BIOETHANOL

• 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.

Sources used to produce Bioethanol.

• 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.

The first generation processes to produce ethanol from corn use only a small fraction of the whole corn plant. The corn starch represented about half of the dry kernel mass will be transformed into ethanol. The next generation processes have two types. The first type would be using enzymes and yeast fermentation to convert the plant cellulose into ethanol. The second type will be using pyrolysis to convert the entire plant to either liquid-state bio-oil or syngas. The second generation processes can too be used with agricultural waste materials (e.g: straw).

PRODUCTION OF BIOETHANOL

• 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

1. 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.
   
   
2. 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.
   
   
3. 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.

Dry Milling Process
- 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).

Chemical reaction 1:

- 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