|MadSci Network: Chemistry|
Crude oils vary in their composition, but generally range around 20% gasoline and naphtha, 35% gas oil, 20% lube distillate, 20% residuum, and 5% light gasoline. Refinery processes turn low quality material into higher quality products.
Plastic manufacturers use processes like refiners, or purchase products to produce the chemicals that are used in synthesizing plastics. Since crude oil contains many molecules, the industry breaks and builds molecules to fill the niche. I'll discuss just a portion of the most notable processes.
Fluid Catalytic Cracking breaks larger molecules into Gases, Gasoline, Gas oil, and Heavy bottoms. The product streams produced by the FCC contain unsaturated hydrocarbons referred to as olefins. The gases are separated and stored, sold, or used in subsequent processes.
Of these gases produced, propene is used in the manufacture of cumene. For information regarding Cumene, see this website. There's a lot of information. http://www.aristechchem.com/products/cumene.htm
Also try this website: Exxon/Mobil: Cumene
The other processes that are important are the reforming and alkylation processes. Reforming converts naphthenes into aromatics like benzene, toluene, xylenes, and alkylbenzenes. These chemicals have their roles in the plastics industry. If you visited the above websites, benzene and propene are the feeds for producing cumene.
Alkylation builds larger molecules from smaller molecules. Typically, butenes are mixed with iso-butanes to produce branched chain hydorcarbon polymers called isoparaffins.
In the United States alone, production of polymers as long ago as 1981 was more than 24 million metric tons, exceeding in volume the production of steel, and is the basis for industries that employs more than 3.5 million people. So, what are polymers?
Polymers are simply very large molecules (macromolecules) that are made up of smaller molecules (monomers) that can be linked together in various ways, resulting in a range of what we call microstructures (e.g., linear chains, branched chains, densely interconnected networks, and so on). Although natural polymers (cotton, wool, silk), have been used throughout recorded history, the first true synthetic polymers were produced relatively recently (in historical terms), at the start of the 20th century. Furthermore, the long chain nature of their chemical structure was not recognized until the 1920s. In the decades that followed, however, an astonishing range of new synthetic materials were quickly produced by polymer chemists, revolutionizing some older industries, like those based on rubber, paint, and natural fibers, and creating new ones associated with the production of plastic goods. Polymers are also a crucial component of other advanced technologies, such as those essential to the electronics industry, where polymers are an integral part of the chip and printed circuit production process.
Clearly, there is a broad range of industries that are based on polymer science and engineering. There are two categories of companies. The first consists of those chemical companies that actually make the resins; poly (ethylene), poly(propylene), poly(styrene), PVC, polyesters, nylons, etc. This part of the industry is dominated by large multinational companies with familiar names; Dupont, Dow, Union Carbide, Bayer, Exxon Mobil, Shell, etc. Most of the materials they now produce can be considered commodities and are sold to companies that constitute the second part of the industry, those firms that process polymers into films, fibers, paints, adhesives, composites (e.g., glass fiber reinforced polyesters) and the extraordinary range of plastic goods that are in modern society. The "chemical" part of the industry has from its inception been on the cutting edge of synthetic and chemical processing technology. Even today, it is still introducing new ways to make "old" polymers through the use of novel catalysts (e.g., metallocenes), which promise superior control over chain structure and hence properties.
The process from crude to plastic has many avenues and this is only a briefoverview of a large wealth of knowledge. I hope this points you in the direction to research your question further.
Try the links in the MadSci Library for more information on Chemistry.