Kinetic and Scale-up Investigations of a Michael Addition in Microreactors

Automated optimization under dynamic flow conditions

The combination of feedback optimization with dynamic operations leads to enhanced data-rich experimentation in flow.

Continuous diameter increase reactor – a reactor concept for maximizing productivity by a controlled diameter extension

This paper presents a novel theoretical approach for maximizing productivity in microreactors by a controlled extension of the tube diameter. A one-dimensional numeric model was developed where the tube diameter increases based on the reaction heat to achieve a constant temperature throughout the reactor length. Through this approach, a basic plug flow reactor model for mass and heat transfer was used with an integrated algorithm for a controlled diameter extension. A parametric study was performed to ensure safe operating conditions concerning thermal runaway. The results show an increase in productivity of approximately 42% for the fictional second-order test reaction.

Graphical abstract

Ion mobility spectrometry-tandem mass spectrometry strategies for the on-line monitoring of a continuous microflow reaction

Continuous flow chemistry is an efficient, sustainable and green approach for chemical synthesis that surpasses some of the limitations of the traditional batch chemistry. Along with the multiple advantages of a flow reactor, it could be directly connected to the analytical techniques for on-line monitoring of a chemical reaction and ensure the quality by design. Here, we aim to use ion mobility, mass and tandem mass spectrometry (IMS-MS and MS/MS) for the on-line analysis of a pharmaceutically relevant chemical reaction. We carried out a model hetero-Diels Alder reaction in a microflow reactor directly connected to the IMS-MS and MS/MS using either electrospray or atmospheric pressure photo ionization methods. We were able to monitor the reaction mechanism of the Diels Alder reaction and structurally characterize the reaction product and synthesis side-products. The chosen approach enabled identification of two isomers of the main reaction product. A new strategy to annotate the ion mobility spectrum in the absence of standard molecules was introduced and tested for its validity. This was achieved by determining the survival yield of each isomer upon ion mobility separation and density functional theory calculations. This approach was verified by comparing the theoretically driven collision cross section values to the experimental data. In this paper, we demonstrated the potential of combined IMS-MS and MS/MS on-line analysis platform to investigate, monitor and characterize structural isomers in the millisecond time scale.

Challenges in transfer of gas-liquid reactions from batch to continuous operation: dimensional analysis and simulations for aerobic oxidation

The transfer of gas-liquid reactions from conventional batch processes into continuous operation using milli and micro reactors is claimed as an important step towards process intensification. Importantly, this transfer step should be realized in an early phase of process development, already, in order to minimize research efforts towards the undesired operation strategy. The main challenge of this approach, therefore, arises from lack of knowledge in the early stage of process development and the resulting system with high degrees of freedom. This contribution presents an approach to tackle this challenge by means of mathematical modelling and simulation for the aerobic oxidation of 9,10-dihydroanthracene (DHA) catalyzed by polyoxometalates (POMs) being used as example for gas-liquid reactions. The reaction was chosen as it provides sufficient complexity, since it consists of three consecutive oxidation steps of DHA and a parallel catalytic redox-cycle according to a Mars-van-Krevelen mechanism. It also provides the challenge of unknown reaction kinetics, which have been estimated in this contribution. The dimensionless balance equations for reactor modeling are derived and parametrized based on early stage experimental results obtained in batch operation mode. The discrimination between batch and continuous operation was performed by means of characteristic dimensionless numbers using the identical mathematical model for comparability reasons. The model was used to perform sensitivity studies with emphasis on the interplay between mass transfer characteristics and reaction kinetics for both the batch and continuous operation mode. The simulation results show that the performance of both operation modes mainly depend on the oxidation state of the POM catalyst, which is caused by the differences in oxygen availability. Therefore, results obtained in batch operation mode are prone to be masked by mass transfer issues, which affects catalyst and reactor development at the same time and may thus cause maldevelopments. With respect to process development it can thus be concluded that the transfer from batch to continuous operation together with mathematical modeling is important in an early phase, already, in order to detect limitations misleading the development. Finally, even simple models with roughly estimated parameters from preliminary experiments are shown to be sufficient in the early phase and can systematically be improved, in the subsequent phases.

Graphical abstract

Synthesis and scale-up of water-soluble quaternary cationic monomers in a continuous flow system

A novel, simple, power-saving and effective method for the synthesis and scale-up of cationic water-soluble polyelectrolytes represented by dimethyldiallylammonium chloride (DMDAAC) with commercially available reagents in a two-step continuous flow system has been developed.

Atom- and Mass-economical Continuous Flow Production of 3-Chloropropionyl Chloride and its Subsequent Amidation

3-Chloropropionyl chloride is a chemically versatile building block with applications in the field of adhesives, pharmaceuticals, herbicides and fungicides. Its current production entails problems concerning safety, prolonged reaction times and the use of excessive amounts of chlorinating reagents. We developed a continuous flow procedure for acid chloride formation from acrylic acid and a consecutive 1,4-addition of hydrogen chloride generating 3-chloropropionyl chloride, as presented in this paper. Up to 94 % conversion was reached in 25 minutes at mild temperatures and pressures. This continuous flow method offers a safer alternative and is highly efficient in terms of consumption of starting product and shorter residence time. Valorization of this building block is exemplified by the synthesis of beclamide, a compound with sedative and anticonvulsant properties. Over 80 % conversion towards this drug was achieved in 1 minute in a continuous flow setup. Further research is needed to telescope the synthesis of 3-chloropropionyl chloride and subsequent beclamide formation without intermediate purification.

Raman and NMR kinetics study of the formation of amidoamines containing N-hydroxyethyl groups and investigations on their Cu(II) complexes in water

Three amidoamines containing the N-hydroxyethyl group (^HOEt), namely (^HOEt)₂N(CH₂)₂C(O)NH₂ (1), [(^HOEt)₂N(CH₂)₂C(O)NH]₂CH₂ (2) and ^HOEtN[(CH₂)₂C(O)NH₂]₂ (3) have been synthesized by reacting diethanolamine ^HOEt₂NH with acrylamide and N,N'-methylenebisacrylamide (respectively 1 and 2) and ethanolamine ^HOEtNH₂ with acrylamide (3). Four other compounds corresponding to 1 and 2, but derived from sec-amines Me₂NH (4 and 5) and Et₂NH (6 and 7) have been prepared for the sake of comparison of the spectroscopic features. All compounds have been obtained by the well-known aza-Michael addition between an N-nucleophile and an activated vinyl group. The reaction in water between diethanolamine and acrylamide leading to 1 has been monitored in situ by Raman and NMR spectroscopy, both techniques confirming second order kinetics and giving values for kinetic constants in excellent agreement. The coordination ability of 1 and 2 towards Cu²⁺ in water has been studied by the Job's plot method. Spectroscopic data indicate that ligand 1 prevalently forms a 4:1 Ligand/Metal complex with a (N,O₃) coordination set on the equatorial plane of Cu²⁺, whereas ligand 2, containing two amide functionalities bridged by a methylene group, appears able to form a 1:1 Ligand/Metal chelate species, again with a (N,O₃) donor set around copper.

Safety assessment in development and operation of modular continuous-flow processes

Improved safety is one of the main drivers for microreactor application in chemical process development and small-scale production.

A. Enzymatic microreactors in biocatalysis: history, features, and future perspectives

Microfluidic reaction devices are a very promising technology for chemical and biochemical processes. In microreactors, the micro dimensions, coupled with a high surface area/volume ratio, permit rapid heat exchange and mass transfer, resulting in higher reaction yields and reaction rates than in conventional reactors. Moreover, the lower energy consumption and easier separation of products permit these systems to have a lower environmental impact compared to macroscale, conventional reactors. Due to these benefits, the use of microreactors is increasing in the biocatalysis field, both by using enzymes in solution and their immobilized counterparts. Following an introduction to the most common applications of microreactors in chemical processes, a broad overview will be given of the latest applications in biocatalytic processes performed in microreactors with free or immobilized enzymes. In particular, attention is given to the nature of the materials used as a support for the enzymes and the strategies employed for their immobilization. Mathematical and engineering aspects concerning fluid dynamics in microreactors were also taken into account as fundamental factors for the optimization of these systems.