Efficiency of Fuels

What is Fuel Efficiency?
Fuel efficiency refers to the measure of the amount of energy from the fuel used to perform a function. The greater the amount of energy from the fuel required to perform a function, the lower the fuel efficiency.
Example: In today's vehicles
Today's common fossil fuel engines are not very efficient. Only about 15% of energy from fuel moves the vehicle, the rest is lost to heat and exhaust. In contrast, an efficient fuel in cars is one that is able to allow the vehicle to travel the greatest distance with the least amount of fuel.

Why is Fuel Efficiency important?
[Economic Benefit]
1. Saves money - A more efficient fuel can perform a function in smaller quantities compared to a less efficient fuel.
[Environmental Benefit]
2. Reduces climate change
3. Reduces dependency on oil / fossil fuels
4. Increases energy sustainability

What affects Fuel Efficiency?
Fuel efficiency is dependent on many parameters of a vehicle including its engine parameters, aerodynamic drag, weight and rolling resistance.

How to calculate Fuel Efficiency in vehicles?
Specifically in vehicles, fuel efficiency is given as a ratio of distance travelled per unit of fuel consumed, typically miles per gallon.
Example: Given that there are 15 gallons of gas in the tank of a car and that this car is able to drive 450 miles without refueling, we can calculate the fuel efficiency of this car to be 450 / 15 = 30 miles / gallon.

What if these fuels are not used to power vehicles? How do we then calculate its fuel efficiency?
Enthalpy change of combustion can be calculated instead. The most efficient fuels are the most exothermic ones which are able to release the most amount of energy per mol.

Example of Calculating Fuel Efficiency through Analysis of Experiment Results
An experiment was conducted to test the effectiveness of fuels by estimating the amount of energy released from burning the fuel. The fuels tested were methanol and cyclohexane (as well as our homemade biodiesel from vegetable oil which unfortunately contained too much water to be able to burn), in which we can compare both fuels to determine the more efficient one. Although it was a pity that none of our homemade biodiesel worked, it was a lesson learnt: homemade biodiesel is tough to make!

Setup of Experiment
A retort stand was used to hold a beaker containing water at a height adjusted according to the height of the tip of the flame for each fuel.

Burning of methanol is a small flame (before adjusting of beaker according to flame height)

Burning of cyclohexane is a large flame, and beaker is already covered in soot

Results of the Experiment

	Initial Temperature / °C	Final Temperature / °C	Time Taken
Methanol	31.0	100.0	1 min
Cyclohexane	31.0	75.0	2 mins

Based on this set of results alone, it seems that Methanol might be a more efficient fuel because when burnt, it heats the water up to a higher temperature in a shorter time. Methanol, too, burns cleaner than cyclohexane in that there is less soot produced.

Calculations
Mass of Water = volume x density = (40cm³ x 0.000001)(998.2kg/m³) = 0.39928kg
∆H = mc∆T where m=mass of water, c=specific heat capacity of water and T=temperature

[Methanol]
∆H of Methanol = (0.39928kg)(4.181KJ/kg K)(100.0°C-31.0°C) = 115.19KJ (to 5sf)
Amount of Methanol used in the experiment (in kg) = (10cm³  x 0.000001)(791.30kg/m³) = 0.007913kg
Amount of Methanol used in the experiment (in mol) = (0.007913kg x 10³) / (12+4+16) = 0.24728mol (to 5 sf)
∆H of Methanol = 115.19KJ / 0.42728mol = 466 KJ/mol (to 3sf)

[Cyclohexane]
Assuming that the temperature of the water heated by the burning of cyclohexane increased linearly over 2 minutes, we can take that the change in temperature of the water heated by burning of cyclohexane in 1 minute is ∆T /2
∆H of Cyclohexane = (0.39928kg)(4.181KJ/kg K)(75.0°C-31.0°C)/2 = 36.727KJ (to 3sf)
Amount of Cyclohexane used in the experiment (in kg) = (10cm³  x 0.000001)(779kg/m³) = 0.00779kg
Amount of Cyclohexane used in the experiment (in mol) = (0.00779kg x 10³) / (12x6+14) = 0.09058mol (to 5 sf)
∆H of Cyclohexane = 36.727KJ / 0.09058mol = 405 KJ/mol (to 3sf)

As with our initial predictions, calculated enthalphy change for both fuels shows that enthalphy change is greater in methanol than in cyclohexane per mol. The above experiment thus concludes that methanol is a more efficient fuel than cyclohexane.

Sources:
http://en.wikipedia.org/wiki/Fuel_efficiency

Green Plastics

What are Green Plastics?
Green Plastics, also known as bioplastics, are plastics derived from renewable biomass sources e.g. starch and oil.

What are some properties of Green Plastics?
1. Bioplastics derived from fatty acids (oil) can be utilised as a fuel resource.
[Thermal Properties]
2. High conductivity increases heat dissipation - can be used in electronics
3. Easy to mold due to lower melting temperature.

How are Green Plastics made?
Bioplastics are made by converting sugar present in plants into plastic.
Example: Production of Polyactic Acid (PLA)
1. Dextrose is fermented to form lactic acid.
2. Lactic acid undergoes dehydration to form polyactic acid oligomer - water molecules have to be removed before polymerisation as formation of water molecules then prevents growing chain of lactic acid molecules from sticking together.
3. Polyactic acid oligomers undergo thermal cracking to form lactide.
4. Lactide undergoes condensation polymerisation to form polylactic acid.

Green Plastic made from Corn Starch
Bioplastic can be easily made from corn starch.
1. Add corn oil and water into a bag, seal the bag then mix the ingredients by rubbing outside bag
2. Add 2 drops of food colouring in the mixture, seal and mix again
3. Microwave on high 25 seconds with zip slightly opened.
Lesson Learnt: Oil should be added in high proportions for the resulting plastic formed to be able to stick nicely together in one piece instead of being shattered.

Result

My small piece of blue plastic that managed to stick together in 1 nice flat piece

What are the pros and cons of using Green Plastics?

Pros	Cons
1. Reduces or eliminates Greenhouse Gases in production 2. Requires less or no petrochemicals 3. Biodegradable 4. Can be utilised as a fuel 5. Slow release of carbon dioxide allows sufficient time for plants to absorb it	1. High cost 2. Use of fertilizer and pesticides on crops 3. Carbon dioxide emissions from harvesting vehicles 4. Fossil fuels typically used to power manufacturing plants 5. Producing bioplastics often requires nearly as much energy as producing conventional plastic

Why are Green Plastics considered to be sustainable while conventional plastics are not?

In terms of the 12 principles of Green Chemistry,

	Green Plastics	Conventional Plastics
1.	Green Plastics are designed so that at the end of their function, they do not persist in the environment and break down into innocuous degradation products. Green plastics are biodegradable, in that they are able to degrade from the action of naturally occurring microorganisms e.g. fungi and bacteria.	Conventional plastics are not biodegradable. Because of its complex entanglements of polymer chains, it is hard to be decomposed.
2.	Green Plastics make use of a renewable raw material e.g. starch and oil.	Conventional Plastics make use of depleting resources e.g. petroleum.

Sources:

http://www.livescience.com/33085-petroleum-derived-plastic-non-biodegradable.html

http://worldcentric.org/biocompostables/bioplastics

Biofuels

What are biofuels?

Biofuels are fuels made from biomass. 

Examples: Bioethanol, Biodiesel, D-Limonene

How are some biofuels derived from biomass?
Below demonstrates how biodiesel and D-Limonene can be derived from biomass.
1. Biodiesel can be derived from vegetable oil. Biodiesel will first undergo hydrolysis to form 3 fatty acids and glycerol - a necessary step because vegetable oil molecules are 3 times as large as biodiesel molecules. Thereafter, transesterification occurs where the ester transforms into another and biodiesel is thus formed. 

Vegetable oil placed in beaker and onto hot plate for heating. Ethanol / KOH mixture was added to the beaker as it heated, at regular intervals of 5 minutes.

After 8 additions of the mixture, the resulting mixture was of the above shown colour. 

2. D-Limonene can be extracted from fruit peel through steam distillation. Since fruit peels are often discarded after consumption of the fruit, these fruit peels can be reused here instead.

Coloured parts of the orange peel were cut out and blended prior to steam distillation to prepare orange rind.

Orange rind then transferred to round-bottom flask at left of set up. A hot plate was initially used but changed to a bunsen burner, as shown above, which heated up the orange rind quicker. As the orange peel puree began to boil, liquid was collected in the conical flask at right of set up. 

Acetic acid was added to the liquid collected to increase separation of 2 layers. Contents of flask were then poured into a separating funnel, the funnel was inverted 5 times and the liquid was left to settle, as shown above. The orange oil rose to the top of the mixture while the water, which formed the bottom layer, was drained out.

The orange oil was collected into test tubes, placed in water baths, and removed of last remaining strains of water which sank to the bottom of the test tube, resulting in the figure as shown above.

All biodiesel was eventually collected in this conical flask.

What are the uses of biofuels?
1. Bioethanol can be used to power car engines.
2.  D-Limonene as an essential oil has many benefits e.g. anti-carcinogenic properties.

Why are biofuels considered to be a sustainable source of energy while fossil fuels are not?

In terms of the 12 principles of Green Chemistry,

	Biofuels	Fossil Fuels
1.	Biofuels prevent waste, which is better than to treat or clean up waste after it is formed. Biofuels are carbon neutral - though they give out carbon dioxide during combustion, carbon dioxide had also been taken in during photosynthesis by the plant of which the biofuel was derived from, achieving net zero carbon emissions.	On the other hand, fossil fuels do not prevent waste. When fossil fuels are burnt, the sulphur which it contains is converted to and released as sulphur dioxide gas. Sulphur dioxide is an acidic air pollutant that dissolves in rainwater to form sulphurous acid, contributing to acid rain.
2.	Biofuels makes use of a raw material which is renewable rather than a depleting one. Biofuels are made of living organisms, usually plants which can be grown e.g. D-Limonene can be extracted from orange fruit peel.	On the other hand, fossil fuels do not make use of a renewable raw material. Fossil fuels e.g. coal and oil are in fact depleting quickly today.