Process Intensification: An Overview of Principles and Practice - Process Intensification for Green Chemistry - page 19

Figure 1.9 Heat- and mass-transfer performance of several intensified units compared to the
jacketed stirred tank. Reproduced from [ref 69] with permission from Britest

2000.

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related to the handling of very viscous materials, which may result in extremely high
pressure drops, although new designs such as the SMX plus mixer have been introduced to
alleviate such processing difficulties [64]. Moreover, unless the structures are very open,
static mixers can be prone to blockages by suspended solids (e.g. catalysts).
Static mixers have found wide applications in many industrial mixing operations
involving gas-liquid dispersion and liquid-liquid extraction for enhanced mass trans-
fer [65], and they have long been regarded as one of the successful applications of PI in
industry. They can also be employed as an in-line mixer in multifunctional heat-exchanger
reactors, where they not only facilitate rapid mixing between reacting species but also
provide additional surfaces for efficient heat transfer [66-68].
The heat- and mass-transfer intensification abilities of the various technologies
described in this section are neatly summed up in Figure 1.9. The comparatively poor
performance of the workhorse of the chemical industry that is the jacketed stirred tank
reactor sits in stark contrast with the intensified systems.

1.4.2 Integrating Process Steps

One of the most important intensification strategies is combining process steps, thereby
reducing the overall number in a process. This can have a range of benefits:
Reduction in capital cost
Reduction in running cost
Reduction in duty of downstream unit operations

One of the most familiar integrations is between reaction and separation. Examples
include:
Membrane Reactors: Membranes that are permeable to only one of the products are
used to remove this product in situ, thereby overcoming equilibrium constraints. In this
way, membrane reactors have often been used to bring equilibrium reactions to
completion.