Encyclopedia of industrial chemistry free download

Although these materials are generally hydrophilic, the surface properties of components they contain may vary within a very narrow range. These small differences can be ampliied by selective adsorption that makes some of the particles hydrophobic. Such hydrophobic particles in a water suspension are loated by attaching them to air bubbles. Making particles hydrophobic and loatable A special surface-active agent surfactant called collector or promoter is added to the suspension.

Collectors are usually C2 to C6 compounds containing polar groups. They include fatty acids, fatty acid amines and sulphonates among others. Collector selection depends on the material being separated. The collector molecule adsorbs on to the solid surface via the polar charged group.

This reaction is known as che- misorption. The hydrocarbon chain is facing the aqueous phase. Because the hydrocarbon chain and the water do not mix, the coated particle surface becomes hydrophobic. By being hydrophobic, a particle repels water. This results in the weakening of the forces acting between the particle surface and water and hence the diminishing of surface-water interactions at solid- surface interface. This causes the displacement of water ilm from the wetted solid surface by air.

In addition to the use of collectors to change the surface property of the particles, other chemicals may be added to further modify either the particles to be loated, or the particles that are to remain in the suspension.

Such chemical subs- tances are called modiiers. It is introduced into the lotation cell. A frothing agent is added to create a generous supply of ine bubbles when air is sparged. Examples of frothers include pine oil and methyl amyl alcohol. The collector and other additives are added. The bubbles with attached mineral particles rise to the surface where the material is removed. Particles that are readily wetted by water hydrophilic tend to remain in the water suspension.

Fractional Distillation Distillation is used to separate a mixture of miscible liquids which have different volatilities. Suppose a mixture with low concentration of the more volatile component is distilled and the vapour condensed.

The condensate which we refer to as distillate will be more concentrated with this component than the feed. If we return the distillate to the distillation apparatus and distill it to a second distillate, this distillate will be more richer in the more volatile component than the irst distillate. If we continue this process, we will approach a pure distillate of the more volatile component. The greater the relative volatility between the two components, the fewer the needed distillation stages.

This is the concept of fractional distillation. Industrially, fractional distillation is carried out in distillation columns also known as distillation towers. They are like many distillation stills stack together vertically. This is done by packing the column with inert solids, or installing plates at regular intervals throu- ghout the column height.

Small distillation columns are normally packed while large distillation columns are plated. In plated columns, we need to provide for both vapour path and liquid paths at each plate. The plates are perforated and the vapour passes through the perforations. The liquid lows through pipes known as downcomers next to the colum wall. In Fig 2. Rectiication and stripping in a distillation column Let us look at what happens inside a distillation column when it is running.

Suppose there are two components A and B being separated with A being more volatile than B. Component A leaves at the top. At each distillation plate, the liquid mixture is at boiling point. We can therefore conclude that the inside of the column becomes colder upwards. Vapour is generated at the reboiler and it rises up from the bottom of the column.

At each distillation stage or plate, a relatively hotter vapour contacts a cooler liquid coming down the column. Some of the vapour condenses and the resulting conden- sate has more of the less volatile component B, thus resulting in a vapour rcher in A. Simultaneously, some of the liquid picks the latent heat generated by the condensing vapour and vapourizes.

The vapourized portion contain more of the more volatile component A and therefore, the liquid leaving the plate is depleted of A and enriched with B. This process is repeated up the column.

After the topmost vapour is condensed at the condenser, some of the distillate is returned to the column at the top plate. The returned liquid is called relux. Enriching the vapour with the more volatile component above the feed location is known as rectiication.

The removal or depletion of this component from the liquid below the feed location is known as stripping. Other Unit Operations There are many unit operations that are employed in the chemical industry. It is impossible to cover all of them in this unit.

In Table 2. Unit Processes In Unit 1, we deined unit processes as chemical transformations or conversions. Unit processes are the core of industrial synthetic chemistry and are dominant in organic processes. We will look at some of the unit processes that we are likely to encounter in subsequent learning activities. Polymerization reactions fall into two general classes: 1. Addition or chain polymerization involving successive stages of reaction initia- tion, propagation and termination.

Examples of addition polymers include polyethylene, polypropylene, polyvinyl chloride and polystyrene. Condensation or step-reaction polymerization. This involves condensation reaction between two polyfunctional molecules, sometimes with the elimina- tion of a small molecule such as water. It is used to make polymers from vinyl monomers, that is, from small molecules containing carbon-carbon double bonds. The spe- cial characteristic of these molecules is that they have an ability to split in unusual way.

When they split, the pair of electrons in the bond, which is broken, separates to produce two initiator fragments, each of which has one unpaired electron.

Molecules like this, with unpaired electrons are called free radicals The carbon-carbon double bond in a vinyl monomer, like ethylene, has a pair of electrons, which is very easily attacked by the free radical. When this happens, a new chemical bond is formed between the initiator fragment and one of the double bond carbons of the monomer molecule.

This electron, having nowhere else to go, associates itself with the carbon atom, which is not bonded to the initiator fragment. Propagation: This new radical reacts with another ethylene molecule in the exact same way as the initiator fragment did. A free radical is formed when this reaction takes place over and over again and the chain grows. The adding of more and more monomer molecules to the growing chain is called propagation.

Because we keep remaking the radical, we can keep adding more and more ethylene molecules, and build a long chain. Self-perpetuating reactions like this are called chain reactions. Termination: Termination is the third and inal step of a chain-growth polymeriza- tion. Free radicals are unstable, and eventually they ind a way to become paired without generating a new radical.

Then the chain reaction will grind to a halt. This happens in several ways. The simplest way is for two growing chain ends to ind each other. The two unpaired electrons then join to form a pair, and a new chemical bond joining their respective chains.

This is called coupling. Coupling is one of two main types of termination reaction. Another way in which the unpaired electrons can shut down polymerization is called disproportionation.

In disproportionation, the unpaired electron of one chain inds an electron in the carbon-hydrogen bond of the next carbon atom forming a double bond at the end of the polymer chain. Sometimes, the unpaired electron at the end of a growing chain pairs with an electron from a carbon-hydrogen bond along the backbone of another polymer chain.

This starts a new chain growing out of the middle of the main chain. This is called chain transfer to polymer, and the result is a branched polymer.

It is especially a problem with polyethylene, so much that linear non-branched polyethylene cannot be made by free radical polymerization. Polymerisation products are numerous with many uses and include phenolic resins, alkyl resins, polyamides, polyesters, elastic foams, silicon polymers, isocyanate po- lymers, epoxy resins, adhesives, coatings, polyethylene, vinyl polymers and acrylic polymers for paint industry to mention but a few.

Emulsion polymerization Emulsion polymerization is a type of free radical polymerization that usually starts with an emulsion consisting of water, monomer and surfactant. The most common type of emulsion polymerization is an oil-in-water emulsion, in which droplets of monomer the oil are emulsiied with surfactants in a continuous water phase.

Emulsion polymerization is used to manufacture several commercially important polymers. Many of these polymers are used as solid materials and must be isolated from the aqueous dispersion after polymerization. In other cases, the dispersion itself is the end product. These emulsions ind applications in ad- hesives, paints, paper and textile coatings. Because they are not solvent-based, they are eco-friendly.

This is considered Smith-Ewart Interval 1. At this point the monomer-swollen micelle has turned into a polymer particle. When both monomer droplets and polymer particles are present in the system, this is considered Smith-Ewart Interval 2. This is considered Smith-Ewart Interval 3. It can also be known as a polymer colloid, a latex, or commonly and inaccurately as an 'emulsion'. Emulsion polymerizations have been used in batch, semi-batch, and continuous pro- cesses.

The choice depends on the properties desired in the inal polymer or dispersion and on the economics of the product. Alkylation Alkylation is the introduction of an alkyl radical by substitution or addition into an organic compound. For example, the combining of an olein to a hydrocarbon is an alkylation reaction.

In the presence of an acid catalyst such as hydrogen luoride or sulphuric acid, this reaction is used for the conversion of gaseous hydrocarbons to gasoline. The processes are usually exothermic and similar to polymerisation. Apart from gasoline, other classes of products from alkylation reactions include pharmaceuticals, detergents, disinfectants, dyes and plastics.

Alkylates of active methylenes are easily prepared using a base such as ethoxide, EtO-. Methyl and primary halides are most suitable for alkylation reactions. In principle both of the hydrogens can be replaced with alkyl groups: This can be utilized to form a cyclic system by using a dihalide as shown below: 2.

Hydrolysis In the hydrolysis of either organic or inorganic compounds, water and another com- pound undergo double decomposition to form two products. However, there are agents that accelerate or catalyse the hydrolysis. Hydrolysis of esters This hydrolysis is referred to as saponiication.

A good example is the saponiication of fats and oils to glycerol and either soap or fatty acids. That is, it can be either acid or alkali catalysed. Addition of acid speeds up reaction without shifting the equilibrium signiicantly. On the other hand, alkali addition accelerates reaction and shifts the reaction to the right so that it goes to completion. In Unit 6, we shall study the application of ester hydrolysis in soap making. Other Unit Processes In table 2. Table 2.

Other unit processes with their industrial applications. Esteriication A chemical process in Production of synthetic ibres like po- which an ester and water lyethylene terephthalate, manufacture are formed when an organic of alkyl resins and polyvinyl acetate, radical is substituted for in preparation of terpene and cellulose a molecule by an ionisable esters hydrogen of an acid.

Halogenation Involves addition of one or Chlorinated compounds are used chlorination, more halogen atoms to an in the chlorohydrocarbons such as bromination organic compound chloroform, ethylene chlorohydrin and iodination freon , DDT, carbon tetrachloride, oleinic acids, acid chlorides, etc.

This is the introduction of Industrial solvents, dyestuffs, explo- one or more nitro groups sives, pharmaceuticals and as inter- Nitration -NO2 into an organic com- mediates in the production of amines pound. Monovalent atoms or groups of atoms are replaced by the nitro group Formative Evaluation 1.

List down the various purposes for size reduction. Explain how a ball mill works. What are the factors that determine the quality of pellets? Describe how agglomerates are made by the layering process 5. Describe how a magnetic separator works 6.

How does a lotation cell operate? How is a vapour enriched with the more volatile component as it moves up a distillation column? Briely discuss the Smith-Ewart-Harkins theory for free radical emulsion polymerization. List down the various types of alkylation reactions Describe the various stages mineral ores go through in a typical ore dressing process. Describe the extractive metallurgy of copper f. Describe the extractive metallurgy of aluminium Summary of Unit In this unit, we shall study how metals are extracted from mineral ores in which they exist with other materials of less value.

Generally, ores are irst taken through size reduction, sorting and agglomeration to transform them into a form that can be taken through extraction processes including calcining, roasting, smelting and reining. Ex- tractive metallurgy of iron, aluminium and copper respectively are then presented. List of relevant readings Das R. The second site has informa- tion on aluminium production.

Mineral ores An ore is a mineral deposit which can be proitably exploited. It may contain three groups of minerals namely: a valuable minerals of the metal which is being sought b compounds of associated metals which may be of secondary value c gangue minerals of minimum value.

Almost all metals are derived from mineral ores. There are also ores that contain non-metals such as sulphur. Generally, the valuable mineral in an ore may be found in the form of native metal, oxides, oxy-salts, sulphides or arsenides. During mining, large open pits are excavated by breaking the ore using explosives. Ores as mined may be in large lumps and therefore, some size reduction is done at the mine.

The ore is shoveled into trucks and transported to the factory. If the mineral ore is found in waterbeds, mining is carried out by dredging. For example, sand is dredged from river beds. Ore dressing Before the ores are subjected to the main chemical treatment steps, they are pre-trea- ted by a series of relatively cheap processes, mainly physical rather than chemical in nature.

These processes constitute what is known as ore dressing. They are meant to effect the concentration of the valuable minerals and to render the enriched material into the most suitable physical condition for subsequent operations.

Such ores can be ground, sized and blended with other ores in order to provide a homoge- neous feed to say, a blast furnace or reaction bed. Size Reduction Size reduction may be carried out by irst crushing the ore down to 7mm maximum followed by grinding to smaller sizes. Jaw crushers can be used deep in the mine to prepare the ore for transportation to the surface e. Sizing Screens are used to separate particles according to size and may not affect the concen- trations of the ore minerals.

Particles are separated into oversize and undersize. Sorting The particles may be sorted by classiication, lotation or magnetic methods. Classiiers These are devices that separate particles according to their different rates of travel under gravity through a luid medium such as water. Particles of different densities, sizes and shapes have different falling velocities. Classiiers include rake classiiers and jigs. Flotation Flotation uses difference in surface properties of the individual minerals.

It is readily applied to very ine concentrates and can distinguish ore mineral from gangue, and also, one ore mineral from another. Magnetic Separation Ferromagnetic magnetite or iron minerals which can be chemically altered to produce magnetite may be sorted out using a magnetic separator as described in Unit 2.

Electrostatic Separation Minerals have a wide range of electrical conductivity and can be distinguished by this property. If several kinds of particles are given an electrostatic charge and are then brought into contact with an electrical conductor at earth potential, the charge will leak away from good conductors much more rapidly than from poor conductors.

While the charge remains, the particle will cling to the conductor by electrostatic attraction. The weakly conducting minerals will therefore remain attached to the conductor longer than the good conductors, so affording a means of separating minerals whose conductivities differ appreciably.

Electrostatic separators operate on thin layers of material. The principle is illustrated in Fig. Dewatering and filtration After sorting and leaching, it is necessary to separate the solid and liquid phases. Coarse solids may be freed from most of their moisture by draining.

Slurries with particles which can settle may be separated from the bulk of the liquid by settling and subsequent decantation. The moisture content may be reduced further by iltration and drying. If the va- luable ore is in the iltrate, it can be recovered by evaporation followed by drying.

Agglomeration When a particle size of an ore or concentrate is too small for use in a later stage of treatment e. These blocks are then dried and hardened by heating. Use of hydraulic cement allows hardening to be carried out cold. Briqueting is not popular in mineral ore agglomeration.

Sintering Sintering involves diffusion of material between particles. It is applied to the conso- lidation of metallic and ceramic powder compacts which are heated to temperatures approaching their melting points to allow diffusion to take place at the points of contact of particles so that they grow together to form a rigid entity. The process can be envisaged as a net migration of vacancies into the solid at the highly curved energy surfaces near points of contact and again at low energy areas away from contact points Sintering may be accompanied by a chemical reaction.

Extraction Processes So far we have been dealing with unit operations that prepare the ore for chemical reactions used to extract the valuable metal from the ore. Now we want to look at extraction and reining of the metal. Calcination This is the thermal treatment of an ore to effect its decomposition and the elimination of a volatile product, usually carbon dioxide or water. Roasting Roasting involves chemical changes other than decomposition, usually with furnace atmosphere.

A roast may effect calcinations and drying as shown below. In the blast furnace, coke is burned into CO2 which reacts further with the carbon to form CO. The ascending gases pre-heat the solid charge descending the stack and reduce metal oxides to metal. This then is a process of drying followed by calcination and roasting. The metal melts and the slag forms gangue and lux.

Where fusion or reduction temperature is above C, electric melting is most appropriately applied. Reining Electrolysis may be used for metal extraction and metal reining. In ire reining, extracted metals are brought into liquid state and their composition inally adjusted.

In some case, this may be simple smelting to allow cathodically entrained hydrogen to escape by diffusion. In other cases, impurities may react to form compounds which are insoluble in the molten state. Converters are used for oxidizing impurities out of blast furnace iron in steel-making and for oxidation of sulphur from copper and nickel matte.

Distillation may also be applied in metal puriication. Extractive Metallurgy Of Iron 3. Uses of iron Iron is used in the forms shown below as material of construction for machines, plants, buildings, locomotives, ships, automobiles, railway lines and for many other things. All these forms are obtained from pig iron which is irst obtained from the iron ore. White cast iron obtained when molten low silicon, high manganese pig iron is rapidly cooled.

Grey pig iron which contain very small amounts of carbon and other impurities but 1. Steel which contain from 0. Hard steel which contain 0. Raw materials The main raw materials for the manufacture of iron and steel are iron ore and limes- tone or dolomite as lux. Coking coal is used as fuel. The fuel serves two purposes: to heat the furnace and to produce CO which acts as the reducing agent. To make special steels other materials such as nickel, chromium, cobalt are added.

The ores include red haematite Fe2O3 , the less inferior brown hydrated haematite also known as limonite 2Fe2O3. The haematite is easily reduced. Removal of impurities in iron ore The presence of impurities in the iron ore not only reduce the iron content in the ore but also increase production costs especially with regard to consumption of lux and fuel.

If limonite is used, it is irst dried before use. When the ore contains large amounts of impurities, appropriate ore dressing operations are carried out on it. When the ore is obtained in small particles, it is sintered into lumps. The main impurities in iron ore are silica and alumina. Silica and alumina in the presence of limestone makes the ore self-fusing with less production costs.

At high temperatures of the blast furnace, the lux reacts with alumina and silica to form a complex of calcium-magnesium aluminium silicate known as slag. Both sulphur and phosphorus, which can also come from the fuel used, are not desired in iron and steel manufacture.

Normally steel should not contain more than 0. Sulphur can be removed in the blast furnace slag. Phosphorus cannot be removed in the slag but passes through to the pig iron where it is combined with steel in the convertor.

As a result, the ores are sometimes classiied as acid or basic ores according to the amount of phosphorus present. Acid ores contain less than 0.

A small amount of manganese is generally present in iron ores. Manganese is ad- vantageous for steel production because it reduces the effect of sulphur by forming manganese sulphide MnS. Sometimes, if manganese is absent from the ores, it is added. Fuel Coke is the fuel used to melt the ore and also to reduce the iron ore to metallic iron.

Coke is produced at the bottom of the blast furnace by carbonization of coal i. It is hard to prevent the formation of CO and its high porosity provides large surface area for the chemical reactions. It is consumed at the rate of one ton per ton of pig iron.

Manufacture of Pig Iron Pig iron is a direct product of smelting iron ore with luxes and fuel in a tall blast furnace. The oxygen is introduced at the top of the furnace, blown or blasted through bronze or copper nozzles over the furnace materials in a number of symmetrically placed tubes, called tuyeres.

The air blast is preheated to a temperature of about C and pressure of 2. Preheating greatly increases the economy of steel production. The molten iron and slag collect at the bottom of the furnace while the gases escape from the top.

The slag layer loats over the heavier iron and is periodically collected as dross and stored as waste material that can be used for cement manufacture or for making loor tiles The pig iron is tapped and is either used to produce cast iron, stored in pigs of sand bags or is taken for steel production.

To make cast iron, the molten metal is poured into moulds of desired size and shape. The metal gets cooled and solidiies taking the desired shape. Fig 3. Schematic diagram of a blast furnace showing the temperatures at relative heights. Reactions of the blast furnace The temperature of the blast furnace progressively rises up from top to bottom. Extractive Metallurgy Of Aluminium Aluminium is the most abundant metal in earth and is commercially extracted from bauxite ores in which it occurs as hydrated aluminium oxide.

Ore dressing may involve washing the ore, size classiication and leaching. Chemical treatment of bauxite At this stage bauxite is crushed and ground to the correct particle size for eficient extraction of the alumina through digestion with hot sodium hydroxide solution which dissolves the aluminium hydroxide, forming a solution of sodium aluminate.

The solution is then seeded with aluminium hydroxide from a previous batch in precipitator tanks, where aluminium hydroxide precipitates from the solution. Reduction of aluminum from aluminium oxide Primary aluminium is produced by the electrolytic reduction of the aluminium oxide. We hope you enjoy the downloads as much as we do!

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