1. Read the text and check your answers.

Crude oil, or petroleum, is a thick, black mixture of hundreds of different compounds, and is practically useless when taken from the ground. About 88% is processed and refined into fuel, asphalt and lubricants. The remaining 12% is converted into other materials such as plastics, and chemical products such as fertilizers and solvents.

Several types of motor, aviation and heating fuel are produced in oil refineries. These are: LPG (liquefied petroleum gas), petrol (gasoline), kerosene and diesel.

Kerosene and LPG are more versatile and are used in domestic heating systems and portable stoves. The primary use of kerosene, however, is as aviation fuel in jet engines. LPG is starting to be used as a 'green gas' to power cars because it produces fewer emissions than either petrol or diesel fuels.

Petrol and diesel are the most widely used fuels for cars, buses and trucks. Most cars have petrol engines, and larger vehicles, e.g., buses, tend to have diesel engines. Diesel engines operate at much higher pressures than petrol engines and, therefore, they have to be built more strongly. However, diesel engines are more efficient than petrol engines and are more economical - they can use up to 40% less fuel.

Diesel is used in industry alongside heavier industrial fuel oil. This is used in ships and factories, and is normally burned in a furnace.

In addition to motor fuels, important products refined from oil are lubricants. Lubricants are essential to ensure moving parts in a machine work smoothly and stop them overheating. Different lubricants are suitable for different jobs. Engine oil is less viscous. Grease is much thicker and is used to protect sealed bearings. Multigrade lubricants can operate at different temperatures without being affected. Lubricants without a temperature-sensitive polymer are more viscous at low temperatures than at high temperatures.

2. Complete the table below with information from the text.

Oil product	Uses	Properties
petrol/gasoline
diesel
LPG
fuel oil
engine oil
grease
multigrade lubricants

Oil refining Read the texts and answer the questions the chemistry of oil and gas

Рис.59

waxes – парафин, воск

tar - смола

bubble cap - колпачок барботажной ректификационной колонны

tray – желоб, лоток

volatile – летучий, легкоиспаряющийся

residue -осадок

alkenes - алкены

pipe off – отводить трубы

The story of oil continues ... Once oil has been found and extracted, it has to be turned into something that we can use.

Рис. 60

A typical refinery might process 10 million tonnes of crude oil per year. The refinery managers must control the processes so that the output of different products from the refinery matches the demand for them. In an oil refinery, fractional distillation, cracking and reforming (as well as other processes such as desulphurisation) are carried out continuously, 24 hours a day, 365 days a year.

Рис. 61

Simplified cross-section of distillation tower showing bubble caps. In practice there may be hundreds of these at each level. There are also many more trays than are shown in the diagram of the tower.

All crude oils are mixtures of hydrocarbons - chains of different lengths (sometimes with rings attached) of carbon and hydrogen atoms. Each carbon atom in the chain is bonded to two hydrogen atoms, except for the end ones which have three. Short-chain hydrocarbons (up to four carbons) are gases, longer ones are liquids which get more viscous as the chains get longer. Very long chains are solids like wax.

Fractional distillation  Crude oil is of little use in the form that it emerges. It has to be refined  before it can be put to use. The first step to converting it into useful products is fractional distillation, which separates the mixture into fractions - groups of hydrocarbons of similar chain length and therefore similar boiling points.

This is done by heating the crude oil to a temperature at which much of it will boil. The hot liquid passes into a distillation tower, where the volatile molecules turn into vapours and rise up the tower. The top of the tower is cooler than the bottom so that the vapours gradually condense as they rise. The tower contains a series of shallow trays that collect the liquid as it condenses. Devices called bubble caps force the rising vapours to pass through the liquid on the trays. The vapours condense to liquid when they arrive at a tray that is sufficiently cool. The liquid which condenses on each tray is piped off separately. Shorter chains have lower boiling points, so the higher the tray the shorter the chain lengths that collect there. Different fractions have different uses.

The lightest fractions that are drawn off from near the top of the tower are used in making petrol. From the middle, we obtain kerosene for use as aircraft fuel after further refining, and from the lower part we obtain gas oil, which is used in diesel-engined road vehicles. Nowadays, all the transport fuels that leave the refinery have been treated with hydrogen to convert the sulphur compounds naturally present in the oil to hydrogen sulphide, which in turn is converted to sulphur and then sold. This avoids sulphur polluting our atmosphere as sulphur dioxide.

The liquid material that leaves the bottom of the distillation tower may be reheated and subjected to distillation in another tower at less than atmospheric pressure. The boiling points of molecules are reduced by the effect of vacuum, so that relatively high boiling point products can be recovered from the vacuum tower for further refining. Lubricating oils and waxes are obtained by this method.

This still leaves a thick, involatile residue from the vacuum distillation. The residue may be used as a fuel in power stations, or after further refining, it may be turned into bitumen, which is used to make roads and pavements.

Cracking  Gasoline, which gives us our petrol, is the crude oil fraction which is most in demand; longer-chain fractions are less so. To avoid having a surplus of long-chain fractions, the process of 'cracking' has been developed. Here, longer chain hydrocarbons are heated under pressure to high temperatures, normally with a catalyst and sometimes in an atmosphere of hydrogen. This breaks the chains into shorter ones such as those that make up petrol.

Reforming  Further chemical processing using heat, pressure and different catalysts is called reforming. Depending on the conditions, this has a variety of effects, one of which is to break up some of the straight hydrocarbon chains and reform them into branched ones. For example the C8 hydrocarbon, called octane, can be reformed into iso-octane which burns more efficiently  in car engines to give more miles per gallon.

Chemical feedstocks  Cracking and reforming also have the effect of removing some of the hydrogen from the hydrocarbon chains. This leaves molecules which are described as unsaturated (having less than the maximum amount of hydrogen). These molecules have carbon-carbon double bonds and are called alkenes. This makes them chemically much more reactive than saturated hydrocarbons, which have few chemical reactions and are normally burnt as fuels.

The extra chemical reactivity of alkenes means that they can be converted into other useful products making them the starting material (or feedstock) for the petrochemicals industry. Another group of products of reforming is unsaturated compounds with rings rather than chains of carbon atoms. These are called aromatic compounds and their special chemical properties make them useful as feedstocks too.

Demand for petrol and lubricating oil A typical family car which does 30 miles to the gallon might do 6,000 miles (10,000 km) between oil changes and therefore use 200 gallons of petrol to one gallon of lubricating oil.

1. What are long chains?

2. Describe the first step of crude oil refining.

3. What forces the rising vapours to pass through the liquid on the trays?

4. Name the ratio between the tray and chain lengths in distillation?

5. What fractions are used in making petrol?

6. In what way are lubricating oils and waxes  obtained?

7. Describe the process of cracking.

8. What are alkenes?

9. What does the extra chemical reactivity of alkenes mean?