Section 5.7: Green Chemistry in Industry
Mini Investigation: Shrinking Styrofoam (Teacher Demonstration), page 223
A. The bubbles were air or other gases such as carbon dioxide that was injected into the
Styrofoam cup when it was manufactured.
B. Styrofoam is so much larger in volume than the polystyrene used to manufacture it. As a
result, the cost of curb-side pick up and transport of Styrofoam to a recycling depot is high. This
makes it difficult to make Styrofoam economically feasible.
Section 5.7 Questions, page 227
1. Some of the strategies a chemical manufacturer may use to improve the efficiency of a
chemical process include redesigning the process so that it uses catalysts rather than chemicals to
convert starting materials into finished products, and improving the energy efficiency of the
process.
2. Catalysts can be reused. Some catalysts can make a manufacturing process greener by
speeding up a slower but safer chemical reaction. Catalysts can also substitute the hazardous
chemical reaction in the original manufacturing process.
3. Preventing pollution by using better pollution control equipment is usually less expensive for a
manufacturer than cleaning up a contaminated ecosystem. In the long run, use of this equipment
will help the manufacturer become more profitable.
4. A reduction in energy consumption means that the manufacturer uses either less fossil fuels or
electricity. Less combustion of fossil fuels results in a direct reduction in greenhouse gas
emissions. Some fossil fuels are also used to generate electricity. Therefore, any reduction in the
use of electricity also reduces greenhouse gas emissions.
5. (a) A manufacturing process that is “benign by design” has been specifically designed so that
its impact on the environment is minimal. This can be done by designing the process so that the
chemicals used are safe and the products can be safely recycled. The process can also be
designed so that it uses minimal amounts of energy.
(b) Answers may vary. Sample answer: Cleaning processes in the home can be made “benign by
design” by using less toxic cleaners and reusable rags rather than disposable paper towels.
6. (a) The contact process is an example of a closed-loop manufacturing process because other
than the starting material and the finished product, no materials leave or are added to the system.
(b) Two advantages of a closed-loop manufacturing process are that the maximum quantity of
starting materials can react to create the product and that the loss of materials to the environment
is kept to a minimum.
7. Two advantages of using food crops to produce raw materials for industry are that the raw
materials are renewable and that there is a greater likelihood that the final production is
biodegradable. One disadvantage is that the increased use of food crops to produce raw materials
may either increase the price of food or decrease its availability.
8. Recycling the water used by pulp mills prevents polluted water from entering the environment
and saves fresh water from becoming polluted. Recycling the water also means that the water
does not have to be treated to the same degree as if it were to be released to the environment.
This is not only better for the environment but more economical for the manufacturer.
Copyright © 2011 Nelson Education Ltd.
Chapter 5: Chemical Processes
5.7-1
9. The pulp and paper industry applies the five principles of green chemistry as seen in the
following examples.
• Many paper mills now use specially planted, fast-growing trees instead of harvested trees from
forests to supply the fibre needed as the starting material.
• Paper manufacturers use less toxic chemicals, such as hydrogen peroxide, instead of the more
toxic chlorine bleach in the bleaching process. This makes the process safer and more benign to
the environment.
• Catalysts that enable pulp to be bleached in a shorter period of time are used to speed up the
bleaching process, making it more time efficient. Catalysts can always be reused.
• Paper manufacturers have been looking for ways to save energy. One way is to use updated
equipment that reduces energy costs and to use alternative energy sources such as wood.
• Pulp and paper mills have made efforts to reduce wastes and control emissions. The use of a
closed-loop system helps prevent materials from escaping into the environment while
maximizing the use of reactant chemicals. Emission gases that are pollutants, such as sulfur
dioxide, are collected and treated using scrubbing technology.
10. Answers may vary. Sample answer: The odour around a pulp mill is caused by a group of
chemicals that contain reduced sulfides. These include dimethyl sulfide, dimethyl disulfide,
hydrogen sulfide, and methyl mercaptan. If the pollution control equipment at the mill is
operating efficiently, over 90 % of these gases will be collected and treated on site by passing
them through scrubbers or by burning them.
Copyright © 2011 Nelson Education Ltd.
Chapter 5: Chemical Processes
5.7-2