The Refining of Oil

A Imagine a world without petroleum; a world without cars, plastics, aviation fuel, tyre or tar-sealed roads, in fact a world without most of the everyday items and systems we take for granted. The reality is that our modern lifestyle could not exist without petroleum

B No one knows exactly how oil was formed, but this is the generally accepted theory. Sometime, between 200 and 400 million years ago, dead organic matter accumulated on the sea floor. As this decaying organic matter built up in the sediment, it acted as a coating that stopped oxidation. Then through the actions of microbes and chemical changes, the decaying matter was turned into a greasy, waxy material. As layers of this material became buried in the sediment the temperature and pressure increased, and over a period of time, perhaps as long as 10 million years, petroleum was created. Today, most petroleum, also known as crude or unprocessed oil, is found in what are believed to be ancient sea beds.

C Crude oil is a valuable fossil fuel because it contains hydrocarbons, which are important for two reasons. Firstly, they contain vast reserves of usable energy. Secondly, petroleum can be used to manufacture a wide variety of products because hydrocarbons come in many sizes, shapes and weights. The smallest hydrocarbon chain is methane (CH4), a gas lighter than air, whilst the heaviest compounds, tar and asphalt, are made up of multiple rings of over 70 carbon atoms.

D The primary purpose of oil refining is to separate out these hydrocarbons into useable substances, as petroleum is useless in its unprocessed form. This is achieved through the relatively simple process of fractional distillation. Hydrocarbon chains have different boiling points depending on the length of their chain. For example, petroleum gas (methane, ethane, propane, butane) which is used for heating, cooking and making plastics will boil before the temperature reaches 104°F (degrees Fahrenheit). Gasoline, however, requires a boiling range of 104 to 401° F, while Kerosene boils between 350 to 617°F. Lubricating oil, a liquid used in motor oil, grease and other lubricants, requires temperatures between 572 and 700° before it will vaporize and heavy gas (fuel oil) used as industrial fuel needs to be between 700 to 1112°F. Even the solid residuals of the refining process are useful. Residuals require a temperature of over 1112°F to vaporize.

E Fractional distillation occurs as the crude oil is heated and then boils to form vapor gases. As the vapor rises up the fractional distillation column, which is fitted with various trays and plates to trap the different hydrocarbon gases, it cools. (Substances with a higher boiling point will condense at a lower point in the column.) When a hydrocarbon vapor reaches the place in the column where the temperature is equal to its boiling point, it begins to condense and form a liquid. As the liquid forms, it is either filtered off into a condenser to cool completely and then to be put into storage tanks, or it goes to another part of the refinery for further processing. F Most of the product that comes out of the fractional distillation process requires further chemical refining. This is done using one of three chemical processes, the first of which is called cracking. In the cracking unit, large hydrocarbon chains are broken into smaller ones. For example, residual from the

distillation process is heated to over 900°F until it ‘cracks’ into heavy oil, gasoline and naphtha, and the residue from this process a catalyst is used, often in the form of a hot liquid (1000°F) that ‘cracks’ heavy gas oil into diesel oil or gasoline. Unification is another common operation in oil refining. This is a chemical process in which smaller hydrocarbons are unified, or combined, to make larger ones. Platinum or platinum-rhenium is often used as a catalyst when unifying naphtha into aromatics used in chemical manufacture and in blending gasoline. The third process is alteration, a chemical process in which the molecular structure is rearranged to produce a new compound. Low weight compounds such as propylene and butylene are mixed in the presence of a catalyst such as hydrofluoric acid or sulphuric acid to form high octane hydrocarbons, which are used when blending gasoline.

G The products of distillation and the various chemical process must then be treated to remove any impurities. Sulphuric acid is used to remove a range of impurities including nitrogen and oxygen compounds. A drying agent removes water and then chemical scrubbers remove the sulphur. The treated products are then cooled and, if necessary, blended together to form new products ready for use.

H The next time you start your car or pick up a plastic container spare a thought for the extraordinary fate of a dying plant or animal millions of years ago whose energy is now being harnessed to fuel your modern lifestyle.

Reading Exercises

Scanning for Numbers

1. Scan the passage quickly to find the following numbers. Then match the numbers with the ideas below. 200 and 400 million years CH4 1112°F 70 over 900°F 10 million years 350°F 700°F a. age of oil b. time taken to create petroleum c. smallest hydrocarbon-methane

d. number of carbon atoms in one ring of heavy hydrocarbons e. lowest boiling point of kerosene

f. highest boiling point of lubricating oil g. lowest boiling point of residuals

h. temperature at which residual oil ‘cracks’

Identifying the structure of the passage

Read the first sentence only of each paragraph. Decide which of the following questions best match the information given in the sentence? Write the letter of the paragraph beside the question that matches best.

a. b. c. d. e. f. g.

Why is petroleum so valuable? _____ What happens when crude oil is heated? _____ What is the chemical refining process? _____ How does petroleum affect my lifestyle? ______ How can the products of the refining process be further improved? ______ Why does petroleum need to be processed? ______ How is crude oil formed? ______

IELTS Type Questions

Classification

According to the information in the passage, classify the following statements according to when they occur:

A. before the fractional distillation process B. during the fractional distillation process C. after the fractional distillation process

Write the correct letter A-C beside the following statements. 1) _____ hydrocarbons are divided out. 2) _____ organic matter accumulates. 3) _____ hydrocarbons exist in crude oil. 4) _____ chemical process the product. 5) _____ petroleum gases are distilled.

6) ______ sediment causes oxidation to cease. 7) ______ vapors rise up the distillation tube.

Matching

Look at the following list of statements on the refining process. Match each statement with the correct process A-C. A. Cracking B. Unification C. Alteration 8) _____ large hydrocarbons are formed from small ones 9) _____ molecules are changed to form a new substance. 10) _____ carbon in its purest form is a by-product. 11) _____ hydrocarbons are processed into small ones. 12) _____ butylene is transformed by another substance. 13) _____ platinum is used as a transforming substances.