What is Coal, oil and Gas (Fuse school) https://www.youtube.com/watch?v=EYeSBNBCjx4

CHEMICAL PROPERTIES OF ALKANES Introduction - fairly unreactive Combustion - make useful fuels complete CH4(g) + 2O2(g) ——> CO2(g) + 2H2O(l) combustion incomplete CH4(g) + 1½O2(g) ——> CO(g) + 2H2O(l) the greater the number of carbon atoms, the more energy produced BUT the greater the amount of oxygen needed for complete combustion. Fuse School: Combustion https://www.youtube.com/watch?v=Nl0bipxyuyk&index=180&list=PLW0gavSzhMlReKGMVfUt6YuNQsO0bqSMV

Processes involving combustion give rise to a variety of pollutants... POLLUTION Processes involving combustion give rise to a variety of pollutants... power stations SO2 emissions produce acid rain internal combustion engines CO, NOx and unburnt hydrocarbons Removal SO2 chimney scrubbers react effluent gases with bases (e.g. CaO) CO and NOx pass exhaust gases through a catalytic converter Catalytic converters In the catalytic converter ... CO is converted to CO2 NOx are converted to N2 Unburnt hydrocarbons are converted to CO2 and H2O e.g. 2NO + 2CO ———> N2 + 2CO2 • leaded petrol must not pass through the catalyst as the lead deposits on the catalyst’s surface and “poisons” it, thus blocking sites for reactions to take place.

The internal combustion engine Boardworks AS Chemistry Alkanes Alkanes with chain lengths of 6-9 carbon atoms are used as fuels This releases carbon dioxide into the atmosphere: nonane + oxygen → carbon dioxide + water C9H20(g) + 14O2(g) → 9CO2(g) + 10H2O(g) Although modern internal combustion engines are more efficient than in the past, incomplete combustion still occurs: nonane + oxygen → carbon monoxide + water 2C9H20(g) + 19O2(g) → 18CO(g) + 20H2O(g) Climate Change https://www.youtube.com/watch?v=gBLQUplzZZo

Carbon dioxide in the atmosphere Boardworks AS Chemistry Alkanes Burning fossil fuels releases carbon dioxide into the atmosphere. Fossil fuels are being burned faster than they are being formed, which means that their combustion leads to a net increase in the amount of atmospheric carbon dioxide. Photo credit: Andrew Horwitz / shutterstock.com It has been suggested that increases in the amount of carbon dioxide and other greenhouse gases may be responsible for apparent changes to the climate.

CO2 is a greenhouse gas

CO2 emissions From Wikipedia

Boardworks AS Chemistry Alkanes Greenhouse gases Carbon dioxide, water vapour and methane have been described as the main greenhouse gases. This is because these have been suggested as the gases responsible for the majority of the greenhouse effect. The greenhouse effect is a theory that has been suggested to explain apparent rises in the average temperature of the Earth. Teacher notes See the ‘Green Chemistry’ presentation for more information about greenhouse gases and global warming. Increasing the amount of any of the greenhouse gases traps more heat energy from the Sun in the Earth’s atmosphere, raising the average temperature.

The Earth is getting warmer From New Scientist

Sea levels are rising From thesilentearth.com

Summary of Pollutant gases Boardworks AS Chemistry Alkanes Summary of Pollutant gases

The combustion engine: nitrogen Boardworks AS Chemistry Alkanes The temperature in engines can reach over 2000 °C. Here, nitrogen and oxygen, which at normal temperatures don’t react, combine to form nitrogen monoxide: N2(g) + O2(g) → 2NO(g) Nitrogen monoxide reacts further forming nitrogen dioxide: 2NO(g) + O2(g) → 2NO2(g) Teacher notes Students could be asked why nitrogen and oxygen require a high temperature to react. Important points are that nitrogen molecules contain a very strong triple bond, and that the activation energy for the reaction is very high. Nitrogen dioxide gas reacts with rain water and more oxygen to form nitric acid, which contributes to acid rain: 4NO2(g) + 2H2O(l) + O2(g) → 4HNO3(aq)

Much SO2 from power stations Catalytic converters in cars remove NOx

Sulfur contamination of fossil fuels Boardworks AS Chemistry Alkanes Sulfur is found as an impurity in crude oil and other fossil fuels. It burns in oxygen to form sulfur dioxide: S(s) + O2(g) → SO2(g) Sulfur dioxide may be oxidized to sulfur trioxide: 2SO2(g) + O2(g) → 2SO3(g) Both of these oxides dissolve in water forming acidic solutions that fall from the clouds as Acid Rain: SO2(g) + H2O(l) → H2SO3(aq) SO3(g) + H2O(l) → H2SO4(aq)

Removing sulphur dioxide pollution Boardworks AS Chemistry Alkanes Sulphur impurities are removed from fuel before it is burnt. Removing the sulfur from coal before it is burnt is not practical. Instead, the acidic sulfur oxides are removed from the waste gases using a base such as calcium oxide. Photo credit: Ian Bracegirdle / shutterstock.com

Much SO2 from power stations, But wait there is a solution Much SO2 from power stations

Remove SO2 by flue gas desulphurisation REMOVING SULPHUR Much SO2 from power stations CaO + SO2  CaSO3 or CaCO3 + SO2  CaSO3 + CO2 Remove SO2 by flue gas desulphurisation

ACID RAIN Damages plants

Branches from a tree in Germany's Black Forest show needle loss and yellowed boughs caused by acid rain

ACID RAIN ……Kills fish

Damages some stones (e.g. limestone) 1908 1968 ACID RAIN Damages some stones (e.g. limestone)

CRACKING

Crude oil and Cracking Lesson objective: To understand that alkane fuels are obtained from the fractional distillation, cracking and reforming of crude oil Outcomes: Describe the process of fractional distillation of crude oil Describe thermal and catalytic cracking Describe the reforming of crude oil Explain why cracking is carried out Explain why alkanes are reformed Explain why the boiling points of different alkanes are different

Crude oil is a thick black viscous liquid that floats on water! It was formed from the remains of sea animals and plants that died and were buried millions of years ago. It is composed of a very large mixture of hydrocarbons

Oil refining involves the separation of these hydrocarbons into mixtures (‘fractions’) which are very important and extremely useful. They are separated by fractional distillation Liquids in a mixture can be separated if they have different boiling points. Because there are so many hydrocarbon molecules in crude oil, the fractions contain groups of molecules will similar molecular masses.

Liebig condenser? Fractioning column round bottomed flask

fractions kerosene contains aviation fuel residue contains tar, lubricating oil gases contain methane, propane fractions Naphtha, the starting point for many other chemicals gasoline contains petrol gas oil contains diesel oil

some products obtained from the fractions plastics Bitumen,tar wax camping gas petrol domestic heating fuel aviation fuel industrial heating oil diesel oil fuel oil lubricating oil

The most volatile fractions. (i. e The most volatile fractions. (i.e. - those with lowest boiling point) come out of the top of the column and are gases, as these have very low molecular masses (e.g. methane). The heaviest compounds fall to the bottom of the column. These compounds have the highest molecular masses and are the least volatile.

From Wikipedia Simple Distil (5 min. UK) https://www.youtube.com/watch?v=86WY2mV9jiU Fuse School (Frac Dis) https://www.youtube.com/watch?v=JZdvsQzOKuk

What is cracking? https://www.youtube.com/watch?v=sJArhELmiUk Boardworks AS Chemistry Alkanes What is cracking? https://www.youtube.com/watch?v=sJArhELmiUk Cracking is a process that splits long chain alkanes into shorter chain alkanes, alkenes and hydrogen. Uses: it increases the amount of gasoline and other economically important fractions it increases branching in chains, an important factor for petrol's octane rating Teacher notes It could be emphasized to students that when cracking takes place, a mixture of products is produced from different cracking reactions occurring at the same time. The equation shown is just an example of a cracking reaction a C10H22 molecule may undergo. Although the reaction shown does not include hydrogen, the mixture of products will contain hydrogen due to reactions such as C10H22  C3H6 + C7H14 + H2 it produces alkenes and arenes, important feedstock for chemicals. There are two main types of cracking: thermal and catalytic.

Catalytic Cracking

-162ºC -89ºC -42ºC -1ºC 36ºC What is the pattern here? What does it have to do with homologues? Why do we need to know this for fractionation? -162ºC -89ºC -42ºC -1ºC 36ºC

Catalytic Cracking Uses something called a zeolite catalyst (hydrated aluminosilicate, Na2Al2Si3O. 2H2O), at a slight pressure and high temperature (about 450oC). Using a catalyst cuts costs, because the reaction is faster at a lower temp and pressure. Zeolite catalysts

Thermal cracking Thermal means heat, it involves heating alkanes to a high temperature (700-1200K),and putting them under high pressure, up to 7000kPa. WOW! That is a lot of Pressure! C H R - C H R - C H R = + Catalytic cracking has almost completely replaced thermal cracking. Why?

Aromatic hydrocarbons PPT - GCSE - Crude oil 18-Jul-19 Thermal cracking Catalytic cracking Temperature Pressure Catalyst Products 900C 450C 70 atm 1-2 atm none zeolites Motor fuels Aromatic hydrocarbons Cyclic alkanes Branched alkanes alkenes

THE WINNER BY FAR Catalytic cracking…..why? Boardworks AS Chemistry Alkanes THE WINNER BY FAR Catalytic cracking…..why? Catalytic cracking BETTER because it: 1) produces a higher proportion of branched alkanes, that burn more easily than straight-chain alkanes, in petrol 2) Uses a lower temperature and pressure so it is cheaper 3) Produces a higher proportion of arenes, which are valuable feedstock chemicals. Ok there is a bad piece of information, nothing is perfect : Catalytic cracking cannot be used on all fractions, such as bitumen, the supply of which is great. Oh my, what an opportunity that is lost!!! Teacher notes Catalytic cracking is the main form of cracking used in the manufacture of petrol.

Boardworks AS Chemistry Alkanes Supply and demand Boardworks AS Chemistry Alkanes The demand for lower boiling point (shorter chain) fractions is greater than the proportion found in crude oil. Crude oil contains too many higher boiling point (longer chain) fractions, which are in lower demand and are less economically valuable. Photo credit: Dmitrijs Dmitrijevs / shutterstock.com Teacher notes Students could be asked to explain why shorter chain fractions are more useful than longer chain fractions. Cars raise the demand for fractions like gasoline, but crude oil contains more of the fractions like bitumen. There is therefore a shortage of shorter chain fractions and a surplus of longer chain ones.