The compounds with lower boiling points rise faster and higher on the column while those with higher boiling points evaporate slower and do not reach the top of the tower (the vapours condense on the lower trays). The distillation process separates the constituents of the crude oil on the basis of their difference in their boiling point. Refinery gas, (methane, ethane, propane and butane) is removed as a composite gas mixture on the top of the column (Figure 1 and Table 1). The second fraction, naphtha/gasoline, boils in the range of 40-180oC. As the other fractions have higher boiling points, they collect on the lower trays.
Cracking converts heavy fractions from the primary distillation into more useful compounds. For example, when C11H24 is cracked, C9H20 and C2H4 are obtained (Hill, G.C and Holman, J.C, 400-401). C9H20 can be used as gasoline, but more importantly C2H4 can be used as a starting material for the manufacture of products such as plastics, alcohol, diols etc. The cracking process also provides more useful branched-chain alkanes.
Catalytic cracking is a process in which long chain alkanes are converted into hydrocarbons of lower molecular weights by the mediation of catalysts at fairly high temperatures. The catalysts normally consist of Al2O3-SiO2 mixtures (Brown, T.L, LeMay, H.E and Bursten, B.E., 947).
Platforming is a process in which linear alkanes are converted into aromatic hydrocarbons. For example, heptane can be converted into toluene in the presence of catalytic amount platinum (Hart, 103).
4. The naphtha fraction from the primary distillation is a starting point of the Petrochemical Industry. List 3 useful chemicals that are made from this fraction stating the uses to which they are put.
Hexane: solvent and fuel
5. Briefly describe ONE potential source of damage to the environment caused by the Petroleum Industry.
Crude oil spillage is catastrophic for the environment. It is very rare that an oil tanker spills large quantities of crude oil, but when it does, a large area of the sea gets contaminated by the thick black fluid. Fish, birds, aquatic plants and even mammals living in affected areas suffer from a major oil spillage. Even though the spillage areas are cleaned, a good part of the crude oil remains in the affected areas during several years, which