- Bioethanol is mainly used to substitute petrol fuel for road transport vehicles ;
- Bioethanol is mainly produced by sugar fermentation process ;
- Ethyl alcohol (otherwise known as Ethanol) is an unclouded and colourless liquid ;
- undergo combustion to produce carbon dioxide and water
- is a high octane fuel
- is blended together with gasoline so as to allow more oxygen into the fuel mixture, resulting in more complete combustion and less polluting emissions
- is biodegradable
- toxicity level is relatively low, therefore it is safe
- little environmental pollution caused if spilled. - Bioethanol could be one of the popular alternative automotive fuel used in the world ;
- Brazil and USA are the world's top largest ethanol producers ;
- Contributed to 65% and above worldwide ethanol production ;
- Brazil produced bioethanol from sugar cane ;
- In North America, bioethanol is produced from corn and used as octane enhancer in gasoline in extremely small portion.
- In the first generation processes, plants such as wheats/corn/sugar cane/sugar beet and sweet sorghum can be used to produce ethanol.
- In the second generation processes, miscanthus and eucalyptus can be used to produce ethanol too.
- Almost any plants that composed largely of sugars (e.g: leaves, grains, wheats) can be used to produce ethanol (as sugar is essential in the production of ethanol).
- Biomass wastes contains cellulose, lignin and hemi-cellulose.
- Biomass must be pre-treated with acids so as to minimize the size of the feedstock before obtaining the sugars in it by the processes of hydrolysis and sugar fermentation.
- During the hydrolysis process, dilute acids broke down the cellulose and hemi-cellulose fragments into sucrose sugar which then undergo the sugar fermentation process to produce ethanol.
- Lignin present in the biomass wastes is usually used as a fuel for the ethanol production plants boilers.
- Three main methods of hydrolysis to extract sugars out from biomass
- concentrated acid hydrolysis
- enzymatic hydrolysis (Not popular)
- dilute acid hydrolysis
- Concentrated Acid Hydrolysis
- About 77% of sulfuric acid is added to the dried biomass to a 10% wet content.
- The acid will then be added in the ratio of 1 and a half quarter acid to 1 biomass under the controlled temperature, 50°C. - Dilute the acid to about 30% with water and heat the mixture (again) to the temperature 100°C for an hour or so.- Gel will be produced and pressed to discharge the acid sugar mixture.
- In order to separate the acid and sugar mixture apart, a chromatographic column is required. - Dilute Acid Hydrolysis
- Considered the simplest yet efficient method of ethanol production from biomass.
- Purpose of dilute acid is to hydrolyse the bio-mass to sucrose (sugar).
- Hemi-cellulose which is present in the biomass undergo hydrolysis with the addition of 7% of sulfuric acid under the temperature 190°C.
- To generate the more resistant cellulose portion, 4% of sulfuric acid is added at the temperature of 215°C. - Enzymatic Hydrolysis
- Instead of acid, enzymes can also be used to bio-degrade the biomass.
- Not used often because the process is extremely pricey and not yet developed.
Wet Milling Processes
- Corn kernel is permeated in warm water, thus breaking down the proteins.
- This release the starch presents in the corn and helps to reduce the kernel for the milling process.
- During milling, the corn produces germ, fibre and starch products.
- The germ is extracted to produce corn oil.
- The starch portion undergoes centrifugation and saccharifcation to produce gluten wet cake.
- In the distillation process, ethanol is produced.
- Wet milling process is usually used in factories that produce several hundred million gallons of ethanol annually.
- It involves cleaning and breaking down the corn kernel into very small particles using a hammer mill process.
- A powder-mixture is formed which contains the corn germ, starch and fibre.
- Sugar solution is produced when the mixture is broken down into sucrose using enzymes or a dilute acid.
- A powder-mixture is formed which contains the corn germ, starch and fibre.
- Sugar solution is produced when the mixture is broken down into sucrose using enzymes or a dilute acid.
- When the mixture is cooled, yeast will be added in order to ferment the mixture into ethanol.
- Dry milling process is usually used in factories producing less than 50 million gallons of ethanol annually.
Sugar Fermentation Process
- Somewhat similar to the dry milling process.
- The hydrolysis process breaks down the biomass cellulosic portion into sugar solutions which will then be fermented into ethanol.- Yeast is added and heated to the solution.
- An enzyme called invertase, which acts as a catalyst and helps to convert the sucrose sugars into glucose and fructose (both C6H12O6).
- The fructose and glucose sugars then combines reaction with zymase to produce ethanol and carbon dioxide.
Chemical reaction 2:
- The fermentation process requires three days to finish and is carried out at a temperature of between 250°C and 300°C.
Fractional Distillation Process
- After the sugar fermentation process, the ethanol still does contain a large quantity of water which have to be removed.
- In the distillation process, it boil both the water and ethanol mixture.
- Ethanol has a lower boiling point than water, therefore ethanol will be converted into the vapour state first.
References :
http://www.eubia.org/212.0.html
http://www.esru.strath.ac.uk/EandE/Web_sites/02-03/biofuels/what_bioethanol.htm
http://en.wikipedia.org/wiki/Ethanol_fuel
