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GREEN CHEMISTRY & CHEMISTRY OF THE AIR
Transcript of GREEN CHEMISTRY & CHEMISTRY OF THE AIR
RECYCLING - WHY?
Recovering resources by collecting, separating, and processing scrap material and using them as raw materials for manufacturing new products.
We are running out of non-renewable resources.
Helps to conserve natural resources.
Reduces pollution caused by waste.
Reduces expense of disposal and creating new products from raw materials.
Eg. Plastic bags that can be used to make batteries
Replenished by biological reproduction or natural processes.
More environmentally friendly
Leads to more sustainable use of materials.
Eg. solar energy, wind energy, hydro-electric power, biomass
Made from living things or their waste products.
Carbon neutral (an activity that has no net annual carbon emissions to the atmosphere)
Made by fermentation of carbohydrates in crops
Takes in carbon as carbon dioxide in the atmosphere
Returns carbon dioxide to the atmosphere when combusted
Appears to be carbon neutral
Energy required to plant crops and ferment it
Fertiliser and pesticides used are pollutants
Crops compete for land for other agricultural uses
Could potentially destroy natural habitats
Aileen Hidajat, Denise Au Eong, Rachael Wong, Lynn Chua
Apparent benefits offset by unexpexted side effects
UV light breaks C-Cl bonds
Free radicals formed speed up depletion of ozone layer
Alternatives are hydrofluoroalkanes (HFCs) and hydrofluorohydrocarbons (HCFCs).
Can still deplete ozone layer though effect is one-tenth of that of CFCs
A short-term replacement until new replacements are developed
Barry Trost advanced the concept of atom economy.
Ideal situation: 100% of starting material is incorporated into desired product so that no undesirable by-products are made.
GREEN CHEMICAL PRINCIPLES
Waste prevention instead of remediation
Atom economy or efficiency
Use of less hazardous and toxic chemicals
Safer products by design
Innocuous solvents and auxiliaries
Energy efficiency by design
Preferred use of renewable raw materials
Shorter syntheses (avoid derivatization)
Catalytic rather than stoichiometric reagents
Design products to undergo degradation in the environment
Analytical methodologies for pollution prevention
Inherently safer processes
Used to lower activation energy.
Can be used to reduce carbon dioxide emissions from the burning of fossil fuels
Better atom economy
WAYS TO REDUCE CARBON DIOXIDE EMISSIONS
Turn of lights and electricity when not in use.
Produce energy from renewable resources and use fuels with lower carbon content.
Use more fuel-efficient vehicles
Main Greenhouse Gases
The Kyoto Protocol
To The United Nations Framework on Climate Change
Signed in 1997
Came into force in 2005
Cut GHG emissions depending on
+ Original emissions
+ Capacity to make reductions
Absence of US
Different bonds have different masses of atoms at either end of the bonds
Resulting in different bond strengths
Bonds vibrate (bending or stretching) at different frequencies
When the gases absorb IR radiation, the amplitude of the vibration of the bonds increases
The bonds re-emit the energy they gained in the form of radiation, in all direction
Less energy is lost into space (70%)
Atmospheric gases trap heat to warm the earth's surface by 32°c
They allow most Shortwave IR radiation from the sun to reach the earth
The earth’s surface then emits Longwave IR radiation
Radiation is absorbed by the gases and re-emitted in every direction
Rate at which energy is absorbed by the Earth's surface and atmospheric gases = Rate at which energy is radiated
Equilibrium = steady temperature
Contribution of GreenHouse Gases depends on:
Ability to absorb IR radiation
Atmospheric lifetime (the time taken for concentration of an emitted gas to be returned to normal levels)
Gases are given a GWP value
Based on gas's ability to absorbed radiation and atmospheric lifetime
This is relative to CO2 (value of 1)
CFCs have a GWP of 25,000
However the concentration of the gases is very small
Global Warming Potential (GWP)
Water Vapour O-H bonds
Source : Evaporation from lakes and oceans
Carbon Dioxide C=O bonds
Source: Volcanic eruptions, respiration, decay of organic materials, burning etc
Methane C-H bonds
Source: Production of coal, natural gases and oil, Product of rotting organic waste, Release from animals as by-product of digestion (fart)
Effect of global warming:
(Antarctic) Ice sheets melting into oceans
(Artic) Ice and permafrost disappearing
(Tropic) More frequent and destructive storms & floods
(Europe) Disappearing glaciers and extreme heatwave
Positive Feedback to Catastrophe
Ice sheets melt causing the intially covered sea and land to absorb more heat
Decomposition of plant materials in previously frozen soil release more CO2 and CH4
Oceans warm up and release more CO2
Ocean level rises
Clathrates on the ocean floor might release more CH4
Solutions to GreenHouse Effect
1. Alternative Fuels
From fossil fuels to:
2. Carbon Capture and Storage (CCS)
CO2 from power stations are captured and stored safely
Immediate strategy to get rid of waste CO2
Storage as liquid CO2 in the deep oceans
Storage in geological formations (underground porous rocks) and old oil and gas fields
H2 produced can be used as fuel from natural gases
Storage by reacting CO2 with metal oxides to form metal carbonates
However, reaction rate is very slow = too much energy is required
CH4(g) + 2H2O(g) -> CO2(g) +4H2(g)
MgO(s) + CO2(g) -> MgCO3(s)
Internal Combustion Engines
Inhibits O2 uptake by
Atmospheric N2 and O2 under /\
Low-level ozone; plants and humans
Hydrocarbons that have not undergone combustion
Toxic and carcinogenic
THE OZONE LAYER
It exists about 25 km above the Earth's Surface in the
STRATOSPHERE. It contains
It's job is to absorb much of the harmful
radiation emitted by the sun.
UV cause damage to DNA in plants and animals & Skin cancer and sunburn among humans.
In the stratosphere, ozone is in
with molecular oxygen 02 atom:
03 02 +0
CHLORINE RADICALS & THE OZONE LAYER
Chlorine free radicals can attack the ozone layer until the point where a hole had developed.
Cl + 03 ClO + 02
Cl0 + 0 Cl + 02
03 + 0 202
1000 ozone molecules may be destroyed as the result of the production of one single chlorine radical.
Nitrogen Monoxide and the ozone layer
Nitrogen Monoxide (NO) is also a potential problem. It is produced during thunderstorms when lightning causes nitrogen and oxygen to combine:
N2(g) + 02(g) 2NO(g)
It may be removed by oxidation and combined with moisture to create nitric acid, which contributes to acid rain. However, a small amount attacks the stratosphere, there is not initiation step because nitrogen monoxide possesses an unpaired electron.
NO + 03 NO2 + 02
NO2 + 0 NO + 02