From building blocks to plastics, fibres and detergents

By the end you will be able to

• Trace the main derivative trees from ethylene, propylene, the C4 stream and the aromatics to finished polymers and surfactants
• Explain the difference between chain-growth and step-growth polymerisation and how Ziegler-Natta and metallocene catalysts shape a polymer
• Compare high-pressure, gas-phase, slurry, solution and suspension processes by how they remove heat and what they make
• Describe how PET, nylon, acrylic and viscose fibres are made, and why melt spinning is cheaper than solution spinning
• Outline the LAB and LAS route and alcohol ethoxylation, and explain why detergents replaced soap
• Estimate the effect of selectivity, monomer use and plant scale on the cost of a commodity polymer

Contents

1. Part 1 Building blocks and their family trees

   A handful of molecules carry most of the tonnage of the polymer industry. Ethylene, propylene, the C4 stream and the aromatics benzene, toluene and xylenes come out of steam crackers and refineries, and each feeds a short list of large derivatives. Knowing these trees, and the yield of each step along them, explains most of what drives cost and demand further downstream.

   • Ethylene goes mostly into polyethylene, with three other big branches
   • Propylene's reactive methyl group gives it a wider spread of chemistry
   • Butadiene and the aromatics feed rubber, nylon and polyester
2. Part 2 How polymers are made

   A polymer is a long chain built from many small molecules called monomers. How the links form, what catalyst guides them, and how the reactor gets rid of the heat decide what chain comes out: its length, its branches and how regularly it is built. Those three features then decide whether the product is film, bottle, fibre or rubber.

   • Chains grow either one monomer at a time or by joining fragments
   • Catalysts decide what shape the chain takes
   • Reactor design is mostly about getting the heat out
   • Grades are set by chain length, branching and regularity
3. Part 3 The big bulk plastics

   Polyethylene, polypropylene, PVC, polystyrene and PET make up most plastic tonnage. They are commodities: many producers sell near-identical grades, so profit depends on cheap monomer, efficient conversion, large plants and integration with the cracker or refinery upstream. This part takes the processes and uses in turn and then looks at the cost structure.

   • Polyethylene and polypropylene are the cheapest and largest polymers
   • PVC and polystyrene hang on chlorine and benzene chains
   • Commodity polymer economics come down to monomer, scale and integration
4. Part 4 Synthetic fibres

   A fibre needs long, straight chains that can be lined up along its length, so only a few polymers qualify. Polyester leads by a wide margin, followed by nylon, polypropylene and acrylic, with viscose as the main fibre made from a natural polymer. How a polymer is spun, from a melt or from a solution, largely decides how cheap the fibre can be.

   • From paraxylene to polyester takes three plants
   • Melt spinning turns molten polymer into fibre at kilometres a minute
   • Nylon 66 and nylon 6 both start from benzene but differ in by-products
   • Acrylic and viscose are spun from solution, which costs more
5. Part 5 Detergents: from benzene, paraffins and ethylene oxide

   Detergents are a different use of the same building blocks. Instead of long chains, the industry makes molecules with an oily tail and a water-loving head. Linear alkylbenzene sulphonate, made from benzene and kerosene paraffins, is the workhorse; alcohol ethoxylates, made with ethylene oxide, are the main nonionic partner. The story of how they displaced soap shows chemistry, regulation and cost working together.

   • Detergents displaced soap because they keep working in hard water
   • Linear alkylbenzene joins kerosene paraffins to benzene, then takes on SO3
   • Ethoxylates and the formulation complete the detergent
6. Wrap-up Key terms, try it in the table, final quiz, sources