Option E - Chemical Industries (SL)
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[edit] E.1 Initial overview
[edit] E.1.1
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, such as metals and their ores.
Air : O2, N2, Ar
Petroleum : Coal, Oil etc...
[edit] E.1.2
A number of factors influence positions for chemical industry establishment. Industry must comply with regulations (i.e. environmental restrictions), have 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 is also a major factor.
[edit] E.1.3
Speciality chemicals : Drugs, Many organic substances (w/ specific uses).
Bulk chemicals : Sulphuric acid, Nitrogen, Oxygen, Ammonia, Sodium hydroxide, Chlorine.
[edit] E.2 Principles of extraction and production
[edit] E.2.1
Metals are rarely found free in nature, and have to be extracted and processed before they can be used. Gold is one prominent counter-example.
[edit] 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).
[edit] E.2.3
Chemical principles in the extraction of useful substance from raw materials ...
Changing into suitable form for oxidation, for example ZnS + O2 -> ZnO + SO2.
Reduction to metal, by electrolysis or chemical reaction (blast furnace).
Also consider : Reduction (Iron), electrolysis (Al2, Al ), equilibrium (Contact and Harber), energy requirements (electrolysis requires lots of energy and heat), catalysts (rate of reaction).
[edit] E.3 Metals - iron and aluminum
[edit] E.3.1
The main sources of iron are iron ores and scrap iron.
[edit] E.3.2
Reactions which occur in a blast furnace (to produce iron)
C(s) + O2(g) -> CO2(g) (carbon is partially oxidized to CO2).
CO2(g) + C(s) -> 2CO(g) (the carbon in CO2 is reduced to CO).
3CO(s) + Fe2O3(s) -> 2Fe(s) + 3CO2(g) (iron (III) oxide is reduced to Fe by the CO).
CaCO3(s) -> CaO(s) + CO2(g) (this bit is about the production of slag, which is going to sit on top of the iron).
CaO(s) + SiO2 -> CaSiO3(l) (CaSiO3 is the slag).
[edit] 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.
[edit] E.3.4
Different forms of iron :
Cast iron : Same as pig iron, high carbon content means it is 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. It's very malleable, but not very hard.
Alloy Steels : The addition of other elements can change the physical properties of the alloy. For example, tool steels have to be strong, corrosion resistant and heat resistant. Stainless steel (18% chromium, 8% nickel) is resistant to corrosion, used in cuttlery and surgical instruments.
[edit] E.3.5
The principle uses of steel is in construction, and as reinforcement, as well as those given above (tools, cutlery, surgical instruments and so on).
[edit] E.3.6
Production of Alumina from bauxite (aka Aluminium oxide, Al2O3) :
Al2O3 will eventually be electrolysed, but first it must be purified.
Al2O3(s) + 2NaOH + 3H2O -> 2NaAl(OH)4(aq) (aluminium oxide produces sodium aluminate, and dissolves out any soluble impurities).
NaAl(OH)4(aq) -- dilution --> Al(OH)3(s) + NaOH(aq) (this occurs when the solution is diluted with water, producing aluminium hydroxide, which is a solid precipitate, and can be removed, leaving impurities behind).
2Al(OH)3(s) -- heat --> Al2O3(s) + 3H2O(g) (after heating, pure anhydrous aluminium oxide is produced).
[edit] E.3.7
The aluminum oxide is then dissolved in molten cryolyte (Na3AlF6) requiring the temperature to be kept above 850oc, and then electrolysed as follows.
Cathode : Al3+ + 3e- -> Al
Anode : 2O2- -> O2 + 4e- followed by C + O2(g) -> CO2(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).
[edit] E.3.8
Properties of aluminium : Aluminium 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.
[edit] E.3.9
Aluminium is widely used due to its resistance to corrosion. Common uses are cans, construction (roofing, fences). Its lightweight nature also makes it useful in cars and airplanes.
Aluminium 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.
[edit] E.3.10
Environmental impacts of Aluminum production :
Mining : Destruction of land, which may require rehabilitation.
Siting : Some effluent and waste gases are inevitable, and so the plant would be best situated away from population centres.
Recycling : Avoids above problems, and may be less expensive than the production from bauxite. Also worth nothing is that bauxite is a non renewable resource.
[edit] E.4 Air
[edit] E.4.1
Gases (oxygen, nitrogen and argon) are obtained by cooling air to below the boiling point of the desired gas
For example, O2 requires -183oc, N2 requires -196oc, but I don't think these will be necessary.
[edit] E.4.2
Uses :
N2 : Producing NH3, HNO3, inert gas in incandescent light bulbs (and as an inert atmosphere in general). Also useful, 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 for welding). Also used as an oxidizer in rocket propellant as liquid with reducer.
Ar : Inert gas used in fluorescent tubes, thermometers (above Hg), and in other cases where an inert gas is needed but N2 can't be used.
[edit] E.5 Equilibrium processes - The Harber and contact processes
[edit] E.5.1
Many industrial processes depend on the manipulation of equilibria (because the valuable products are usually those which are hard to make). The ones we're going to see here are the harber and contact processes. First the harber process (this is sort of a recap from Topic 8).
N2(g) + 3H2(g) <=> 2NH3(g), ΔH = -92.4 Kj/mol
Considerations : LCP predicts that the best yield will occur with low temperature and high pressure, but rate requires a high temperature for fast reaction. Equipment to maintain high pressure is expensive.
Generally we use 450oc, 250 atm and a catalyst (finely divided iron) which produces about 30% yield. NH3 is separated by liquifying (NH3 melts at about 20oc) other gases are returned to the reaction.
[edit] E.5.2
Uses of ammonia :
- Essential nutrient for healthy plant growth - problem (nitrogen fixation) . It is difficult to use N2(g) from the atmosphere, thus nitrogen based fertilizers are used.
- Used to make nitric acid (HNO3), for the nitration of benzene.
- Used for production of TNT (tir-nitro toluene, which is methyl benzene with 3 substituted NO2 groups at 2,4,6).
- Used to make dyes.
[edit] E.5.3
Contact process (this is the production of H2SO4).
2SO2(g) + O2(g) <=> 2SO3(g), ΔH = -191 Kj/mol.
LCP suggests low temperature and high pressure (other considerations as above).
We generally use 450oc, 1 atm and vanadium (v) oxide catalyst. This produces about a 97% yield, so a higher pressure is not really necessary.
SO3(g) + H2SO4 -> H2S2O7. When this is diluted in H2O, H2SO4 will be produced.
[edit] E.5.4
Uses of sulphuric acid :
- Making fertilizers, explosives, dyes, production of other acids, detergents
- Catalyst for making esters
- Producing nitrating mixture
- As a dehydrating mixture.
Sulphuric acid is the most important industrial acid, and apparently you need to understand that.
[edit] E.6 The oil industry
[edit] E.6.1
Importance of oil as a chemical feed-stock :
About 90% of the crude oil products from fractional distillation are used in transport, heating fuels and electricity production. The other 10% is used as a feed-stock for the production of other organic chemicals, but it is still the most significant source of organic chemicals.
[edit] E.6.2
There are three types of cracking; catalytic cracking, thermal cracking and hydrocracking.
Catalytic cracking : Superior to thermal cracking. Occurs at a lower temp (250oc) 1 atm pressure and a catalyst. Produces high quality gasoline with less CH4 and more useful C3 and C4 molecules and many alkenes rather than alkanes.
Thermal cracking : 500oc, 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 H2, so products are saturated (alkanes not alkenes).
[edit] E.6.3
Reforming comes in a number of different types.
Catalytic reforming : Produces branched carbon chains, which have a higher octane number. This is done at 500oc in an atmosphere of hydrogen.
Aromatisation : The production of aromatic molecules (benzene rings) (usually 500oc and H2 atmosphere like catalytic).
Cyclisation : The production of cyclic molecules, again at 500oc 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 then used as an input to the harber process.
[edit] 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, so it's a good idea to remove it first.
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.
[edit] E.6.5
Refinery products as feed-stock :
Can produce from spare fractions of crude oil : solvents, plastics, pesticides, food additives, pharmaceuticals, detergents, cosmetics, dyes.
[edit] E.6.6
Properties and uses of polymers :
Polythene : Long branched molecules produce a soft, malleable substance, useful in packaging.
Polyvinyl Chloride : Considerably more rigid, and this stronger due to polar C-Cl bonds. Useful for glue and as a sealant.
Nylon : Strong, long fibres, commonly used in tights or stockings, but also to as strength to other fibres (i.e. carpets are a combination of wool and nylon).
Polyester : Long chain fabrics with great strength which do not rot. Commonly used in sails, ropes and other fibres which must be strong and not rot.
[edit] 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).
[edit] E.7 Other chemical industries
[edit] E.7.1
Other chemical industries include the production of alloys, cement, ceramics, glasses, paper, silicones and natural products.
[edit] 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).
