Petroleum refining
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Description
Petroleum refining generally has an input of crude oil and an output of a variety of more or less purified products. The simplest process is fractional distillation, which separates the molecules into a range of boiling points.
Detailed description
With simple distillation, the range of products include, from the lightest to their heaviest, natural gas, liquefied petroleum gas, light motor fuels, kerosene (including Jet Aviation A), diesel fuel, light fuel oil, heavy fuel oil, basis for lubricating oils, light bitumen, heavy bitumen and still bottoms. The proportions of these different fractions are more or less constant for a given type of crude oil and with simple distillation it is impossible to adjust the proportions into those required by the market. Generally speaking, in most markets, the demand for light fuels is much higher than the natural proportions of most oils. This is corrected by a process called cracking, which splits some of the heavier molecules into lighter ones. This allows the refineries to adjust their output according to the market demand. Of course, this is a simplification and many more processes are carried out in the modern refinery. Most products are engineered by means of their composition and additives to best suit a particular purpose.
The opposite of cracking is polymerisation, which can be used to make heavier molecules out of light ones. This is used, for example, in gas to liquids conversions. However, this process is more expensive than cracking.
An important part of the refining process in recent years has been the desulfurisation of fuels to reducing emissions of sulfur dioxide when they are burnt. The sulfur dioxide is an important component of acid rains.
