Oil Refining, Fuels and Thermochemistry

What are fossil fuels? Give 3 examples

fuels formed from the remains of plants and animals that lived millions of years ago, hydrocarbons such as oil, crude oil and natural gas

What is natural gas?

a mixture of hydrocarbons - primarily methane

How is methane produced?

animal waste and dead plants are decomposed by anaerobic bacteria, naturally produced in slurry pits, coal mines and refuse dumps

Give an advantage of methane production

very good fuel

Outline a hazard of methane production

accidents in mines because methane forms an explosive mixture with air-explosions have occurred

Give a disadvantage of methane production

causes global warming

What is crude oil/petroleum?

mixture of many different hydrocarbons

What is fractional distillation/fractionation of crude oil?

Used to separate crude oil into its component hydrocarbons based on their specific molecular mass/boiling points

Why is fractional distillation of crude oil carried out?

Crude oil itself is of little use but it's component hydrocarbons are extremely useful

Give the process of fractional distillation

1. crude oil heated at the base of the column and becomes vapour

2. vapour moves up through a series of trays with the temperature decreasing going up the column

3. different fractions of hydrocarbons come off on a specific tray as they condense into a liquid once the temperature drops below their boiling point

4. larger molecules with higher boiling points come off at lower levels, smaller molecules with lower boiling points come off higher up

Based on what 2 properties are the hydrocarbons separated?

boiling point and molecular mass

Give the 6 fractions in order from top to bottom

refinery gas

light gasoline

naphtha

kerosene

gas oil

residue

What is a use of refinery gas fraction?

domestic gas (LPG)

What is a use of light kerosene?

petrol for cars

What is a use for naphtha fraction?

petrol for cars, feedstock for the petrochemical industry to make plastics, solvents and detergents

What is a use for kerosene fraction?

fuel for jet aircraft and oil for home central heating

What is a use for gas oil?

diesel for vehicles, lubricant for engines

What is a use for residue?

bitumen for road surfacing

Why is the bottom fraction known as the residue fraction?

It is the fraction that is left over at the bottom of the fractioning column, it has the highest boiling point

What does LPG stand for? What's it made from? What's it used for?

liquid petroleum gas

propane and butane, sold as domestic gas for heating and cooking

What are mercaptans and why are they used?

sulfur containing compounds added to natural gas to give it an unpleasant smell so that leaks can be detected

What is autoignition?

premature ignition of the petrol air mixture before a spark is produced by spark plugs

What are the results of autoignition?

loss of power, damage to the engine

What property of petrols leads to autoignition?

long, straight chained alkanes eg heptane, octane and nonane

What is meant by octane number?

measure of the tendency of a fuel to resist autoignition

Give 3 factors that effect a fuels octane number

length of chain

degree of branching

cyclic structure

What are the two reference hydrocarbons for octane number?

heptane (0) and 2,2,4 trimethylpentane (100)

Why are lead compounds not used in fuel?

harmful to environment and peoples health

poisons the catalytic converters in cars

Give 4 ways in which the octane number of a fuel can be increased

isomerisation

dehydrocyclisation

catalytic cracking

adding oxygenates

Describe isomerisation

changing straight chained alkanes into branched alkanes with the same molecular formula but different structural formula.

Achieved by heating the straight chained alkanes with a catalyst causing the chains to break, when the chains reform they are likely to be branched

Describe dehyldrocyclisation

use of a catalyst to form ring compounds from straight chained compounds with hydrogen produced as a by product

describe catalytic cracking

Uses heat and a catalyst to break down long chained hydrocarbons into shorter chained molecules for which there is greater demand

What are formed by catalytic cracking? What can they be used for?

Alkenes making plastics

Describe the addition of oxygenates

addition of compounds that contain oxygen

Give 2 examples of oxygenates

alcohols eg methanol

MTBE (methyl tert butyl ether)

Give a second advantage of adding oxygenates to petrol

give rise to much less pollution