Industrial Chemistry

Industrial chemistry translates laboratory chemistry into large-scale, economical and safe production. A successful process must combine favourable thermodynamics and kinetics with cheap raw materials, energy efficiency, environmental compliance and reliable engineering. Modern industrial chemistry is dominated by a handful of bulk chemicals (sulfuric acid, ammonia, ethylene, chlorine, sodium hydroxide) that act as feedstocks for tens of thousands of derivative products.

Sulfuric acid — the Contact process

Sulfuric acid is the most-produced industrial chemical (over 250 million tonnes/year). Three steps:

1. Burn sulfur: S + O₂ → SO₂
2. Catalytic oxidation: 2 SO₂ + O₂ ⇌ 2 SO₃ (V₂O₅ catalyst at 450 °C, 1–2 atm)
3. Absorption: SO₃ + H₂SO₄ → H₂S₂O₇ (oleum); oleum + H₂O → 2 H₂SO₄

Why not SO₃ + H₂O directly? Because that reaction is highly exothermic and forms a fine acid mist that is dangerous and hard to collect.

Ammonia — the Haber–Bosch process

Ammonia synthesis was developed by Fritz Haber (Nobel 1918) and scaled up by Carl Bosch (Nobel 1931). It feeds roughly half the world's population via nitrogenous fertilisers.

N₂(g) + 3 H₂(g) ⇌ 2 NH₃(g) ΔH° = −92 kJ/mol

Conditions are a compromise dictated by thermodynamics and kinetics:

• High pressure (150–300 atm) favours the lower-mole side (NH₃).
• Moderate temperature (~450 °C) — high enough for adequate rate, low enough not to suppress equilibrium too much.
• Iron catalyst (promoted with K₂O, Al₂O₃) speeds the reaction.

Hydrogen comes from steam reforming of natural gas: CH₄ + H₂O → CO + 3 H₂.

Nitric acid — the Ostwald process

NH₃ is oxidised to nitric acid in three steps over a Pt-Rh gauze:

4 NH₃ + 5 O₂ → 4 NO + 6 H₂O (≈900 °C, Pt-Rh, exothermic) 2 NO + O₂ → 2 NO₂ 3 NO₂ + H₂O → 2 HNO₃ + NO

Nitric acid feeds explosives (TNT), dyes, fertilisers (ammonium nitrate) and nylon.

Petrochemicals

The world's bulk organic chemicals come from petroleum and natural gas:

1. Fractional distillation of crude oil separates fractions by boiling range: gases (C₁–C₄), naphtha (C₅–C₁₀), kerosene (C₁₀–C₁₆), gas-oil/diesel (C₁₄–C₂₀), bitumen.
2. Cracking (thermal or catalytic) breaks long alkanes into shorter, more useful ones, especially ethylene and propylene — the building blocks of plastics.
3. Reforming rearranges straight-chain naphtha into branched and aromatic compounds for high-octane petrol and feedstocks (benzene, toluene, xylenes).

Ethylene's downstream chemistry alone yields polyethylene, ethylene oxide (glycols, antifreeze), ethylene dichloride → vinyl chloride → PVC, and ethylbenzene → styrene → polystyrene.

Chlor-alkali industry

Electrolysis of brine (concentrated NaCl) produces three valuable products in one step:

2 NaCl + 2 H₂O → 2 NaOH + Cl₂ + H₂

Modern plants use membrane cells (Nafion ion-exchange membrane separating anode and cathode), having largely replaced older diaphragm and mercury cells. Chlorine is used for PVC, water disinfection, and bleach; NaOH for soap, paper and many syntheses.

Cement and construction materials

Portland cement is manufactured by heating limestone (CaCO₃) with clay (alumino-silicates) in a rotary kiln at ~1450 °C. The clinker is ground with gypsum (CaSO₄·2H₂O) to control setting time. The main hydration reactions involve tricalcium silicate (Ca₃SiO₅) and dicalcium silicate (Ca₂SiO₄), forming a calcium-silicate-hydrate gel that gives concrete its strength. Glass is melted silica with sodium and calcium oxides; steel is iron + carbon (~0.1–2 %) with alloying additions.

Green chemistry

Modern industrial chemistry follows the 12 principles of green chemistry (Anastas & Warner, 1998), aimed at minimising waste, hazard and energy use. Trends include:

• Replacing toxic solvents (CCl₄, benzene) with safer alternatives (water, scCO₂).
• Atom-economical reactions (Diels–Alder, click chemistry).
• Biocatalysts (immobilised enzymes) for stereoselective syntheses.
• Renewable feedstocks (bioethanol, plant oils) replacing petrochemicals.
• Carbon capture, utilisation and storage (CCUS) to mitigate CO₂ emissions.

The industrial chemist's craft is therefore as much about choosing the right conditions and minimising externalities as it is about getting the equation balanced.