Production of anti knock compound

The Octel Amlwch site was built in the early 1950s to produce bromine from sea water which was then used to produce ethylene dibromide (EDB) which was essential for the production of tetra ethyl lead (TEL) anti knock compound.  The anti knock compound was blended with gasoline to prevent ” knock” within a cylinder engine which can lead to damage and loss of performance. To learn more about engine knock please view the video below.

The use of TEL on it’s own was shown to reduce engine knock, however other problems became apparent. A grayish yellow residue of lead oxide was deposited on spark plugs, exhaust valves and in the cylinder combustion chamber leading to reduced performance and engine life. However it was discovered that if ethylene dibromide (EDB) was added to the TEL it prevented the formation of the lead deposits as they were cnverted to lead bromide which was volatile at engine operting temperatures and so was expelled from the exhaust system into the air.

The mixture of TEL and EDB became known as the anti knock compound and it was this which was produced at Octel Ellesmere Port using an autoclave batch process which is shown in the diagram below.

Production of anti knock compound

The electrolysis of dry sodium chloride in Downs cells produced chlorine gas and molten sodium.

downs cellThe sodium is reacted with molten lead to produce a lead sodium allow which is cooled to solidify and then flaked under nitrogen.

In another part of the plant, electrolysis of brine produces hydrogen and chorine



These are combusted together to form hydrogen chloride which is then used in the hydro chlorination of ethylene to produce ethyl chloride. (EC)

Chlorine is reacted directly with ethylene to produce ethylene dichloride (EDC).  Some chlorine is also exported to Amlwch in rail tankers where it is used to extract bromine from sea water which is then reacted with ethylene to produce ethylene dibromide. (EDB)

The flacked sodium lead alloy is batch charged into a steel autoclave fitted with agitators. Ethyl chloride is added over a few hours and the reaction temp maintained at 70-75 C by refluxing the ethyl chloride and external cooling. Once the reaction is complete the autoclave is vented and discharged into water containing steam stills. The unreacted ethyl chloride is removed by steam distillation and then the TEL. The crude TEL is water washed and then blended with the required amounts of EDC and or EDB together with a dye to produce the antiknock compound (AKC). The AKC is used in a concentration of 3ml/gal of gasoline in leaded fuel.