Green chemistry and careers

The principles of green chemistry, calculating atom economy, greener routes to medicines, hydrogen and steel, the chemistry and policy of plastic recycling in NSW, using household chemicals safely, and careers that use chemistry.

In the 1960s, making ibuprofen took six steps and threw away about 60% of the atoms that went into the reactor. In 1992 a new route did it in three steps, and the only by-product was collected and sold. Millions of kilograms of waste a year disappeared, not by cleaning it up, but by never making it in the first place.

What is green chemistry?

Green chemistry means designing chemical products and processes that reduce or eliminate hazardous substances and waste. It was set out as twelve principles by the American chemists Paul Anastas and John Warner in 1998. The big idea is that it is better to prevent waste than to treat it afterwards. Some of the principles:

Principle	Example
Prevent waste and maximise atom economy	The newer ibuprofen route puts 77% of reactant atoms into the product, compared with 40% for the old route.
Use catalysts rather than reactants that get used up	Enzymes in cold-wash detergents; catalysts in nearly every industrial process (4E).
Use safer solvents	Coffee is decaffeinated with supercritical carbon dioxide instead of chlorinated solvents.
Design for energy efficiency	Run reactions near room temperature and pressure where possible.
Use renewable feedstocks	Plastics and fuels from plant sugars and waste rather than crude oil.
Design products to break down after use	Detergents and pesticides that biodegrade instead of building up in rivers.

Atom economy

A reaction can have a 100% yield (all the reactants react) and still make lots of waste, because some atoms end up in by-products nobody wants. Atom economy measures how much of the mass of the reactants ends up in the wanted product:

atom economy = (mass of wanted product ÷ total mass of reactants) × 100%

You calculate it from the balanced equation, using the relative formula masses (add up the relative atomic masses from the periodic table: H = 1, C = 12, N = 14, O = 16, Ca = 40).

Worked example: making quicklime

CaCO₃ → CaO + CO₂. The wanted product is calcium oxide.

The equation

CaCO₃ = 40 + 12 + 3 × 16 = 100. CaO = 40 + 16 = 56. (CO₂ = 12 + 2 × 16 = 44, and 56 + 44 = 100, so mass is conserved.)

Formula masses

56 ÷ 100 × 100% = 56%.

Atom economy

Nearly half the mass of limestone leaves the kiln as carbon dioxide. No catalyst or clever engineering can change that, which is why cement makers are looking at capturing the CO₂ or using other materials.

What it means

Two routes to the painkiller ibuprofen. The BHC route has a much higher atom economy, and its one by-product is collected and used.

Reactions that join molecules together, such as addition polymerisation and the Haber process, have 100% atom economy. Reactions that split molecules or swap parts always make by-products. A by-product isn't necessarily waste, though: if it can be sold or used, the process becomes greener.

InteractiveCount the wasted atoms

Try this

Choose "Quicklime from limestone" and check the atom economy is 56%, as in the worked example.
Compare the two ways of making ethanol. Which has the higher atom economy? Which uses a renewable raw material? Which would you choose?
Choose "Hydrogen by electrolysis". The atom economy is only 11%. Now turn on "count useful by-products". Why does it jump?
Compare the blast furnace with hydrogen ("green") steel. The atom economies are similar, so what is the real advantage of the hydrogen route?
Find all the reactions with 100% atom economy. What kind of reaction are they?

Recycling plastics: chemistry and choices

Resin identification codes tell recyclers which polymer an item is made of. They don't mean the item can be recycled where you live.

Different polymers melt at different temperatures and don't mix well when melted, a bit like oil and water, so recycled plastic is only useful if it is sorted by type. The resin identification code (the number in the triangle) tells recyclers which polymer an item is made of. Rigid PET, HDPE and polypropylene containers are the most widely recycled in NSW. Look for the Australasian Recycling Label on packaging, which tells you which bin each part belongs in.

Return and Earn, NSW's container deposit scheme, started in December 2017. You get 10 cents for most drink containers, and billions have been returned, cutting litter and giving recyclers clean, sorted PET and aluminium.
Soft plastics (bags, wrappers) jam kerbside sorting machines. The REDcycle supermarket collection scheme collapsed in 2022 when it was found that recyclers couldn't keep up and huge stockpiles had built up in warehouses. New collection programs have since restarted in some supermarkets.
Bans: NSW banned lightweight plastic shopping bags in June 2022, and items such as plastic straws, cutlery and polystyrene food containers in November 2022.
Chemical recycling breaks polymers back down into monomers or oils that can make new plastic. It can handle mixed and dirty plastics, but uses a lot of energy and is still being tested at scale.
Bioplastics such as PLA are made from plant sugars, but most only break down in industrial composting at around 60 °C. In a home compost or the ocean they last for years, and they contaminate PET recycling if put in the wrong bin.

Recycling is only part of the answer. Reducing and reusing come first, because even good recycling uses energy and each cycle shortens the polymer chains.

Using chemicals safely

Chemistry has learned hard lessons. Lead, mercury and cadmium were once common in paints, batteries and thermometers; they are now restricted because they build up in the body and damage the brain, kidneys and nerves. Today every chemical sold for work use comes with a safety data sheet (SDS) describing its hazards and how to handle, store and dispose of it, and labels use standard hazard pictograms. At home:

read the label, and never mix cleaning products: bleach and acid cleaners together release toxic chlorine gas, and bleach with ammonia makes toxic chloramines;
keep chemicals in their original containers, out of reach of children;
never pour paints, solvents, pool chemicals or pesticides down the drain. NSW councils run free Household Chemical CleanOut days, and used batteries and fluorescent globes go to collection points.

Careers that use chemistry

Chemistry underpins mining, energy, farming, medicine, food, water and manufacturing, so it leads to a huge range of jobs. New technologies keep creating new ones, such as battery recycling and green hydrogen.

Career	What they do	Typical pathway
Chemical engineer	Design and run large-scale plants, such as ammonia, lithium refining or water treatment	University engineering degree
Analytical chemist	Test water, food, soil, medicines and minerals for what they contain	University science degree
Environmental scientist	Monitor pollution, clean up contaminated sites, advise on regulations	University science degree
Materials scientist	Develop new polymers, alloys, composites, batteries and solar cells	University science or engineering, often a PhD
Metallurgist	Extract and refine metals from ores, a major field in Australian mining	University degree
Pharmacist or medicinal chemist	Dispense medicines or design and test new ones	University pharmacy or science degree
Forensic scientist	Analyse evidence such as drugs, fibres, paint and DNA for police	University science degree
Laboratory technician	Prepare samples, run tests and maintain equipment in schools, hospitals and industry	TAFE certificate or diploma
Process plant operator	Run and monitor equipment in refineries, smelters and food factories	Traineeship or TAFE

HSC Chemistry is the usual starting point for university pathways. Many careers combine chemistry with other skills, such as data science, law (patents and regulation), business or teaching.

Test yourself

The main idea of green chemistry is to
For the reaction C₂H₄ + H₂O → C₂H₅OH, the atom economy for ethanol is
Fermenting glucose, C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂, has an atom economy for ethanol of about (C₆H₁₂O₆ = 180, C₂H₅OH = 46)
The resin identification code on a plastic item tells you
You should never mix bleach with an acidic cleaner because it

Name the polymer for each resin code.

Sort each choice.

Atom measures how much of the reactants' mass ends up in the wanted product. Reactions that join molecules together, such as polymerisation, have 100% atom economy. Plants are a feedstock for fuels and plastics. A safety sheet describes a chemical's hazards. NSW's container deposit scheme is called Return and .

5 marks

Hydrogen can be made by steam reforming, CH₄ + 2H₂O → CO₂ + 4H₂, or by electrolysis, 2H₂O → 2H₂ + O₂. Calculate the atom economy for hydrogen in each (H = 1, C = 12, O = 16), and evaluate which method is greener.

Your answer