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Through addition of HCl, the acetyl-D-amino acid was neutralized, increasing its ethyl
acetate solubility, while the L-amino acid was separated by water. Separation was
carried out through a membrane on the microchannel surface, which enabled the
selective extraction of the product [280].
Knoevenagel reactions between benzaldehyde and ethyl cyanoacetate, ethyl acetoace-
tate and diethyl malonate were carried out in a membrane microreactor. Water generated as
a result of condensation was removed from the reaction mixture by pervaporation through a
zeolite micromembrane. The best reaction yield was obtained by locating the CsNaX
catalyst adjacent to the membrane. For microreactor operation with powder catalyst, a
selectivity of 58% is found; the presence of a thin CsNaX film led the selectivity increase
to 78% [281,282].
4.4.3.2 Integration of Process Control and Sensing
The integration of microreactors with sensors, actuators and automated fluid handling is
useful for fast, continuous automation of reaction screening and optimization using online
monitoring [283].
A microreactor system for self-contained and standalone portable energy generation
contained integrated microfabricated sensors and actuators. The latter were used for
effective control strategy, especially concerning system start-up and controllability for
rapid load changes. On-chip sensing was done with a MEMS-based thin-film flow sensor to
measure the rate of hydrogen production. In this way, 100% conversion, rapid turn-on and
responsiveness to varying hydrogen loads were achieved [284].
An integrated gas-phase microreactor system comprised a 1
m
m thin platinum film
catalyst coated underneath a silicon nitride membrane. This system was assembled as a
computer chassis with modular boards. Seven platinum heaters and temperature sensors
were placed on top of the silicon nitride membrane. Various pins were used as electrical
contacts to allow onboard controlling and sensing [285].
The same group, in cooperation with the DuPont Company, further constructed a
MEMS-based system from first principles that had the same functionalities as a more
conventional laboratory-scale system used by DuPont. The components were designed and
fabricated as prototype electromechanical boards [286].
4.4.3.3 Thermal Integration on the Process Level
Complete thermal integration of a methanol micro fuel processor and fuel cell system is
essential to reducing full system size and enabling portability. With such a goal in mind,
heat losses were experimentally determined for various pathways from the planar micro-
reactor structure for catalytic methanol steam reforming. This allowed fundamental heat
management issues to be addressed, such as the transfer of heat between reactor compo-
nents, control of temperature, insulation and heat losses. In this way, a design/packaging
and scale-up proposal with reduced convective and radiative losses was made [287,288].
4.4.3.4 Integration of Units on Racks, Backbones, Frames, Interfaces or Similar
A commercial plastic socket, normally used for integrated circuit testing, was adapted
for installation of the reactor chip to allow alignment with the electrical contacts.
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