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1.10 To compare plastic and paper bags in terms of acquisition of raw materials, manufacturing
and processing, use and disposal, we’ll use data provided by Franklin Associates, a nationally
known consulting firm whose clients include the U.S. Environmental Protection Agency as well
as many companies and industry groups. In 1990, Franklin Associates compared plastic bags to
paper bags in terms of their energy and air/water emissions in manufacture, use, and disposal.
Table 1.9 presents the results of their study:
Table/1.9 Results of Study Comparing Plastic and Paper Bags
Life Cycle Stages
Air Emissions
(pollutants) oz/bag
Energy Required
BTU/bag
Paper
Plastic
Paper
Plastic
Materials manufacture,
product manufacture,
product use
0.0516
0.0146
905
464
Raw materials
acquisition, product
disposal
0.0510
0.0045
724
185
(a)Which bag would you choose if you were most concerned about air pollution? (Note that the
information does not tell you if these are toxic air emissions or greenhouse gas emissions) (b) If
you assume that two plastic bags equal one paper bag, does the choice change? (c) Compare the
energy required to produce each bag. Which bag takes less energy to produce?
Solution:
a) For paper: 0.0516 + 0.0510 = 0.1026 oz/bag
b) For paper: 0.0516 + 0.0510 = 0.1026 oz/bag
c) For paper = 905 + 724 = 1629 BTU/bag
1.11 You are preparing a life cycle analysis of three different electrification options for
powering your 1,200 square foot home in rural Connecticut. The options you’re considering
include: 1) just using your local grid, 2) putting in a solar installation on your roof, or 3) building
a transmission extension to join up with your neighbor’s already-built wind turbine. Write a
possible goal, scope, function, and functional unit for this LCA. Explain your reasoning.
Solution:
Student’s answers may vary.
1.12 Consider the full life cycle of each of the three electrification options (possibly beyond
whatever you’ve selected for the scope of your LCA) in Problem 1.11. Discuss which of the life
cycle stages is most impactful for each electrification type. You will need to take into account
the life cycle impacts of primary through final energy in each case. As a reminder, life cycle
stages typically include: resource extraction, manufacture, transportation, use, and end of life.
Solution:
Student responses will vary but below is an example solution.
1.13 Draw causal loop diagram for corn-based ethanol production using the following variables:
climate change, corn-based ethanol use, fertilizer demand, CO2 emissions, Fuel demand, Fossil
fuel use, and Corn demand.
Solution:
1.14 (a) Is centralized drinking water treatment and distribution more or less resilient than point
of use water treatment technologies? Why or why not? (b) Does it matter whether these water
treatment systems are implemented in the developing or developed world?
Solution:
Student responses will vary.
1.15 The design team for a building project was formed at your company last week and they
have already held two meetings. Why is it so important for you to get involved immediately in
the design process?
Solution:
1.16 Provide an example of a product either commercially available or currently under
development that uses biomimicry as the basis for its design. Explain how the design is
mimicking a product, process, or system found in nature.
Solution:
Student responses will vary.
1.17 Two reactants, benzyl alcohol and tosyl chloride, react in the presence of an auxiliary,
triethylamine, and the solvent toluene to produce the product sulfonate ester (see Table 1.10).
Calculate the E factor for the reaction. What would happen to the E factor if the solvents and
auxiliary chemicals were included in the calculation? Should these types of materials and
chemicals be included in an efficiency measure? Why or why not?
Table 1.10. Useful information needed to solve Problem 1.17
Reactant
Benzyl alcohol
10.81 g
0.10 mole
MW 108.1
g/mole
Reactant
Tosyl chloride
21.9 g
0.115 mole
MW 190.65
g/mole
Solvent
Toluene
500 g
Auxiliary
Triethylamine
15 g
MW 101 g/mole
Product
Sulfonate ester
23.6 g
0.09 mole
MW 262.29
g/mole
Solution:
Without solvent:
( )
10.81 21.9 1.4
23.6
1.4 kg waste produced / kg of product
E factor +
−= =
⇒
With solvent and auxiliary:
( )
10.81 21.9 500 15 23.2
23.6
23.2 kg waste produced / kg of product
E factor + ++
−= =
⇒
If solvents and auxiliary chemicals are included the E factor increases 20-fold. These chemicals
should be included if they are not recovered and recycled because they also contribute to the total
waste of the process. These chemicals are also important because many solvents are VOCs and
toxics.
1.18 Choose three of the principles of green engineering. For each one, (a) explain the principle
in your own words; (b) find an example (commercially available or under development), and
explain how it demonstrates the principle; and (c) describe the associated environmental,
economic, and societal benefits, identifying which ones are tangible and which ones are
intangible.
Solution:
1.19 (a) Develop five sustainability metrics or indicators for a corporation or an industrial sector
analogous to those presented for communities in Table 1-4. (b) Compare them with traditional
business metrics or indicators. (c) Describe what new information can be determined from the
new sustainability metrics or indicators.
Solution:
Student responses will vary.
1.20 A car company has developed a new car, ecoCar, that gets 100 miles per gallon (mpg), but
the cost is slightly higher than cars currently on the market. What type of incentives could the
manufacturer offer or ask Congress to implement to encourage customers to buy the new
ecoCar?
Solution:
Students’ responses will vary. Here is an example response:
1.21 Do you agree or disagree with the following statement? Why or why not? (3-5 sentences)
“Technology-forcing pollution regulations are preferable to standards- or outcome-based
regulations”.
Solution:
Student responses will vary.
1.22 You are about to buy a car that will last 7 years before you have to buy a new one, and
Congress has just passed a new tax on greenhouse gases. Assume a 5% annual interest rate.
You have two options: (a) Purchase a used car for $12,000, upgrade the catalytic converter at a
cost of $1,000, and pay a $500 annual carbon tax. This car has a salvage value of $2,000. (b)
Purchase a new car for $16,500 and pay only $100 annually in carbon tax. This car has a salvage
value of $4,500. Based on the annualized cost of these two options, which car would you buy?
Solution:
