An Introduction to Petrochemicals
1. The petroleum era was ushered in by the 1859 finding at Titusville, Pennsylvania, but the flourishing of chemicals from petroleum has been only since the early twentieth century. Natural gas and petroleum are in fact our chief sources of hydrocarbons. Natural gas is quite variable in composition, but the major constituent （>60%） is methane. Other components are the homologous alkanes, ethane, propane, and higher hydrocarbons. In terms of volume, most of the natural gas produced is used for fuel, although a substantial amount is used as raw material for the synthesis of various types of chemicals.
2. The chemical industry depends very heavily on petroleum, natural gas, and natural gas liquids as sources of raw materials. It is likely that in excess of 90% of the literally thousands of different basic organic chemicals employed today are derived from these sources.
3. The petrochemical industry has grown with the petroleum industry and is considered by some to be a mature industry. However, as is the case with the latest trends in changing crude oil types, it must also evolve to meet changing technological needs.
4. The manufacture of chemicals or chemical intermediates from petroleum and natural gas constituents is an excellent example of the conversion of such materials to more valuable products. The individual chemicals made from petroleum and natural gas are numerous and include industrial chemicals, household chemicals, fertilizers, and paints, as well as intermediates for the manufacture of products, such as synthetic rubber and plastics.
5. The processing of petroleum hydrocarbon to yield materials that are, essentially, the building blocks of other chemicals industries, is now very extensive.
6. Petrochemicals are generally chemical compounds derived from petroleum either by direct manufacture or by indirect manufacture as by-products from the variety of processes that are used during the refining of petroleum. Gasoline, kerosene, fuel oils, Lubricating oils, waxes, asphalts, and the like are excluded from the definition of petrochemicals, since they are not, in the true sense, chemical compounds but are in fact intimate mixtures of hydrocarbons.
7. The classification of materials such as petrochemicals is used to indicate the source of the chemical compounds, but it should be remembered that many common petrochemicals can be made from other sources, and the terminology is therefore a matter of source identification.
8. The starting materials for the petrochemical industry are obtained from crude petroleum in one of two general ways. They may be present in the virgin petroleum and as such, are isolated by physical methods, such as distillation or solvent extraction. On the other hand, they may be present in trace amounts and are synthesized during the refining operations. In fact, unsaturated hydrocarbons, which are not usually present in virgin petroleum, are nearly always manufactured as intermediates during the various refining sequences.
9. The manufacture of chemicals from petroleum is based on the ready response of the various compound types to basic chemical reactions, such as oxidation, halogenation, nitration, dehydrogenation, addition, polymerization, and alkylation. The low-molecular-weight paraffins and olefins, as found in natural gas and refinery gases, and the simple aromatic hydrocarbons have so far been of the most interest because it is these individual species that can readily be isolated and dealt with. A wide range of compounds is possible, many are being manufactured, and we are now progressing the stage in which a sizable group of products is being prepared from the heavier fractions of petroleum. For example, the various reactions of petroleum heavy ends, in particular the asphaltenes, indicate that these materials may be regarded as chemical entities and are able to participate in numerous chemical or physical conversions to, perhaps, more useful materials. The overall effect of these modifications is the production of materials that either afford good-grade aromatic cokes comparatively easily or the formation of products bearing functional groups that may be employed as a nonfuel material.
10. For example, the sulfonated and sulfomethlated materials and their derivatives have satisfactorily undergone tests as drilling mud thinners, and the results are comparable to those obtained with commercial mud thinners. In addition, these compounds may also find use as emulsifiers for the in situ recovery of heavy oils. There are also indications that these materials and other similar derivatives of the asphaltenes, especially those containing such functions as carboxylic or hydroxyl, readily exchange cations and could well compete with synthetic zeolites. Other uses of the hydroxyl derivatives and / or the chloroasphaltenes include high-temperature packings or heat transfer media.
11. Reactions incorporating nitrogen and phosphorus into the asphaltenes are particularly significant at a time when the effects on the environment of many materials containing these elements are receiving considerable attention. Various measures have been and will be taken to release such effects.
12. Nevertheless, the main objective in producing chemicals from petroleum is the formation of a variety of well-defined chemical compounds that are the basis of the petrochemical industry. It must be remembered, however, that ease of separation of a particular compound from petroleum does not guarantee its use as a petrochemical building block. Other parameters, particularly the economics of the reaction sequences, including the costs of the reactant equipment, must also be taken into consideration.