C1.5 Other Useful Substances From Crude Oil

C1.5 Other Useful Substances From Crude Oil

1. C1.5.1 Obtaining Useful Substances From Crude Oil

   • Hydrocarbons can be cracked to produce smaller, more useful molecules: the hydrocarbons are heated, the vapours are either passed over a hot catalyst or mixed with steam and heated to a very high temperature so that thermal decomposition reactions then occur.
     • The products of cracking include alkanes and unsaturated hydrocarbons called alkenes. Alkenes have the general formula CnH2n.
       • Alkenes are unsaturated hydrocarbons; they contain a double covalent bond. The presence of this double bond allows alkenes to react in ways that alkanes cannot. They can react with oxygen in the air, so they could be used as fuels. They can be used to make ethanol and polymers.
         • Alkenes react with bromine water, turning it from orange to colourless.

2. C1.5.2 Polymers

   • Alkenes can be used to make polymers such as poly(ethene) and poly(propene). In these reactions, many small molecules (monomers) join together to form very large molecules (polymers).
     • Polymers have many useful applications and new uses are being developed: new packaging materials, waterproof coatings for fabrics, dental polymers, wound dressings, hydrogels, smart materials (including shape memory polymers).
       • Many polymers are not biodegradable, so they are not broken down by microbes leading to problems with waste disposal.
         • Plastic bags are being made from polymers and cornstarch so that they break down more easily. Biodegradable plastics made from cornstarch have been developed.
           • Many polymers can be recycled reducing the disposal problems and the amount of crude oil used but the different polymers must be separated from each other first, which can be difficult and expensive to do.

3. C1.5.3 Ethanol

   • Ethanol can be produced by hydration of ethene with steam in the presence of a catalyst; ethene + steam → ethanol
     • Ethanol can also be produced by fermentation with yeast, using renewable resources; sugar → carbon dioxide + ethanol