science    in   ACTION
     GREENSCOPE: Sustainable Process Modeling

     The chemical industry is
     fundamental in the U.S. This sector
     accounts for five percent of the U.S.
     nominal gross domestic product and
     six percent of the total U.S. energy
     consumption, directly employs
     approximately 800,000 people
     nationwide, and is the source for
     11% of all U.S. patents granted

     The chemical industry faces
     environmental and health challenges
     that are common across business
     sectors. From the use of
     nonrenewable feedstocks, to the cost
     and handling of waste disposal and
     workers' exposure to toxic
     substances, the industry must
     overcome complex hurdles to secure
     a more sustainable future.


     EPA researchers are responding to
     the problems outlined above by
     incorporating sustainability into
     process design and evaluation. EPA
     researchers are developing a tool
     that allows users to assess
     modifications to existing and new
     chemical processes to determine
     whether changes in critical sub-
     processes or substances will make
     the overall process more or less

     The GREENSCOPE (Gauging
     Reaction Effectiveness for
     Environmental Sustainability of
     Chemistries with a multi-Objective
     Process Evaluator) research project
     focuses on developing a systematic
     methodology and software tool that
     can assist researchers from industry,
              academia, and government agencies
              in developing more sustainable
              processes. In the project, the
              sustainability of a process is
              measured in terms of Environmental,
              Efficiency, Energy and Economic
              indicators (the 4 E's), with each
              indicator being mathematically
              defined. The indicators express
              diverse aspects of performance in a
              format that is easily understood,
              supporting realistic usage. The
              indicators enable and demonstrate
              the effectiveness of the application
              of green chemistry and green
              engineering principles in the
              sustainability context.

              Sustainability Indicators

              To evaluate the environmental
              aspects of alternative chemistries or
              technologies, GREENSCOPE
              employs the Waste Reduction
              (WAR) algorithm (Young and
              Cabezas, 1999). The WAR
              algorithm determines the potential
              environmental impacts of releases
              from a process in eight impact
              categories: human toxicity by
              ingestion and dermal/inhalation
              routes, aquatic toxicity, terrestrial
              toxicity, acidification, photo-
              chemical oxidation, global warming
              and ozone depletion. While these
              potential impacts are defined as mid-
              point indicators (as opposed to end-
              point indicators), the measures for
              the categories are well defined,
              which is a substantial improvement
              over arbitrary environmental or
              mass-based scores.

              Efficiencies for chemical reactions
              are reflected in values such as
              conversion and selectivity, which
track yields, product distributions,
and recycle flows needed to make a
desired amount of product. Another
measure of how green a reaction is
can be obtained from the atom
economy (i.e., how many atoms
from the feed are in the product).
These measures, which are well
known in green chemistry, are
related to environmental impacts
since the product distribution defines
what chemicals (and amounts) may
leave a process. These efficiencies
represent a bridge between the lab-
scale experiments of a chemist and
further engineering calculations.

Energy is a basic component of
chemical processes. Its use depletes
resources and creates potential
environmental impacts. Connecting
to yet another sustainability
indicator, a less efficient process can
be expected to use more energy.

Without a positive economic
performance, no industrial process is
sustainable. The economics of
processes are measured according to
their costs. For economists, this is an
oversimplified view of markets, but
for engineering calculations, the
annualized costs are significant
measures. The costs are tied into the
process through efficiencies, energy,
and environmental impacts.

Another novel aspect of the
GREENSCOPE methodology and
tool is that each indicator is placed
on a sustainability scale enclosed by
scenarios representing the best target
(100% of sustainability) and the
worst case (0% of sustainability).
This sustainability scale allows the
transformation of any indicator score
            U.S. Environmental Protection Agency
            Office of Research and Development
                                                          EPA 600-F11020
                                                                 July 2011

       to a dimensionless form using the
       worst and best scenarios.

       A process that is better in
       environmental, efficiency, energy,
       and economic terms will most likely
       be sustainable, although one can
       expect that tradeoffs will need to be
       Below, the indicators for a
       hypothetical process illustrate
       measures (in blue) that fall between
       0 and 100% of sustainability.
        Data Needs

        GREENSCOPE requires diverse
        data. These data can be obtained
        from experimental work, process
        modeling, physical and
        thermodynamic multi/pure
        component properties, product and
        process design specifications, life
        cycle inventory, physical and
        thermodynamic commercial
        databases,  and emissions, discharge,
        and consumption data from agencies
        such as EPA, the U.S. Department of
        Energy, the U.S. Department of
        Agriculture, and non-governmental
        organizations such as the World
Resources Institute and the Carbon
Disclosure Project.


Development of the methodology
has centered around three focal
points. The first is a taxonomy that
describes the indicators and provides
absolute scales for their evaluation.
The use of best and worst limits (100
and 0% of sustainability,
respectively) for each indicator
allows the user to know the status of
       the process under study in
       relation to understood values
       and to strive towards
       realizable targets.

       A second area is advancing
       definitions of data needs for
       the many indicators. Each
       indicator has specific data
       that are necessary for its
       calculation. Values needed
       and data sources have been
       identified. These needs can
       be mapped according to the
       information source (e.g.,
       input stream, output stream,
       external data, etc.). The user
       can visualize data-indicator
       relationships before choosing
       indicators for evaluation.

       The third focus is on case
studies. Example calculations were
performed on an alternative catalyst
for the oxidation of cyclohexane.
The results indicate how beneficial
the new catalyst technology could
be. For this and future studies, once
one knows what success would
mean, the  decision to pursue
research can be  made on a firmer

In addition, the scalability of
GREENSCOPE results was
addressed to ensure that optimized
sustainable designs, as well as
experimental studies at the lab scale,
would be reflected at the process
Current and Future Research

The methodology is being applied to
the production of biodiesel.
Analyses identify where biodiesel
processes can be made more
sustainable based on environmental,
economic, efficiency, and energy
measures. Process improvements
can be suggested or those that were
made can be evaluated.

Future work will incorporate models
and experiments in an iterative
process using a  GREENSCOPE
software tool to support sustainable
chemical process synthesis. An
integrated computational tool for
multi-objective  chemical simulation
software will be developed.


Smith, R. L. and Gonzalez, M. A.
Methods for evaluating the
sustainability of green processes.
Comp. Aided Chem. Eng., 2004,
Vol. 18, 1135-1140.

Gonzalez, M. A. and Smith, R. L. A
methodology to evaluate process
sustainability. Env. Prog., 2003,
Vol. 22 (4), 269-276.

Young, D.M. and Cabezas, H.
Designing Sustainable Processes
with Simulation: The Waste
Reduction (WAR) Algorithm.
Comput. Chem.  Eng., 1999, Vol. 23,


Michael A. Gonzalez, Ph.D., Office of
Research & Development, 513-569-
7998, gonzalez.michael@epa.gov

Raymond Smith,  Ph.D., Office of
Research & Development, 513-569-
7161, smith.raymond@epa.gov

Gerardo Ruiz-Mercado, Ph.D., Office of
Research & Development, 513-569-
7030, ruiz-mercado.gerardo@epa.gov
                U.S. Environmental Protection Agency
                Office of Research and Development
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