Industrial Chemistry notes

MDCAT Chemistry

Industrial chemistry applies chemical principles to manufacture useful materials such as adhesives, dyes, polymers, cement, fertilizers, petroleum products and chemicals. This chapter explains the preparation, properties, uses and environmental effects of these industrial products.

Industrial Chemistry and Macromolecules

Industrial chemistry deals with the large-scale manufacture of chemical substances and materials. Raw materials are converted into useful products by suitable chemical reactions and physical processes.

Many industrial materials are macromolecules. A macromolecule is a very large molecule formed by joining many small repeating units. The small units are called monomers, and the process of joining them is called polymerization.

Macromolecules are large molecules built from small repeating units called monomers.
A polymer is a substance made of many repeating monomer units.
Polymerization is the chemical process by which monomers combine to form polymers.
Natural polymers include cellulose, starch, proteins and natural rubber.
Synthetic polymers include polyethylene, PVC, nylon, Terylene and polystyrene.
Natural rubber is a hydrocarbon polymer because it contains carbon and hydrogen only.
Polymers may be classified as natural or synthetic, and as addition or condensation polymers.

Adhesives

Adhesives are substances used to join two surfaces by forming a strong bond between them. They may be natural or synthetic. Their bonding action depends on adhesion to the surfaces and cohesion within the adhesive.

Adhesives are used in woodwork, paper products, textiles, packaging, construction, footwear and furniture. A good adhesive should spread easily, form a strong bond and become sufficiently hard after application.

An adhesive is a substance used for joining two surfaces.
Natural adhesives include starch paste, dextrin, casein and animal glue.
Synthetic adhesives include polyvinyl acetate, epoxy resins and phenol-formaldehyde resins.
Polyvinyl acetate, commonly written as PVA, is a colourless, non-toxic resin with a characteristic odour and is widely used as an adhesive.
PVA is prepared by polymerization of vinyl acetate monomers.
Adhesives may be classified as water-based, solvent-based, hot-melt or chemically setting adhesives.
The strength of an adhesive bond depends on surface cleanliness, temperature, pressure, setting time and the nature of the surfaces.

Dyes and Their Classification

Dyes are coloured organic compounds that impart colour to materials such as fibres, leather, paper, food or hair. A dye should have colour and should be capable of attaching to the material being dyed.

Dyes are classified according to their chemical structure or method of application. Important classes include azo dyes, triphenylmethane dyes, acidic dyes, basic dyes, direct dyes, vat dyes and reactive dyes.

A dye is a coloured substance that can impart a reasonably permanent colour to a suitable material.
A chromophore is the colour-bearing group in a dye molecule.
An auxochrome is a group that intensifies colour and helps the dye attach to fibres.
Azo dyes contain the azo linkage, -N=N-.
Azo dyes are commonly prepared by coupling a diazonium salt with an aromatic compound.
Malachite green and rosaniline are triphenylmethane dyes.
Triphenylmethane dyes contain a triphenylmethane-based structure and are usually bright coloured compounds.
Dyes differ from pigments because dyes are generally soluble or can be made soluble during application, whereas pigments are insoluble coloured particles.

Methods of Dyeing and Hair Dyes

The method used to apply a dye depends on the type of dye and the material being coloured. Some dyes are applied from an aqueous solution, while others are formed inside the fibre or directly on the fabric.

Azotic dyeing is a method in which an insoluble azo dye is produced directly on the fabric. The fabric is treated with suitable components that react to form the coloured azo compound within the fibre.

Azotic dyeing produces a water-insoluble azo dye directly on the fabric.
In direct dyeing, the dye is applied directly from solution and is held by the fibre through attraction and other forces.
Vat dyes are applied in a soluble reduced form and are oxidized inside the fibre to produce the insoluble coloured dye.
Reactive dyes form chemical bonds with suitable fibres, especially cellulose fibres.
Temporary hair dyes contain relatively large molecules that remain on the hair shaft and are removed easily with one shampoo.
Permanent hair dyes produce colour inside the hair fibre and are not removed by a single shampoo.
Semi-permanent hair dyes remain for several washes and last longer than temporary dyes.

Polymers and Polymerization

Polymers are formed by addition polymerization or condensation polymerization. In addition polymerization, unsaturated monomers join without the elimination of a small molecule. In condensation polymerization, monomers having two or more functional groups join with the elimination of small molecules such as water or hydrogen chloride.

The properties of a polymer depend on the monomer, chain length, branching, cross-linking and intermolecular forces. Thermoplastics soften on heating and can often be reshaped, while thermosetting polymers become permanently hard after setting.

Addition polymers are formed from unsaturated monomers, usually containing a carbon-carbon double bond.
Polyethylene is formed by addition polymerization of ethene, CH2=CH2.
PVC is formed from chloroethene, also called vinyl chloride, CH2=CHCl.
The major environmental problem with many addition polymers is non-biodegradability.
The inert carbon backbone of many addition polymers resists attack by microorganisms.
Acrylonitrile has the formula CH2=CH-CN and is used to prepare polyacrylonitrile and some copolymers.
Nylon is a polymer that contains nitrogen because its repeating units contain amide groups.
Teflon is the trade name of polytetrafluoroethene, PTFE, formed from tetrafluoroethene.

Condensation Polymers, Polyesters and Fibres

Condensation polymers are prepared from monomers containing two or more reactive functional groups. Each step of chain formation is accompanied by the elimination of a small molecule, commonly water.

Polyesters contain ester linkages in their chains. They are useful in fibres, films, bottles, coatings and resins. Terylene is a well-known polyester fibre.

Polyesters are formed by condensation reactions involving alcohol and carboxylic acid functional groups.
Polyester resins are produced by the reaction of a dihydric alcohol with a dicarboxylic aromatic acid.
Terylene is formed from ethylene glycol and terephthalic acid.
Ethylene glycol is a dihydric alcohol with two hydroxyl groups.
Terephthalic acid is an aromatic dicarboxylic acid with two carboxyl groups.
The ester linkage in a polyester is -COO-.
Nylon is a condensation polymer containing repeating amide linkages.
Polyester fibres are strong, crease-resistant and commonly used in clothing and blended fabrics.

Cement, Fertilizers and Environmental Materials

Cement is a binding material used in construction. Portland cement is manufactured mainly from limestone and clay. The raw materials are heated strongly in a rotary kiln to form clinker, which is ground with a small amount of gypsum.

Fertilizers supply essential nutrients required for plant growth. Nitrogen is an essential plant nutrient and is present in many important fertilizers. Organic fertilizers are obtained from plant or animal materials.

The main raw materials for cement are limestone, CaCO3, and clay.
The rotary kiln used in cement manufacture has four zones: drying zone, heating zone, burning zone and cooling zone.
Gypsum is added to cement in about 2 to 3 percent quantity.
Gypsum controls the setting time of cement and prevents very rapid setting.
Organic fertilizers include farmyard manure, compost, bone meal and fish meal.
Inorganic fertilizers include urea, ammonium sulphate, ammonium nitrate and superphosphate.
Nitrogen is an essential element commonly supplied by fertilizers, but not every fertilizer contains nitrogen.
Newspaper can be recycled a limited number of times because paper fibres become shorter and weaker during repeated processing; the commonly stated textbook figure is about five times.

Petroleum, Catalytic Cracking and Industrial Chemicals

Petroleum is separated into useful fractions by fractional distillation. Large hydrocarbon molecules are converted into smaller and more useful molecules by cracking. Catalytic cracking gives petrol and other valuable products from heavier fractions.

The chlor-alkali process is an important industrial process. It uses electrolysis of concentrated aqueous sodium chloride, called brine, to produce chlorine, sodium hydroxide and hydrogen.

The primary purpose of catalytic cracking is to break large hydrocarbon molecules into smaller, more valuable molecules.
Catalytic cracking produces smaller alkanes, alkenes and branched hydrocarbons suitable for fuels and petrochemical manufacture.
Fluid catalytic cracking uses a finely divided solid catalyst.
In fluid catalytic cracking, the solid catalyst behaves like a fluid when it is aerated with vapour or gas.
Catalysts used in cracking are commonly solid acidic materials such as zeolites.
The chlor-alkali process involves electrolysis of brine, which is aqueous NaCl.
The three main products of the chlor-alkali process are chlorine, sodium hydroxide and hydrogen.
At the anode, chloride ions form chlorine. At the cathode, water forms hydrogen and hydroxide ions.

Related Industrial Organic Products

Several organic substances used in daily life are produced industrially. Nail polish contains a film-forming material, a plasticizer, pigments and volatile solvents. Hair dyes and pharmaceutical substances also depend on organic chemical manufacture.

Care is needed when identifying the function of each ingredient. A solvent helps dissolve and spread the material, while a film-forming agent remains after drying and forms the solid coating.

Ethyl acetate is a volatile solvent commonly used in nail polish and helps the polish spread and dry quickly.
Nitrocellulose is a common film-forming material in nail polish.
A film-forming agent produces the continuous solid film left after the solvent evaporates.
Solvents in nail polish evaporate after application and should not be confused with the main film-forming substance.
Substances that affect the central nervous system and induce sleep are called hypnotics or sleep-inducing drugs.
Tranquilizers reduce anxiety and nervous tension; some may also cause drowsiness or sleep.
Industrial chemistry requires distinguishing a product's trade name from its chemical name, such as Teflon for PTFE.

Key terms

Industrial chemistry: The branch of chemistry concerned with the manufacture of chemicals and useful materials on a large scale.
Macromolecule: A very large molecule formed from many smaller repeating units.
Monomer: A small molecule that joins with other molecules to form a polymer.
Polymer: A substance made of long chains or networks of repeating monomer units.
Polymerization: The process by which monomers chemically combine to form polymers.
Adhesive: A substance that joins two surfaces by forming a bond between them.
Dye: A coloured organic substance that imparts colour to a material.
Chromophore: The colour-bearing group responsible for absorption of visible radiation in a dye.
Auxochrome: A group that intensifies the colour of a dye and often helps it attach to fibres.
Azo dye: A dye containing the characteristic -N=N- azo linkage.
Triphenylmethane dye: A dye whose structure is based on a triphenylmethane framework, such as malachite green.
Addition polymerization: Polymerization in which unsaturated monomers join without eliminating a small molecule.
Condensation polymerization: Polymerization in which monomers join with elimination of small molecules such as water.
Polyester: A polymer containing repeated ester linkages in its main chain.
Nylon: A synthetic polyamide polymer containing nitrogen in its repeating amide groups.
Teflon: The trade name for polytetrafluoroethene, PTFE.
Catalytic cracking: The conversion of large hydrocarbon molecules into smaller hydrocarbons using heat and a catalyst.
Chlor-alkali process: The electrolysis of brine to produce chlorine, sodium hydroxide and hydrogen.
Gypsum: Calcium sulphate dihydrate added to cement to control its setting time.
Fertilizer: A natural or manufactured substance added to soil to supply essential plant nutrients.

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Chemistry shortcuts

Finding the limiting reactant and percentage composition

Convert every given mass or volume into moles first. The reactant that produces the least amount of the required product is the limiting reactant.

Write the balanced equation and calculate moles using n = mass/Mr.
Use the mole ratio to calculate the product. For percentage composition, use percentage = mass of element in one mole of compound divided by molar mass, multiplied by 100.
Example: Percentage of nitrogen in KNO3 = 14/101 × 100 = 13.86%.
Answer: 13.86% nitrogen.

Use gas volume at molar volume only when the gas conditions are stated or are standard conditions.

Using gas volume, pressure and temperature relations

At the same temperature and pressure, gas volume is directly proportional to the number of molecules. For changing conditions, use P1V1/T1 = P2V2/T2.

At constant temperature and pressure, divide or multiply the volume in the same ratio as the number of molecules.
Example: 10 mL H2 contains 2 × 10^3 molecules. Oxygen in 200 mL contains 20 × 2 × 10^3 = 4 × 10^4 molecules.
Answer: 4 × 10^4 molecules.
For a rigid container, increasing temperature increases molecular speed and mean free path if the gas remains in the same phase.

The direct volume to molecule ratio does not apply when temperature or pressure changes.

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