oil refinery

Turning up the heat separates crude into a variety of higher molecules. Oil refining begins by heating the crude to 335oC in a furnace. The crude is being separated by the heat into various components because each one vaporizes at a different temperature. They cool and condense or liquefy in trays at various levels of the distillation tower as the vapors rise. At each tray level, the liquids collected are called cuts or fractions. Methane, the lightest cut is collected from the top of this fractioning tower. From the tower, the medium naphtha collected is used to make the reformate, the blending component for petrol. Other cuts from the tower can also be converted into petrol, diesel and kerosene after further processing

Breaking up is hard to do, but it's worth the petrol. The most desired refinery product is vehicle fuels. Distillation produces only a small amount of medium naphtha for direct blending into petrol, kerosene and diesel. Refiners developed a process to break up crude's large and heavy molecules from the distillation tower and turn them into smaller, lighter molecules used to make vehicle fuels. This process which is called cracking, which can double the yield of petrol, kerosene and diesel fuels per barrel.
There are 3 cracking techniques.Thermal cracking
Thermal cracking breaks down the residues or bottoms of the distillation process using heat. Large, heavy hydrocarbon molecules are broken up into light gases, diesel fuel and medium naphtha.

Catalytic cracking
Catalytic or cat cracking breaks large molecules of naphtha of heavy naphtha coming off the distillation tower using chemical catalysts. It breaks it into a variety of smaller molecules like methane, propane, light gas oils and medium naphtha. The rate of reaction is modified and increased by the catalyst, which is aluminum or platinum.

Hydrocracking
Hydrocracking is cat cracking in the presence of hydrogen. Greater yields and a large variety of higher quality products including medium naphtha are produced. Hydrocracking occurs at much higher pressures but at lower temperatures than catalytic cracking. Large, thick-walled chambers are required to contain the reactions and pressure.



Putting it all together to make high-octane petrol the naphtha, which is drawn from the distillation column and produced in the cracking process, is upgraded into high-octane naphtha in the reforming unit. Impurities are filtered out and some of the larger, low octane molecules are forced to lose hydrogen atoms, turning them into smaller, higher-octane naphtha molecules. This product, reformate is then ready for blending into high-octane petrol.

Why is reforming necessary?
To meet market requirements, reforming has developed better quality petrol. Thermal reforming which heated heavy naphtha to temperatures of 540oC at a pressure of about 600psi was first developed in the late 1920s. Naphtha is being transformed from low-octane to petrol of higher octane.