Page | 1

Unit2, module 3:

Industry and the EnvironmentLocating industrial plants; benefits and risk

Industrial location is an increasingly important decision facing both national and international firms. The general critical factors of industrial location are transportation, labor, raw materials, markets, industrial sites, utilities, government attitude, tax structure, climate, and community. In addition, for international location considerations, four general factors are identified: political situation of foreign countries, global competition and survival, government regulations, and economic factors.

Some factors which influence a plant site

1. Proximity to raw materials

2. Easily accessible to the workforce

3. Proximity to good infrastructure (seaport, railway, airport, roads)

4. Type of terrain (flat, rugged or slightly rolling hills)

5. Distance from general populace

Checkpoint A

Think of the cement factory in Rockfort, which of the factors listed above would be the most important in relation to the location of the plant site and give reasons why.……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

All industrial plants have general safety requirements. These requirements include head covering, eye protection, feet protection, and ears as well. Industrial plants can be very hazardous; falling objects, loud noises as well as fire protection and toxic fumes alerts. However not all safety requirements have the same level of emphasis placed upon them

Checkpoint B

Compare a cement plant to a petroleum refinery plant. Which safety requirements would be the most critical for each and why?

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Risk Of Accidents And / Or Harmful Exposures : Areas of Concern

Dangerous Materials ii) Hazards of Pressure Vessels iii) Hazardous Chemical Reactionsiv) Hazardous of Unit Operations v) Flammable Gases, Vapours And Dust Hazardsvi) Health Hazards vii) Hazards due to corrosion viii) Entry in To Confined Spaces ix) Working with Pipelines x) Plant Alteration and modification xi) Sampling and Gauging xii) Hazards due to Instrument Failures.Dangerous Materialsi)Explosives ii) Gases iii) Inflammable Liquids iv) Inflammable Solids v) Oxidising substancesvi) Toxic and Infectious substances vii)Radio Active Substances viii)Corrosive Substancesix)Miscellaneous Dangerous Substances

Hazards Due To CorrosionWeakening and falling of structures and sheds.Falling of workers from height due to breaking of raised platforms, hand rails, toe boards, stairs and ladders.Spills and toxic releases from pipelines due to corrosion.Leakages and bursting of vessels due to corrosion.

Entry into Confined Spaces1.Oxygen Deficiency 2. Toxic Contamination 3. Flammable Environment4.Possibility of Electrocutions through electric equipments5.Possibility of Toxic gas generation during the work 6.Lack of

Page | 2

Ventilation 7.Difficulty in welfare monitoring 8.Failure to escape on emergency 9.Combustible Substances

Hazards Of Pressure Vessels1.Leakage or Bursting of Pressure Vessels 2.Design defects 3.Failure of Relief Systems 4.Lack of hydraulic testing. 5. Lack of Proper Instrumentation or Instrumentation Failure 6.Lack of N.D.Tests 7.Corrosion of Vessels. 8. Lack of routine inspections 9. Attempt of Pneumatic testing

GENERAL SAFETY REQUIREMENTS FOR INDUSTRY

Hazardous Chemical ReactionsUnderstanding about the behaviours of reactions and adopting precautionary and emergency measuresHazards of Unit operationsUnderstanding the hazards inherent in each unit operation and adopting precautionary and emergency measures.Flammable Gases, Vapours And Dust Hazards• Identification of potential areas, where possibility

of flammable mixture are possible.• Efforts to avoid hazardous mixtures, by inert gas

purging and other methods.• Declaring hazard zones and providing flame proof

electrical fittings and equipments.• Providing Explosion Vents in spaces with

possibility of air-vapour mixtures.• Explosive meter testing.• Providing adequate fire control devices.• Providing arrangements to avoid static sparks. Etc.

• Corrosion monitoring and control.• Testing and inspection of vessels and

structures to ensure safetySafety While Entry into Confined Spaces Thorough cleaning and purging before hot work. Safety belt with one end outside. Life line to monitor welfare. On going ventilation. A person to watch the welfare. Low voltage electric appliances. Self contained breathing apparatus. Environmental monitoring for oxygen, toxic gases

and flammable gases before entry. Pipeline isolation before entry Electric isolation before entry. Proper ladder for entry.

Health Hazards• Identification of potential health hazards.• Assessment of levels of physical and chemical health hazards.• Control of hazards by various techniques• Adequate awareness among the workers.• Periodic medical examination of the workers.• Personal protection for occasional exposures.• Proper hygiene and decontamination facilities. etc.

ALUMINIUM

Extracting aluminium from bauxite

Aluminium is too high in the electrochemical series (reactivity series) to extract it from its ore using carbon reduction. The temperatures needed are too high to be economic.

Instead, it is extracted by electrolysis. The ore is first converted into pure aluminium oxide by the Bayer Process, and this is then electrolysed in solution in molten cryolite - another aluminium compound. The aluminium oxide has too high a melting point to electrolyse on its own.

Aluminium ore

The usual aluminium ore is bauxite. Bauxite is essentially an impure aluminium oxide. The major impurities include iron oxides, silicon dioxide and titanium dioxide.

Purifiying the aluminium oxide - the Bayer Process

Reaction with sodium hydroxide solution

Crushed bauxite is treated with moderately concentrated sodium hydroxide solution. The concentration, temperature and pressure used depend on the source of the bauxite and exactly what form of aluminium oxide it contains. Temperatures are typically from 140°C to 240°C; pressures can be up to about 35 atmospheres.

High pressures are necessary to keep the water in the sodium hydroxide solution liquid at temperatures above 100°C. The higher the temperature, the higher the pressure needed.

Page | 3

With hot concentrated sodium hydroxide solution, aluminium oxide reacts to give a solution of sodium tetrahydroxoaluminate.

The impurities in the bauxite remain as solids. For example, the other metal oxides present tend not to react with the sodium hydroxide solution and so remain unchanged. Some of the silicon dioxide reacts, but goes on to form a sodium aluminosilicate which precipitates out.

All of these solids are separated from the sodium tetrahydroxoaluminate solution by filtration. They form a "red mud" which is just stored in huge lagoons (mud lakes).

Precipitation of aluminium hydroxide

The sodium tetrahydroxoaluminate solution is cooled, and "seeded" with some previously produced aluminium hydroxide. This provides something for the new aluminium hydroxide to precipitate around.

Formation of pure aluminium oxide

Aluminium oxide (sometimes known as alumina) is made by heating the aluminium hydroxide to a temperature of about 1100 - 1200°C.

Conversion of the aluminium oxide into aluminium by electrolysis

The aluminium oxide is electrolysed in solution in molten cryolite, Na3AlF6. Cryolite is another aluminium ore, but is rare and expensive, and most is now made chemically.

The electrolysis cell

The diagram shows a very simplified version of an electrolysis cell.

The electrode reactions

This is the simplification:

Aluminium is released at the cathode. Aluminium ions are reduced by gaining 3 electrons.

Oxygen is produced initially at the anode.

However, at the temperature of the cell, the carbon anodes burn in this oxygen to give carbon dioxide and carbon monoxide.

Continual replacement of the anodes is a major expense.

Although the carbon lining of the cell is labelled as the cathode, the effective cathode is mainly the molten aluminium that forms on the bottom of the cell.

Molten aluminium is syphoned out of the cell from time to time, and new aluminium oxide added at the top.

The cell operates at a low voltage of about 5 - 6 volts, but at huge currents of 100,000 amps or more. The heating effect of these large currents keeps the cell at a temperature of about 1000°C.

Economic considerations

The high cost of the process because of the huge amounts of electricity it uses. This is so high because to produce 1 mole of aluminium which only weighs 27 g you need 3 moles of electrons. You are having to add a lot of electrons (because of the high charge on the ion) to produce a small mass of aluminium (because of its low relative atomic mass).

Energy and material costs in constantly replacing

Page | 4

the anodes. Energy and material costs in producing the cryolite,

some of which gets lost during the electrolysis. Transport of the finished aluminium.

Extracting aluminium from the bauxite

Loss of landscape due to the size of the chemical plant needed, and in the production and transport of the electricity.

Noise. Atmospheric pollution from the

various stages of extraction. For example: carbon dioxide from the burning of the anodes (greenhouse effect); carbon monoxide (poisonous); fluorine (and fluorine compounds) lost from the cryolite during the electrolysis process (poisonous).

Pollution caused by power generation (varying depending on how the electricity is generated.)

Disposal of red mud into unsightly lagoons.

Environmental problems in mining and transporting the bauxite

Loss of landscape due to mining, processing and transporting the bauxite.

Noise and air pollution (greenhouse effect, acid rain) involved in these operations

Recycling

Saving of raw materials and particularly electrical energy by not having to extract the aluminium from the bauxite. Recycling aluminium uses only about 5% of the energy used to extract it from bauxite.

Avoiding the environmental problems in the extraction of aluminium from the bauxite.

Not having to find space to dump the unwanted aluminium if it wasn't recycled.

(Offsetting these to a minor extent) Energy and pollution costs in collecting and transporting the recycled aluminium.

Uses of aluminium

Aluminium is usually alloyed with other elements such as silicon, copper or magnesium. Pure aluminium isn't very strong, and alloying it adds to it strength.

Aluminium is especially useful because it

has a low density; is strong when alloyed; is a good conductor of electricity; has a good appearance; resists corrosion because of the strong thin layer of aluminium oxide on its surface. This

layer can be strengthened further by anodising the aluminium.

Anodising essentially involves etching the aluminium with sodium hydroxide solution to remove the existing oxide layer, and then making the aluminium article the anode in an electrolysis of dilute sulphuric acid. The oxygen given off at the anode reacts with the aluminium surface, to build up a film of oxide up to about 0.02 mm thick.

As well as increasing the corrosion resistance of the aluminium, this film is porous at this stage and will also take up dyes. (It is further treated to make it completely non-porous afterwards.) That means that you can make aluminium articles with the colour built into the surface.Some uses include:

aluminium is used for because

aircraft light, strong, resists corrosion

other transport such as ships' superstructures, container vehicle bodies, tube trains (metro trains)

light, strong, resists corrosion

overhead power cables (with a steel core to strengthen them)

light, resists corrosion, good conductor of electricity

saucepanslight, resists corrosion, good appearance, good conductor of heat

firefighter suits High reflective nature

Checkpoint C

Page | 5

CRUDE OIL

Fractional distillation of crude oil is the first step in the production of many of the materials we have come to rely on in modern life.All our fossil fuels, virtually all our plastics, detergents and commercial alcohols are made from products of this process.

Fractional Distillation of Crude Oil

Page | 6

In order to separate the different length chains in the crude mix, it is heated to a very high temperature. The temperature is set so that all those fractions with a Carbon chain length of 20 and below are evaporated from the crude mix. The temperature cannot be set higher than this as there is a risk that the lighter fractions will ignite.

The remaining liquid, which is composed of only the heavier fractions, passes to a second location where it is heated to a similar temperature, but at lower pressure. This has the effect of making the heavy Hydrocarbon fractions more likely to evaporate.

How the Distillation Tower Works

The way the Distillation Tower works is by becoming progressively cooler from the base to the top. All the Hydrocarbon fractions start off in gas form, as they have been heated to that point. The gases then rise up the tower.

The gas mixture then encounters a barrier through which there are are only openings into the bubble caps. The gas mixture is then forced to go through a liquid before continuing upwards. The liquid in the first tray is at a cool enough temperature to get the heaviest gas fractions to condense into liquid form, while the lighter fractions stay gaseous.

In this way the heaviest hydrocarbon fractions are separated out from the mixed gas. The remaining gas continues its journey up the tower until it reaches another barrier. Here the bubble cap process is repeated but at a lower temperature than before, which then filters out the next lightest set of fractions.

This process continues until only the very lightest fractions, those of 1 to 4 Carbon atoms, are left. These stay in gas form and are collected at the top of the tower.

The separation of the heavier elements in the second tower follows exactly the same process but at lower pressure.

After the Fractional Distillation of Crude Oil

The separated fractions still contain a mixture of different hydrocarbons. After their initial separation the fractions require further processing and purification. Treatment of the initial products of the fractional distillation of crude oil also occurs in the refinery. The results of these processes are the products we use in everyday life.

Uses of Crude Oil

In reality, crude oil is a much larger part of our lives than many of us realize. There are more than 4,000 different petrochemical products. These products are manufactured by refining crude oil.

Here are some common products that are made from oil:

Page | 7

GasolineDiesel fuelHeating oilJet fuelBunker fuelPaintFertilizers/pesticides

PlasticsSynthetic rubberSynthetic fibersFertilizers/pesticidesDyesDetergentPhotographic film

Food additives (canned food)MedicineSynthetic fibers (such as polyester, nylon, acrylic)Make-upCandles

The Impact Of The Petroleum Industry On The EnvironmentACCIDENTS: Oil rig accidents, broken pipelines, oil tanker wrecks etc. all have terrible effects on the plant and animal life of the locality as we see from the horrible TV pictures of seabirds coated in oil, and toxic oil slicks covering the beaches and sands. There is also the risk to humans from fires and explosions on rigs or at oil refinery installations and fuel storage depots etc.Thick oil smothers animals such as birds and sea otters. It clogs the feeding and breathing mechanisms of filter-feeders. It can also poison animals who swallow it. Over the long term, oil can cause cancer in marine life, destroy the skin and gill tissues of fishes, upset their equilibrium, and disrupt the chemical receptors in lobsters and fish that are necessary for attracting mates.RISING CARBON DIOXIDE LEVELS:

THE GREENHOUSE EFFECT: (see notes on the atmosphere below)

ACID RAIN: Fossil fuels contain compounds of the element sulphur When the fuel is burned the sulphur compounds also burn to form sulphur dioxide. This is an acidic gas and dissolves in rainwater, it then reacts with water and oxygen to form a very dilute solution of sulphuric acid.sulphur + oxygen ==>sulphur dioxideS(in fuel molecules) + O2(g) ==> SO2(g)

Sulphur dioxide is a harmful gas and lung irritant and contributed to 5000 extra deaths in the great 'London Smog' in the 1950's as well as being a major acid-rain gas. It reacts with oxygen (in air) and water (rain) and gets oxidised to form very dilute sulphuric acid - acid rain and the overall change is represented by the equation below.SO2(g-air) + O2(g-air) + 2H2O(l-rain) ==> 2H2SO4(aq-rain)

The formation of acid rain has several bad effects on the environment e.g.the low pH causes plant damage, particularly trees,kills certain life forms and so damages eco cycles and food chains in rivers or lakes harming wildlife like trout,increases the 'weathering' corrosion rates of building stone (particularly limestone).

OTHER POLLUTANTS: High temperature combustion also produces other pollutants including ...Nitrogen oxides collectively denoted by NOx: NO is formed in car engines and changes to NO2, which is acidic, contributing further to acid rain (above), and are also involved in the chemistry of 'photochemical smog' - which produces chemicals harmful to respiration, irritating to eyes and contributes to acid rain. Many of the reactions are initiated by sunlight.nitrogen monoxide is formed in high temperature combustion situations e.g. car engines, power station furnace burning coal, oil or natural gas.nitrogen + oxygen ==> nitrogen monoxideN2(g) + O2(g) ==> 2NO(g)

and in air the nitrogen monoxide rapidly combines with the oxygen in airnitrogen monoxide + oxygen ==>  nitrogen dioxide (acidic gas)2NO(g) + O2(g) ==> 2NO2(g)

The nitrogen dioxide is oxidised to nitric acid by the reaction with oxygen from air when it dissolves in rainwater. The overall process is summarised in the equation below.4NO2(g-air) + O2(g-air) + 2H2O(l-rain) ==> 4HNO3(aq-rain)

Carbon monoxide CO, which is toxic, and also involved in the chemistry of 'photochemical smog'. This is formed by inefficient combustionUnburned hydrocarbons, CxHy, which can be carcinogenic and are also involved in photochemical smog chemistry.But catalytic converters* can significantly reduced these three unwanted emissions (see above for CO and NO removal, and CxHy gets oxidised to CO2 and H2O). * e.g. using platinum-rhodium transition metal catalysts, these are dispersed on ceramic bed to give a big surface area for the best reaction rate.There are other indirect pollution problems to do with burning fossil fuels:Lead compounds are added to petrol to improve engine performance. This produces lead compound emissions into the environment. Lead compounds are nerve toxins so it is fortunate they are being phased out in many countries.

AMMONIA

MANUFACTURE OF AMMONIA -THE HABER PROCESS

The Haber Process combines nitrogen from the air with hydrogen derived mainly from natural gas (methane) into ammonia. The reaction is reversible and the production of ammonia is exothermic.

Page | 8

A flow scheme for the Haber Process looks like this:

Hydrogen gas is obtained by reacting methane with steam over a nickel catalyst. This is called steam reforming: CH4 + H2O → CO + 3 H2

Nitrogen gas is obtained via fractional distillation of liquid air

According to Le Chatelier’s Principle, a lower temperature and a higher pressure would increase the yield of ammonia. However, too low a temperature would slow the rate of the reaction and high pressures are costly as materials must be strengthened to withstand the pressure to resist to risk of explosion. Thus a compromise is reached, where the temperature is not too low nor too high and the pressure also not too high but high enough to shift the equilibrium position to the right.Under these conditions, the conversion rate to ammonia is 15%. However it occurs quickly and unreacted gases are recycled to improve efficiency.Separating the ammonia: When the gases leave the reactor they are hot and at a very high pressure. Ammonia is easily liquefied under pressure as long as it isn't too hot, and so the temperature of the mixture is lowered enough for the ammonia to turn to a liquid. The nitrogen and hydrogen remain as gases even under these high pressures, and can be recycled.

Uses of Ammonia in Agriculture and the Chemical IndustryAgricultural industries are the major users of ammonia.  Ammonia is a very valuable source of nitrogen that is essential for plant growth.  Depending on the particular crop being grown, up to 200 pounds of ammonia per acre may be applied for each growing season.

1. Manufacture of fertilisers and/or used as a fertiliser itself2. Ammonia used as a source of protein for livestock3. Used in the manufacture of nitric acid, drugs and various textiles4. Used in water treatment for control of pH5. used by the leather industry as a curing agent6. widely used as commercial and household cleaners and detergents.

The impact of the ammonia industry on the environment

Atmospheric depositionAmmonia gas which is emitted falls to the ground over land, often during rainfall. This results in terrestrial eutrophication i.e. the enrichment of nitrogen content on land. This ultimately causes the disruption of plant ecosystems, with a few common fast growing species to dominate over greater variety of plants often of conversation value.EutrophicationOver-use of ammonium fertilisers. These fertilisers are water soluble and excess is leached from the soil during rainfall or irrigation, causing the bacterial levels in nearby water bodies to increase substantially. This large increase in bacteria robs the water body of adequate oxygen causing other aquatic life to die.Acid soilsThe overuse of fertilisers causes the soil to become acidic. Acidic soils cannot support several crops needed today and the soil must be neutralised before anymore crops are planted. This neutralisation must be done on a continuous basis to ensure the viability of the soil.Air pollutionHigh concentrations of ammonia in air can damage vegetation such as lichen and moss. It also contributes to the formation of haze in the atmosphere which reduces visibility and the formation of particulate matter which can cause respiratory problems. Checkpoint B

Page | 9

SULPHURIC ACID

THE MANUFACTURE OF SULPHURIC ACID - THE CONTACT PROCESS

The process can be divided into three stages:1. Preparation and purification of sulphur dioxide2. Catalytic oxidation (using vanadium pentoxide catalyst) of sulphur dioxide to sulphur trioxide3. Conversion of sulphur trioxide to sulphuric acid

Stage1: Making the sulphur dioxide

This can either be made by burning sulphur in an excess of air:

. . . or by heating sulphide ores like pyrite in an excess of air:

Purification of air and SO2 (using an electrostatic precipitator) is necessary to avoid catalyst poisoning. The gas is then washed with water and dried by sulphuric acid.

To conserve energy, the mixture is heated by exhaust gases from the catalytic converter by heat exchangers.

Stage 2: Catalytic oxidation

Sulphur dioxide and oxygen then react in the manner as follows:2 SO2(g) + O2(g) ⇌ 2 SO3(g) : ΔH = −197 kJ mol−1

To increase the reaction rate, high temperatures (450 °C), medium pressures (1-2 atm), and vanadium(V) oxide (V2O5) are used to ensure a 96% conversion.

Stage3: Conversion of sulphur trioxide to sulphuric acid

Hot sulfur trioxide passes through the heat exchanger and is dissolved in concentrated H2SO4 in the absorption tower to form oleum:

H2SO4(l) + SO3(g) → H2S2O7(l)

Note that directly dissolving SO3 in water is impractical due to the highly exothermic nature of the reaction. Acidic vapour or mists are formed instead of a liquid.

Oleum is reacted with water to form concentrated H2SO4.The average percentage yield of this reaction is around 30%.

H2S2O7(l) + H2O(l) → 2 H2SO4(l)

Page | 10

Uses of Sulphur in IndustriesMicrofined sulphur, and derivatives of sulphur are sprayed on plants and trees to destroy the fungus, insects, bacteria etc. that attack them.

In chemical industriesSulphuric acid is by far, the most important chemical produced from sulphur. Sulphuric acid is used as a basic reagent in almost all the chemical preparations and in many industrial processes. It might well be said that the industrial progress of a nation is directly proportional to the amount of sulphuric acid that it consumes.

Other important compounds of sulphur produced are:Sulphur dioxide : Used in bleaching straw, wool, etc.Calcium bisulphite : Used for bleaching wood pulpPhosphorus trisulphide : Used in safety matchesCarbon disulphide : Used as an industrial solvent etc.

In explosive industrySulphur is an important constituent of explosives, like gunpowder, fireworks and fire crackers.

In the vulcanization of rubberRaw rubber is soft, but many commercial applications of rubber require it to be hard and resistant to wear and tear caused through friction. For e.g., the rubber of automobile and aeroplane tyres is very hard. Vulcanization is the process where raw rubber is boiled with sulphur to make it hard. It is named after Vulcan, the Roman god of "fire".

Practice Questions

ETHANOL: Making ethanol by fermentation

This method only applies to ethanol. You can't make any other alcohol this way.

The process: To manufacture alcoholic beverages, there are essentially two processes that must occur: fermentation to produce the alcohol and then distillation to purify and increase the alcohol content.

Page | 11

Yeast is added to a sugar source e.g. sugarcane, molasses, grapes etc with various nutrients and the correct temperature and pH and in the absence of oxygen. Sugar is first broken down into glucose and fructose by the enzyme sucrase. Eventually glucose molecules are respired anaerobically to produce ethanol and carbon dioxide gas by the enzyme zymase.

C6H12O6 → 2C2H5OH + 2CO2

The ethanol content rises as high as 12% before the yeast cells are killed.

Yeast is killed by ethanol concentrations in excess of about 15%, and that limits the purity of the ethanol that can be produced. The ethanol is separated from the mixture by fractional distillation to give 96% pure ethanol.

For theoretical reasons, it is impossible to remove the last 4% of water by fractional distillation.

Uses of ethanol

1. As a fuel (gasohol) 10 - 20% ethanol2. Alcoholic beverages3. Antiseptic use4. Base chemical for petro-chemical industry5. Manufacture pharmaceutical drugs

As a solvent: Ethanol is widely used as a solvent. It is relatively safe, and can be used to dissolve many organic compounds which are insoluble in water. It is used, for example, in many perfumes and cosmetics.

Industrial methylated spirits (meths): Ethanol is usually sold as industrial methylated spirits which is ethanol with a small quantity of methanol added and possibly some colour. Methanol is poisonous, and so the industrial methylated spirits is unfit to drink.

The social and economic impact of alcohol production and consumptionThe social and economic problems of alcohol use not only affect those who drink but also those around them, and society as a whole.

1.  In the work environment alcohol can lead to absences, work accidents, and lower performance, which, in turn, may lead to unemployment. This has a cost for the employee, employer, and the social security system.

2.  Drinking can impair how a person performs as a parent or partner. Drinking can lead a person to be violent, to spend more time away from home, to leave other family members destitute, or to cause them anxiety, fear and depression. Parental drinking, both during pregnancy and after birth, can have lasting physical or psychological effects on children.

3. The economic consequences of alcohol consumption can be severe, particularly for the poor. This is not only due to the amount spent on drinks, but also to lost wages, and to medical and other expenses.

4.  Violence between husbands and wives often occurs in situations when one or both partners have been drinking. Heavy drinking has been strongly linked to violence between partners and to a lesser extent to violence towards others, possibly because proximity increases the opportunities for violence. However, further data is needed to clarify the complex role of alcohol in such incidents.

5.  Alcohol consumption imposes economic and social costs on society as a whole. Estimating these costs is often difficult, but it can help improve policies aiming to reduce harm from alcohol. The few national estimates that have been made so far indicate the significant cost of alcohol use to society.

Physiological effects of alcohol consumption

Page | 12

CHLORINE (a major product of the chlor-alkali industry )

MANUFACTURING CHLORINE USING A DIAPHRAGM CELL

Background chemistry: Chlorine is manufactured by electrolyzing brine (concentrated sodium chloride solution).

The electrolysis of sodium chloride solution can be used to make three useful substances - chlorine, sodium hydroxide and hydrogen.

The chemistry of the electrolysis process

Sodium chloride solution contains:

sodium ions, chloride ions, hydrogen ions (from the water), hydroxide ions (from the water).

The hydrogen and hydroxide ions come from the equilibrium:

At any one time, the concentration of hydrogen ions or hydroxide ions will be very small - the position of equilibrium lies well to the left-hand side.

At the anode: The negative ions, chloride and hydroxide, get attracted towards the positively charged anode. It is actually easier to liberate hydroxide ions (to give oxygen) than chloride ions (to give chlorine), but there are far, far more chloride ions arriving at the anode than hydroxide ions.

The major reaction at the anode is therefore:

Two chloride ions each give up an electron to the anode, and the atoms produced combine to give chlorine gas.

The chlorine is, however, contaminated with small amounts of oxygen because of a reaction involving hydroxide ions giving up electrons as well.

The chlorine has to be purified to remove this oxygen.

Note:  Strictly speaking, this is a simplification. The H+

(aq)ions could be better shown as hydroxonium ions, H3O+. That would need two water molecules on the left-hand side of the equilibrium. The simplification is fine for this topic.

At the cathode: Sodium ions and hydrogen ions (from the water) are attracted to the negative cathode. It is much easier for a hydrogen ion to pick up an electron than for a sodium ion. So this reaction happens:

As the hydrogen ions are converted into hydrogen gas, the water equilibrium tips to the right to replace them.

The net effect of this is that there is a build up of sodium ions and these newly-produced hydroxide ions around the cathode. In other words, sodium hydroxide solution is being formed around the cathode.

The need to keep all the products separate

If chlorine comes into contact with hydrogen, it produces a mixture which will explode violently on exposure to sunlight or heat. Hydrogen chloride gas would be produced. Obviously, the two gases need to be kept apart.However, chlorine also reacts with sodium hydroxide solution to produce a mixture of sodium chloride and sodium chlorate (I) - also known as sodium hypochlorite. This mixture is commonly sold as bleach.Therefore, if you are trying to manufacture chlorine and sodium hydroxide rather than bleach, you have to keep the chlorine and sodium hydroxide apart as well.The diaphragm and membrane cells are designed so that all the products are kept separate.

Page | 13

The diaphragm cell Note:  This is a simplification of a real cell. For example, in a real diaphragm cell, the electrodes are not a single block of metal. If you are interested, you can find pictures and descriptions of real electrodes by doing a Google search on diaphragm cell and looking for manufacturers' websites.

The diaphragm: The diaphragm is made of a porous mixture of asbestos and polymers. The solution can seep through it from the anode compartment into the cathode side.

Notice that there is a higher level of liquid on the anode side. That makes sure that the flow of liquid is always from left to right - preventing any of the sodium hydroxide solution formed finding its way back to where chlorine is being produced.

Production of the chlorine: Chlorine is produced at the titanium anode according to the equation:

It is contaminated with some oxygen because of the reaction:

The chlorine is purified by liquifying it under pressure. The oxygen stays as a gas when it is compressed at ordinary temperatures.

Production of the hydrogen

The hydrogen is produced at the steel cathode:

Production of the sodium hydroxide: A dilute solution of sodium hydroxide solution is also produced at the cathode (see above for the explanation of what happens at the cathode). It is highly contaminated with unchanged sodium chloride solution.

The sodium hydroxide solution leaving the cell is concentrated by evaporation. During this process, most of the sodium chloride crystallises out as solid salt. The salt can be separated, dissolved in water, and passed through the cell again.

Even after concentration, the sodium hydroxide will still contain a small percentage of sodium chloride.

Industrial importance of the halogens and their compounds

fluorine Used in the making of non-stick coatings for saucepans, aerosol propellants, refrigerants, glass etching

chlorine Used in the making of bleaches(eg. Sodium hypochlorite NaClO), disinfectants (eg. Chlorine dioxide), antiseptics (eg. TCP and Dettol), PVC, aerosol propellants (eg. Chlorofluorocarbons), refrigerants, solvents for dry cleaning and degreasing, insecticides(eg. DDT), anaethestics, hydrochloric acid, dyes, textiles

bromine Pesticides, flame retardants, photographic chemicalsiodine Antiseptics, photographic film, potassium iodideEnvironmental issues within the chlor/alkali industryThere are several environmental concerns that have made a significant impact on the growth of the chlor-alkali industry over the past twenty years and will dictate the future growth as well. These issues are highly debated, and the associated "chemophobia" is likely to adversely affect the chlorine consumption profile in the future.

Page | 14

Chlorine bleaching of wood pulp and dioxin emissions to the environmentPresence of dioxin, at parts per trillion (ppt) levels, in paper and paper based products and chlorinated organics in pulp mill effluents led to decreased chlorine demand. In the U.S., chlorine consumption in the pulp and paper industry, decreased from 15% in 1987 to 7% in 1998. The U.S. Environmental protection agency promulgated "Cluster Rules" in late 1998, mandating the use of elemental chlorine-free bleaching. These rules, which went into effect in April 2001, lowered the chlorine utilization in the North American pulp and paper bleaching operations in favor of sodium chlorate, hydrogen peroxide and oxygen.

Ozone layer depletionBecause of their contribution to the ozone layer depletion, production of chlorinated fluorocarbons (CFC's), carbon tetrachloride (CCl4), and 1,1,1-trichloroethane was banned in 1997 following the Montreal Accord.

Polyvinyl chloride plasticThere are two major environmental issues with PVC, which include their lack of biodegradability and generation of dioxins when they are incinerated for energy recovery and for controlled waste recycling. Hydrochloric acid formation during the thermal decomposition of PVC is another issue that environmentalists are strongly invoking for the substitution of chlorine-free products for PVC.

Mercury emissionsBetween 1930 and 1960, several tons of mercury waste was dumped in Minamata Bay in Japan. Thousands of people living around the bay developed methyl mercury poisoning through the consumption of contaminated fish. The victims suffered from severe neurological damage, which later became known as Minamata Disease. Thousands were afflicted and more than 900 died.

AsbestosAsbestos is used as a separator material in diaphragm cells. However, asbestos is a toxic material, causing lung cancer, asbestosis, and mesothelioma. As a result, in 2007, a bill was adopted to ban most uses of asbestos in the United States. Chlor-Alkali plants were exempt because few cost effective alternatives exist for this technology.

Practice Question

What is the ratio of moles of NaCl used to moles of Cl2 produced?Use this ratio to determine mass of NaCl in kg required to produce 2.5 x 1010 kg of Cl2

WATER

The water cycle, also known as the hydrologic cycle or H2O cycle, describes the continuous movement of water on, above and below the surface of the Earth. Water can change states among liquid, vapour, and ice at various places in the water cycle.

Page | 15

Importance of the water cycle

Water is continually being recycled in nature. This recycling:1. Ensures a constant supply of water is available to plants for photosynthesis.2. Ensures a constant supply of water is available to all living organisms to keep their cells hydrated and to act as a

solvent.

3. Ensures aquatic organisms have a constant environment in which to live.

4. Purifies water, replenishes the land with freshwater, and transports minerals to different parts of the

globe.

5. Helps to reshape the geological features of the Earth, through such processes as erosion and

sedimentation

6. Through the process of evaporation, takes up energy from the surroundings and cools the environment

7. Through the process of condensation, releases energy to its surroundings, warming the environment.

Methods of Water purification 

Water purification is the process of removing undesirable chemicals, materials, and biological contaminants

from contaminated water. The goal is to produce water fit for a specific purpose. Most water is purified for

human consumption (drinking water) but water purification may also be designed for a variety of other

purposes, including meeting the requirements of medical, pharmacology, chemical and industrial applications.

Please note that desalination can also be considered a process of water purification via the use of reverse osmosis

SedimentationThe water, after coagulation, is left in settling basin further for sufficient period to allow sedimentation of remaining materials. Sedimentation however considerably reduces microbial population of the water aside from removing most of the suspended particles.

FlocculationWater from raw water reservoirs (natural sources) is collected in large tanks/basins for a sufficient time period to permit large particulate matter to settle down at the bottom. This material is removed and then the water is treated with flocculants such aluminium sulphate which form a floc that precipitates and carriers with it microorganisms on the surface. Suspended organic matter settle onto the bottom of the tanks/basins. In this ways most substances that impart turbidity to water get coagulated.

Page | 16

FiltrationAfter sedimentation, water is subjected to sand filters to remove flocks of living organisms. The process of filtration is highly critical and important as it can remove protozoan cysts and also about 98-99% of bacteria from water. The water may also be filtered through activated charcoal to remove potentially toxic organic compounds and organic compounds that impart undesirable colour and/or taste to the water.

DisinfectionDisinfection is the final step is municipal water purification and it ensures that no pathogenic microorganisms are carried through water. For water supplies of small towns and localities sodium or calcium hypochlorite (NaOCl or CaOCl2 respectively) may be used to disinfect water, but for larger cities, however, chloroamine (as opposed to chlorine) is now the method for disinfection.

Importance of Dissolved Oxygen

All aquatic life depend on the amount of dissolved oxygen (DO) present. This allows all aquatic life to conduct their metabolic processes essential to life. High levels of DO (above 90%) indicate “healthy” water bodies. DO can also be related indirectly to biological oxygen demand (BOD), the higher the DO, the lower the BOD. Once DO levels begin to drop, this usually indicates some form of pollution is present in the water body.

Sources of water pollution

Pollutant Source Effect on environmentNitrates Manmade fertilisers Drinking water that gets contaminated with

nitrates can prove fatal especially to infants that drink formula milk as it restricts the amount of oxygen that reaches the brain causing the ‘blue baby’ syndrome as well as eutrophication.

Phosphates Manmade fertilisers and detergents EutrophicationHeavy metals (e.g. lead and mercury)

Use of lead pipes causes dissolved lead ions to form in the water, improper disposal of mercury from industrial processes

Lead affects the nervous system and can ultimately lead to death. Mercury stunts physical development of organisms

Cyanides Improper disposal after used in making fabrics

Acts as a poison

Trace metals mining waste and tailings, landfills, or hazardous waste dumps.

Hazardous effects on nervous systems and physical development

Pesticides and herbicides Run off from backyards, farms and golf courses

Accumulate up the food chain and cause impairment of physical development of aquatic life

Petroleum residues From underground storage tanks Similar to pesticidesSuspended particles Industrial processes e.g. cement

manufactureRespiratory problems, covers wide area in fine dust

Tests for pollutants in water

Nitrate NO3– Add NaOH(aq) Add Devarda’s alloy (powdered Zn, Al) Heat & hold moist red litmus at

mouth of test tubeNH3 evolved, litmus paper red blueFind out about the tests for phosphates, cyanide and lead in water

Practice Questions

1.

Page | 17

2.

THE ATMOSPHEREOzone: The atmosphere surrounding the Earth contains a small amount of ozone (O3), a gas with molecules consisting of three oxygen atoms bound together, instead of the two which form the normal oxygen molecule (O2) that makes up 21% of the air we breathe.

The average concentration of ozone in the atmosphere is about 300 parts per billion by volume (ppbv) that is, there are about 3 molecules of ozone for every ten million air molecules. Most of it (~90%) is contained in the stratosphere about 15 - 30 km above the Earth's surface where it is present at levels of several parts per million by volume (ppmv). If all the ozone in the atmosphere were compressed to atmospheric pressure, it would form a band ~3 mm thick. Even though it is present in such small quantities, it plays a vital role in supporting life on Earth. The natural ozone levels in the atmosphere allow most harmful solar radiation to be absorbed before it can reach the Earth's surface; ozone absorbs a significant portion of the ultraviolet light known as the UV-B, which has been linked to various types of skin cancer, cataracts and damage to the human immune system; UV-B is also known to be harmful to some

How the concentration of ozone in the atmosphere is maintained?

When an oxygen molecule receive a photon (h v), it dissociates into monoatomic (reactive) atoms - a process called photodissociation. These atoms attack an oxygen molecule to form ozone, O3.

O2 + h v  O + OO2 + O  O3

The last reaction requires a third molecule to take away the energy associated with the free radical O and O2, and the reaction can be represented by

O2 + O + M  O3 + M*The over all reaction between oxygen and ozone formation is:

3 O2  2 O3

The absorption of UV B and C leads to the destruction of ozone

O3 + h v  O + O2

O3 + O  2 O2

A dynamic equilibrium is established in these reactions. The ozone concentration varies due to the amount of radiation received from the sun.

Page | 18

crops and some forms of marine life. Any changes in the amount of radiation that penetrates to the Earth's surface as a result of the thinning of the ozone layer can have potentially serious implications for human health and ecological systems, and also for global climate.

How do CFCs help depleting ozone?

A relatively recent concern is the depletion of ozone, O3 due to the presence of chlorine in the troposphere, and eventually their migration to the stratosphere. A major source of chlorine is Freons: CFCl3 (Freon 11), CF2Cl2 (Freon 12), C2F3Cl3 (Freon 113), C2F4Cl2 (Freon 114). Freons decompose in the troposphere. For example,

CFCl3  CFCl2 + ClCF2Cl3  CF2Cl + Cl.

The chlorine atoms catalyze the decomposition of ozone,

Cl + O3  ClO + O2

andClO molecules further react with O generated due to photochemical decomposition of ozone:

O3 + h v  O + O2,ClO + O  Cl + O2

O + O3  O2 + O2.The net result or reaction is2 O3  3 O2

Thus, the use of CFCs is now a world wide concern. In 1987, one hundred and forty nine (149) nations signed the Montreal Protocol. They agreed to reduce the manufacturing of CFCs by half in 1998. They also agree to phase out CFCs.

What are CFCs?

Chemist Roy J. Plunkett discovered tetrafluoroethylene resin while researching refrigerants at DuPont. Known by its trade name, Teflon, Plunkett's discovery was found to be extremely heat-tolerant and stick-resistant. After ten years of research, Teflon was introduced in 1949. His continued research led to the usage of chlorofluorohydrocarbons known as CFCs or freon as refrigerants.

CFCs are made up of carbon, hydrogen, fluorine, and chlorine.

The nontoxic and nonflammable CFCs have been widely used as refrigerants, in aerosol spray, and dry cleaning liquid, foam blowing agents, cleansers for electronic components in the 70s, 80s and early 90s.

In 1973, James Lovelock demonstrated that all the CFCs produced up to that time have not been destroyed, but spread globally throughout the troposphere.

Effects of ozone on human life

When enough ozone molecules are present, it forms a pale blue gas. It is an unstable molecule that readily combines with other atoms. Ozone has the same chemical structure whether it is found in thestratosphere or the troposphere. Where we find ozone in the atmosphere determines whether we consider it to be Dr. Jekyll or Mr. Hyde.

In the troposphere, the ground-level or "bad" ozone is an air pollutant that damages human health, vegetation, and many common materials. It is a key ingredient of urban smog. In the stratosphere, we find the "good" ozone that protects life on earth from the harmful effects of the sun's ultraviolet rays.

Ozone may be the most harmful air pollutant.1. It readily attacks organic materials with

C=C bonds, for example in the lungs.2. Ozone produces harmful irritation in the

respiratory system. It is believed that, because ozone damages lung tissue, it leads to a decreased resistance to infectious disease.

3. One abiological effect of ozone is to attack rubber (e.g., rubber tires). This effect is noticeable in the cracking of the sidewalls of tires. Tires of garaged vehicles last longer.

Ozone in the Stratosphere

Ozone and oxygen molecules in the stratosphere absorb ultraviolet light from the sun, providing a shield that prevents this radiation from passing to the earth's surface. While both oxygen and ozone together absorb 95 to 99.9% of the sun's ultraviolet radiation, only ozone effectively absorbs the most energetic ultraviolet light, known as UV-C and UV-B, which causes biological damage. The protective role of the ozone layer in the upper atmosphere is so vital that scientists believe life on land probably would not have evolved - and could not exist today - without it.

About 90% of the ozone in the earth's atmosphere lies in the region called the stratosphere between 16 and

Ozone in the Troposphere

The other 10% of the ozone in the earth's atmosphere is found in the troposphere, which is the portion of the atmosphere from the earth's surface to about 12 km or 7 miles up. In the troposphere, ozone is not wanted. Ozone is even more scarce in the troposphere than the stratosphere with concentrations of about 0.02 to 0.3 parts per million. But even in such small doses, this molecule can do a lot of damage.

Page | 19

And just to confuse things even further, ozone in the troposphere is one of the greenhouse gases. As discussed in the Greenhouse Effect section, the naturally occurring greenhouse gases (including ozone) are what make earth habitable for life as we know it. But scientists are very concerned about the warming effects of increased greenhouse gases caused by human activity. So, in the troposphere, accelerated ozone levels deal us a double whammy - as a key ingredient in smog and as a powerful greenhouse gas.

48 kilometers (10 and 30 miles) above the earth's surface. Ozone forms a kind of layer in the stratosphere, where it is more concentrated than anywhere else, but even there it is relatively scarce. Its concentrations in the ozone layer are typically only 1 to 10 parts of ozone per 1 million parts of air, compared with about 210,000 parts of oxygen per 1 million parts of air.

Maintaining the Balance of Carbon Dioxide Concentration in the Atmosphere

The carbon cycle

Life is built on the conversion of carbon dioxide into the carbon-based organic compounds of living organisms. The carbon cycle illustrates the central importance of carbon in the biosphere. Different paths of the carbon cycle recycle the element at varying rates. The slowest part of the cycle involves carbon that resides in sedimentary rocks, where most of the Earth's carbon is stored. When in contact with water that is acidic (pH is low), carbon will dissolve from bedrock; under neutral conditions, carbon will precipitate out as sediment such as calcium carbonate (limestone). This cycling between solution and precipitation is the background against which more rapid parts of the cycle occur.

Short-term cycling of carbon occurs in the continual physical exchange of carbon dioxide (CO2) between the atmosphere and hydrosphere. Carbon dioxide from the atmosphere becomes dissolved in water (H2O), with which it reacts to form carbonic acid (H2CO3), which dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3

-), which further dissociate into hydrogen and carbonate ions (CO32-). The more alkaline the water (pH

above 7.0 is alkaline), the more carbon is present in the form of carbonate, as is shown in the following reversible reactions:

Here is the exact flow of events, as carbon flows from one layer to another as shown in the diagram above.

1. In the process of photosynthesis, atmospheric carbon is absorbed by plants.

Page | 20

2. This carbon is transferred form plants to the animals feeding on them, and further moves up the food chain.

3. Respiration, digestion and metabolism plants and animals result in some transfer of carbon back to the atmosphere.

4. Some carbon also moves to the lithosphere when these living organisms die or when wood and leaves decay or when animals excrete. Some of these living beings buried millions of years ago have been converted to fossil fuels.

5. Mining and burning of fossil fuels cause this carbon to move from the lithosphere to the atmosphere.6. Some of this atmospheric carbon gets dissolved in the oceans and thus completes the cycle.

Question: Explain the importance of maintaining the balance of carbon dioxide concentration in the atmosphere

THE GREENHOUSE EFFECT: The burning of oil and other fossil fuels is contributing to the 'Greenhouse Effect' or global warming. The Earth's land-water surfaces absorbs the Sun's radiation in the form of infra-red (main heating effect) and visible/ultraviolet sunlight. Carbon dioxide and other gases including methane, water vapour and CFC's absorb the re-radiated lower frequency infrared energy from the Earth's surface and so warming the atmosphere, rather like a greenhouse allows the sunlight in but not out. The effects are predicted to be dramatic e.g. rising sea levels as polar ice melts causing flooding in low lying land, more energy in the global weather system leads to more frequent violent weather patterns etc.

Effects of the Products of Combustion of Hydrocarbon-Based Fuels

When fossil fuels burn efficiently in an excess of air/oxygen the only products are carbon dioxide and water e.g.

o methane + oxygen ==> water + carbon dioxide

o CH4(g) + 2O2(g) ==> CO2(g) + 2H2O(l)

If there is not enough oxygen present to completely burn the fuel to carbon dioxide and water other products may form causing pollution and fuel inefficiency.

o This is referred to as incomplete combustion.

The most common partially burned products are likely to be carbon C (soot) and deadly carbon monoxide CO.

Carbon-soot, a fine black powder-dust is potentially harmful and readily formed in fires i.e. its classically produced by smoky yellow flames. The soot, like any fine solid 'dust' is harmful when absorbed on the sensitive tissue of the linings of the nose, throat and lungs. Soot deposits cause coughing and sore throat and are ejected from your body through sneezing, coughing, and nose blowing. Coarse particles (10 microns) are inhaled into your windpipe and settle there, causing irritation and more coughing.  Soot is also a 'carrier' of polycyclic aromatic hydrocarbons (PAH's) on it which are carcinogenic.

Even very low concentrations of carbon monoxide can be fatal. Why? Oxygen is carried around the body by a complicated protein molecule in red blood cells called haemoglobin. The bonding between oxygen and haemoglobin is quite weak to allow easy oxygen transfer for cell respiration. Unfortunately, the bonding between carbon monoxide and haemoglobin is stronger, so oxygen is replaced by carbon monoxide and blocks normal cell respiration. The consequences are reduced blood oxygen concentration leading to unconsciousness and eventually death!

Effects of urban smog - NOX

GLOBAL WARMING is the increase in the average temperature of Earth's near-surface air and oceans since the mid-20th century and its projected continuation.PHOTOCHEMICAL SMOG: air pollution produced by the action of light on oxygen, nitrogen oxides, and unburned fuel from automobile exhaust to form ozone and other pollutants.

The reduction of fossil fuel burning is the only way to reduce photochemical smog e.g. using photovoltaic cells to harness solar energy to produce electricity. Using solar power indirectly in this way to run electric cars is potentially a good partial solution to the problem

The equations for incomplete combustion below show the formation of carbon-soot and 'deadly' carbon monoxide when there is a lack of oxygen for complete combustion. As mentioned already, soot is obviously a 'dirty' pollutant coating any surface (including your lungs!) that the soot particles settle on and they contain unburned carcinogenic hydrocarbons AND carbon monoxide is involved in the chemistry of photochemical smogs - so all in all, inefficient combustion of fossil-hydrocarbon fuels is very undesirable!

Carbon monoxide is unfortunately emitted by all car exhausts, though catalytic converters help reduce this by converting nitrogen monoxide (another pollutant) and carbon monoxide into harmless nitrogen and carbon dioxide.

Page | 21

o NO2 has a brown color; it makes our smoggy skies brownish-yellow. Nitrogen dioxide is a lung and eye irritant, and, along with nitrogen monoxide, it is involved in the complex chemistry of photochemical smogs which can also produce ozone and other harmful chemicals in the air.NOX compounds can lead to chronic lung damage.They can exacerbate asthma. They increase the susceptibility of the very young and the very old to respiratory infections.

NOX contributes to the nitrification (over-fertilization) of bays and wetlands, leading to algal blooms, and can lead to fish kills.

  2NO(g) + 2CO(g) ==> N2(g) + 2CO2(g)

Transition metals like platinum and rhodium are used in the catalytic converter.

Nitrogen monoxide, NO, is formed by the combination of nitrogen and oxygen at high temperature in automobile engines (cars, lorries, buses etc. - its all the same!)

N2(g) + O2(g) ==> 2NO(g)

Nitrogen monoxide readily forms nitrogen dioxide by combining with oxygen in air on exit from the engine exhaust.

2NO(g) + O2(g) ==> 2NO2(g)

How the atmospheric concentrations of the oxides of nitrogen may be altered

The nitrogen cycle is the process by which nitrogen is converted between its various chemical forms. This transformation can be carried out via both biological and non-biological processes. Important processes in the nitrogen cycle include nitrogen fixation , nitrogen assimilation, ammonification, nitrification, and denitrification.

The majority of Earth's atmosphere (approximately 78%) is nitrogen,[1] making it the largest pool of nitrogen. However, atmospheric nitrogen is unavailable for biological use, leading to a scarcity of usable nitrogen in many types of ecosystems. Human activities such as fossil fuel combustion, use of artificial nitrogen fertilizers, and release of nitrogen in wastewater have dramatically altered the global nitrogen cycle.

The atmospheric concentrations of the oxides of nitrogen may be altered via the following processes:

o Nitrogen monoxide, NO, is formed by the combination of nitrogen and oxygen at high temperature in automobile engines (cars, lorries, buses etc. - its all the same!)

N2(g) + O2(g) ==> 2NO(g)

o Nitrogen monoxide readily forms nitrogen dioxide by combining with oxygen in air on exit from the engine exhaust.

Page | 22

2NO(g) + O2(g) ==> 2NO2(g)

o Nitrogen oxides dissolve in rainwater to form an acidic solution of nitric acid which contributes to acid rain.

o The conversion of nitrogen oxides to non-toxic products in the catalytic convertors of cars.

2NO(g) + 2CO(g) ==> N2(g) + 2CO2(g)

Methods of control/prevention of atmospheric pollution

The fact is that human activities contribute the most to air pollution. Considering the harmful effects of air pollution, now it is very essential that everyone should contribute a bit to prevent air pollution. There are certain ways that one can help to reduce the emission of air pollutants in the atmosphere. Following are some tips for preventing air pollution:

Car Pool: Forming and implementing a car pool will reduce the number of cars, thereby, preventing air pollution by cutting down the use of fossil fuels. This way, it will help in the sustainable use of fossil fuel and its conservation for the future generations.

Vehicle Care: Timely servicing of the car helps to keep it in a good condition and also minimizes fuel exhaust. Driving the car at an average speed and turning off in traffic is a key to saving fuel. Make sure to use unleaded petrol and opt for regular pollution checking of your car. 

Public Transport: Whenever possible, try to travel by public transports. This helps in two ways; prevents air pollution and increases public income. If you are going to a nearby place, go by walking or use bicycle, instead of using your vehicle. The objective is to minimize the use of fuels, as far as possible. 

Alternative Energy Source: Another effective way to prevent air pollution is to use alternative energy sources such as solar energy, hydroelectric energy and wind energy. Nowadays, sophisticated technologies such as wind turbine, solar water heaters are introduced to generate electricity and other energy forms for the household use. 

Saving Energy: Saving energy will, of course, help to prevent air pollution. Switch off the lights, fans, air conditioners, televisions, and other appliances, when not in use. You can also share a room with others when the air conditioner or fan is on, instead of switching them on in every room. 

Minimize Air Pollutants: Always try to minimize smoke emission, as it can contribute to air pollution. One way is to compost dried leaves and kitchen waste, instead of burning them. Composting will also give you organic fertilizer for your garden. While buying the products, always choose air-friendly and recyclable products that will minimize the emission of pollutants. 

Social awareness about air pollution is the most essential step to be taken for the prevention of air pollution. Awareness programs and/or advertisements should be encouraged, so that people understand the potential health hazards of air pollution. Improvement of transport facilities and proper use of land for the sake of social benefits are equally important for controlling air pollution.

Air Pollution Control Equipment

Here are a few air pollution control systems that are being used by vehicles and industries. They help to either remove pollutants from a stream of exhaust before they are emitted into the air or destroy them. 

Air Pollution Control Systems To Reduce Particulate Matter

Wet Scrubbers: These include a number of devices that remove pollutants from furnace flue gas as well as other gas streams. The pollutants are removed by the polluted gas stream being forced through a scrubbing liquid or by using some other method of bringing it into contact with the liquid. Wet scrubbers are used in a number of industries like large power plants, asphalt plants, steel plants, fertilizer plants, and acid plants.

Electrostatic Precipitator (ESP): Also known as Electrostatic Air Cleaners, this air pollution control system is a particulate collecting device which uses the force created by an induced electrostatic charge to remove particulate matter from any flowing gas, e.g. air. These filtration devices are highly efficient and are very effective in removing fine particles like smoke and dust from the air stream. ESPs are used for controlling particulate emissions in various industries like oil refineries, pulp mills, and oil and coal fired utilities that

Page | 23

generate electricity which produce smoke. 

Dust Cyclones: These are used to remove particulate matter from a gas or air stream, without using filters, using vortex separation instead. Mixtures of fluids and solids are separated by using gravity and rotational effects. There is large scale use of cyclones in oil refineries as well as the cement industry wherein they form a part of the kiln preheaters.

Air Pollution Control Systems To Reduce NOx (Nitrogen Dioxide and Nitrogen Oxide)

Exhaust Gas Recirculation (EGR): This is a technique used for reducing NOx that is used in most diesel and gasoline engines. A part of the exhaust of an engine is recirculated back into its cylinders. When the incoming air is intermixed with the recirculated exhaust gas, it results in diluting the mixture with inert gas, reducing the adiabatic flame temperature and also lowering the excessive oxygen in diesel engines. The peak combustion temperature is also lowered because the specific heat capacity of the mix is increased by the exhaust gas. Since high temperatures cause Nox to form much faster, EGR helps in limiting NOx from being generated. Nox is produced when a mixture of oxygen and nitrogen is subjected to high temperatures.

Catalytic Converter: This is a device that is used to diminish the toxicity of emissions that are produced by internal combustion engines. First introduced in 1975 in the US in order to comply with the tightening regulations by the Environmental Protection Agency, catalytic converters are still used most commonly in the exhaust systems of motor vehicles. Some of the other places they are use in are: trains, mining equipment, forklifts, generator sets, and other machines equipped with engines.

Air Pollution Control Systems To Decrease Volatile Organic Compounds (VOC):

Gas Flare: Also called a flare stack, this is a chimney that is erected on oil rigs or oil wells, as well as landfills, chemical plants, and refineries. When flammable gas or unusable waste gas plus liquids are discharged by pressure relief valves, this device is used to burn them off. This device is also used in landfills to burn and/or vent the waste gas that is produced by the decomposing materials.

Biofilters: This is a technique for pollution control which uses living matter to trap and biologically degrade pollutants. In air pollution control, the pollutants in the air are subjected to microbiotic oxidation. In other words, when it is applied in the filtration and purification of air, microorganisms, such as fungi and bacteria that are embedded in a biofilm, are used to degrade the air pollutant.

Solid Waste What is Solid Waste?Solid waste is defined as any garbage, refuse, sludge from waste treatment plant, water supply treatment plant, or air pollution control facility and other materials, including solid, liquid, semisolid, contained gaseous resulting from industrials, commercials, mining and agricultural operations from community activities.

Characteristics of wastes

• Corrosive: these are wastes that include acids or bases that are capable of corroding mental containers, e.g. tanks

• Ignitability: this is waste that can create fires under certain condition, e.g. waste oils and solvents

• Reactive: these are unstable in nature; they cause explosions, toxic fumes when heated.

• Toxicity: waste which are harmful or fatal when ingested or absorb

Types of waste

• Non Hazardous waste: refuse, garbage, sludge, municipal trash.

• Hazardous waste: solvents acid, heavy metals, pesticides, and chemical sludges

• Radioactive: high and low-level radioactive waste

• Mixed waste: Radioactive organic liquids, radioactive heavy metals. Waste treatment Waste disposal

• • Incineration:

• Solidification: solid waste are melted or evaporated to produce a sand like residue.

• Landfills: waste is placed into or onto the land in disposal facilities.

• Underground injection wells: waste are

Page | 24

• Heat treatment: Heat applied at moderate temperature, is used in treating volatile solvents.

• Chemical treatment: is the application of chemical treatment in the treatment of corrosive solid.

injected under pressure into a steel and concrete-encased shafts placed deep in the earth.

• Waste piles: is accumulations of insoluble solid, non flowing hazard waste. Piles serves as temporary or final disposal.)

• land treatment: is a process in which solid waste, such as sludge from wastes is applied onto or incorporated into the soil surface.

• Waste are disposed in flowing rivers in less developed countries.

Impacts of solid waste on Terrestrial environment

Effects of Solid Waste on Animals and Aquatics life

• • Chemical poisoning through chemical inhalation

• Uncollected waste can obstruct the storm water runoff resulting in flood

• Low birth weight

• Cancer

• Congenital malformations

• Neurological disease

• Nausea and vomiting

• Increase in hospitalization of diabetic residents living near hazard waste sites.

• Mercury toxicity from eating fish with high levels of mercury

• Increase in mercury level in fish due to disposal of mercury in the rivers.

• Plastic found in oceans ingested by birds• Resulted in high algal population in rivers and

sea.• Degrades water and soil quality

• Impacts of solid waste on Environment

• • Waste breaks down in landfills to form methane, a potent greenhouse gas

• Change in climate and destruction of ozone layer due to waste biodegradable

• Littering, due to waste pollutions, illegal dumping, Leaching: is a process by which solid waste enter soil and ground water and contaminating them.

What is Solid Waste Management? Process involved in waste reduction

Solid Waste Management is the process of reducing, re-using and recycling waste products.

• Proper management of solid waste

• Involving public in plans for waste treatment and disposal

• Provide the public accurate, useful information about the whole projects, including the risks and maintain formal communication with public

• Educate people on different ways of handling waste.

• Waste Minimization is a process of reducing waste produce by individuals, communities and companies, which reduces the impact of chemical wastes on the environment to the greatest extent.

• Household level of proper segregation of waste, recycling and reuse.

• Process and product substitution e.g. use paper bag instead of plastic bags.

It requires a change in our habits but does not necessarily mean a return to a more difficult lifestyle. Good solid waste management improves our standard of living. In fact if we do not reduce waste, the economic and social cost of waste disposal will continue to increase and communities large and small will face increasingly harder decisions about managing their trash.

Precycling & RecyclingPrecycling is making purchasing decisions that will reduce waste. Recycling on the other hand is the process of producing goods from waste products or where possible, finding other uses for them.

We need to start re-using Paper

Glass Bottles

Aluminum Wrapping

Organic Waste such as spoilt or unwanted portions of food items, for example, banana skins

Plastics

Helpful Tips on Managing Solid Waste in the Home

Page | 25

1. Use sheets of used writing paper to make a message pad

2. Choose cloth diapers over disposable ones