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What is bioethanol? To answer this question, it is better to define ethanol first. Ethanol has been known for more than two thousand years and is also known as alcohol, ethyl alcohol or drinking alcohol. Its chemical formula is written as C2H6O, CH3CH2OH or C2F5OH and is abbreviated as EtOH. The naming of this compound has been done systematically and in accordance with the standards of the International Conference of Applied and Pure Chemistry (IUPAC), in such a way that this substance is an alkyl group with two carbon atoms (prefix eth-) connected by a single bond. -an-) and the functional group -OH (suffix -ol) is formed and it is called ethanol.
In terms of chemical composition, a methyl group (-CH3) is connected to a methylene group (-CH2) and a hydroxyl group (-OH). A high concentration of ethanol in the human body can cause brain dysfunction and poisoning. As an addictive and psychoactive drug, this substance is considered one of the oldest and most common recreational substances, and its high consumption can lead to severe poisoning (drunkenness) and neurotoxicity. In addition, ethanol is widely used as a solvent, fuel and raw material in the production of other chemicals.
Bioethanol , which is known as vegetable fuel and clean fuel, is used in different countries as an effective additive to improve the combustion properties of gasoline and reduce engine pollution. In Iran, this fuel has not yet received enough attention, but according to the plans of other countries, it seems that Iran will soon be required to use this fuel, at least as an additive.
The characteristics of the fuel have a great influence on its performance and determine which fuel is suitable for what type of vehicle or engine. Therefore, fuels have different characteristics according to the type of engines. With the advancement of technology and the introduction of higher quality products, global organizations have established rules to reduce energy consumption and reduce environmental pollution. These laws have led to the formulation of various standards for fuels.
The characteristics that are considered in fuel companies are very diverse and dozens of different characteristics are considered. Global standards have also been established in this field and new and stricter standards are introduced every year. Gasoline as a fuel must have suitable characteristics and for this reason, many characteristics are taken into consideration in the set of compiled standards. Adding ethanol and other alcohols to gasoline affects a number of important fuel properties.
Suggested article: What is biodiesel fuel?
In recent years, with the introduction of vegetable and alternative fuels as well as the increase in the global price of petroleum products, the variety of fuels has increased significantly. This variety made the car and fuel manufacturers to move towards developing agreements for the global standardization of fuels. For this reason, in 1998, a new group called the WORLDWIDE FUEL CHARTER was established, which included the Association of European Automobile Manufacturers, the Union of Automobile Manufacturers, the Association of Engine Manufacturers and the Association of Japanese Automobile Manufacturers.
The purpose of this charter was to achieve the standardization of fuel quality at the global level in order to achieve proper performance by engine and car manufacturers. In fact, its main purpose was to provide guidelines for the production of fuels with specified standards that would allow engine and vehicle manufacturers to easily adapt their products to classified fuels.
When a fuel such as ethanol is added to gasoline, a certain thermodynamic behavior occurs. Electrostatic interactions between chemical species in gasoline solutions with ethers and alcohols can lead to the creation of new species that play an important role in reactions. These effects can lead to changes in the final properties of the fuel, which is of particular importance. In order to prevent the change of fuel quality, in addition to paying attention to the quality of the fuel itself, it is necessary to use particle and water filters before the pump and peripheral equipment.
Bioethanol has four generations, which we have discussed in detail below
Ethanol production from sources such as sugarcane, starch, corn, molasses, animal fats and vegetable oils, which are food sources, is known as the first generation of biofuels. However, sugarcane, corn and molasses are mostly used in practice. Globally, sugarcane and corn produce 21 and 60 million cubic meters of ethanol, respectively. Sugar extraction from these sources and their use include mechanical pretreatment processes (shredding and grinding), enzymatic hydrolysis, fermentation and ethanol production, and its separation from products through distillation and dehydration.
Currently, 90% of global ethanol production takes place in the United States of America. In 2017, on average, 211 plants in the US produced about 290,000 cubic meters of ethanol per year (comprising 95.8% of production) and other starchy sources.
The major difference between the processes of using different primary sources, such as starch and sugar, is in the hydrolysis step of starch to glucose for microorganisms. Because usually, microorganisms are not able to absorb polymeric starch directly. For example, the yeast Saccharomyces cerevisiae cannot consume starch directly, but it can absorb sucrose disaccharide with the help of an enzyme. On the other hand, there are amylatic yeasts that are able to consume starch directly, but this method is not economically viable and these yeasts have less tolerance in facing starch in the culture medium.
The second generation of biofuels is mainly produced from lignocellulosic biomass, which is widely and cheaply found in nature. These biomasses include sources such as grass, forest residues, and agricultural waste (such as bagasse, grain crop waste, rice husk and stalk, etc.) and do not interfere with food sources. There are challenges in different stages of production of this generation of fuel, including pretreatment and fermentation, to achieve cost-effective and sustainable production. However, the second generation of biofuels has great potential for production and it is predicted that only 10% of the world’s waste can supply about 50% of the total biofuels requirement.
Features of the second generation: Unlike the first generation, the second generation of biofuels is produced from non-food sources such as lignocellulosic biomass and has no restrictions on food consumption. However, the use of agricultural waste in the production of this generation still faces challenges in commercialization. The crystalline structure of cellulose and non-homogeneous compounds of hemicellulose in these biomasses require chemical or physical pretreatment and enzymatic processes, which can increase overall costs and hinder the development of this generation of fuel. The use of these resources has the least harm to the environment and does not compete with food supply, but the mass production of this generation faces problems, including high costs and low efficiency of converting raw materials into ethanol, which is mainly due to the presence of lignin in the composition of this resources. In addition, there is a need for advanced technology and facilities to support the production process.
In general, conversion of lignocellulosic sources to ethanol can be done by two biochemical and thermochemical methods. In the biochemical method, using enzymes, cell biomass is converted into ethanol, and this process includes four stages: physical-chemical pretreatment, enzymatic hydrolysis of sugar polymers into constituent units, fermentation of these units using microorganisms such as Saccharomyces cerevisiae, Zymomonas mobilis or Clostridium ljungdahlii, and finally distillation. In the thermochemical method, the raw material is subjected to high heat to produce carbon monoxide, hydrogen and carbon dioxide gases, and then these gases are converted into the final product using chemical catalysts such as molybdenum disulfide.
The third generation of bioethanol is based on the use of marine organisms such as algae as a source of cell mass. Algae are a suitable option for this purpose due to their high amount of fat and carbohydrates, easy cultivation in aquatic environments, and less need for the environment compared to consuming more carbon dioxide. Algae cell mass production can reach up to 365 tons of dry weight per hectare per year. One of the most important advantages of algae in ethanol production is the low amount of lignin and hemicellulose in them.
Currently, the use of this generation is still in its infancy. Algae with high potential can be directly converted into energy as a source of cell mass for third generation bioethanol production. In general, the use of these resources for bioethanol production depends on factors such as the technologies used and the environmental conditions for growing algae. The advantages of this method are non-interference with food sources, easy growth, low cost, high content of fat and carbohydrates, as well as energy supply. Some types of algae that are considered as raw materials for fuel production include Chaetocero scalcitrans, Isochrysis galbana, Nanochloropsis sp., Schizochytrium limacinum, Chlorella species, Scenedesmus and Botryococcus braunii.
The fourth generation of biofuels is considered as a new field in the production of biofuels and is superior to previous generations in some aspects. In this technology, raw materials are used along with the absorption of carbon dioxide (CO₂). This process includes the design and engineering of raw materials, devices and biological systems. The main goal of this generation is sustainable energy production along with CO₂ absorption.
In this generation, raw materials that are genetically modified and capable of consuming high carbon dioxide are used. Some suitable algae for this application include Botryococcus braunii, Schizochytrium, Chlorella and Scenedesmus. Also, genetically modified microorganisms that have a high production of biofuels, such as Bacillus subtilis, Acinetobacter calcoaceticus and Arthrobacter sp, are also proposed as suitable options for the production of fourth generation bioethanol.
Today, human energy sources are mainly composed of three sources: fossil, nuclear and renewable. In recent years, the major use of fossil resources has caused environmental damage, greenhouse gas production, and global warming. Moreover, these resources are non-renewable and will run out in the near future. Despite its advantages, nuclear sources also have disadvantages such as the production of nuclear waste that remains in nature for thousands of years and is highly radioactive and dangerous. In addition, the high costs of establishing nuclear power plants and the limitation of uranium resources, which are non-recyclable, are other disadvantages of these resources.
Another problem with these energy sources is the cost of nuclear waste disposal and the risk of leaking radioactive materials during their transportation. Therefore, it is necessary to find sustainable and economical sources as an alternative. Renewable sources such as solar energy, geothermal energy, wind, sea energy, hydrogen and biomass have a high potential for replacement. One of these alternative fuels can be ethanol.
Burning ethanol in air produces carbon dioxide and water, and it can be mixed with gasoline to produce benzene.
CH3CH2OH + 3O2 → 2CO2 + 3H2O
Ethanol is mainly used as motor fuel and fuel additives and is also used in rocket fuel. More recently, it is also used in the fuel of light-weight racing aircraft.
The benefits of bioethanol (bioethanol) production and consumption for the environment and public health can be generally divided into two main categories: first, the benefits of using bioethanol as a supplement or substitute for gasoline; and second, the benefits of reducing or eliminating the use of gasoline and petrochemical products using bioethanol. In the following, we will mention some of these benefits separately:
Development of cultivation of energy plants
Cultivation of energy-producing plants for bioethanol production helps to increase the country’s green surface and can also help to use agricultural waste and residues.
Absorption of excess carbon from the atmosphere
The use of water sources unsuitable for traditional agriculture, such as brackish water, as well as treated or untreated wastewater in the cultivation of energy plants, contributes to the carbon balance in the atmosphere.
Coping with desertification
Cultivation of energy-producing plants in desert areas instead of non-productive plants can prevent desertification and improve desertification activities.
Control of fine dust
Cultivation of energy-producing plants in desert areas helps to reduce the phenomenon of fine dust.
Increasing productivity and profitability
The development of genetically modified energy plants that are not used for human and animal feed can increase productivity and profitability and optimize the use of water, fertilizers and pesticides.
Production of electrical and thermal energy
Using the residues of energy-producing plants and other agricultural products to produce electrical and thermal energy, and selling surplus energy production to the power grid, leads to a reduction in fossil fuel consumption.
Reducing the use of harmful agricultural products
The production of DDGS as a byproduct of bioethanol provides the protein needed by livestock and reduces the consumption of chemical fertilizers and poisons.
Utilization of industrial waste
The use of industrial waste and urban waste in the production of bioethanol can have many environmental benefits and help to ensure public health.
Replacement of MTBE
The use of bioethanol instead of MTBE in gasoline can help reduce the pollution of water and soil resources and reduce the problems of contamination caused by MTBE, which is common in different countries, including Iran, especially in remote areas.
In general, replacing bioethanol with traditional and petrochemical fuels can help improve the environment and public health and reduce the problems caused by the use of harmful chemicals.
To clarify the importance of controlling fuel properties, we can mention fuel vapor pressure, which is one of the characteristics of fuel volatility. For example, in fuel tanks, gasoline vapor pressure is discharged through special vapor control valves or recovered by vapor recovery units. In the United States, the permissible range of this fuel characteristic varies in different states and in different seasons of the year. In some states, the addition of ethanol to gasoline is regulated so that the vapor pressure of the blended fuel is up to one unit higher than that of pure gasoline.
Fuel volatility is one of the key characteristics of gasoline that greatly affects its performance. This feature is related to the fuel’s ability to change from liquid to vapor. Gasoline and other liquid fuels such as alcohols are used in various types of engines with various operating conditions.
Engines and cars work in different weather conditions, and their working conditions are very variable in different places in terms of ambient temperature and pressure. Therefore, fuel fugitive characteristics of spark ignition engines are among the critical characteristics. There are several parameters for measuring fuel volatility, including vapor pressure, distillation chart, vapor-to-liquid ratio, and vapor lock index.
Fuels that do not evaporate easily may cause engine starting problems in cold weather. Engines equipped with fuels that do not evaporate easily will not have enough agility and will not heat up in time. Conversely, fuels that vaporize excessively will cause problems at high temperatures, as the fuel mixture may become rich and damage the cylinder and piston during combustion.
Sometimes, fuel vapors collect in the fuel lines and impede the flow of fuel to the engine. Excessive evaporation leads to gas lock or vapor lock. By adjusting the fugitive characteristics of fuel in different seasons of the year and in different climate zones, these problems can be avoided and the performance of the engine can be improved. Therefore, the standard of the fuel in terms of the tendency to evaporate is of particular importance.
In order for ethanol to be used effectively with gasoline or diesel, the properties of the blended fuel must be reviewed to meet the relevant standards. The main characteristics to evaluate are vapor pressure, vapor lock, air-fuel ratio, octane number, and distillation characteristics. In the following, we will examine the effect of adding bioethanol to gasoline on these characteristics.
1. Steam pressure
Fuel vapor pressure is one of the key characteristics that greatly affects engine performance and the amount of evaporative emissions before combustion. The graph below shows that adding ethanol to gasoline increases the vapor pressure. The maximum amount of vapor pressure is observed in a mixture with 10% ethanol, and with increasing amount of ethanol, the vapor pressure decreases. The effect of ethanol addition on fuel vapor pressure is clear; Therefore, to reduce pollution, improve fuel performance and increase energy efficiency, it is necessary to pay attention to this parameter. Research has shown that in order to use ethanol in gasoline, especially in small amounts (below 20%), manufacturers must take precautions in their fuel components.
Another point is that properties such as vapor pressure may change in different seasons of the year and depending on environmental conditions. With proper management, it is possible to use ethanol in Iran, which has a wide variety of climates. Also, the effect of fuel vapor pressure on pollution encourages society and officials to standardize fuel and pay attention to different characteristics of fuel in different regions and seasons of the country.
The graph below shows the effect of ethanol on the vapor lock index of the fuel. Reducing the vapor lock index means reducing transportation risks, improving engine start-up in hot weather, and reducing evaporative pollution. This graph shows that by adding ethanol to gasoline, the vapor lock index first increases and then decreases.
2. Agility
The graph below depicts the effect of ethanol on the agility index of gasoline. Gasoline agility index indicates the ability of gasoline to start quickly and heat the engine effectively. Decreasing the agility index means that the engine warms up faster and reaches the desired temperature, which is improved by adding ethanol to gasoline. However, the graph shows that as the percentage of ethanol increases, the effect of these changes decreases and finally the agility index increases again.
3. Stoichiometric ratio
The following graphs show the effect of ethanol on the amount of oxygen in the fuel and the stoichiometric ratio of air to fuel, respectively. These properties play an important role in engine performance and are changed by adding ethanol. To optimize engine performance and achieve optimal combustion, it is necessary to make necessary changes in the intelligent engine control system.
The positive effects of bioethanol production and consumption on the environment and public health are related to the life cycle of this fuel. Life cycle analysis of bioethanol compared to fossil fuels shows that the use of biofuels does not increase the amount of carbon in the atmosphere, unlike fossil fuels. This allows bioethanol producers to enjoy the benefits of agreements such as the Kyoto Protocol and other environmental agreements, subject to compliance with environmental principles and balance in energy consumption and production.
The life cycle of bioethanol, which starts from water resources and agricultural products on the farm and ends at the exhaust of the car, is divided into two main parts. The first part includes the stages of supplying raw materials, production and logistics of bioethanol from the farm to the car tank. The second part includes from the tank of the car to the movement of the wheels and the exit of gases resulting from the combustion of ethanol (water vapor and carbon dioxide) from the exhaust of the car.
Each of these steps has specific benefits for the environment and public health. For this reason, countries that only import and consume bioethanol in their transportation system and neglect the production stage, experience only part of the benefits of this environmentally friendly fuel.
Another point is that the use of plant (agricultural and forest), industrial and urban wastes and residues for the production of bioethanol can bring more environmental benefits and evaluate the life cycle of this product in a different way. This issue needs a more detailed investigation and discussion.
Replacing part of the gasoline used by cars, especially in big cities, can be done at three different levels:
1. Low substitution: In this case, gasoline is blended with lower percentages of ethanol, typically 5, 10, or 15 percent. This method is similar to the method used in many countries.
2. Medium substitution: At this level, the amount of ethanol in gasoline reaches 5-35%. This method is used in some countries, such as Brazil.
3. High substitution: In this approach, ethanol is used at the rate of 85% or even 100%. To use this type of fuel, special vehicles called FFV (Flex-Fuel Vehicles) are needed. These types of cars are able to use gasoline, ethanol or a combination of both in any ratio. Countries such as Brazil, the United States of America and the European Union are gradually implementing this method. In Brazil, almost all new vehicles are FFVs and can run on gasoline, ethanol, or a mixture of them.
These replacements lead to the reduction of pollutants from the exhaust of cars, which are caused by the combustion and sometimes incomplete combustion of fossil fuels.
In the case of higher quality gasolines that contain aromatics, especially benzene, using this type of gasoline can reduce emissions to a lesser extent, but not completely eliminate them. On the other hand, the combustion of bioethanol in cars, in addition to helping to burn gasoline, does not bring the usual pollutants of fossil fuels such as carbon monoxide, nitrogen oxides and sulfur.
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Petro Imen Sharif Engineering Company was founded in 2010 by a group of engineers and specialists graduated from top universities in Iran, who believe in the motto “Desire creates” and with a focus on advancing scientific movements in the field of environmental protection.
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