Chemistry Reference
In-Depth Information
Table 1.3
Global 'lost work' in major chemical processes
Theoretical work potential (kJ mol
-
1
final product)
Process
Raw materials
Final product
a
Thermodynamic efficiency (%)
Natural gas
+
air
Æ
methanol
1136
717
63
Natural gas
+
air
Æ
hydrogen
409
236
58
Ammonia (from natural gas
+
air)
Æ
nitric acid
995
43
4
Copper ore
Æ
copper
1537
130
9
Bauxite
Æ
aluminium
4703
888
19
a
Excludes any 'steam credit'.
The term 'green chemistry' is becoming the world-
wide term used to describe the development of
more eco-friendly, sustainable chemical products
and processes. The term was coined almost ten years
ago by the US Environmental Protection Agency and
has been defined as:
2.8 x 10
9
ha available
0.8 x 10
9
ha
available for
non-foods
2.0 x 10
9
ha
for food
production
for 10 bn people
'The utilisation of a set of principles that reduces
or eliminates the use or generation of hazardous
substances in the design, manufacture and appli-
cation of chemical products' (Paul Anastas)
@ 40 t ha
-
1
a
-
1
32 x 10
9
ta
-
1
+ forests
+ waste streams
This is elaborated further in the form of the so-called
Principles of Green Chemistry:
50 x 10
9
ta
-
1
of biomass
• Waste prevention is better than treatment or
clean-up
• Chemical synthesis should maximise the incorpo-
ration of all starting materials
• Chemical synthesis ideally should use and gener-
ate non-hazardous substances
• Chemical products should be designed to be non-
toxic
• Catalysts are superior to reagents
• The use of auxiliaries should be minimised
• Energy demands in chemical syntheses should be
minimised
• Raw materials increasingly should be renewable
• Derivations should be minimised
• Chemical products should break down into in-
nocuous products
• Chemical processes require better control
• Substances should have minimum potential for
accidents
1 x 10
9
ta
-
1
for organics
>40 x 10
9
ta
-
1
for energy
= 2 x 10
20
Ja
-
1
Fig. 1.6
Biomass utilisation in 2040.
novative engineering, clean synthesis and process
improvements.
It is, perhaps, worth focusing briefly on one of
these principles as we enter the century where oil
reserves will be seriously diminished: 'Raw materi-
als increasingly should be renewable'. Can we base
the future chemical industry on biomass? Remark-
ably, at least some of the better calculations show
that this is a very likely scenario [10]. With a modest
increase in farming efficiency to improve crop yield
to about 40 t ha
-1
year
-1
we will need only less than
1% of the biomass available globally to provide all
the raw material necessary to feed the entire organic
chemicals industry by 2040 (Fig. 1.6).
The chemical technologies, both new and estab-
lished, that are described in this topic address these
principles by considering atom efficiency, alternative
energy sources, the use of alternative feedstocks, in-
