Transcript CHAPTER 4

CHEMISTRY & SOCIETY
RECYCLING
Dr. Victor Vilchiz
Spring 2011
The price of technology
• Recall from the first 2 weeks of the course
we discussed the costs of a comfortable life.
– Lets think about cell phones…
– How many have cell phones?
– Most likely your cell phone is powered by a LiCd battery. How long will it last?
• 2 Yrs?
• Then what?
Batteries and Waste
• At least this one you can recharge but eventually it
will join the Energizer, Ever-Ready, Duracell….
– IN THE TRASH
– Cd is not an environmentally friendly metal
• How much waste do you think you produce in one
day?
– Wrappers, left-overs, smog, plastic bags, light bulbs,
batteries, paper, dirty water…
• 4 lbs a day per person  1 billion lbs of trash A DAY
What happens to trash?
• It does not disappear once it is picked up.
• Depending on where you live it may:
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Buried
Burned
Thrown in the ocean (illegal now)
Sending it into space has been considered
RECYCLE
Type of Systems
• There are three different types of systems.
– Open System: one where both mass and energy
are free go in and out.
– Closed System: one where energy is allowed in
and out but mass is not.
– Isolated System: one where neither mass nor
energy can go in or out.
Nature’s Recycling
• Mother Nature has organized the biggest
recycling programs.
– It recycles water, carbon matter, and oxygen
(the 3 most important ones).
– We humans have impacted these recycling
processes as we will see later in this lecture.
The Earth
• In our planet we have energy coming in
from the sun and energy going out. There is
usually no mass going out (unless we send
the space shuttle to space). And unless we
have a meteor coming into our atmosphere
there is no mass coming in.
– The planet earth is a Closed System.
Energy from the sun
• What does the energy from the sun do for
us?
– Ever notice when you feel like you are coming
down with something during the day you feel
ok but at night you feel sick again?
• Like plants you are sucking up energy from the sun
– Provides energy for plants
Carbon Cycle
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Energy from the sun is absorbed by plants.
Fruit or vegetables grow.
We eat fruit/vegetable.
We produce waste.
Goes to landfill.
Organic matter goes into the soil.
Organic Matter is used by plants again.
Water Cycle
• The sun provides the energy required to
evaporate water form large bodies of water
(seas, lakes, and streams).
• Evaporated water forms clouds.
• It rains
• Water go into reservoirs or underground
• Perspiration of the soil
• Evaporation…
Oxygen and CO2 Cycles
• Along with the CO2 cycle they are the basis
of life on earth.
• During respiration Oxygen is consumed and
CO2 is produced
• During Photosynthesis CO2 is consumed
and Oxygen is produced.
Chemical Reactions
• Both the Oxygen and Carbon Cycle are
intertwined through 2 chemical reactions.
– Respiration
• Inhale = Oxygen
• Exhale= Carbon Dioxide
– Photosynthesis
• Input = Carbon Dioxide
• Output = Oxygen
Chemical Reactions
• There are two misconceptions about
chemical reactions:
– A chemical reaction represents what actually
happens.
• Writing chemical reactions is like looking at the
ingredients for a meal and the final product.
• They do not provide any idea as to the intermediate
steps.
Chemical Reaction
• There are two misconceptions about
chemical reactions:
– Chemical reactions go to completion
• Unlike cooking where everything that goes into the
pot is cooked, in a chemical reaction not all the
starting materials are used by the time we are done.
• Even when you start with the exact amount of what
you need, there will be left-overs.
Chemical Reactions
• Misconception #1
– If you want to know everything that happens
• You need to know the Mechanism
– Series of Elementary (single events) Reactions
• Misconception #2
– Want to know how much of a reaction occcurs?
• You need to study the Thermodynamics of the Rxn
– Tells you about the equilibrium of the reaction
Human Intervention
• We have interfere with many of nature’s
processes.
– We have cut down trees, this reduces the
amount of O2 produce and the amount of CO2
removed.
– We continue to use many non-replenishable
resources.
– It is time we try to slow down our damage and
if possible reverse it.
Recycling
• Just because we recycle it does not mean we
are mending what we have damaged.
• But it certainly mitigates the damage we do
everyday.
• We can recycle just about everything… lets
concentrated on Aluminum.
Aluminum cans
• Cans are made of Al, Mn, Fe, Mg, Si, Cu.
• The aluminum used in new cans comes
from Bauxite, Al2O3.
• Aluminum is the third most abundant
element on the earth’s crust.
• The two most abundant are Si, and O in the
form or SiO2, SAND.
Aluminum Ores
Ruby
Al2O3 +Cr
Bauxite & a Penny
Al(OH)3
Bauxite Shell
Rock Core
Bauxite
• It is so abundant that we probably can go on
using new cans from the point of view
running out of Al.
• But is the abundance of Bauxite the only
important factor?
– NO
– How much energy goes into making a new can?
Making a can
• The bauxite is mixed with other chemicals
and must be heated to 1000C.
– Is it cheaper, energy wise to recycle the can we
just used?
– To make 1 metric ton (1000kg) of aluminum
from bauxite we used energy equivalent to
120,000 kg of coal.
Making a can
– That is about ¼ of a million pounds of coal
– We use about 110 billion cans a year
– We recycle about 60 million cans a year
(~60%)
– We only used 10% of the energy if we recycle.
– While we may not run out of bauxite to make
new cans we may run out of coal to process the
bauxite.
Making a can
• How is a soda can made anyways?
– It is mostly aluminum but there are other
materials needed as well.
• The can is made out of an alloy of Mg, Mn, Fe, Si,
and Cu. The lid which is a bit harder contains
slightly more Mg.
• Now, I am sure you do not want your soda tasking
like aluminum so a coating of plastic is applied to
the inside.
• We must know what kind of soda we are about to
buy so some paint is used in the outside.
Recycling the can
• Before melting the can it must be dry. If
liquid water comes into contact with molten
Aluminum an explosion can occur.
• The paint must be removed in a furnace.
• The can is melted; due to the higher content
of Mg on the can’s lid the resulting molten
alloy is not suitable for new cans.
Recycling the can
• On the same token because the can contains
less Mg than the lid the molten alloy is not
suitable for lids.
– Add Mg to make it suitable for lids or
– Add Aluminum to make it suitable for cans.
• Alloy: A physical homogeneous blend of
metals with different properties than the
initial components.
Recycling Metals
• It is possible to recycle metals even when
they are “lost” in solution.
– Silver, Gold, etc (precious metals) are
recovered making use of the reactivity metal
series through RedOx reactions.
• Reactivity Series: a list that ranks how
“reactive metals are in solution”
Reactivity Series
• A metal that is more reactive than another
will “push” the less reactive metal out of
solution.
– For example, Copper is more reactive than
silver; therefore, a copper wire put into a
solution containing silver ions will push the
silver out.
Cu(s) + 2Ag+(aq)  Cu2+(aq) + 2Ag(s)
RedOx Reactions
• RedOx reactions are arguably the most
important type of reactions there are.
• They are responsible for transforming
breathable oxygen to usable oxygen.
• They are responsible for most cellular
reactions.
• They are responsible for the ATP-ADP
cycle.
RedOx Reactions
• A RedOx reaction is broken down into two
parts
• REDuction Reaction: A reaction in which
electrons are gained.
– Ag+(aq) + e-  Ag(s)
• OXidation Reaction: A reaction in which
electrons are lost.
– Cu(s)  Cu2+(aq) + 2e-
RedOx reactions
• We cannot have one without the other since
the electrons gained in the reduction
reaction must had to have come from
somewhere (oxidation reaction).
Plastics
• Plastics is just the common name for a
group of chemicals.
• The general common name of plastics is
POLYMERS.
• A polymer is a long chain of MONOMER
units.
• They are separated (recycling) by a number.
Plastics/Polymers
• Polymers are made mainly through two
different processes.
– Condensation Polymerization
• Produces Water and usually small(er) chains
• Produces “pure” polymers (no impurities)
– Radical Polymerization
• Requires Initiator and Quencher (impurities)
• Can create large(r) chains
• Can create “living” polymers
Plastic Recycling
• The number inside the
triangle determines which
type of plastic you have. Not
all plastics are recycled
everywhere. Some processes
are more expensive than
others.
Uses of Recycled Plastic
• Used to make:
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Rugs
Sleeping Bag Fillings
Clothing (jackets)
Packing (Styrofoam beans)
Bottles
Recycling Plastic
• What the numbers mean…
– #1 PETE (PolyEthylene TEraphthalate)
• Soda bottles, food trays… they become rug carpets
– #2 HDPE (High Density PolyEthylene)
• Milk & Water Jugs… they become new containers
or “lumber”
– #3 Vinyl but mainly PVC (PolyVinyl Chloride)
• Plumbing Pipe… it can be recycled but not enough
discarded to make it worth it to do so.
Recycling Plastic
• What the numbers mean…
– #4 LDPE (Low Density PolyEthylene)
• Plastic Bags… become new bags or “lumber” BUT most cities
won’t collect them since they are too light… you can take them
to businesses that collect them for sell to recycling centers.
– #5 PP (PolyPropylene)
• “though” containers like yougurt, butter tubs… Not enough
produced to make it worth recycling.
– #6 PS (Polystyrene)
• It cannot be recycled for savings… but broken down
(physically) for packaging.
– #7 Other
• Not recycled as it is a blend of many polymers.
State of Recycling
• Paper of Plastic?
– This decision should depend on many things
not only in if you are environmentally
conscious.
– The biggest contributor to landfills is paper.
– Not all cities recycle plastic (Chesterfield
county does not recycle plastic bags)
State of Recycling
• The aluminum recycling industry is thriving
and will continue to do so until other
recycling processes catch on with the
public.
• Plastic Recycling is a relatively new
industry and many cities still need to
develop programs to recycle a larger
number of plastic types.
Green Chemistry
• Green Chemistry is a philosophy that is in
tune with environmental efforts to reduce
the amount of waste we produce.
• It is based in an “Atom Economy”
– We must used as many atoms from the initial
chemicals as possible.
• It is based on Six guidelines
Green Chemistry Guidelines
• Prevention is better than cleanup
– And it is also cheaper.
• Maximizing the atom economy.
– Use as much as possible and you may profit
more.
• Use safer chemicals in the production
process.
– Less likely to create a problem.
Green Chemistry Guidelines
• Use non hazardous solvents
– If an accident happens it does not harm the
environment
• Reduce use of energy
– Pay attention at secondary resources
• Biodegradable Products
– If a product will cease to serve its purpose
make sure it will be absorb by the earth quickly.