Understanding Recycling

Types of recycling

There are several different types of recycling

Type Description Examples
Re-use Further use is made of the product. May include some cleaning or re-working of material

Re-using carrier bags

Making sandals from old tyres

Resale of reconditioned equipment

Reconstitution (physical or mechanical recycling) The product is cleaned, shredded or melted, and the material used to manufacture something else

Making fleece filler/fibres from PET bottles

Using nylon pellets from old carpets to make car components

Purifying and re-using sulphuric acid

Manufacture of wood-substitute products from old plastic

Recycling of scrap steel and aluminium

Remanufacture (chemical recycling) Waste material is decomposed chemically, and the substances used to make new products

Making fresh caprolactam from old nylon carpets and using it to make new nylon for carpets

Decomposition of used sulphuric acid and use of products to make new acid

Chemical or thermal decomposition of plastics to create monomers and other intermediate chemicals, used as feedstock

Energy value recovery Burning the waste as a fuel to release energy

Burning rubber "crumb" from old tyres in cement kilns

Using plastic waste from nylon recycling as heat at other stages in the process


 

Open and Closed Loop Recycling

In some cases waste from one product is recovered and used in the manufacture of another, lower quality product. This may be referred to as open loop recycling. It reduces the amount of fresh feedstock needed, and the amount of waste going to landfill.
Sometimes waste material is used to manufacture the same product with no loss in quality - the process can theoretically be carried on indefinitely. In practice there will always be some loss of quantity so small amounts of "top-up" feedstock will be needed. This may be referred to as closed loop recycling.

 

diagram: open loop recycling of PET

Recycling Process Chemicals and Catalysts

Chemical manufacturers will always recycle materials used in processes as it makes good economic sense. Sulphuric acid, mentioned above, is routinely recycled.

image: sulphuric acid

The manufacture of nylon by conventional methods generates dinitrogen monoxide (N2O), an atmospheric pollutant. By using an alternative reaction, it is possible to recycle N2O within the process


During nitric acid manufacture some of the expensive platinum catalyst is vaporised. This is captured, and recovered for re-use

diagram: closed loop recycling of nylon

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