Almost all of the organic chemicals produced by the chemical industry are obtained from seven basic chemicals: methane, ethylene, propylene, butadiene, benzene, toluene, and xylene. Methane is the primary constituent of natural gas. Although some minor sources are available for the rest of the basic organic chemicals, they are invariably derived from petroleum, and chemicals derived from petroleum are collectively termed petrochemicals. Ethylene is the largest-volume organic chemical produced worldwide, followed by propylene. The largest use of these chemicals is in the manufacture of polymers, such as polyethylene, polypropylene, polybutadiene and rubbers, and polyesters (polyethylene terephthalate [PET] and polybutylene terephthalate [PBT]). The other important chemicals produced from these chemicals include ethylene oxide and vinyl chloride, propylene oxide and isopropyl alcohol, cyclohexane, toluene diisocyanate, and phthalic anhydride. Many of these derived chemicals are, in turn, used in manufacture of other organic compounds, including polymers such as polyvinyl chloride (PVC) and polyurethanes.
Figure 2.2 provides an overview of the basic organic chemicals and petrochemical products. The top level in the hierarchical representation shows the different sources of the basic chemicals. As mentioned previously, petroleum (crude oil) is the primary source for the chemicals; however, these chemicals, particularly methane, are also obtained from coal. The middle level in the figure shows the seven basic organic chemicals; methane is separate primarily to indicate that it is predominantly obtained from natural gas. The lower level provides a brief glimpse into the world of petrochemicals: the intermediates such as butadiene, ethylene dichloride, acrylonitrile, formaldehyde, and countless others that are precursors to a vast number of chemical products that go into objects used universally by practically every individual.
Figure 2.2 Overview of basic organic chemicals and petrochemical products.
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