Technical Note
Two-Phase Flow Oxidation of Valeraldehyde with O in a
2
Microstructured Reactor
Tobias Baumeister, Hannes Kitzler, Klemens Obermaier, Stefan Zikeli, and Thorsten Ro
†
‡
‡
‡
der*,†
̈
†
Institute of Chemical Process Engineering, Mannheim University of Applied Sciences, Paul-Wittsack-Str. 10, 68163 Mannheim,
Germany
‡
one-A Engineering Austria, See-Str. 11, 4844 Regau, Austria
S Supporting Information
*
ABSTRACT: Microstructured reactors are the ideal device for highly exothermic reactions. In this work, the highly exothermic
two-phase reaction of valeraldehyde with oxygen to valeric acid was carried out in a microreactor. The used device from one-A
Engineering Austria GmbH is designed for process development and intensification and can be applied in the scale-up process to
small-scale commercial production. The atom economic oxidation of valeraldehyde is performed at 0 to 40 °C with a catalytic
amount of manganese(II) acetate. A continuous flow oxidation of aldehydes in such reactors can be a safe and beneficial
alternative to commercial batch processes.
INTRODUCTION
or hydrogen peroxide. By modifying the periodic narrowings
along the complete reactor channel, the degree of mixing and
the generation of the gas−liquid interface can be seamlessly
adjusted to the reaction conditions. Due to the robust metallic
design, the microreactor can be used from lab scale to
production scale.
■
Aldehydes can be obtained by the economically efficient
transition-metal-catalyzed hydroformylation of olefins known as
1
the oxo synthesis. The oxidation of aldehydes with oxygen to
the corresponding carboxylic acids has been widely studied in
2
,3
4
terms of reaction mechanism, kinetics, and the influence of
5
,6
7
8
From a green chemistry perspective, oxygen is the ideal
oxidizing agent. Furthermore, because of the mild reaction
conditions and the high atom efficiency the metal catalyzed
oxidation with oxygen has some advantages over other reported
different catalysts and solvents. Vanoye et al. recently
reported the oxidation of different aldehydes in a perfluor-
oalkoxy alkane (PFA) tubing microreactor with promising
results. One beneficial reason for the use of microstructured
reactors is the improved mass transfer of oxygen. Due to the
11
aldehyde oxidation methods.
9
low solubility of oxygen in aldehydes and the fast chemical
reaction, the progress of reaction in conventional reactors like
stirred tank reactors and bubble column reactors are limited by
the mass transfer of O2.
A further benefit of microstructured reactors is the increased
MATERIALS AND METHODS
■
The conversion of valeraldehyde to valeric acid with oxygen
was carried out in a microstructured reactor from one-A
Engineering Austria GmbH (Figure 1a). The reactor was
engineered for research and development and can be applied in
production processes. Due to the modular design, the reactor
can be used in various settings. For the conducted reaction, a
setting with 10 microchannels in series (length: 750 mm;
internal diameter: 1 mm) and a total volume of 5.82 mL was
used. The inserted capillaries were made of Hastelloy with
periodical narrowings to increase the mixing performance for
an improved mass transfer (Figure 1b).
process safety, which is achieved by a low hold up of critical
material and the fast removal of reaction heat. Due to the
efficient heat transfer, a critical hot spot or a thermal runaway is
1
0
unlikely. This is an important factor, especially for fast and
exothermic reactions such as the oxidation of aldehydes with
pure oxygen.
In this paper, a general demonstration of the valeraldehyde
oxidation with pure oxygen in a microstructured reactor is
presented (Scheme 1). The reactor design is based on
meander-shaped pipes from a nickel based alloy which are
mounted in a metal housing. Due to the capillary design with
periodically arranged narrowings, the microreactor is especially
suited for multiphase oxidation reactions with oxygen, ozone,
All substrates were obtained from commercial suppliers and
were used without further purification. The homogeneous
valeraldehyde solution, containing the manganese(II) catalyst
and the octanoic acid, was added continuously into the reactor
by a syringe pump (SyrDos 2 with 10 mL syringes, HiTec Zang
GmbH, Germany) and preheated in 2 of the 10 available
microchannels. The oxygen flow rate (purity: 99.5%, Linde AG,
Germany) was measured with a rotameter (Model E: 0.1−0.8 L
Scheme 1. General reaction of valeraldehyde (I) with oxygen
to valeric acid (II)
Special Issue: Oxidation and Oxidative Reactions
Received: June 1, 2015
©
XXXX American Chemical Society
A
Org. Process Res. Dev. XXXX, XXX, XXX−XXX