Chemistry Reference
In-Depth Information
organic solvents. To determine the exergy consumption of a plant one must consider its capacity ('
system
boundary') and perform calculations taking into account the physical boundaries of the plant and the resources
passing those boundaries. These include the resources purchased by the pharmaceutical company to perform
the separation and produce the racemic mixture, the cooling and industrial water, the cooling and heating
medium, steam and the cost of storing the product. Preparative SFC appears to be more advantageous because
it requires about 30
β
less resources than preparative HPLC as quantified in exergy. However, the cumulative
exergy extracted from the natural environment to deliver all the mass and energy flows to the
%
α
and
β
system
boundaries via the overall industrial network (
γ
system boundary) reveals that preparative SFC actually
requires about 34
more resources than preparative HPLC. The astonishing conclusion of the work [31] is
that the most sustainable process in terms of integral resource consumption is preparative HPLC. The authors
reason that the electricity required for heating and cooling and the production of liquid CO
2
argues against
the use of preparative SFC. Therefore, the actual greenness of elevated temperature chromatography cannot
be proven until a thorough exergy life cycle analysis has been performed. It is hoped that exergy calculations
will progress from academic exercises to organizational policy issues.
%
15.5
Efficient laboratory equipment
D. Raynie [33] has divided laboratory equipment into three categories, based on the energy it consumes per
sample (see Table 15.1)
The energy assessment Table 15.1 indicates that wet chemistry methods such as titration and those based
on biochemical assays will be in the 'green' area. Simple instrumental methods such as GC and, HPLC are
in the 'yellow' zone. More complicated and combined instrumental methods are energy intensive and they
are therefore in the 'red' column. High sample throughput is clearly important because it reduces energy
consumption per sample. Solvents create additional energy requirements. Solvent evaporation is directly
related to energy use, and a method that requires the evaporation of high volumes of solvent is unfavourable.
Spectroscopic methods require remarkably little energy. Many of them are reagentless, non-destructive, fast
and able to determine several analytes in the same run. For these reasons, they are environmentally friendly
and can be considered green analytical methods [34]. Unique analytical characteristics, such as high sensitivity,
Table 15.1
Instrument ranking according to energy consumption.
≤
0.1 kWh per sample
green
≤
1.5 kWh per sample
yellow
> 1.5 kWh per sample
red
SPE (vacuum assistance)
Hot plate solvent evaporation is less
than 2.5 h with a green instrument
Hot plate solvent evaporation is more
than 2.5 h with a green instrument
Rotavap
ASE
SPME
SFE
Ultrasound probe
Hot plate solvent evaporation is more
than 1 h with a yellow instrument
Sonicator
FTIR
Microwave
Soxhlet
UV-Vis spectrometer
AA spectrometer (flame or furnace)
Fluorescence spectrometer
ICP-MS
NMR
UPLC
GC
GC-MS
Titration
LC
LC-MS
Immunoassay
X-ray diffractometer
Microbiological assay
Hot plate solvent evaporation
is less than 10 min
Hot plate solvent evaporation is less
than 1 h with a yellow instrument
