4a. Atmospheric pollution: The Incomplete Combustion of hydrocarbons CO

• When fossil fuels burn efficiently in an excess of air/oxygen the only products are carbon dioxide and water e.g.

  • examples of complete combustion burning are for example natural gas and petrol

  • methane + oxygen ==> water + carbon dioxide

  • CH_4(g) + 2O_2(g) ==> CO_2(g) + 2H₂O_(l)

  • pentane + oxygen ==> water + carbon dioxide

  • C₅H_12(g) + 8O_2(g) ==> 5CO_2(g) + 6H₂O_(l)

• Power stations burn huge quantities of fossil fuels in the form of mainly coal, but significant quantities of gas ans some oil. The heat from the very exothermic combustion is used turn water into steam and steam driven turbines power the electrical generators (very big dynamos!).

• If there is not enough oxygen present to completely burn the fuel to carbon dioxide and water other products may form causing pollution and fuel inefficiency.

  • This is referred to as incomplete combustion.

• The most common partially burned products are likely to be carbon C (soot) and deadly carbon monoxide CO.

  • Carbon-soot, a fine black powder-dust is potentially harmful and readily formed in fires i.e. its classically produced by smoky yellow flames and inefficient motor vehicle engines.

    • The soot, like any fine solid 'dust' is harmful when absorbed on the sensitive tissue of the linings of the nose, throat and lungs.

    • Soot deposits cause coughing and sore throat and are ejected from your body through sneezing, coughing, and nose blowing.

    • Coarse particles (10 microns) are inhaled into your windpipe and settle there, causing irritation and more coughing.

    • Soot is also a 'carrier' of polycyclic aromatic hydrocarbons (PAH's) on it which are carcinogenic.

  • Even very low concentrations of carbon monoxide can be fatal. Why?

    • Oxygen is carried around the body by a complicated protein molecule in red blood cells called haemoglobin.

    • The bonding between oxygen and haemoglobin is quite weak to allow easy oxygen transfer for cell respiration.

    • Unfortunately, the bonding between carbon monoxide and haemoglobin is stronger, so oxygen is replaced by carbon monoxide and blocks normal cell respiration.

    • The consequences are reduced blood oxygen concentration leading to unconsciousness and eventually death!

    • This is why long road tunnels are ventilated and you should never run a car engine in a closed garage!

• It would appear that the hydrogen in the fuel molecules is more easily burned and usually forms water so the equations for incomplete combustion below show the formation of carbon-soot and 'deadly' carbon monoxide when there is a lack of oxygen for complete combustion. As mentioned already, soot is obviously a 'dirty' pollutant coating any surface (including your lungs!) that the soot particles settle on and they contain unburned carcinogenic hydrocarbons AND carbon monoxide is involved in the chemistry of photochemical smogs - so all in all, inefficient combustion of fossil-hydrocarbon fuels is very undesirable!

• There is also less heat released in incomplete combustion compared to complete combustion since not all the carbon atoms of the fuel are fully combined with the maximum amount of oxygen.

  • e.g. for the incomplete combustion of methane the word and symbol equations are as follows ...

    • methane + oxygen ==> carbon + water

    • CH_4(g) + O_2(g) ==> C_(s) + 2H₂O_(l)

    • for soot (mainly carbon) formation

    • and

    • methane + oxygen ==> carbon monoxide + water

    • 2CH_4(g) + 3O_2(g) ==> 2CO_(g) + 4H₂O_(l)

    • for the formation of carbon monoxide

• Therefore it is extremely important that any combustion system is as efficient as possible e.g. gas heaters, furnaces etc. must all have excellent ventilation for complete combustion to harmless water and carbon dioxide.

• If there is any smell of gas, make sure (i) all appliances are turned off, (ii) all sources of ignition are absent, and (iii) ring the gas board!

• Faulty gas appliances have led to tragic deaths. Carbon monoxide is colourless and odourless and even low concentrations in the air can be fatal. It also accounts for why long road tunnels need to be well ventilated too.

• Carbon monoxide is unfortunately emitted by all car exhausts, though catalytic converters help reduce this by converting nitrogen monoxide (another pollutant) and carbon monoxide into harmless nitrogen and carbon dioxide.

  •  2NO_(g) + 2CO_(g) ==> N_2(g) + 2CO_2(g)

  • Transition metals like platinum and rhodium are used in the catalytic converter.

  • Nitrogen monoxide, NO, is formed by the combination of nitrogen and oxygen at high temperature in automobile engines (cars, lorries, buses etc. - its all the same!)

  • N_2(g) + O_2(g) ==> 2NO_(g)

  • Nitrogen monoxide readily forms nitrogen dioxide by combining with oxygen in air on exit from the engine exhaust.

  • 2NO_(g) + O_2(g) ==> 2NO_2(g)

  • Nitrogen dioxide is a lung and eye irritant, and, along with nitrogen monoxide, it is involved in the complex chemistry of photochemical smogs which can also produce ozone and other harmful chemicals in the air.

  • The reduction of fossil fuel burning is the only way to reduce photochemical smog e.g. using photovoltaic cells to harness solar energy to produce electricity. Using solar power indirectly in this way to run electric cars is potentially a good partial solution to the problem.

• See also pollution problems of plastics

4b. Energy resource evaluation - What makes a good fossil fuel?

Factors that should be taken into consideration - often factors overlap

• Energy value: e.g. kJ of heat energy released per kg;

• Availability: Geographical convenience - is it imported?, fluctuations in oil production levels and the market price

• Storage and distribution: Health and safety issues e.g. coal very safe, natural gas (explosive flammable gas) much more dangerous to store, but the gas is easy and more convenient to distribute via pipes.

• Production Costs:

  • Costs of exploration and extraction can be high for oil

  • Coal mines are dangerous to operate, good health and safety policies don't come cheaply, and its the same for operating oilfields and petrochemical complexes - oil refineries.

  • Costs of transporting the fuel

  • AND even after considering all of these factors ...

    • ... the market price can fluctuate with market forces and may also depend on political situations too!

    • eg the politics of the Middle East or European countries importing Russian natural gas etc.!

• Toxicity, Pollution and climate change:

  • Greenhouse effect - which fuel produces the least or most carbon dioxide for the energy released?

  • The sulphur content of fuel (most removed before fuel used to minimise sulphur dioxide and acid rain formation)

  • The efficiency of combustion e.g. minimum carbon monoxide and soot levels.

• Ease of use: Transferred easily e.g. oil and gas readily piped around and readily ignited for a quick start in power station. Coal is more trouble to transport and does not ignite as easily.

• See also

  • Section 2. Fossil fuels from crude oil

  • Section 9. biofuels eg bioethanol, biodiesel, alternative renewable fuels

  • Some other ideas for alternative fuels (page originally designed for AS level).

• also on OP02

4d. Atmospheric pollution: Other Pollution aspects of the Petrochemical Industry

More on Oil Products and Environment Problems & what can we can?

(see also plastics)

• 'COSTS'?: Our economy, like many other countries has become very dependent on the extraction, sale and use of oil based products. BUT, there is high price to be paid at times whether it be pollution effects or warring countries with oil economics factors.

• ACCIDENTS: Oil rig accidents, broken pipelines, oil tanker wrecks etc. all have terrible effects on the plant and animal life of the locality as we see from the horrible TV pictures of seabirds coated in oil, and toxic oil slicks covering the beaches and sands.

  • Birds get poisoned when trying to clean themselves and other animals like sea otters, whales can be poisoned too.

  • In fact the whole marine ecosystem of an area can be devastated so that even creatures not directly poisoned can be affected if their food chain is disrupted.

  • There is also the risk to humans from fires and explosions on rigs or at oil refinery installations and fuel storage depots etc.

• RISING CARBON DIOXIDE LEVELS - greenhouse gases - climate change - global warming

• 

  • The graph shows the steady rise in the concentration of carbon dioxide in the atmosphere from 1959-2004 as measured at the Mauna Loa mountain top observatory on the Pacific island of Hawaii.

    • In 2012 the carbon dioxide concentration in the air has reached 400 ppm.

    • This represents the highest carbon dioxide levels in the atmosphere for at least 250,000 years. This is known because trapped air bubbles in ice cores from the arctic regions can be analysed to obtain their % composition. Every year snow falls form a new layer that become compacted into thin layers of ice which become buried beneath successive yearly precipitations so a long geological record of the earth's atmosphere is preserved.

  • It is a good base-line for our planet because it is well away from any industry involving fossil fuel burning.

  • The concentration of CO₂ is in ppm (parts per million).

  • 1ppm means 1 in 10⁶ of air molecules is CO₂. In % volume terms, 1 ppm = 100 x 1 / 10⁶ = 0.0001%.

  • The graph shows that the CO₂ has risen from 0.0316% (316 ppm) in 1959 to 0.0378% (378 ppm) in 2004.

    • I haven't updated the graph for 2005-2012 data yet, but the carbon dioxide concentration continues to rise at about 2 ppm per year.

  • This doesn't seem much of an increase, BUT on a global scale, the extra 'Greenhouse CO₂ Gas' could have drastic consequences (see next paragraph), but the computer model predictions have a high degree of uncertainty.

  • I've started a new page of extra material including graphs, explanations and discussion points

    • on My Global Warming page More work will be done on it as I learn more myself!

• The burning of oil and other fossil fuels is believed to be contributing to the 'Greenhouse Effect' or global warming.

  • The Earth's land-water surfaces absorbs the Sun's radiation in the form of infra-red (main heating effect) and visible/ultraviolet sunlight.

  • The infrared light re-emitted from the warmed earth's surface is absorbed by gases like carbon dioxide, and the absorbed energy causes the rise in temperature.

• Carbon dioxide from fossil fuel burning, and other gases including methane, water vapour and CFC's absorb the re-radiated lower frequency infrared energy from the Earth's surface and so warming the atmosphere, rather like a greenhouse allows the sunlight in but not out. The effects are predicted to be dramatic e.g. rising sea levels as polar ice melts causing flooding in low lying land, more energy in the global weather system leads to more frequent violent weather patterns etc. etc.

  • See further note from IPCC report 2007) BUT there is considerable uncertainty as to what might actually happen, but the consensus amongst scientists is that fossil fuel burning is raising the global temperature by a small, but not insignificant amount.

  • What can we do about it? i.e. how can we reduce our 'carbon footprint' to reduce global warming?

    1. Reduce the amount of fossil fuels we burn in power stations, but the international community is struggles to come to an agreement over this issue and the huge, and fast growing economies of India and China are demanding the building of large numbers of fossil fuel power stations (in 2006 China is starting to build one every week!).

    2. 'Green' alternative renewable energy resources can be more exploited, but not without problems e.g.

       • wind turbines - weather dependant

       • wave power - subject to storm damage

       • hydroelectric power -

         • damming the exit from a valley or canyon, but who wants their valley flooded!

         • a large tidal barrage across a river estuary, but what about environmental-ecological effects, and possible silting up.

       • photovoltaic cells - depends on intensity of sunlight and varies from country to country, through the day and the seasons

       • solar power panels in roofs etc. - comments as above!

         • all reduce acid rain pollution and CO₂ production by using less fossil fuels.

         • Many are good for domestic and small communities but only nuclear power and large scale hydroelectric power schemes are suitable for large scale energy production for the highly populated countries with large industrial economies.

    3. Like 2., nuclear power is another option that does not produce carbon dioxide and is suitable for large scale power generation, but there are real public fears about the safety of nuclear power generation 'fuelled' by the consequences of the nuclear power plant accident at Chernobyl, Russia in 1986. It is extremely costly to build nuclear power stations and there are added extra long term costs in decommissioning nuclear power stations, safely processing the waste and safely storing the residual radioactive waste for hundreds to thousands of years.

    4. Recent ideas include storing the CO₂ from fossil fuel power stations underground in rocks under pressure - but I don't know any details or how feasible it is.

    5. Use less electricity and heat energy from fuel combustion by being careful of its use e.g. increase home insulation and more efficient electrical appliances like 'low energy' light bulbs.

    6. Burning wood is sustainable and the CO₂ formed on its combustion is recycled via photosynthesis BUT (i) it does not burn cleanly, (ii) its energy density is low (heat energy released per mass of fuel) and (iii) no good for large scale power generation.

• Global dimming. This makes the predictions about global warming even more uncertain.

  • As the earth warms up, more water vapour can exist in the atmosphere.

  • The more cloud that is formed in the upper atmosphere the more sunlight is reflected, so less radiated energy reaches the Earth's surface, leading to the opposite of global warming.

  • It has been suggested that cloud formation could be encouraged by seeding the atmosphere with crystals to promote cloud formation.

  • It is ironic that the vapour trails of aircraft, with their heavy use of fossil fuels, actually contribute to global dimming as well as to global warming at the same time!

  • The effect of global dimming was noticed in the aftermath of the 9/11 terrorist attacks on New York's World Trade Center Twin Towers in 2001.

  • All aircraft were grounded in the USA and many parts of the world for several days after the attacks and sunlight gauges showed a small but abnormal increase in sunlight levels reaching the Earth's surface.

    • There was also other evidence from monitoring stations which measure rates of water evaporation from large tanks, when a small but abnormal increase in evaporation rate from extra sunlight was noted.

  • It is believed that small (fine) solid particles like soot/carbon or ash in the atmosphere can cause global dimming because they form the nucleii of water condensation producing the fine water drops of clouds.

• ACID RAIN: Fossil fuels contain compounds of the element sulphur When the fuel is burned the sulphur compounds also burn to form sulphur dioxide. This is an acidic gas and dissolves in rainwater, it then reacts with water and oxygen to form a very dilute solution of sulphuric acid.

  • sulphur + oxygen ==> sulphur dioxide

    • S_{(in fuel molecules)} + O_2(g) ==> SO_2(g)

  • Sulphur dioxide is a harmful gas and lung irritant and contributed to 5000 extra deaths in the great 'London Smog' in the 1950's as well as being a major acid-rain gas.

    • Sulfur dioxide reacts with oxygen (in air) and water (rain) and gets oxidised to form very dilute sulphuric acid - the origin of acid rain, and the overall change is represented by the equation below.

    • SO_2(g-air) + O_2(g-air) + 2H₂O_(l-rain) ==> 2H₂SO_4(aq-rain)

  • The formation of acid rain has several bad effects on the environment e.g.

    • the low pH causes plant damage, particularly trees,

    • kills certain life forms and so damages eco cycles and food chains in rivers or lakes harming wildlife like trout,

    • increases the 'weathering' corrosion rates of building stone and statues (particularly those made of limestone).

  • All fuels are processed at the oil refinery to reduce the concentration of sulfur/sulphur compounds (the process of desulfurisation/desulphurisation) but this adds to the cost and not all the sulphur/sulfur is removed.

    • However, low sulfur content petrol and diesel are being introduced.

    • Of course, the less fossil fuels we burn, the less pollution results, so strategies to design more efficient road vehicles, using less energy in the home, renewable energy resources etc. will all help in the long run to reduce pollution.

    • Power stations can be fitted acid gas scrubbers eg removing the acidic sulfur dioxide with an alkaline mixture of water mixed with powdered lime/limestone.

• OTHER POLLUTANTS: High temperature combustion also produces other pollutants including ...

  • Nitrogen oxides collectively denoted by NO_x: NO is formed in car engines and changes to NO₂, which is acidic, contributing further to acid rain (above), and are also involved in the chemistry of 'photochemical smog' - which produces chemicals harmful to respiration, irritating to eyes and contributes to acid rain. Many of the reactions are initiated by sunlight.

    • nitrogen monoxide is formed in high temperature combustion situations e.g. car engines, power station furnace burning coal, oil or natural gas.

      • nitrogen + oxygen ==> nitrogen monoxide

        • N_2(g) + O_2(g) ==> 2NO_(g) 

    • and in air the nitrogen monoxide rapidly combines with the oxygen in air

      • nitrogen monoxide + oxygen ==>  nitrogen dioxide (acidic gas)

        • 2NO_(g) + O_2(g) ==> 2NO_2(g) 

    • The nitrogen dioxide is oxidised to nitric acid by the reaction with oxygen from air when it dissolves in rainwater.

      • The overall process is summarised in the equation below.

      • 4NO_2(g-air) + O_2(g-air) + 2H₂O_(l-rain) ==> 4HNO_3(aq-rain)

  • Carbon monoxide CO, which is toxic, and also involved in the chemistry of 'photochemical smog' (see 4a). This is formed by inefficient combustion

  • Unburned hydrocarbons, C_xH_y, which can be carcinogenic and are also involved in photochemical smog chemistry.

    • But catalytic converters* can significantly reduced these three unwanted emissions (see above for CO and NO removal, and C_xH_y gets oxidised to CO₂ and H₂O). * e.g. using platinum-rhodium transition metal catalysts, these are dispersed on ceramic bed to give a big surface area for the best reaction rate.

  • There are other indirect pollution problems to do with burning fossil fuels:

  • Lead compounds are added to petrol to improve engine performance.

    • This produces lead compound emissions into the environment.

    • Lead compounds are nerve toxins so it is fortunate they are being phased out in many countries.

  • Photochemical smog is mentioned in the previous paragraph.

4e. Alternative fuels to fossil fuels - more on other energy resources

• OIL IS A VALUABLE CHEMICAL RESOURCE

  • Apart from the obvious value of crude oil as an non-renewable energy source, should we using this very valuable source of organic chemicals by merely burning most of it?

  • AND how long will oil reserves last?

  • AND what happens if the oil runs out?

  • Therefore isn't it in our own interest to manage the finite oil reserves remaining and conserve them?

  • AND seek other sources of energy to power our lives?

  • AND perhaps influence the course of global warming?

  • BUT the trouble is, oil is very convenient, readily available, and new reserves are still being found and the oil and gas trapped in deep layers of shale are being exploited,

  • AND it will take time to develop new technologies.

• It should be noted that liquid fuels like petrol, diesel, central heating oil etc. are east to store and distribute to wherever they are need in homes or factories and they are so readily available, that change may be necessary, but progress will be slow.

• HYDROGEN - FUEL of the FUTURE?:

  • Hydrogen gas can be used as fuel and a long-term possible alternative to fossil fuels.

  • It burns with a pale blue flame in air reacting with oxygen to be oxidised to form water.

    • hydrogen + oxygen ==> water

    • 2H_2(g) + O_2(g) ==> 2H₂O_(l) 

  • It is a non-polluting clean fuel since the only combustion product is water and so its use would not lead to all environmental problems associated with burning fossil fuels.

    • It is easily distributed in pipes like natural gas, but there are health and safety issues to do with storage and distribution since it is, like natural gas, highly flammable and explosive.

  • It would be ideal if it could be manufactured by electrolysis of water e.g. using solar voltaic-cells or some kind of but the technology is in its infancy.

  • Hydrogen can be used to power fuel cells see the "Extra Electrochemistry" page

• Other alternative renewable fuels are discussed on other pages ...

  • Nuclear power and 'green' renewable energy sources have been mentioned above

  • In the biofuels like bioethanol or biodiesel are other smaller scale possibilities.

Multiple Choice Quizzes and Worksheets

KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products (easier-foundation-level)

KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products (harder-higher-level)

KS4 Science GCSE/IGCSE m/c QUIZ on other aspects of Organic Chemistry

and 3 linked easy Oil Products gap-fill quiz worksheets

ALSO gap-fill ('word-fill') exercises originally written for ...

... AQA GCSE Science Useful products from crude oil AND Oil, Hydrocarbons & Cracking etc.

... OCR 21st C GCSE Science Worksheet gap-fill C1.1c Air pollutants etc ...

... Edexcel 360 GCSE Science Crude Oil and its Fractional distillation etc ...

... each set are interlinked, so clicking on one of the above leads to a sequence of several quizzes

Advanced Level Organic Chemistry revision notes

Revise KS4 Science GCSE/IGCSE/O level Chemistry Revision-Information Study Notes for revising for AQA GCSE Science, Edexcel GCSE Science/IGCSE Chemistry & OCR 21stC Science, OCR Gateway Science WJEC/CBAC GCSE science-chemistry CCEA/CEA GCSE science-chemistry (and courses equal to US grades 8, 9, 10)