letslearnscience, production of ethanol from sugar cane(HSC chemistry)
Retrieved 26/11/12
4)To Ethanol or Not to Ethanol? That is the question.
--A worthy method of extracting glucose from crop wastes needs to be found to prevent specifying large amounts of land for the production of glucose.
--Solar power is a renewable source should be used to supply the large energy for the distillation process.
--The economic cost needs to be reduced with the help of government funding and awareness needs to be spread among communities to prevent alienation from this new fuel type.
-- Additional research and experimenting needs to be taken in consideration as calculations and methods studies are not completely accurate and have higher penalties.
-- The Australian government encourages the production of ethanol knowing its high expenses so it gives subsidies. Yet, petrol suppliers take this opportunity to excessively blend amounts of ethanol in petrol to gain the subsides leaving car tanks with incidents. The public is gradually gaining awareness of the amount of ethanol available in their fuel are apprehensive able its use and the effect it has on the mileage on their car In order to prevent this action inspectors need to regularly test the fuel and the amount of ethanol.
--Car manufactures need to release cars with ethanol-friendly tanks.
The use of ethanol as an alternative fuel is introduced but only with 10-20% because car tanks need to be modified to suit the tanks. However, the current use is slowly increasing allowing manufactures to build new tanks that agree with the properties of ethanol. For example, flex fuel vehicles(FFV) are designed to run on 85% ethanol(E85).this type of fuel has the same performance as any other fuel when on the road but since it contains less combustion energy it runs about 25-30%less km per litre. This technology has been available since 1980.
At this point in time, its disadvantages out weight the benefits; the costs associated with production are the same as normal fuel. While the cost of E85 is only 10% less expensive, it produces less energy so the price of fuel may be a little cheaper and less in quantity, so the consumer will buy more fuel than usual with a slightly lower price.
Other alternative fuel that can be used is biodiesel. It is a renewable fuel manufactured from vegetable oil, animal fat or recycled restaurant grease suitable for petroleum diesel tanks. The importance of using it is it increases energy security, improves public health, saves the environment because it’s clean and provides various reasonable profits.
3)Importance and difficulties of ethanol as a fuel
Advantages
§a renewable fuel extracted from plants that contain glucose then processed
It will reduce the need for non-renewable sources.
§The technology is widely studied and has already been proven.
Scientists have already made their calculations and experiments hence the method is available.
§it is greenhouse friendly(neutral effect)
The atmosphere won't be affected because CO2 emission are absorbed by the plants; hence becomes part of a cycle
§Up to 20% can be mixed with petrol and used without any modification to the current engine.
Disadvantages
§75% of agriculture land is needs to be devoted for sugar crops to use as an alternative fuel.
This means that the land used to grow food crops will decrease, dedicating only 25% for human food. A shortage of food supplies and economic problems will be caused including an end to export and import exchanges of crops and other problems such as famine.
§Distillation process requires huge amount of energy.
The energy needed for distillation is used from coal so greenhouse is still affected. Also, the disposal of large amounts of fermentation liquids would have major environmental problems.
§New engines need to be designed and produced for pure Ethanol fuel which will end up deteriorating rubber and plastic materials in the tank therefore it cannot be used in unmodified tanks.
§The cost for manufactures and motor owners is too high.
The upcoming equation shows the combustion of ethanol producing carbon dioxide and water.
C2H5OH (l) +3O2 (g) -----à2CO2 (g) + 3H20 (l)
Also this table shows the heat combustion value of some alcohols.
Heat combustion
Fuel
KJ/gram
KJ/MOL
Methanol
22.7
726
Ethanol
29.7
1367
Propanol
33.6
2021
Butanol
36.1
2676
When comparing alcohols with one another the trend noticed is the heat combustion increase with the increasing molecule size. Therefore, ethanol has a lower heat combustion value than petroleum fuels thus; it is an ideal potential fuel due to its low energy fuel.
The recycle of Ethanol(cabon cycle)
As shown in the previous figure ethanol is a suitable renewable alternate fuel made from carbon dioxide, water and sunlight (from photosynthesis). When it undergoes combustion it releases CO2 and water which is absorbed by plants and reconverted.
This helps reduce greenhouse effect condition, only recently has the Australian government encouraged using of only 10% ethanol fuel consumption. The reason being is because use 100% pure ethanol a totally new engine is required to be designed because of the different propertiessuch as ignition temperature, corrosive , different energy content and burning leaving factories redesign new engines. In the future, it will beunlikely to use more than 20% ethanol as in fuel because of the high production cost.
In addition, 75% of the world’s Arable land will need to grow ethanol crops to sustain the demand.
The rapid increase of the use of motor cars has led to a large demand for producing high quality yet cheaper fuel. Fossil fuels such as crude oil, petroleum, coal, natural gas are non-renewable, non-biodegradable and produce pollution. In addition, they are most likely to end in the next 30 years depending on the rates of consumption. When this supply runs out we will face shortage of fuel and vital chemicals for manufacturing and heating purposes.
Consequently, we anxiously search for alternative sources to replace fossil fuel with renewable sources, as only limited supplies are remaining.
Scientists are experimenting with other sources to produce energy. So far, the best solution known is “Biomass” an organic renewable matter produced from plants. Cellulose found in wood, leaves and plant cell walls is an example of a biomass condensation polymer produced from the monomer glucose then processed to give ethanol.
Industrial Production
Ethanol can be made from corn, sugar cane and other waste products depending on the manufactured country. However, sugar cane is the most suitable source as it contains an abundant amount of sugar compared to other resources. Before started the process of producing ethanol, the following is required
-carbohydrate source (sugar cane,starch,corn)
-live yeast that reacts
-Constant temperature from 22-25C
-Anaerobic conditions (no oxygen) because if O2 is present it will react with yeast producing CO2 andH2O.
The industrial production of ethanol from sugar cane involves various steps as following:
1)fermentation
--sugar cane is harvested then crushed and mashed to form sucrose juice (sugar pulp).
--Sugar pulp is heated to 100C forming sucrose molassc.
-- Diluted sulfaric acid is added to kill bacteria.
--This is then placed in an anaerobic fermentation chamber at approximately 25C with yeast called (Saccharomyces Cerevisiae).This process takes 2 days producing 15% ethanol and 85% water breaking down glucose into ethanol.
Glucose-------àEthanol + Carbon Dioxide(in presence of yeast)
C6H1206 (aq) -------à2C2H50H (aq)+2CO2(g)
The above equation shows fermentation of glucose to form ethanol. Although it is only shown in one equation, many stages take place such as reacting with different enzymes and catalyses.
2) Distillation to purify and remove water (97%ethanol)This requires a large amount of energy.
