the cracking and reforming of crude oil fractions presentation
TRANSCRIPT
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The Cracking and Reforming of Crude Oil Fractions
By Brandeice Barrett
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THE COST OF CRUDE OIL OUT OF THE GROUND IS $US120 PER BARREL
THE PRIMARY DISTILLATION PRODUCES ABOUT 2% OF THE INITIAL CRUDE AS A PETROLEUM FRACTION (8carbon atom per chain)
The industry cannot afford to waste 98% of the contents of each barrel (about 250ml)
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The larger molecules left after distillation (paraffin, wax, bitumen) have a limited market
They are broken down into smaller chain lengths by the process of cracking and reforming
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The petroleum fractions
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Paraffins (alkanes)
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Aromatic
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Naphthenes (cycloalkanes)
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Cracking
Cracking allows large hydrocarbon molecules to be broken down into smaller, more useful hydrocarbon molecules
Two types of cracking are heat (thermal) and catalytic
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The Cracked Products
The cracked products maybe smaller alkanes, alkenes and hydrogen molecules.
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Thermal Cracking
This involves rapidly heating the hydrocarbon to temperatures of about 800oC and then cooling it all occurring within a mere 2 seconds. The heat supplied to the mixture can cause the C-C bond to break homolytically thus forming radicals.
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Catalytic Cracking
Catalytic cracking involves the breaking of hydrocarbon bonds by the use of a catalyst at lower temperatures. The catalyst most often used is a powdered mixture of alumina and silica at about 500oC.
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Catalytic Cracking
Catalytic cracking is used to break up the fractions of distillation such as diesel oil kerosene into smaller fractions. The cracked fractions are important for use as fuel as well as feedstock for the petrochemical industry. The alkenes are suitable starting materials to make plastics, detergents, cosmetics, solvents, paint and many petrochemicals.
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Reforming
Reforming is a process which uses heat, pressure and a catalyst (usually containing platinum) to bring about chemical reactions which upgrade naphthas into high octane petrol and petrochemical feedstock.
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Reforming of Crude Oil Fractions
Reforming converts a portion of these compounds to isoparaffins and aromatics, which are used to blend higher octane petrol.
paraffins are converted to isoparaffins paraffins are converted to naphthenes naphthenes are converted to aromatics
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What reforming involves
Reforming is the effect of numerous reactions such as isomerisation, alkylation and catalytic reforming.
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Isomerization
Isomerisation refers to chemical rearrangement of straight-chain hydrocarbons (paraffins), so that they contain branches attached to the main chain (isoparaffins). This is done for two reasons:
they create extra isobutane feed for alkylation
they improve the octane of straight run pentanes and hexanes and hence make them into better petrol blending components.
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Alkylation
Olefins such as propylene and butylene are produced by catalytic and thermal cracking. Alkylation refers to the chemical bonding of these light molecules with isobutane to form larger branched-chain molecules (isoparaffins) that make high octane petrol.
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Catalytic Reforming
This process uses a catalyst (platinum, platinum-rhenium mix) at a temperature of 500o C and a pressure of 20atm to convert low weight naphtha into aromatics, which are used in making chemicals and in blending gasoline.
Benzene, toluene and xylenes are some of the main aromatic products of reforming the C6 –C8 hydrocarbons from the naphtha fraction
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Impact of the industry on the Environment
Air, water and land can all be affected by refinery operations. Refineries are well aware of their responsibility to the community and employ a variety of processes to safeguard the environment.
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Air
Preserving air quality around a refinery involves controlling the following emissions:
sulphur oxides hydrocarbon vapours smoke smells
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Water
Oil spills- the oil products are transported via tankers and sometimes there is a spillage.
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Land
The refineries safeguard against pollution of the land recycling the waste products
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Thank You for Listening