has cumulatively produced and consumed more than 19.83 million tons of fuel ethanol.
In terms of agriculture, more than 14.31 million tons of corn, rice and wheat that can not be eaten by humans and animals were digested, and 12.42 million tons of high-protein feed were produced as by-products. By solving farmers' difficulties in selling grain, the government has directly employed 50,000 people and indirectly benefited 5 million agricultural people.
In terms of energy - blending 200 million tons of gasoline, improving the existing energy consumption structure, and indirectly reducing crude oil consumption by 110 million tons, which is equivalent to recreating a Tarim oil field.
In terms of environmental protection, the cumulative emission reduction of carbon dioxide equivalent of 25.51 million tons, reduce the emission of harmful substances from automobile exhaust, replace the use of MTBE, and protect groundwater. It plays an important role in international climate negotiations.
Biofuel ethanol in the future development prospects are very considerable, if it can be widely used in the future, the result must be a win-win situation. On the one hand, it relieves the pressure on traditional energy materials such as gasoline; On the other hand, it is an environmentally friendly energy source, because the use of carbon-containing substances in plants can reduce carbon dioxide emissions in the atmosphere and slow down the process of greenhouse effect. Therefore, it is worthy to conduct our exploration, research and development.