Orifice microreactor for the production of an organic peroxide – non-reactive and reactive characterization

In this article, the transfer of a two-step, biphasic, and exothermic peroxide synthesis into a microreactor assisted process is discussed as well as the non-reactive and reactive characterization of the developed orifice microreactor. Residence time distribution measurements showed nearly ideal plug-flow behaviour. The Bodenstein number at a flow rate of 21 mL min-1 is 180 and the corresponding cell number is 90, indicating a narrow residence time distribution. The determined residence times at two different flow rates are in good agreement with the theoretical values of 3.2 s and 1.5 s. The influence of flow rate on droplet size distribution is discussed as well as the influence of orifice geometry on the resulting energy density. These measurements showed a very small droplet size distribution over a wide range of flow rates applied. The smallest mean droplet size of 7 µm was obtained for a flow rate of 75 mL min-1. It is shown that a change from baffle type to conical orifices allows increasing of the throughput by keeping the homogenizing pressure similar to the baffle type system at a lower throughput. The measurement of the temperature profile on top of the thin reaction plate, covering the reaction channel is possible due to a special design of the orifice microreactor and enables monitoring the heat production under reactive conditions. A benchmark based on the product output of an industrial semi-continuous process points out the potential of micro process technology to intensify existing processes. On the examples of four fictive production scale microreactor assisted processes, it is shown that the footprint as well as the reaction volume can significantly be reduced. Using an orifice microreactor of the size of a shoebox the calculated space–time-yield for a product output of ca. 196 kg L-1 h-1 is 905 kg L-1 h-1. This is orders of magnitude higher than for the industrial semi-continuous process

Novel process window for the safe and continuous synthesis of tert.-butyl peroxy pivalate in a micro reactor

In this paper, the two step synthesis of tert.-butyl peroxy pivalate using two different flow regimes is introduced, in particular the use of segmented flow and the concept of dispersed flow . The use of the segmented flow process, in this case, is challenging due to the very low interfacial tension of 4 mN/m at room temperature between potassium tert.-butyl peroxide and pivaloyl chloride, which causes an unstable fluid interface and results in a broad segment length distribution. This low interfacial tension is further decreased by the heat of reaction (126 kJ/mol pivaloyl chloride [1]), which is partially released at the contacting point of both fluids. It is investigated to compensate the occurring instabilities by dilution of both fluids, resulting in a more regular droplet formation. The applicability of the dispersed flow concept employing a mixer-tube set-up to create a large interfacial area for the synthesis of tert.-butyl peroxy pivalate is discussed together with the influence of increased process temperature, as a Novel Process Window, on the reaction performance. An approximate benchmark against two processes described in a patent [2] is given to point out the benefits obtained, e.g. higher space time yield, using a pre-stage micro-reactor device

Process design accompanying life cycle management and risk analysis as a decision support tool for sustainable biodiesel production

The search for sustainable synthesis pathways for biodiesel generation is still ongoing, although extensive research and development work on this topic has already led to a broad variety of process alternatives, utilizing different feedstocks, alcohols, catalysts and process parameters. Thus, the choice for the most sustainable option is not an easy task, depending on related costs and environmental impacts deriving from up-stream and down-stream processes, but also on safety constraints. The aim of our work presented herein is to demonstrate a decision support procedure for the best suited process design of biodiesel production in front of a pilot plant construction. The development of a novel biodiesel production alternative was accompanied by Life Cycle Management and Risk Analysis in an iterative procedure nearly from the beginning in order to point out favorable process parameter combinations in parallel to experimental optimization. The transesterification of waste oil via supercritical processing in intensifying continuous flow reactors, using the feedstock methanol, was found to be the most favourable option

Pseudo 3-D simulation of a falling film microreactor based on realistic channel and film profiles

A falling film microreactor has demonstrated in the past high potential for sustainable chemical processes, e.g. by better use of resources (selectivity), enabling direct routes (saving of waste), or smaller reactor footprint (space-time yield). Due to the extremely high liquid based specific area (up to ) it is especially equipped to carry out fast exothermic and mass transfer limited reactions. However, to maximize the process intensification in the falling film microreactor there is a need to characterize and investigate the design parameters of the reactor. In general, the major rate limiting steps occur on the liquid side. Therefore a realistic description of the liquid film is needed which requires the use of a 3-D reactor model. In the current study we present a so-called pseudo 3-D computational fluid dynamic (CFD) model. Based on the realistic channel geometry profiles we compute liquid menisci, flow velocities, species transport, and reactions. The reactor model was developed and validated experimentally by the absorption of CO2 in NaOH aqueous solution. This 3-D model allows investigating the effects of channel fabrication precision, liquid flow distribution, gas chamber height, and hydrophilic–hydrophobic plate material. Result shows that fabrication imprecisions of the investigated microchannels by 11% in channel width and 6% in channel depth has only a 2% impact on the reaction conversion. Moreover we show that a liquid flow mal distribution, in the parallel microchannels assembled on plate, with a relative standard deviation of 0.37 lowers the reaction conversion by about 2%. A reduction of gas chamber height slightly improves the conversion and gas phase mass transfer limitation can be overcome. Moreover the material of the reactor plate has to provide sufficient wetability for the liquid falling film

Ionic liquid synthesis in a microstructured reactor for process intensification

Ionic liquids (IL) are the focus of growing interest over the last few years due to their low vapour pressure being beneficial for replacing common organic solvents with high vapour pressure. IL synthesised via alkylation are produced in batch or semi-batch stirred tank reactors. The reaction is highly exothermic and the kinetics was shown to be fast. The heat management during the reactor operation is a crucial point leading to high quality IL product and avoiding thermal runaway. This study reports the use of a microstructured reactor (MSR) system for the production of ethylmethylimidazole ethylsulfate by a solvent-free alkylation reaction. A combination of MSR and two tubular capillary reactors operating at two different cooling temperatures has been proposed. The save and stable operation of this reactor system is proven experimentally rendering the IL of high quality. The specific reactor performance was about 4 kg m-3 s-1 being ca. 3 orders of magnitude higher as compared to more traditional reactors

Size controlled polymersomes by continuous self-assembly in micromixers

The formation of vesicles based on the self-assembly of amphiphilic poly(butadiene)-b-poly(ethylene oxide) (PB130-b-PEO66) block copolymer in water has been studied using THF as co-solvent. To obtain a highly controlled mixing process for the polymer/THF- and the water-phase, we employed micro mixers with different mixing geometries. The high impact of this preparation method on the selfassembling process was verified by TEM and DLS characterization of the obtained structures. Spherical micelles, vesicles and worm-like micelles were found depending on the parameters of mixing. By additional parameter adjustment in the vesicle regime, the size of the assembled vesicles was controlled between 45 and 100 nm. This demonstrates the continuous preparation of narrowly distributed vesicle structures with controlled sizes