1 3
Topics in Current Chemistry (2018) 376:44
Moreover, fluid properties such as viscosity vary significantly and typically rheological phenomena occur during the polymerization, rendering the process much
more complex than small-molecular reaction processes. Apparently, the obvious
increase of viscosity would weaken transport properties of reactors, thus resulting
in more difficulty on the control over polymerization processes. In particular, some
polymerization processes such as reversible addition–fragmentation chain-transfer
(RAFT) polymerization require strict reaction conditions such as cryogenic and oxygen-free operations when batch reactors are applied, further aggravating the process
complexity. Consequently, precise control over polymerization processes is of vital
importance, and advanced reactor technologies are required to deal with stubborn
problems associated with the polymerization processes.
As one of the most important process intensification strategies, microreactor
technology has received increasing attention from both academia and industry in the
past two decades due to its features [11–13]. In comparison with conventional batch
reactors, microreactors have many advantages such as higher surface area-to-volume
ratios, enhanced heat and mass transfer rates, precise control over process parameters, improved chemistry and excellent process safety, continuous-flow operation,
and the ease of the throughput increase via numbering-up, etc. [14–27]. With these
advantages, microreactors have been widely applied for various reaction processes,
especially for highly exothermic and fast-reaction processes such as oxidation, sulfonation, nitration, Friedel–Crafts alkylation, condensation, rearrangement reaction,
and so on, to produce fine chemicals and active pharmaceutical ingredients (APIs)
[28–32]. Moreover, increased radiation homogeneity can be easily obtained resulting from extremely small characteristic dimensions of microreactors, and thus photochemical transformations for organic synthesis can be significantly improved with
the application of microreactors. In particular, the drawbacks associated with batch
reactors for polymerization processes, might be overcome by utilizing microreactor technology. Various kinds of polymers with narrow molecular weight distributions, well-controlled molecular weights, structures, and shapes can be synthesized
in microreactors [33–39].
There are many review articles about microreactor technology and its applications
on different fields [33, 40–46], in which hydrodynamics, mass transport, and reaction
characteristics in microreactors are systematically discussed. On the other hand, microreactor technology shows significant application potential for polymerization processes
and there are numerous relevant reports [8, 34, 47]. Even though several literature
reviews about polymerization processes in microreactors can be found elsewhere, the
engineering principles behind the use of microreactors for polymerization processes
have not been clearly described up to now. In fact, rheological phenomena and nonNewtonian fluids are usually involved in polymerization processes, and thus the hydrodynamics and transport properties vary significantly in microreactors during polymerization. Therefore, a general description on its specific mass transport properties in
microreactors during polymerization will be beneficial for process design and optimization, which is an important starting point in this current chapter. The characteristics
of heat transfer and energy dissipation in microreactors for polymerization processes
are also analyzed. Next, the application examples of microreactors on homogeneous
polymerization, heterogeneous polymerization, and photopolymerization are classified,
149
Reprinted from the journal
Topics in Current Chemistry (2018) 376:44
Moreover, fluid properties such as viscosity vary significantly and typically rheological phenomena occur during the polymerization, rendering the process much
more complex than small-molecular reaction processes. Apparently, the obvious
increase of viscosity would weaken transport properties of reactors, thus resulting
in more difficulty on the control over polymerization processes. In particular, some
polymerization processes such as reversible addition–fragmentation chain-transfer
(RAFT) polymerization require strict reaction conditions such as cryogenic and oxygen-free operations when batch reactors are applied, further aggravating the process
complexity. Consequently, precise control over polymerization processes is of vital
importance, and advanced reactor technologies are required to deal with stubborn
problems associated with the polymerization processes.
As one of the most important process intensification strategies, microreactor
technology has received increasing attention from both academia and industry in the
past two decades due to its features [11–13]. In comparison with conventional batch
reactors, microreactors have many advantages such as higher surface area-to-volume
ratios, enhanced heat and mass transfer rates, precise control over process parameters, improved chemistry and excellent process safety, continuous-flow operation,
and the ease of the throughput increase via numbering-up, etc. [14–27]. With these
advantages, microreactors have been widely applied for various reaction processes,
especially for highly exothermic and fast-reaction processes such as oxidation, sulfonation, nitration, Friedel–Crafts alkylation, condensation, rearrangement reaction,
and so on, to produce fine chemicals and active pharmaceutical ingredients (APIs)
[28–32]. Moreover, increased radiation homogeneity can be easily obtained resulting from extremely small characteristic dimensions of microreactors, and thus photochemical transformations for organic synthesis can be significantly improved with
the application of microreactors. In particular, the drawbacks associated with batch
reactors for polymerization processes, might be overcome by utilizing microreactor technology. Various kinds of polymers with narrow molecular weight distributions, well-controlled molecular weights, structures, and shapes can be synthesized
in microreactors [33–39].
There are many review articles about microreactor technology and its applications
on different fields [33, 40–46], in which hydrodynamics, mass transport, and reaction
characteristics in microreactors are systematically discussed. On the other hand, microreactor technology shows significant application potential for polymerization processes
and there are numerous relevant reports [8, 34, 47]. Even though several literature
reviews about polymerization processes in microreactors can be found elsewhere, the
engineering principles behind the use of microreactors for polymerization processes
have not been clearly described up to now. In fact, rheological phenomena and nonNewtonian fluids are usually involved in polymerization processes, and thus the hydrodynamics and transport properties vary significantly in microreactors during polymerization. Therefore, a general description on its specific mass transport properties in
microreactors during polymerization will be beneficial for process design and optimization, which is an important starting point in this current chapter. The characteristics
of heat transfer and energy dissipation in microreactors for polymerization processes
are also analyzed. Next, the application examples of microreactors on homogeneous
polymerization, heterogeneous polymerization, and photopolymerization are classified,
149
Reprinted from the journal