Production of materials Flashcards
What is catalytic cracking?
the splitting (cracking) of large hydrocarbon molecules into smaller molecules in the presence of a catalyst. The more controlled process.
What are the products of catalytic cracking?
Alkanes and alkenes. (Both are useful, the shorter alkanes can be blended with petrol to increase the supply. Alkenes (particularly ethylene) are very useful ‘building block’ substances for making useful chemicals.
What catalyst is used in catalytic cracking?
Zeolite crystals.
What are zeolites?
Crystalline aluminosilicates (crystalline substance composed of substances made of Al, Si, and O). It has high thermal stability and is non-toxic (no effects on environment/humans)
What is the structure of Zeolites?
3D structure containing a large number of pores in which the reactant molecules are absorbed thereby weakening bonds and lowering the activation energy.
What are the conditions for catalytic cracking to be carried out at?
500°C, in the absence of air, with pressure just above atmospheric pressure.
What is thermal/steam cracking and what are the conditions?
Mixture of alkanes with steam passed through very hot metal tubes (700˚C to 1000˚C) with the absence of air and at just above atmospheric pressure to decompose the alkanes. DOES NOT USE A CATALYST.
Why is steam used in thermal cracking?
The use of steam is that is allows for easy flow of hydrocarbon gases, it dilutes the mixture to create smooth reactions, and it removes carbon deposits in the metal tubes.
Why is ethylene so reactive?
Ethylene is an alkene and due to the carbon double bond is highly reactive.
Why does ethylene having a double bond make it reactive?
Many substances can react with alkenes through breaking open the double bond into two single bonds, creating an addition reaction where other atoms/molecules can be added to the hydrocarbon.
How is ethylene used to make Ethylene Glycol?
Large quantities of ethylene are oxidised (reacted with oxygen) at about 250˚C with silver as a catalyst to produce ethylene oxide (which can be used as a fumigant). The ethylene oxide is then hydrolysed at 100˚C to form ethylene glycol which is used as a solvent to make antifreeze to put in cooling systems of cars and trucks. (also in manufacturing of polyester)
How is ethylene used to make ethanol?
Ethylene can be hydrated to produce ethanol. This is done at high pressure at about 300˚C using a H3PO4 catalyst. Ethanol is then used in fuel, industrial commercial and domestic solvent, and as a cleaning and disinfecting fluid.
What is polymerisation?
A chemical reaction where identical monomers combine to form a polymer.
Is ethylene a monomer?
Ethylene is a monomer that polymerises to form polyethylene. Double bond is broken and links made: 300 to 3000 monomers
Identify polyethylene as an addition polymer and explain the meaning of this.
Addition polymerisation is the process that happens when the monomer units join together forming the polymer. Nothing is lost (atoms, electrons), the double bond simply ‘opens’ and monomers attach.
