Crude Oil Flashcards
What is Crude Oil?
Crude oil is a mixture of compounds called hydrocarbons
How can crude oil be separated?
Fractional Distillation
What is a hydrocarbon?
It is a compound made up of hydrogen and carbon atoms joined by covalent bonds. Most of the hydrocarbons in crude oil are alkanes.
An example of a hydrocarbon
Ethane C2H6 two C’s and six H’s
What are alkanes?
Alkanes are saturated hydrocarbons. This means that their carbon atoms are joined to each other by single bonds. This makes them relatively unreactive, apart from burning or combustion, which is their reaction with oxygen in the air.
What is distillation and how does it work?
Distillation is a process that can be used to separate a pure liquid from a mixture of liquids. It works when the liquids have different boiling points.
The sequence of events in distillation
heating → evaporating → cooling → condensing
How is fractional distillation different to distillation?
It separates a mixture into a number of different parts, called fractions.
How does fractional distillation work?
A tall column is fitted above the mixture, with several condensers coming off at different heights. The column is hot at the bottom and cool at the top. Substances with high boiling points condense at the bottom and substances with lower boiling points condense on the way to the top. The crude oil is evaporated and its vapours condense at different temperatures in the fractionating column. Each fraction contains hydrocarbon molecules with a similar number of carbon atoms.
How do oil fractions work?
The top of the column is cool (25 degrees Celsius). Fractions taken from here have small molecules, low boiling points, are very volatile, flow easily and ignite easily. Crude oil enters at the bottom of the column and is heated to 350 degrees Celsius. Fractions taken here have large molecules, high boiling points, are not very volatile, and don’t flow or ignite easily. From top to bottom the fractions are: Refinery gases (bottled gas), gasoline (petrol), naphtha (used for making chemicals), kerosene (aircraft fuel), diesel oil (fuel for cars, and lorries, etc.), fuel oil (fuel for ships, power stations), residue (bitumen for roads and roofs).
Fractioning column
As you go up the fractionating column, the hydrocarbons have: lower boiling points lower viscosity (they flow more easily) higher flammability (they ignite more easily). This means that in general hydrocarbons with small molecules make better fuels than hydrocarbons with large molecules.
What is complete combustion?
Fuels burn when they react with oxygen in the air. If there is plenty of air, complete combustion happens. Coal is mostly carbon. During complete combustion, carbon is oxidised to carbon dioxide: carbon + oxygen → carbon dioxide
What kind of gas is carbon dioxide?
A greenhouse gas
What happens to hydrogen during combustion?
Hydrocarbon fuels contain carbon and hydrogen. During combustion, hydrogen is oxidised to water (remember that water, H2O, is an oxide of hydrogen). In general: hydrocarbon + oxygen → carbon dioxide + water
What is incomplete combustion?
If there is insufficient air for complete combustion, incomplete combustion (also called partial combustion) happens. Hydrogen is still oxidised to water, but carbon monoxide forms instead of carbon dioxide. Carbon monoxide is a toxic gas, so adequate ventilation is important when burning fuels. Solid particles (particulates) are also released. These contain carbon and are seen as soot or smoke.
What do particulates cause?
Global dimming and they reduce the amount of light reaching the Earth’s surface.
What are the effects of acid rain?
Acid rain reacts with metals and rocks such as limestone, causing damage to buildings and statues. Acid rain damages the waxy layer on the leaves of trees. This makes it more difficult for trees to absorb the minerals they need for healthy growth and they may die. Acid rain also makes rivers and lakes too acidic for some aquatic life to survive.
What happens to the sulphur in fuel when it burns?
sulphur + oxygen → sulphur dioxide This gas dissolves in water to form an acidic solution. It is a cause of acid rain.
Are crude oil and coil renewable or non-renewable resources?
Non-renewable, they take so long to form that they cannot be replaced once they have all been used up. This means that these fossil fuels are likely to become more expensive as they begin to run out.
Which substances are produced when fuels made from crude oil are burned?
Petrol, diesel and other fuels produced from crude oil make a range of harmful substances when they are burned, including: carbon dioxide carbon monoxide water vapour particulates (solid particles) sulphur dioxide oxides of nitrogen or NOx.
What are biofuels?
Biofuels are fuels produced from plant material. They have some advantages and disadvantages compared to fossil fuels.
What is biodiesel made from?
Biodiesel is made from rapeseed oil and other plant oils. It can be used in diesel-powered vehicles without needing any modifications to the engine.
What is bioethanol?
Ethanol, C2H5OH, is not a hydrocarbon because it contains oxygen as well as hydrogen and carbon. However, it is a liquid fuel that burns well. Bioethanol is made by fermenting sugars from sugar cane, wheat and other plants. It cannot be used on its own unless the engine is modified. However, modern petrol engines can use petrol containing up to 10 percent ethanol without needing any modifications, and most petrol sold in the UK contains ethanol.
What are some ethical issues surrounding the use of biofuels?
There are ethical issues surrounding the use of biofuels. For example, crops that could be used to feed people are used to provide the raw materials for biofuels instead. This could cause food shortages or increases in the price of food. There are other economic issues surrounding the use of biofuels, including: human resources -more people are needed to produce biofuels than are needed to produce petrol and diesel increased income - for farmers lower fuel prices - biofuels limit the demand for fossil fuels, helping to reduce increases in fuel prices.
What are the environmental issues with biofuels?
There are environmental issues surrounding the use of biofuels. Biodiesel naturally contains little sulphur. For example, it may be said that they are carbon neutral – the amount of carbon dioxide released when they are used is the same as the amount absorbed by the plants as they grew. If so, this would reduce the production of this greenhouse gas. However, while biofuels produce less carbon dioxide overall, they are not carbon neutral. This is because fossil fuels are used in their production, for example in making fertilisers for the growing plants.
