Lesson 5: Bioethanol and Biodiesel

PART 1: Bioethanol and Biodiesel

About bioethanol:

  • produced from fermentation of glucose
  • glucose is found in the fruit flesh and hence, the glucose found in the flesh can be used to make bioethanol
  • the fruit peel contains cellulose which can also be fermented to ethanol because both cellulose and glucose are made up of glucose monomers, the only difference is in the way they are linked.

Fermentation:

fer

Conditions:

  • presence of yeast
  • anaerobic surroundings
  • room temperature

Fractional Distillation can then be done to separate ethanol (b.p: 78 degree Celsius) and water (b.p: 100 degree Celsius).

From Vegetable Oil to Biodiesel

  • vegetable oil molecules are three times as large as biodiesel molecules
  • as such, there is a need to break up the large molecules into 3 smaller molecules because large molecules are inefficient as fuels. Amount of energy yield from large fuels is low due to high mass.
  • vegetable oils are esters with 3 fatty acids bonded to glycerol ie. vegetable oils are triglycerides
  • fatty acids are carboxylic acids with a long carbon chain (to be specific, fatty acids have a carbon chain 18 carbons long)

triglyc

  • When the triglyceride is broken up, the ester linkages are broken, and 3 fatty acids and 1 glycerol molecule will be formed as the product
  • vegetable oils undergo transesterification (transforming one ester into another) to form biodiesel
  • concentrated sulfuric acid is needed for transesterification

Procedure

  1. Determine the mass of a clean, dry 250mL conical flask. Measure 100.0mL of vegetable oil using a measuring cylinder and add it to the flask. Record the exact mass of vegetable oil.
  2. Add the stirrer bar to the mixture and place the flask on the hot plate. Start heating the mixture to about 55-go degree Celsius while stirring.  1384344_739485129401748_245898195_n
  3. In a separate flask, add 20.0mL of methanol and the appropriate amount of NaOH catalyst. Carefully swirl or stir the flask until the NaOH has dissolved. Important ratios: Methanol : Oil : Catalyst is 2: 10: 1. 994608_739485196068408_2076620942_n
  4. Add the methanol/NaOH mixture to the warm oil in 8 5 minute intervals until the mixture has reacted for 45 mins. Make sure the temperature does not rise too much.
  5. At the end of the reaction, separate the mixture in a separating funnel. 1377049_739485252735069_2046887304_n
  6. Add 10mL of 0.1 M acetic acid to the biodiesel in the separating funnel. Stopper tightly and invert gently 5 times. Then, allow the two layers to separate again (biodiesel is the least dense solution out of all the other solutions and hence will float on top) and collect the top yellowish layer in a beaker.
  7. Repeat the extraction step using 10mL of distilled water
  8. Pour the washed biodiesel through the top of the separating funnel into a dry, pre-weighed 100mL beaker. Place the sample in a water bath for 10-15mins to evaporate residual water as residual water will inhibit the igniting of the biodiesel later.                                                                       1395840_739485296068398_754340378_n
  9. Obtain the mass of the dry biodiesel.                     1384392_739485329401728_345364280_n

Concept behind experiment

  • when heated at high temperatures in the presence of water from food, the triglycerides in vegetable oil begin to break down by a chemical reaction called hydrolysis, producing fatty acids and glycerol
  • Base catalyst NaOH catalyzes reaction between fatty acid and methanol to form esters
  • Fatty acids will react with methanol to form methyl esters (Note: transforming the triglyceride (triester) into a methyl ester. Hence TRANSesterification).
  • Methyl esters are thus, the main components of Biodiesel and are the compounds burnt to produce energy

biodieselproduction1

Importance of washing the biodiesel

  • if the biodiesel is not washed properly, the contaminating ethanol could create a fire hazard and other contaminants will negatively affect combustion and engine performance
  • If water is not remove properly, the water will later react with the vegetable oil in the reaction and make soap which then complicates the steps after the transesterication reaction that are needed to separate the biodiesel from leftover methanol, the NaOH or KOH catalyst, and the glycerol byproduct.

Advantages of Biodiesel

  • non-toxic
  • renewable
  • less greenhouse gases produced
  • less expensive compared to other forms of liquid fuel

Disadvantages

  • accelerate rate of deforestation as forests are cleared to grow plants for biodiesel
  • usage of food crops to make the fuel

PART 2: Testing the Efficiency of Fuels

Fuel efficiency: using the least amount of fuel to travel the greatest distance

Importance of Fuel Efficiency

  • saves money
  • reduces climate change
  • reduces dependency on oil/fossil fuels
  • increases energy sustainability

Factors affecting fuel efficiency

  • weight/mass of a vehicle
  • engine design
  • vehicle design
  • vehicle maintenance

Today’s vehicles

  • only 15% of energy from fossil fuel move the vehicle or run accessories. The rest if lost to heat and exhaust

Calculating fuel efficiency

  • units: miles per gallon
  • Amount of heat released when fuel is burnt is equal to the amount of heat used to change the temperature of water. Amount of heat can be found by the following equation: Thermal energy (Q) = mass of water (m) x specific heat capacity of water (c) x change in temperature of water (ΔΘ)
  • using the calculated thermal energy, we can divide this by the number of moles of fuel that was combusted

Procedure

  1. Place a small wad of cotton in a crucible.
  2. Measure 10mL of cyclohexane using a measuring cylinder. Pour the cyclohexane onto the cotton wool in the evaporating dish. Determine the mass of cyclohexane used.
  3. Measure 10mL of water into a 25mL beaker and record the initial temperature of the water. Use a retort stand to hold the beaker in place directly above the crucible.
  4. Using a lighted splint, set fire to the cyclohexane.
  5. Immediately start the stopwatch and note the final temperature at the end of 2 minutes.                                                                 1391534_739484916068436_1248353283_n
  6. Repeat the above steps for methanol

Calculations

Fuel used

Temperature of water/ oC

Density of Fuel (g/ml)

Mass of fuel used/g

(density x 10ml)

Duration/mins

Initial

Final

Cyclohexane

31.0

75.0

0.7781

7.781

2

Methanol

31.0

100

0.7918

7.918

<2

B46276D1-EA79-4353-BE30-F83B1613D244 (1)

Note that Q is calculated by the following formula: Thermal energy (Q) = mass of water (m) x specific heat capacity of water (c) x change in temperature of water (ΔΘ)

From the above calculations, we can conclude that cyclohexane is a more efficient fuel than methanol, as it releases 19.9J of energy per mole burnt while methanol only releases 11.7J. Such results reinforce the fact that alkanes are better fuels than alcohols, as the combustion of alkanes is more exothermic, thereby releasing more energy than alcohols when burnt.

Assumptions

  • heat transfer is to water ONLY
  • 1mL of all aqueous solutions equal to 1g

Source:

Campbell Biology 9th edition Chapter 5 Page 119

http://www.goshen.edu/chemistry/biodiesel/chemistry-of/

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