Chemistry Reference
In-Depth Information
Waste
reduction
at source
Recycling
Product
changes
Good
housekeeping
Feedstock
changes
On site
Off site
New technology
Cleaner
processes
Retro-fitting
Fig. 1.5
Options for waste
management within a chemical
manufacturing process.
Table 1.1
'Atom accounts' for a typical partial oxidation
reaction using chromate
Table 1.2
Relative efficiencies of different chemicals
manufacturing sectors
Element
Fate
Atom utilisation
By-product weight/
Industry sector
Product tonnage
Product weight
C
Product(s)
Up to 100%
H
Product(s)
+
waste acid
<
100%
Oil refining
10
6
-10
8
<
0.1
Cr
Chromium waste
0%
Bulk chemicals
10
4
-10
6
1-5
Na
Salt waste
0%
Fine chemicals
10
2
-10
4
5-50
+
S
Salt waste (after acid
0%
Pharmaceuticals
10-16
3
25-100
+
neutralisation)
O
Product(s)
+
waste
<<
100%
An interesting variation of the quantification of
the efficiency of chemical processes is to consider
their energy efficiency via 'lost work'. This has been
estimated by calculating the theoretical work poten-
tial of the raw materials and of the final product. In
this way the thermodynamic efficiency, and hence
the lost work for industrial processes, can be calcu-
lated [9]. When this exercise is carried out for some
of the largest scale chemical processes, even these
often are shown to be very inefficient (Table 1.3).
Thus, although large-scale chemical processes often
may be relatively atom efficient, at least compared
with the largely inefficient reactions utilised at the
lower volume end of chemicals manufacturing, these
can show low energetic efficiencies. It seems that we
cannot be proud of the effective utilisation of pre-
cious resources because very little of that goes on in
chemical manufacturing.
furic) and a solvent. Ironically, the substrate usually
is the minor component in this witches' brew! The
'atom accounts' for the process make alarming
reading (Table 1.1) [7], with only carbon likely to
approach 100% atom efficiency, and this depends on
reaction selectivity.
It is also revealing to compare the relative effi-
ciencies of process types or even industrial sectors
on the basis of the amount of waste produced di-
vided by the amount of product. This so-called E
factor [8] is a clear indication of how the traditional
organic chemicals manufacturing processes that
have been the lifeblood of the fine, speciality and
pharmaceutical chemicals industries are no longer
acceptable in these environmentally conscious days
(Table 1.2).
