Alkanes and alcohols
Students should be familiar with the fact that chemists group organic compounds together into different families with similar properties, in the same way that they use the periodic table to group elements with similar properties together. Students will have already been introduced to the chemistry of alkanes and alkenes.
Alcohols are another ‘family’ of organic compounds, with ethanol being the best known member of the group. Structurally, they are like alkanes but one of the H’s is replaced with an –OH group. They have some similar properties to alkanes, e.g. they burn, giving carbon dioxide and water. Students will know that alcohols are flammable but may not have considered the use of alcohols as a fuels.
Students need to be able to compare and contrast the different methods for the production of ethanol: by fermentation, from biomass or synthesised from ethene. There are a number of discussion points which can be raised with students. For example, the fact that fermentation can be done with very simple technology, allowing people in the developing world to produce ethanol from crops.
Students should be able to consider and evaluate the cost, yield and concentration of alcohol production using the different methods.
Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS, SSERC or recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance.
Making Ethanol from Ethene
This is the second method for production of ethanol which students can explore and compare with the fermentation method. This can be demonstrated to students.
Ethanol can be made by hydrating ethene (from oil refining) using steam in the presence of phosphoric acid, which acts as a catalyst. The ethene comes from cracking the distillation products of crude oil. The reaction has a theoretical atom economy of 100%, but some side reactions do occur. . The equilibrium of this exothermic reaction is shifted towards the product by using a low temperature and a high pressure of steam. A temperature of 300°C, a pressure of 60–70 atmospheres and a steam:ethene ratio of 0.6:1 is used.
It is a continuous process is used to recycle unreacted ethene and steam around the plant. This raises the yield from about 5% for a single ‘pass’ to 95% overall. This process always produces a mixture of ethanol and water and even distillation results in a mixture of 96% ethanol and 4% water. The water is removed by refluxing with a dehydrating agent, although more recently zeolites have been used to remove the water without further heating.
Biofuels
This resource includes two methods for ethanol production and provides a useful environmental comparison between industrial processes.
Activity 3 (pages 27, 36 & 37) is the fermentaion method which uses distillation to puring the ethanol.
Activity A4 introduces the production of ethanol from E.coli bacteria - this is a research activity. Students can research this method of ethanol production and compare/contrast with the other two methods that they have already explored.
Genetically modified E.coli bacterium can be used to convert water biomass into ethanol. To get round yeast’s limitations of only converting simple sugars such as glucose to ethanol, a genetically modified bacterium called KO11 has been developed. It converts the large complex polymers made from sugars, such as hemicellulose, in biomass to ethanol. This makes it cost effective to use biomass such as wood waste corn stalks and rice husks that would not be economic for yeast fermentation.
The greener industry website provides an overview of all the processes which can be used as a summary.
Fantastic Plastic *suitable for home teaching*
This SEP Booklet provides many engaging practicals and activities to highligh the range of ploymers and plastics that can be made from organic monomers.
The easiest polymerisation reaction to exlpain to students is the addition polymerisation of ethene to make polyethene. The RSC Addition Ploymerisation reaction can be demostrated to the students. These reactions involve monomers that have a double bonds somewhere along the carbon chain.
Condensation Polymerisation and Making Nylon - the 'Nylon Rope Trick' from the RSC can be demostrated to students. The monomers that react to form these polymers do not have a double bond and therefore results in the loss of a small molecule e.g. water. In the manufacture of Nylon the reaction produces HCl as a vapour. It is best to only use very small quantities of the two reactants as this will make quite a long strand of Nylon. Make sure you wash the Nyon with plenty of water before you allow the students to touch it.