Sasol

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.

Interesting Fact:

The first interest in coal chemistry started as early as the 1920's. As a result, the government-sponsored 'South African Coal, Oil and Gas Corporation Ltd' (commonly called 'Sasol') 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.

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.

Sasol today: Technology and production

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.

Coal to liquid fuels

Sasol is involved in mining coal and converting it into synthetic fuels, using the Fischer-Tropsch technology. Figure 1 is a simplified diagram of the process that is involved.

**Figure 1:** The gasification of coal to produce liquid fuels

Coal gasification is also known as the Sasol/Lurgi gasification process, and involves converting low grade coal to a synthesis gas. Low grade coal has a low percentage carbon, and contains other impurities. The coal is put under extremely high pressure and temperature in the presence of steam and oxygen. The gas that is produced has a high concentration of hydrogen ( $H_{2}$ ) and carbon monoxide ( $CO$ ). That is why it is called a 'synthesis gas', because it is a mixture of more than one gas.

In the Sasol Advanced Synthol (SAS) reactors, the gas undergoes a high temperature Fischer-Tropsch conversion. Hydrogen and carbon monoxide react under high pressure and temperature and in the presence of an iron catalyst, to produce a range of hydrocarbon products. Below is the generalised equation for the process. Don't worry too much about the numbers that you see in front of the reactants and products. It is enough just to see that the reaction of hydrogen and carbon monoxide (the two gases in the synthesis gas) produces a hydrocarbon and water.

$(2 n + 1) H_{2} + nCO \to C_{n} H_{2 n + 2} + {nH}_{2} O$

A range of hydrocarbons are produced, including petrol, diesel, jet fuel, propane, butane, ethylene, polypropylene, alcohols and acetic acids.

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.

Table 1
Compound	Description
Petroleum (crude oil)	A naturally occurring liquid that forms in the earth's lithosphere (see Grade 11 notes). It is a mixture of hydrocarbons, mostly alkanes, ranging from $C_{5} H_{12}$ to $C_{18} H_{38}$ .
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 (branched) 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.

You will notice in the diagram that Sasol doesn't only produce liquid fuels, but also a variety of other chemical products. Sometimes it is the synthetic fuels themselves that are used as feedstocks to produce these chemical products. This is done through processes such as hydrocracking and steamcracking. Cracking is when heavy hydrocarbons are converted to simpler light hydrocarbons (e.g. LPG and petrol) through the breaking of $C - C$ bonds. A heavy hydrocarbon is one that has a high number of hydrogen and carbon atoms (more solid), and a light hydrocarbon has fewer hydrogen and carbon atoms and is either a liquid or a gas.

Definition 1: Hydrocracking: 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.

Definition 2: Steam cracking: 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 850 ℃. Steam cracking is used to convert ethane to ethylene. Ethylene is a chemical that is needed to make plastics. Steam cracking is also used to make propylene, which is an important fuel gas.

Production of crude oil

Sasol obtains crude oil off the coast of Gabon (a country in West Africa) and refines this at the Natref refinery (Figure 2). Sasol also sells liquid fuels through a number of service stations.

Figure 2: Crude oil is refined at Sasol's Natref refinery to produce liquid fuels
Liquid fuels from natural gas

Sasol produces natural gas in Mozambique and is expanding its 'gas to fuel' technology. The gas undergoes a complex process to produce linear-chained hydrocarbons such as waxes and paraffins (Figure 3).

Figure 3: Conversion of natural gas to liquid fuels

In the autothermal reactor, methane from natural gas reacts with steam and oxygen over an iron-based catalyst to produce a synthesis gas. This is a similar process to that involved in coal gasification. The oxygen is produced through the fractional distillation of air.

Definition 3: Fractional distillation

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.

The syngas is then passes through a Sasol Slurry Phase Distillate (SSPD) process. In this process, the gas is reacted at far lower temperatures than in the SAS reactors. Apart from hard wax and candle wax, high quality diesel can also be produced in this process. Residual gas from the SSPD process is sold as pipeline gas while some of the lighter hydrocarbons are treated to produce kerosene and paraffin. Ammonia is also produced, which can be used to make fertilisers.

Interesting Fact:

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.

Exercise 1: Sasol processes

Problem 1:

Refer to the diagrams summarising the three main Sasol processes, and use these to answer the following questions:

Explain what is meant by each of the following terms:

crude oil
hydrocarbon
coal gasification
synthetic fuel
chemical feedstock

Answer 1:

1. A naturally occurring liquid that forms in the earth’s lithosphere. It is a mixture of hydrocarbons, mostly alkanes, ranging from $C_{5} H_{12}$ to $C_{18} H_{38}$ .

2. An organic compound containing hydrogen and carbon, usually in a long chain.

3. Coal gasification is also known as the Sasol/Lurgi gasification process, and involves converting low grade coal to a synthesis gas.

4. Any fuel that is derived from naturally occurring sources. Also any fuel that does not occur naturally.

5. A chemical feedstock is any chemical that can be used to make more useful compounds.

Problem 2:

What is diesel?
Describe two ways in which diesel can be produced.

Answer 2:

1. Diesel is a long chain hydrocarbon derived from petroleum.

2. From coal gasification and from crude oil refining

Problem 3:

Describe one way in which lighter chemical products such as ethylene, can be produced.

Answer 3:

Coal gasification is also known as the Sasol/Lurgi gasification process, and involves
converting low grade coal to a synthesis gas. Low grade coal has a low percentage carbon, and contains other impurities. The coal is put under extremely high pressure and temperature in the presence of steam and oxygen. The gas that is produced has a high concentration of hydrogen and carbon monoxide.
In the Sasol Advanced Synthol (SAS) reactors, the gas undergoes a high temperature Fischer-Tropsch conversion. Hydrogen and carbon monoxide react under high pressure and temperature and in the presence of an iron catalyst, to produce a range of hydrocarbon products. Below is the generalised equation for the process. Don’t worry too much about the numbers that you see in front of the reactants and products. It is enough just to see that the reaction of hydrogen and
carbon monoxide (the two gases in the synthesis gas) produces a hydrocarbon and water.

Problem 4:

Coal and oil play an important role in Sasol's technology.

In the table below, summarise the similarities and differences between coal, oil and natural gas in terms of how they are formed ('origin'), their general chemical formula and whether they are solid, liquid or gas.

Table 2
	Coal	Oil	Natural gas
Origin
General chemical formula
Solid, liquid or gas

In your own words, describe how coal is converted into liquid fuels.
Explain why Sasol's 'coal to liquid fuels' technology is so important in meeting South Africa's fuel needs.
Low grade coal is used to produce liquid fuels. What is the main use of higher grade coal in South Africa?

Answer 4:

	Coal	Oil	Natural gas
Origin	South Africa, from mining	Gabon	Mozambique
General chemical formula	$C$	$C_{5} H_{12} to C_{18} H_{38}$	$C_{n} H_{2 n}$
Solid, liquid or gas	solid	liquid	gas

2. Coal gasification is also known as the Sasol/Lurgi gasification process, and involves converting low grade coal to a synthesis gas. Low grade coal has a low percentage carbon, and contains other impurities. The coal is put under extremely high pressure and temperature in the presence of steam and oxygen. The gas that is produced has a high concentration of hydrogen and carbon
monoxide. In the Sasol Advanced Synthol (SAS) reactors, the gas undergoes a high temperature
Fischer-Tropsch conversion. Hydrogen and carbon monoxide react under high pressure and temperature and in the presence of an iron catalyst, to produce a range of hydrocarbon products.

3. South Africa has a large supply of coal and so a technology that can convert what is easily available without paying costly import fees is very important in meeting the fuel needs of the country.

4. Higher grade coal is used for heating homes.

Case study 1: Safety issues and risk assessments

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 enquiry into the explosion was concluded last Tuesday. It was convened by the labour department. The evidence led at the enquiry 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 practise.

Explain what is meant by a 'risk assessment'.
Imagine that you have been asked to conduct a risk assessment of the Sasol/Lurgi gasification process. What information would you need to know in order to do this assessment?
In groups, discuss the importance of each of the following in ensuring the safety of workers in the chemical industry:
- employing experienced Safety, Health and Environment personnel
- regular training to identify hazards
- equipment maintenance and routine checks
What other precautions would you add to this list to make sure that working conditions are safe?

Sasol and the environment

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.

Exercise 2: Consumption of resources

Problem 1:

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.

Table 3
Water use (1000 m³)	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

Explain what is meant by 'potable' water.

Answer 1:

Potable water is water of a high purity or quality that is considered safe for consumption (drinking) by human beings.

Problem 2:

Describe the trend in Sasol's water use that you see in the above statistics.

Answer 2:

Water usage increased in 2003 and then decreased from 2004 to 2005. The use of potable water decreased to 2004 and then increased in 2005, while the use of river water increased to 2004 and then decreased in 2005.

The general trend is a decrease in water use.

Problem 3:

Suggest possible reasons for this trend.

Answer 3:

Sasol is likely to be more environmentally aware and is possibly trying to reduce water usage to help save a limited resource.

Problem 4:

List some of the environmental impacts of using large amounts of river water for industry.

Answer 4:

Using large amounts of river water means that many aquatic animals habits are reduced and threatened. Also there is less water in times of drought.

Any reasonable answer is acceptable.

Problem 5:

Suggest ways in which these impacts could be reduced

Answer 5:

Some examples are:Finding ways to use less water, carefully considering the ecosystems of the area, etc.

Interesting Fact:

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.

Exercise 3: Industry and the environment

Problem 1:

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)

Table 4
Greenhouse gases and air pollutants (kilotonnes)	2002	2003	2004	2005
Carbon dioxide ( ${CO}_{2}$ )	57 476	62 873	66 838	60 925
Hydrogen sulfide ( $H_{2} S$ )	118	105	102	89
Nitrogen oxides ( ${NO}_{x}$ )	168	173	178	166
Sulphur dioxide ( ${SO}_{2}$ )	283	239	261	222

Draw line graphs to show how the quantity of each pollutant produced has changed between 2002 and 2005.

Answer 1:

We plot carbon dioxide on a separate system of axes since the values are much larger than that of the other gases:

The general trend for all the pollutants is to increase to 2004 and then decrease in 2005.

Problem 2:

Describe what you see in the graphs, and suggest a reason for this trend.

Answer 2:

The general trend is for the pollutants to increase to 2004 and then decrease in 2005. However, hydrogen sulfide has been decreasing from 2002 to 2005 and sulfur dioxide initially decreased, then increased in 2004 before decreasing again. A possible reason may be that Sasol started trying to reduce emissions on environmental grounds.

Problem 3:

Explain what is meant by each of the following terms:

greenhouse gas
global warming

Answer 3:

A greenhouse gas is any gas that contributes to the warming effect of the Earth known as the greenhouse effect.
Global warming is the gradual increase in the Earth's temperature that may be a result of the greenhouse effect.

Problem 4:

Describe some of the possible effects of global warming.

Answer 4:

Higher sea levels, melting ice caps, warmer winters, any other reasonable answer.

Problem 5:

When sulphur dioxide is present in the atmosphere, it may react with water vapour to produce sulphuric acid. In the same way, nitrogen dioxide and water vapour react to form nitric acid. These reactions in the atmosphere may cause acid rain. Outline some of the possible consequences of acid rain.

Answer 5:

Acid rain causes trees and plants to die and it erodes statues and buildings.

Problem 6:

Many industries are major contributors towards environmental problems such as global warming, environmental pollution, over-use of resources and acid rain. Industries are in a difficult position: On one hand they must meet the ever increasing demands of society, and on the other, they must achieve this with as little environmental impact as possible. This is a huge challenge.

Work in groups of 3–4 to discuss ways in which industries could be encouraged (or in some cases forced) to reduce their environmental impact.
Elect a spokesperson for each group, who will present your ideas to the class.
Are the ideas suggested by each group practical?
How easy or difficult do you think it would be to implement these ideas in South Africa?

Answer 6:

This question is an open-ended discussion question suitable for class debates. Some of the ideas that could be discussed include reducing water usage, reducing power usage, investing money into finding cleaner chemical processes, finding uses for waste products, careful waste disposal and being proactive in the environment by planting trees, etc. Groups could discuss what steps companies could take and could investigate carbon footprints and carbon standards.

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Everything

Science

Sasol

Interesting Fact:

Sasol today: Technology and production

Interesting Fact:

Exercise 1: Sasol processes

Case study 1: Safety issues and risk assessments

Sasol and the environment

Exercise 2: Consumption of resources

Interesting Fact:

Exercise 3: Industry and the environment