Turning Polyethylene Waste into Fuel

Low density polyethylene, LDPE, is used to make many things we use everyday such as plastic milk containers, cling wrap, and plastic bags. LDPE can be recycled quite easily, but a lot of LDPE ends up as rubbish in land fills.
Chemists in India have developed a commercially viable way to turn LDPE into a liquid fuel by heating the LDPE waste to between 400 and 500^oC over a kaolin catalyst which causes the long chain polymer chains to break apart. This process is known as thermo-catalytic degradation: thermo means heat, the catalyst is kaolin, and degradation means breaking apart. This thermo-catalytic degradation of LDPE produces much smaller carbon-based molecules. Gas Chromatography was used to characterise these smaller molecules, and it was found that they were mainly alkanes and alkenes between 10 and 16 carbon atoms long. This makes the mixture very similar to that found in petrochemical fuels. For example, the hydrocarbons in gasoline (petrol) typically have a chain length of between 4 and 12 carbon atoms while diesel fuel typically contains hydrocarbons with a chain length between 8 and 21 carbon atoms.

The catalyst, kaolin, is a layered, aluminosilicate clay mineral with the formula Al₂Si₂O₅(OH)₄. It acts as a catalyst by providing a large surface on which the polymer molecules can sit in an orientation favourable to the degradation under heat.

Using the kaolin catalyst at 450^oC, the thermo-catalytic degradation of 1 kg of LDPE produced 700 g of liquid fuel.

Reference:
Achyut Kumar Panda, Raghubansh Kumar Singh. Thermo-catalytic degradation of low density polyethylene to liquid fuel over kaolin catalyst. International Journal of Environment and Waste Management, 2014; 13 (1): 104 DOI: 10.1504/IJEWM.2014.058803

Further Reading:
Polythene (polyethylene): Properties, Production and Uses 
Gas Chromatography 
Alkanes: properties and uses
Alkenes: properties and uses
Ethene (ethylene): properties and uses
Silicates: structure and formula

Suggested Study Questions:

1. Give the molecular structure for ethene (ethylene).
2. Write an equation showing how ethene (ethylene) molecules can be polymerized to form polythene (polyethylene).
3. Name the type of polymerization reaction being described by the equation in question 2.
4. Explain, using a diagram of the partial structure of polythene (polyethylene), what happens when polyethylene undergoes thermo-catalytic degradation.
5. Describe the differences in the structures of alkanes and alkenes.
6. Draw a straight chain alkane with 10 carbon atoms.
7. Draw a structural isomer of the molecule in question 6.
8. Draw a straight chain alkene with 10 carbon atoms.
9. How many structural isomers of the molecule in question 8 do you think there would be? Support your answer with the structural formula for each of these structural isomers.
10. Why do you not find short carbon chain alkanes, between 1 and 4 carbon atoms long, in the liquid petrochemical fuels like gasoline (petrol) and diesel?

Scientific Method and Designing an Experiment

AUS-e-TUTE has just added two new resources sets:

• Scientific Method
• Experimental Design

All the Chemistry Syllabus Study Guides in the Test Centre have been updated to include these new resources.

Chemistry Add-in for Word Introduction

There is a FREE chemistry add-in for Microsoft's Word 2013 program that will make writing your chemistry lab reports and assignments so much easier!
First you will need to go to http://chem4word.codeplex.com/releases/view/102798 and

1. Download the archive Chem4Word 1.1.zip and save to a convenient location on your computer.
2. Double-click to open the archive and run the setup.exe program.

Once you have done this you will have a new "Chemistry" tab next to the "View" tab on your Word menu.
This new tab will help make your chemistry lab reports and assignments look very professional.
Let's start with a quick introduction to a couple of things this new tab will do for:

• change from a chemical name (or molecular formula) to a structural formula
• change from a chemical name (or structural formula) to a molecular formula

We are going to work through an example in which we will switch between the name, structural formula and molecular formula for acetic acid (or ethanoic acid) in a Word document.

1. Open a new Word document.
2. Type acetic acid (or ethanoic acid).
3. Highlight what you have typed.
4. Click on the new "Chemistry" tab.
5. On the new toolbar that pops up, click the "mark as chemistry" icon.
6. Highlight "acetic acid" (or ethanoic acid) again (you may need to click within the highlight area to get the chemistry box up).
7. Click "View" icon on the new chemistry toolbar.
8. Click "2D" on the drop-down menu. This will replace the name you have typed with a structural formula:
   
9. With the structural formula highlighted, click the "View" button again.
10. Click "acetic acid" from the drop-down menu to change the structural formula back to the name.
11. With the name highlighted, click the "View" icon again.
12. Click  C_{2}H_{4}O_{2} from the drop-down menu which will change the name to the molecular formula, C₂H₄O₂
13. With the molecular formula highlighted, you can click the "View" button again to select either the name or 2D options again.
14. When you are happy with your selection, just click on the document away from your chemical and it will remain as it is.

Now, isn't that a really useful tool to have!

Suggested Reading:
Naming Organic (Carbon) Compounds
http://ausetute.com.au/namsanes.html
http://ausetute.com.au/nambanes.html
http://ausetute.com.au/namisane.html
http://ausetute.com.au/namisene.html
http://ausetute.com.au/namishalk.html


Suggested Activities:
Type each of the following names into a Word document and switch between the name, structural formula and molecular formula for each one:

1. ethanol
2. water
3. ozone
4. carbon dioxide
5. methane
6. butane
7. carbon monoxide
8. ammonia
9. hydrogen cyanide
10. benzene
11. citric acid
12. stearic acid

Exploding Pool Chemicals

Sydney Morning Herald, Sunday 12^th January 2014, "Sydney man severely injured mixing chlorine for pool"
In summary, the victim of this accident had a backyard pool which had turned green. He had been advised to add 2 kilograms of "chlorine" to his pool to turn it sparkling blue again. He went home, put 2 kg of the "chlorine" granules into a bucket, and added water. Within 30 seconds the mixture exploded. The man was taken to hospital in a critical condition.

Now, for some chemistry....

From the description of the "chlorine" it sounds like it was calcium hypochlorite, Ca(OCl)₂ , a white solid at room temperature and pressure that is commonly sold as "pool chlorine".
When added to water, calcium hypochlorite produces hypochlorous acid, HOCl, and calcium hydroxide, Ca(OH)₂(aq).

Word equation:	calcium hypochlorite	+	water	gives	hypochlorous acid	+	calcium hydroxide
Chemical equation:	Ca(OCl)2	+	2H2O	→	2HOCl	+	Ca(OH)2

Dissolving calcium hypochlorite in water produces energy. The heat (or enthalpy) of solution is about 630 kJ mol^-1
We can now calculate how much energy was released when the man added water to 2 kg of calcium hypochlorite in the bucket.
First we need to calculate how many moles of calcium hypochlorite were in the bucket:
moles (Ca(OCl)₂ ) = mass ÷ molar mass
            and mass (Ca(OCl)₂) = 2 kg = 2 x 1000 = 2,000 g
            and molar mass (Ca(OCl)₂) = 40 + 2(16 + 35.5) = 143 g mol^-1
moles (Ca(OCl)₂ )  = 2000 ÷ 143 ≈ 14 mol
Now,  from the heat (enthalpy) of solution, we know that 1 mole of calcium hypochlorite dissolves in water to produce 630 kJ of energy.
We can calculate how much energy is released when 14 mol of calcium hypochlorite dissolves in water:
energy released = moles x energy in kJ mol^-1
energy released  = 14 x 630 = 8820 kJ
which is equivalent to exploding about 100 g of TNT in the bucket !

Reference:
http://www.smh.com.au/nsw/sydney-man-severely-injured-mixing-chlorine-for-pool-20140111-30nl3.html

Suggested Reading:
Defining Enthalpy Change 
Energy Profiles 
Strength of Acids
Strength of Bases 
pH of Aqueous Salt Solutions 


Suggested Study Questions:

1.  What is the name given to the type of reaction that produced energy?
2.  What name is given to the type of reaction that absorbs energy in order to produce products?
3. Sketch an energy profile diagram for the reaction between calcium hypochlorite and water.
4. Sketch an energy profile diagram for the explosion of TNT.
5. For 2 kg of calcium hypochlorite completely dissolving in water, calculate the moles of calcium hydroxide that would be produced.
6. For 2 kg of calcium hypochlorite dissolving in water, calculate the mass of hypochlorous acid that would be produced.
7. Assume the man used a 30 L of water in a 40 L bucket, what is the concentration of calcium hydroxide expected to be?
8. Hypochlorous acid is considered to be a very weak acid. What does this mean? 
9. Calcium hydroxide is considered to be a strong base. What does this mean?
10. What is the approximate pH of the solution when 2 kg of calcium hypochlorite is dissolved in  30 L of water?
11. What safety precautions do you think pool owners should take when mixing calcium hypochlorite granules with water?
12. Design a safety poster that could be displayed in a pool shop clearly showing the safest way to mix calcium hypochlorite granules with water. 

Student Safety Contract

The new Student Safety Agreement (or Student Safety Contract) is now available  as a pdf to download from

http://www.ausetute.com.au

you will find it on the downloads page.

The online version of the Student Safety Quiz is available in the Class/School Group Members area, while the printable version of the same quiz is available in the Teachers Only area of the AUS-e-TUTE website.

Safety in the Laboratory

Do you need teaching and learning resources to educate students about safety in the laboratory?
AUS-e-TUTE's Safety in the Laboratory topic now has a new tutorial, game, test and exam!

Visit http://www.ausetute.com.au and click on the "Safety in the Laboratory" links.

AUS-e-TUTE Members should log-in to the Members Only area to get the full range of resources on this topic.