From building blocks to plastics, fibres and detergents: Key terms, quiz and sources

Understanding Chemicals / Module 6: From building blocks to plastics, fibres and detergents Wrap-up

From building blocks to plastics, fibres and detergents: review

Key terms

Monomer: A small molecule, such as ethylene or terephthalic acid, that links with others to form a polymer chain.
Chain-growth polymerisation: Polymerisation in which an active centre adds monomers one at a time in a fraction of a second; also called addition polymerisation.
Step-growth polymerisation: Polymerisation in which molecules with reactive end groups join repeatedly, often releasing water, so chains lengthen over time; also called condensation.
Selectivity: The share of a reacted feedstock that ends up as the wanted product rather than by-products.
Conversion per pass: The fraction of feed that reacts each time it goes through the reactor; the rest is separated and recycled.
Ziegler-Natta catalyst: A solid catalyst of titanium chloride with an aluminium alkyl that builds linear, regular polyolefin chains at low pressure.
Metallocene catalyst: A single-site catalyst with identical active sites that gives a narrow spread of chain lengths and even comonomer distribution.
Isotactic: Describes a polymer such as polypropylene in which every side group points the same way, allowing it to crystallise.
Comonomer: A second monomer added in small amounts, such as 1-butene in LLDPE, to adjust branching, density and toughness.
Crystallinity: The fraction of a polymer in which chains are packed in ordered regions; it raises stiffness, density and melting point.
Glass transition temperature (Tg): The temperature below which the amorphous parts of a polymer are glassy and brittle rather than rubbery.
Melt spinning: Making fibre by pumping molten polymer through a spinneret and cooling the filaments in air.
Spinneret: A plate with many fine holes through which melt or polymer solution is extruded to form filaments.
Drawing: Stretching spun filament several times its length to align and crystallise the chains, which gives the fibre strength.
Purified terephthalic acid (PTA): Terephthalic acid cleaned of 4-carboxybenzaldehyde by hydrogenation so it can be polymerised directly with glycol into PET.
Surfactant: A molecule with an oil-loving tail and a water-loving head that lowers surface tension and lifts oily soil into water.
Linear alkylbenzene sulphonate (LAS): The main synthetic anionic surfactant, made by sulphonating benzene carrying a straight C10-C14 chain.
Alcohol ethoxylate: A nonionic surfactant made by adding ethylene oxide units to a fatty alcohol.
Co-product: A second product made unavoidably in fixed ratio with the main one, such as acetone with phenol or styrene with propylene oxide.

Try it in the table

Open the Ethylene tile and compare its listed derivatives with the tree in Part 1: check whether polyethylene is still about 60% of demand and where Monoethylene glycol and Vinyl chloride monomer sit in its value chain.
On the Polypropylene tile, look at where production is growing and connect it to the on-purpose routes in Part 1; then open Propylene and see how much now comes from propane dehydrogenation.
Open Paraxylene, Purified terephthalic acid, PET resin and Polyester fibre in turn and use the 0.64 t PX per t PTA and 0.865 t PTA per t PET ratios from Part 4 to test whether their stated tonnages are consistent.
On the Caprolactam and Nylon (PA6, PA66) tiles, look for any mention of ammonium sulphate by-product or newer by-product-free routes, and compare with the 4.4 t per t figure in Part 4.
Open Linear alkylbenzene and Surfactants and check how the regional demand shown compares with the soap versus synthetic detergent pattern described in Part 5.
Compare the PVC tile with Chlorine and Caustic soda: note how PVC demand ties up chlorine and what that implies for caustic soda supply.

Final quiz

Which share of US ethylene went into the three polyethylenes in 2000, according to Wittcoff's table?

HDPE 25.2%, LLDPE 14.4% and LDPE 13.7% add to about 53%. About 90% is the share taken by all the listed major derivatives together.

Why could polypropylene not be made usefully until Ziegler-Natta catalysts arrived?

The allylic hydrogens transfer and terminate radical chains. Ziegler-Natta catalysts insert monomer at a metal site without touching them, and also make the chains isotactic.

In the gas-phase polyethylene process, what removes most of the heat of polymerisation?

Only 2-3% of the gas reacts per pass; the rest carries heat out and is cooled and recompressed.

A modern polypropylene catalyst gives 75,000 lb of polymer per lb of catalyst. What practical effect does this have on the plant?

At such low catalyst content the residue can stay in the polymer, and with 97% isotactic content the atactic removal step also disappears.

Why does PTA manufacture use acetic acid as the solvent?

The low solubility of terephthalic acid lets it separate from the intermediates. Some acetic acid is burned and must be replaced.

Viscose is spun at about 100 m/min while polyester partially oriented yarn is spun at 3,000-4,000 m/min. What mainly explains the difference?

Wet spinning depends on chemical reactions and diffusion in the bath; melt spinning only needs the filament to freeze in air, so it can run far faster.

Each tonne of caprolactam made by the classic route gives about how much ammonium sulphate?

Wittcoff gives 4.4 lb per lb: 1.6 from hydroxylamine sulphate, 1.1 from the oxime step and 1.7 from the Beckmann rearrangement.

Compared with oleum, what is the main advantage of air-diluted SO3 sulphonation of LAB?

Kent gives 95-98% product with 1-2% sulphuric acid for SO3, against about 90% with 6-10% spent acid for oleum, although SO3 plants cost more to build.

Next module: Scale, capacity and feedstock: which chemical plants get built →

Sources for this module

Wittcoff, H.A., Reuben, B.G. and Plotkin, J.S., Industrial Organic Chemicals, 2nd ed., Wiley, 2004 · Ch 1 pdf pp. 58-59; Ch 2 pdf pp. 97-99; Ch 3 pdf pp. 126-165; Ch 4 pdf pp. 193-237; Ch 5 pdf pp. 249-262; Ch 7 pdf pp. 293-327; Ch 8 pdf pp. 338-340; Ch 9 pdf pp. 346-362; Ch 15 pdf pp. 485-547
Kent, J.A. (ed.), Handbook of Industrial Chemistry and Biotechnology, 12th ed., Springer, 2012 · Ch 12 Manufactured textile fibers pdf pp. 429-462; Ch 15 Synthetic resins and plastics pdf pp. 582-601, 624; Ch 16 Rubber pdf pp. 630-640; Ch 36 Soap, fatty acids and synthetic detergents pdf pp. 1431-1463
Austin, G.T., Shreve's Chemical Process Industries, 5th ed., McGraw-Hill, 1984 · Ch 29 Soap and detergents pdf pp. 547-562; Ch 34 Plastic industries pdf pp. 658, 674-677; Ch 35 Man-made fiber and film industries pdf pp. 684-692
IEA, The Future of Petrochemicals: Towards more sustainable plastics and fertilisers, OECD/IEA, 2018 · pdf pp. 17-23, 39-40, 72-75
Brennan, D., Process Industry Economics, 2nd ed., Elsevier, 2020 · Ch 2 pdf pp. 55-56; Ch 7 pdf pp. 188-189