Introduction - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 4

environment-benign substances, including solvents, whenever possible; c) the design of
energy efficient processes; and d) the best form of waste disposal: not to create it in the first
place. The 12 principles are:

(1) It is better to prevent waste than to treat or clean up waste after it is formed.

(2) Synthetic methods should be designed to maximize “atom efficiency.”

(3) Wherever practicable, synthetic methodologies should be designed to use and generate

substances that possess little or no toxicity to human health and the environment.

(4) Chemical products should be designed to preserve efficacy of function while reducing

toxicity.

(5) The use of auxiliary substances (e.g. solvents, separation agents, etc.) should be made

unnecessary wherever possible and innocuous when used.

(6)

Energy requirements should be recognized for their environmental and economic
impacts and should be minimized. Synthetic methods should be conducted at ambient
temperature and pressure.

(7) A raw material or feedstock should be renewable rather than depleting wherever

technically and economically practicable.

(8) Reduce derivatives d Unnecessary derivatization (blocking group, protection/

deprotection, and temporary modification) should be avoided whenever possible.

(9) Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.

(10) Chemical products should be designed so that at the end of their function they do not

persist in the environment and break down into innocuous degradation products.

(11) Analytical methodologies need to be further developed to allow for real-time, in-

process monitoring and control prior to the formation of hazardous substances.

(12) Substances and the form of a substance used in a chemical process should be chosen to

minimize potential for chemical accidents, including releases, explosions, and fires.

One example of green chemistry achievements is the polylactic acid (or PLA). In 2002,
Cargill Dow (now NatureWorks) won the Greener Reaction Conditions Award for their
improved PLA polymerization process. Lactic acid is produced by fermenting corn and con-
verted to lactide, the cyclic dimmer ester of lactic acid using an efficient, tin-catalyzed cycliza-
tion. The L,L-lactide enantiomers are isolated by distillation and polymerized in the melt to
make a crystallizable polymer, which is used in many applications including textiles and
apparel, cutlery, and food packaging. Wal-Mart has announced that it is using/will use PLA
for its produce packaging. The NatureWorks PLA process substitutes renewable materials
for petroleum feedstocks, does not require the use of hazardous organic solvents typical in
other PLA processes and results in a high-quality polymer that is recyclable and compostable.
Understanding the concept of green chemistry holds a special position for bioprocess engi-
neers. Processes we design and operate must have minimal potential environmental impacts
while optimized for maximum benefit. Basic steps for green chemistry that are what bio-
process engineering do include:

(1) Developing products and processes based on renewable resources, such as plant

biomass.

(2) Design processes that bypass dangerous/toxic chemical intermediates.

(3) Design processes that avoid dangerous/toxic solvent use.