Ozone

1
Biomass as renewable energy
Carbon cycling in the biosphere CO2 H2O hv ?
CH2O O2 CH2O O2 ? CO2 H2O Biomass is
burned, but no net CO2 is introduced into the
atmosphere.
Energy density is lower than fossil fuel

• Sources
• agricultural waste
• explicit energy crops

2
Production of ethanol from biomass
Ethanol production is based on (anaerobic)
fermentation of sugars Ethanol is mixed with
gasoline (improve octane) or used as E85 Very
successful in Brazil (sugar cane)

• Ethanol fermentation starts from pyruvate CO2
  production
• makes the resulting mixture carbonated (beer),
  or causes
• dough to rise (bakers yeast).
• Pyruvate is the product of a 10-step enzyme
  pathway that breaks down glucose
• (glycolysis)

3
Production of ethanol from biomass

• Crops are harvested and processed to yield
  glucose or other sugars that
• can be fermented to ethanol.
• Processing to glucose from non-cellulosic
  material is much easier (amylase)
• Cellulase enzymes are found only in certain fungi
  and bacteria and are
• much harder to adapt in industrial processes

4

• Efficiency of energy conversion from corn
• ethanol is extremely poor. Why?
• Fermentation plant requires fossil fuel input
• Corn harvesting and ethanol transport
• Fertilizers! Ultimately depend on CH4
• Corn ethanol interest in the US is driven
• by politics, not science

5
Processing from cellulosic ethanol is
difficult Cellulose is covered in hemicellulose
requiring acid treatment Hemicellulose lignin
5-carbon sugar polymer Once uncovered
cellulose has to be processed with cellulases
? glucose Xylose requires separate fermentation
from glucose
This processing currently limits noncellulosic
ethanol production to pilot-scale Dedication of
land to biomass production also is limiting
lignin
xylose
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7
Hydrogen Economy
16 May 1937 Lakehurst, NJ Hindenberg H2
explosion
POSSIBLE H2 INFRASTRUCTURES
H2 fuel cells in vehicles
8
Electrochemistry
GALVANIC CELL
0.76 V
Standard H2 reference electrode
Oxidation (anode) Zn ? Zn2 2e- Reduction
(cathode) 2H 2e- ? H2 Overall reaction
2H(aq) Zn(s) ? Zn2(aq) H2(g)
Oxidation and reduction reactions
separated Favorable thermodynamic flow of e- from
Zn to H is directed through external wire Porous
bridge allows ion flow to keep the net charge
zero on each side
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• Electrochemistry Principles
• Write half reactions, balance,
• and determine favorable redox
• direction
• At 1M concentrations DG -nFE
• n e- transferred
• F Faraday const 96485 C/mol e-
• (1 volt 1 J/C)
• If nonideal Nernst equation
• E E - RT/nF ln (Q)
• Q reaction quotient

VO2 2H e- ? VO H2O E 1.00 V Zn2
2e- ? Zn E -0.76 V
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GALVANIC CELL ELECTROLYTIC CELL
Electrolysis forcing a current through the cell
to produce a chemical change that is
otherwise unfavorable Electrolysis of
water Anode 2 H2O ? O2 4H 4e- -E
-1.23 V Cathode 4 H2O 4 e- ? 2 H2 4 OH- E
-0.83 V Net 2 H2O ? 2 H2 O2 E -2.06
V Hydrogen production -1.23 V in pure
water H OH- 10-7 M
12
Hydrogen Fuel Cell --a galvanic cell with
continuous reactant supply Anode 2 H2 ? 4 H
4 e- Cathode 4 e- O2 4 H ? 2 H2O Net 2 H2
(g) O2 (g) ? 2 H2O (l) E 1.23 V
13
H2 fuel cell

• Fuel cell designs differ by
• type of electrolyte
• nature of the electrodes
• Issues
• ions move toward cathode to
• counterbalance e- flow ?
• electrolyte resistance use high-
• conductance electrolyte
• reactants and products approaching
• and leaving the electrodes
• (mass transfer resistance) ?
• increase surface area of electrodes
• activation energy of the reactions
• (use catalysts)

14
H2 fuel cell
PEM (proton exchange membrane) appears to be
best design for mobile transport
-fluorocarbon polymer w/attached (-)
sulfonate groups allow fast proton but not
electron passage -about 60 energy efficiency
has been obtained -operates at 60 - 100C -low
temperature requires platinum catalysts
(catalyst poisoning by CO if H2 comes from
methane)
ANODE
CATHODE
Pt reactions H2 2 Pt ? 2 Pt-H 2 Pt-H ? 2
Pt 2 H 2 e-
15
Batteries
Set of galvanic cells connected in series Lead
storage battery - still used Anode Pb HSO4- ?
PbSO4 H 2e- Cathode PbO2 HSO4- 3 H 2
e- ? PbSO4 2 H2O Overall Pb(s) PbO2(s)
2H(aq) 2 HSO4-(aq) ? 2PbSO4(s) 2H2O(l)
Overall voltage 12 V (6 2V cells in
series) Recharging by forcing current in
opposite direction (electrolysis)
16

• Hydrogen use in transportation (alternative cars)
• All-electric cars all power from an on-board
  battery
• Lead-acid batteries
• Nickel-cadmium
• Nickel-metal hydride
• Technology has not developed high cost, low
  driving range
• Hybrid combustion/electric power vehicles (eg,
  Toyota Prius)
• Continuous battery recharging while gas engine
  operates
• Both gas engine and electric motor provide power
• Parallel direct electric and internal combustion
  drive trains
• High fuel efficiency
• Nickel-metal hydride battery
• Technology is available now

17

• Hydrogen use in transportation (alternative cars)
• Hydrogen internal combustion vehicles
• Internal combustion engine runs on hydrogen
• Need for fueling stations and other H2
  infrastructure
• ? Might spur construction of an infrastructure
  fuel cell vehicles will need
• Less efficient than fuel cells, but could be set
  up with electric hybrids
• Internal combustion with air means that nitric
  oxide is still generated
• Engineering issues very flammable (pre-ignition
  knocking) low density
• How to store the H2 onboard?
• Hydrogen fuel cell vehicles
• How to store the H2 onboard?
• Large, high-pressure cylinders
• Supercooled liquid hydrogen (T lt -253 C)
• Metal hydrides

18
Hydrogen Delivery

• Hydrogen could either be
• produced at large power plants and transported to
  users,
• produced locally at smaller stations, eliminating
  the need for long-distance transport.
• New pipelines would need to be built to transport
  hydrogen long distances
• current liquid pipelines cannot be used to
  transport hydrogen
• very few hydrogen pipelines are in operation in
  the U.S. Building these pipeline systems would be
  expensive.

19
Hydrogen Storage

• Cost-effective methods of storing hydrogen are a
  challenge.
• Hydrogen contains more energy per weight than any
  other energy carrier, it contains much less
  energy by volume
• Difficult to store a large amount of hydrogen in
  a small space, like the gas tank of your car.
• Innovative ways to store hydrogen, such as
• High-pressure storage tanks. Hydrogen gas can be
  compressed and stored in storage tanks at high
  pressure, but these tanks must be very strong.
• Liquid hydrogen. Hydrogen can be stored as a
  liquid. In this form, more hydrogen can be stored
  per volume, but it must be kept at very cold
  temperature (about -253 C).
• Metal hydrides. Hydrogen combines chemically with
  some metals, which can store it more efficiently
  than high-pressure storage tanks.
• Carbon nanotubes. Carbon nanotubes are
  microscopic tubes of carbon, two nanometers
  (billionths of a meter) across, which store
  hydrogen in their microscopic pores.

20
Hydrogen Safety

• Hydrogen, has a high energy content and must be
  handled properly to be safe
• Hydrogen is odorless, flammable (like gasoline),
  and burns with an invisible flame that can make
  it difficult to detect or extinguish.
• Hydrogen has been used safely for decades by
  industry in a wide variety of applications and
  conditions, and it can be used safely by
  consumers with proper handling and engineering
  controls.
• Hydrogen has several properties that make it
  safer than other fuels used today.
• non-toxic (unlike gasoline)
• it dissipates rapidly when released, such as from
  a leak
• As with any other fuel, engineers will have to
  design products that use hydrogen safely
• Users will have to become familiar with hydrogen
  and its properties so they can use it without
  incident.