Page 442 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

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Encyclopedia of Physical Science and Technology EN012I-591 July 26, 2001 15:54

608 Pollution Prevention from Chemical Processes

hazardous waste. These organic solvents were used to ity impacts. Initial concerns about product quality were
dissolve and add a polymerization inhibitor to the pro- unfounded. Total waste generation was reduced by the
cess. Alternative nonhazardous solvents were considered quantity of dehydration water which is reused.
and rejected because these solvents would not work in
the existing equipment. However, with the help of process
2. Groundwater Protection
analysis techniques, the intermediate monomer was found
to have the same dissolution capacity as the original or- At a grassroots facility, one company utilized a groundwa-
ganic solvents. As a result, the site replaced the organic ter protection strategy which included several construction
solvents with the intermediate monomer. By utilizing ex- tactics not required by current environmental regulations.
isting equipment, realizing savings in solvent recovery, Chemical storage tanks were designed with double bot-
and reducing operating and incineration costs, the project toms to allow leak detection before environmental dam-
achieved a 33% internal rate of return (IRR) and a 100% age. Similarly, one nonhazardous process water pond was
reduction in the use of the original solvents. constructed with synthetic liners to eliminate the possibil-
ity of groundwater impact from any pollutants. Nonhaz-
ardous process water ditches, traditionally used in chem-
E. R&D Phase
ical plants, were replaced with hard-piped sewer lines to
1. Waste Reduction through Control eliminate the leak potential inherent with concrete.
of the Reaction Pathway
G. Existing Process Operation
In hydrocarbon oxidation processes to produce alcohol,
there is always a degree of overoxidation. The alcohol 1. Reduced Hazardous Waste Generation
is often further oxidized to waste carboxylic acids and
At a chemical manufacturing site, a series of distillation
carbon oxides. If boric acid is introduced to the reactor,
the alcohol reacts to form a borate ester, which protects columns are used to purify different product crudes in sep-
arate campaigns. At the conclusion of each campaign, a
the alcohol from further oxidation. The introduction of
portion of product crude was used to wash out the equip-
boric acid terminates the by-product formation pathway
ment. When the crude became too contaminated, it was
and greatly increases the product yield. The borate ester
sent for destruction in a hazardous waste incinerator. First,
of alcohol is then hydrolyzed, releasing boric acid for re-
an analysis of the washing procedure of a decant tank in-
cycle back to the process. This kind of reaction pathway
dicated that only 1/10 of the product crude wash material
control has been applied to a commercial process, result-
was really needed to effect cleaning. Second, a dedicated
ing in about a 50% reduction in waste generation once the
pipeline for each crude was installed, thus eliminating the
process was optimized.
need to flush the line between campaigns. Third, an ex-
tended and improved drainage procedure was developed
2. Waste Reduction through Catalyst Selection for a large packed-bed distillation column. Finally, the
product specifications were relaxed, so that fewer washes
For chemical processes involving catalysis, proper selec-
were required to maintain product specifications. Capital
tion of catalysts can have a major impact on product for-
investment for these process changes was $700,000; how-
mation. One example is the ammoxidation of propylene
ever, the project had a positive net present value of more
to form acrylonitrile. Different catalysts result in a wide
than $3 million, and realized a 78% reduction in waste
range of product and by-product yields. By-product yields
generation.
of 50–80% (based on carbon) have been reported in the
literature. Use of a different catalyst provided a 50% re-
duction in waste generation by increasing product yield XIV. CONCLUSION
from 60% to 80%.
Pollution prevention is becoming an integral part of busi-
F. Process and Design Engineering Phase ness operations, both new and existing. As the drive to-
ward a more sustainable human society strengthens, pol-
1. Reuse Reaction Water in Wash Step
lution prevention will become even more necessary for a
A dehydration reaction generates a continuous stream of business to survive. There are large opportunities to do
water, which requires disposal. A separate product wash both pollution prevention and improve the economic re-
step uses deionized water, which is also disposed. Test- turn on manufacturing processes. Everyone in a business
ing verified that the dehydration water could replace the can contribute to reducing manufacturing waste. In this ar-
deionized water in the wash step without product qual- ticle we described pollution sources, pollution prevention