Chemistry Reference
In-Depth Information
Chapter 15: Process Intensification
for Green Chemistry
ROSHAN JACHUCK
chemical at any time in a smaller intensified unit. In
addition, one of the objectives of process intensifica-
tion is to move away from batch processing to small
continuous reactors, the latter giving more efficient
overall operation, especially in the case of hugely
exothermic reactions whereby the heat can be
removed continuously as it is being released. The
inherent safety aspect of process-intensification-
based technologies and its role in minimising hazards
in the chemical and process Industries have been dis-
cussed in a recent article [3]. Design considerations
that may be taken into account for intensifying a
process are presented in Table 15.1.
1 Introduction
The chemicals industry worldwide is facing the chal-
lenges of stringent environmental regulations amidst
severe market competitiveness. There is a growing
demand for processes that are clean, energy efficient,
intrinsically safe and responsive to market needs. In
order to meet these objectives it is essential to
rethink the process design philosophy and adopt a
multidisciplinary approach towards problem solving.
It is essential that chemists, material scientists, math-
ematicians and engineers work together as a team
and discuss process issues at the outset.
In order to exploit the advances made in the field
of green chemistry, it is essential to develop process
technology based on the concepts of process intensi-
fication. Process intensification was pioneered by
Ramshaw [1] in the 1980s and may be defined as a
strategy that aims to achieve process miniaturisation,
reduction in capital cost, improved inherent safety
and energy efficiency and often improved product
quality. In recent times process intensification has
been seen to provide processing flexibility, just-in-
time (JIT) manufacturing capabilities and the oppor-
tunity for distributed manufacturing. In order to
develop an intensified process plant, it is essential
that all the unit operation systems are intensified, i.e.
reactors, heat exchangers, distillation columns, sep-
arators, etc. Wherever possible, the aim should be to
develop and use multifunctional modules for per-
forming heat transfer, mass transfer and separation
duties. Process intensification encompasses [2] not
only the development of novel, more compact
equipment but also the development of intensified
methods of processing, such as the use of ultrasonic
and radiation as energy sources.
Additional benefits of process intensification are
improved intrinsic safety, easier scale-up and
increased energy efficiency. Adopting the process
intensification approach can improve substantially
the intrinsic safety of a process by having a signifi-
cantly reduced volume of potentially hazardous
2 Relevance to Green Chemistry
Process intensification may be seen as an ideal
vehicle for performing chemical reactions based on
green chemistry. It can provide appropriate reactor
technologies for utilising opportunities offered by
heterogeneous catalysis, phase-transfer catalysis,
supercritical chemistry and ionic liquids. It allows the
use of more intense chemistry for a given process by
using intensified reactors, such as the spinning disc
reactors, HEX reactors, oscillatory baffle reactors,
microwave reactors, microreactors, cross-corrugated
membrane reactors and catalytic plate reactors. For
instance, an intensified reactor may permit the use
of higher reactant concentrations, which signifi-
cantly influence the kinetics, selectivity and inven-
tory. Often, due to the heat/mass transfer and mixing
limitations of the reactor, the reactant concentrations
are compromised resulting in slow speed, poor selec-
tivity and extensive downstream separation process.
Process intensification presents a range of exciting
processing tools/opportunities for chemists to try out
chemistry that could not be considered in the past,
as seen in Table 15.2.
On the aesthetic side, because intensified process
plants will have smaller footprints it is likely that
they will be below the tree line, making it far less of
an eyesore for the general public than the unsightly
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