Chemical Industrial Technology

1

This section covers the manufacture of alkalies through the chlor-alkali industries producing soda ash, chlorine and caustic soda, the acid industries producing sulphuric, hydrochloric, nitric and phosphoric acids, industrial gases including carbon dioxide, dry ice, hydrogen, nitrogen, oxygen and acetylene, the production of synthesis gas and the gasification of coal, ammonia, and the manufacture of industrial solvents such as methanol, diethyl ether and acetone.

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The Chlor-Alkali Industry • Electrolysis of brine produces chlorine at the anode, hydrogen at the cathode and caustic soda in the cathode compartment, in the fixed ratio of about 1 tonne of chlorine to 1.1 tonnes of caustic soda — a coupling that dominates the economics of the whole industry, since neither product can be made without the other. • Three cell types, and their comparison is examined directly: • Mercury (Castner-Kellner) cell: gives the purest and most concentrated caustic (about 50 per cent, needing no evaporation), but the mercury is a severe environmental hazard and the process is being phased out worldwide. • Diaphragm cell: uses an asbestos or polymer diaphragm; gives a dilute caustic (10-12 per cent) contaminated with salt, requiring costly evaporation, but has a lower electrical energy demand. • Membrane cell: uses a cation-selective perfluorosulphonic acid membrane that passes sodium ions but not chloride.

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It gives high-purity caustic at about 32 per cent with the lowest total energy consumption and no mercury or asbestos, and is the modern standard for all new plants. • Solvay (ammonia-soda) process for soda ash:

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NaCl + NH₃ + CO₂ + H₂O → NaHCO₃ + NH₄Cl, the bicarbonate being filtered off and calcined to give Na₂CO₃, CO₂ and water.

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The ammonia is recovered with lime and recycled, so it is not consumed — it is the key feature of the process — and the by-product is calcium chloride, which has limited market value and is the main disposal problem.

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Limestone supplies both the carbon dioxide and, via the lime kiln, the lime for ammonia recovery. • The Solvay process cannot economically make potassium carbonate, because potassium bicarbonate is too soluble to precipitate — a favourite examination point.

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Sulphuric Acid and the Other Mineral Acids • Contact process for sulphuric acid, the largest-tonnage chemical in the world, proceeds in three steps: • 1.

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S + O₂ → SO₂ by burning sulphur (or roasting pyrites, or from smelter off-gas). • 2.

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2SO₂ + O₂ ⇌ 2SO₃ over a vanadium pentoxide (V₂O₅) catalyst on a silica support at about 400-450 °C, in four beds with interstage cooling, because the reaction is exothermic and reversible — the classic application of the equilibrium argument from Chapter 2. • 3.

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SO₃ + H₂SO₄ → H₂S₂O₇ (oleum), then dilution with water to give acid of the required strength. • The critical operating fact:

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SO₃ is absorbed in 98 per cent sulphuric acid, never directly in water, because absorption in water produces a fine, persistent acid mist that cannot be captured.

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Modern plants use double absorption (double contact), removing SO₃ between beds to shift the equilibrium and reach over 99.5 per cent conversion, which is also the principal emission control measure. • Platinum was the original catalyst but is readily poisoned by arsenic; vanadium pentoxide is cheaper and far more poison resistant, which is why it displaced platinum. • Hydrochloric acid is made by direct synthesis from hydrogen and chlorine (giving the purest acid), as a by-product of organic chlorination, or from the salt-cake reaction of sodium chloride with sulphuric acid (the Mannheim furnace). • Nitric acid — the Ostwald process, in three steps: catalytic oxidation of ammonia over platinum-rhodium gauze at about 900 °C and 4-10 bar to give NO; oxidation of NO to NO₂ on cooling; and absorption of NO₂ in water to give HNO₃ with NO recycled.

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The gauze catalyst loses platinum by volatilisation, recovered on palladium getter gauzes.

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Ordinary absorption gives about 60 per cent acid; concentrated (98 per cent) acid requires extractive distillation with sulphuric acid or magnesium nitrate, because nitric acid and water form a maximum-boiling azeotrope at about 68 per cent. • Phosphoric acid is made by the wet process (treated in 7.3) or by the furnace (thermal) process, which burns elemental phosphorus and gives a purer, food-grade acid at much higher energy cost.

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Industrial Gases Gas Principal source or process Notes Oxygen and nitrogen Cryogenic distillation of liquefied air;

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PSA and membranes for smaller scale Air is 78 % N₂, 21 % O₂, 0.93 % Ar; nitrogen boils at −196 °C, oxygen at −183 °C, so nitrogen comes off first Hydrogen Steam reforming of natural gas; partial oxidation; electrolysis; by-product of chlor-alkali Steam reforming over nickel catalyst at 700-900 °C is the dominant industrial route Carbon dioxide By-product of ammonia synthesis, fermentation, lime kilns and flue gas capture Recovered by absorption in amine solution and regenerated by heating Dry ice Solid CO₂, made by expanding liquid CO₂ to snow and pressing into blocks Sublimes at −78.5 °C at atmospheric pressure, leaving no liquid residue Acetylene Hydrolysis of calcium carbide; or from natural gas by partial oxidation or arc process CaC₂ + 2H₂O → C₂H₂ + Ca(OH)₂; cannot be compressed above about 2 bar alone, so it is dissolved in acetone on a porous filler Argon Side draw from the air separation column Inert shielding gas for welding and metallurgy • Synthesis gas (syngas) is a mixture of carbon monoxide and hydrogen and is the pivot of much of the heavy chemical industry.

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Routes are steam reforming of natural gas (CH₄ + H₂O ⇌ CO + 3H₂, endothermic, nickel catalyst), partial oxidation, autothermal reforming, and gasification of coal or biomass. • The water-gas shift reaction CO + H₂O ⇌ CO₂ + H₂ adjusts the hydrogen-to-carbon-monoxide ratio and is run in a high-temperature stage over iron-chromium catalyst followed by a low-temperature stage over copper-zinc. • Coal gasification: water gas (CO + H₂) is made by passing steam over incandescent coke, an endothermic reaction that cools the bed, so it is alternated with an air blow that reheats it — the blow-and-run cycle.

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Producer gas, made by passing air (or air and steam) through the bed, is much poorer in calorific value because it is diluted with nitrogen.

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Gasifier types are fixed (moving) bed, fluidized bed and entrained flow. • Chemicals from coal come chiefly from coal carbonisation to coke, which yields coke oven gas, coal tar (the source of benzene, toluene, naphthalene, anthracene, phenol and creosote) and ammoniacal liquor.

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Ammonia and Industrial Solvents • Haber-Bosch process:

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N₂ + 3H₂ ⇌ 2NH₃, exothermic with a decrease in moles, over a promoted iron catalyst (magnetite reduced to iron, with alumina and potassium oxide promoters) at about 400-500 °C and 150-300 bar.

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Single-pass conversion is only 15-25 per cent, so ammonia is condensed out and the unconverted gas recycled.

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High pressure favours the equilibrium, and the temperature is a compromise between a favourable equilibrium and an acceptable rate — the standard worked illustration of Chapter 2's argument.

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Sulphur and carbon monoxide poison the catalyst, so the syngas must be purified. • Methanol:

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CO + 2H₂ → CH₃OH over a copper-zinc oxide-alumina catalyst at about 250 °C and 50-100 bar — the modern low-pressure process, which replaced the old zinc-chromium high-pressure route. • Diethyl ether: by dehydration of ethanol with sulphuric acid at about 140 °C; raising the temperature to about 170 °C gives ethylene instead, which is the standard distinction.

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It is also a by-product of ethanol manufacture by ethylene hydration. • Acetone: overwhelmingly from the cumene process, in which benzene and propylene give cumene, which is oxidised to cumene hydroperoxide and cleaved with acid to give phenol and acetone together.

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Older routes are the dehydrogenation of isopropanol and the fermentation-based acetone-butanol-ethanol process.

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The cumene process is notable for producing two major products in fixed proportion, roughly 1 tonne of acetone per 1.6 tonnes of phenol.

1

This section covers the manufacture of Portland cement, its types and compounds, setting and hardening, other cements, refractories and their classification, the glass industry and the manufacture of ordinary and special glasses, and the surface coating industries producing paints, pigments, varnishes, enamels and lacquers.

2

Portland Cement • Raw materials: a calcareous material (limestone, chalk or marl) supplying lime, and an argillaceous material (clay or shale) supplying silica, alumina and iron oxide, in a ratio of roughly 4:1. • Manufacture is by the wet or dry process, the dry process now dominating because it uses far less fuel — no water has to be evaporated.

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Raw materials are crushed, ground, proportioned and fed to a rotary kiln that reaches about 1450 °C, where the charge partially fuses to form clinker.

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The clinker is cooled and ground with about 3-5 per cent gypsum. • The role of gypsum is examined directly: it retards the setting of the cement by controlling the very rapid hydration of C₃A.

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Without it, the cement would flash set and be unusable.

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Bogue compound Formula Abbreviation Typical % Role Tricalcium silicate 3CaO·SiO₂ C₃S (alite) 45-55 Early strength, up to 7 days; high heat of hydration Dicalcium silicate 2CaO·SiO₂ C₂S (belite) 20-30 Late strength, beyond 28 days; low heat of hydration Tricalcium aluminate 3CaO·Al₂O₃ C₃A 8-12 Flash set; highest heat; poor sulphate resistance Tetracalcium aluminoferrite 4CaO·Al₂O₃·Fe₂O₃ C₄AF 6-10 Contributes little strength; gives cement its grey colour • Setting and hardening: cement sets by hydration, a chemical reaction with water, not by drying — which is why concrete hardens under water and must be cured wet.

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This point is asked repeatedly.

8

The silicates hydrate to calcium silicate hydrate (C-S-H) gel, which provides essentially all the strength, and calcium hydroxide.

9

Hydration is exothermic, so mass concrete must be cooled to avoid thermal cracking. • Types of Portland cement: ordinary (OPC); rapid hardening (higher C₃S and finer grinding); low heat (higher C₂S and lower C₃A, for mass concrete such as dams); sulphate resisting (C₃A held below about 5 per cent);

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Portland pozzolana (blended with fly ash);

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Portland slag (blended with granulated blast-furnace slag); and white cement (iron content minimised). • Other cements: high alumina cement (very rapid strength gain and good chemical resistance, but loses strength by conversion in warm, damp conditions); expansive cement; and oil-well cements formulated for high temperature and pressure.

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Refractories • A refractory withstands high temperature without softening, and the standard measure is the pyrometric cone equivalent (PCE), the temperature at which a standard cone bends.

13

Other key properties are refractoriness under load, porosity, thermal shock (spalling) resistance, slag resistance and thermal conductivity. • Classification by chemical character, which is the examined scheme: • Acidic — silica, fireclay, zirconia; attacked by basic slags. • Basic — magnesite, dolomite, chrome-magnesite; used in steelmaking furnaces where the slag is basic. • Neutral — chromite, carbon, graphite, silicon carbide; resist both. • The governing rule: an acidic refractory must not be used with a basic slag, and vice versa, because they would react.

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Match the lining to the slag chemistry. • Porosity is important in two opposing ways: high porosity gives good insulation and thermal shock resistance but poor strength and poor slag resistance; low porosity gives the reverse.

15

Insulating refractories are deliberately made porous.

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Glass • Glass is an amorphous, supercooled liquid with no definite melting point; it softens progressively over a range, which is what makes it formable. • Raw materials: silica sand (the network former), soda ash (a flux, lowering the melting point), limestone (a stabiliser, giving chemical durability), and cullet (recycled broken glass, which reduces energy use).

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Without lime the product would be water glass, which is soluble. • Manufacture: melting at about 1500 °C in a tank furnace, refining to remove bubbles, forming (blowing, pressing, drawing, casting or floating), and annealing in a lehr to relieve internal stresses.

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Omitting the annealing step leaves stresses that cause spontaneous fracture — another point often asked. • Float process (Pilkington): molten glass is floated on a bath of molten tin, producing flat sheet with perfectly parallel, fire-polished surfaces without grinding or polishing.

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It is the universal process for window glass.

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Glass Composition feature Property and use Soda-lime glass Silica, soda, lime Ordinary windows, bottles, about 90 % of production; poor thermal shock resistance Borosilicate (Pyrex) Boron oxide replaces some alkali Low thermal expansion, high thermal shock resistance; laboratory ware and cookware Lead (flint) glass Lead oxide replaces lime High refractive index and brilliance; optical glass, tableware, radiation shielding Silica (quartz) glass Almost pure silica Extremely low expansion, very high temperature, ultraviolet transmitting; expensive Tempered (toughened) glass Rapid surface cooling puts the surface in compression Several times stronger; breaks into blunt fragments; cannot be cut after tempering Laminated glass Polyvinyl butyral interlayer between sheets Fragments adhere to the interlayer; windscreens and safety glazing Optical fibre Ultrapure silica with a graded refractive index Total internal reflection; telecommunications Surface Coatings • A paint consists of four components, and their functions are a standard question: • Pigment — provides colour, opacity (hiding power) and some corrosion protection.

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Titanium dioxide is the dominant white pigment because of its very high refractive index and hence opacity; it displaced white lead on toxicity grounds.

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Red lead and zinc chromate are anti-corrosive pigments, and carbon black, iron oxides and organic pigments supply colour. • Binder (vehicle or film former) — holds the pigment, forms the continuous film and determines adhesion, durability and gloss; it is the component that defines the paint type: drying oils, alkyds, acrylics, epoxies, polyurethanes. • Solvent (thinner) — adjusts viscosity for application and evaporates completely, contributing nothing to the dry film. • Additives — driers (cobalt, manganese and lead naphthenates, which catalyse oxidative curing), anti-skinning agents, dispersants, biocides, defoamers and flow agents. • Drying mechanisms: simple solvent evaporation (lacquers), oxidative cross-linking of unsaturated oils with atmospheric oxygen (oil paints and alkyds), or chemical curing between two reactive components (epoxies and polyurethanes). • Manufacture runs pre-mixing, dispersion or grinding of the pigment in a ball, roller, sand or bead mill to break agglomerates, let-down with the remaining binder and solvent, tinting, straining and filling.

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The grinding stage does not reduce the primary particle size; it disperses agglomerates and wets the pigment surface.

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Product Composition Character Paint Pigment + binder + solvent + additives Opaque, decorative and protective Varnish Resin + drying oil + solvent, with no pigment Transparent, glossy protective film; oleoresinous (long, medium or short oil) or spirit type Enamel Finely ground pigment in a varnish base Hard, smooth, glossy and durable; the gloss comes from the varnish medium Lacquer Cellulose nitrate or acrylic resin dissolved in a volatile solvent, with plasticiser Dries by evaporation alone, very fast; re-dissolvable; used on furniture and vehicles • Lacquer is distinguished from the others by drying purely by solvent evaporation with no chemical change, so it can be re-dissolved by its own solvent and re-coated without sanding.

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Lacquer oils — drying oils such as linseed, tung, castor and soya — are added to some formulations to improve flexibility and adhesion.

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The high solvent content is the reason lacquers face environmental restriction on volatile organic compounds.

1

This section covers the phosphate industries producing phosphoric acid by the wet process, normal and triple superphosphate, monoammonium phosphate and diammonium phosphate; the nitrogen industries producing synthetic ammonia, nitric acid, urea, ammonium nitrate and ammonium sulphate; and the potassium industries producing potassium chloride and potassium sulphate.

2

Fertilizer Fundamentals • The three primary nutrients are nitrogen, phosphorus and potassium, and fertilizer grade is quoted as the N-P-K analysis, giving the percentages of N, P₂O₅ and K₂O — note that phosphorus and potassium are expressed as the oxides by convention, not as the elements, which is a standard examination point. • A straight fertilizer supplies one nutrient; a complex or compound fertilizer supplies two or more in each granule; a mixed fertilizer is a physical blend. • Nitrogen promotes vegetative growth, phosphorus root development and flowering, and potassium disease resistance and water regulation.

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Phosphate Fertilizers • Raw material is phosphate rock, essentially fluorapatite Ca₅(PO₄)₃F, which is insoluble and so almost useless to plants as mined — the whole purpose of processing is to convert it to a soluble, plant-available form. • Wet process phosphoric acid:

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Ca₅(PO₄)₃F + H₂SO₄ + H₂O → H₃PO₄ + CaSO₄·nH₂O + HF.

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The calcium sulphate by-product is phosphogypsum, produced in very large quantity — roughly 5 tonnes per tonne of P₂O₅ — and its disposal is the major environmental issue of the industry.

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Fluorine is evolved as hydrogen fluoride and silicon tetrafluoride and must be scrubbed, often recovered as fluosilicic acid. • The dihydrate, hemihydrate and anhydrite processes differ in the crystal form of the calcium sulphate produced, which is controlled by temperature and acid concentration and governs filtration behaviour.

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Filtration of the gypsum is the rate-limiting step of the whole plant. • Wet process acid is impure and used for fertilizer; furnace (thermal) acid is pure and used for food and technical grades.

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Product Reaction / route Typical grade Notes Normal (single) superphosphate, SSP Phosphate rock + sulphuric acid 16-20 % P₂O₅ Cheapest; contains gypsum as a diluent; supplies sulphur and calcium as well Triple superphosphate, TSP Phosphate rock + phosphoric acid 44-48 % P₂O₅ No gypsum diluent, so roughly three times the concentration; no sulphur Monoammonium phosphate, MAP Phosphoric acid + 1 mol ammonia 11-52-0 Slightly acidic in reaction; good handling and storage Diammonium phosphate, DAP Phosphoric acid + 2 mol ammonia 18-46-0 The most widely used phosphate fertilizer; highest combined N and P₂O₅ • The SSP-versus-TSP distinction is a certainty in the examination: both are made from the same rock, but SSP uses sulphuric acid and retains the calcium sulphate formed, which dilutes the product, while TSP uses phosphoric acid and forms no gypsum, so its P₂O₅ content is about three times as high.

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The active constituent in both is monocalcium phosphate. • Nitrophosphate (Odda) process uses nitric acid instead of sulphuric to digest the rock, avoiding gypsum production altogether and supplying nitrogen at the same time.

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Nitrogen Fertilizers • Ammonia (Haber-Bosch, covered in 7.1) is the parent of the entire nitrogen fertilizer industry — urea, ammonium nitrate, ammonium sulphate and the ammonium phosphates all derive from it, as does nitric acid via Ostwald. • Urea is made from ammonia and carbon dioxide in two steps:

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2NH₃ + CO₂ → NH₂COONH₄ (ammonium carbamate, fast and strongly exothermic), then NH₂COONH₄ → NH₂CONH₂ + H₂O (dehydration, slow and endothermic), at about 180-200 °C and 150-200 bar.

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The carbon dioxide comes from the ammonia plant itself, so the two are always built together. • Urea is the most important solid nitrogen fertilizer because it has the highest nitrogen content of any solid — 46 per cent N.

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It is finished as prills or granules.

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Biuret, formed when urea is overheated, is phytotoxic and must be held below about 1 per cent — a regularly examined detail. • Ammonium nitrate:

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NH₃ + HNO₃ → NH₄NO₃, 34 per cent N, half in the readily available nitrate form and half as ammonium.

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It is strongly hygroscopic, so it is coated and conditioned, and being an oxidiser it presents a serious explosion hazard, which is why its storage and transport are tightly regulated.

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Calcium ammonium nitrate (CAN) dilutes it with limestone for safer handling. • Ammonium sulphate:

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21 per cent N plus 24 per cent sulphur, made by neutralising sulphuric acid with ammonia, as a by-product of caprolactam manufacture, or from coke-oven gas.

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It is physiologically acidic, so it acidifies the soil over time — useful on alkaline soils but a drawback elsewhere. • Slow and controlled release products — sulphur-coated or polymer-coated urea, urea-formaldehyde, and urease and nitrification inhibitors — reduce losses by volatilisation, leaching and denitrification, which can otherwise account for a large fraction of the nitrogen applied.

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Potassium Fertilizers • Potassium chloride (muriate of potash, KCl) supplies about 60 per cent K₂O and is by far the cheapest and most widely used potash fertilizer, accounting for the great majority of consumption.

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It is produced from sylvinite ore (KCl with NaCl) by fractional crystallisation exploiting the different temperature dependence of the two solubilities, or by froth flotation with amine collectors, or by solution mining. • Potassium sulphate (sulphate of potash, K₂SO₄) supplies about 50 per cent K₂O and is more expensive but chloride free, which matters for chloride-sensitive crops such as tobacco, potatoes, grapes and most fruit.

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It is made by the Mannheim process, reacting potassium chloride with sulphuric acid, or from natural langbeinite. • Potassium nitrate supplies both potassium and nitrogen in fully available forms and is chloride free, but is expensive and is used mainly in horticulture and fertigation.

1

This section covers pulp and pulping processes with black liquor recovery and paper making, sugar from cane and its refining, starch, industrial microbial processes and edible oils including ethyl alcohol, citric acid, vegetable oils and animal fats, soaps and detergents with glycerine recovery, fibre and rubber industries including polyamides, polyesters, rayon and SBR, and the classification and manufacture of dyes and pesticides.

2

Pulp and Paper • Wood consists of cellulose (the fibre itself, about 40-50 per cent), hemicellulose (20-30 per cent) and lignin (20-30 per cent), which binds the fibres together.

3

The whole object of chemical pulping is to dissolve the lignin and free the cellulose fibres with as little damage to them as possible.

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Process Chemicals Characteristics Kraft (sulphate) Sodium hydroxide and sodium sulphide (white liquor) The dominant process; strong pulp; tolerates any wood species; efficient chemical recovery; odour problem from mercaptans Sulphite Calcium, magnesium, sodium or ammonium bisulphite Brighter, more easily bleached pulp but weaker; limited to certain species; recovery harder Soda Sodium hydroxide alone Used for straws, bagasse and non-wood fibres Mechanical (groundwood) None; logs ground against a stone or refined Very high yield (90-95 %) but lignin remains, so paper yellows; newsprint Chemi-mechanical Mild chemical pre-treatment then refining Intermediate yield and strength • Kraft chemical recovery — the feature that makes the process economic, and a standard examination topic: the spent black liquor is concentrated in multiple-effect evaporators and burned in a recovery furnace.

5

There, the organic matter provides all the plant's steam, while the inorganic chemicals collect as a smelt of sodium carbonate and sodium sulphide.

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The smelt is dissolved to give green liquor, which is causticised with lime to convert carbonate to hydroxide, regenerating the white liquor; the calcium carbonate formed is calcined in a lime kiln to recover the lime.

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Both the chemicals and the energy are thus recovered, and the recovery furnace is normally the largest single item in the mill. • Papermaking then proceeds through beating and refining (which fibrillate the fibres and develop bonding), the addition of fillers such as clay and calcium carbonate for opacity and smoothness, sizing with rosin or synthetic agents to control water penetration, and formation on the wire of a Fourdrinier machine followed by pressing, drying and calendering.

8

Bleaching with chlorine dioxide, oxygen, ozone or peroxide has largely replaced elemental chlorine to avoid dioxin formation.

9

Sugar and Starch • Cane sugar manufacture: milling or diffusion to extract juice; clarification by liming and heating (the defecation process), with sulphitation or carbonatation for whiter sugar; concentration in multiple-effect evaporators; crystallisation in vacuum pans; separation in centrifuges; and drying.

10

Molasses is the final mother liquor from which no more sugar can economically be crystallised, and bagasse, the fibrous residue, is burned to raise all the steam and power the mill needs — so a cane sugar mill is normally energy self-sufficient. • Refining of raw sugar proceeds by affination (washing the crystals), melting, clarification with phosphoric acid or carbonation, decolourisation with bone char, granular carbon or ion-exchange resin, and recrystallisation. • Starch is obtained by wet milling of maize, wheat, potato or cassava, separating the starch granules from protein, fibre and germ.

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It is converted to glucose syrup and dextrose by acid or enzymatic hydrolysis, and to high-fructose syrup with glucose isomerase, and modified physically and chemically for use as a thickener, adhesive and paper additive.

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Industrial Microbial Processes and Edible Oils • Ethyl alcohol is produced by fermentation of molasses, cane juice, starch hydrolysate or lignocellulosic sugars with Saccharomyces cerevisiae, followed by distillation.

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Rectified spirit is about 95 per cent ethanol, which is the azeotropic limit; absolute alcohol requires azeotropic or extractive distillation, or molecular sieve dehydration — the point already met in Chapter 6.

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The synthetic route by direct hydration of ethylene over phosphoric acid catalyst is used where petrochemical feedstock is cheap. • Citric acid is made by submerged fermentation of molasses or glucose with Aspergillus niger, and recovered classically by precipitation as calcium citrate followed by acidification with sulphuric acid, or by solvent extraction.

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Deficiency of trace metals, particularly iron and manganese, is essential for a high yield. • Vegetable oils are recovered by mechanical expelling for high-oil seeds and by solvent extraction with hexane for low-oil seeds such as soya, usually in combination.

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Refining then runs through degumming, neutralisation of free fatty acids with caustic, bleaching with activated earth, and deodorisation by steam stripping under vacuum. • Hydrogenation converts liquid oils to solid fats over a nickel catalyst by saturating carbon-carbon double bonds — the basis of vanaspati and margarine.

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Partial hydrogenation also produces trans fatty acids, which are now restricted on health grounds, so full hydrogenation with interesterification has largely replaced it.

18

The iodine value measures unsaturation and falls as hydrogenation proceeds; the saponification value measures average molecular weight.

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Soaps and Detergents • Soap is made by saponification — the alkaline hydrolysis of a fat or oil with caustic soda, giving soap and glycerine.

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Glycerine is a valuable by-product recovered from the spent lye by evaporation and distillation, and it is asked about directly. • Hot process (kettle) boiling with graining out by salt separates the soap from the lye; modern plants use continuous fat splitting with high-pressure steam to give fatty acids and glycerine, followed by neutralisation of the acids, which gives a purer glycerine. • Sodium soaps are hard and potassium soaps soft; toilet soap is milled and plodded to develop a fine crystalline structure, with superfatting, perfume and titanium dioxide added. • Detergents are synthetic surfactants, and their decisive advantage is that they do not form insoluble scum with the calcium and magnesium ions of hard water, whereas soap does — the standard comparison question. • Surfactant classes: anionic (linear alkylbenzene sulphonate, the workhorse), cationic (quaternary ammonium, used as fabric softeners and disinfectants), non-ionic (ethoxylates, low foaming) and amphoteric.

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Branched alkylbenzene sulphonate was replaced by the linear form because the branched chain resists biodegradation and caused river foaming. • A formulated detergent powder contains surfactant, builders (which sequester hardness ions — sodium tripolyphosphate traditionally, now often zeolites and citrates because phosphates cause eutrophication), enzymes, optical brighteners, bleach, anti-redeposition agents and fillers.

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Fibres, Rubber, Dyes and Pesticides Product Type / chemistry Notes Nylon 6,6 Polyamide by condensation of hexamethylene diamine and adipic acid Two monomers, each of six carbons, hence the name Nylon 6 Polyamide by ring-opening of caprolactam A single monomer; similar properties to nylon 6,6 Polyester (PET) Condensation of ethylene glycol with terephthalic acid or its dimethyl ester The largest-volume synthetic fibre; also bottles and film Rayon (viscose) Regenerated cellulose: cellulose + NaOH + CS₂ → xanthate, spun into acid A regenerated natural polymer, not a synthetic one Acrylic Polyacrylonitrile Wool-like; also the precursor of carbon fibre SBR Copolymer of about 75 % butadiene and 25 % styrene by emulsion or solution polymerisation The largest-volume synthetic rubber; tyres; cheaper and more wear resistant than natural rubber but lower resilience • Vulcanisation, discovered by Goodyear, cross-links rubber chains with sulphur, converting a soft thermoplastic material into a strong, elastic one with far better temperature stability.

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More sulphur gives harder rubber, up to ebonite at about 30 per cent. • Dyes are classified by chemical constitution — azo (much the largest class, containing the −N=N− group), anthraquinone, indigoid, triphenylmethane, phthalocyanine — or by application — direct, reactive, vat, disperse, acid, basic, sulphur and mordant.

24

A dye needs a chromophore, the group that absorbs light, and an auxochrome, which deepens the colour and provides affinity for the fibre.

25

Vat dyes are insoluble and must be reduced to a soluble leuco form, applied, and re-oxidised in the fibre — indigo on denim being the familiar case — which gives outstanding fastness.

26

Reactive dyes form a covalent bond with cellulose. • Pesticides are classified by target — insecticide, herbicide, fungicide, rodenticide, nematicide — and by chemistry — organochlorine (DDT, now banned under the Stockholm Convention for persistence and bioaccumulation), organophosphate (malathion, parathion; cholinesterase inhibitors, less persistent but acutely toxic), carbamate, pyrethroid (synthetic analogues of natural pyrethrins, low mammalian toxicity) and neonicotinoid (systemic, restricted in some jurisdictions over pollinator harm).

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Formulations are dusts, wettable powders, emulsifiable concentrates, granules and suspension concentrates.

28

Pesticide regulation changes frequently and approvals differ between countries, so any specific product status must be checked against current national rules.

1

This section covers petroleum exploration and the constituents of petroleum, refinery processes including crude distillation, conversion processes such as catalytic cracking and catalytic reforming, the petrochemical industry with its precursors and the manufacture of ethylene and propylene, and polymer-based industries covering engineering plastics, commercial resins, thermoplastics such as PE, PP and PVC, and the phenol-, urea- and melamine-formaldehyde and epoxy resins.

2

Petroleum and Its Constituents • Crude oil is a mixture of paraffins (alkanes), naphthenes (cycloalkanes), aromatics and, in small amounts, olefins, together with sulphur, nitrogen, oxygen and metal compounds.

3

Crude oil contains essentially no olefins as produced; they are created by cracking — a point worth holding. • Classification: light or heavy by API gravity (°API = 141.5/SG − 131.5, so a higher API means a lighter crude); sweet or sour by sulphur content, with the dividing line at about 0.5 per cent.

4

Light sweet crude commands the highest price because it yields more of the valuable light products and needs less desulphurisation. • Exploration uses seismic surveying, gravity and magnetic methods, and exploratory drilling, followed by well logging.

5

Recovery proceeds through primary (natural pressure), secondary (water or gas injection) and tertiary or enhanced recovery (thermal, chemical or miscible gas methods).

6

Crude Distillation Fraction Approximate boiling range Principal use Fuel gas and LPG Below about 20 °C Refinery fuel, bottled gas, petrochemical feed Light and heavy naphtha 20-200 °C Gasoline blending, reformer feed, petrochemical cracker feed Kerosene 175-275 °C Jet fuel, illuminating oil Gas oil (diesel) 250-375 °C Diesel fuel, heating oil, cracker feed Atmospheric residue Above about 375 °C Feed to the vacuum unit Vacuum gas oil 375-550 °C equivalent Feed to catalytic cracking and hydrocracking Vacuum residue Above 550 °C equivalent Bitumen, fuel oil, coker or visbreaker feed • The crude is first desalted, then heated in a furnace and flashed into the atmospheric tower, which has side strippers for each product cut and pump-around circuits for heat recovery. • Vacuum distillation follows because the residue would crack thermally if heated further at atmospheric pressure — reducing the pressure lowers the boiling temperature and allows the heavier fractions to be separated without decomposition.

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This is the standard reason asked for in the examination.

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Conversion Processes Process Purpose Conditions and catalyst Thermal cracking / visbreaking Reduce viscosity of residue Heat alone, about 450-500 °C; no catalyst Fluid catalytic cracking (FCC) Convert vacuum gas oil to gasoline and olefins Zeolite catalyst, about 500 °C, near atmospheric pressure; continuous catalyst regeneration by burning off coke Hydrocracking Convert heavy feed to middle distillate with hydrogen Bifunctional catalyst, 350-450 °C and 100-200 bar; produces saturated, low-sulphur products Catalytic reforming Raise the octane number of naphtha Platinum-rhenium on chlorided alumina, about 500 °C and 10-30 bar; hydrogen is a valuable by-product Alkylation Combine small olefins with isobutane to make high-octane gasoline Sulphuric or hydrofluoric acid catalyst at low temperature Isomerisation Convert straight-chain to branched paraffins Raises octane of light naphtha Coking (delayed or fluid) Convert vacuum residue to lighter products plus petroleum coke About 500 °C; the ultimate route for the heaviest residue Hydrotreating Remove sulphur, nitrogen and metals; saturate olefins Cobalt-molybdenum or nickel-molybdenum on alumina with hydrogen • Keep the three main conversion ideas clearly apart, because questions turn on the distinction: cracking breaks large molecules into smaller ones; reforming rearranges molecules of the same size, converting paraffins and naphthenes into aromatics to raise the octane number, and releases hydrogen; alkylation joins small molecules into larger ones. • Catalytic cracking versus thermal cracking: the catalytic route gives a higher yield of gasoline with a higher octane number, more branched and aromatic products, less gas and less coke, and operates at lower temperature. • The FCC unit is the heart of a modern refinery; its distinguishing feature is that the catalyst circulates continuously between reactor and regenerator, where the coke deposited on it is burned off, supplying the heat the endothermic cracking reaction needs — a neat example of heat integration. • Octane number measures resistance to knock: iso-octane is defined as 100 and n-heptane as 0.

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Branched and aromatic hydrocarbons have high octane; straight-chain paraffins have low octane.

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Cetane number measures the opposite quality for diesel — ease of ignition — so straight-chain paraffins have a high cetane number and aromatics a low one.

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A good gasoline component is therefore generally a poor diesel component, which is a favourite examination point.

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Petrochemicals • The primary petrochemical building blocks are the olefins (ethylene, propylene, butadiene) and the aromatics (benzene, toluene, xylenes, known as BTX). • Ethylene and propylene are made by steam cracking (pyrolysis) of ethane, propane, naphtha or gas oil at 800-900 °C with steam as a diluent and a residence time of under a second, followed by rapid quenching.

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The feedstock determines the product slate: ethane gives predominantly ethylene, while naphtha gives a wider spread including propylene, butadiene and aromatics.

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Propylene also comes from FCC off-gas and from dedicated propane dehydrogenation. • Ethylene is the largest-volume organic chemical in the world, going to polyethylene, ethylene oxide and glycol, vinyl chloride, styrene and ethanol.

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Aromatics come from catalytic reforming and from pyrolysis gasoline, and are separated by extractive distillation and adsorption.

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Polymers and Resins • The mechanism distinction, which is the most examined idea in the section: addition (chain-growth) polymerisation adds monomer units to a growing chain without eliminating anything, so the polymer has the same empirical formula as the monomer, and it requires an unsaturated monomer.

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Condensation (step-growth) polymerisation joins monomers with the elimination of a small molecule, usually water, and requires monomers with two or more functional groups.

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Polyethylene, PP, PVC and polystyrene are addition polymers; nylon, polyester, and the formaldehyde and epoxy resins are condensation polymers. • Thermoplastic versus thermoset: thermoplastics consist of linear or branched chains held by weak intermolecular forces, so they soften on heating and can be remoulded and recycled repeatedly.

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Thermosets are three-dimensionally cross-linked, so once cured they cannot be softened or remoulded; they char and decompose instead. • Polymerisation techniques: bulk, solution, suspension and emulsion — emulsion polymerisation gives high molecular weight at high rate with good heat removal and is used for SBR and PVC.

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Polymer Monomer and route Properties and use LDPE Ethylene, high pressure free radical; branched chains Flexible, low density, film and packaging HDPE Ethylene, Ziegler-Natta or chromium catalyst at low pressure; linear Rigid, stronger, higher density; bottles, pipe, crates Polypropylene Propylene, Ziegler-Natta; isotactic High melting point, fatigue resistant; fibres, automotive, housewares PVC Vinyl chloride, suspension polymerisation Rigid or, with plasticiser, flexible; pipe, cable, flooring; the plasticiser content decides which Polystyrene Styrene Clear, brittle, easily foamed; packaging and insulation PET Ethylene glycol + terephthalic acid, condensation Fibre, bottle and film; readily recycled Engineering plastics Polycarbonate, PA, POM, PBT, PPO, PTFE High strength, dimensional stability and heat resistance; replace metals • Thermosetting resins: • Phenol-formaldehyde (Bakelite) — the first fully synthetic plastic.

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Novolac uses excess phenol with an acid catalyst and needs a curing agent such as hexamine; resol uses excess formaldehyde with a base catalyst and cures on heating alone.

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Used for electrical fittings, laminates and foundry binders; it is dark coloured, so it cannot be made in light shades. • Urea-formaldehyde — light coloured and cheaper than phenolic, used for particle-board adhesive, electrical fittings and moulding powder, but with poorer water and heat resistance and a tendency to release formaldehyde. • Melamine-formaldehyde — the best of the three in hardness, water resistance, heat resistance and surface quality, and light coloured; used for tableware and decorative laminates.

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The ranking in performance and cost is phenolic < urea < melamine, with melamine highest in both. • Epoxy resins — made from bisphenol A and epichlorohydrin, cured with amine or anhydride hardeners.

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They give outstanding adhesion, chemical resistance and very low cure shrinkage, and are used as adhesives, protective coatings, and the matrix of fibre-reinforced composites.

1

This section covers the introduction to nanoparticles and nanostructured materials, the classification of nanomaterials, and the application of nanomaterials and nanotechnology devices in daily life, in medicine, and in agriculture and the food industry.

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Definitions and the Origin of Nanoscale Behaviour • Nanotechnology is the understanding and control of matter at dimensions of roughly 1 to 100 nanometres, where 1 nm = 10−9 m.

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A nanomaterial has at least one external dimension, or an internal structure, in this range. • Why properties change at the nanoscale — the two reasons that must be given: • 1.

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The surface-area-to-volume ratio rises sharply as particle size falls, so a much larger fraction of the atoms lies at the surface.

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Since surface atoms are more reactive than those in the bulk, catalytic activity, adsorption capacity, solubility and reactivity all increase dramatically.

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Halving the particle diameter doubles the specific surface area. • 2.

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Quantum confinement: when the particle becomes comparable in size to the wavelength of the electron, the electronic energy levels become discrete and size dependent, so optical and electronic properties change with size.

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Quantum dots emit different colours purely as a function of their diameter — smaller dots emit at shorter wavelengths — which is the most striking illustration. • Consequences: gold, inert in bulk, is an excellent catalyst as nanoparticles; gold nanoparticles appear red rather than gold; the melting point of a nanoparticle falls markedly below the bulk value; and mechanical strength rises as grain size decreases.

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Classification of Nanomaterials Class Dimensions in the nanorange Examples Zero-dimensional (0-D) All three dimensions below 100 nm Nanoparticles, quantum dots, fullerenes (C₆₀) One-dimensional (1-D) Two dimensions in the nanorange, one extended Nanotubes, nanowires, nanorods, nanofibres Two-dimensional (2-D) One dimension in the nanorange, two extended Graphene, thin films, nanoplates, nanocoatings Three-dimensional (3-D) Bulk material built from nanoscale units Nanocrystalline solids, nanocomposites, aerogels • By chemistry, nanomaterials are grouped as carbon based (fullerenes, carbon nanotubes, graphene), metal and metal oxide (gold, silver, titanium dioxide, zinc oxide, iron oxide), semiconductor quantum dots, polymeric (dendrimers, micelles) and composite. • The carbon allotropes are asked about directly: fullerene C₆₀ is a closed cage of 60 carbon atoms; a carbon nanotube is a rolled sheet of graphene with exceptional tensile strength — many times that of steel at a fraction of the weight — and conductivity that is metallic or semiconducting depending on the chirality of the roll; graphene is a single atomic layer of carbon in a hexagonal lattice, the strongest material measured and an excellent conductor of heat and electricity. • Two synthesis philosophies: top-down, breaking bulk material down (ball milling, lithography, laser ablation), which is simpler but gives less uniform products; and bottom-up, assembling from atoms and molecules (sol-gel, chemical vapour deposition, self-assembly, colloidal and precipitation methods), which gives better control of size and structure.

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The distinction between the two is a standard question. • Characterisation uses electron microscopy (SEM and TEM), atomic force microscopy, X-ray diffraction for crystallite size, dynamic light scattering for particle size in suspension, and BET for surface area.

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Applications Field Application Basis Daily life Self-cleaning and anti-fogging glass; stain-resistant textiles TiO₂ photocatalysis and superhydrophobic nanostructured surfaces Sunscreens using ZnO and TiO₂ nanoparticles Block ultraviolet while being transparent rather than white Scratch-resistant coatings, antibacterial silver in textiles and appliances Nanocomposite hardness; silver ion release Lithium-ion battery electrodes, supercapacitors, fuel cell catalysts High surface area and short diffusion path Electronics Sub-10 nm transistors, memory, displays, quantum dot screens Quantum confinement and nanofabrication Medicine Targeted drug delivery by liposomes, dendrimers and polymer nanoparticles Delivers the drug to the diseased tissue, reducing dose and side effects Contrast agents for MRI using superparamagnetic iron oxide Magnetic behaviour at the nanoscale Magnetic hyperthermia for tumours; nanoparticle-based diagnostics and biosensors Local heating in an alternating field; high surface for capture Tissue engineering scaffolds; antimicrobial wound dressings Nanofibre architecture mimics the extracellular matrix Agriculture and food Nano-fertilizers and nano-pesticides with controlled release Less chemical applied for the same effect; lower runoff Nanosensors for soil moisture, nutrients and pathogen detection High sensitivity from large surface area Nanocomposite food packaging with barrier and antimicrobial properties Clay nanocomposite barrier; silver or zinc oxide antimicrobials Nanoencapsulation of vitamins, flavours and nutraceuticals Protects the ingredient and improves bioavailability Environment Water treatment by nano-adsorbents, nano-membranes and photocatalysis High capacity and catalytic destruction of pollutants Risks and Responsible Use • The very properties that make nanomaterials useful also raise concerns: high reactivity, the ability of very small particles to cross biological barriers including the lung and potentially the blood-brain barrier, persistence in the environment, and the difficulty of detecting and measuring them. • Nanotoxicology studies these effects, and the consistent finding is that toxicity depends on size, shape, surface chemistry and solubility, not on chemical composition alone — so a material that is safe in bulk cannot be assumed safe at the nanoscale.

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This is the key conceptual point. • Occupational exposure control relies on containment, local exhaust ventilation with HEPA filtration and appropriate personal protection, since conventional exposure limits set on a mass basis may be inappropriate when the biologically relevant dose metric is surface area or particle number. • Regulation of nanomaterials is developing and differs considerably between jurisdictions, particularly for food, cosmetics and medicines, so any specific requirement must be checked against current national rules.