Forming ethanol Comparing two methods for producing ethanol: Fermentation or industrial formation from ethene Fermentation glucose ethanol + carbon dioxide C6H12O6 2 CH3CH2OH + 2 CO2 The conditions needed are: •Yeast •No air •temperatures 30 –40oC The optimum temperature for fermentation is around 38oC At lower temperatures the reaction is too slow. At higher temperatures the yeast dies and the enzymes denature. Fermentation is done in an absence of air because the presence of air can cause extra reactions to occur. It oxidises the ethanol produced to ethanoic acid (vinegar). Advantages •sugar is a renewable resource •production uses low level technology / cheap equipment Disadvantages •Batch process which is slow and gives high production costs •ethanol made is not pure and needs purifying by fractional distillation •Depletes land used for growing food crops CH2=CH2 (g) + H2O (g) CH3CH2OH (l) Essential Conditions high temperature 300 °C high pressure 70 atm strong acidic catalyst of conc H3PO4 Reagent: ETHENE – from cracking of fractions from distilled crude oil From ethene Advantages: •faster reaction •purer product •continuous process (which means cheaper manpower) Disadvantages: •High technology equipment needed (expensive initial costs) •ethene is non-renewable resource (will become more expensive when raw materials run out) •High energy costs for pumping to produce high pressures Type of reaction: Fermentation Type of reaction: Hydration/addition Definition: Hydration is the addition of water to a molecule N Goalby chemrevise.org 6 C C H H H H C C + H H H H H O H H C C O + H H H H H H H C C O H H H H H H H + H+ Acid catalysed addition mechanism for hydration of ethene The H+ comes from the conc H3PO4
18.104.22.168 Alcohol production
Alcohols are produced industrially by hydration of alkenes in the presence of an acid catalyst.
Ethanol is produced industrially by fermentation of glucose.
The conditions for this process.
Ethanol produced industrially by fermentation is separated by fractional distillation and can then be used as a biofuel.
Students should be able to:
• justify the conditions used in the production of ethanol by fermentation of glucose
• outline the mechanism for the formation of an alcohol by the reaction of an alkene with steam in the presence of an acid catalyst