Exam Questions Stories

Green Chemistry: NEWSand and NEWOil

The chemistry behind how old things are made new

In ultra-modern Singapore where everything is spanking new, it’s old news to report on openings, debuts, and launches. So it becomes really refreshing to hear about the old for a change. On July 29th, Minister Masagos shared about the national effort to convert discarded waste into NEWSand and NEWOil. This gives old material a new lease of life, to serve as construction material and fuel. His post contains many geeky chemical terms, which got your journalist very excited and typing away!

Rise from the Ashes: NEWSand

Like how NEWater is recycled water, NEWSand is recycled from rubbish by modifying the way it is burned at incineration plants.

Old-School Incineration of Waste

In Singapore we clear most waste by incineration. We burn our trash, reducing them to incineration ashes that we then bury. However, this is not sustainable. Our landfill is filling up faster as we produce ever more waste.

To solve this, scientists and engineers at Nanyang Technological University have modified the waste clearance process, such that useful sand is produced instead of incineration ashes.

New Process of Making Slag

The new process runs at 1600 °C, much higher than the temperature at which trash incinerates typically. Engineers raise the temperature by mixing trash with charcoal. The added charcoal undergoes combustion to release a larger amount of heat.

The higher temperature produces a mixture of molten slag and molten metal. When the molten slag is separated, it is cooled down to form solid slag. Superficially, when solidified, slag looks like glass. But chemically, slag comprises oxides like silicon dioxide, aluminium oxide and iron(III) oxide (Kwak et al, 2005).

No, we can’t slack even after we get the slag. Engineers pulverise and process it further to form NEWSand, and then use it to make concrete. As concrete made from NEWSand is a novelty, the university and government agencies are testing it rigorously to ensure that it is as safe, sturdy, and durable. They do it demonstration sites like the footpath near Our Tampines Hub.

Juicing Plastic for Oil: NEWOil

Another recycling process that Singapore is exploring is the chemical conversion of plastic waste into oil.

A common type of plastic is poly(ethene). It is a large macromolecule formed by joining up many small molecules of ethene. We call this process polymerisation.

We can see the conversion of plastic to NEWOil as the reverse process. Long chains of macromolecule break down into small molecules, though they may not be exactly the same as those used to make the plastic initially. The small molecules produced have a lower melting point than the large macromolecule, and so they exist as liquid oil.

On its own, plastic decomposes and breaks down into small molecules very slowly. This explains why plastic is such a terrible, recalcitrant pollutant that lingers in the wild. In the chemical conversion of plastic to oil, temperature and pressure are elevated to speed up the reaction. Catalysts are also used.

Environmental Friendliness of NEWOil

However, the use of elevated temperature and pressure drive up energy consumption and cost. Some metal catalysts can also pollute the environment. That’s why NEWOil is still in its infancy stage of development. With more research and funding into green chemistry, there are hopes to discover better processes and catalysts that are more environmentally friendly.

With hope, NEWOil can transform Singapore into a greener society. But rather than waiting for science and magic to happen, we can do that right now by simply reducing our plastic use.

Data-Based Questions à la Paper 2 Section B

QUESTION 1: Chemical Equation

Write a chemical equation, with state symbols, for the incomplete combustion of carbon in charcoal.

2C (s) + O2 (g) ⟶ 2CO (g)

Marker’s note: Incomplete combustion forms carbon monoxide, while complete combustion in excess oxygen forms carbon dioxide.

QUESTION 2: Energy from Chemicals

The incomplete combustion of carbon-containing charcoal increases the temperature of the furnace to 1600 °C. State and explain if this is an endothermic or exothermic reaction.

Exothermic reaction. As the surrounding temperature increases during the reaction, it suggests that heat is given off by the reaction.

QUESTION 3: Metals

In the extraction of iron from haematite, carbon is also used.

Compare the use of carbon in iron extraction to that in NEWSand production.

In both processes, carbon undergoes combustion to release heat, driving up the temperature of the furnace.

However, carbon has an additional role in the extraction of iron. It is converted to carbon monoxide, which is a reducing agent that reduces iron(III) oxide to iron.

QUESTION 4: Metals

The production of NEWSand also resembles the extraction of iron in another way. Both processes involve the formation of slag.

Compare the slag formed in iron extraction to that in NEWSand production.

In both processes, slag is produced in the molten state due to the high temperature of the furnace.

On the other hand, there are two differences.

Firstly, slag is formed during iron extraction by adding silicon dioxide to the calcium oxide impurities. However, it is formed during NEWSand production by simply heating trash to 1600 °C.

Secondly, slag from iron extraction contains calcium silicate. However, that from NEWSand production contains a mixture of oxides.

QUESTION 5: Macromolecules

NEWOil is a way of recycling plastic. A common type of plastic is poly(ethene).

Describe the formation of poly(ethene) and state one use of poly(ethene).

Poly(ethene) is formed by the addition polymerisation of ethene monomers, whereby they are joined together without losing any atom or molecule. This occurs at high pressure and temperature, in the presence of catalysts.

As poly(ethene) can be moulded into different shapes, it is used to make plastic bags and cling films.

QUESTION 6: Atmosphere

Do you agree that the adoption of NEWSand and NEWater will reduce pollution? Explain.

In your explanation, you could consider:

  • How chemically recycled materials can reduce the need to excavate and extract new natural resources, a process that leads to land pollution
  • In the Singapore context, how materials recycled locally can reduce the needs to import natural resources, which in turn decreases the air pollution caused by shipping
  • How the production of NEWSand and NEWater involve high temperature, high pressure or catalysts, which can still lead to air pollution from energy production and water pollution if metal catalysts are released into water

Marker’s comment: Like a humanities essay question, there is no right or wrong; you could either agree or disagree with the statement, so long as it is well explained.

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