green chemistry what is it? encourages environmentally conscious behaviour reduces and prevents...

GREEN CHEMISTRYGREEN CHEMISTRY

What is it? • encourages environmentally conscious behaviour• reduces and prevents pollution• reduces the destruction of the planet

CONTENTS• Greenhouse gases

• Greenhouse effect

• Ozone layer

• Pollutants

• Catalytic converters

CHEMISTRY OF THE AIRCHEMISTRY OF THE AIR

GREENHOUSE GASESGREENHOUSE GASES

Definition :

A greenhouse gas traps/absorbs/reflects IR (radiation) / heat re-radiating from the earth

Examples of green house gases:

CO2 , H2O, Methane

CARBON DIOXIDE CO2 contains C = O bonds

WATER VAPOUR H2O contains O - H bonds

METHANE CH4 contains C - H bonds

The ‘Greenhouse Effect’ of a given gas is dependent on its...

• atmospheric concentration

• ability to absorb infrared radiation


Different covalent bonds have different strengths due to the masses of different atoms at either end of the bond. As a result, they vibrate at different frequencies (imagine two balls on either end of a spring) . The frequency of vibration can be found by detecting when the molecules absorb electro-magnetic radiation.



Various types of vibration are possible. Bending and stretching are two examples and are found in water molecules. Each occurs at a different frequency.



Various types of vibration are possible. Bending and stretching are two examples and are found in water molecules. Each occurs at a different frequency.

Symmetric Bending Asymmetricstretching stretching



Various types of vibration are possible. Carbon dioxide also undergoes bending and stretching.

Bending in a carbon dioxide molecule


The frequencies lie in the INFRA REDINFRA RED part of the electromagnetic spectrum and can be detected using infra red spectroscopy.

An infra red spectrum of atmospheric air

It is the absorption of infra red radiation by atmospheric gases such as methane, carbon dioxide and water vapour that contributes to global warming.

H2O

H2OCO2

CO2

THE GREENHOUSE EFFECTTHE GREENHOUSE EFFECT

energy from the sun is in the ultra violet, visible and infra red regions



47% reaches the earth



radiation re-emitted from the earth is in the infra red region





70% of the radiation returns to space







greenhouse gasesabsorb the remainder







energy is returned to earth to keep it warm


SummarySummary

• energy from the sun is in the ultra violet, visible and infra red regions

• the earth is warmed up by the energy

• radiation re-emitted from the earth is in the infra red region

• 70% of the radiation (between 7000nm and 12500nm) returns to space

• greenhouse gases absorb the remainder

Gas wavelength of radiation adsorbed / nmCO2 12500 - 17000H2O 4500 - 7000 and above 17000

• they can return this energy to earth to keep it warm


ProblemsAn increase in the concentration of greenhouse gases leads to climate change / global warming.



PossibleEffects



PossibleEffects • higher temperatures

• melting ice caps

• rise in sea levels

• flooding of low-lying lands

• changes in crop patterns

• deserts move north

• change in food webs

• extinction of some species


What can chemists do to minimise climate change from global warming?

• provide scientific evidence to governments to confirm it is taking place

• monitor progress against initiatives such as the Kyoto protocol

• investigate solutions to environmental problems


What can chemists do to minimise climate change from global warming?

• provide scientific evidence to governments to confirm it is taking place

• monitor progress against initiatives such as the Kyoto protocol

• investigate solutions to environmental problems

plus

CARBON CAPTURE AND STORAGE (CCS)

• removal of waste carbon dioxide as a liquid injected deep in the oceans

• storage underground in deep geological formations

• reaction with metal oxides to form stable carbonate minerals.

MgO(g) + CO2(g) —> MgCO3(s)

or CaO(g) + CO2(g) —> CaCO3(s)

CCARBON DOXIDE ARBON DOXIDE CCAPTURE & APTURE & SSTORAGETORAGE


What is it?

• CO2 is collected from industrial processes and power generation

• it is separated and purified

• it is then transported to a suitable long-term storage site


What is it?




Storage possibilities

• gaseous storage in deep geological formations

• liquid storage in the ocean

• solid storage by reaction as stable carbonates


What is it?




Storage possibilities

• gaseous storage in deep geological formations

• liquid storage in the ocean

• solid storage by reaction as stable carbonates

How can it help?

• could reduce CO2 emissions from power stations by 80%

• could be used to store CO2 emitted from fermentation processes


CO2 in geological structures is actually a naturally occurring phenomenon

• CO2 is pumped deep underground

• it is compressed by the higher pressures

• it becomes a liquid, which is trapped between the grains of rock

• impermeable rock prevents the CO2 rising back to the surface • drilling for CO2 can be used for enhanced oil or gas recovery

Over time CO2 can react with the minerals in the rock, forming new minerals and providing increased storage security.

DEPLETION OF THE OZONE LAYERDEPLETION OF THE OZONE LAYER

Although ozone is a reactive and poisonous gas, it protects us from harmful UV radiation which would affect life on earth. UV radiation can cause skin cancer.



Ozone in the stratosphere 2O3 —> 3O2

breaks down naturally

Ozone (trioxygen) can break up O3 —> O• + O2

to give ordinary oxygen and anoxygen radical



Ozone in the stratosphere 2O3 —> 3O2

breaks down naturally

Ozone (trioxygen) can break up O3 —> O• + O2

to give ordinary oxygen and anoxygen radical

Ultra violet light can supply the energy for the process. That is why the ozone layer is important as it protects us from the harmful rays.

BUTbreakdown is easier in the presence of chlorofluorocarbons (CFC's)


REACTIONS OF CFC’SREACTIONS OF CFC’S

CFC's break down in the presence ofUV light to form chlorine radicals CCl2F2 —> Cl• + •CClF2

chlorine radicals react with ozone

chlorine radicals are regenerated


OXIDES OF NITROGEN NOxOXIDES OF NITROGEN NOx

Oxides of nitrogen, NOx, formed during thunderstorms or by aircraft break down to give NO (nitrogen monoxide) which also catalyses the breakdown of ozone.

NO(•) + O3 (•)NO2 + O2 •NO2 + O3 NO• + 2O2 ------------------------------------

Overoll : 2O3 3O2

1 NO molecule can break large number of ozone molecules as NO radical is reformed

POLLUTANTSPOLLUTANTS

POLLUTANT GASES FROM INTERNAL COMBUSTION ENGINESPOLLUTANT GASES FROM INTERNAL COMBUSTION ENGINES

Carbon monoxide CO

Origin • incomplete combustion of hydrocarbons in petrolbecause not enough oxygen was present

Effect • poisonous • combines with haemoglobin in blood • prevents oxygen being carried to cells

Process C8H18(g) + 8½O2(g) —> 8CO(g) + 9H2O(l)



Oxides of nitrogen NOx - NO, N2O and NO2

Origin • combination of atmospheric nitrogen andoxygen under high temperature

Effect • aids formation of photochemical smog which is irritating to eyes, nose, throat

• aids formation of low level ozone which affects plants and is irritating to eyes, nose and throat

Process sunlight breaks oxides NO2 —> NO + Oozone is produced O + O2 —> O3



Unburnt hydrocarbons CxHy

Origin • hydrocarbons that have not undergone combustion

Effect • toxic and carcinogenic (cause cancer)


POLLUTANT FORMATIONPOLLUTANT FORMATION

Nitrogen combines with oxygenN2(g) + O2(g) —> 2NO(g)

Nitrogen monoxide is oxidised2NO(g) + O2(g) —> 2NO2(g)

Incomplete hydrocarbon combustionC8H18(g) + 8½O2(g) —> 8CO(g) + 9H2O(l)


POLLUTANT REMOVALPOLLUTANT REMOVAL

Oxidation of carbon monoxide2CO(g) + O2(g) —> 2CO2(g)

Removal of NO and CO2CO(g) + 2NO(g) —> N2(g) + 2CO2(g)

Aiding complete hydrocarbon combustionC8H18(g) + 12½O2(g) —> 8CO2(g) + 9H2O(l)

CATALYTIC CONVERTERSCATALYTIC CONVERTERS

REMOVAL OF NOx and COREMOVAL OF NOx and CO

• CO is converted to CO2

• NOx are converted to N2

2NO(g) + 2CO(g) —> N2(g) + 2CO2(g)





2NO(g) + 2CO(g) —> N2(g) + 2CO2(g)

• Unburnt hydrocarbons converted to CO2 and H2O

C8H18(g) + 12½O2(g) —> 8CO2(g) + 9H2O(l)





2NO(g) + 2CO(g) —> N2(g) + 2CO2(g)

• Unburnt hydrocarbons converted to CO2 and H2O

C8H18(g) + 12½O2(g) —> 8CO2(g) + 9H2O(l)

• catalysts are rare metals - RHODIUM, PALLADIUM

• metals are finely divided for a greater surface area - this provides more active sites

GREEN CHEMISTRYGREEN CHEMISTRY

What is it? • encourages environmentally conscious behaviour• reduces and prevents pollution• reduces the destruction of the planet

Basics • better to prevent waste than to treat it afterwards

• aim for maximum atom economy

• use processes which require fewer chemicals

• don’t make products that are toxic to human health

• don’t make products that are toxic to the environment

• reduce the energy requirements of processes

• use alternative energy resources

• use renewable raw materials, not finite resources

• use catalysts where possible

• waste products should be designed to be biodegradable

• reduce the risk of explosions and fires

RECYCLINGRECYCLING

Definition “Recovering resources by collecting, separating, andprocessing scrap materials and using them as rawmaterials for manufacturing new products.”

RECYCLINGRECYCLING

Definition “Recovering resources by collecting, separating, andprocessing scrap materials and using them as rawmaterials for manufacturing new products.”

Why do it? • world resources are running out and are non-renewable

• we need to reduce the waste of valuable resources

• reduces the expense of disposal

• reduces expense of making things from raw materials

• avoids environmental problems posed by waste

- landfill sites- greenhouse gases (mainly methane)- destroying habitats- de-forestation leading to climate change and the destruction of ecosystems

RENEWABLE RESOURCES AND ENERGYRENEWABLE RESOURCES AND ENERGY


Renewableresources • can be replenished by natural processes

• their rate of replenishment is equal or greater than the rate of consumption

• often do not contribute to global warming

• often far more environmentally friendly

• lead to more sustainable use of materials; resources can be used indefinitely


Renewableresources • can be replenished by natural processes

• their rate of replenishment is equal or greater than the rate of consumption

• often do not contribute to global warming

• often far more environmentally friendly

• lead to more sustainable use of materials; resources can be used indefinitely

Renewableenergy • plant-based substances such as wood

• solar energy• tidal energy• biomass• hydro-electric power (HEP)• wind power

GREEN CHEMISTRY – EXAMPLESGREEN CHEMISTRY – EXAMPLES

CFC’sCFC’sApparent benefits were offset by unexpected side effects.



GOOD • created in 1928 as a non-toxic, non-flammable refrigerant• also used as solvents and in air conditioners• low reactivity and volatility




BAD • UV light in the upper atmosphere easily breaks the C-Cl bonds• free radicals formed speeded up the depletion of the ozone layer




BAD • UV light in the upper atmosphere easily breaks the C-Cl bonds• free radicals formed speeded up the depletion of the ozone layer

CFC's break down in the presence ofUV light to form chlorine radicals CCl2F2 —> Cl• + •CClF2

chlorine radicals react with ozone O3 + Cl• —> ClO• + O2

chlorine radicals are regenerated ClO• + O —> O2 + Cl•

Overall, chlorine radicals are not used up so a small amount of CFC's candestroy thousands of ozone molecules before the termination stage.


BIOFUELSBIOFUELS• fuels made from a living things or the waste produced by them• renewable and potentially carbon neutral.



Carbon neutral refers to “an activity that has no net annual carbon (greenhouse gas) emissions to the atmosphere”. Ethanol is a biofuel.




ETHANOLETHANOL

GOOD




ETHANOLETHANOL

GOOD • bio-ethanol is made from crops (corn and sugar cane)• takes in carbon as carbon dioxide in the atmosphere• when burnt, it returns CO2 to the atmosphere• appears to be carbon neutral




ETHANOLETHANOL


BAD




ETHANOLETHANOL


BAD • energy is required to - plant and harvest- convert plants to ethanol

• fertiliser and pesticides used are pollutants• crops compete for land with… crops / animals / forests• could destroy natural habitats and reduce biodiversity


PLASTICS & POLYMERSPLASTICS & POLYMERSPlastics have made life much easier.



GOOD



GOOD • many are chemically inert• non-toxic• waterproof• easy to mould• non-biodegradable• lightweight




BAD




BAD • made from crude oil which is a finite resource• non-biodegradable so take hundreds of years to decompose• can form toxic products during incineration• a lot of energy is used in their formation• disposal in landfill sites is - a waste of resources

- environmentally unsound- takes up valuable space


CATALYSTSCATALYSTS• can be used to lower the energy required for a reaction to take place• can reduce the CO2 emissions from burning of fossil fuels• can give a better atom economy

SOME MORE THINGS YOU SHOULD KNOW

Anthropogenic: results from human activities, e.g. burning fossil fuels and deforestation. These increase levels of CO2, methane and other gases over relatively short timescales. Natural climate change: natural processes such as dissolving of CO2 in sea water or formation of carbonates in rocks over hundreds of years. Volcanic eruptions can also cause climate change.

Carbon neutral : a process that gives out as much CO2 as it takes in

The fuel petrol is definitely not carbon neutral - releases CO2 into atmosphere which was trapped in the earth millions of years ago.

Hydrogen gas can be carbon neutral .

Carbon footprint : a measure of the impact on environment from how much greenhouse gas is produced. (Measured in CO2)

Catalysts : enable a reaction to go under lower temperatures and pressures to save energy. Catalysts need to be cheap, very active and produce no by-products

Crude oil vs Bio fuelsBiofuels are renewable but cude oil is not renewable

Consequences of global warmingSea level rize / floodingMelting polar ice caps Changing sea currents Changing weather patterns

Whether hydrogen or ammonia can currently be consideredto be long term replacements for fossil fuels??No because hydrogen is obtainedfrom fossil fuels (and ammonia from hydrogen)ORYes because hydrogen can beobtained by electrolysis of water

Using high pressure when recycling ??

(High cost of) energy needed (togenerate the pressure) (High cost of) construction/maintenance of the equipment(High cost of) the equipmentrequired to withstand / contain thehigh pressure

fules should have these qualities ??

Less Cost / Ease of Production Easy to StoreEasy to TransportRenewableLess environmental effect

•Carbon monoxide from incomplete combustion of fuels toxic to breathe

•Sulfur dioxide and nitrogen oxide (from industrial and vehicular exhaust causes of acid rain

•Chlorofluorocarbon (CFC) • used as aerosol / propellant / spray cans• refrigerant•OR (degreasing) solvent•OR fire retardant causes destruction of the ozone layer)

Some Green house gases : * Water vapour (H2O)

* Carbon dioxide (CO2) (fossil fuel burning and greenhouse gas),

* Methane (CH4) (cow farming, landfill emissions and natural sources, greenhouse gas)

* Nitrous oxide (N2O)

* Ozone (which is bad at low altitudes and does not survive to replenish the high altitude ozone layer which protects us from UV light)

SOME MORE THINGS YOU SHOULD DISCUSSAFTER THE ENED OF THE LESSON

a ) demonstrate an understanding that the processes in the chemicalindustry are being reinvented to make them more sustainable(‘greener’) by:

i ) changing to renewable resources

ii ) finding alternatives to very hazardous chemicals

iii ) discovering catalysts for reactions with higher atom economies, eg the development of methods used to produce ethanoic acid based on catalysts of cobalt, rhodium and iridium

iv ) making more efficient use of energy, eg the use of microwave energy to heat reactions in the pharmaceutical industry

v ) reducing waste and preventing pollution of the environment

b) discuss the relative effects of different greenhouse gases asabsorbers of IR and hence on global warming

c ) discuss the difference between anthropogenic and naturalclimate change over hundreds of thousands of years

d ) demonstrate understanding of the terms ‘carbon neutrality’ and‘carbon footprint’

e ) apply the concept of carbon neutrality to different fuels, such aspetrol, bio-ethanol and hydrogen

f ) discuss and explain, including the mechanisms for the reactions,the science community’s reasons for recommending that CFCsare no longer used due to their damaging effect on the ozonelayer.

green chemistry what is it? encourages environmentally conscious behaviour reduces and prevents...

Documents

different frequency

different frequencies

different strengths

masses of different

frequency of vibration

electromagnetic radiation

red regions47

red region47