Everything Science Grade 12

5.2 CHAPTER 5. THE CHEMICAL INDUSTRY

DEFINITION: Steam cracking

Steam cracking occurs under very high temperatures. During the pro-

cess, a liquid or gaseous hydrocarbon is dilutedwith steam and then

briefly heated in a furnace at a temperature of about 850 circC. Steam

cracking is used to convert ethane to ethylene. Ethylene is a chemical

that is needed to makeplastics. Steam crackingis also used to make

propylene, which is an important fuel gas.

2. Production of crude oil
   Sasol obtains crude oiloff the coast of Gabon(a country in West Africa) and
   refines this at the Natrefrefinery (figure 5.2). Sasol also sells liquid fuelsthrough
   a number of service stations.

Imported

crude oil

Oil processed

at Natref

refinery

Linear-chained hydrocarbons

e.g. waxes, paraffins

and diesel.

Figure 5.2: Crude oil isrefined at Sasol’s Natrefrefinery to produce liquid fuels

3. Liquid fuels from natural gas
   Sasol produces naturalgas in Mozambique and is expanding its ’gasto fuel’
   technology. The gas undergoes a complex process to produce linear-chained
   hydrocarbons such as waxes and paraffins (figure 5.3).

Mozambique

natural

gas

Autothermal

reactor

Sasol Slurry

Phase F-T

reactor

Linear-chained hydrocarbons

e.g. waxes and paraffins

Figure 5.3: Conversion of natural gas to liquid fuels

In the autothermal reactor, methane from natural gas reacts with steam andoxy-

gen over an iron-basedcatalyst to produce a synthesis gas. This is a similar

process to that involvedin coal gasification. Theoxygen is produced through the

fractional distillation ofair.