Programme 11: Industrial Chemistry

Programme Outline

This programme looks at the making of fertilisers from nitrogen and hydrogen, polystyrene from crude oil and sulphuric acid from sulphur. Each process is shown in the laboratory, along with the facilities used to carry it out on an industrial level. Computer graphics illustrate and animate explanations of the principles and dynamic processes involved.

The programme is divided into three parts:

11.1 Ammonia and Fertilisers
11.2 Plastics and Polymers
11.3 Sulphur and Sulphuric Acid

11.1 Ammonia and Fertilisers

Fertilisers increase the nitrogen content of the soil and aid crop production. They are made from ammonium nitrate, which is itself made from ammonia gas and nitric acid.

Ammonia is made from nitrogen and hydrogen mixed under pressure.

An animated diagram shows how the molecular structures reverse back and forth in this reaction. In industry, this reaction takes place in a pressurised tower using an iron catalyst at a temperature of 450°C, and at a pressure 250 times greater than atmospheric pressure. It is called the Haber–Bosch process.

Nitric acid is produced in several stages. Firstly, ammonia is oxidised with a platinum catalyst to form nitrogen monoxide.

Nitrogen monoxide is further oxidised to form nitrogen dioxide, a brown gas. When water is added, the gas goes clear as nitric acid is formed.

Ammonium nitrate is made by adding ammonia to the nitric acid.

11.2 Plastics and Polymers

The raw materials for making plastics are made from crude oil. The first stage is 'cracking' the molecules. In the laboratory, cracking is demonstrated with liquid paraffin, a derivative of crude oil. Liquid paraffin consists of chains of 20 or more carbon atoms joined with single bonds. Such chains are called alkanes. To crack them, paraffin is poured onto glass wool and heated with a ceramic catalyst. The colourless gas released contains alkenes, which are shorter carbon chains than alkanes and have a double carbon bond. Alkenes turns bromine solution from red-brown to colourless. The alkenes are monomers or building blocks of polymers.

Polystyrene is made from monomers called styrenes. If the styrenes are heated in a water bath for a few hours, they bond into the polymer, polystyrene. The molecular structure of this is shown.

11.3 Sulphur and Sulphuric Acid

Sulphur is extracted from rocks. When it is heated in air it burns, with a characteristic blue flame, and forms sulphur dioxide.

The next stage is to further oxidise the sulphur dioxide to sulphur trioxide. This is done at a temperature of 450°C, using a catalyst, and must be carefully controlled to stop the reaction reversing completely.

Sulphur trioxide plus water, in a sulphuric acid solution, makes more sulphuric acid.

Sulphuric acid is widely used in industry. One of its properties is its ability to absorb water. This is seen when it is added to sugar. Water is absorbed from the sugar and released as steam, leaving pure carbon.