Modeling Temperature and Species Concentration Profiles on a Continuous-Flow Reactor Applied to Aldol Condensation

This paper presents the modeling of a continuous-flow reactor used for the synthesis of organic products. The finite element method software, COMSOL Multiphysics, was used to model transport phenomena and reaction kinetics. The temperature is one of the most important kinetic factors that may modify the reaction. A rise in temperature can generate a positive reaction but also secondary side reactions. The design of our system and of many other continuous systems makes it impossible, however, to measure the temperature throughout the reactor. In this paper, we modeled the temperature profile within the reactors as a function of the flow rate, temperature set point, and type of reactor material. The results demonstrated that although it is not a good thermal conductor, polytetrafluoroethylene can be used like other materials. The desired temperature was not reached for any of the reactor material likely to affect the product yield. The model gave the residence time required to reach the stabilized temperature. The comparison of calculated and experimental values of outlet temperature showed good agreement, with a maximum relative difference of only 5%. Knowledge of the temperature profile made it possible to control the concentration distribution of the chemical species in the reactor. The aldol condensation was chosen to determine the kinetic parameters of this reaction as the products of this reaction are found in many natural molecules and drugs. To integrate the chemical model, the kinetic parameters were determined by using experimental data. An equilibrium concentration of 0.2 mol/L was found with initial reactant concentrations of 0.45 mol/L. The chemical modeling gave the species concentrations throughout the reactor. Calculated concentrations were in good agreement with experimental data, with a maximum relative difference of less than 9%. By modeling this reaction, the reaction yield as a function of reactant concentration, temperature, and residence times was estimated.

Nanocatalysis in Flow

Nanocatalysis in flow is catalysis by metallic nanoparticles (NPs; 1-50 nm) performed in microstructured reactors. These catalytic processes make use of the enhanced catalytic activity and selectivity of NPs and fulfill the requirements of green chemistry. Anchoring catalytically active metal NPs within a microfluidic reactor enhances the reagent/catalyst interaction, while avoiding diffusion limitations experienced in classical approaches. Different strategies for supporting NPs are reviewed herein, namely, packed-bed reactors, monolithic flow-through reactors, wall catalysts, and a selection of novel approaches (NPs embedded on nanotubes, nanowires, catalytic membranes, and magnetic NPs). Through a number of catalytic reactions, such as hydrogenations, oxidations, and cross-coupling reactions, the advantages and possible drawbacks of each approach are illustrated.

Life cycle analysis within pharmaceutical process optimization and intensification: case study of active pharmaceutical ingredient production

As the demand for new drugs is rising, the pharmaceutical industry faces the quest of shortening development time, and thus, reducing the time to market. Environmental aspects typically still play a minor role within the early phase of process development. Nevertheless, it is highly promising to rethink, redesign, and optimize process strategies as early as possible in active pharmaceutical ingredient (API) process development, rather than later at the stage of already established processes. The study presented herein deals with a holistic life-cycle-based process optimization and intensification of a pharmaceutical production process targeting a low-volume, high-value API. Striving for process intensification by transfer from batch to continuous processing, as well as an alternative catalytic system, different process options are evaluated with regard to their environmental impact to identify bottlenecks and improvement potentials for further process development activities.

Agile green process design for the intensified Kolbe-Schmitt synthesis by accompanying (simplified) life cycle assessment

In order to investigate the potential for process intensification, various reaction conditions were applied to the Kolbe-Schmitt synthesis starting from resorcinol. Different CO₂ precursors such as aqueous potassium hydrogencarbonate, hydrogencarbonate-based ionic liquids, DIMCARB, or sc-CO₂, the application of microwave irradiation for fast volumetric heating of the reaction mixture, and the effect of harsh reaction conditions were investigated. The experiments, carried out in conventional batch-wise as well as in continuously operated microstructured reactors, aimed at the development of an environmentally benign process for the preparation of 2,4-dihydroxybenzoic acid. To provide decision support toward a green process design, a research-accompanying simplified life cycle assessment (SLCA) was performed throughout the whole investigation. Following this approach, it was found that convective heating methods such as oil bath or electrical heating were more beneficial than the application of microwave irradiation. Furthermore, the consideration of workup procedures was crucial for a holistic view on the environmental burdens.

Functionalization of polycarbonate with proteins; open-tubular enzymatic microreactors

This paper examines a set of techniques for the immobilization of enzymes on the surface of microchannels fabricated in polycarbonate (PC). Our experiments identify the method that uses combined physico-chemical immobilization on a layer of polyethyleneimine (PEI) as a reproducible vista for the robust immobilization of proteins. As an example, we demonstrate the fabrication, throughput and stability of an open-tubular reactor draped with alkaline phosphatase (ALP, EC 3.1.3.1) as a model enzyme. As PC is suitable for industrial applications the method could potentially be used to immobilize proteins in numbered-up implementations.