Introduction - Micromixers Fundamentals Design and Fabrication - page 6

be needed. Thus, the design of micromixers for synthesis should be ready for numbering up in the case
of a large-scale production [4] .
Micromixers as microreactors will potentially have a large impact on chemical technology.
Because of their small size, micromixers allow control over a number of parameters of production
processes in chemistry and the pharmaceutical industry. Reaction conditions that are unusual in
macroscale are technically possible in micromixers. The advantages of reaction in micromixers are
small thermal inertia, uniform temperature, high gradient of the different physical fields, short
residence time, and a high surface-to-volume ratio. The small thermal inertia allows fast and
precise temperature control in micromixers. Miniaturization leads to higher rates of heat and mass
transfer. Compared to their macroscale counterparts, micromixers can offer more aggressive
reaction conditions. The large surface-to-volume ratio allows for an effective suppression of
homogenous side reactions in heterogeneously catalyzed gas-phase reactions. The small size makes
reaction in micromixers safe because of the suppression of flames and explosions. Explosions can
be suppressed by using mixing channels with hydraulic diameter less than the quenching distance
[5] . For instance, the fluorination of toulene with fluorine can be carried out at -10 Cinmicro-
mixers. Conventional reactors would require a temperature of -70 C due to the explosive nature of
the reaction [5] . In the case of accidents, the small amounts of hazardous reaction products are easy
to contain.
Micromixers as microreactors enable a faster transfer of research results into production. Since
scaling up the mixer design is not possible, lab setup can immediately be transferred into large-scale
production by numbering up. Since numbering up is the only option for micromixers, scaling law leads
to high ratio between device material and reaction volume. This means, fixed production costs will
increase with miniaturization because of the higher costs of materials and infrastructure. If micro-
reactors deliver a similar performance to their conventional macroscale counterparts, the higher
production costs will make micromixers unprofitable for chemical production. However, for some
particular products, the smaller production capacity may save costs through other factors such as
replacing a batch process by a continuous process. For instance, due to slow mass and heat transfer in
macroscale reactors, reaction time for fine chemicals is determined by mixing and is much longer than
needed for reaction kinetics. Replacing a batch-based macroscale reactor by a continuous-flow
microreactor can significantly reduce the reaction time. The reactor volume is smaller, but the total
throughput per unit time is higher. As a result, for the same amount of products the reaction process
would be carried out faster in microreactors.
In addition, as illustrated in Fig. 1.2 , selectivity of the reaction may increase with micromixers.
Production yields of microreactors could exceed those of batch-based macroscale reactors. The next
cost-saving factor of micromixers for chemical production is the intensification process. The larger
surface-to-volume ratio provides more surface for catalyst incorporation. Compared to its macroscale
counter part, the amount of catalyst needed in a microreactor can be decreased by a factor of 1000. If
the cost of the catalysts is significant in the overall production, saving catalysts can compensate for the
large amount of construction materials needed for numbering-up microreactors.
Micromixers have an indirect impact on national security due to the possibility of on-side portable
detection systems for chemical weapons and explosive. However, due to its portability, micromixers
could be misused by criminals and terrorists [5] . A miniature chemical plant fitted into a suitcase could
be misused for the production of drugs and hazardous gases. Raw chemicals may not be detectable
prior to reactions in these miniature plants. Lethal nerve gases could be formed by two primary