The crude oil and wet gas (natural gas saturated with more complex hydrocarbons) pumped from underground reservoirs are energy-rich, organic concentrates: mixtures of hundreds of molecular compounds with tremendous potential. At the refinery, the strategy for separating these compounds is based on the different properties of the components. Nothing is wasted and the byproducts from one process are often integral to another. For example, from wet gas we get ethane, which is used to create ethylene, a component of many consumer plastics. Different hydrocarbons can be separated by their boiling points. The smallest hydrocarbon is methane (natural gas) and the longest chains are like wax or tar. The more carbons in a molecule, the higher the boiling point. This is done through fractional distillation. The steps of fractional distillation mirror those of distillation in a chemistry lab.
- heat with high pressure steam to about 1112 °F.
- boiling creates gases and vapors that rise in a column.
- as the vapor goes through the column it cools and condenses where the temperature of the column is equal to that of the substance’s boiling point (substance with the lowest boiling point will condense at the highest point in the column).
- various liquid fractions are collected.
- liquid fractions pass into condensers for further cooling and are transported for further chemical processing and blended to produce a variety of petrochemical products.
Refineries use chemical reactions on some of the fractions (a process called conversion) to create many products. Cracking is used to break large hydrocarbons into smaller ones. Reforming takes smaller hydrocarbons and combines them to make larger ones. During alkylation, the molecules of one fraction are rearranged to produce another. The distilled and chemically treated fractions are treated to remove impurities, cooled and blended to make gasoline, lubricating oils, jet fuel, heating oil and chemicals of various grades for making plastics and other polymers.