Crude oil I will be using crude oil as a recurring example during my PowerPoint (it represent the mixture). It is an exceptionally valuable resource that is made up mostly of alkanes. Crude oil is not renewable as it takes years to form, this makes it ever more precious. It is very impure, but oil is more efficient when it is pure. As there is a limited amount of oil, we need to minimise the amount of waste. A mechanism used to minimise waste is fractional distillation. The process will be repeated to furthermore to decrease the amount of waste.
Fractional distillation Fractional distillation is the breaking down of a mixture into its component parts. This is done by boiling the mixture and separating the products by their varying boiling points.
Method summary The mixture is separated by boiling and collecting each substance as it boils. Each substance is called a fraction, this is a mixture of hydrocarbons of similar chain length. As they are of similar chain length they have similar properties and therefore boil at a similar time.
Method stages The crude oil is heated in a furnace. A mixture of both liquid and vapour rise, and pass into a tower that is cooler at the top than the bottom. The vapours pass up this tower in which there are trays stacked at different levels, the trays contain bubble caps to trap the vapour. As the vapour rises it gets cooler, once sufficiently cool the vapour will condense into liquid and will therefore be collected in the tray below. The shorter chained hydrocarbons condense in the trays nearer to the top of the tower and vice versa. This occurs as they have lower boiling points, and are therefore liquids in lower temperatures.
Products NameApprox boiling temperature (C)Uses Petrol40Vehicle Fuel Naptha180Industrial cleaners and solvents, petrol industry Kerosene (paraffin)200Used as a gas for some heaters Diesel Oil250Vehicles e.g. lorries (produces less CO2 than petrol) Lubricating Oil280Reduce friction between multiple parts Fuel Oil310The fuel used in ships and power stations Greases and Wax340Used to make things like candles Bitumen367Used for road tar and roofing
Method flaws Small collections/pockets of certain length hydrocarbons may get trapped in trays that don’t corresponded with there boiling point. Also some substances have overlapping boiling points (as shown in the table) and will therefore remain mixed. Pollutants are created, some pollutants may induce taxes or disposal expenses. There are lots of products that are less valuable that are produced. ProductGasesPetrolNapthaKersosen e Gas oilFuel oil and wax Approxi mate boiling point/ K 310310-450400-490430-523590-620Above 620 Chain length 1-55-108-1211-1616-2425+ Percenta ge Present 2810142145
Industrial cracking Individual fractions all have different values, the general trend is that the longer the fractions are the less valuable they are. The naphtha fraction from the fractional distillation of crude oil is in huge demand, this makes it valuable as buyers will be competing for it. This fraction is desired for petrol and by the chemical industry. Industrial cracking is used to crack larger chains into more valuable shorter chains. An additional benefit of cracking is that some alkenes are produced, alkenes are more reactive than alkanes and therefore have some desirable uses. There are two sub-categories of industrial cracking. Thermal cracking and Catalytic cracking
Thermal cracking This involves heating alkanes to a high temperature (700-1200K),and putting them under high pressure, up to 7000kPa. Such high amounts of energy are required to break carbon-carbon bonds. These bonds break in a way that one electron from the pair in the covalent bond goes to the end carbon atom in each chain, one of chains pulls hydrogen off of the other, consequently one of the chains needs to be double bonded to fulfil the necessary amount of bonds, this is how the alkenes are formed. CCCC HHH HHHH H RR----- Thermal Cracking. CC HH HH R--CC H HH H R--. CC H H H R = + CC H HH H HR--- Free radicals- electrons= dot
Catalytic cracking Catalytic cracking is very similar to thermal cracking, but less energy is used (lower temperature and pressure), temperature approx. 720K. As there is less energy used a catalyst is required to make the reaction successful. The catalyst used is a Zeolite catalyst. Zeolites have a honeycomb structure with an enormous surface area, because of these properties it will have particularly regular collisions. The products of catalytic converting are mostly branched alkanes, such as cyclokanes and aromatic compounds.