Chemicals from Petroleum
Petroleum is the main source of hydrocarbon materials since late 19th century, when industrial and scientific laboratories started to utilize it as feedstock to manufacture organic chemicals. The previous achievements in the field of the chemistry of coal-tar products helped chemists to understand the petroleum potential, but it was not an easy task because of the presence of numerous hydrocarbons in crude petroleum which had to be isolated before they could be utilized for organic synthesis1. Like the chemistry of coal-tar products, that of petroleum hydrocarbons began its development with the study of the low-boiling compounds, which could be separated in good quantities by fractional distillation.
Following, new experiments run at high-boiling points opened the possibility to produce a larger set of good hydrocarbons, but they showed some flaws. First, working at higher temperature implies major energy costs; second, it presented limitations to the ease of hydrocarbons isolation and separation; eventually the commercial quantities availability of the individual substances at the beginning was pretty modest. Another factor contributing to the progress of the petroleum chemical industry between the two World Wars was the organization of the marketing and distributing facilities of petroleum companies, which were best suited for handling products in bulk quantities. No immediate profit was expected from this new chemical business: much time was needed to pay off the initial investment, and the income derived from selling chemicals represented little addition to ordinary profits earned by refining normal petroleum products (e.g. kerosene, fuel oils, lubricants, etc.).
Big chemical companies were the first to use petroleum hydrocarbons as raw materials for synthesizing chemicals. The petroleum industry has been able to supply them at a reasonable cost only in the 1930s, because of complications involved in isolating them from crude petroleum. In the 1940s, the manufacture of chemicals from petroleum reached a well-established basis and boomed in the 1950s when a number of petroleum companies began to be actively engaged in supplying the market with chemicals and in developing new sources of income from their sale. Because of their reactivity, the unsaturated petroleum hydrocarbons are best suited for the manufacture of chemicals. These hydrocarbons are obtained in large quantities in the course of the cracking process.
Methane is the only hydrocarbon possessing a single carbon atom in the molecule, and it is found in large quantities in the petroleum fields. But, because of its saturated nature and relative inertness, little has been done toward utilizing it in the manufacture of chemicals. It is widely used as fuel, but after carefully controlled oxidation it can be transformed into formaldehyde, which finds application in the preparation of synthetic resins such as bakelite, and as a disinfectant. Methane can also be converted into acetylene by exposure to very high temperatures produced by an electric arc. Commercial plants of this type have been developed in Europe and Nord American in the 1930s, but wide adoption of the process by the industry has been slowed down still in the 1940s because of the high operational costs. Acetylene obtained with methane was successfully employed in welding, converted into benzene or acetic acid, and used for the preparation of other organic compounds. By processing together methane with chlorine can be easily obtained carbon tetrachloride, chloroform, methylene dichloride and methyl chloride. In the early 1940s, methane has been also successfully used for the preparation of nitromethane, which is used as a solvent.
Ethane may be utilized in the same ways as methane. On oxidation it can be converted into ethyl alcohol and in addition with chlorine it yields a number of chlorinated compounds, like ethylene dichloride. Ethylene since the 1930s is commercially appreciated because of its unsaturated nature, and it is utilized in preference to ethane for the manufacture of ethyl alcohol and ethylene dichloride - the starting point in making certain types of synthetic rubber. In the presence of water and chlorine, ethylene forms chlorohydrin which may be converted into ethylene glycol (antifreeze); ethylene oxide (mixed with carbon dioxide yields a fumigant).
Propane on oxidation or chlorination yields the corresponding oxygen and chlorine derivatives. Commercially, however, propylene is employed in preference to propane for easiness in processing and better yield for synthetic plastics. Isopropyl alcohol is formed combining propylene with water in the presence of sulfuric acid acting as a catalyst. Isopropyl alcohol can be converted by the same process into isopropyl ether, which has been proposed for improving antiknock properties of aviation fuels. Also glycerin can be produced by treating propylene with chlorine and water.
Butanes and butenes (known also as butylene) have also found commercial applications in the chemical industry together with their use in the manufacture of synthetic fuels. An example is the Methyl ethyl ketone, solvent employed in dewaxing petroleum oils, which is prepared from butenes. The turning point for these hydrocarbons arrived in the early 1930s because of their use as raw materials in the production of synthetic rubber. In the beginning of the synthetic rubbers legacy, they were classified in several categories depending by the commercial importance.
Neoprene rubbers were produced from butadiene which has one of its hydrogen atoms replaced by chlorine. The raw materials usually employed in their manufacture are coke, lime and hydrochloric acid. Buna rubbers, considered then the best substitutes for natural rubber, are prepared by combining butadiene with other substances, such as styrene or acrylonitrile. Other classes of synthetic rubbers are made from ethylene, chlorine and sodium sulfide, isobutene and vinyl chloride. During WWII it was launched the butyl rubber, a reaction product of butadiene and isobutene2.
Pentanes obtained by fractionating natural gasoline are chlorinated and converted into alcohols by hydrolysis; hydrogen chloride is another product of the reaction. Mixtures of amyl alcohols or similar mixtures of butyl alcohols and their derivatives of the ether and ester types are utilized to produce solvents. Processes are also available for manufacturing derivatives of aromatic hydrocarbons, like benzene, using the unsaturated hydrocarbons obtained from cracked petroleum residual gases. Besides, by employing phenol instead it was possible to develop good quality germicides.
A large number of other compounds are obtained by further synthesis. Petroleum fractions containing hydrocarbons boiling above pentane yet in the 1930s were considered not suited for manufacturing pure chemicals because of the difficulties encountered in isolating the individual components. However, processes have been devised for converting such fractions by various chemical reactions into mixtures which started to find industrial applications. Example is the polymerization of highly cracked petroleum distillates in the presence of aluminum, iron or zinc chlorides, which yields resinous substances suitable for paints and varnishes manufacture. Drying oils which may be used as substitutes for linseed oil are obtained by processing with clay the highly cracked distillates containing conjugated dienes. Oxidation of kerosene yields good quality solvents for lacquers; oxidation of paraffin wax produces acids suitable for the making of soaps, while chlorination of wax yields oiliness additives that serve for the processing of high-pressure lubricants. Besides the above-mentioned hydrocarbons, a number of other valuable compounds are found in crude petroleum or are obtained during the refining process into the fractionation column.
It is possible to obtain from petroleum also a series of useful acids. Naphthenic acids are present in considerable quantities in certain crudes, but they present some complications in the refining operations due to their corrosive effects on distillation equipment. Naphthenic acids are separated from petroleum with a bath composed of caustic solutions. They are chiefly used as dryers for paints and lacquers, as emulsifying or demulsifying agents, and in the manufacture of soaps. Sulfonic acids are obtained as by-products from refining oils with sulfuric acid. The sulfonic acids soluble in petroleum are classified as Mahogany Acids, while those soluble Green Acids. Mahogany acids are extracted from the oil with alcohol which is then removed by distillation. Sulfonic acids are used as emulsifying agents, detergents, or for mixing certain lubricants; they can be produced by interaction of solvent extracts with sulfuric acid.
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