Ethanol – Use and Manufacture

Describe the dehydration of ethanol to ethylene and identify the need for a catalyst in this process and the catalyst used

The ability to write the chemical equation is important, so take the time to remember what molecules are present in the reactants and in the products, and then balance as a last step.

Although ethanol can be readily dehydrated to form ethylene, a strong catalyst is required as the hydroxyl functional group (-OH) is bonded relatively strongly to the CH3CH2 chain. As such, a catalyst lowers the activation energy required for a chemical reaction to take place by providing an alternate pathway for the reaction to occur. Most commonly, concentrated sulfuric acid or phosphoric acid is used as the catalyst.

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Water is a product as well, so don’t forget to include it.

Remember- The dehydration of ethanol to ethylene involves the conversion of ethanol into ethylene and water using a catalyst of concentrated sulfuric acid.

Describe the addition of water to ethylene resulting in the production of ethanol and identify the need for a catalyst in this process and the catalyst used

Understanding why this reaction only requires a weak catalyst to occur will save you the pain of memorising the specific catalysts required. If you find yourself confused as to which catalyst is required (concentrated or dilute), simply ask yourself which bonds are easier to break: The reactive double bond in ethylene, or the strong hydrogen bonding in ethanol? Clearly a dilute acid is appropriate for the double bonds, whereas concentrated sulfuric acid would be appropriate for breaking the bonds in ethanol.

Just as ethanol may be dehydrated to form ethylene, the addition of water to ethylene will produce ethanol. However, unlike the dehydration process, the presence of the double bonds within ethylene considerably decreases the energy required in order for the reaction to occur. As such, a weaker catalyst such as dilute sulfuric acid may be used.

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Once again, do not forget the presence of the water molecule, which is of course on the reactants side for this equation.

Remember- The hydration of ethylene to ethanol involves the conversion of ethylene and water into ethanol using a catalyst of dilute sulfuric acid.

Process information from secondary sources such as molecular model kits, digital technologies or computer simulations to model the addition of water to ethylene and the dehydration of ethanol

If you are able to write down these reactions from scratch, remembering the presence of catalysts and understanding why they match the given reaction, this dotpoint will prove little trouble. Below are the equations once again for your reference.

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Process information from secondary sources to summarise the processes involved in the industrial production of ethanol from sugar cane

The last step is common with the industrial production of ethanol.

  1. Suitable crops such as sugar cane are cultivated and glucose is
  2. A sugary mixture with yeast added is heated at room temperature in anaerobic
  1. A concentration of 15% ethanol can be reached through this process, after which the yeast will no longer produce
  2. The solution may be distilled to obtain higher concentrations of ethanol

Describe and account for the many uses of ethanol as a solvent for polar and non-polar substances

This dotpoint will largely call upon fundamentals taught in the preliminary course such as the polarity of molecules, as well as the meaning of dipole-dipole bonds, or dispersion forces. Simply keep in mind the adage ‘Like dissolves like’ and there should be no problem. What this means is that a polar solution is likely to dissolve a polar substance, and the same with a non-polar solution.

The structure of ethanol, C2H5OH, accounts for its many uses as a solvent for both polar and non-polar substances.

The slightly polar hydroxyl functional group (-OH) allows ethanol to act as a solvent for polar substances, as electronegative species are able to dissolve via dipole-dipole interactions, or through hydrogen bonding. In addition, the dispersion forces (temporary induced dipole forces) present within the CH bonds combined with the hydrogen bonding present within the molecule serve to dissolve non-polar substances.

It is for this reason that ethanol is seen as the second-most important solvent after water.

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Remember- It is due to the presence of a polar, OH end as well as a non-polar CH end that ethanol is effective as a solvent.

 

Outline the use of ethanol as a fuel and explain why it can be called a renewable resource

Once again, be prepared to provide the formula for the combustion of ethanol. This will prove invaluable in demonstrating the low concentration of oxygen required for complete combustion (Of which the products are always carbon dioxide and water). Keep in mind many petrol stations in Australia already sell fuel with an ethanol content of approximately 10%, so this is a question that is very much relevant to current affairs.

Characteristics of ethanol which favour its use as a fuel include:

  • The presence of an oxygen atom within each molecule, allowing for ethanol to burn relatively The cleaner a fuel burns, the less harmful by-products are produced, such as carbon monoxide. Shown below, 3 moles of oxygen gas allow for the complete combustion of 1 mole of ethanol. In contrast, octane fuel requires 12.5 moles of oxygen gas. As such, the use of ethanol increases the chances of complete combustion, and carbon monoxide emissions can be reduced up to 20% if ethanol is substituted for octane.

C_2H_5 OH_{(l)} + 3 O_{2 (g)}2 CO_{2 (g)} + 3 H_{2}O_{(l) }+ Heat

  • Ethanol is easily
  • Ethanol has a heat of combustion of 1360 kJ/mol, giving a fairly high energy-per-mole output.
  • Current motors can already accept a 10-20% mixture of ethanol mixed with current petrol. However, ethanol attracts water molecules, and without the implementation of engine modifications, the use of ethanol is restricted to this relatively low-ratio

Ethanol is fermented from glucose, which consists of carbon dioxide and water. As such, sugar cane farming, which has high levels of glucose, is an effective primary source of the components used to produce ethanol. It is for this reason that ethanol is called a renewable fuel.

Remember- Ethanol’s primary benefit comes from its nature as a renewable fuel, a fuel which can be reproduced without fear of diminishing resources. When combined with its high energy-per-mole output, cleaner burning nature, and ease of transport, ethanol has great potential as an alternative fuel.

 

Identify the IUPAC nomenclature for straight-chained alkanols from C1 to C8

Prefix Number of carbon atoms
Meth- 1
Eth- 2
Prop- 3
But- 4
Pent- 5
Hex- 6
Hept- 7
Oct- 8

Naming a straight-chained alkanol is fairly simple if you focus on the number of carbon atoms present in the molecule. Above is a list of the prefixes for the first eight straight-chained alkanols.

Identify data sources, choose resources and perform a first-hand investigation to determine and compare heats of combustion of at least three liquid alkanols per gram and per mole

Understanding that the heat released by the fuel is theoretically equal to the heat absorbed by the water in the copper can is crucial to this experiment. However, you must also note that this experiment will often yield large errors, as heat will be lost to the environment. It is extremely likely that examination questions will raise this, so be prepared with methods of reducing the errors obtained. At the end of this dotpoint is a list of measures that you can go through, many applied in the procedure outlined above.

Materials

  • Copper can
  • Retort stand and ring clamp
  • Glass rod
  • 3 spirit burners filled with methanol, ethanol and 1-propanol
  • 100mL measuring cylinder
  • Thermometer
  • Balance

Diagram:

 

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Procedure:

  1. Light the first spirit
  1. Adjust the height of the can so that the tip of the flame just touches the
  1. Replace the cap on the spirit burner to extinguish the flame. Do not blow out the flame in order to extinguish
  2. Weigh the burner with its liquid contents and
  1. Add 200 mL of cold water to the copper can using a measuring Place the thermometer in the water and record its initial temperature.
  2. Light the wick and stir the water gently with the stirring rod to ensure uniform
  3. Monitor the temperature and extinguish the flame by replacing the cap when the temperature has risen by 10◦ The thermometer should be kept halfway in the water.
  4. Reweigh the
  5. Remove soot from the bottom of the can and replace the water in the copper can before testing the next

Expected results:

Now,

H1 = Heat absorbed by water (Joules)

= mCT

 

where

m = Mass of water

C = 4.18 (Specific heat capacity of water)

T = Change in temperature

Of course, the heat released by the fuel is equal to the heat absorbed by the water, ignoring loss of heat the environment.

Therefore

H2 = Heat released by fuel (Joules)

= −∆H1

per x grams of fuel used (i.e. A multiple of the heat released per gram). Thus,

 

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Methods of reducing error when determining heats of combustion

  • Ensure the tip of the flame touches the bottom of the can so as to minimise heat lost
  • Use a copper can in order to contain as much of the heat as
  • Enclose the experiment within a covering of aluminium foil in order to minimise the loss of heat into the

Remember- The amount of energy absorbed by the water is equal to the amount of energy released by the fuel combusting (Ignoring loss of heat to the environment). However, this loss of energy can be considerably large, and thus large inaccuracies will occur in your findings. Note the above improvements to the experiment, as the reduction of such errors is integral to this dotpoint.

 

Define the molar heat of combustion of a compound and calculate the value for ethanol from first-hand data

The molar heat of combustion is the amount of energy released in the form of heat when one mole of a substance is combusted to form products in their standard states (solid, liquid or gas) at 100 kPa and 25◦C (298K).

Ethanol’s molar heat of combustion is 1360 kJ/mol.

Remember- The molar heat of combustion is simply the amount of energy released as heat from one mole of a substance. This is not indicative of the energy released by one unit of a substance (E.g., one gram, or one millilitre).

 

Process information from secondary sources to summarise the use of ethanol as an alternative car fuel, evaluating the success of current usage

This dotpoint serves largely to bring attention to current applications of ethanol as a fuel. Brazil is a great example for this, so be sure to mention it if it is relevant to the question.

As supplies of non-renewable sources of fuel are slowly dwindling, governments are gradually turning towards renewable sources such as ethanol. However, the lack of significant research in the field has led to considerable costs, costs which have deterred many from pursuing ethanol as an alternative fuel within the near future. Despite his, it is undeniable that there has been an increasing trend in the turn towards ethanol as an alternative car fuel.

The Brazilian government subsidised the production of ethanol during the 1970s in order to reduce oil imports and stimulate employment growth. By using sugar cane waste to produce ethanol, approximately a third of the motor vehicles in Brazil (over four million) were able to use pure ethanol as a sole source of fuel. Today, approximately 50% of Brazilian cars are able to use 100% ethanol as fuel. The majority of the remaining vehicles use a mixture containing at least 20% ethanol.

Currently, many countries (Including Australia) make use of fuel with 10-15% ethanol. Although further engine modifications are required before this concentration can increase, research and inno- vation coupled with rising petrol prices offer much incentive to see this change undergone as soon as possible.

Remember- Despite such potential, the viability of using ethanol as a fuel is largely limited by the costs of producing large quantities through industrial fermentation of glucose-high crops such as sugar cane.

 

Assess the potential of ethanol as an alternative fuel and discuss the advan- tages and disadvantages of its use

The advantages and disadvantages of ethanol as an alternative fuel will be listed out for the purposes of this dotpoint. Depending on the question asked, feel free to elaborate on these points.

If the question requires it, include a stance. Do this by acknowledging the potential of ethanol, but the current costs of producing ethanol, as well as the practical issue of redesigning engines to cope with higher concentrations of ethanol. It may be of use to note, and perhaps mention that vehicles in countries such as Brazil have achieved compatibility with 100% ethanol fuels.

Advantages:

  • Ethanol is renewable, reducing the consumption of non-renewable
  • Greenhouse gas emissions could be reduced due to the cleaner-burning nature of ethanol, which could potentially reduce carbon monoxide emissions by up to 20%.

Disadvantages:

  • Large areas of arable land would need to be devoted to the cultivation of suitable plants such as sugar This would lead to erosion, deforestation, salinity, and many other environmental problems.
  • Much of the biomass produced in the production of glucose is not used in the actual fer- mentation process. Unless other uses are found for such products, this can present major environmental
  • The process requires a lot of energy, energy which is currently provided by fossil In some cases, the energy used to produce ethanol via the combustion of fossil fuels can be higher than the energy produced by the resulting ethanol.
  • As a result of requiring larger inputs of energy, ethanol is currently more expensive to obtain than
  • Although ethanol burns more cleanly, whether or not it reduces the greenhouse effect is debat- able, as many greenhouse gases are released during the harvesting of the crops used to produce ethanol as well as the distillation of the
  • Ethanol reduces less energy per mole than
  • Engine modifications are required if ethanol is ever to be used in compositions larger than 20%.

Solve problems, plan and perform a first-hand investigation to carry out the fermentation of glucose and monitor mass changes

This experiment is fairly simple, only requiring some time for it to carry out to completion. As such, try to attempt this experiment early on in the day so that hourly observations can be made. Always keep in mind in any experiment methods of improving the experiment in turns of reliability and accuracy, and these inevitably appear in exams. As such, keep in mind possible errors which may arise in simple tasks such as measuring weight, and formulate possible solutions such as using an electronic scale, or perhaps increasing the sample size.

Procedure:

  1. Place warm water, glucose, and yeast in a flask and stopper the top with either a cork, or cotton
  2. Weigh the flask and its contents and record the
  1. Place the flask in a warm area such as the window sill, and allow to sit. Ideally, set this experiment up in the morning, and take measurements regularly (In hourly intervals) over four hours, recording the weight at each
  2. Reweigh the flask and its contents, and record the results along with the difference in

Optional: Connect a cork and rubber tubing to the flask, running the end of the tubing into a flask of limewater. The limewater turning cloudy indicates the presence of carbon dioxide.

Expected results:

The loss in mass should be equal to the carbon dioxide produced. The end solution is likely to be an extremely dilute solution of ethanol.

If you monitored the mass changes at regular intervals, you will notice that the rate of change decreases over time, gradually coming to a complete stop after a few hours.

Describe conditions under which fermentation of sugars is promoted

Several other factors are often included in various publications. However, the four points below are really the only crucial points necessary to gain full marks. As a point of interest, the yeast itself is not required, but rather an enzyme secreted by yeast known as zymase is what actually brings about the fermentation process. However, simply stating yeast as a requirement is fine.

Fermentation is simply the process by which glucose is broken down to form ethanol and carbon dioxide. Several conditions must be satisfied in order for fermentation to successfully take place:

  • A glucose-containing solution must be If a solid containing glucose is used, water must be added to form a solution.
  • Yeast must be
  • The reaction must be conducted in anaerobic conditions, e. no oxygen.
  • A temperature roughly at body temperature is best, e. 37◦C.

 

figure 9

Although a temperature of 37◦C is not necessary for the reaction, which will occur at lower tem- peratures, a higher temperature will cause the reaction to occur faster. However, the temperature should not be raised above 37◦C, as the yeast cannot survive.

Remember- The conditions necessary for fermentation to occur: A glucose solution, yeast, anaerobic conditions, and a temperature of approximately 37C.

 

Summarise the chemistry of the fermentation process

The yeast included in the reaction secretes an enzyme complex known as zymase which catalyses the process of glucolysis, which refers to the conversion of glucose into ethanol and carbon dioxide. An ethanol percentage of 15% can be successfully produced, at which point the yeast will begin to die due to the concentration of ethanol, and the reaction will halt.

 

figure 9Remember- Fermentation is the process whereby glucose is converted into ethanol and carbon dioxide.

Present information from secondary sources by writing a balanced equation for the fermentation of glucose to ethanol

This dotpoint will have been covered quite sufficiently by this point, but as the equation is quite important, it is written again below. Do not forget to include the necessary condition of ‘yeast’ when writing the equation.

 

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