Ethanol - fermentation
Ethanol can be made by fermentation:
1. Fermentation uses yeast to convert sugars into ethanol. CO2 is also released.
sugar------>ethanol + carbon dioxide
2. The yeast cells contain zymase, an enzyme that acts as a catalyst in fermentation.
3. Fermentation happens fastest at about 30 degrees c. This is because zymase works best at this temp. At lower temps the reaction slows down. If the temp is too high the zymase is denatured (destroyed).
4. Zymase also work best at a pH of about 4 - a stongly acidic or alkaline solution will stop it working.
5. It's important to prevent oxygen getting to the fermentaion process. Oxygen converts the ethanol to ethanoic acid, which lowers the pH and can help stop the enzymes working.
6. When the concentration of ethanol reaches about 10 to 20%, the fermentaion reaction stops, because the yeast gets killed off by the ethanol.
Ethanol - concentration and distillation
Ethanol solution can be concentrated by distillation:
1. The ethanol solution is put in a flask below a fractionating column as shown.
2. Teh solution is heated so that the ethanol boils. The ethanol vapour travels up the column, cooling down as it goes.
3. The temp is such that anything with a higher boiling point than ethanol cools to a liquid and flows back into the solution at the bottom.
4. This means that only pure ethanol vapour reaches the top of the column.
5. The ethanol vapour flows through a condenser - where it is cooled to a liquid, which is then collected.
Ethanol - Fermentation a sustainable process?
Is ferementation a sustainable process?
1. Will the raw materials run out?
2. How good is the atom economy?
3. What do I do with my watse products?
4. What are the energy costs?
5. Will it damage the environment?
6. What are the health and safety riskd?
7. Are there any benefits or risks to the society?
8. Is it a profiatble process?