What are Petrochemicals?
Taking the mystery out of petrochemicals
The term ‘petrochemicals’ can bring a glazed look to many faces while words such as ‘butadiene’ and ‘paraxylene’ can sound very complicated. They conjure up a world of mystery, yet the products from petrochemicals are taken very much for granted. They impact modern life in the home, office, when travelling and in our leisure activities. And many do not realise that our modern life styles would not be possible without petrochemicals.
So where do petrochemicals come from? They are initially derived from crude oil and natural gas which are extracted from the ground. This oil and gas goes through a number of refining processes before being produced into petrochemicals.
But the petrochemicals do not reach the final consumer. They again undergo several transformations to make products that seem to bear no relation whatsoever to the initial starting point. As a result, few of us make the connection between the petrochemical industry and, for example, the clothes we wear, the shampoo we wash our hair with, the packaging of food, home furnishings, CDs and computers.
How did the petrochemical industry begin?
The petrochemical industry is relatively young – it did not start to take off until the 1940s. However, its origins go back to the 18th century when coal began to be mined and cheap energy became available. In the next century it was realised that the liquor from gas works and coal tar could become an important source of chemicals. In Britain and Germany new industries sprang up making dyes, solvents and rubbers.
Particular developments during the 19th century included the first aniline dye (mauve) and a safer explosive, dynamite, made from nitroglycerine. Wood pulp also became a raw material for the chemical industry leading to products such as celluloid and rayon.
But the greatest discovery in the 19th century was not a new chemical as such, but a new source of chemicals – oil. The first oil well was drilled in Pennsylvania in 1859 and the oil extracted was refined to obtain paraffin for lamps and heating. However, with the advent of the motor car, this source of energy was rapidly adopted due to its versatility.
Oil also provided many of the raw materials that the petrochemical industry needs. The early 20th century witnessed the developments of products such as synthetic rubbers, Bakelite, polystyrene and nylon. During World War II, demand grew for synthetic materials to replace costly and less efficient products, as well as replacing essential supplies of raw materials that had been cut off by the conflicts.
When the war ended, the skills of the chemical companies were set to develop new processes and catalysts for the production of modern plastics and fibres such as polyethylene and polypropylene. In addition, the cheap oil and gas available through the 1950s and 1960s allowed the petrochemical industry to grow at a phenomenal rate. Growth in the developed countries has now slowed as markets for these new products have become penetrated while higher raw material costs have also impacted the industry.
Petrochemical companies evolve
As the petrochemical industry has grown and evolved, the companies involved have also changed. Going back to the 19th century, the origins of companies such as BASF, ICI and DuPont can be traced. The technical knowledge and skills of these chemical companies allowed them to become major petrochemical players during the 20th century. Later, the oil companies – ExxonMobil, Shell, BP, etc – also became involved in petrochemical manufacture in order to derive further value from their oil refining businesses.
After the oil shocks of the 1970s and 1980s, some of the traditional chemical companies left the petrochemical business for competitive reasons, one example being ICI who had been the inventor of Perspex and polyethylene (Polythene). More recently, there has been the emergence of petrochemical companies in the high growth Asian countries and the energy-rich Middle East.
Where are petrochemicals derived?
The manufacture of petrochemicals begins with crude oil and natural gas which were formed millions of years ago, deep in the earth’s crust, from the slow and lengthy decay of plants and animals. The crude oil and gas are extracted from the ground, either on land or under the oceans, by sinking oil or gas wells. They are then transported by ship and/or pipelines to refineries.
Crude oil is not a chemical compound as such but is made up of thousands of different compounds. All these compounds contain carbon and hydrogen atoms, hence called hydrocarbons. Some of the hydrocarbons are simple, containing only a few carbon atoms, but others are complex with as many as 85 carbon atoms. Natural gas also contains a number of hydrocarbons but they are much simpler and contain only a few carbon atoms.
At the refinery, physical and chemical changes are made to these hydrocarbon compounds by a number of specialised processes. One of these processes is distillation. By heating the crude oil, it is possible to separate the more complex (heavier) compounds from the simpler (lighter) ones into groups called fractions.
One of these fractions, called naphtha, although used to make gasoline, is also a major source from which petrochemicals can be derived. Gas oil is another fraction that can be used in petrochemical manufacture.
In the case of natural gas, a process called natural gas liquefaction is used to separate the fractions. The simplest, called methane, is commonly piped into our homes to be used in heating and cooking. The next, ethane, is used mainly for petrochemicals. Propane and butane can also be converted into petrochemicals but are also used as a fuel in homes and factories. At home, these gases are stored and used from gas cylinders.
Where petrochemical manufacture begins
In petrochemical manufacture, the raw materials (often called feedstocks) from the refinery are processed through an operation called cracking. In this operation, the longer hydrocarbon molecules are ‘cracked’ apart by heat into smaller, more valuable fractions. Hence the plant where these operations are conducted is called a cracker.
Most petrochemicals are made in a steam cracker where steam and high temperatures are employed. When a catalyst is used, the process is known as catalytic cracking, which is used mainly to make gasoline but can also be a source of petrochemicals.
Once the cracking process has been completed, the new hydrocarbon products are separated out. They become the building blocks of the petrochemical industry: olefins such as ethylene, propylene and butadiene; and the aromatics, so called because of their sweet oil smell, being mainly benzene, toluene and xylenes.
These building block chemicals are then processed in a number of steps with each other or other chemicals to make the end products which are used by the so-called downstream industries, the customers of petrochemicals. These downstream industries make the final product bought by the consumer such as plastic items, detergents, clothes, paints, etc.
Below are examples of end products from the cracker-derived petrochemicals:
- Ethylene – the largest derivative is polyethylene which is used to make plastic carrier bags, wire and cable, packaging containers, plastic kitchen items, toys, pipes, etc.
- Propylene – the main outlet is polypropylene which is a very versatile plastic which has many uses such as carpets, yoghurt pots, household cleaners’ bottles, electrical appliances, outdoor furniture, rope, etc.
- C4 derivatives – the main one is butadiene which is used in the manufacture of synthetic rubber for automobile tyres, footwear, golf balls, etc.
- Benzene – the largest volume aromatic compound is used to make polystyrene which ends up in products such as insulation, cups, packaging for carry-out foods, casings for electrical goods and computers, etc.
- Toluene – it can be used to make polyurethanes for use in furniture, bedding, footwear, varnishes, adhesives, etc.
- Xylenes – the main xylene is paraxylene which is the raw material for polyesters used in clothes, tapes, water and soft drink bottles, etc.
Where petrochemicals have impacted different industries
A huge variety of petrochemical products are found in many different industries. In fact, some industries such as electronics and computer sectors could have not developed without petrochemicals. Petrochemicals are also used to meet fundamental human needs, such as health, hygiene, housing and food. It is an inventive business sector that is constantly adapting to new environments and meeting new challenges.
The quantum leap in communications technology has been made possible by petrochemicals. For example, the computer could not function without microchips, made using petrochemicals, while the computer housings and keyboards are made from styrenic plastics. CDs and CD-ROMs start with a simple piece of plastic made from polycarbonate, a plastic derived from benzene and propylene. The transparent box in which CDs are stored is usually made from polystyrene.
In the transport sector, petrochemicals contribute to saving energy and improving safety. For example, synthetic rubber gives tyres better road-hugging ability while phenolic resins are used in binders for friction materials in brakes and clutches. Special coatings to give unusual colour effects have been developed for cars. Approximately 100kg of petrochemical-based plastics in a modern car can replace 200 to 300kg of traditional materials. So nylons are replacing metals and polycarbonate is replacing glass.
Petrochemicals make a contribution to the progress in health care and hygiene. For example, cumene and phenol are used as a starting material to make aspirin and penicillin. Some petrochemical resins are used in drug purification, making it easier to mass produce drugs. Plastics are essential for making disposable syringes, containers for storing blood and vaccines as well as medical devices such as inhalers.
In the construction sector, petrochemicals are used in the pipes, windows and paints found in buildings. A more unusual application is the use of polyurethane chemicals in the insulating panels for a luxury hotel in Dubai. The transparent roof the Olympic stadium in Athens is manufactured from polycarbonate.
In the home, products based on petrochemicals are found everywhere. Working surfaces, shelves and tables are easy to wash thanks to laminates manufactured from petrochemicals. The cooker, microwave oven and refrigerator are amongst the numerous fixtures moulded from polymers. Non-stick frying pans coated with petrochemicals are easy to use and do not need to be scrubbed while liquid detergents made from ethylene make dish washing quicker and more hygienic.
In the bathroom, we find petrochemical-derived products from floor tiles through shampoo bottles to the toothbrush. Easy-care clothing, carpets, curtains and furnishing fabrics are made from man-made fibres derived from petrochemicals.
These examples illustrate that it is an exceptionally large industry that is also very global.