The development of sustainable industrial processes according
to
the 12 principles of green chemistry poses challenges, such as the
use of atom-efficient catalysis, the application of green solvents,
the use of mild process conditions, and the retention of valuable
catalysts in the process. One way to combine these desired but partially
opposing aspects into a single reaction system is the use of homogeneous
catalysis in microemulsions, where the catalyst is solubilized in
water and brought into intensive contact with organic substrates through
a surfactant. The valuable transition metal catalyst can then be recovered
through a simple phase separation after the reaction. The key challenge
addressed in this work is the implementation of reductive amination
(RA) as an example of a complex synthesis route for fine chemicals
in a continuous production process using a microemulsion system. The
investigated reaction network includes equilibrium, subsequent, and
side reactions, which make it challenging to implement in a stable
mini-plant operation. A proof of concept for continuous operation
in a mini-plant is achieved in a 200 h continuous operation by applying
our previously developed structured workflow for the design and operation
of reactive processes in liquid multiphase systems to the RA. At 25
bar and 110 °C with a residence time of 6 h, an undecanal conversion
of (59.9 ± 3.4)% is achieved, which matches the performance from
lab-scale investigations and thus proves a successful scale up by
a factor of 68. Stable phase separation is maintained for 200 h, where
only 0.12% of the rhodium catalyst entering the settler is leached
into the product phase and 99.88% is recycled to the reactor in active
form. These results are further proof that continuous and robust operation
of homogeneous catalysis in microemulsions with excellent catalyst
retention is possible and that previously developed workflows for
the design and operation of mini-plants are applicable. Reactions
in microemulsions have thus reached technology readiness level 5 and
are ready for industrial-scale demonstration.