CH1 Fuels From Crude Oil

7/30/2019 CH1 Fuels From Crude Oil

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Crude oil is extracted from the Earths crust. It is formed

over millions of years from plant and animal remains

buried under layers of rock.

Crude oil is not very useful as it is it is thick,

black, sticky and doesnt burn too well but

modern society is critically dependent onproducts which are obtained from crude oil:

e.g. petrol and other fuels

plastics and fabrics

medicines

crude oil

Oils and fuelsobtained from

crude oil


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Crude oil is a finite resource. This means there is a limited amount of it. Since it

takes millions of years to form we say it is non-renewable.

We can be sure that it will run out completely if we carry on using it at the rate we

have been doing. Some estimates put the remaining crude oil reserves at about40 years left.

What has to be done ?

1) Develop alternative fuels and energy sources which are renewable e.g. biofuels

2) Develop alternative routes to manufacture plastics, medicines etc.

3) Conserve existing crude oil reserves reduce wasted fuel use, recycle plastics


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Crude oil is not a single substance, but a mixture containing many different

chemical compounds

The majority of these are hydrocarbons which means that they are made only

from carbon and hydrogen atoms. The carbon atoms form a chain and thehydrogen atoms connect to the carbon atoms:

carbon atomshydrogen

atoms

Four different hydrocarbon molecules of the kind found in crude oil


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Note that each carbon atom has fourbonds and that each hydrogen has one bond.

This is always true in hydrocarbon molecules.

The family of substances with a carbon chain and hydrogen atoms connected to all

the other places where bonds can form is called the ALKANES.

The smallest alkane, with one carbon atom, is METHANE CH4The next smallest, with two carbon atoms is ETHANE C2H6Then comes a 3-carbon chain, called PROPANE C3H8 and a 4-carbon chain, called BUTANE C

4

H10

and a 5-carbon chain, called PENTANE C5H12

In general, for an alkane with n carbon atoms, the formula is:

We call this the GENERAL FORMULA for the alkanes

Natural gas

contains 90%

methane Petrol contains alkanes such asoctane, 8 carbons long

CnH2n+2


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Drawing such detailed pictures of the molecules is time-consuming and chemists

prefer to use a simpler notation:

The molecular formula tells you how many of each atom are present in the

molecule, but not how the atoms are connected

e.g. The molecular formula formethane is CH4The molecular formula forpropane is C3H8

The displayed formula uses the element symbols and shows

which atoms are connected to which other atoms in the molecule

e.g. The displayed formula formethane is

The displayed formula forpropane is


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One property of any mixture is that it can be separated

by physical means (i.e. without doing any chemical

reactions). Physical means could include filtering, or

using magnets, or evaporation, for example.

Different mixtures require different physical means. In

the case of crude oil, the mixture is separated using

boiling and condensing.

The process is called fractional distillation. It works

because each different hydrocarbon has a differentboiling point:

The longerthe chain the higherthe temperature

has to be in order to turn the hydrocarbon from

liquid to gas i.e. the higher the boiling point

The process starts by heating the crude oil up until all

of the hydrocarbon molecules are gases. They are

then passed into the bottom of a fractionating

column


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Hydrocarbons

enter here as

gases.

The fractionating

column gets

cooler the further

up the molecules

travel.

Each molecule

rises up the tower

until it gets to the

point where it

condenses backinto a liquid trays

collect the liquid at

different levels.

The liquid collected in each

tray contains hydrocarbons

with a specific range of chain

lengths these are called

fractions

Some very short chain hydrocarbons

come out of the top still as gases

they are collected too


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The different fractions obtained by fractional distillation of crude oil have different

properties and therefore different uses. Some are shown below:

Name Alkanes in this fraction Uses

Refinery gas CH4 to C4H10

Gasoline C4H10 to C12H26

Kerosine C11H24 to C15H32

Diesel C15H32 to C18H38

Residue C50H102 and longer(bitumen for

road repairs)

Note:you dont

have to learn

names of specific

fractions, or the

range of

hydrocarbons in

each, but you

should know theuses, and be able

to relate uses to

the typical size of

the hydrocarbon

molecules


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As the length of the

carbon chain in an

alkane increases

The boiling point

increases

It gets harder to turn

the hydrocarbon into

a gas

It gets less runny

and more thick and

sticky

It gets harder to

ignite, burning with a

more smoky flame


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Evaluating fuels

You may be asked to discuss how good or bad a fuel is, comparing it to other

fuels for example.

A good fuel needs to be: Easy to ignite, but not so flammable that it is dangerous to handle

Easy to transport and pump around (liquids are better than solids or gases)

Safe to handle and store

Cheap and readily available not expensive to produce

Clean - polluting as little as possible when it burns

(examine the products of combustion, including any trace substances which may

be present e.g. sulphur in fossil fuels)

vs.


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Burning pure hydrocarbons

Burning is a chemical reaction between a fuel and oxygen, in which energy is

released. With most fuels, each of the elements it is made of can react with oxygen to

make an oxide.

If there is enough oxygen available - The carbon reacts with oxygen to make carbon dioxide

(CO2)

The hydrogen reacts with oxygen to make hydrogen oxide

(H2O aka water!)

If there isnt enough oxygen available

Water will still be made, but The carbon may react to form carbon monoxide (CO) Pure carbon (soot) may be produced

(this is what makes a flame yellow and luminous)

hydrocarbon + oxygen carbon dioxide + water

(e.g. methane)

hydrocarbon + oxygen carbon monoxide + water

(e.g. methane)


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Inside a motor vehicle engine, the fuel is mixed with air before it is ignited. This is

so that there is oxygen available to react with the hydrocarbon molecules.

Unfortunately that isnt all the oxygen reacts with.

Fossil fuels also contain traces ofsulphur. When the sulphur in the fuel is burned itreacts with oxygen in the air to form sulphur dioxide, which can be emitted in the

exhaust of the vehicle.

At the temperatures inside engines, nitrogen in the air is also burned, reacting with

oxygen to form nitrogen oxides. These gases can also be emitted in the exhaust.

Both nitrogen oxides and sulphur

dioxide can dissolve in rain droplets,

reacting to form strongly acidic

solutions, and falling as acid rain

(see next section for the problems

this causes, and what can be done

to reduce them).


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Alternatives to fuels from crude oil 1) Hydrogen

Hydrogen can be obtained by electrolysis of water. It is a gas, lighter than air, and

extremely flammable. Technology is currently under development to use hydrogen

as a fuel, but there are lots of challenges remaining.

Evaluating hydrogen as a fuel:

Available ? Yes easy to produce

Clean ? Yes the only product when it burns is water

Storage ? Not easy its a gas so its bulky. New technology needed.

Perhaps hydrogen could be made by a reaction as it is needed

Safe to use ? Not as safe as petrol ignites much more easilyProblems for safe storage and safe refuelling

Ignition ? Very easy (too easy !) to ignite

A hydrogen-fuelled carHistorically, using hydrogenhas a bad reputation !


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Alternatives to fuels from crude oil 2) Ethanol

Ethanol can be made using products from crude oil, but it can also be made by

fermentation of plant matter this is called bioethanol. Biofuels such as this do not

deplete our crude oil reserves so they are called renewable fuels. They can be used

as alternatives to petrol/diesel.

Evaluating bioethanol as a fuel:

Available ? Yes easy to produce, but requires a lot of land to grow plants.

Clean ? Same main products, CO2 and H2O - but no sulphur dioxide.

Storage ? Much the same as petrol to store and transport. Its a liquid.

Safe to use ? Similar to petrol less damaging to environment if spilled

because it gets broken down more easily.

Ignition ? Easy to ignite more so than petrol.

An ethanol-fueled car

Ethanol can be

blended with

petrol to help

conserve crude oil

reserves and to

reduce the cost of

the fuel


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When fossil fuels burn, a variety of products may be formed which have impact on

health and the environment:

Carbon dioxide formed when the carbon in hydrocarbons reacts with a plentiful

supply of oxygen. Causes Global Warming.

Carbon monoxide formed when the carbon in hydrocarbons reacts with a limited

supply of oxygen. Toxic, colourless and odourless Dangerous to Health !.

Particulates particles of carbon formed when hydrocarbons burn in a limited

supply of oxygen. May also be coated with unburned fuel. Cause Global Dimming.

Sulphur dioxide formed when traces of sulphur in fossil fuels burn, reacting with

oxygen in the air. Causes acid rain.


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Global warming and the Greenhouse Effect

Carbon dioxide and other greenhouse gases form a

layer in the upper atmosphere which allows the suns

energy to pass through, warming the Earths surface.

Rather than escaping back into space, the radiated

heat from the Earths surface is trapped by this layer (in

the same way the glass in a greenhouse traps the heat

from the sun). This causes temperatures to get steadily

warmer the phenomenon is termed Global Warming.

NOTE: THIS HAS NOTHING TO DO WITH THE OZONE LAYER !

Effects of Global Warming:

include drought and flooding and melting of the polar ice caps

Then

Now


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Carbon monoxide poisoning

Carbon monoxide is deadly. This is because it is colourless, odourless and

poisonous, so you wont be able to tell if you are breathing it in. Its toxic effect

works by preventing respiration from happening properly. A headache is one of the

first symptoms.

Rather than haemoglobin in the blood transporting oxygen to where it is needed, as

it should, the haemoglobin bonds to carbon monoxide molecules instead, and

oxygen starvation to the tissues and organs occurs.

Badly-maintained gas fires or water heaters are a common source of carbonmonoxide poisoning. This happens when the air-holes get blocked and the gas

burns with less oxygen from the air than it should.


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Global Dimming

As the atmosphere becomes contaminated

with particulates (soot, particles of

unburned fuel) so the light from the sun

will be progressively blocked out. The

particles will scatter back into space sunlight

which would otherwise have reached Earth.

The effects of Global Dimming would be:

1) Decreased light levels affecting rates of crop growth and healthiness of plants

2) Lower temperatures as less of the Suns energy heats the Earths surface

Increased amounts of particulates in the air willalso have effects on health increased

respiratory problems such as asthma, so putting

more particulates into the atmosphere is not a

cure for Global Warming !


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Acid RainGases such as sulphur dioxide and nitrogen oxides,

formed when fossil fuels are burnt, cause acid rain.

These gases dissolve in droplets of waterin the

atmosphere (i.e. rain droplets) to form strongly acidic

solutions, which can damage trees and aquatic

ecosystems as well as slowly attacking building

materials such as limestone.

Carbon dioxide also forms an acidic solution when itdissolves in water droplets, but it is much more weakly

acidic.

Because the atmosphere is constantly moving, the place

where acid rain falls may be in an entirely different

country to the place where the polluting gases wereformed. Remote areas of great natural beauty can be

destroyed by acid rain from urban areas many hundreds

of miles upwind.


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Reducing the damage that acid rain causes

Two approaches are used:

1) Remove the sulphur from the fuelOil refineries can process fractions which are to be used as fuels in order to

remove the traces of sulphur from the fuel. This is called desulphurisation.

At petrol stations, look for pumps labelled as Ultra-low sulphur fuel

2) Remove the sulphur dioxide from the emissionsWhen fossil fuels are burnt in power stations, huge

quantities of fuel are consumed, so it is not cost effective

to buy desulphurised fuels. The fuels do contain traces of

sulphur, and the flue-gases do contain sulphur dioxide.

What is done here is to install a scrubber. This is a

system that the flue gases pass through which removesthe sulphur dioxide by reacting it with quicklime. The

process is called flue-gas desulphurisation.

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CH1 Fuels From Crude Oil