Chemistry Reference
In-Depth Information
the cost is too high,
regardless
of the environmental
benefits.
More frequently, the argument is being made that
a 'green' approach is also the more economical
approach. The industry is facing increasing regula-
tory and cost pressures regarding environmental
issues that are driving the industry to more envi-
ronmentally friendly processes. The cost for envi-
ronmental controls has been estimated at about 3%
of sales revenue, or about $10 billion each year [1].
Deeper evaluation of these numbers by industry has
revealed that there might be generally unrecognised
and positive economic drivers beyond simple raw
material and capital costs to encourage green chem-
istry growth in the industry. This is certainly the case
in the evaluation of new projects. For example, the
cost of safety issues in the design of a new plant is
always evaluated. Safety costs are found to have a
relative factor of unity at the research stage but a
factor of 10
4
if an incident occurs [5]. It would be
reasonable to assume that similar factors also apply
to the environmental impact of a new process. Other
analyses have pointed out where positive economic
benefits accrue through waste minimisation and
capital expenditures on green process technology
rather than end-of-pipe treatments [6].
Reduction of waste and elimination of toxic by-
products can be translated directly into economic
benefit. A useful quantitative measure of the impact
of a technology based on the amount of waste it gen-
erates was developed by Sheldon, and measures the
ratio of the weight of by-products in a process to the
weight of product formed [7a]. This E value has been
cited in many subsequent papers and is summarised
in Table 14.1.
Table 14.1 indicates that the industry segment
handling the largest amount of chemical products
also generates the smallest amount of waste, at least
as a function of product tonnage. The pharmaceuti-
cal industry with its reliance on multistep syntheses
and somewhat exotic reagents and solvents is, by this
evaluation, 'dirtiest' [7b]. However, in absolute
terms, the oil refining industry still generates the
biggest pile of material to dispose. To address this
component of the issue, Sheldon also has tried to
incorporate an 'unfriendliness factor' into the eval-
uation. Fairly innocuous waste products (such as
NaCl), which are more common in large-scale com-
modity manufacture, could be given an unfriendli-
ness factor of 1, whereas the generation of heavy
metal waste (e.g. Cr waste from an oxidation step)
might be given a factor of 100 or 1000. This factor is
multiplied by the E value to give an environmental
quotient (EQ), which would be a measure of the
overall impact of the waste. Evaluation of the EQ
could indicate that small-scale processes have a very
large impact. A goal for green technology would be
to direct all manufacturing routes, large and small,
to the lowest possible EQ.
Quantitative evaluations of the relative greenness
of a process can be debated. If an improvement
results in less waste, but not zero waste, is it accept-
able? If a process or product is renewables-based, is
it automatically green? Some evaluations have pro-
jected that routes employing renewable feedstocks
actually may consume more energy and generate
more waste than those currently used [8]. If an
industry decides to use a biotechnological step for
production, are the cell waste or metabolic by-prod-
ucts less damaging to the environment than some of
those generated by the fine chemical or pharmaceu-
tical industries, i.e. what is a reasonable unfriendli-
ness factor for newly developing technology? If one
uses catalysis, how many additional manufacturing
steps can be included before the effectiveness is lost?
For example, a BASF procedure uses a catalytic
hydroformylation step in the production of vitamin
A [9]. However, the process also uses a very atom-
uneconomical
Wittig coupling in a subsequent step.
What is the overall impact?
From a broader viewpoint, should separate tech-
nology for the manufacture of reagents needed for
a particular transformation also be evaluated?
Reagents H
2
O
2
, O
2
and O
3
are widely considered as
benign oxidants, but the production of H
2
O
2
or O
3
is
energy intensive. What is the environmental impact
of their production? [10]. Electrochemistry fre-
quently is suggested as a very clean method for the
production of new compounds, and a large-scale
Table 14.1
The E values for different chemical industry
segments
Industry segment
Product tonnage
E value
Refining
10
6
-10
8
~0.1
Bulk chemicals
10
4
-10
6
<
1-5
Fine chemicals
10
2
-10
4
5-50
Pharmaceutical
10
1
-10
3
25 to
>
100
