Biomass is a renewable energy supply with increased prospective fuel resource for the generation of steam as well as electricity, transport fuel, pharmacologic producing industries as well as certain substances in the laboratory. The more resourceful utility of biomass, a derivative of Bioethanol is claimed to resolve the global predicament like exhaustion of fossil fuel and global warming due to the gas emissions from grrenhouse effects. Research considerations in the subject of bioethanol manufacture from organic waste materials became apparent in the later part of 1980s.
Considerable improvements in the extraction of lignocellulosic substance as well as enzymatic hydrolysis have been accounted for in the last ten years or so; nevertheless, sustained investigative endeavors are necessary for the development of technologically practicable and cost-effectively feasible across-the-board enzyme-based biomass-to-ethanol alteration processes. In this paperwork i will talk about bioethanol. How its produced, main advantages and disadvantages. 1. What is Bioethanol? The principle fuel used as a petrol substitute for road transport vehicles.
Bioethanol fuel is mainly produced by the sugar fermentation process, although it can also be manufactured by the chemical process of reacting ethylene with steam. The main sources of sugar required to produce ethanol come from fuel or energy crops. These crops are grown specifically for energy use and include corn, maize and wheat crops, waste straw, willow and popular trees, sawdust, reed canary grass, cord grasses, jerusalem artichoke, myscanthus and sorghum plants. There is also ongoing research and development into the use of municipal solid wastes to produce ethanol fuel.
Ethanol or ethyl alcohol (C2H5OH) is a clear colourless liquid, it is biodegradable, low in toxicity and causes little environmental pollution if spilt. Ethanol burns to produce carbon dioxide and water. Ethanol is a high octane fuel and has replaced lead as an octane enhancer in petrol. By blending ethanol with gasoline we can also oxygenate the fuel mixture so it burns more completely and reduces polluting emissions. Ethanol fuel blends are widely sold in the United States. The most common blend is 10% ethanol and 90% petrol (E10).
Vehicle engines require no modifications to run on E10 and vehicle warranties are unaffected also. Only flexible fuel vehicles can run on up to 85% ethanol and 15% petrol blends (E85). 2. Bioethanol Production Ethanol can be produced from biomass by the hydrolysis and sugar fermentation processes. Biomass wastes contain a complex mixture of carbohydrate polymers from the plant cell walls known as cellulose, hemi cellulose and lignin. In order to produce sugars from the biomass, the biomass is pre-treated with acids or enzymes in order to reduce the size of the feedstock and to open up the plant structure.
The cellulose and the hemi cellulose portions are broken down (hydrolysed) by enzymes or dilute acids into sucrose sugar that is then fermented into ethanol. The lignin which is also present in the biomass is normally used as a fuel for the ethanol production plants boilers. There are three principle methods of extracting sugars from biomass. These are concentrated acid hydrolysis, dilute acid hydrolysis and enzymatic hydrolysis. 3. 1. Concentrated Acid Hydrolysis Process The Arkanol process works by adding 70-77% sulphuric acid to the biomass that has been dried to a 10% moisture content.
The acid is added in the ratio of 1. 25 acid to 1 biomass and the temperature is controlled to 50C. Water is then added to dilute the acid to 20-30% and the mixture is again heated to 100C for 1 hour. The gel produced from this mixture is then pressed to release an acid sugar mixture and a chromatographic column is used to separate the acid and sugar mixture. 2. 2. Dilute Acid Hydrolysis The dilute acid hydrolysis process is one of the oldest, simplest and most efficient methods of producing ethanol from biomass. Dilute acid is used to hydrolyse the biomass to sucrose. The first stage uses 0. % sulphuric acid at 190C to hydrolyse the hemi cellulose present in the biomass.
The second stage is optimised to yield the more resistant cellulose fraction. This is achieved by using 0. 4% sulphuric acid at 215C. The liquid hydrolates are then neutralised and recovered from the process. 2. 3. Enzymatic Hydrolysis Instead of using acid to hydrolyse the biomass into sucrose, we can use enzymes to break down the biomass in a similar way. However this process is very expensive and is still in its early stages of development. 2. 4. Wet Milling Processes Corn can be processed into ethanol by either the dry milling or the wet milling process.
In the wet milling process, the corn kernel is steeped in warm water, this helps to break down the proteins and release the starch present in the corn and helps to soften the kernel for the milling process. The corn is then milled to produce germ, fibre and starch products. The germ is extracted to produce corn oil and the starch fraction undergoes centrifugation and saccharifcation to produce gluten wet cake. The ethanol is then extracted by the distillation process. The wet milling process is normally used in factories producing several hundred million gallons of ethanol every Year.
Dry Milling Process The dry milling process involves cleaning and breaking down the corn kernel into fine particles using a hammer mill process. This creates a powder with a course flour type consistency. The powder contains the corn germ, starch and fibre. In order to produce a sugar solution the mixture is then hydrolysed or broken down into sucrose sugars using enzymes or a dilute acid. The mixture is then cooled and yeast is added in order to ferment the mixture into ethanol. The dry milling process is normally used in factories producing less than 50 million gallons of ethanol every Year. 2. 6.
Sugar Fermentation Process The hydrolysis process breaks down the cellulostic part of the biomass or corn into sugar solutions that can then be fermented into ethanol. Yeast is added to the solution, which is then heated. The yeast contains an enzyme called invertase, which acts as a catalyst and helps to convert the sucrose sugars into glucose and fructose (both C6H12O6). The chemical reaction is shown below: The fructose and glucose sugars then react with another enzyme called zymase, which is also contained in the yeast to produce ethanol and carbon dioxide. The chemical reaction is shown below:
The fermentation process takes around three days to complete and is carried out at a temperature of between 250C and 300C. 2. 7. Fractional Distillation Process The ethanol, which is produced from the fermentation process, still contains a significant quantity of water, which must be removed. This is achieved by using the fractional distillation process. The distillation process works by boiling the water and ethanol mixture. Since ethanol has a lower boiling point (78. 3C) compared to that of water (100C), the ethanol turns into the vapour state before the water and can be condensed and separated.
Ethanol-based engines Ethanol is most commonly used to power automobiles, though it may be used to power other vehicles, such as farm tractors, boats and airplanes. Ethanol (E100) consumption in an engine is approximately 51% higher than for gasoline since the energy per unit volume of ethanol is 34% lower than for gasoline. The higher compression ratios in an ethanol-only engine allow for increased power output and better fuel economy than could be obtained with lower compression ratios. In general, ethanol-only engines are tuned to give lightly better power and torque output than gasoline-powered engines.
In flexible fuel vehicles, the lower compression ratio requires tunings that give the same output when using either gasoline or hydrated ethanol. For maximum use of ethanol’s benefits, a much higher compression ratio should be used. Current high compression neat ethanol engine designs are approximately 20 to 30% less fuel efficient than their gasoline-only counterparts. Ethanol is hygroscopic, meaning it will absorb water vapor directly from the atmosphere.
Because absorbed water dilutes the fuel value of the ethanol (although it suppresses engine knock) and may cause phase separation of ethanol-gasoline blends, containers of ethanol fuels must be kept tightly sealed. This high miscibility with water means that ethanol cannot be efficiently shipped through modern pipelines, like liquid hydrocarbons, over long distances. Mechanics also have seen increased cases of damage to small engines, in particular, the carburetor, attributable to the increased water retention by ethanol in fuel.
A 2004 MIT study and an earlier paper published by the Society of Automotive Engineers identify a method to exploit the characteristics of fuel ethanol substantially better than mixing it with gasoline. The method presents the possibility of leveraging the use of alcohol to achieve definite improvement over the cost-effectiveness of hybrid electric. The improvement consists of using dual-fuel direct-injection of pure alcohol (or the azeotrope or E85) and gasoline, in any ratio up to 100% of either, in a turbocharged, high compression-ratio, small-displacement engine having performance similar to an engine having twice the displacement.
Each fuel is carried separately, with a much smaller tank for alcohol. The high-compression (which increases efficiency) engine will run on ordinary gasoline under low-power cruise conditions. Alcohol is directly injected into the cylinders (and the gasoline injection simultaneously reduced) only when necessary to suppress ‘knock’ such as when significantly accelerating. Direct cylinder injection raises the already high octane rating of ethanol up to an effective 130. The calculated over-all reduction of gasoline use and CO2 emission is 30%.
The consumer cost payback time shows a 4:1 improvement over turbo-diesel and a 5:1 improvement over hybrid. The problems of water absorption into pre-mixed gasoline (causing phase separation), supply issues of multiple mix ratios and cold-weather starting are also avoided. Ethanol’s higher octane rating allows an increase of an engine’s compression ratio for increased thermal efficiency. In one study, complex engine controls and increased exhaust gas recirculation allowed a compression ratio of 19. 5 with fuels ranging from neat ethanol to E50.
Thermal efficiency up to approximately that for a diesel was achieved. This would result in the fuel economy of a neat ethanol vehicle to be about the same as one burning gasoline. Since 1989 there have also been ethanol engines based on the diesel principle operating in Sweden. They are used primarily in city buses, but also in distribution trucks and waste collectors. The engines, made by Scania, have a modified compression ratio, and the fuel (known as ED95) used is a mix of 93. 6 % ethanol and 3. 6 % ignition improver, and 2. 8%denaturants.
The ignition improver makes it possible for the fuel to ignite in the diesel combustion cycle. It is then also possible to use the energy efficiency of the diesel principle with ethanol. These engines have been used in the United Kingdom by Reading Transport but the use of bioethanol fuel is now being phased out. 4. Environment A 2006 University of California Berkley study, after analyzing six separate studies, concluded that producing ethanol from corn uses much less petroleum than producing gasoline. Carbon dioxide, a greenhouse gas, is emitted during fermentation and combustion.
This is canceled out by the greater uptake of carbon dioxide by the plants as they grow to produce the biomass. When compared to gasoline, depending on the production method, ethanol releases less greenhouse gases. 5. Advatages and disadvantages of bioethanol fuel Like all other fuels ethanol fuel also has certain advantages and disadvantages. One of the most obvious advantages of ethanol fuel is the fact that ethanol fuel is a renewable energy source, meaning that is not exhaustible like the fossil fuels are. By using more ethanol countries would be less dependent on foreign oil import, and volatile oil prices.
Big domestic production of ethanol would ensure that domestic money stays in country instead being spent on expensive foreign oil. Of course increased domestic ethanol production would also create more jobs, and would also very likely lower the fuel costs. Othet advandages: * The use of ethanol-blended fuels such as E85 (85% ethanol and 15% gasoline) can reduce the net emissions of greenhouse gases by as much as 37. 1%, which is a significant amount. * Ethanol-blended fuel as E10 (10% ethanol and 90% gasoline) reduces greenhouse gases by up to 3. 9%.
The net effect of ethanol use results in an overall decrease in ozone formation, an important environmental issue. (The emissions produced by burning ethanol are less reactive with sunlight than those produced by burning gasoline, which results in a lower potential for forming the damaging ozone). * It benefits energy security as it shifts the need for some foreign-produced oil to domestically-produced energy sources. * It reduces greenhouse gases. * It burns more cleanly (more complete combustion). * It reduces the amount of high-octane additives.
The fuel spills are more easily biodegraded or diluted to non toxic concentrations. Ethanol fuel also has some disadvantages. Large share of ethanol production comes from food crops which has the potential to increase the cost of food prices and even lead to food shortages. This is the main issue of fuel vs food debate because by significantly increasing ethanol production much of the arable land would be used for ethanol production instead to produce food, and this would lead to food shortage and increased food prices, and would likely result in even more hunger in the world. Ethanol has 34% lower energy per unit volume compared to gasoline which results in around 51% higher consumption in pure ethanol (E100) consumption in an engine. * Ethanol tends to be very corrosive because it can easily absorb water and dirt and without the proper filtration system ethanol can soon cause the corrosion inside the engine block.
Specialized gas stations that offer E85 ethanol are still pretty rare so many drivers would have to drive further distances to find them. Current high compression ethanol-only engine designs have 20-30% smaller fuel efficiency compared to gasoline-only engine designs. * Ethanol tends to increase fuel enthalpy of vaporization meaning that engine that uses high ethanol blend may have problem starting during the cold weather (will talk about that more later) * Burning pure ethanol in a vehicle will result in a 34% reduction in miles per US gallon, given the same fuel economy, compared to burning pure gasoline in a vehicle. 5. 1. Engine cold start during the winter
High ethanol blends present a problem to achieve enough vapor pressure for the fuel to evaporate and spark the ignition during cold weather (since ethanol tends to increase fuel enthalpy of vaporization). When vapor pressure is below 45 kPa starting a cold engine becomes difficult. In order to avoid this problem at temperatures below 11 °C and to reduce ethanol higher emissions during cold weather, both the US and the European markets adopted E85 as the maximum blend to be used in their flexible fuel vehicles, and they are optimized to run at such a blend.
At places with harsh cold weather, the ethanol blend in the US has a seasonal reduction to E70 for these very cold regions, though it is still sold as E85. At places where temperatures fall below ? 12 °C during the winter, it is recommended to install an engine heater system, both for gasoline and E85 vehicles. Sweden has a similar seasonal reduction, but the ethanol content in the blend is reduced to E75 during the winter months. 7. Numbers talk Burning E85 in vehicles, instead of gasoline, reduces the amount of pollution released by 10-80%. Pollution Reduction – E85 Versus Gasoline:
Also, E85 cost less (Lt/l) : EU is today the third producer of fuel-bioethanol in the world behind the United States and Brazil, its production is however much lower than the first two (by a factor of about 10). In 2009, the production of fuel-bioethanol amounted to 3’703 Ml, i. e. an increase of 30% compared to 2009. The table below shows the evolution of bioethanol production over the past 7 years in the 10 major producing countries in the EU. Evolution of fuel-bioethanol production in the EU (2003-2009): CO2 emissions g/km: General CO2 emissions per km while using E85, E10, premium 98 Ron: