Chemistry Reference
In-Depth Information
Table 12.16 (Continued
)
Green chemistry fundamentals
Membrane processes properties
Catalysis:
Catalytic reagents (as selective as possible)
are superior to stoichiometric reagents.
Use of heterogenized or free (bio)catalyst in
membrane reactor with improved selectivity
and productivity.
Real-time analysis for pollution prevention:
Analytical methodologies need to be further
developed to allow for real-time, in-
process monitoring and control prior to
the formation of hazardous substances.
Possibility to produce mebrane (bio)sensors to
monitor and control hazardous compounds.
Ineretly safer chemistry for accident
prevention:
Alternative processes able to substitute
conventinal methodologies (e.g. membrane
(bio)reactor) using rationalized solvet feed,
selective removal of products, controlled
supply of one reagent in order to keep low
concentration, mass transport controll and
multistep reaction.
Substances and the form of a
substance used in a chemical process
should be chosen to minimize potential
for chemical accidents, including
releases, explosions, and fires.
The strategy of PI is one of the key aspects of green chemistry. A European Roadmap
has been prepared by an international team of experts to identify the potential benefits
of PI and illustrate the actions needed to accelerate PI implementation in the process
industry [111]. In this roadmap, membrane technologies are indicated as being one of
the interesting options in the PI strategy. The benefits and state of development
of membrane technologies, according to the criteria established by European experts
in this roadmap, are shown in Table 12.15. Among the membrane processes considered,
membrane-assisted reactive distillation is deemed the most efficient in terms of energy
saving, CO
2
impact and high-quality compound production. These properties, together
with the economic feasibility, paint a future in which this methodology will replace
traditional options. The other membrane technologies analysed (membrane crystalli-
zation, membrane distillation, membrane reactor) show great potential in the same
direction.
Despite membrane operations offering important process potentials, some standards for
fundamental/strategic research are needed in order to promote industrial-scale develop-
ment. At the moment, microfiltration, ultrafiltration, reverse osmosis and electrodialysis
are well-established unit operations, while nanofiltration, gas separation and pervaporation
are at a developing level. Membrane contactors remain at an emerging step of development
and major problems need to be solved before industrial systems will be installed on a large
scale. Such problems include additional resistance to mass transfer offered by the
membrane, limited operating pressure below the breakthrough value, relatively low
membrane lifetime and high replacement costs.
The robustness and suitability of membrane technology are proven in various fields at
commercial scales. Interesting examples are in sea water desalination (El Paso desalination
plant, Texas, 104m
3
/day), in waste water treatment and reuse (submerged membrane
system from Zenon) and in the treatment of gas streams.
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