1crude oil Flashcards
crude oil
mixture of hydrocarbons
each fraction
consists of groups pf hydrocarbons of similar chain lengths
each fraction in petroleum is separated in a process called
fractional distillation
the molecules in each fraction have
similar boiling points and properties
the size and length of each hydrocarbon molecule determines
in which fraction it will be separated into
fractional distillation is carried out in a fractionating column which is
very hot at the bottom and cool at the top
crude oil enters
the fractionating column and is heated so vapours rise
boiling points in a fractionating column
low bp at the top, high at bottom
fractions with smaller hydrocarbons are collected at
the top and the bigger ones at the bottom
viscosity
This refers to the ease of flow of a liquid. High viscosity liquids are thick and flow less easily. If the number of carbon atoms increases, the attraction between the hydrocarbon molecules also increases which results in the liquid becoming more viscous with the increasing length of the hydrocarbon chain. The liquid flows less easily with increasing molecular mass
colour
As carbon chain length increases the colour of the liquid gets darker as it gets thicker and more viscous
mp/bp
As the molecules get larger, the intermolecular attraction becomes greater. So more heat is needed to separate the molecules. With increasing molecular size there is an increase in boiling point
combustion of fossil fuels is
the major source of atmospheric pollution
the burning of fossil fuels releases gases such as
carbon dioxide, carbon monoxide, oxides of nitrogen and oxides of sulfur as well as unburned hydrocarbons and carbon particulates
a fuel is
a substance which releases energy in an exothermic reaction
complete combustion occurs when
there is excess oxygen
incomplete combustion occurs when there is
insufficient oxygen to burn
carbon dioxide is
a toxic and odourless gas which can cause dizziness, loss of consciousness and eventually death
nitrogen and nitrogen oxides are formed when
nitrogen and oxygen react in the high pressure and temperature conditions of internal combustion engines and blast furnaces
exhaust gases contain
unburned hydrocarbons and carbon monoxide
cars are fitted with
catalytic converters which form a part of their exhaust systems- their function is to render these exhaust gases harmless
catalytic converters contain a series of
transition metal catalysts including platinum and rhodium,
sulfur dioxide sources
combustion of fossil fuels- especially coal
fossil fuels are often contaminated with
small amounts of sulfur impurities- when these contaminated fossil fuels are combusted, the sulfur in the fuels get oxidised to sulfur dioxide
the sulfur dioxide produces from
the combustion of fossil fuels dissolves in rainwater droplets to form sulfuric acid
nitrogen dioxide also contributes to
acid rain
alkanes are
saturated compounds
alkenes are
unsaturated compounds
cracking is
converting long chain alkanes into short chain alkenes which are more useful
kerosene and diesel oil are often cracked to
produce petrol
methods of cracking
catalytic cracking and steam cracking
catalytic cracking
Catalytic cracking involves heating the hydrocarbon molecules to around 470 – 550°C to vaporise them
The vapours then pass over a hot powdered catalyst of aluminium oxide
This process breaks covalent bonds in the molecules as they come into contact with the surface of the catalyst, causing thermal decomposition reactions
The molecules are broken up in a random way which produces a mixture of smaller alkanes and alkenes
Hydrogen and a higher proportion of alkenes are formed at higher temperatures and higher pressure
why is cracking necessary
Crude oils vary considerably in their composition and some need more refining than others
Supply is how much of a particular fraction can be produced from refining the crude oil
Demand is how much customers want to buy
General the demand for certain fractions outstrips the supply so this is why cracking is necessary to convert surplus unwanted fractions into more useful ones
This is mostly larger, heavier fractions that are cracked into smaller lighter fractions
cracking is used to
convert long chain alkane molecules into short chain molecules which are more useful
what is produced during cracking
small alkenes and hydrogen
kerosene and diesel oil are often
cracked to produce petrol, other alkenes and hydrogen
methods of cracking
catalytic cracking and steam cracking
