Lecture Topic 6: Safety and Waste Issues
Ref: “Introduction to Green Chemistry”, by A. S. Matlock; “Industrial Organic
Chemistry”, by K. Weissermel and H.-J. Arpe; “Inorganic Chemistry: An
Industrial and Environmental Perspective”, by T. W. Swaddle.
Premise:
The chemical industry must consider the health
and safety of the workers, community and
environment.
Goal:
Students should be able to
1) discuss the concept of “toxicity” and give
examples of known toxins
2) give a brief explanation of why accidents
occur, using examples
3) define “green chemistry”, with examples
4) discuss waste issues and give examples of
current recycling techniques
Toxicity of Chemicals in the
Environment
• The public’s perception of toxicity and risk often differs from that
found by scientific testing.
• The idea that “natural” is better than “chemical” is overly
simplistic.
• Many chemicals found in nature are extremely potent biologically.
COOH
O
HO
O
N CH
3
H
O
O
OH
O
O
HN H
N
HN
O
OH
O
HO
O
OCH 3
Aflatoxin B1
HN
Lysergic Acid
OH
Tetrodotoxin
OH
Safrole
Toxicity of Chemicals in the
Environment
The U.S. Congress added the Delaney clause to the Food, Drug and
Cosmetic Act in 1958.
“No additive shall be deemed to be safe if it is found to
induce cancer when ingested by man or animal, or if it is found,
after tests which are appropriate for the evaluation of the safety of
food additives, to induce cancer in man or animal.”
NH 2
O
NH 2
N
NH
S
O O
Saccharin
(o-benzoic sulfimide)
H3C
N
N
N
N CH
3
N CH
3
N
typical heterocyclic amine mutaagens occuring in
fried beef and broiled fish
Toxicity of Chemicals in the
Environment
• Chemical safety is an international challenge.
• Complete health effects data are available for only about 7% of the
chemicals produced in > 106 lb annually.
• It is not always easy to determine the relative toxicity of chemicals.
• Toxicity can vary with age, gender and species of the animal.
• Toxicity can also vary with the manner of application.
Toxicity of Chemicals in the
Environment
•LD50 data on chemicals generally does not determine the longterm effects caused by bioaccumulation.
• Populations of animals can also be decimated by chemical effects
that do not kill the animals.
e.g.,
Cl
Cl
Cl
Cl
Cl
DDT
dichlorodiphenyltrichloroethane
[1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane]
• causes eggshell thinning and
nesting failure in peregrine
falcons, bald eagles, osprey
and brown pelicans.
Safety in the Workplace
Toxic chemicals
e.g., HCN
average fatal dose for a human: 50-60 mg !!
Explosives
e.g., ammonium nitrate … used as “34-0-0” fertilizer
NH4NO3
gentle heat
to 170 C
N2O + 2 H2O
Flammable Materials
e.g., carbon disulfide CS2
NH 4NO 3
N2 + 2 H2O + 1/2O2
>250 C
or shock
b.p. 46°C
flashpoint -33.9°C
autoignition 100°C
Non-flammable gasses
e.g., nitrogen gas or liquid nitrogen
Accidents with Chemicals
Chemistry is a relatively safe occupation.
• In 1996, in the U.S., the nonfatal injury rate for chemical
manufacturing was 4.8% for full-time workers….compared to 10.6%
for all manufacturing.
• There were 34 deaths in the chemical industry, about 5% of those for
all manufacturing.
However…
• About 60, 000 chemical accidents are reported annually in the U.S.
• In the past decade, these accidents caused an average of 226 deaths
and 2000 injuries.
Bhopal, India. Dec.3, 1984
• 40 tons of methyl isocyanate escaped from a pesticide plant into a
densely populated area.
• 3500 deaths and 150,000 injuries
• At the time of the accident, a refrigeration system, a temperature
indicator, and a flare tower were not functioning.
• According to reviews, the accident …
“… was the ultimate outcome of faulty technological design, years of poor
management of an unprofitable and highly dangerous facility, years of ignoring an
outrageously bad safety record on the part of both the parent company and the Indian
government, inadequate education and training of the work force, uncontrolled
growth of an industrial population center, a nonexistent emergency response system
and the community’s ignorance about the dangers in its midst.”
More Accidents with Chemicals
• In 1994, failure of a storage tank at Occidental Chemical in
Delaware allowed as much as 500 lb of Cl2 to escape.
• In 1998, an explosion at a Sierra Chemical explosives plant in
Nevada killed 4 and injured 3. The explosion occurred when an
operator turned on a mixing pot motor causing detonation of
explosives that had solidified on standing overnight.
• An explosion and fire at Shell Chemical’s Belpre, Ohio,
thermoplastic elastomer plant revealed that…
“… roughly 7 times the normal amount of butadiene had inadvertently been
added to the reactor. Alarms indicated that the reactor had been overcharged,
but interlocks were manually overridden to initiate the transfer of raw
materials into the reactor vessel, contrary to established procedures.”
Accident Prevention
• Engineering steps may be taken to produce a fail-safe system:
e.g., additional alarms, interlocks, automatic shut-offs etc.
• Written safe operation procedures.
• Adequate formal training (NOT informal “on-the-job” training!)
• Highly qualified personnel.
• The use of less dangerous chemicals! … “green chemistry”
What is “green chemistry”?
Green Chemistry is the choice to use less toxic materials over
more toxic ones and to try to minimize the use of flammable,
explosive, or highly reactive materials.
NOTE:
It is not always easy to figure out which is the least toxic chemical.
RECALL:
• Long term effects caused by bioaccumulation are difficult to test.
• Effects other than toxicity may not be anticipated.
O
N
O
NH
O O
Thalidomide
CFCs
chlorofluorocarbons
Pb(Et)4
tetraethyllead
A “Green” Approach: Examples
• Nuclear reactor accidents (e.g., Chornobyl) can be avoided by
using alternative electrical power generation techniques:
….wind, wave power, geothermal and solar energy
• The explosion at a BASF plant in Ludwigshafen, Germany could
have been avoided by using nitrogen or carbon dioxide to blow
polystyrene instead of pentane.
• A hydrogen cyanide leak at a Rohm&Haas plant in Texas sent 32
workers to hospital. HCN was being used in the synthesis of
methyl methacrylate. An alternative route, using isobutylene, is
known.
Catalysis: the “key” to green
chemistry
It has been suggested that the “key” to reducing the incidence and
severity of accidents, waste, toxicity of chemicals, and amount of
energy used is the development of more sophisticated catalysts.
• enantioselective catalysts - to prepare bioactive optical isomer only
• biocatalysts - to run reactions at low temperatures in aqueous media
• oxidation with air or H2O2 instead of heavy metal-containing oxidants
• solid acids rather than HF or H2SO4 in alkylation reactions
A Word on Waste
Waste is not waste if it can be reused!
Examples:
• Calcium sulfate from flue gas desulfurization ends up in dry wall
for houses in Denmark and Japan.
• DuPont markets a number of intermediates from its
manufacturing of fibers.
• Rhone-Poulenc-Ruhrchemie uses a water-soluble rhodium
phosphine complex to catalyze the hydroformylation of propene to
butyraldehyde. In 10 years, 2 x 106 tonnes of butyraldehyde were
manufactured with the loss of only 2 kg of rhodium!
Recycling
Used Plastics:
Most proposals for chemical recycling of used plastics are based
on synthesis gas recovery (CO / H2) from used plastics by the
addition of acid and water.
Used PVC:
Discarded PVC can be recycled by pyrolysis at 1200°C in a
rotary kiln to generate HCl (chlorine recycling).
Unwanted CFCs:
Hoechst has developed a process for the disposal of CFCs by
thermal cleavage in an O2 / H2 flame at 2100°C in an acidresistant graphite reactor. This thermal cracking of CFCs yields a
mixture of HCl, HF, CO2, H2O and Cl2 (> 99.99% conversion!)
Recycling
Chlorine-containing residues:
• Chlorination of methane
• Manufacture of vinyl chloride
• Manufacture of allyl chloride
• Manufacture of chlorobenzene
• Manufacture of propylene oxide via chlorohydrin
Generate
residues
with high
chlorine
content
Gas-phase cracking of these chlorinated hydrocarbon residues,
with simultaneous chlorination, yields either mixtures of CCl4,
Cl2C=CCl2, and Cl2C=CHCl or only CCl4.
Process variables such as pressure, temperature, residence time,
and Cl2/hydrocarbon ratio determine the selectivity of the
chlorinolysis.
Recycling
Waste paper:
The processing of scrap paper does not require delignification
with sulfur chemicals, since lignin was removed in the
manufacture of the of the new paper.
If scrap paper is to be used for packing materials and chipboard,
the colour is unimportant and deinking is unnecessary.
About 20% of recycled paper is used for printing paper. Deinking
is achieved by either ink washing or ink flotation.
Recycling
Scrap iron and steel:
Typically, iron is produced by reducing iron ore (Fe2O3) in a blast
furnace.
Iron and steel can also be produced from recycled scrap which, of
course, does not need to be reduced and can be melted down
directly in an electric arc furnace.
The main problem is the presence of other metal impurities
(particularly Sn with S) called “tramps”
brittle product.
Reprocessed scrap usually must be mixed with new steel to
ensure tramps < 0.13%...good enough for new automobile bodies.