The Cracking and Reforming of Crude Oil Fractions Presentation

The Cracking and Reforming of Crude Oil Fractions

By Brandeice Barrett

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)

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

The petroleum fractions

Paraffins (alkanes)

Aromatic

Naphthenes (cycloalkanes)

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

The Cracked Products

The cracked products maybe smaller alkanes, alkenes and hydrogen molecules.

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.

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.

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.

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.

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

What reforming involves

Reforming is the effect of numerous reactions such as isomerisation, alkylation and catalytic reforming.

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.

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.

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

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.

Air

Preserving air quality around a refinery involves controlling the following emissions:

sulphur oxides hydrocarbon vapours smoke smells

Water

Oil spills- the oil products are transported via tankers and sometimes there is a spillage.

Land

The refineries safeguard against pollution of the land recycling the waste products

Thank You for Listening