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This chapter is a summary of recent advances in microreactors, which have become increasingly important in process development and chemical research. Microstructured chemical reactors are characterized by dimensions in the submillimeter range and, thus, surface-to-volume ratios are roughly two orders of magnitude greater than those of conventional reactors. The fundamentals of design and operation of microreactors are explained, and the necessary heat and mass transfer considerations are presented. Various designs are discussed, their key features are illustrated, and examples of successful applications are given. Emphasis is placed on the methods of introducing a catalyst into a microstructured reactor (MSR). The advantages of microreactor technology—and also the difficulties in development—are highlighted. Because of the small reactor dimensions, diffusion times are short, and the influence of mass transfer on the rate of reaction can be efficiently reduced or even be avoided. Because the heat transfer is greatly improved relative to that in conventional reactors, higher reaction temperatures, pressures, and reactant concentrations are attainable, leading to reduced reactor volumes and amounts of catalyst. Therefore, MSRs are particularly advantageous for fast reactions that are highly exothermic or highly endothermic. Isothermal conditions combined with short residence times and narrow residence time distributions allow optimization of the contact time in the reactor and avoidance of unwanted consecutive reactions. The rational design of catalytic microreactors requires the simultaneous development of the catalyst and the reactor. The catalyst design should be closely integrated with the reactor design, with consideration taken of the intrinsic reaction kinetics and transport phenomena. The accurate tuning and control of the reaction conditions lead to impressively high product selectivity and energy efficiency. Thus, MSRs are versatile tools for the development of sustainable processes. Further objectives of the application of miniaturized reactors concern the generation of chemical information, facilitation of catalyst development, optimization, and characterization of reaction kinetics.

Ozonation membrane contact was carried out with a tubular membrane module to study the effects of the flow rates and the temperatures of the liquid phase on ozone transfer and on the enhancement of mass fluxes. Changes in liquid temperature gave both positive and negative effects on the ozone fluxes for the nitrite solutions. The increase of the ozone fluxes with temperature was observed until the temperature approached approximately 40 degrees C. Ozonation membrane contact was also applied to decolorize Norwegian natural organic matter (NOM) at typical color concentrations in the range of 15-20 mg Pt/L. The ozone consumption for NOM decolourization tended to decrease with the liquid flow rates. A simple mass transfer model was proposed for the ozonation membrane contactor for the NOM decolourization studied here. The model was developed based on the concepts of the ozone consumption and the enhancement factor and can be used to describe the influence of mass transfer on the effluent colour concentration of the NOM. The experimental results validated the proposed model with deviations in the range of -9 to + 7%. The decolourization rate constants obtained from the concentration-time (C-tau) model for the ozonation membrane contactor were found to be in the range of 139.44-298.81 M-1 s(-1). Simple concept to design ozonation membrane contactor for NOM decolourization was proposed. The kinetic characteristics for the NOM decolourization in ozonation membrane contactor are discussed in this paper. (c) 2005 Elsevier B.V. All rights reserved.

Disposable cylindrical shaken bioreactors using plastic bags or vessels represent a promising alternative to stainless steel bioreactors, because they are flexible, cost-effective and can be pre-sterilized. Unlike conventional well-established steel bioreactors, however, such disposable bioreactor systems have not yet been precisely characterized. Thus, the aim of this current work is to introduce a new power input correlation as a potential means to characterize the hydrodynamics of these new systems. A set of rel- evant power input variables was defined and transformed into dimensionless numbers by using the Buckingham’s pi-Theorem. These numbers were then experimentally varied to quantify the relationship among the numbers. A simple correlation was generated for the power input with seven variables. The application of this new correlation was validated using 200 L and 2000 L orbitally shaken bioreactors. In conclusion, the proposed correlation is a useful tool to predict the power input and hydrodynamics during cell cultivation in cylindrical shaken bioreactors of all scales.

An investigation of the mobility, viability, and activity of polycyclic aromatic hydrocarbon (PAH) degrading bacteria in an electric field is presented. Bench-scale model aquifers were used to test electrophoresis and electroosmosis as potential mechanisms for bacterial dispersion in contaminated sites. Glass beads, alluvial sand from Lake Geneva, and historically polluted clayey soil were used as packing materials. The green-fluorescent protein labeled PAH-degrading bacteria Sphingomonas sp. L138 and Mycobacterium frederiksbergense LB501TG were used as test organisms because of the known differing physicochemical surface and adhesion properties of the corresponding wild-type strains. No adverse effects of the electric current on bacterial viability and PAH-degradation were observed in the system chosen. Up to 90% of the weakly negatively charged and moderately adhesive cells of strain L138 were transported by electroosmosis, whereas 0-20% were transported by electrophoresis. By contrast, poor electrokinetic transport of strongly charged and highly adhesive cells of M. frederiksbergense LB501TG occurred in the different model aquifers. Treatment of bacteria with the nonionic surfactant Brij35 resulted in up to 80% enhanced electrokinetic dispersion of both strains. Our findings demonstrate that electroosmosis may be a valuable mechanism to transport bacteria in the subsurface with transport efficiencies heavily depending on the retention of the bacteria by the solid phase.

The huge emission of greenhouse gases from fossil-fuelled power plants is emphasizing the need for efficient Carbon Capture and Storage (CCS) technologies. The biomimetic CO2 absorption in aqueous solutions has been recently investigated as a promising innovative alternative for post-combustion CCS. The carbonic anhydrase (CA) - a broad group of ubiquitous enzymes - may catalyse the CO2 hydration reaction and then to promote CO2 absorption rate into aqueous solutions. Nevertheless the research on this issue is quite active, the reliable designing of absorption units still requires more details. The present study proposes the design of a random packing absorption column operated with alkaline solvents supplied with CA. The height of the packed bed to fulfil the 80% of CO2 abatement from a flue gas stream was as large as 15-20 m. A comprehensive discussion of effects of operating conditions and of CA features on unit performance is reported.

BACKGROUND For several years, orbitally shaken cylindrical bioreactors (OSRs) have become a new approach for propagation of mammalian cells cultivated under suspension. With new commercial cell culture media available today, allowing exceptionally high cell densities, the identification of suitable operating conditions presents a special challenge. Balancing hydrodynamic stress and other factors in reactors, this is particularly true for gas transfer rates providing sufficient oxygen (O-2) to cultures that can attain ten-fold greater biomasses than just a decade ago. This challenge is more profound the larger the working volume of the reactor becomes. RESULT For 10-L working volume cylindrical OSRs, we established a computational fluid dynamics model to evaluate the impacts of different operational conditions. Both fluid velocity distributions and O-2 transfer coefficients (k(L)a) were calculated for different filling volumes and shaking speeds. Also, hydrodynamic stress parameters were investigated considering the most critical working conditions. CONCLUSION The fluid velocity decreased with larger working volumes and, as expected, was found to increase with higher shaking frequency. Gas transfer rates between 10 and 54 h(-1) were found in working volumes from 2.5 to 10 L and under shaking frequencies from 100-160 rpm. Critically assessing the obtained data, with no liquid-submerged gas supply, we conclude that an air flow into the head-space of a disposable bag appears to be satisfactory under certain operating conditions to support the culture of the most sensitive mammalian or insect cell cultures towards high cell density, presently in fed-batch cultures achieving

The paper describes a coupling of the geometric Volume-of-Fluid (VOF) method with a sharp-interface phase-change model for Cartesian and axisymmetric grids. Both the interfacial position and the temperature field are resolved with subgrid accuracy. Species transport with implicit diffusion is considered in the gas phase. The numerical implementation of the method developed here is described in detail, as well as its coupling with the incompressible Navier-Stokes solver PSI-BOIL, which features a hybrid, finite-volume/finite-difference approach based on a fixed, rectangular grid. Several verification cases have been undertaken to ensure correct implementation of the method in the code and to evaluate its performance. These include simulations of the Stefan problem, sucking problem and bubble growth in superheated liquid. In all cases, very good agreement with the analytical solution has been reached and grid convergence has been demonstrated. Simulations of evaporating and condensing rising bubbles, for which high-quality measured data are available, are also presented to serve as validation tests. Reasonable agreement of simulation results with experimental data has been recorded and applicability of the method to problems without inherent symmetry and featuring turbulence is shown. This work represents the first successful application of a geometric VOF method coupled with a sharp-interface phase-change model and species transport to non-trivial problems. The achieved performance of our algorithm in the verification and validation exercise represents an important step in the development of multiphase codes capable of accurately resolving complex three-dimensional multiphase flows. (C) 2021 The Author(s). Published by Elsevier Ltd.

Process intensification is the term which describes an innovative design approach in chemical engineering aiming on a significant increase of the specific performance of chemical reactors and plants miniaturization, of at least an order of magnitude. In addition, the running costs should be reduced and the process should be more efficient, safer, and less polluting than the existing ones. Micro process technology is considered as means of process intensification leading to better use of raw materials and energy. Chemical micro-structured reactors (MSR) are devices containing open paths for fluids with dimensions in the sub-millimeter range. Mostly they consist of multiple parallel channels with diameters between ten and several hundred micrometers where the chemical transformations occur. This results in a high specific surface area in the range of 10,000 to 50,000 m2m−3 and allows a more efficient mass and heat transfer compared to traditional chemical reactors having usually ∼100 m2m−3. Another important feature of micro-structured reactors is that the heat exchange and the reaction are mostly performed in the same gadget. Intensification of heterogeneous catalytic processes involves besides of innovative engineering of micro-structured reactors, the proper design of the catalyst. This requires the simultaneous development of the catalyst and the reactor. The catalyst design should be closely integrated with the reactor design taking into consideration the reaction mechanism, mass/heat transfer and the energy supply / evacuation resulting in high selectivity and yield of the target products. Besides general criteria for the choice and proper design of micro-structured reactors for process intensification, particular needs for homogeneous and multiphase reactions will be discussed.

The solvent-free selective hydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-buten-2-ol (MBE) was studied over a Pd/ZnO structured catalyst and compared to its behavior in water-assisted conditions. The catalytic behavior was correlated with the surface properties of the catalysts which were characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The catalyst showed high selectivity and stability with the performance being superior to that of the industrial Lindlar catalyst (50%). The addition of a sulphur-containing modifier in the reaction mixture was found to affect the activity and to hinder the over-hydrogenation reaction. The MBE yield of similar to 97% was attained at MBY conversion >99%. The reuse of the catalyst showed that it deactivated by a 38% and that its selectivity slightly increased (similar to 0.5%) over 10 runs. The reaction kinetics was modeled using a Langmuir-Hinshelwood mechanism considering competitive adsorption for the organic species and dissociative adsorption for hydrogen. The kinetic experiments were planned and the results analyzed following a design of experiments (DOE) methodology. This approach led not only to a robust model that predicts the reaction rate in a wide range of reaction conditions but also to the determination of its kinetic parameters. (C) 2008 Elsevier B.V. All rights reserved.