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Refractory Materials
Refractory materials are those that are resistant to heat, and this is a desirable quality if, say, you are building a furnace. Industrial processes often involve working with liquid metal. This is not especially challenging if you are working with liquid tin, which has a melting point of only 450 degrees Fahrenheit. Iron, on the other hand, has a melting point of 2,800 degrees Fahrenheit, and industry uses far more iron than tin. Furnaces are therefore lined with refractory materials, such as magnesia, which has a melting point of 5,070 degrees.
Thermal Cracking
Crude oil contains a mixture of hydrocarbons. Some of these are very large molecules. Smaller hydrocarbons are generally more valuable than large ones. Hydrocarbons in gasoline and fuel oils should have no more than about 22 carbon atoms. Thermal cracking is a refining process in which large hydrocarbons are broken down into smaller hydrocarbons through heat and pressure. Oils that are resistant to thermal cracking are called refractory oils.
Refractory Oils
Oils can come in different varieties, based on the shape of their carbon chains. The carbons can be arranged in a straight chain. These are called paraffinic hydrocarbons, and they are generally easy to thermally crack. If the carbon atoms are arranged in a ring, these are called aromatic hydrocarbons. Aromatic hydrocarbons are much more difficult to crack using thermal processes. Refractory oils contain a mixture of thermally resistant, aromatic hydrocarbons.
Processing Refractory Oils
Chemical engineers have devised approaches to refining the heat-resistant refractory oils. One of these involves using sulfides of metal from group 6 on the periodic table, notably molybdenum and tungsten. Molybdenum sulfide provides better results. Using molybdenum or tungsten sulfide catalysts, refiners can process refractory oils that are resistant to thermal cracking.