OCTANE NUMBER OF PETROLS

Different car engines require slightly different fuels to work at their maximum efficiency. One measure of the suitability of petrol for a particular car engine is the octane number. This is a number, close to 100, which shows the percentage of 2,2,4-trimethylpentane in a mixture of 2,2,4-trimethylpentane and heptane which gives the same performance characteristics as the petrol.95-Octane petrol will behave as would a mixture of 95% iso- octane and 5% heptane.

The principle of the internal combustion engine is that the petrol and air are mixed in a particular ratio and then compressed by piston in the cylinder. A spark ignites the mixture as the piston reaches its highest point in the cylinder. At these raised temperatures and pressures, it is not always easy to set the reaction off at exactly the right moment. The hydrocarbon mixture can explode prematurely. This is called pre-ignition and causes ‘knocking’ in the engine. Such pre-ignition means that power is lost and the engine is less efficient; it may also cause severe damage to the engine.

REFORMING DEFINITION Reforming is an industrial process in which straight chain hydrocarbons are converted into branched chain and cyclic hydrocarbons, using high temperature, high pressure and a catalyst. One important process which improves the quality of the fuels we use is reforming. The octane number of a fuel can be raised by increasing the proportion of branched or cyclic hydrocarbons.

Reforming does just that- it changes the arrangement of the atoms in the molecule. An example of branching is: In the cyclisation reaction both aromatic and alicyclic compounds are formed. The formation of an alicyclic compound releases one hydrogen molecule. The formation of aromatic benzene rings results in four hydrogen molecules being formed. Al2O3 500°C 40 atm Hexane 2-Methylpentane

ISOMERIZATION This involves breaking up straight chain hydrocarbons and reassembling them as branched chain isomers. This reaction takes place at about 500°c in the presence of an aluminium chloride catalyst.

ALKYLATION In this process tertiary alkanes combine with alkenes to make longer branched chain alkanes. The reaction occurs at room temperature and is catalyzed by concentrated sulphuric acid.

IMPACT OF THE OIL INDUSTRY ON THE ENVIRONMENT

In the oil industry pollution may occur during: Extraction Transportation Refining

EXTRACTION Extraction of crude oil involves emissions of pollutants from the first seismic survey until the field is shut down. Well drilling discharges oil into surrounding soil and water. This can damage fragile ecosystems by destroying habitats and killing organisms.

Oil Drilling OIL WELL ON LAND OIL WELL IN WATER

TRANSPORTATION Oil is usually transported through pipelines and in large ocean tankers. Therefore it is possible for accidental leaks and spills to occur in the ocean. Oil spills are detrimental as organisms are at risk of inhaling or ingesting the oil which can poison them. Oil spills also ruin coral reefs and beaches thereby affecting the tourism industry.

TYPES OF TRANSPORTATION CRUDE OIL IN LARGE TANKERS CRUDE OIL IN PIPELINES

OIL SPILL Lost of animal life Water pollution

Refining In the refining process, hazardous and toxic air pollutants such as carbon monoxide, hydrogen sulphide, nitrogen oxides, sulphur dioxide and BTEX compounds (benzene, toluene, ethylbenzene and xylene) are emitted into the atmosphere.

AIR POLLUTION

Dangers of the Air pollutants emitted By the oil industry

CO SO2 & NO2 AIR POLLUTANTS BTEX Compounds

CARBON MONOXIDE CO is toxic because it combines readily with hemoglobin in the blood to form the stable compound carboxyhemoglobin. This makes the hemoglobin unable to transport oxygen which results in the cells of the body being deprived of oxygen. A concentration as little as 400ppm in the air can be fatal.

Medical Effects of Carbon Monoxide Carbon monoxide is a colorless, odorless, tasteless and toxic gas produced as a by-product of combustion. Any fuel burning appliance, vehicle, tool or other device has the potential to produce dangerous levels of carbon monoxide gas. Carbon monoxide inhibits the blood's ability to carry oxygen to body tissues including vital organs such as the heart and brain. When CO is inhaled, it combines with the oxygen carrying hemoglobin of the blood to form carboxyhemoglobin (COHb). Once combined with the hemoglobin, that hemoglobin is no longer available for transporting oxygen. How quickly the carboxyhemoglobin builds up is a factor of the concentration of the gas being inhaled (measured in parts per million or PPM) and the duration of the exposure. Compounding the effects of the exposure is the long half-life of carboxyhemoglobin in the blood. Half-life is a measure of how quickly levels return to normal. The half-life of carboxyhemoglobin is approximately 5 hours. This means that for a given exposure level, it will take about 5 hours for the level of carboxyhemoglobin in the blood to drop to half its current level after the exposure is terminated.

Sulphur Dioxide & Nitrogen Oxides These gases contribute to the formation of acid rain. FORMATION OF ACID RAIN:

EXPLAINATION OF DIAGRAN Acid rain is caused by the release of the gases SO2 (sulphur dioxide) and NO2 (nitrous oxides). The main sources of NO2 emissions are vehicles and fuel combustion. Sulphur dioxide reacts with water, vapour and sunlight to form sulphuric acid. Likewise NO2 form nitric acid in the air. These reactions takes hours, or even days, during which polluted air may move hundreds of kilometers. Thus acid rain can fall far from the source of pollution.

BTEX Compounds BTEX compounds are benzene, toulene, ethylbenzene and xylene. These are possible carcinogens and may cause reproductive and developmental problems. They may also aggravate respiratory conditions such as asthma. A carcinogen is a substance that is capable of causing cancer i.n humans or animals

Solutions to the problem of oil spills on the surface of water There are several different methods for dealing with oil spills on the surface of the water. Some of these are: A floating barrier called a boom is placed around the oil to keep it from spreading. The oil can be ignited within the boom A giant vacuum can be used to suck up the surface oil. Solvent compounds are used to break down light oil spills and disperse it. Absorbents are used to collect the oil left behind from suctioning . Natural absorbents like clay and sand can hold up to 20 times their weight in oil while synthetic absorbents like polyethene can hold up to 70 times its weight in oil.