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Chapter: The Chemical Industry - Grade 12
The chemical industry has been around for a very long time, but not always in the way we think of it today! Dyes, perfumes, medicines and soaps are all examples of products that have been made from chemicals that are found in either plants or animals. However, it was not until the time of the Industrial Revolution that the chemical industry as we know it today began to develop. At the time of the Industrial Revolution, the human population began to grow very quickly and more and more people moved into the cities to live. With this came an increase in the need for things like paper, glass, textiles and soaps. On the farms, there was a greater demand for fertilisers to help produce enough food to feed all the people in cities and rural areas. Chemists and engineers responded to these growing needs by using their technology to produce a variety of new chemicals. This was the start of the chemical industry.
In South Africa, the key event that led to the growth of the chemical industry was the discovery of diamonds and gold in the late 1800's. Mines needed explosives so that they could reach the diamonds and gold-bearing rock, and many of the main chemical companies in South Africa developed to meet this need for explosives. In this chapter, we are going to take a closer look at one of South Africa's major chemical companies, Sasol, and will also explore the chloralkali and fertiliser industries.
Oil and natural gas are important fuel resources. Unfortunately, South Africa has no large oil reserves and, until recently, had very little natural gas. One thing South Africa does have however, is large supplies of coal. Much of South Africa's chemical industry has developed because of the need to produce oil and gas from coal, and this is where Sasol has played a very important role.
Sasol was established in 1950, with its main aim being to convert low grade coal into petroleum (crude oil) products and other chemical feedstocks. A 'feedstock' is something that is used to make another product. Sasol began producing oil from coal in 1955.
The first interest in coal chemistry started as early as the 1920's. In the early 1930's a research engineer called Etienne Rousseau was employed to see whether oil could be made from coal using a new German technology called the Fischer-Tropsch process. After a long time, and after many negotiations, Rousseau was given the rights to operate a plant using this new process. As a result, the government-sponsored 'South African Coal, Oil and Gas Corporation Ltd' (commonly called 'Sasol') was formed in 1950 to begin making oil from coal. A manufacturing plant was established in the Free State and the town of Sasolburg developed around this plant. Production began in 1955. In 1969, the Natref crude oil refinery was established, and by 1980 and 1982 Sasol Two and Sasol Three had been built at Secunda.
Today, Sasol is an oil and gas company with diverse chemical interests. Sasol has three main areas of operation: Firstly, coal to liquid fuels technology, secondly the production of crude oil and thirdly the conversion of natural gas to liquid fuel.
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Different types of fuels It is important to understand the difference between types of fuels and the terminology that is used for them. The table below summarises some of the fuels that will be mentioned in this chapter.
| Compound | Description |
| Petroleum (crude oil) | A naturally occurring liquid that forms in the earth's lithosphere (see (Reference) in chapter (Reference)). It is a mixture of hydrocarbons, mostly alkanes, ranging from C |
| Natural gas | Natural gas has the same origin as petroleum, but is made up of shorter hydrocarbon chains. |
| Paraffin wax | This is made up of longer hydrocarbon chains, making it a solid compound. |
| Petrol (gasoline) | A liquid fuel that is derived from petroleum, but which contains extra additives to increase the octane rating of the fuel. Petrol is used as a fuel in combustion engines. |
| Diesel | Diesel is also derived from petroleum, but is used in diesel engines. |
| Liquid Petroleum Gas (LPG) | LPG is a mixture of hydrocarbon gases, and is used as a fuel in heating appliances and vehicles. Some LPG mixtures contain mostly propane, while others are mostly butane. LPG is manufactured when crude oil is refined, or is extracted from natural gas supplies in the ground. |
| Paraffin | This is a technical name for the alkanes, but refers specifically to the linear alkanes. Isoparaffin refers to non-linear alkanes. |
| Jet fuel | A type of aviation fuel designed for use in jet engined aircraft. It is an oil-based fuel and contains additives such as antioxidants, corrosion inhibitors and icing inhibitors. |
Hydrocracking is a cracking process that is assisted by the presence of an elevated partial pressure of hydrogen gas. It produces chemical products such as ethane, LPG, isoparaffins, jet fuel and diesel.
Steam cracking occurs under very high temperatures. During the process, a liquid or gaseous hydrocarbon is diluted with steam and then briefly heated in a furnace at a temperature of about
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Fractional distillation is the separation of a mixture into its component parts, or fractions. Since air is made up of a number of gases (with the major component being nitrogen), fractional distillation can be used to separate it into these different parts.
Sasol is a major player in the emerging Southern African natural gas industry, after investing 1.2 billion US dollars to develop onshore gas fields in central Mozambique. Sasol has been supplying natural gas from Mozambique's Temane field to customers in South Africa since 2004.
Refer to the diagrams summarising the three main Sasol processes, and use these to answer the following questions:
| Coal | Oil | Natural gas | |
| Origin | |||
| General chemical formula | |||
| Solid, liquid or gas |
Safety issues are important to consider when dealing with industrial processes. Read the following extract that appeared in the Business report on 6th February 2006, and then discuss the questions that follow.
Cape Town - Sasol, the petrochemicals group, was likely to face prosecution on 10 charges of culpable homicide after an explosion at its Secunda plant in 2004 in which 10 people died, a Cape Town labour law specialist said on Friday. The specialist, who did not want to be named, was speaking after the inquiry into the explosion was concluded last Tuesday. It was convened by the labour department.
The evidence led at the inquiry showed a failure on the part of the company to conduct a proper risk assessment and that: Sasol failed to identify hazards associated with a high-pressure gas pipeline running through the plant, which had been shut for extensive maintenance work, in the presence of hundreds of people and numerous machines, including cranes, fitters, contractors, and welding and cutting machines. Because there had never been a risk assessment, the hazard of the high-pressure pipeline had never been identified.
Because Sasol had failed to identify the risk, it did not take any measures to warn people about it, mark the line or take precautions. There had also been inadequacy in planning the shutdown work. In the face of a barrage of criticism for the series of explosions that year, Sasol embarked on a comprehensive programme to improve safety at its operations and appointed Du Pont Safety Resources, the US safety consultancy, to benchmark the petrochemical giant's occupational health and safety performance against international best practice.
From its humble beginnings in 1950, Sasol has grown to become a major contributor towards the South African economy. Today, the industry produces more than 150 000 barrels of fuels and petrochemicals per day, and meets more than 40% of South Africa's liquid fuel requirements. In total, more than 200 fuel and chemical products are manufactured at Sasolburg and Secunda, and these products are exported to over 70 countries worldwide. This huge success is largely due to Sasol's ability to diversify its product base. The industry has also helped to provide about 170 000 jobs in South Africa, and contributes around R40 billion to the country's Gross Domestic Product (GDP).
However, despite these obvious benefits, there are always environmental costs associated with industry. Apart from the vast quantities of resources that are needed in order for the industry to operate, the production process itself produces waste products and pollutants.
Any industry will always use up huge amounts of resources in order to function effectively, and the chemical industry is no exception. In order for an industry to operate, some of the major resources that are needed are energy to drive many of the processes, water, either as a coolant or as part of a process and land for mining or operations.
Refer to the data table below which shows Sasol's water use between 2002 and 2005 (Sasol Sustainable Development Report 2005), and answer the questions that follow.
| Water use ( |
2002 | 2003 | 2004 | 2005 |
| River water | 113 722 | 124 179 | 131 309 | 124 301 |
| Potable water | 15 126 | 10 552 | 10 176 | 10 753 |
| Total | 157 617 | 178 439 | 173 319 | 163 203 |
Large amounts of gases and pollutants are released during production, and when the fuels themselves are used. Refer to the table below, which shows greenhouse gas and atmospheric pollution data for Sasol between 2002 and 2005, and then answer the questions that follow. (Source: Sasol Sustainable Development Report 2005)
| Greenhouse gases and air pollutants (kilotonnes) | 2002 | 2003 | 2004 | 2005 |
| Carbon dioxide ( |
57 476 | 62 873 | 66 838 | 60 925 |
| Hydrogen sulfide ( |
118 | 105 | 102 | 89 |
| Nitrogen oxides ( |
168 | 173 | 178 | 166 |
| Sulfur dioxide ( |
283 | 239 | 261 | 222 |
Sasol is very aware of its responsibility towards creating cleaner fuels. From 1st January 2006, the South African government enforced a law to prevent lead from being added to petrol. Sasol has complied with this. One branch of Sasol, Sasol Technology also has a bio-diesel research and development programme focused on developing more environmentally friendly forms of diesel. One way to do this is to use renewable resources such as soybeans to make diesel. Sasol is busy investigating this new technology.
The chlorine-alkali (chloralkali) industry is an important part of the chemical industry, and produces chlorine and sodium hydroxide through the electrolysis of salt (NaCl). The main raw material is brine which is a saturated solution of sodium chloride (NaCl) that is obtained from natural salt deposits.
The products of this industry have a number of important uses. Chlorine is used to purify water, and is used as a disinfectant. It is also used in the manufacture of many every-day items such as hypochlorous acid, which is used to kill bacteria in drinking water. Chlorine is also used in paper production, antiseptics, food, insecticides, paints, petroleum products, plastics (such as polyvinyl chloride or PVC), medicines, textiles, solvents, and many other consumer products. Many chemical products such as chloroform and carbon tetrachloride also contain chlorine.
Sodium hydroxide (also known as 'caustic soda') has a number of uses, which include making soap and other cleaning agents, purifying bauxite (the ore of aluminium), making paper and making rayon (artificial silk).
Chlorine and sodium hydroxide can be produced through a number of different reactions. However, one of the problems is that when chlorine and sodium hydroxide are produced together, the chlorine combines with the sodium hydroxide to form chlorate (
Electrolytic cells
Electrolytic cells are used to split up or loosen ions. They are made up of an electrolyte and two electrodes, the cathode and the anode. An electrolytic cell is activated by applying an external electrical current. This creates an electrical potential across the cathode and anode, and forces a chemical reaction to take place in the electrolyte. Cations flow towards the cathode and are reduced. Anions flow to the anode and are oxidised. Two new products are formed, one product at the cathode and one at the anode.
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To separate the chlorine from the sodium hydroxide, the two half-cells were traditionally separated by a porous asbestos diaphragm, which needed to be replaced every two months. This was damaging to the environment, as large quantities of asbestos had to be disposed. Today, the asbestos is being replaced by other polymers which do not need to be replaced as often.
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| Mercury cell | Diaphragm cell | Membrane cell | |
| Main raw material | |||
| Mechanism of separating Cl | |||
| Anode reaction | |||
| Cathode reaction | |||
| Purity of NaOH produced | |||
| Energy consumption | |||
| Environmental impact |
Another important part of the chloralkali industry is the production of soaps and detergents. You will remember from an earlier chapter, that water has the property of surface tension. This means that it tends to bead up on surfaces and this slows down the wetting process and makes cleaning difficult. You can observe this property of surface tension when a drop of water falls onto a table surface. The drop holds its shape and does not spread. When cleaning, this surface tension must be reduced so that the water can spread. Chemicals that are able to do this are called surfactants. Surfactants also loosen, disperse and hold particles in suspension, all of which are an important part of the cleaning process. Soap is an example of one of these surfactants. Detergents contain one or more surfactants. We will go on to look at these in more detail.
A surfactant is a wetting agent that lowers the surface tension of a liquid, allowing it to spread more easily.
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Soaps can be made from either fats or oils. Beef fat is a common source of fat, and vegetable oils such as palm oil are also commonly used.
Soap is a surfactant that is used with water for washing and cleaning. Soap is made by reacting a fat with either sodium hydroxide (NaOH) or potassium hydroxide (KOH).
Detergents are compounds or mixtures of compounds that are used to assist cleaning. The term is often used to distinguish between soap and other chemical surfactants for cleaning.
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Nutrients are very important for life to exist. An essential nutrient is any chemical element that is needed for a plant to be able to grow from a seed and complete its life cycle. The same is true for animals. A macronutrient is one that is required in large quantities by the plant or animal, while a micronutrient is one that only needs to be present in small amounts for a plant or an animal to function properly.
A nutrient is a substance that is used in an organism's metabolism or physiology and which must be taken in from the environment.
In plants, the macronutrients include carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P) and potassium (K). The source of each of these nutrients for plants, and their function, is summarised in Table 6. Examples of micronutrients in plants include iron, chlorine, copper and zinc.
| Nutrient | Source | Function |
| Carbon | Carbon dioxide in the air | Component of organic molecules such as carbohydrates, lipids and proteins |
| Hydrogen | Water from the soil | Component of organic molecules |
| Oxygen | Water from the soil | Component of organic molecules |
| Nitrogen | Nitrogen compounds in the soil | Part of plant proteins and chlorophyll. Also boosts plant growth. |
| Phosphorus | Phosphates in the soil | Needed for photosynthesis, blooming and root growth |
| Potassium | Soil | Building proteins, part of chlorophyll and reduces diseases in plants |
Animals need similar nutrients in order to survive. However since animals can't photosynthesise, they rely on plants to supply them with the nutrients they need. Think for example of the human diet. We can't make our own food and so we either need to eat vegetables, fruits and seeds (all of which are direct plant products) or the meat of other animals which would have fed on plants during their life. So most of the nutrients that animals need are obtained either directly or indirectly from plants. Table 7 summarises the functions of some of the macronutrients in animals.
| Nutrient | Function |
| Carbon | Component of organic compounds |
| Hydrogen | Component of organic compounds |
| Oxygen | Component of organic compounds |
| Nitrogen | Component of nucleic acids and proteins |
| Phosphorus | Component of nucleic acids and phospholipids |
| Potassium | Helps in coordination and regulating the water balance in the body |
Micronutrients also play an important function in animals. Iron for example, is found in haemoglobin, the blood pigment that is responsible for transporting oxygen to all the cells in the body.
Nutrients then, are essential for the survival of life. Importantly, obtaining nutrients starts with plants, which are able either to photosynthesise or to absorb the required nutrients from the soil. It is important therefore that plants are always able to access the nutrients that they need so that they will grow and provide food for other forms of life.
Plants are only able to absorb soil nutrients in a particular form. Nitrogen for example, is absorbed as nitrates, while phosphorus is absorbed as phosphates. The nitrogen cycle (chapter (Reference)) describes the process that is involved in converting atmospheric nitrogen into a form that can be used by plants.
However, all these natural processes of maintaining soil nutrients take a long time. As populations grow and the demand for food increases, there is more and more strain on the land to produce food. Often, cultivation practices don't give the soil enough time to recover and to replace the nutrients that have been lost. Today, fertilisers play a very important role in restoring soil nutrients so that crop yields stay high. Some of these fertilisers are organic (e.g. compost, manure and fishmeal), which means that they started off as part of something living. Compost for example is often made up of things like vegetable peels and other organic remains that have been thrown away. Others are inorganic and can be made industrially. The advantage of these commercial fertilisers is that the nutrients are in a form that can be absorbed immediately by the plant.
A fertiliser is a compound that is given to a plant to promote growth. Fertilisers usually provide the three major plant nutrients and most are applied via the soil so that the nutrients are absorbed by plants through their roots.
When you buy fertilisers from the shop, you will see three numbers on the back of the packet e.g. 18-24-6. These numbers are called the NPK ratio, and they give the percentage of nitrogen, phosphorus and potassium in that fertiliser. Depending on the types of plants you are growing, and the way in which you would like them to grow, you may need to use a fertiliser with a slightly different ratio. If you want to encourage root growth in your plant for example, you might choose a fertiliser with a greater amount of phosphorus. Look at the table below, which gives an idea of the amounts of nitrogen, phosphorus and potassium there are in different types of fertilisers. Fertilisers also provide other nutrients such as calcium, sulfur and magnesium.
| Description | Grade (NPK %) |
| Ammonium nitrate | 34-0-0 |
| Urea | 46-0-0 |
| Bone Meal | 4-21-1 |
| Seaweed | 1-1-5 |
| Starter fertilisers | 18-24-6 |
| Equal NPK fertilisers | 12-12-12 |
| High N, low P and medium K fertilisers | 25-5-15 |
The industrial production of fertilisers may involve several processes.
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The Haber process developed in the early 20th century, before the start of World War 1. Before this, other sources of nitrogen for fertilisers had included saltpeter (
Eutrophication is the enrichment of an ecosystem with chemical nutrients, normally by compounds that contain nitrogen or phosphorus. Eutrophication is considered a form of pollution because it promotes plant growth, favoring certain species over others. In aquatic environments, the rapid growth of certain types of plants can disrupt the normal functioning of an ecosystem, causing a variety of problems. Human society is impacted as well because eutrophication can decrease the resource value of rivers, lakes, and estuaries making recreational activities less enjoyable. Health-related problems can also occur if eutrophic conditions interfere with the treatment of drinking water.
Eutrophication refers to an increase in chemical nutrients in an ecosystem. These chemical nutrients usually contain nitrogen or phosphorus.
In some cases, eutrophication can be a natural process that occurs very slowly over time. However, it can also be accelerated by certain human activities. Agricultural runoff, when excess fertilisers are washed off fields and into water, and sewage are two of the major causes of eutrophication. There are a number of impacts of eutrophication.
South Africa's Department of Water Affairs and Forestry has a 'National Eutrophication Monitoring Programme' which was set up to monitor eutrophication in impoundments such as dams, where no monitoring was taking place.
Despite the impacts, there are a number of ways of preventing eutrophication from taking place. Cleanup measures can directly remove the excess nutrients such as nitrogen and phosphorus from the water. Creating buffer zones near farms, roads and rivers can also help. These act as filters and cause nutrients and sediments to be deposited there instead of in the aquatic system. Laws relating to the treatment and discharge of sewage can also help to control eutrophication. A final possible intervention is nitrogen testing and modeling. By assessing exactly how much fertiliser is needed by crops and other plants, farmers can make sure that they only apply just enough fertiliser. This means that there is no excess to run off into neighbouring streams during rain. There is also a cost benefit for the farmer.
In many cases, the damage from eutrophication is already done. In groups, do the following:
Why we need fertilisers
There is likely to be a gap between food production and demand in several parts of the world by 2020. Demand is influenced by population growth and urbanisation, as well as income levels and changes in dietary preferences.
The facts are as follows:
Conclusion: Fertilisers are needed!
The flow diagram below shows the main steps in the industrial preparation of two important solid fertilisers.
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You will remember from chapter (Reference) that a galvanic cell (also known as a voltaic cell) is a type of electrochemical cell where a chemical reaction produces electrical energy. The emf of a galvanic cell is the difference in voltage between the two half cells that make it up. Galvanic cells have a number of applications, but one of the most important is their use in batteries. You will know from your own experience that we use batteries in a number of ways, including cars, torches, sound systems and cellphones to name just a few.
A battery is a device in which chemical energy is directly converted to electrical energy. It consists of one or more voltaic cells, each of which is made up of two half cells that are connected in series by a conductive electrolyte. The voltaic cells are connected in series in a battery. Each cell has a positive electrode (cathode), and a negative electrode (anode). These do not touch each other but are immersed in a solid or liquid electrolyte.
Each half cell has a net electromotive force (emf) or voltage. The voltage of the battery is the difference between the voltages of the half-cells. This potential difference between the two half cells is what causes an electric current to flow.
Batteries are usually divided into two broad classes:
The capacity of a battery, in other words its ability to produce an electric charge, depends on a number of factors. These include:
In a lead-acid battery, each cell consists of electrodes of lead (Pb) and lead (IV) oxide (PbO
The chemical half reactions that take place at the anode and cathode when the battery is discharging are as follows:
Anode (oxidation):
Cathode (reduction):
The overall reaction is as follows:
The emf of the cell is calculated as follows:
EMF = E (cathode)- E (anode)
EMF = +1.685 V - (-0.356 V)
EMF = +2.041 V
Since most batteries consist of six cells, the total voltage of the battery is approximately 12 V.
One of the important things about a lead-acid battery is that it can be recharged. The recharge reactions are the reverse of those when the battery is discharging.
The lead-acid battery is made up of a number of plates that maximise the surface area on which chemical reactions can take place. Each plate is a rectangular grid, with a series of holes in it. The holes are filled with a mixture of lead and sulfuric acid. This paste is pressed into the holes and the plates are then stacked together, with suitable separators between them. They are then placed in the battery container, after which acid is added (Figure 14).
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Lead-acid batteries have a number of applications. They can supply high surge currents, are relatively cheap, have a long shelf life and can be recharged. They are ideal for use in cars, where they provide the high current that is needed by the starter motor. They are also used in forklifts and as standby power sources in telecommunication facilities, generating stations and computer data centres. One of the disadvantages of this type of battery is that the battery's lead must be recycled so that the environment doesn't become contaminated. Also, sometimes when the battery is charging, hydrogen gas is generated at the cathode and this can cause a small explosion if the gas comes into contact with a spark.
A simplified diagram of a zinc-carbon cell is shown in Figure 15.
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A zinc-carbon cell is made up of an outer zinc container, which acts as the anode. The cathode is the central carbon rod, surrounded by a mixture of carbon and manganese (IV) oxide (MnO
The paste of ammonium chloride reacts according to the following half-reaction:
The manganese(IV) oxide in the cell removes the hydrogen produced above, according to the following reaction:
The combined result of these two reactions can be represented by the following half reaction, which takes place at the cathode:
Cathode:
The anode half reaction is as follows:
Anode:
The overall equation for the cell is:
Alkaline batteries are almost the same as zinc-carbon batteries, except that the electrolyte is potassium hydroxide (KOH), rather than ammonium chloride. The two half reactions in an alkaline battery are as follows:
Anode:
Cathode:
Zinc-carbon and alkaline batteries are cheap primary batteries and are therefore very useful in appliances such as remote controls, torches and radios where the power drain is not too high. The disadvantages are that these batteries can't be recycled and can leak. They also have a short shelf life. Alkaline batteries last longer than zinc-carbon batteries.
The idea behind today's common 'battery' was created by Georges Leclanche in France in the 1860's. The anode was a zinc and mercury alloyed rod, the cathode was a porous cup containing crushed MnO
While batteries are very convenient to use, they can cause a lot of damage to the environment. They use lots of valuable resources as well as some potentially hazardous chemicals such as lead, mercury and cadmium. Attempts are now being made to recycle the different parts of batteries so that they are not disposed of in the environment, where they could get into water supplies, rivers and other ecosystems.
A dry cell, as shown in the diagram below, does not contain a liquid electrolyte. The electrolyte in a typical zinc-carbon cell is a moist paste of ammonium chloride and zinc chloride.
NOTE TO SELF: Insert diagram
The paste of ammonium chloride reacts according to the following half-reaction:
Manganese(IV) oxide is included in the cell to remove the hydrogen produced during half-reaction (a), according to the following reaction:
The combined result of these two half-reactions can be represented by the following half reaction:
(DoE Exemplar Paper 2, 2007)
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| Column A | Column B |
| The electrode metal | Lead sulphate |
| Electrolyte | Mercury |
| A product of the overall cell reaction | Electrolytic |
| An oxidising agent in the cathode half-reaction | Lead |
| Type of cells in a lead-acid battery | Sulfuric acid |
| Ammonium chloride | |
| Lead oxide | |
| Galvanic |
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This work is licensed by Rory Adams, Free High School Science Texts Project, and Mark Horner under a Creative Commons Attribution License (CC-BY 3.0), and is an Open Educational Resource.
Last edited by Mark Horner on Aug 14, 2009 7:03 am GMT-5.
