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Revision:Chemical Industries - E (Standard)

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TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Chemistry > Chemical Industries - E (Standard)

E.1 Initial overview

E.1.1 : Sources of materials

Raw materials: Natural substances which can be converted by chemical processes into useful products.

By-Products: Substances produced as a result of a chemical process, but not the major (or important) product.

Waste products: Substances produced that have no value/are dangerous and must be disposed of.

Minerals: Naturally occurring inorganic substances ... metals and their ores.

Air: O₂, N₂, Ar

Petroleum: Coal, Oil etc...

E.1.2 : Factors influencing positions for chemical industry establishment

Must comply with regulations (ie environmental restrictions), good transport access to market and raw materials, availability and cost of labour, land, plant, equipment and energy source (electricity). Availability and cost of raw materials.

E.1.3 : Specialty vs Bulk chemicals

Specialty: Drugs, Many organic substances (w/ specific uses)

Bulk: Sulphuric acid, Nitrogen, Oxygen, Ammonia, Sodium hydroxide, Chlorine

E.2 Principles of extraction and production

E.2.1

Metals are rarely found free in nature, and have to be extracted and processed before they can be used ... with the exception of Gold and some other stuff like that.

E.2.2 : Physical separation and purification from ores

Concentration of ores: Froth, flotation etc

Separation: Filtration, Centrifuge type stuff, magnetic properties, chromatography

Purification: Zone refining (explained later)

E.2.3

Chemical principles in the extraction of useful substance from raw materials.

Changing into suitable form for oxidation:

$\mathsf{ZnS + O_2 \longrightarrow ZnO + SO_2}$ .

Reduction to metal, by electrolysis or chemical reaction (blast furnace)

Also consider: Reduction (Iron), electrolysis (Al₂, Al ), equilibrium (Contact and Harber), energy requirements (electrolysis...lots of energy and heat), catalysts (rate of reaction)

E.3 Metals - iron and aluminum

E.3.1

Main sources of iron are iron ores and scrap iron - not much else to say.

E.3.2

Reactions which occur in a blast furnace (to produce iron)

$\mathsf{C_{(s)} + O_{2(g)} \longrightarrow CO_{2(g)}}$

Carbon is partially oxidized to CO₂.

$\mathsf{CO_{2(g)} + C_{(s)} \longrightarrow 2CO_{(g)}}$

The carbon in CO₂ is reduced to CO.

$\mathsf{3CO_{(s)} + Fe_2O_{3(s)} \longrightarrow 2Fe_{(s)} + 3CO_{2(g)}}$

Iron (III) oxide is reduced to Fe by the CO.

$\mathsf{CaCO_{3(s)} \longrightarrow CaO_{(s)} + CO_{2(g)}}$

This bit is about the production of slag, which is going to sit on top of the iron.

$\mathsf{CaO_{(s)} + SiO_2 \longrightarrow CaSiO_{3(l)}}$

CaSiO₃ is the slag.

E.3.3

Conversion of iron to steel in oxygen converter (steel is iron with a low proportion of carbon)

First, the converter is charged with about 25% scrap steel. In the bottom of the converter is also calcium oxide (lime) which reacts with impurities to form slag. Molten iron is then poured into the converter. In the converter there is also a tube blowing super heated oxygen into the molten iron. This will react with the carbon in the steel to produce CO₂, which then escapes. When The steel has been produced, the converter is tipped and the steel is tapped off through an outlet pipe.

E.3.4 : Different forms of iron

Cast iron - same as pig iron, high carbon content -> relatively brittle, but also harder

Wrought iron - more malleable (due to lower carbon content). Hammering/rolling removes impurities.

Carbon steel - Small ( >1% ) carbon content + Iron ... thus it's very malleable, but not very hard.

Alloy Steels - The addition of other elements can change the physical properties of the alloy. eg Tool steels have to be strong, corrosion resistant and heat resistant. Stainless steel (18% chromium, 8% nickel) is resistant to corrosion, used in cutlery and surgical instruments.

E.3.5

The principle uses of steel is in construction, and as reinforcement. Plus the ones given above...tools, cutlery, surgical instruments and so on.

E.3.6

Production of Alumina from bauxite (aka Aluminum oxide, Al₂O₃)...

Al₂O₃ will eventually be electrolysed, but first it must be purified...

$\mathsf{Al_2O_3{(s)} + 2NaOH + 3H_2O \longrightarrow 2NaAl(OH)_{4(aq)}}$

Aluminum oxide produces sodium aluminate (and dissolves out any soluble impurities)

$\mathsf{NaAl(OH)_{4(aq)} -{}_{dilution}-> Al(OH)_{3(s)} + NaOH_{(aq)}}$

This occurs when the solution is diluted with water, producing aluminum hydroxide...which is a solid precipitate, and can be removed (leaving impurities behind)

$\mathsf{2Al(OH)_{3(s)} -{}_{heat}-> Al_2O_{3(s)} + 3H_2O_{(g)}}$

after heating, Pure anhydrous aluminum oxide is produced.

E.3.7

The aluminum oxide is then dissolved in molten cryolite (Na₃AlF₆)..requiring the temperature to be kept above 850^oC and then electrolysed:

Cathode: $\mathsf{Al^{3+} + 3e^- \longrightarrow Al}$

Anode: $\mathsf{2O^{2-} \longrightarrow O_2 + 4e^-}$

followed by:

$\mathsf{C + O_{2(g)} \longrightarrow CO_{2(g)}}$

because the anode is made of carbon.

The molten aluminum is then tapped off from the bottom of the container, since it is more dense than the cryolyte.

Cryolyte is used because it greatly reduces the amount of energy to keep the aluminum oxide in a molten state. The cell is generally produced as a large 'vat' ... The cryolyte is in this, which is lined with carbon to be used as the cathode. Carbon anodes are dipped at intervals along it, and are slowly lowered as are eaten away (by the production of CO₂).

E.3.8 : Properties of aluminum

Aluminum is resistant to corrosion (because it naturally forms a protective coating on Al₂O₃). it is also very lightweight, and inexpensive compared to some alloys (stainless steel). It can not be made hard by the addition of carbon like iron.

E.3.9

Aluminum is widely used due to its resistance to corrosion. Common uses are cans, construction (roofing, fences) and its lightweight nature also makes it useful in cars and airplanes. Aluminum can not be made hard and so it is not very useful for tools, but doesn't corrode, making it useful in areas such as roofing, where steel would corrode, and stainless steel is too expensive.

E.3.10 : Environmental impacts of Aluminum production

Mining: Destruction of land - may require rehabilitation

Siting: some effluent and waste gases are inevitable, and so the plant would be best situated away from population centers.

Recycling: Avoids above problems, and may be less expensive than the production from bauxite. Also, bauxite is a non renewable resource.

E.4 Air

E.4.1

Gases (oxygen, nitrogen and argon) are obtained by cooling air to below the boiling point of the gas wanted ... O₂ -> 183^oC, N₂ ->196^oC, but I don't think these will be necessary.

E.4.2 : Uses

N₂: Producing NH₃, HNO₃, Inert gas in incandescent light bulbs (and as an inert atmosphere in general). Also, as a liquid coolant for freezing food etc.

O₂: Respiration (to air, eg oxygen rich air), production of steel, fuel (O₂ + C₂H₂ or O₂ + H₂ -> welding) oxidizer in rocket propellant as liquid with reducer.

Ar: Inert gas -> fluorescent tubes, thermometers (above Hg), where an inert gas is needed but N₂ can't be used.

E.5 Equilibrium processes : The Harber and contact processes

E.5.1

Many industrial processes depend on the manipulation of equilibria. (because the expensive products are usually those which are had to make ;) - the ones we're going to see here ar the harber and contact processes. First the harber process (this is sort of a recap from Topic 8...)

$\mathsf{N_{2(g)} + 3H_{2(g)} \leftrightarrows 2NH_{3(g)} : \Delta H =}$ -92.4 Kj/mol

Considerations: LCP predicts that the best yield will occur with low temperature and high pressure. Rate requires high temp for fast reaction. Equipment to maintain high pressure is expensive.

Generally used: 450^oC, 250 atm and a catalyst (finely divided iron)

-> about 30% yield - NH₃ is separated by liquifying (NH₃ melts at about 20^oC) ... other gases are returned to the reaction.

E.5.2 : Uses of ammonia

Essential nutrient for healthy plant growth - Problem (nitrogen fixation) . It is difficult to use N_2(g) from the atmosphere, thus nitrogen based fertilizers are used. Used to make nitric acid (HNO₃), for the nitration of benzene. Also, for production of TNT (tir-nitro toluene ... methyl benzene with 3 substituted NO₂ groups...at 2,4,6). and it's used to make dyes.

E.5.3 : Contact process

This is the production of H₂SO₄.

$\mathsf{2SO_{2(g)} + O_{2(g)} \leftrightarrows 2SO_{3(g)} : \Delta H =}$ -191 Kj/mol.

LCP suggests low temperature and high pressure. (other considerations as above)

Generally used: 450^oC, 1 atm and vanadium (v) oxide catalyst ... this produces about a 97% yield...high pressure not really necessary.

$\mathsf{SO_{3(g)} + H_2SO_4 \longrightarrow H_2S_2O_7}}$

when this is diluted in H₂O, H₂SO₄ will be produced.

E.5.4 : Uses of sulphuric acid

Making fertilizers, explosives, dyes, production of other acids, detergents, catalyst for making esters, producing nitrating mixture and as a dehydrating mixture. It's the most important industrial acid...understand that ;)

E.6 The oil industry

E.6.1 : Importance of oil as a chemical feedstock

About 90% of the crude oil products from fractional distillation is used in transport, heating fuels and electricity production. The other 10% is used as a feedstock for the production of other organic chemicals, but it is still the most significant source of organic chemicals.

E.6.2 : Cracking

Three types: catalytic cracking, thermal cracking and hydrocracking.

Catalytic cracking: Superior to thermal cracking. Occurs at a lower temp (250^oC) 1 atm pressure and a catalyst. Produces high quality gasoline ... less CH₄, more useful C₃ and C₄ molecules and many alkenes rather than alkanes.

Thermal cracking: 500^oC, 50 atm pressure (older and possibly out of date).

Hydrocracking: variation of thermal cracking using sodium aluminosilicate where some Na⁺ is replaced by Pt. Performed in the presence of H₂2, so products are saturated (alkanes not alkenes).

E.6.3 : Reforming

A bunch of types:

Catalytic reforming : Produces branched carbon chains, which have a higher octane number. This is done at 500^oC in an atmosphere of hydrogen.

Aromatisation: The production of aromatic molecules (benzene rings) (usually 500^oC and H₂ atmosphere like catalytic)

Cyclisation: The production of cyclic molecules ... again at 500^oC and in atmosphere of H₂.

Alyklation: the reaction of alkanes and alkenes to form branched alkanes.

In all of these, hydrogen will be produced, which is commonly used in the harber process.

E.6.4 : Removal of sulphur from crude oil

S in crude oil, when heated or burned forms SO₂ (and some SO₃). which can dissolve in water and form acid rain....Removal...

SO₂ formed in fractional distillation can be removed by reaction with MgO or NaOH., both of which react with SO₂/SO₃ to form a salt and water. The SO₂/SO₃ can then be used in the production of H₂SO₄.

E.6.5 : Refinery products as feedstock

Can produce from spare fractions of crude oil -- solvents, plastics, pesticides, food additives, pharmaceuticals, detergents, cosmetics, dyes.

E.6.6 : Properties and uses of polymers

Polythene: Long branched molecules produce a soft, malleable substance, useful in packaging.

Polyvinal Chloride: Considerably more rigid, and this stronger due to polar C-Cl bonds. Useful for glue and as a sealant.

Nylon: Strong, long fibers, commonly used in tights or stockings, but also to as strength to other fibers (ie carpets are a combination of wool and nylon).

Polyester: Long chain fabrics with great strength and do not rot. Commonly used in sails, ropes and other fibers which must be strong and not rot.

E.6.7

These polymers will not break down naturally and can not be burnt without the production of toxic gases. They are also produced from oil non-renewable resource (but can sometimes come from agricultural products).

E.7 Other chemical industries

E.7.1

Other chemical industries include the production of:

alloys,
cement,
ceramics,
glasses,
paper,
silicones
natural products.

E.7.2

Biotechnology is also an important source of some chemicals, such as ethanol, insulin and biopolymers (such as starch, rubber, proteins, wool, cotton, paper).